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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Guile Reference Manual. | |
bf7c2e96 | 3 | @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 |
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4 | @c Free Software Foundation, Inc. |
5 | @c See the file guile.texi for copying conditions. | |
6 | ||
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7 | @node Simple Data Types |
8 | @section Simple Generic Data Types | |
9 | ||
10 | This chapter describes those of Guile's simple data types which are | |
11 | primarily used for their role as items of generic data. By | |
12 | @dfn{simple} we mean data types that are not primarily used as | |
13 | containers to hold other data --- i.e.@: pairs, lists, vectors and so on. | |
14 | For the documentation of such @dfn{compound} data types, see | |
15 | @ref{Compound Data Types}. | |
16 | ||
17 | @c One of the great strengths of Scheme is that there is no straightforward | |
18 | @c distinction between ``data'' and ``functionality''. For example, | |
19 | @c Guile's support for dynamic linking could be described: | |
20 | ||
21 | @c @itemize @bullet | |
22 | @c @item | |
23 | @c either in a ``data-centric'' way, as the behaviour and properties of the | |
24 | @c ``dynamically linked object'' data type, and the operations that may be | |
25 | @c applied to instances of this type | |
26 | ||
27 | @c @item | |
28 | @c or in a ``functionality-centric'' way, as the set of procedures that | |
29 | @c constitute Guile's support for dynamic linking, in the context of the | |
30 | @c module system. | |
31 | @c @end itemize | |
32 | ||
33 | @c The contents of this chapter are, therefore, a matter of judgment. By | |
34 | @c @dfn{generic}, we mean to select those data types whose typical use as | |
35 | @c @emph{data} in a wide variety of programming contexts is more important | |
36 | @c than their use in the implementation of a particular piece of | |
37 | @c @emph{functionality}. The last section of this chapter provides | |
38 | @c references for all the data types that are documented not here but in a | |
39 | @c ``functionality-centric'' way elsewhere in the manual. | |
40 | ||
41 | @menu | |
42 | * Booleans:: True/false values. | |
43 | * Numbers:: Numerical data types. | |
050ab45f MV |
44 | * Characters:: Single characters. |
45 | * Character Sets:: Sets of characters. | |
46 | * Strings:: Sequences of characters. | |
b242715b | 47 | * Bytevectors:: Sequences of bytes. |
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48 | * Symbols:: Symbols. |
49 | * Keywords:: Self-quoting, customizable display keywords. | |
50 | * Other Types:: "Functionality-centric" data types. | |
51 | @end menu | |
52 | ||
53 | ||
54 | @node Booleans | |
55 | @subsection Booleans | |
56 | @tpindex Booleans | |
57 | ||
58 | The two boolean values are @code{#t} for true and @code{#f} for false. | |
59 | ||
60 | Boolean values are returned by predicate procedures, such as the general | |
61 | equality predicates @code{eq?}, @code{eqv?} and @code{equal?} | |
62 | (@pxref{Equality}) and numerical and string comparison operators like | |
63 | @code{string=?} (@pxref{String Comparison}) and @code{<=} | |
64 | (@pxref{Comparison}). | |
65 | ||
66 | @lisp | |
67 | (<= 3 8) | |
68 | @result{} #t | |
69 | ||
70 | (<= 3 -3) | |
71 | @result{} #f | |
72 | ||
73 | (equal? "house" "houses") | |
74 | @result{} #f | |
75 | ||
76 | (eq? #f #f) | |
77 | @result{} | |
78 | #t | |
79 | @end lisp | |
80 | ||
81 | In test condition contexts like @code{if} and @code{cond} (@pxref{if | |
82 | cond case}), where a group of subexpressions will be evaluated only if a | |
83 | @var{condition} expression evaluates to ``true'', ``true'' means any | |
84 | value at all except @code{#f}. | |
85 | ||
86 | @lisp | |
87 | (if #t "yes" "no") | |
88 | @result{} "yes" | |
89 | ||
90 | (if 0 "yes" "no") | |
91 | @result{} "yes" | |
92 | ||
93 | (if #f "yes" "no") | |
94 | @result{} "no" | |
95 | @end lisp | |
96 | ||
97 | A result of this asymmetry is that typical Scheme source code more often | |
98 | uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to | |
99 | represent an @code{if} or @code{cond} false value, whereas @code{#t} is | |
100 | not necessary to represent an @code{if} or @code{cond} true value. | |
101 | ||
102 | It is important to note that @code{#f} is @strong{not} equivalent to any | |
103 | other Scheme value. In particular, @code{#f} is not the same as the | |
104 | number 0 (like in C and C++), and not the same as the ``empty list'' | |
105 | (like in some Lisp dialects). | |
106 | ||
107 | In C, the two Scheme boolean values are available as the two constants | |
108 | @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}. | |
109 | Care must be taken with the false value @code{SCM_BOOL_F}: it is not | |
110 | false when used in C conditionals. In order to test for it, use | |
111 | @code{scm_is_false} or @code{scm_is_true}. | |
112 | ||
113 | @rnindex not | |
114 | @deffn {Scheme Procedure} not x | |
115 | @deffnx {C Function} scm_not (x) | |
116 | Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}. | |
117 | @end deffn | |
118 | ||
119 | @rnindex boolean? | |
120 | @deffn {Scheme Procedure} boolean? obj | |
121 | @deffnx {C Function} scm_boolean_p (obj) | |
122 | Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else | |
123 | return @code{#f}. | |
124 | @end deffn | |
125 | ||
126 | @deftypevr {C Macro} SCM SCM_BOOL_T | |
127 | The @code{SCM} representation of the Scheme object @code{#t}. | |
128 | @end deftypevr | |
129 | ||
130 | @deftypevr {C Macro} SCM SCM_BOOL_F | |
131 | The @code{SCM} representation of the Scheme object @code{#f}. | |
132 | @end deftypevr | |
133 | ||
134 | @deftypefn {C Function} int scm_is_true (SCM obj) | |
135 | Return @code{0} if @var{obj} is @code{#f}, else return @code{1}. | |
136 | @end deftypefn | |
137 | ||
138 | @deftypefn {C Function} int scm_is_false (SCM obj) | |
139 | Return @code{1} if @var{obj} is @code{#f}, else return @code{0}. | |
140 | @end deftypefn | |
141 | ||
142 | @deftypefn {C Function} int scm_is_bool (SCM obj) | |
143 | Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else | |
144 | return @code{0}. | |
145 | @end deftypefn | |
146 | ||
147 | @deftypefn {C Function} SCM scm_from_bool (int val) | |
148 | Return @code{#f} if @var{val} is @code{0}, else return @code{#t}. | |
149 | @end deftypefn | |
150 | ||
151 | @deftypefn {C Function} int scm_to_bool (SCM val) | |
152 | Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0} | |
153 | when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error. | |
154 | ||
155 | You should probably use @code{scm_is_true} instead of this function | |
156 | when you just want to test a @code{SCM} value for trueness. | |
157 | @end deftypefn | |
158 | ||
159 | @node Numbers | |
160 | @subsection Numerical data types | |
161 | @tpindex Numbers | |
162 | ||
163 | Guile supports a rich ``tower'' of numerical types --- integer, | |
164 | rational, real and complex --- and provides an extensive set of | |
165 | mathematical and scientific functions for operating on numerical | |
166 | data. This section of the manual documents those types and functions. | |
167 | ||
168 | You may also find it illuminating to read R5RS's presentation of numbers | |
169 | in Scheme, which is particularly clear and accessible: see | |
170 | @ref{Numbers,,,r5rs,R5RS}. | |
171 | ||
172 | @menu | |
173 | * Numerical Tower:: Scheme's numerical "tower". | |
174 | * Integers:: Whole numbers. | |
175 | * Reals and Rationals:: Real and rational numbers. | |
176 | * Complex Numbers:: Complex numbers. | |
177 | * Exactness:: Exactness and inexactness. | |
178 | * Number Syntax:: Read syntax for numerical data. | |
179 | * Integer Operations:: Operations on integer values. | |
180 | * Comparison:: Comparison predicates. | |
181 | * Conversion:: Converting numbers to and from strings. | |
182 | * Complex:: Complex number operations. | |
183 | * Arithmetic:: Arithmetic functions. | |
184 | * Scientific:: Scientific functions. | |
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185 | * Bitwise Operations:: Logical AND, OR, NOT, and so on. |
186 | * Random:: Random number generation. | |
187 | @end menu | |
188 | ||
189 | ||
190 | @node Numerical Tower | |
191 | @subsubsection Scheme's Numerical ``Tower'' | |
192 | @rnindex number? | |
193 | ||
194 | Scheme's numerical ``tower'' consists of the following categories of | |
195 | numbers: | |
196 | ||
197 | @table @dfn | |
198 | @item integers | |
199 | Whole numbers, positive or negative; e.g.@: --5, 0, 18. | |
200 | ||
201 | @item rationals | |
202 | The set of numbers that can be expressed as @math{@var{p}/@var{q}} | |
203 | where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but | |
204 | pi (an irrational number) doesn't. These include integers | |
205 | (@math{@var{n}/1}). | |
206 | ||
207 | @item real numbers | |
208 | The set of numbers that describes all possible positions along a | |
209 | one-dimensional line. This includes rationals as well as irrational | |
210 | numbers. | |
211 | ||
212 | @item complex numbers | |
213 | The set of numbers that describes all possible positions in a two | |
214 | dimensional space. This includes real as well as imaginary numbers | |
215 | (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part}, | |
216 | @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of | |
217 | @minus{}1.) | |
218 | @end table | |
219 | ||
220 | It is called a tower because each category ``sits on'' the one that | |
221 | follows it, in the sense that every integer is also a rational, every | |
222 | rational is also real, and every real number is also a complex number | |
223 | (but with zero imaginary part). | |
224 | ||
225 | In addition to the classification into integers, rationals, reals and | |
226 | complex numbers, Scheme also distinguishes between whether a number is | |
227 | represented exactly or not. For example, the result of | |
9f1ba6a9 NJ |
228 | @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile |
229 | can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly. | |
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230 | Instead, it stores an inexact approximation, using the C type |
231 | @code{double}. | |
232 | ||
233 | Guile can represent exact rationals of any magnitude, inexact | |
234 | rationals that fit into a C @code{double}, and inexact complex numbers | |
235 | with @code{double} real and imaginary parts. | |
236 | ||
237 | The @code{number?} predicate may be applied to any Scheme value to | |
238 | discover whether the value is any of the supported numerical types. | |
239 | ||
240 | @deffn {Scheme Procedure} number? obj | |
241 | @deffnx {C Function} scm_number_p (obj) | |
242 | Return @code{#t} if @var{obj} is any kind of number, else @code{#f}. | |
243 | @end deffn | |
244 | ||
245 | For example: | |
246 | ||
247 | @lisp | |
248 | (number? 3) | |
249 | @result{} #t | |
250 | ||
251 | (number? "hello there!") | |
252 | @result{} #f | |
253 | ||
254 | (define pi 3.141592654) | |
255 | (number? pi) | |
256 | @result{} #t | |
257 | @end lisp | |
258 | ||
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259 | @deftypefn {C Function} int scm_is_number (SCM obj) |
260 | This is equivalent to @code{scm_is_true (scm_number_p (obj))}. | |
261 | @end deftypefn | |
262 | ||
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263 | The next few subsections document each of Guile's numerical data types |
264 | in detail. | |
265 | ||
266 | @node Integers | |
267 | @subsubsection Integers | |
268 | ||
269 | @tpindex Integer numbers | |
270 | ||
271 | @rnindex integer? | |
272 | ||
273 | Integers are whole numbers, that is numbers with no fractional part, | |
274 | such as 2, 83, and @minus{}3789. | |
275 | ||
276 | Integers in Guile can be arbitrarily big, as shown by the following | |
277 | example. | |
278 | ||
279 | @lisp | |
280 | (define (factorial n) | |
281 | (let loop ((n n) (product 1)) | |
282 | (if (= n 0) | |
283 | product | |
284 | (loop (- n 1) (* product n))))) | |
285 | ||
286 | (factorial 3) | |
287 | @result{} 6 | |
288 | ||
289 | (factorial 20) | |
290 | @result{} 2432902008176640000 | |
291 | ||
292 | (- (factorial 45)) | |
293 | @result{} -119622220865480194561963161495657715064383733760000000000 | |
294 | @end lisp | |
295 | ||
296 | Readers whose background is in programming languages where integers are | |
297 | limited by the need to fit into just 4 or 8 bytes of memory may find | |
298 | this surprising, or suspect that Guile's representation of integers is | |
299 | inefficient. In fact, Guile achieves a near optimal balance of | |
300 | convenience and efficiency by using the host computer's native | |
301 | representation of integers where possible, and a more general | |
302 | representation where the required number does not fit in the native | |
303 | form. Conversion between these two representations is automatic and | |
304 | completely invisible to the Scheme level programmer. | |
305 | ||
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306 | C has a host of different integer types, and Guile offers a host of |
307 | functions to convert between them and the @code{SCM} representation. | |
308 | For example, a C @code{int} can be handled with @code{scm_to_int} and | |
309 | @code{scm_from_int}. Guile also defines a few C integer types of its | |
310 | own, to help with differences between systems. | |
311 | ||
312 | C integer types that are not covered can be handled with the generic | |
313 | @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for | |
314 | signed types, or with @code{scm_to_unsigned_integer} and | |
315 | @code{scm_from_unsigned_integer} for unsigned types. | |
316 | ||
317 | Scheme integers can be exact and inexact. For example, a number | |
318 | written as @code{3.0} with an explicit decimal-point is inexact, but | |
319 | it is also an integer. The functions @code{integer?} and | |
320 | @code{scm_is_integer} report true for such a number, but the functions | |
321 | @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only | |
322 | allow exact integers and thus report false. Likewise, the conversion | |
323 | functions like @code{scm_to_signed_integer} only accept exact | |
324 | integers. | |
325 | ||
326 | The motivation for this behavior is that the inexactness of a number | |
327 | should not be lost silently. If you want to allow inexact integers, | |
877f06c3 | 328 | you can explicitly insert a call to @code{inexact->exact} or to its C |
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329 | equivalent @code{scm_inexact_to_exact}. (Only inexact integers will |
330 | be converted by this call into exact integers; inexact non-integers | |
331 | will become exact fractions.) | |
332 | ||
333 | @deffn {Scheme Procedure} integer? x | |
334 | @deffnx {C Function} scm_integer_p (x) | |
909fcc97 | 335 | Return @code{#t} if @var{x} is an exact or inexact integer number, else |
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336 | @code{#f}. |
337 | ||
338 | @lisp | |
339 | (integer? 487) | |
340 | @result{} #t | |
341 | ||
342 | (integer? 3.0) | |
343 | @result{} #t | |
344 | ||
345 | (integer? -3.4) | |
346 | @result{} #f | |
347 | ||
348 | (integer? +inf.0) | |
349 | @result{} #t | |
350 | @end lisp | |
351 | @end deffn | |
352 | ||
353 | @deftypefn {C Function} int scm_is_integer (SCM x) | |
354 | This is equivalent to @code{scm_is_true (scm_integer_p (x))}. | |
355 | @end deftypefn | |
356 | ||
357 | @defvr {C Type} scm_t_int8 | |
358 | @defvrx {C Type} scm_t_uint8 | |
359 | @defvrx {C Type} scm_t_int16 | |
360 | @defvrx {C Type} scm_t_uint16 | |
361 | @defvrx {C Type} scm_t_int32 | |
362 | @defvrx {C Type} scm_t_uint32 | |
363 | @defvrx {C Type} scm_t_int64 | |
364 | @defvrx {C Type} scm_t_uint64 | |
365 | @defvrx {C Type} scm_t_intmax | |
366 | @defvrx {C Type} scm_t_uintmax | |
367 | The C types are equivalent to the corresponding ISO C types but are | |
368 | defined on all platforms, with the exception of @code{scm_t_int64} and | |
369 | @code{scm_t_uint64}, which are only defined when a 64-bit type is | |
370 | available. For example, @code{scm_t_int8} is equivalent to | |
371 | @code{int8_t}. | |
372 | ||
373 | You can regard these definitions as a stop-gap measure until all | |
374 | platforms provide these types. If you know that all the platforms | |
375 | that you are interested in already provide these types, it is better | |
376 | to use them directly instead of the types provided by Guile. | |
377 | @end defvr | |
378 | ||
379 | @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max) | |
380 | @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max) | |
381 | Return @code{1} when @var{x} represents an exact integer that is | |
382 | between @var{min} and @var{max}, inclusive. | |
383 | ||
384 | These functions can be used to check whether a @code{SCM} value will | |
385 | fit into a given range, such as the range of a given C integer type. | |
386 | If you just want to convert a @code{SCM} value to a given C integer | |
387 | type, use one of the conversion functions directly. | |
388 | @end deftypefn | |
389 | ||
390 | @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max) | |
391 | @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max) | |
392 | When @var{x} represents an exact integer that is between @var{min} and | |
393 | @var{max} inclusive, return that integer. Else signal an error, | |
394 | either a `wrong-type' error when @var{x} is not an exact integer, or | |
395 | an `out-of-range' error when it doesn't fit the given range. | |
396 | @end deftypefn | |
397 | ||
398 | @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x) | |
399 | @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x) | |
400 | Return the @code{SCM} value that represents the integer @var{x}. This | |
401 | function will always succeed and will always return an exact number. | |
402 | @end deftypefn | |
403 | ||
404 | @deftypefn {C Function} char scm_to_char (SCM x) | |
405 | @deftypefnx {C Function} {signed char} scm_to_schar (SCM x) | |
406 | @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x) | |
407 | @deftypefnx {C Function} short scm_to_short (SCM x) | |
408 | @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x) | |
409 | @deftypefnx {C Function} int scm_to_int (SCM x) | |
410 | @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x) | |
411 | @deftypefnx {C Function} long scm_to_long (SCM x) | |
412 | @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x) | |
413 | @deftypefnx {C Function} {long long} scm_to_long_long (SCM x) | |
414 | @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x) | |
415 | @deftypefnx {C Function} size_t scm_to_size_t (SCM x) | |
416 | @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x) | |
417 | @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x) | |
418 | @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x) | |
419 | @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x) | |
420 | @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x) | |
421 | @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x) | |
422 | @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x) | |
423 | @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x) | |
424 | @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x) | |
425 | @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x) | |
426 | @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x) | |
427 | When @var{x} represents an exact integer that fits into the indicated | |
428 | C type, return that integer. Else signal an error, either a | |
429 | `wrong-type' error when @var{x} is not an exact integer, or an | |
430 | `out-of-range' error when it doesn't fit the given range. | |
431 | ||
432 | The functions @code{scm_to_long_long}, @code{scm_to_ulong_long}, | |
433 | @code{scm_to_int64}, and @code{scm_to_uint64} are only available when | |
434 | the corresponding types are. | |
435 | @end deftypefn | |
436 | ||
437 | @deftypefn {C Function} SCM scm_from_char (char x) | |
438 | @deftypefnx {C Function} SCM scm_from_schar (signed char x) | |
439 | @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x) | |
440 | @deftypefnx {C Function} SCM scm_from_short (short x) | |
441 | @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x) | |
442 | @deftypefnx {C Function} SCM scm_from_int (int x) | |
443 | @deftypefnx {C Function} SCM scm_from_uint (unsigned int x) | |
444 | @deftypefnx {C Function} SCM scm_from_long (long x) | |
445 | @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x) | |
446 | @deftypefnx {C Function} SCM scm_from_long_long (long long x) | |
447 | @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x) | |
448 | @deftypefnx {C Function} SCM scm_from_size_t (size_t x) | |
449 | @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x) | |
450 | @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x) | |
451 | @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x) | |
452 | @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x) | |
453 | @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x) | |
454 | @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x) | |
455 | @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x) | |
456 | @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x) | |
457 | @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x) | |
458 | @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x) | |
459 | @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x) | |
460 | Return the @code{SCM} value that represents the integer @var{x}. | |
461 | These functions will always succeed and will always return an exact | |
462 | number. | |
463 | @end deftypefn | |
464 | ||
08962922 MV |
465 | @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop) |
466 | Assign @var{val} to the multiple precision integer @var{rop}. | |
467 | @var{val} must be an exact integer, otherwise an error will be | |
468 | signalled. @var{rop} must have been initialized with @code{mpz_init} | |
469 | before this function is called. When @var{rop} is no longer needed | |
470 | the occupied space must be freed with @code{mpz_clear}. | |
471 | @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details. | |
472 | @end deftypefn | |
473 | ||
9f1ba6a9 | 474 | @deftypefn {C Function} SCM scm_from_mpz (mpz_t val) |
08962922 MV |
475 | Return the @code{SCM} value that represents @var{val}. |
476 | @end deftypefn | |
477 | ||
07d83abe MV |
478 | @node Reals and Rationals |
479 | @subsubsection Real and Rational Numbers | |
480 | @tpindex Real numbers | |
481 | @tpindex Rational numbers | |
482 | ||
483 | @rnindex real? | |
484 | @rnindex rational? | |
485 | ||
486 | Mathematically, the real numbers are the set of numbers that describe | |
487 | all possible points along a continuous, infinite, one-dimensional line. | |
488 | The rational numbers are the set of all numbers that can be written as | |
489 | fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers. | |
490 | All rational numbers are also real, but there are real numbers that | |
995953e5 | 491 | are not rational, for example @m{\sqrt{2}, the square root of 2}, and |
34942993 | 492 | @m{\pi,pi}. |
07d83abe MV |
493 | |
494 | Guile can represent both exact and inexact rational numbers, but it | |
c960e556 MW |
495 | cannot represent precise finite irrational numbers. Exact rationals are |
496 | represented by storing the numerator and denominator as two exact | |
497 | integers. Inexact rationals are stored as floating point numbers using | |
498 | the C type @code{double}. | |
07d83abe MV |
499 | |
500 | Exact rationals are written as a fraction of integers. There must be | |
501 | no whitespace around the slash: | |
502 | ||
503 | @lisp | |
504 | 1/2 | |
505 | -22/7 | |
506 | @end lisp | |
507 | ||
508 | Even though the actual encoding of inexact rationals is in binary, it | |
509 | may be helpful to think of it as a decimal number with a limited | |
510 | number of significant figures and a decimal point somewhere, since | |
511 | this corresponds to the standard notation for non-whole numbers. For | |
512 | example: | |
513 | ||
514 | @lisp | |
515 | 0.34 | |
516 | -0.00000142857931198 | |
517 | -5648394822220000000000.0 | |
518 | 4.0 | |
519 | @end lisp | |
520 | ||
c960e556 MW |
521 | The limited precision of Guile's encoding means that any finite ``real'' |
522 | number in Guile can be written in a rational form, by multiplying and | |
523 | then dividing by sufficient powers of 10 (or in fact, 2). For example, | |
524 | @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided | |
525 | by 100000000000000000. In Guile's current incarnation, therefore, the | |
526 | @code{rational?} and @code{real?} predicates are equivalent for finite | |
527 | numbers. | |
07d83abe | 528 | |
07d83abe | 529 | |
c960e556 MW |
530 | Dividing by an exact zero leads to a error message, as one might expect. |
531 | However, dividing by an inexact zero does not produce an error. | |
532 | Instead, the result of the division is either plus or minus infinity, | |
533 | depending on the sign of the divided number and the sign of the zero | |
534 | divisor (some platforms support signed zeroes @samp{-0.0} and | |
535 | @samp{+0.0}; @samp{0.0} is the same as @samp{+0.0}). | |
536 | ||
537 | Dividing zero by an inexact zero yields a @acronym{NaN} (`not a number') | |
538 | value, although they are actually considered numbers by Scheme. | |
539 | Attempts to compare a @acronym{NaN} value with any number (including | |
540 | itself) using @code{=}, @code{<}, @code{>}, @code{<=} or @code{>=} | |
541 | always returns @code{#f}. Although a @acronym{NaN} value is not | |
542 | @code{=} to itself, it is both @code{eqv?} and @code{equal?} to itself | |
543 | and other @acronym{NaN} values. However, the preferred way to test for | |
544 | them is by using @code{nan?}. | |
545 | ||
546 | The real @acronym{NaN} values and infinities are written @samp{+nan.0}, | |
547 | @samp{+inf.0} and @samp{-inf.0}. This syntax is also recognized by | |
548 | @code{read} as an extension to the usual Scheme syntax. These special | |
549 | values are considered by Scheme to be inexact real numbers but not | |
550 | rational. Note that non-real complex numbers may also contain | |
551 | infinities or @acronym{NaN} values in their real or imaginary parts. To | |
552 | test a real number to see if it is infinite, a @acronym{NaN} value, or | |
553 | neither, use @code{inf?}, @code{nan?}, or @code{finite?}, respectively. | |
554 | Every real number in Scheme belongs to precisely one of those three | |
555 | classes. | |
07d83abe MV |
556 | |
557 | On platforms that follow @acronym{IEEE} 754 for their floating point | |
558 | arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values | |
559 | are implemented using the corresponding @acronym{IEEE} 754 values. | |
560 | They behave in arithmetic operations like @acronym{IEEE} 754 describes | |
561 | it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}. | |
562 | ||
07d83abe MV |
563 | @deffn {Scheme Procedure} real? obj |
564 | @deffnx {C Function} scm_real_p (obj) | |
565 | Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note | |
566 | that the sets of integer and rational values form subsets of the set | |
567 | of real numbers, so the predicate will also be fulfilled if @var{obj} | |
568 | is an integer number or a rational number. | |
569 | @end deffn | |
570 | ||
571 | @deffn {Scheme Procedure} rational? x | |
572 | @deffnx {C Function} scm_rational_p (x) | |
573 | Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise. | |
574 | Note that the set of integer values forms a subset of the set of | |
995953e5 | 575 | rational numbers, i.e.@: the predicate will also be fulfilled if |
07d83abe | 576 | @var{x} is an integer number. |
07d83abe MV |
577 | @end deffn |
578 | ||
579 | @deffn {Scheme Procedure} rationalize x eps | |
580 | @deffnx {C Function} scm_rationalize (x, eps) | |
581 | Returns the @emph{simplest} rational number differing | |
582 | from @var{x} by no more than @var{eps}. | |
583 | ||
584 | As required by @acronym{R5RS}, @code{rationalize} only returns an | |
585 | exact result when both its arguments are exact. Thus, you might need | |
586 | to use @code{inexact->exact} on the arguments. | |
587 | ||
588 | @lisp | |
589 | (rationalize (inexact->exact 1.2) 1/100) | |
590 | @result{} 6/5 | |
591 | @end lisp | |
592 | ||
593 | @end deffn | |
594 | ||
d3df9759 MV |
595 | @deffn {Scheme Procedure} inf? x |
596 | @deffnx {C Function} scm_inf_p (x) | |
10391e06 AW |
597 | Return @code{#t} if the real number @var{x} is @samp{+inf.0} or |
598 | @samp{-inf.0}. Otherwise return @code{#f}. | |
07d83abe MV |
599 | @end deffn |
600 | ||
601 | @deffn {Scheme Procedure} nan? x | |
d3df9759 | 602 | @deffnx {C Function} scm_nan_p (x) |
10391e06 AW |
603 | Return @code{#t} if the real number @var{x} is @samp{+nan.0}, or |
604 | @code{#f} otherwise. | |
07d83abe MV |
605 | @end deffn |
606 | ||
7112615f MW |
607 | @deffn {Scheme Procedure} finite? x |
608 | @deffnx {C Function} scm_finite_p (x) | |
10391e06 AW |
609 | Return @code{#t} if the real number @var{x} is neither infinite nor a |
610 | NaN, @code{#f} otherwise. | |
7112615f MW |
611 | @end deffn |
612 | ||
cdf1ad3b MV |
613 | @deffn {Scheme Procedure} nan |
614 | @deffnx {C Function} scm_nan () | |
c960e556 | 615 | Return @samp{+nan.0}, a @acronym{NaN} value. |
cdf1ad3b MV |
616 | @end deffn |
617 | ||
618 | @deffn {Scheme Procedure} inf | |
619 | @deffnx {C Function} scm_inf () | |
c960e556 | 620 | Return @samp{+inf.0}, positive infinity. |
cdf1ad3b MV |
621 | @end deffn |
622 | ||
d3df9759 MV |
623 | @deffn {Scheme Procedure} numerator x |
624 | @deffnx {C Function} scm_numerator (x) | |
625 | Return the numerator of the rational number @var{x}. | |
626 | @end deffn | |
627 | ||
628 | @deffn {Scheme Procedure} denominator x | |
629 | @deffnx {C Function} scm_denominator (x) | |
630 | Return the denominator of the rational number @var{x}. | |
631 | @end deffn | |
632 | ||
633 | @deftypefn {C Function} int scm_is_real (SCM val) | |
634 | @deftypefnx {C Function} int scm_is_rational (SCM val) | |
635 | Equivalent to @code{scm_is_true (scm_real_p (val))} and | |
636 | @code{scm_is_true (scm_rational_p (val))}, respectively. | |
637 | @end deftypefn | |
638 | ||
639 | @deftypefn {C Function} double scm_to_double (SCM val) | |
640 | Returns the number closest to @var{val} that is representable as a | |
641 | @code{double}. Returns infinity for a @var{val} that is too large in | |
642 | magnitude. The argument @var{val} must be a real number. | |
643 | @end deftypefn | |
644 | ||
645 | @deftypefn {C Function} SCM scm_from_double (double val) | |
be3eb25c | 646 | Return the @code{SCM} value that represents @var{val}. The returned |
d3df9759 MV |
647 | value is inexact according to the predicate @code{inexact?}, but it |
648 | will be exactly equal to @var{val}. | |
649 | @end deftypefn | |
650 | ||
07d83abe MV |
651 | @node Complex Numbers |
652 | @subsubsection Complex Numbers | |
653 | @tpindex Complex numbers | |
654 | ||
655 | @rnindex complex? | |
656 | ||
657 | Complex numbers are the set of numbers that describe all possible points | |
658 | in a two-dimensional space. The two coordinates of a particular point | |
659 | in this space are known as the @dfn{real} and @dfn{imaginary} parts of | |
660 | the complex number that describes that point. | |
661 | ||
662 | In Guile, complex numbers are written in rectangular form as the sum of | |
663 | their real and imaginary parts, using the symbol @code{i} to indicate | |
664 | the imaginary part. | |
665 | ||
666 | @lisp | |
667 | 3+4i | |
668 | @result{} | |
669 | 3.0+4.0i | |
670 | ||
671 | (* 3-8i 2.3+0.3i) | |
672 | @result{} | |
673 | 9.3-17.5i | |
674 | @end lisp | |
675 | ||
34942993 KR |
676 | @cindex polar form |
677 | @noindent | |
678 | Polar form can also be used, with an @samp{@@} between magnitude and | |
679 | angle, | |
680 | ||
681 | @lisp | |
682 | 1@@3.141592 @result{} -1.0 (approx) | |
683 | -1@@1.57079 @result{} 0.0-1.0i (approx) | |
684 | @end lisp | |
685 | ||
c7218482 MW |
686 | Guile represents a complex number as a pair of inexact reals, so the |
687 | real and imaginary parts of a complex number have the same properties of | |
688 | inexactness and limited precision as single inexact real numbers. | |
689 | ||
690 | Note that each part of a complex number may contain any inexact real | |
691 | value, including the special values @samp{+nan.0}, @samp{+inf.0} and | |
692 | @samp{-inf.0}, as well as either of the signed zeroes @samp{0.0} or | |
693 | @samp{-0.0}. | |
694 | ||
07d83abe | 695 | |
5615f696 MV |
696 | @deffn {Scheme Procedure} complex? z |
697 | @deffnx {C Function} scm_complex_p (z) | |
07d83abe MV |
698 | Return @code{#t} if @var{x} is a complex number, @code{#f} |
699 | otherwise. Note that the sets of real, rational and integer | |
679cceed | 700 | values form subsets of the set of complex numbers, i.e.@: the |
07d83abe MV |
701 | predicate will also be fulfilled if @var{x} is a real, |
702 | rational or integer number. | |
703 | @end deffn | |
704 | ||
c9dc8c6c MV |
705 | @deftypefn {C Function} int scm_is_complex (SCM val) |
706 | Equivalent to @code{scm_is_true (scm_complex_p (val))}. | |
707 | @end deftypefn | |
708 | ||
07d83abe MV |
709 | @node Exactness |
710 | @subsubsection Exact and Inexact Numbers | |
711 | @tpindex Exact numbers | |
712 | @tpindex Inexact numbers | |
713 | ||
714 | @rnindex exact? | |
715 | @rnindex inexact? | |
716 | @rnindex exact->inexact | |
717 | @rnindex inexact->exact | |
718 | ||
654b2823 MW |
719 | R5RS requires that, with few exceptions, a calculation involving inexact |
720 | numbers always produces an inexact result. To meet this requirement, | |
721 | Guile distinguishes between an exact integer value such as @samp{5} and | |
722 | the corresponding inexact integer value which, to the limited precision | |
07d83abe MV |
723 | available, has no fractional part, and is printed as @samp{5.0}. Guile |
724 | will only convert the latter value to the former when forced to do so by | |
725 | an invocation of the @code{inexact->exact} procedure. | |
726 | ||
654b2823 MW |
727 | The only exception to the above requirement is when the values of the |
728 | inexact numbers do not affect the result. For example @code{(expt n 0)} | |
729 | is @samp{1} for any value of @code{n}, therefore @code{(expt 5.0 0)} is | |
730 | permitted to return an exact @samp{1}. | |
731 | ||
07d83abe MV |
732 | @deffn {Scheme Procedure} exact? z |
733 | @deffnx {C Function} scm_exact_p (z) | |
734 | Return @code{#t} if the number @var{z} is exact, @code{#f} | |
735 | otherwise. | |
736 | ||
737 | @lisp | |
738 | (exact? 2) | |
739 | @result{} #t | |
740 | ||
741 | (exact? 0.5) | |
742 | @result{} #f | |
743 | ||
744 | (exact? (/ 2)) | |
745 | @result{} #t | |
746 | @end lisp | |
747 | ||
748 | @end deffn | |
749 | ||
750 | @deffn {Scheme Procedure} inexact? z | |
751 | @deffnx {C Function} scm_inexact_p (z) | |
752 | Return @code{#t} if the number @var{z} is inexact, @code{#f} | |
753 | else. | |
754 | @end deffn | |
755 | ||
756 | @deffn {Scheme Procedure} inexact->exact z | |
757 | @deffnx {C Function} scm_inexact_to_exact (z) | |
758 | Return an exact number that is numerically closest to @var{z}, when | |
759 | there is one. For inexact rationals, Guile returns the exact rational | |
760 | that is numerically equal to the inexact rational. Inexact complex | |
761 | numbers with a non-zero imaginary part can not be made exact. | |
762 | ||
763 | @lisp | |
764 | (inexact->exact 0.5) | |
765 | @result{} 1/2 | |
766 | @end lisp | |
767 | ||
768 | The following happens because 12/10 is not exactly representable as a | |
769 | @code{double} (on most platforms). However, when reading a decimal | |
770 | number that has been marked exact with the ``#e'' prefix, Guile is | |
771 | able to represent it correctly. | |
772 | ||
773 | @lisp | |
774 | (inexact->exact 1.2) | |
775 | @result{} 5404319552844595/4503599627370496 | |
776 | ||
777 | #e1.2 | |
778 | @result{} 6/5 | |
779 | @end lisp | |
780 | ||
781 | @end deffn | |
782 | ||
783 | @c begin (texi-doc-string "guile" "exact->inexact") | |
784 | @deffn {Scheme Procedure} exact->inexact z | |
785 | @deffnx {C Function} scm_exact_to_inexact (z) | |
786 | Convert the number @var{z} to its inexact representation. | |
787 | @end deffn | |
788 | ||
789 | ||
790 | @node Number Syntax | |
791 | @subsubsection Read Syntax for Numerical Data | |
792 | ||
793 | The read syntax for integers is a string of digits, optionally | |
794 | preceded by a minus or plus character, a code indicating the | |
795 | base in which the integer is encoded, and a code indicating whether | |
796 | the number is exact or inexact. The supported base codes are: | |
797 | ||
798 | @table @code | |
799 | @item #b | |
800 | @itemx #B | |
801 | the integer is written in binary (base 2) | |
802 | ||
803 | @item #o | |
804 | @itemx #O | |
805 | the integer is written in octal (base 8) | |
806 | ||
807 | @item #d | |
808 | @itemx #D | |
809 | the integer is written in decimal (base 10) | |
810 | ||
811 | @item #x | |
812 | @itemx #X | |
813 | the integer is written in hexadecimal (base 16) | |
814 | @end table | |
815 | ||
816 | If the base code is omitted, the integer is assumed to be decimal. The | |
817 | following examples show how these base codes are used. | |
818 | ||
819 | @lisp | |
820 | -13 | |
821 | @result{} -13 | |
822 | ||
823 | #d-13 | |
824 | @result{} -13 | |
825 | ||
826 | #x-13 | |
827 | @result{} -19 | |
828 | ||
829 | #b+1101 | |
830 | @result{} 13 | |
831 | ||
832 | #o377 | |
833 | @result{} 255 | |
834 | @end lisp | |
835 | ||
836 | The codes for indicating exactness (which can, incidentally, be applied | |
837 | to all numerical values) are: | |
838 | ||
839 | @table @code | |
840 | @item #e | |
841 | @itemx #E | |
842 | the number is exact | |
843 | ||
844 | @item #i | |
845 | @itemx #I | |
846 | the number is inexact. | |
847 | @end table | |
848 | ||
849 | If the exactness indicator is omitted, the number is exact unless it | |
850 | contains a radix point. Since Guile can not represent exact complex | |
851 | numbers, an error is signalled when asking for them. | |
852 | ||
853 | @lisp | |
854 | (exact? 1.2) | |
855 | @result{} #f | |
856 | ||
857 | (exact? #e1.2) | |
858 | @result{} #t | |
859 | ||
860 | (exact? #e+1i) | |
861 | ERROR: Wrong type argument | |
862 | @end lisp | |
863 | ||
864 | Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for | |
865 | plus and minus infinity, respectively. The value must be written | |
866 | exactly as shown, that is, they always must have a sign and exactly | |
867 | one zero digit after the decimal point. It also understands | |
868 | @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value. | |
869 | The sign is ignored for `not-a-number' and the value is always printed | |
870 | as @samp{+nan.0}. | |
871 | ||
872 | @node Integer Operations | |
873 | @subsubsection Operations on Integer Values | |
874 | @rnindex odd? | |
875 | @rnindex even? | |
876 | @rnindex quotient | |
877 | @rnindex remainder | |
878 | @rnindex modulo | |
879 | @rnindex gcd | |
880 | @rnindex lcm | |
881 | ||
882 | @deffn {Scheme Procedure} odd? n | |
883 | @deffnx {C Function} scm_odd_p (n) | |
884 | Return @code{#t} if @var{n} is an odd number, @code{#f} | |
885 | otherwise. | |
886 | @end deffn | |
887 | ||
888 | @deffn {Scheme Procedure} even? n | |
889 | @deffnx {C Function} scm_even_p (n) | |
890 | Return @code{#t} if @var{n} is an even number, @code{#f} | |
891 | otherwise. | |
892 | @end deffn | |
893 | ||
894 | @c begin (texi-doc-string "guile" "quotient") | |
895 | @c begin (texi-doc-string "guile" "remainder") | |
896 | @deffn {Scheme Procedure} quotient n d | |
897 | @deffnx {Scheme Procedure} remainder n d | |
898 | @deffnx {C Function} scm_quotient (n, d) | |
899 | @deffnx {C Function} scm_remainder (n, d) | |
900 | Return the quotient or remainder from @var{n} divided by @var{d}. The | |
901 | quotient is rounded towards zero, and the remainder will have the same | |
902 | sign as @var{n}. In all cases quotient and remainder satisfy | |
903 | @math{@var{n} = @var{q}*@var{d} + @var{r}}. | |
904 | ||
905 | @lisp | |
906 | (remainder 13 4) @result{} 1 | |
907 | (remainder -13 4) @result{} -1 | |
908 | @end lisp | |
ff62c168 | 909 | |
8f9da340 | 910 | See also @code{truncate-quotient}, @code{truncate-remainder} and |
ff62c168 | 911 | related operations in @ref{Arithmetic}. |
07d83abe MV |
912 | @end deffn |
913 | ||
914 | @c begin (texi-doc-string "guile" "modulo") | |
915 | @deffn {Scheme Procedure} modulo n d | |
916 | @deffnx {C Function} scm_modulo (n, d) | |
917 | Return the remainder from @var{n} divided by @var{d}, with the same | |
918 | sign as @var{d}. | |
919 | ||
920 | @lisp | |
921 | (modulo 13 4) @result{} 1 | |
922 | (modulo -13 4) @result{} 3 | |
923 | (modulo 13 -4) @result{} -3 | |
924 | (modulo -13 -4) @result{} -1 | |
925 | @end lisp | |
ff62c168 | 926 | |
8f9da340 | 927 | See also @code{floor-quotient}, @code{floor-remainder} and |
ff62c168 | 928 | related operations in @ref{Arithmetic}. |
07d83abe MV |
929 | @end deffn |
930 | ||
931 | @c begin (texi-doc-string "guile" "gcd") | |
fd8a1df5 | 932 | @deffn {Scheme Procedure} gcd x@dots{} |
07d83abe MV |
933 | @deffnx {C Function} scm_gcd (x, y) |
934 | Return the greatest common divisor of all arguments. | |
935 | If called without arguments, 0 is returned. | |
936 | ||
937 | The C function @code{scm_gcd} always takes two arguments, while the | |
938 | Scheme function can take an arbitrary number. | |
939 | @end deffn | |
940 | ||
941 | @c begin (texi-doc-string "guile" "lcm") | |
fd8a1df5 | 942 | @deffn {Scheme Procedure} lcm x@dots{} |
07d83abe MV |
943 | @deffnx {C Function} scm_lcm (x, y) |
944 | Return the least common multiple of the arguments. | |
945 | If called without arguments, 1 is returned. | |
946 | ||
947 | The C function @code{scm_lcm} always takes two arguments, while the | |
948 | Scheme function can take an arbitrary number. | |
949 | @end deffn | |
950 | ||
cdf1ad3b MV |
951 | @deffn {Scheme Procedure} modulo-expt n k m |
952 | @deffnx {C Function} scm_modulo_expt (n, k, m) | |
953 | Return @var{n} raised to the integer exponent | |
954 | @var{k}, modulo @var{m}. | |
955 | ||
956 | @lisp | |
957 | (modulo-expt 2 3 5) | |
958 | @result{} 3 | |
959 | @end lisp | |
960 | @end deffn | |
07d83abe MV |
961 | |
962 | @node Comparison | |
963 | @subsubsection Comparison Predicates | |
964 | @rnindex zero? | |
965 | @rnindex positive? | |
966 | @rnindex negative? | |
967 | ||
968 | The C comparison functions below always takes two arguments, while the | |
969 | Scheme functions can take an arbitrary number. Also keep in mind that | |
970 | the C functions return one of the Scheme boolean values | |
971 | @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C | |
972 | is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x, | |
973 | y))} when testing the two Scheme numbers @code{x} and @code{y} for | |
974 | equality, for example. | |
975 | ||
976 | @c begin (texi-doc-string "guile" "=") | |
977 | @deffn {Scheme Procedure} = | |
978 | @deffnx {C Function} scm_num_eq_p (x, y) | |
979 | Return @code{#t} if all parameters are numerically equal. | |
980 | @end deffn | |
981 | ||
982 | @c begin (texi-doc-string "guile" "<") | |
983 | @deffn {Scheme Procedure} < | |
984 | @deffnx {C Function} scm_less_p (x, y) | |
985 | Return @code{#t} if the list of parameters is monotonically | |
986 | increasing. | |
987 | @end deffn | |
988 | ||
989 | @c begin (texi-doc-string "guile" ">") | |
990 | @deffn {Scheme Procedure} > | |
991 | @deffnx {C Function} scm_gr_p (x, y) | |
992 | Return @code{#t} if the list of parameters is monotonically | |
993 | decreasing. | |
994 | @end deffn | |
995 | ||
996 | @c begin (texi-doc-string "guile" "<=") | |
997 | @deffn {Scheme Procedure} <= | |
998 | @deffnx {C Function} scm_leq_p (x, y) | |
999 | Return @code{#t} if the list of parameters is monotonically | |
1000 | non-decreasing. | |
1001 | @end deffn | |
1002 | ||
1003 | @c begin (texi-doc-string "guile" ">=") | |
1004 | @deffn {Scheme Procedure} >= | |
1005 | @deffnx {C Function} scm_geq_p (x, y) | |
1006 | Return @code{#t} if the list of parameters is monotonically | |
1007 | non-increasing. | |
1008 | @end deffn | |
1009 | ||
1010 | @c begin (texi-doc-string "guile" "zero?") | |
1011 | @deffn {Scheme Procedure} zero? z | |
1012 | @deffnx {C Function} scm_zero_p (z) | |
1013 | Return @code{#t} if @var{z} is an exact or inexact number equal to | |
1014 | zero. | |
1015 | @end deffn | |
1016 | ||
1017 | @c begin (texi-doc-string "guile" "positive?") | |
1018 | @deffn {Scheme Procedure} positive? x | |
1019 | @deffnx {C Function} scm_positive_p (x) | |
1020 | Return @code{#t} if @var{x} is an exact or inexact number greater than | |
1021 | zero. | |
1022 | @end deffn | |
1023 | ||
1024 | @c begin (texi-doc-string "guile" "negative?") | |
1025 | @deffn {Scheme Procedure} negative? x | |
1026 | @deffnx {C Function} scm_negative_p (x) | |
1027 | Return @code{#t} if @var{x} is an exact or inexact number less than | |
1028 | zero. | |
1029 | @end deffn | |
1030 | ||
1031 | ||
1032 | @node Conversion | |
1033 | @subsubsection Converting Numbers To and From Strings | |
1034 | @rnindex number->string | |
1035 | @rnindex string->number | |
1036 | ||
b89c4943 LC |
1037 | The following procedures read and write numbers according to their |
1038 | external representation as defined by R5RS (@pxref{Lexical structure, | |
1039 | R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic | |
a2f00b9b | 1040 | Language Scheme}). @xref{Number Input and Output, the @code{(ice-9 |
b89c4943 LC |
1041 | i18n)} module}, for locale-dependent number parsing. |
1042 | ||
07d83abe MV |
1043 | @deffn {Scheme Procedure} number->string n [radix] |
1044 | @deffnx {C Function} scm_number_to_string (n, radix) | |
1045 | Return a string holding the external representation of the | |
1046 | number @var{n} in the given @var{radix}. If @var{n} is | |
1047 | inexact, a radix of 10 will be used. | |
1048 | @end deffn | |
1049 | ||
1050 | @deffn {Scheme Procedure} string->number string [radix] | |
1051 | @deffnx {C Function} scm_string_to_number (string, radix) | |
1052 | Return a number of the maximally precise representation | |
1053 | expressed by the given @var{string}. @var{radix} must be an | |
1054 | exact integer, either 2, 8, 10, or 16. If supplied, @var{radix} | |
1055 | is a default radix that may be overridden by an explicit radix | |
679cceed | 1056 | prefix in @var{string} (e.g.@: "#o177"). If @var{radix} is not |
07d83abe MV |
1057 | supplied, then the default radix is 10. If string is not a |
1058 | syntactically valid notation for a number, then | |
1059 | @code{string->number} returns @code{#f}. | |
1060 | @end deffn | |
1061 | ||
1b09b607 KR |
1062 | @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix) |
1063 | As per @code{string->number} above, but taking a C string, as pointer | |
1064 | and length. The string characters should be in the current locale | |
1065 | encoding (@code{locale} in the name refers only to that, there's no | |
1066 | locale-dependent parsing). | |
1067 | @end deftypefn | |
1068 | ||
07d83abe MV |
1069 | |
1070 | @node Complex | |
1071 | @subsubsection Complex Number Operations | |
1072 | @rnindex make-rectangular | |
1073 | @rnindex make-polar | |
1074 | @rnindex real-part | |
1075 | @rnindex imag-part | |
1076 | @rnindex magnitude | |
1077 | @rnindex angle | |
1078 | ||
3323ec06 NJ |
1079 | @deffn {Scheme Procedure} make-rectangular real_part imaginary_part |
1080 | @deffnx {C Function} scm_make_rectangular (real_part, imaginary_part) | |
1081 | Return a complex number constructed of the given @var{real-part} and @var{imaginary-part} parts. | |
07d83abe MV |
1082 | @end deffn |
1083 | ||
c7218482 MW |
1084 | @deffn {Scheme Procedure} make-polar mag ang |
1085 | @deffnx {C Function} scm_make_polar (mag, ang) | |
34942993 | 1086 | @cindex polar form |
c7218482 | 1087 | Return the complex number @var{mag} * e^(i * @var{ang}). |
07d83abe MV |
1088 | @end deffn |
1089 | ||
1090 | @c begin (texi-doc-string "guile" "real-part") | |
1091 | @deffn {Scheme Procedure} real-part z | |
1092 | @deffnx {C Function} scm_real_part (z) | |
1093 | Return the real part of the number @var{z}. | |
1094 | @end deffn | |
1095 | ||
1096 | @c begin (texi-doc-string "guile" "imag-part") | |
1097 | @deffn {Scheme Procedure} imag-part z | |
1098 | @deffnx {C Function} scm_imag_part (z) | |
1099 | Return the imaginary part of the number @var{z}. | |
1100 | @end deffn | |
1101 | ||
1102 | @c begin (texi-doc-string "guile" "magnitude") | |
1103 | @deffn {Scheme Procedure} magnitude z | |
1104 | @deffnx {C Function} scm_magnitude (z) | |
1105 | Return the magnitude of the number @var{z}. This is the same as | |
1106 | @code{abs} for real arguments, but also allows complex numbers. | |
1107 | @end deffn | |
1108 | ||
1109 | @c begin (texi-doc-string "guile" "angle") | |
1110 | @deffn {Scheme Procedure} angle z | |
1111 | @deffnx {C Function} scm_angle (z) | |
1112 | Return the angle of the complex number @var{z}. | |
1113 | @end deffn | |
1114 | ||
5615f696 MV |
1115 | @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im) |
1116 | @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y) | |
1117 | Like @code{scm_make_rectangular} or @code{scm_make_polar}, | |
1118 | respectively, but these functions take @code{double}s as their | |
1119 | arguments. | |
1120 | @end deftypefn | |
1121 | ||
1122 | @deftypefn {C Function} double scm_c_real_part (z) | |
1123 | @deftypefnx {C Function} double scm_c_imag_part (z) | |
1124 | Returns the real or imaginary part of @var{z} as a @code{double}. | |
1125 | @end deftypefn | |
1126 | ||
1127 | @deftypefn {C Function} double scm_c_magnitude (z) | |
1128 | @deftypefnx {C Function} double scm_c_angle (z) | |
1129 | Returns the magnitude or angle of @var{z} as a @code{double}. | |
1130 | @end deftypefn | |
1131 | ||
07d83abe MV |
1132 | |
1133 | @node Arithmetic | |
1134 | @subsubsection Arithmetic Functions | |
1135 | @rnindex max | |
1136 | @rnindex min | |
1137 | @rnindex + | |
1138 | @rnindex * | |
1139 | @rnindex - | |
1140 | @rnindex / | |
b1f57ea4 LC |
1141 | @findex 1+ |
1142 | @findex 1- | |
07d83abe MV |
1143 | @rnindex abs |
1144 | @rnindex floor | |
1145 | @rnindex ceiling | |
1146 | @rnindex truncate | |
1147 | @rnindex round | |
ff62c168 MW |
1148 | @rnindex euclidean/ |
1149 | @rnindex euclidean-quotient | |
1150 | @rnindex euclidean-remainder | |
8f9da340 MW |
1151 | @rnindex floor/ |
1152 | @rnindex floor-quotient | |
1153 | @rnindex floor-remainder | |
1154 | @rnindex ceiling/ | |
1155 | @rnindex ceiling-quotient | |
1156 | @rnindex ceiling-remainder | |
1157 | @rnindex truncate/ | |
1158 | @rnindex truncate-quotient | |
1159 | @rnindex truncate-remainder | |
ff62c168 MW |
1160 | @rnindex centered/ |
1161 | @rnindex centered-quotient | |
1162 | @rnindex centered-remainder | |
8f9da340 MW |
1163 | @rnindex round/ |
1164 | @rnindex round-quotient | |
1165 | @rnindex round-remainder | |
07d83abe MV |
1166 | |
1167 | The C arithmetic functions below always takes two arguments, while the | |
1168 | Scheme functions can take an arbitrary number. When you need to | |
1169 | invoke them with just one argument, for example to compute the | |
ecb87335 | 1170 | equivalent of @code{(- x)}, pass @code{SCM_UNDEFINED} as the second |
07d83abe MV |
1171 | one: @code{scm_difference (x, SCM_UNDEFINED)}. |
1172 | ||
1173 | @c begin (texi-doc-string "guile" "+") | |
1174 | @deffn {Scheme Procedure} + z1 @dots{} | |
1175 | @deffnx {C Function} scm_sum (z1, z2) | |
1176 | Return the sum of all parameter values. Return 0 if called without any | |
1177 | parameters. | |
1178 | @end deffn | |
1179 | ||
1180 | @c begin (texi-doc-string "guile" "-") | |
1181 | @deffn {Scheme Procedure} - z1 z2 @dots{} | |
1182 | @deffnx {C Function} scm_difference (z1, z2) | |
1183 | If called with one argument @var{z1}, -@var{z1} is returned. Otherwise | |
1184 | the sum of all but the first argument are subtracted from the first | |
1185 | argument. | |
1186 | @end deffn | |
1187 | ||
1188 | @c begin (texi-doc-string "guile" "*") | |
1189 | @deffn {Scheme Procedure} * z1 @dots{} | |
1190 | @deffnx {C Function} scm_product (z1, z2) | |
1191 | Return the product of all arguments. If called without arguments, 1 is | |
1192 | returned. | |
1193 | @end deffn | |
1194 | ||
1195 | @c begin (texi-doc-string "guile" "/") | |
1196 | @deffn {Scheme Procedure} / z1 z2 @dots{} | |
1197 | @deffnx {C Function} scm_divide (z1, z2) | |
1198 | Divide the first argument by the product of the remaining arguments. If | |
1199 | called with one argument @var{z1}, 1/@var{z1} is returned. | |
1200 | @end deffn | |
1201 | ||
b1f57ea4 LC |
1202 | @deffn {Scheme Procedure} 1+ z |
1203 | @deffnx {C Function} scm_oneplus (z) | |
1204 | Return @math{@var{z} + 1}. | |
1205 | @end deffn | |
1206 | ||
1207 | @deffn {Scheme Procedure} 1- z | |
1208 | @deffnx {C function} scm_oneminus (z) | |
1209 | Return @math{@var{z} - 1}. | |
1210 | @end deffn | |
1211 | ||
07d83abe MV |
1212 | @c begin (texi-doc-string "guile" "abs") |
1213 | @deffn {Scheme Procedure} abs x | |
1214 | @deffnx {C Function} scm_abs (x) | |
1215 | Return the absolute value of @var{x}. | |
1216 | ||
1217 | @var{x} must be a number with zero imaginary part. To calculate the | |
1218 | magnitude of a complex number, use @code{magnitude} instead. | |
1219 | @end deffn | |
1220 | ||
1221 | @c begin (texi-doc-string "guile" "max") | |
1222 | @deffn {Scheme Procedure} max x1 x2 @dots{} | |
1223 | @deffnx {C Function} scm_max (x1, x2) | |
1224 | Return the maximum of all parameter values. | |
1225 | @end deffn | |
1226 | ||
1227 | @c begin (texi-doc-string "guile" "min") | |
1228 | @deffn {Scheme Procedure} min x1 x2 @dots{} | |
1229 | @deffnx {C Function} scm_min (x1, x2) | |
1230 | Return the minimum of all parameter values. | |
1231 | @end deffn | |
1232 | ||
1233 | @c begin (texi-doc-string "guile" "truncate") | |
fd8a1df5 | 1234 | @deffn {Scheme Procedure} truncate x |
07d83abe MV |
1235 | @deffnx {C Function} scm_truncate_number (x) |
1236 | Round the inexact number @var{x} towards zero. | |
1237 | @end deffn | |
1238 | ||
1239 | @c begin (texi-doc-string "guile" "round") | |
1240 | @deffn {Scheme Procedure} round x | |
1241 | @deffnx {C Function} scm_round_number (x) | |
1242 | Round the inexact number @var{x} to the nearest integer. When exactly | |
1243 | halfway between two integers, round to the even one. | |
1244 | @end deffn | |
1245 | ||
1246 | @c begin (texi-doc-string "guile" "floor") | |
1247 | @deffn {Scheme Procedure} floor x | |
1248 | @deffnx {C Function} scm_floor (x) | |
1249 | Round the number @var{x} towards minus infinity. | |
1250 | @end deffn | |
1251 | ||
1252 | @c begin (texi-doc-string "guile" "ceiling") | |
1253 | @deffn {Scheme Procedure} ceiling x | |
1254 | @deffnx {C Function} scm_ceiling (x) | |
1255 | Round the number @var{x} towards infinity. | |
1256 | @end deffn | |
1257 | ||
35da08ee MV |
1258 | @deftypefn {C Function} double scm_c_truncate (double x) |
1259 | @deftypefnx {C Function} double scm_c_round (double x) | |
1260 | Like @code{scm_truncate_number} or @code{scm_round_number}, | |
1261 | respectively, but these functions take and return @code{double} | |
1262 | values. | |
1263 | @end deftypefn | |
07d83abe | 1264 | |
5fbf680b MW |
1265 | @deftypefn {Scheme Procedure} {} euclidean/ @var{x} @var{y} |
1266 | @deftypefnx {Scheme Procedure} {} euclidean-quotient @var{x} @var{y} | |
1267 | @deftypefnx {Scheme Procedure} {} euclidean-remainder @var{x} @var{y} | |
1268 | @deftypefnx {C Function} void scm_euclidean_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1269 | @deftypefnx {C Function} SCM scm_euclidean_quotient (SCM @var{x}, SCM @var{y}) | |
1270 | @deftypefnx {C Function} SCM scm_euclidean_remainder (SCM @var{x}, SCM @var{y}) | |
ff62c168 MW |
1271 | These procedures accept two real numbers @var{x} and @var{y}, where the |
1272 | divisor @var{y} must be non-zero. @code{euclidean-quotient} returns the | |
1273 | integer @var{q} and @code{euclidean-remainder} returns the real number | |
1274 | @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and | |
5fbf680b | 1275 | @math{0 <= @var{r} < |@var{y}|}. @code{euclidean/} returns both @var{q} and |
ff62c168 MW |
1276 | @var{r}, and is more efficient than computing each separately. Note |
1277 | that when @math{@var{y} > 0}, @code{euclidean-quotient} returns | |
1278 | @math{floor(@var{x}/@var{y})}, otherwise it returns | |
1279 | @math{ceiling(@var{x}/@var{y})}. | |
1280 | ||
1281 | Note that these operators are equivalent to the R6RS operators | |
1282 | @code{div}, @code{mod}, and @code{div-and-mod}. | |
1283 | ||
1284 | @lisp | |
1285 | (euclidean-quotient 123 10) @result{} 12 | |
1286 | (euclidean-remainder 123 10) @result{} 3 | |
1287 | (euclidean/ 123 10) @result{} 12 and 3 | |
1288 | (euclidean/ 123 -10) @result{} -12 and 3 | |
1289 | (euclidean/ -123 10) @result{} -13 and 7 | |
1290 | (euclidean/ -123 -10) @result{} 13 and 7 | |
1291 | (euclidean/ -123.2 -63.5) @result{} 2.0 and 3.8 | |
1292 | (euclidean/ 16/3 -10/7) @result{} -3 and 22/21 | |
1293 | @end lisp | |
5fbf680b | 1294 | @end deftypefn |
ff62c168 | 1295 | |
8f9da340 MW |
1296 | @deftypefn {Scheme Procedure} {} floor/ @var{x} @var{y} |
1297 | @deftypefnx {Scheme Procedure} {} floor-quotient @var{x} @var{y} | |
1298 | @deftypefnx {Scheme Procedure} {} floor-remainder @var{x} @var{y} | |
1299 | @deftypefnx {C Function} void scm_floor_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1300 | @deftypefnx {C Function} SCM scm_floor_quotient (@var{x}, @var{y}) | |
1301 | @deftypefnx {C Function} SCM scm_floor_remainder (@var{x}, @var{y}) | |
1302 | These procedures accept two real numbers @var{x} and @var{y}, where the | |
1303 | divisor @var{y} must be non-zero. @code{floor-quotient} returns the | |
1304 | integer @var{q} and @code{floor-remainder} returns the real number | |
1305 | @var{r} such that @math{@var{q} = floor(@var{x}/@var{y})} and | |
1306 | @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{floor/} returns | |
1307 | both @var{q} and @var{r}, and is more efficient than computing each | |
1308 | separately. Note that @var{r}, if non-zero, will have the same sign | |
1309 | as @var{y}. | |
1310 | ||
a6b087be | 1311 | When @var{x} and @var{y} are exact integers, @code{floor-remainder} is |
8f9da340 MW |
1312 | equivalent to the R5RS integer-only operator @code{modulo}. |
1313 | ||
1314 | @lisp | |
1315 | (floor-quotient 123 10) @result{} 12 | |
1316 | (floor-remainder 123 10) @result{} 3 | |
1317 | (floor/ 123 10) @result{} 12 and 3 | |
1318 | (floor/ 123 -10) @result{} -13 and -7 | |
1319 | (floor/ -123 10) @result{} -13 and 7 | |
1320 | (floor/ -123 -10) @result{} 12 and -3 | |
1321 | (floor/ -123.2 -63.5) @result{} 1.0 and -59.7 | |
1322 | (floor/ 16/3 -10/7) @result{} -4 and -8/21 | |
1323 | @end lisp | |
1324 | @end deftypefn | |
1325 | ||
1326 | @deftypefn {Scheme Procedure} {} ceiling/ @var{x} @var{y} | |
1327 | @deftypefnx {Scheme Procedure} {} ceiling-quotient @var{x} @var{y} | |
1328 | @deftypefnx {Scheme Procedure} {} ceiling-remainder @var{x} @var{y} | |
1329 | @deftypefnx {C Function} void scm_ceiling_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1330 | @deftypefnx {C Function} SCM scm_ceiling_quotient (@var{x}, @var{y}) | |
1331 | @deftypefnx {C Function} SCM scm_ceiling_remainder (@var{x}, @var{y}) | |
1332 | These procedures accept two real numbers @var{x} and @var{y}, where the | |
1333 | divisor @var{y} must be non-zero. @code{ceiling-quotient} returns the | |
1334 | integer @var{q} and @code{ceiling-remainder} returns the real number | |
1335 | @var{r} such that @math{@var{q} = ceiling(@var{x}/@var{y})} and | |
1336 | @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{ceiling/} returns | |
1337 | both @var{q} and @var{r}, and is more efficient than computing each | |
1338 | separately. Note that @var{r}, if non-zero, will have the opposite sign | |
1339 | of @var{y}. | |
1340 | ||
1341 | @lisp | |
1342 | (ceiling-quotient 123 10) @result{} 13 | |
1343 | (ceiling-remainder 123 10) @result{} -7 | |
1344 | (ceiling/ 123 10) @result{} 13 and -7 | |
1345 | (ceiling/ 123 -10) @result{} -12 and 3 | |
1346 | (ceiling/ -123 10) @result{} -12 and -3 | |
1347 | (ceiling/ -123 -10) @result{} 13 and 7 | |
1348 | (ceiling/ -123.2 -63.5) @result{} 2.0 and 3.8 | |
1349 | (ceiling/ 16/3 -10/7) @result{} -3 and 22/21 | |
1350 | @end lisp | |
1351 | @end deftypefn | |
1352 | ||
1353 | @deftypefn {Scheme Procedure} {} truncate/ @var{x} @var{y} | |
1354 | @deftypefnx {Scheme Procedure} {} truncate-quotient @var{x} @var{y} | |
1355 | @deftypefnx {Scheme Procedure} {} truncate-remainder @var{x} @var{y} | |
1356 | @deftypefnx {C Function} void scm_truncate_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1357 | @deftypefnx {C Function} SCM scm_truncate_quotient (@var{x}, @var{y}) | |
1358 | @deftypefnx {C Function} SCM scm_truncate_remainder (@var{x}, @var{y}) | |
1359 | These procedures accept two real numbers @var{x} and @var{y}, where the | |
1360 | divisor @var{y} must be non-zero. @code{truncate-quotient} returns the | |
1361 | integer @var{q} and @code{truncate-remainder} returns the real number | |
1362 | @var{r} such that @var{q} is @math{@var{x}/@var{y}} rounded toward zero, | |
1363 | and @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{truncate/} returns | |
1364 | both @var{q} and @var{r}, and is more efficient than computing each | |
1365 | separately. Note that @var{r}, if non-zero, will have the same sign | |
1366 | as @var{x}. | |
1367 | ||
a6b087be MW |
1368 | When @var{x} and @var{y} are exact integers, these operators are |
1369 | equivalent to the R5RS integer-only operators @code{quotient} and | |
1370 | @code{remainder}. | |
8f9da340 MW |
1371 | |
1372 | @lisp | |
1373 | (truncate-quotient 123 10) @result{} 12 | |
1374 | (truncate-remainder 123 10) @result{} 3 | |
1375 | (truncate/ 123 10) @result{} 12 and 3 | |
1376 | (truncate/ 123 -10) @result{} -12 and 3 | |
1377 | (truncate/ -123 10) @result{} -12 and -3 | |
1378 | (truncate/ -123 -10) @result{} 12 and -3 | |
1379 | (truncate/ -123.2 -63.5) @result{} 1.0 and -59.7 | |
1380 | (truncate/ 16/3 -10/7) @result{} -3 and 22/21 | |
1381 | @end lisp | |
1382 | @end deftypefn | |
1383 | ||
5fbf680b MW |
1384 | @deftypefn {Scheme Procedure} {} centered/ @var{x} @var{y} |
1385 | @deftypefnx {Scheme Procedure} {} centered-quotient @var{x} @var{y} | |
1386 | @deftypefnx {Scheme Procedure} {} centered-remainder @var{x} @var{y} | |
1387 | @deftypefnx {C Function} void scm_centered_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1388 | @deftypefnx {C Function} SCM scm_centered_quotient (SCM @var{x}, SCM @var{y}) | |
1389 | @deftypefnx {C Function} SCM scm_centered_remainder (SCM @var{x}, SCM @var{y}) | |
ff62c168 MW |
1390 | These procedures accept two real numbers @var{x} and @var{y}, where the |
1391 | divisor @var{y} must be non-zero. @code{centered-quotient} returns the | |
1392 | integer @var{q} and @code{centered-remainder} returns the real number | |
1393 | @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and | |
5fbf680b | 1394 | @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}. @code{centered/} |
ff62c168 MW |
1395 | returns both @var{q} and @var{r}, and is more efficient than computing |
1396 | each separately. | |
1397 | ||
1398 | Note that @code{centered-quotient} returns @math{@var{x}/@var{y}} | |
1399 | rounded to the nearest integer. When @math{@var{x}/@var{y}} lies | |
1400 | exactly half-way between two integers, the tie is broken according to | |
1401 | the sign of @var{y}. If @math{@var{y} > 0}, ties are rounded toward | |
1402 | positive infinity, otherwise they are rounded toward negative infinity. | |
5fbf680b MW |
1403 | This is a consequence of the requirement that |
1404 | @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}. | |
ff62c168 MW |
1405 | |
1406 | Note that these operators are equivalent to the R6RS operators | |
1407 | @code{div0}, @code{mod0}, and @code{div0-and-mod0}. | |
1408 | ||
1409 | @lisp | |
1410 | (centered-quotient 123 10) @result{} 12 | |
1411 | (centered-remainder 123 10) @result{} 3 | |
1412 | (centered/ 123 10) @result{} 12 and 3 | |
1413 | (centered/ 123 -10) @result{} -12 and 3 | |
1414 | (centered/ -123 10) @result{} -12 and -3 | |
1415 | (centered/ -123 -10) @result{} 12 and -3 | |
8f9da340 MW |
1416 | (centered/ 125 10) @result{} 13 and -5 |
1417 | (centered/ 127 10) @result{} 13 and -3 | |
1418 | (centered/ 135 10) @result{} 14 and -5 | |
ff62c168 MW |
1419 | (centered/ -123.2 -63.5) @result{} 2.0 and 3.8 |
1420 | (centered/ 16/3 -10/7) @result{} -4 and -8/21 | |
1421 | @end lisp | |
5fbf680b | 1422 | @end deftypefn |
ff62c168 | 1423 | |
8f9da340 MW |
1424 | @deftypefn {Scheme Procedure} {} round/ @var{x} @var{y} |
1425 | @deftypefnx {Scheme Procedure} {} round-quotient @var{x} @var{y} | |
1426 | @deftypefnx {Scheme Procedure} {} round-remainder @var{x} @var{y} | |
1427 | @deftypefnx {C Function} void scm_round_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r}) | |
1428 | @deftypefnx {C Function} SCM scm_round_quotient (@var{x}, @var{y}) | |
1429 | @deftypefnx {C Function} SCM scm_round_remainder (@var{x}, @var{y}) | |
1430 | These procedures accept two real numbers @var{x} and @var{y}, where the | |
1431 | divisor @var{y} must be non-zero. @code{round-quotient} returns the | |
1432 | integer @var{q} and @code{round-remainder} returns the real number | |
1433 | @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and | |
1434 | @var{q} is @math{@var{x}/@var{y}} rounded to the nearest integer, | |
1435 | with ties going to the nearest even integer. @code{round/} | |
1436 | returns both @var{q} and @var{r}, and is more efficient than computing | |
1437 | each separately. | |
1438 | ||
1439 | Note that @code{round/} and @code{centered/} are almost equivalent, but | |
1440 | their behavior differs when @math{@var{x}/@var{y}} lies exactly half-way | |
1441 | between two integers. In this case, @code{round/} chooses the nearest | |
1442 | even integer, whereas @code{centered/} chooses in such a way to satisfy | |
1443 | the constraint @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}, which | |
1444 | is stronger than the corresponding constraint for @code{round/}, | |
1445 | @math{-|@var{y}/2| <= @var{r} <= |@var{y}/2|}. In particular, | |
1446 | when @var{x} and @var{y} are integers, the number of possible remainders | |
1447 | returned by @code{centered/} is @math{|@var{y}|}, whereas the number of | |
1448 | possible remainders returned by @code{round/} is @math{|@var{y}|+1} when | |
1449 | @var{y} is even. | |
1450 | ||
1451 | @lisp | |
1452 | (round-quotient 123 10) @result{} 12 | |
1453 | (round-remainder 123 10) @result{} 3 | |
1454 | (round/ 123 10) @result{} 12 and 3 | |
1455 | (round/ 123 -10) @result{} -12 and 3 | |
1456 | (round/ -123 10) @result{} -12 and -3 | |
1457 | (round/ -123 -10) @result{} 12 and -3 | |
1458 | (round/ 125 10) @result{} 12 and 5 | |
1459 | (round/ 127 10) @result{} 13 and -3 | |
1460 | (round/ 135 10) @result{} 14 and -5 | |
1461 | (round/ -123.2 -63.5) @result{} 2.0 and 3.8 | |
1462 | (round/ 16/3 -10/7) @result{} -4 and -8/21 | |
1463 | @end lisp | |
1464 | @end deftypefn | |
1465 | ||
07d83abe MV |
1466 | @node Scientific |
1467 | @subsubsection Scientific Functions | |
1468 | ||
1469 | The following procedures accept any kind of number as arguments, | |
1470 | including complex numbers. | |
1471 | ||
1472 | @rnindex sqrt | |
1473 | @c begin (texi-doc-string "guile" "sqrt") | |
1474 | @deffn {Scheme Procedure} sqrt z | |
40296bab | 1475 | Return the square root of @var{z}. Of the two possible roots |
ecb87335 | 1476 | (positive and negative), the one with a positive real part is |
40296bab KR |
1477 | returned, or if that's zero then a positive imaginary part. Thus, |
1478 | ||
1479 | @example | |
1480 | (sqrt 9.0) @result{} 3.0 | |
1481 | (sqrt -9.0) @result{} 0.0+3.0i | |
1482 | (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i | |
1483 | (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i | |
1484 | @end example | |
07d83abe MV |
1485 | @end deffn |
1486 | ||
1487 | @rnindex expt | |
1488 | @c begin (texi-doc-string "guile" "expt") | |
1489 | @deffn {Scheme Procedure} expt z1 z2 | |
1490 | Return @var{z1} raised to the power of @var{z2}. | |
1491 | @end deffn | |
1492 | ||
1493 | @rnindex sin | |
1494 | @c begin (texi-doc-string "guile" "sin") | |
1495 | @deffn {Scheme Procedure} sin z | |
1496 | Return the sine of @var{z}. | |
1497 | @end deffn | |
1498 | ||
1499 | @rnindex cos | |
1500 | @c begin (texi-doc-string "guile" "cos") | |
1501 | @deffn {Scheme Procedure} cos z | |
1502 | Return the cosine of @var{z}. | |
1503 | @end deffn | |
1504 | ||
1505 | @rnindex tan | |
1506 | @c begin (texi-doc-string "guile" "tan") | |
1507 | @deffn {Scheme Procedure} tan z | |
1508 | Return the tangent of @var{z}. | |
1509 | @end deffn | |
1510 | ||
1511 | @rnindex asin | |
1512 | @c begin (texi-doc-string "guile" "asin") | |
1513 | @deffn {Scheme Procedure} asin z | |
1514 | Return the arcsine of @var{z}. | |
1515 | @end deffn | |
1516 | ||
1517 | @rnindex acos | |
1518 | @c begin (texi-doc-string "guile" "acos") | |
1519 | @deffn {Scheme Procedure} acos z | |
1520 | Return the arccosine of @var{z}. | |
1521 | @end deffn | |
1522 | ||
1523 | @rnindex atan | |
1524 | @c begin (texi-doc-string "guile" "atan") | |
1525 | @deffn {Scheme Procedure} atan z | |
1526 | @deffnx {Scheme Procedure} atan y x | |
1527 | Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}. | |
1528 | @end deffn | |
1529 | ||
1530 | @rnindex exp | |
1531 | @c begin (texi-doc-string "guile" "exp") | |
1532 | @deffn {Scheme Procedure} exp z | |
1533 | Return e to the power of @var{z}, where e is the base of natural | |
1534 | logarithms (2.71828@dots{}). | |
1535 | @end deffn | |
1536 | ||
1537 | @rnindex log | |
1538 | @c begin (texi-doc-string "guile" "log") | |
1539 | @deffn {Scheme Procedure} log z | |
1540 | Return the natural logarithm of @var{z}. | |
1541 | @end deffn | |
1542 | ||
1543 | @c begin (texi-doc-string "guile" "log10") | |
1544 | @deffn {Scheme Procedure} log10 z | |
1545 | Return the base 10 logarithm of @var{z}. | |
1546 | @end deffn | |
1547 | ||
1548 | @c begin (texi-doc-string "guile" "sinh") | |
1549 | @deffn {Scheme Procedure} sinh z | |
1550 | Return the hyperbolic sine of @var{z}. | |
1551 | @end deffn | |
1552 | ||
1553 | @c begin (texi-doc-string "guile" "cosh") | |
1554 | @deffn {Scheme Procedure} cosh z | |
1555 | Return the hyperbolic cosine of @var{z}. | |
1556 | @end deffn | |
1557 | ||
1558 | @c begin (texi-doc-string "guile" "tanh") | |
1559 | @deffn {Scheme Procedure} tanh z | |
1560 | Return the hyperbolic tangent of @var{z}. | |
1561 | @end deffn | |
1562 | ||
1563 | @c begin (texi-doc-string "guile" "asinh") | |
1564 | @deffn {Scheme Procedure} asinh z | |
1565 | Return the hyperbolic arcsine of @var{z}. | |
1566 | @end deffn | |
1567 | ||
1568 | @c begin (texi-doc-string "guile" "acosh") | |
1569 | @deffn {Scheme Procedure} acosh z | |
1570 | Return the hyperbolic arccosine of @var{z}. | |
1571 | @end deffn | |
1572 | ||
1573 | @c begin (texi-doc-string "guile" "atanh") | |
1574 | @deffn {Scheme Procedure} atanh z | |
1575 | Return the hyperbolic arctangent of @var{z}. | |
1576 | @end deffn | |
1577 | ||
1578 | ||
07d83abe MV |
1579 | @node Bitwise Operations |
1580 | @subsubsection Bitwise Operations | |
1581 | ||
1582 | For the following bitwise functions, negative numbers are treated as | |
1583 | infinite precision twos-complements. For instance @math{-6} is bits | |
1584 | @math{@dots{}111010}, with infinitely many ones on the left. It can | |
1585 | be seen that adding 6 (binary 110) to such a bit pattern gives all | |
1586 | zeros. | |
1587 | ||
1588 | @deffn {Scheme Procedure} logand n1 n2 @dots{} | |
1589 | @deffnx {C Function} scm_logand (n1, n2) | |
1590 | Return the bitwise @sc{and} of the integer arguments. | |
1591 | ||
1592 | @lisp | |
1593 | (logand) @result{} -1 | |
1594 | (logand 7) @result{} 7 | |
1595 | (logand #b111 #b011 #b001) @result{} 1 | |
1596 | @end lisp | |
1597 | @end deffn | |
1598 | ||
1599 | @deffn {Scheme Procedure} logior n1 n2 @dots{} | |
1600 | @deffnx {C Function} scm_logior (n1, n2) | |
1601 | Return the bitwise @sc{or} of the integer arguments. | |
1602 | ||
1603 | @lisp | |
1604 | (logior) @result{} 0 | |
1605 | (logior 7) @result{} 7 | |
1606 | (logior #b000 #b001 #b011) @result{} 3 | |
1607 | @end lisp | |
1608 | @end deffn | |
1609 | ||
1610 | @deffn {Scheme Procedure} logxor n1 n2 @dots{} | |
1611 | @deffnx {C Function} scm_loxor (n1, n2) | |
1612 | Return the bitwise @sc{xor} of the integer arguments. A bit is | |
1613 | set in the result if it is set in an odd number of arguments. | |
1614 | ||
1615 | @lisp | |
1616 | (logxor) @result{} 0 | |
1617 | (logxor 7) @result{} 7 | |
1618 | (logxor #b000 #b001 #b011) @result{} 2 | |
1619 | (logxor #b000 #b001 #b011 #b011) @result{} 1 | |
1620 | @end lisp | |
1621 | @end deffn | |
1622 | ||
1623 | @deffn {Scheme Procedure} lognot n | |
1624 | @deffnx {C Function} scm_lognot (n) | |
1625 | Return the integer which is the ones-complement of the integer | |
1626 | argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0. | |
1627 | ||
1628 | @lisp | |
1629 | (number->string (lognot #b10000000) 2) | |
1630 | @result{} "-10000001" | |
1631 | (number->string (lognot #b0) 2) | |
1632 | @result{} "-1" | |
1633 | @end lisp | |
1634 | @end deffn | |
1635 | ||
1636 | @deffn {Scheme Procedure} logtest j k | |
1637 | @deffnx {C Function} scm_logtest (j, k) | |
a46648ac KR |
1638 | Test whether @var{j} and @var{k} have any 1 bits in common. This is |
1639 | equivalent to @code{(not (zero? (logand j k)))}, but without actually | |
1640 | calculating the @code{logand}, just testing for non-zero. | |
07d83abe | 1641 | |
a46648ac | 1642 | @lisp |
07d83abe MV |
1643 | (logtest #b0100 #b1011) @result{} #f |
1644 | (logtest #b0100 #b0111) @result{} #t | |
1645 | @end lisp | |
1646 | @end deffn | |
1647 | ||
1648 | @deffn {Scheme Procedure} logbit? index j | |
1649 | @deffnx {C Function} scm_logbit_p (index, j) | |
a46648ac KR |
1650 | Test whether bit number @var{index} in @var{j} is set. @var{index} |
1651 | starts from 0 for the least significant bit. | |
07d83abe | 1652 | |
a46648ac | 1653 | @lisp |
07d83abe MV |
1654 | (logbit? 0 #b1101) @result{} #t |
1655 | (logbit? 1 #b1101) @result{} #f | |
1656 | (logbit? 2 #b1101) @result{} #t | |
1657 | (logbit? 3 #b1101) @result{} #t | |
1658 | (logbit? 4 #b1101) @result{} #f | |
1659 | @end lisp | |
1660 | @end deffn | |
1661 | ||
1662 | @deffn {Scheme Procedure} ash n cnt | |
1663 | @deffnx {C Function} scm_ash (n, cnt) | |
1664 | Return @var{n} shifted left by @var{cnt} bits, or shifted right if | |
1665 | @var{cnt} is negative. This is an ``arithmetic'' shift. | |
1666 | ||
1667 | This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and | |
1668 | when @var{cnt} is negative it's a division, rounded towards negative | |
1669 | infinity. (Note that this is not the same rounding as @code{quotient} | |
1670 | does.) | |
1671 | ||
1672 | With @var{n} viewed as an infinite precision twos complement, | |
1673 | @code{ash} means a left shift introducing zero bits, or a right shift | |
1674 | dropping bits. | |
1675 | ||
1676 | @lisp | |
1677 | (number->string (ash #b1 3) 2) @result{} "1000" | |
1678 | (number->string (ash #b1010 -1) 2) @result{} "101" | |
1679 | ||
1680 | ;; -23 is bits ...11101001, -6 is bits ...111010 | |
1681 | (ash -23 -2) @result{} -6 | |
1682 | @end lisp | |
1683 | @end deffn | |
1684 | ||
1685 | @deffn {Scheme Procedure} logcount n | |
1686 | @deffnx {C Function} scm_logcount (n) | |
a46648ac | 1687 | Return the number of bits in integer @var{n}. If @var{n} is |
07d83abe MV |
1688 | positive, the 1-bits in its binary representation are counted. |
1689 | If negative, the 0-bits in its two's-complement binary | |
a46648ac | 1690 | representation are counted. If zero, 0 is returned. |
07d83abe MV |
1691 | |
1692 | @lisp | |
1693 | (logcount #b10101010) | |
1694 | @result{} 4 | |
1695 | (logcount 0) | |
1696 | @result{} 0 | |
1697 | (logcount -2) | |
1698 | @result{} 1 | |
1699 | @end lisp | |
1700 | @end deffn | |
1701 | ||
1702 | @deffn {Scheme Procedure} integer-length n | |
1703 | @deffnx {C Function} scm_integer_length (n) | |
1704 | Return the number of bits necessary to represent @var{n}. | |
1705 | ||
1706 | For positive @var{n} this is how many bits to the most significant one | |
1707 | bit. For negative @var{n} it's how many bits to the most significant | |
1708 | zero bit in twos complement form. | |
1709 | ||
1710 | @lisp | |
1711 | (integer-length #b10101010) @result{} 8 | |
1712 | (integer-length #b1111) @result{} 4 | |
1713 | (integer-length 0) @result{} 0 | |
1714 | (integer-length -1) @result{} 0 | |
1715 | (integer-length -256) @result{} 8 | |
1716 | (integer-length -257) @result{} 9 | |
1717 | @end lisp | |
1718 | @end deffn | |
1719 | ||
1720 | @deffn {Scheme Procedure} integer-expt n k | |
1721 | @deffnx {C Function} scm_integer_expt (n, k) | |
a46648ac KR |
1722 | Return @var{n} raised to the power @var{k}. @var{k} must be an exact |
1723 | integer, @var{n} can be any number. | |
1724 | ||
1725 | Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)} | |
1726 | in the usual way. @math{@var{n}^0} is 1, as usual, and that includes | |
1727 | @math{0^0} is 1. | |
07d83abe MV |
1728 | |
1729 | @lisp | |
a46648ac KR |
1730 | (integer-expt 2 5) @result{} 32 |
1731 | (integer-expt -3 3) @result{} -27 | |
1732 | (integer-expt 5 -3) @result{} 1/125 | |
1733 | (integer-expt 0 0) @result{} 1 | |
07d83abe MV |
1734 | @end lisp |
1735 | @end deffn | |
1736 | ||
1737 | @deffn {Scheme Procedure} bit-extract n start end | |
1738 | @deffnx {C Function} scm_bit_extract (n, start, end) | |
1739 | Return the integer composed of the @var{start} (inclusive) | |
1740 | through @var{end} (exclusive) bits of @var{n}. The | |
1741 | @var{start}th bit becomes the 0-th bit in the result. | |
1742 | ||
1743 | @lisp | |
1744 | (number->string (bit-extract #b1101101010 0 4) 2) | |
1745 | @result{} "1010" | |
1746 | (number->string (bit-extract #b1101101010 4 9) 2) | |
1747 | @result{} "10110" | |
1748 | @end lisp | |
1749 | @end deffn | |
1750 | ||
1751 | ||
1752 | @node Random | |
1753 | @subsubsection Random Number Generation | |
1754 | ||
1755 | Pseudo-random numbers are generated from a random state object, which | |
77b13912 | 1756 | can be created with @code{seed->random-state} or |
679cceed | 1757 | @code{datum->random-state}. An external representation (i.e.@: one |
77b13912 AR |
1758 | which can written with @code{write} and read with @code{read}) of a |
1759 | random state object can be obtained via | |
1d454874 | 1760 | @code{random-state->datum}. The @var{state} parameter to the |
77b13912 AR |
1761 | various functions below is optional, it defaults to the state object |
1762 | in the @code{*random-state*} variable. | |
07d83abe MV |
1763 | |
1764 | @deffn {Scheme Procedure} copy-random-state [state] | |
1765 | @deffnx {C Function} scm_copy_random_state (state) | |
1766 | Return a copy of the random state @var{state}. | |
1767 | @end deffn | |
1768 | ||
1769 | @deffn {Scheme Procedure} random n [state] | |
1770 | @deffnx {C Function} scm_random (n, state) | |
1771 | Return a number in [0, @var{n}). | |
1772 | ||
1773 | Accepts a positive integer or real n and returns a | |
1774 | number of the same type between zero (inclusive) and | |
1775 | @var{n} (exclusive). The values returned have a uniform | |
1776 | distribution. | |
1777 | @end deffn | |
1778 | ||
1779 | @deffn {Scheme Procedure} random:exp [state] | |
1780 | @deffnx {C Function} scm_random_exp (state) | |
1781 | Return an inexact real in an exponential distribution with mean | |
1782 | 1. For an exponential distribution with mean @var{u} use @code{(* | |
1783 | @var{u} (random:exp))}. | |
1784 | @end deffn | |
1785 | ||
1786 | @deffn {Scheme Procedure} random:hollow-sphere! vect [state] | |
1787 | @deffnx {C Function} scm_random_hollow_sphere_x (vect, state) | |
1788 | Fills @var{vect} with inexact real random numbers the sum of whose | |
1789 | squares is equal to 1.0. Thinking of @var{vect} as coordinates in | |
1790 | space of dimension @var{n} @math{=} @code{(vector-length @var{vect})}, | |
1791 | the coordinates are uniformly distributed over the surface of the unit | |
1792 | n-sphere. | |
1793 | @end deffn | |
1794 | ||
1795 | @deffn {Scheme Procedure} random:normal [state] | |
1796 | @deffnx {C Function} scm_random_normal (state) | |
1797 | Return an inexact real in a normal distribution. The distribution | |
1798 | used has mean 0 and standard deviation 1. For a normal distribution | |
1799 | with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m} | |
1800 | (* @var{d} (random:normal)))}. | |
1801 | @end deffn | |
1802 | ||
1803 | @deffn {Scheme Procedure} random:normal-vector! vect [state] | |
1804 | @deffnx {C Function} scm_random_normal_vector_x (vect, state) | |
1805 | Fills @var{vect} with inexact real random numbers that are | |
1806 | independent and standard normally distributed | |
1807 | (i.e., with mean 0 and variance 1). | |
1808 | @end deffn | |
1809 | ||
1810 | @deffn {Scheme Procedure} random:solid-sphere! vect [state] | |
1811 | @deffnx {C Function} scm_random_solid_sphere_x (vect, state) | |
1812 | Fills @var{vect} with inexact real random numbers the sum of whose | |
1813 | squares is less than 1.0. Thinking of @var{vect} as coordinates in | |
1814 | space of dimension @var{n} @math{=} @code{(vector-length @var{vect})}, | |
1815 | the coordinates are uniformly distributed within the unit | |
4497bd2f | 1816 | @var{n}-sphere. |
07d83abe MV |
1817 | @c FIXME: What does this mean, particularly the n-sphere part? |
1818 | @end deffn | |
1819 | ||
1820 | @deffn {Scheme Procedure} random:uniform [state] | |
1821 | @deffnx {C Function} scm_random_uniform (state) | |
1822 | Return a uniformly distributed inexact real random number in | |
1823 | [0,1). | |
1824 | @end deffn | |
1825 | ||
1826 | @deffn {Scheme Procedure} seed->random-state seed | |
1827 | @deffnx {C Function} scm_seed_to_random_state (seed) | |
1828 | Return a new random state using @var{seed}. | |
1829 | @end deffn | |
1830 | ||
1d454874 AW |
1831 | @deffn {Scheme Procedure} datum->random-state datum |
1832 | @deffnx {C Function} scm_datum_to_random_state (datum) | |
1833 | Return a new random state from @var{datum}, which should have been | |
1834 | obtained by @code{random-state->datum}. | |
77b13912 AR |
1835 | @end deffn |
1836 | ||
1d454874 AW |
1837 | @deffn {Scheme Procedure} random-state->datum state |
1838 | @deffnx {C Function} scm_random_state_to_datum (state) | |
1839 | Return a datum representation of @var{state} that may be written out and | |
1840 | read back with the Scheme reader. | |
77b13912 AR |
1841 | @end deffn |
1842 | ||
07d83abe MV |
1843 | @defvar *random-state* |
1844 | The global random state used by the above functions when the | |
1845 | @var{state} parameter is not given. | |
1846 | @end defvar | |
1847 | ||
8c726cf0 NJ |
1848 | Note that the initial value of @code{*random-state*} is the same every |
1849 | time Guile starts up. Therefore, if you don't pass a @var{state} | |
1850 | parameter to the above procedures, and you don't set | |
1851 | @code{*random-state*} to @code{(seed->random-state your-seed)}, where | |
1852 | @code{your-seed} is something that @emph{isn't} the same every time, | |
1853 | you'll get the same sequence of ``random'' numbers on every run. | |
1854 | ||
1855 | For example, unless the relevant source code has changed, @code{(map | |
1856 | random (cdr (iota 30)))}, if the first use of random numbers since | |
1857 | Guile started up, will always give: | |
1858 | ||
1859 | @lisp | |
1860 | (map random (cdr (iota 19))) | |
1861 | @result{} | |
1862 | (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12) | |
1863 | @end lisp | |
1864 | ||
1865 | To use the time of day as the random seed, you can use code like this: | |
1866 | ||
1867 | @lisp | |
1868 | (let ((time (gettimeofday))) | |
1869 | (set! *random-state* | |
1870 | (seed->random-state (+ (car time) | |
1871 | (cdr time))))) | |
1872 | @end lisp | |
1873 | ||
1874 | @noindent | |
1875 | And then (depending on the time of day, of course): | |
1876 | ||
1877 | @lisp | |
1878 | (map random (cdr (iota 19))) | |
1879 | @result{} | |
1880 | (0 0 1 0 2 4 5 4 5 5 9 3 10 1 8 3 14 17) | |
1881 | @end lisp | |
1882 | ||
1883 | For security applications, such as password generation, you should use | |
1884 | more bits of seed. Otherwise an open source password generator could | |
1885 | be attacked by guessing the seed@dots{} but that's a subject for | |
1886 | another manual. | |
1887 | ||
07d83abe MV |
1888 | |
1889 | @node Characters | |
1890 | @subsection Characters | |
1891 | @tpindex Characters | |
1892 | ||
3f12aedb MG |
1893 | In Scheme, there is a data type to describe a single character. |
1894 | ||
1895 | Defining what exactly a character @emph{is} can be more complicated | |
bb15a36c MG |
1896 | than it seems. Guile follows the advice of R6RS and uses The Unicode |
1897 | Standard to help define what a character is. So, for Guile, a | |
1898 | character is anything in the Unicode Character Database. | |
1899 | ||
1900 | @cindex code point | |
1901 | @cindex Unicode code point | |
1902 | ||
1903 | The Unicode Character Database is basically a table of characters | |
1904 | indexed using integers called 'code points'. Valid code points are in | |
1905 | the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to | |
1906 | @code{#x10FFFF} inclusive, which is about 1.1 million code points. | |
1907 | ||
1908 | @cindex designated code point | |
1909 | @cindex code point, designated | |
1910 | ||
1911 | Any code point that has been assigned to a character or that has | |
1912 | otherwise been given a meaning by Unicode is called a 'designated code | |
1913 | point'. Most of the designated code points, about 200,000 of them, | |
1914 | indicate characters, accents or other combining marks that modify | |
1915 | other characters, symbols, whitespace, and control characters. Some | |
1916 | are not characters but indicators that suggest how to format or | |
1917 | display neighboring characters. | |
1918 | ||
1919 | @cindex reserved code point | |
1920 | @cindex code point, reserved | |
1921 | ||
1922 | If a code point is not a designated code point -- if it has not been | |
1923 | assigned to a character by The Unicode Standard -- it is a 'reserved | |
1924 | code point', meaning that they are reserved for future use. Most of | |
1925 | the code points, about 800,000, are 'reserved code points'. | |
1926 | ||
1927 | By convention, a Unicode code point is written as | |
1928 | ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that | |
1929 | this convenient notation is not valid code. Guile does not interpret | |
1930 | ``U+XXXX'' as a character. | |
3f12aedb | 1931 | |
050ab45f MV |
1932 | In Scheme, a character literal is written as @code{#\@var{name}} where |
1933 | @var{name} is the name of the character that you want. Printable | |
1934 | characters have their usual single character name; for example, | |
bb15a36c MG |
1935 | @code{#\a} is a lower case @code{a}. |
1936 | ||
1937 | Some of the code points are 'combining characters' that are not meant | |
1938 | to be printed by themselves but are instead meant to modify the | |
1939 | appearance of the previous character. For combining characters, an | |
1940 | alternate form of the character literal is @code{#\} followed by | |
1941 | U+25CC (a small, dotted circle), followed by the combining character. | |
1942 | This allows the combining character to be drawn on the circle, not on | |
1943 | the backslash of @code{#\}. | |
1944 | ||
1945 | Many of the non-printing characters, such as whitespace characters and | |
1946 | control characters, also have names. | |
07d83abe | 1947 | |
15b6a6b2 MG |
1948 | The most commonly used non-printing characters have long character |
1949 | names, described in the table below. | |
1950 | ||
1951 | @multitable {@code{#\backspace}} {Preferred} | |
1952 | @item Character Name @tab Codepoint | |
1953 | @item @code{#\nul} @tab U+0000 | |
1954 | @item @code{#\alarm} @tab u+0007 | |
1955 | @item @code{#\backspace} @tab U+0008 | |
1956 | @item @code{#\tab} @tab U+0009 | |
1957 | @item @code{#\linefeed} @tab U+000A | |
1958 | @item @code{#\newline} @tab U+000A | |
1959 | @item @code{#\vtab} @tab U+000B | |
1960 | @item @code{#\page} @tab U+000C | |
1961 | @item @code{#\return} @tab U+000D | |
1962 | @item @code{#\esc} @tab U+001B | |
1963 | @item @code{#\space} @tab U+0020 | |
1964 | @item @code{#\delete} @tab U+007F | |
1965 | @end multitable | |
1966 | ||
1967 | There are also short names for all of the ``C0 control characters'' | |
1968 | (those with code points below 32). The following table lists the short | |
1969 | name for each character. | |
07d83abe MV |
1970 | |
1971 | @multitable @columnfractions .25 .25 .25 .25 | |
1972 | @item 0 = @code{#\nul} | |
1973 | @tab 1 = @code{#\soh} | |
1974 | @tab 2 = @code{#\stx} | |
1975 | @tab 3 = @code{#\etx} | |
1976 | @item 4 = @code{#\eot} | |
1977 | @tab 5 = @code{#\enq} | |
1978 | @tab 6 = @code{#\ack} | |
1979 | @tab 7 = @code{#\bel} | |
1980 | @item 8 = @code{#\bs} | |
1981 | @tab 9 = @code{#\ht} | |
6ea30487 | 1982 | @tab 10 = @code{#\lf} |
07d83abe | 1983 | @tab 11 = @code{#\vt} |
3f12aedb | 1984 | @item 12 = @code{#\ff} |
07d83abe MV |
1985 | @tab 13 = @code{#\cr} |
1986 | @tab 14 = @code{#\so} | |
1987 | @tab 15 = @code{#\si} | |
1988 | @item 16 = @code{#\dle} | |
1989 | @tab 17 = @code{#\dc1} | |
1990 | @tab 18 = @code{#\dc2} | |
1991 | @tab 19 = @code{#\dc3} | |
1992 | @item 20 = @code{#\dc4} | |
1993 | @tab 21 = @code{#\nak} | |
1994 | @tab 22 = @code{#\syn} | |
1995 | @tab 23 = @code{#\etb} | |
1996 | @item 24 = @code{#\can} | |
1997 | @tab 25 = @code{#\em} | |
1998 | @tab 26 = @code{#\sub} | |
1999 | @tab 27 = @code{#\esc} | |
2000 | @item 28 = @code{#\fs} | |
2001 | @tab 29 = @code{#\gs} | |
2002 | @tab 30 = @code{#\rs} | |
2003 | @tab 31 = @code{#\us} | |
2004 | @item 32 = @code{#\sp} | |
2005 | @end multitable | |
2006 | ||
15b6a6b2 MG |
2007 | The short name for the ``delete'' character (code point U+007F) is |
2008 | @code{#\del}. | |
07d83abe | 2009 | |
15b6a6b2 MG |
2010 | There are also a few alternative names left over for compatibility with |
2011 | previous versions of Guile. | |
07d83abe | 2012 | |
3f12aedb MG |
2013 | @multitable {@code{#\backspace}} {Preferred} |
2014 | @item Alternate @tab Standard | |
3f12aedb | 2015 | @item @code{#\nl} @tab @code{#\newline} |
15b6a6b2 | 2016 | @item @code{#\np} @tab @code{#\page} |
07d83abe MV |
2017 | @item @code{#\null} @tab @code{#\nul} |
2018 | @end multitable | |
2019 | ||
bb15a36c MG |
2020 | Characters may also be written using their code point values. They can |
2021 | be written with as an octal number, such as @code{#\10} for | |
2022 | @code{#\bs} or @code{#\177} for @code{#\del}. | |
3f12aedb | 2023 | |
0f3a70cf MG |
2024 | If one prefers hex to octal, there is an additional syntax for character |
2025 | escapes: @code{#\xHHHH} -- the letter 'x' followed by a hexadecimal | |
2026 | number of one to eight digits. | |
6ea30487 | 2027 | |
07d83abe MV |
2028 | @rnindex char? |
2029 | @deffn {Scheme Procedure} char? x | |
2030 | @deffnx {C Function} scm_char_p (x) | |
2031 | Return @code{#t} iff @var{x} is a character, else @code{#f}. | |
2032 | @end deffn | |
2033 | ||
bb15a36c | 2034 | Fundamentally, the character comparison operations below are |
3f12aedb MG |
2035 | numeric comparisons of the character's code points. |
2036 | ||
07d83abe MV |
2037 | @rnindex char=? |
2038 | @deffn {Scheme Procedure} char=? x y | |
3f12aedb MG |
2039 | Return @code{#t} iff code point of @var{x} is equal to the code point |
2040 | of @var{y}, else @code{#f}. | |
07d83abe MV |
2041 | @end deffn |
2042 | ||
2043 | @rnindex char<? | |
2044 | @deffn {Scheme Procedure} char<? x y | |
3f12aedb MG |
2045 | Return @code{#t} iff the code point of @var{x} is less than the code |
2046 | point of @var{y}, else @code{#f}. | |
07d83abe MV |
2047 | @end deffn |
2048 | ||
2049 | @rnindex char<=? | |
2050 | @deffn {Scheme Procedure} char<=? x y | |
3f12aedb MG |
2051 | Return @code{#t} iff the code point of @var{x} is less than or equal |
2052 | to the code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2053 | @end deffn |
2054 | ||
2055 | @rnindex char>? | |
2056 | @deffn {Scheme Procedure} char>? x y | |
3f12aedb MG |
2057 | Return @code{#t} iff the code point of @var{x} is greater than the |
2058 | code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2059 | @end deffn |
2060 | ||
2061 | @rnindex char>=? | |
2062 | @deffn {Scheme Procedure} char>=? x y | |
3f12aedb MG |
2063 | Return @code{#t} iff the code point of @var{x} is greater than or |
2064 | equal to the code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2065 | @end deffn |
2066 | ||
bb15a36c MG |
2067 | @cindex case folding |
2068 | ||
2069 | Case-insensitive character comparisons use @emph{Unicode case | |
2070 | folding}. In case folding comparisons, if a character is lowercase | |
2071 | and has an uppercase form that can be expressed as a single character, | |
2072 | it is converted to uppercase before comparison. All other characters | |
2073 | undergo no conversion before the comparison occurs. This includes the | |
2074 | German sharp S (Eszett) which is not uppercased before conversion | |
2075 | because its uppercase form has two characters. Unicode case folding | |
2076 | is language independent: it uses rules that are generally true, but, | |
2077 | it cannot cover all cases for all languages. | |
3f12aedb | 2078 | |
07d83abe MV |
2079 | @rnindex char-ci=? |
2080 | @deffn {Scheme Procedure} char-ci=? x y | |
3f12aedb MG |
2081 | Return @code{#t} iff the case-folded code point of @var{x} is the same |
2082 | as the case-folded code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2083 | @end deffn |
2084 | ||
2085 | @rnindex char-ci<? | |
2086 | @deffn {Scheme Procedure} char-ci<? x y | |
3f12aedb MG |
2087 | Return @code{#t} iff the case-folded code point of @var{x} is less |
2088 | than the case-folded code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2089 | @end deffn |
2090 | ||
2091 | @rnindex char-ci<=? | |
2092 | @deffn {Scheme Procedure} char-ci<=? x y | |
3f12aedb MG |
2093 | Return @code{#t} iff the case-folded code point of @var{x} is less |
2094 | than or equal to the case-folded code point of @var{y}, else | |
2095 | @code{#f}. | |
07d83abe MV |
2096 | @end deffn |
2097 | ||
2098 | @rnindex char-ci>? | |
2099 | @deffn {Scheme Procedure} char-ci>? x y | |
3f12aedb MG |
2100 | Return @code{#t} iff the case-folded code point of @var{x} is greater |
2101 | than the case-folded code point of @var{y}, else @code{#f}. | |
07d83abe MV |
2102 | @end deffn |
2103 | ||
2104 | @rnindex char-ci>=? | |
2105 | @deffn {Scheme Procedure} char-ci>=? x y | |
3f12aedb MG |
2106 | Return @code{#t} iff the case-folded code point of @var{x} is greater |
2107 | than or equal to the case-folded code point of @var{y}, else | |
2108 | @code{#f}. | |
07d83abe MV |
2109 | @end deffn |
2110 | ||
2111 | @rnindex char-alphabetic? | |
2112 | @deffn {Scheme Procedure} char-alphabetic? chr | |
2113 | @deffnx {C Function} scm_char_alphabetic_p (chr) | |
2114 | Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}. | |
07d83abe MV |
2115 | @end deffn |
2116 | ||
2117 | @rnindex char-numeric? | |
2118 | @deffn {Scheme Procedure} char-numeric? chr | |
2119 | @deffnx {C Function} scm_char_numeric_p (chr) | |
2120 | Return @code{#t} iff @var{chr} is numeric, else @code{#f}. | |
07d83abe MV |
2121 | @end deffn |
2122 | ||
2123 | @rnindex char-whitespace? | |
2124 | @deffn {Scheme Procedure} char-whitespace? chr | |
2125 | @deffnx {C Function} scm_char_whitespace_p (chr) | |
2126 | Return @code{#t} iff @var{chr} is whitespace, else @code{#f}. | |
07d83abe MV |
2127 | @end deffn |
2128 | ||
2129 | @rnindex char-upper-case? | |
2130 | @deffn {Scheme Procedure} char-upper-case? chr | |
2131 | @deffnx {C Function} scm_char_upper_case_p (chr) | |
2132 | Return @code{#t} iff @var{chr} is uppercase, else @code{#f}. | |
07d83abe MV |
2133 | @end deffn |
2134 | ||
2135 | @rnindex char-lower-case? | |
2136 | @deffn {Scheme Procedure} char-lower-case? chr | |
2137 | @deffnx {C Function} scm_char_lower_case_p (chr) | |
2138 | Return @code{#t} iff @var{chr} is lowercase, else @code{#f}. | |
07d83abe MV |
2139 | @end deffn |
2140 | ||
2141 | @deffn {Scheme Procedure} char-is-both? chr | |
2142 | @deffnx {C Function} scm_char_is_both_p (chr) | |
2143 | Return @code{#t} iff @var{chr} is either uppercase or lowercase, else | |
5676b4fa | 2144 | @code{#f}. |
07d83abe MV |
2145 | @end deffn |
2146 | ||
0ca3a342 JG |
2147 | @deffn {Scheme Procedure} char-general-category chr |
2148 | @deffnx {C Function} scm_char_general_category (chr) | |
2149 | Return a symbol giving the two-letter name of the Unicode general | |
2150 | category assigned to @var{chr} or @code{#f} if no named category is | |
2151 | assigned. The following table provides a list of category names along | |
2152 | with their meanings. | |
2153 | ||
2154 | @multitable @columnfractions .1 .4 .1 .4 | |
2155 | @item Lu | |
2156 | @tab Uppercase letter | |
2157 | @tab Pf | |
2158 | @tab Final quote punctuation | |
2159 | @item Ll | |
2160 | @tab Lowercase letter | |
2161 | @tab Po | |
2162 | @tab Other punctuation | |
2163 | @item Lt | |
2164 | @tab Titlecase letter | |
2165 | @tab Sm | |
2166 | @tab Math symbol | |
2167 | @item Lm | |
2168 | @tab Modifier letter | |
2169 | @tab Sc | |
2170 | @tab Currency symbol | |
2171 | @item Lo | |
2172 | @tab Other letter | |
2173 | @tab Sk | |
2174 | @tab Modifier symbol | |
2175 | @item Mn | |
2176 | @tab Non-spacing mark | |
2177 | @tab So | |
2178 | @tab Other symbol | |
2179 | @item Mc | |
2180 | @tab Combining spacing mark | |
2181 | @tab Zs | |
2182 | @tab Space separator | |
2183 | @item Me | |
2184 | @tab Enclosing mark | |
2185 | @tab Zl | |
2186 | @tab Line separator | |
2187 | @item Nd | |
2188 | @tab Decimal digit number | |
2189 | @tab Zp | |
2190 | @tab Paragraph separator | |
2191 | @item Nl | |
2192 | @tab Letter number | |
2193 | @tab Cc | |
2194 | @tab Control | |
2195 | @item No | |
2196 | @tab Other number | |
2197 | @tab Cf | |
2198 | @tab Format | |
2199 | @item Pc | |
2200 | @tab Connector punctuation | |
2201 | @tab Cs | |
2202 | @tab Surrogate | |
2203 | @item Pd | |
2204 | @tab Dash punctuation | |
2205 | @tab Co | |
2206 | @tab Private use | |
2207 | @item Ps | |
2208 | @tab Open punctuation | |
2209 | @tab Cn | |
2210 | @tab Unassigned | |
2211 | @item Pe | |
2212 | @tab Close punctuation | |
2213 | @tab | |
2214 | @tab | |
2215 | @item Pi | |
2216 | @tab Initial quote punctuation | |
2217 | @tab | |
2218 | @tab | |
2219 | @end multitable | |
2220 | @end deffn | |
2221 | ||
07d83abe MV |
2222 | @rnindex char->integer |
2223 | @deffn {Scheme Procedure} char->integer chr | |
2224 | @deffnx {C Function} scm_char_to_integer (chr) | |
3f12aedb | 2225 | Return the code point of @var{chr}. |
07d83abe MV |
2226 | @end deffn |
2227 | ||
2228 | @rnindex integer->char | |
2229 | @deffn {Scheme Procedure} integer->char n | |
2230 | @deffnx {C Function} scm_integer_to_char (n) | |
3f12aedb MG |
2231 | Return the character that has code point @var{n}. The integer @var{n} |
2232 | must be a valid code point. Valid code points are in the ranges 0 to | |
2233 | @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive. | |
07d83abe MV |
2234 | @end deffn |
2235 | ||
2236 | @rnindex char-upcase | |
2237 | @deffn {Scheme Procedure} char-upcase chr | |
2238 | @deffnx {C Function} scm_char_upcase (chr) | |
2239 | Return the uppercase character version of @var{chr}. | |
2240 | @end deffn | |
2241 | ||
2242 | @rnindex char-downcase | |
2243 | @deffn {Scheme Procedure} char-downcase chr | |
2244 | @deffnx {C Function} scm_char_downcase (chr) | |
2245 | Return the lowercase character version of @var{chr}. | |
2246 | @end deffn | |
2247 | ||
820f33aa JG |
2248 | @rnindex char-titlecase |
2249 | @deffn {Scheme Procedure} char-titlecase chr | |
2250 | @deffnx {C Function} scm_char_titlecase (chr) | |
2251 | Return the titlecase character version of @var{chr} if one exists; | |
2252 | otherwise return the uppercase version. | |
2253 | ||
2254 | For most characters these will be the same, but the Unicode Standard | |
2255 | includes certain digraph compatibility characters, such as @code{U+01F3} | |
2256 | ``dz'', for which the uppercase and titlecase characters are different | |
2257 | (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case, | |
2258 | respectively). | |
2259 | @end deffn | |
2260 | ||
a1dcb961 MG |
2261 | @tindex scm_t_wchar |
2262 | @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c}) | |
2263 | @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c}) | |
2264 | @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c}) | |
2265 | ||
2266 | These C functions take an integer representation of a Unicode | |
2267 | codepoint and return the codepoint corresponding to its uppercase, | |
2268 | lowercase, and titlecase forms respectively. The type | |
2269 | @code{scm_t_wchar} is a signed, 32-bit integer. | |
2270 | @end deftypefn | |
2271 | ||
050ab45f MV |
2272 | @node Character Sets |
2273 | @subsection Character Sets | |
07d83abe | 2274 | |
050ab45f MV |
2275 | The features described in this section correspond directly to SRFI-14. |
2276 | ||
2277 | The data type @dfn{charset} implements sets of characters | |
2278 | (@pxref{Characters}). Because the internal representation of | |
2279 | character sets is not visible to the user, a lot of procedures for | |
2280 | handling them are provided. | |
2281 | ||
2282 | Character sets can be created, extended, tested for the membership of a | |
2283 | characters and be compared to other character sets. | |
2284 | ||
050ab45f MV |
2285 | @menu |
2286 | * Character Set Predicates/Comparison:: | |
2287 | * Iterating Over Character Sets:: Enumerate charset elements. | |
2288 | * Creating Character Sets:: Making new charsets. | |
2289 | * Querying Character Sets:: Test charsets for membership etc. | |
2290 | * Character-Set Algebra:: Calculating new charsets. | |
2291 | * Standard Character Sets:: Variables containing predefined charsets. | |
2292 | @end menu | |
2293 | ||
2294 | @node Character Set Predicates/Comparison | |
2295 | @subsubsection Character Set Predicates/Comparison | |
2296 | ||
2297 | Use these procedures for testing whether an object is a character set, | |
2298 | or whether several character sets are equal or subsets of each other. | |
2299 | @code{char-set-hash} can be used for calculating a hash value, maybe for | |
2300 | usage in fast lookup procedures. | |
2301 | ||
2302 | @deffn {Scheme Procedure} char-set? obj | |
2303 | @deffnx {C Function} scm_char_set_p (obj) | |
2304 | Return @code{#t} if @var{obj} is a character set, @code{#f} | |
2305 | otherwise. | |
2306 | @end deffn | |
2307 | ||
2308 | @deffn {Scheme Procedure} char-set= . char_sets | |
2309 | @deffnx {C Function} scm_char_set_eq (char_sets) | |
2310 | Return @code{#t} if all given character sets are equal. | |
2311 | @end deffn | |
2312 | ||
2313 | @deffn {Scheme Procedure} char-set<= . char_sets | |
2314 | @deffnx {C Function} scm_char_set_leq (char_sets) | |
2315 | Return @code{#t} if every character set @var{cs}i is a subset | |
2316 | of character set @var{cs}i+1. | |
2317 | @end deffn | |
2318 | ||
2319 | @deffn {Scheme Procedure} char-set-hash cs [bound] | |
2320 | @deffnx {C Function} scm_char_set_hash (cs, bound) | |
2321 | Compute a hash value for the character set @var{cs}. If | |
2322 | @var{bound} is given and non-zero, it restricts the | |
2323 | returned value to the range 0 @dots{} @var{bound - 1}. | |
2324 | @end deffn | |
2325 | ||
2326 | @c =================================================================== | |
2327 | ||
2328 | @node Iterating Over Character Sets | |
2329 | @subsubsection Iterating Over Character Sets | |
2330 | ||
2331 | Character set cursors are a means for iterating over the members of a | |
2332 | character sets. After creating a character set cursor with | |
2333 | @code{char-set-cursor}, a cursor can be dereferenced with | |
2334 | @code{char-set-ref}, advanced to the next member with | |
2335 | @code{char-set-cursor-next}. Whether a cursor has passed past the last | |
2336 | element of the set can be checked with @code{end-of-char-set?}. | |
2337 | ||
2338 | Additionally, mapping and (un-)folding procedures for character sets are | |
2339 | provided. | |
2340 | ||
2341 | @deffn {Scheme Procedure} char-set-cursor cs | |
2342 | @deffnx {C Function} scm_char_set_cursor (cs) | |
2343 | Return a cursor into the character set @var{cs}. | |
2344 | @end deffn | |
2345 | ||
2346 | @deffn {Scheme Procedure} char-set-ref cs cursor | |
2347 | @deffnx {C Function} scm_char_set_ref (cs, cursor) | |
2348 | Return the character at the current cursor position | |
2349 | @var{cursor} in the character set @var{cs}. It is an error to | |
2350 | pass a cursor for which @code{end-of-char-set?} returns true. | |
2351 | @end deffn | |
2352 | ||
2353 | @deffn {Scheme Procedure} char-set-cursor-next cs cursor | |
2354 | @deffnx {C Function} scm_char_set_cursor_next (cs, cursor) | |
2355 | Advance the character set cursor @var{cursor} to the next | |
2356 | character in the character set @var{cs}. It is an error if the | |
2357 | cursor given satisfies @code{end-of-char-set?}. | |
2358 | @end deffn | |
2359 | ||
2360 | @deffn {Scheme Procedure} end-of-char-set? cursor | |
2361 | @deffnx {C Function} scm_end_of_char_set_p (cursor) | |
2362 | Return @code{#t} if @var{cursor} has reached the end of a | |
2363 | character set, @code{#f} otherwise. | |
2364 | @end deffn | |
2365 | ||
2366 | @deffn {Scheme Procedure} char-set-fold kons knil cs | |
2367 | @deffnx {C Function} scm_char_set_fold (kons, knil, cs) | |
2368 | Fold the procedure @var{kons} over the character set @var{cs}, | |
2369 | initializing it with @var{knil}. | |
2370 | @end deffn | |
2371 | ||
2372 | @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs] | |
2373 | @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs) | |
2374 | This is a fundamental constructor for character sets. | |
2375 | @itemize @bullet | |
2376 | @item @var{g} is used to generate a series of ``seed'' values | |
2377 | from the initial seed: @var{seed}, (@var{g} @var{seed}), | |
2378 | (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{} | |
2379 | @item @var{p} tells us when to stop -- when it returns true | |
2380 | when applied to one of the seed values. | |
2381 | @item @var{f} maps each seed value to a character. These | |
2382 | characters are added to the base character set @var{base_cs} to | |
2383 | form the result; @var{base_cs} defaults to the empty set. | |
2384 | @end itemize | |
2385 | @end deffn | |
2386 | ||
2387 | @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs | |
2388 | @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs) | |
2389 | This is a fundamental constructor for character sets. | |
2390 | @itemize @bullet | |
2391 | @item @var{g} is used to generate a series of ``seed'' values | |
2392 | from the initial seed: @var{seed}, (@var{g} @var{seed}), | |
2393 | (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{} | |
2394 | @item @var{p} tells us when to stop -- when it returns true | |
2395 | when applied to one of the seed values. | |
2396 | @item @var{f} maps each seed value to a character. These | |
2397 | characters are added to the base character set @var{base_cs} to | |
2398 | form the result; @var{base_cs} defaults to the empty set. | |
2399 | @end itemize | |
2400 | @end deffn | |
2401 | ||
2402 | @deffn {Scheme Procedure} char-set-for-each proc cs | |
2403 | @deffnx {C Function} scm_char_set_for_each (proc, cs) | |
2404 | Apply @var{proc} to every character in the character set | |
2405 | @var{cs}. The return value is not specified. | |
2406 | @end deffn | |
2407 | ||
2408 | @deffn {Scheme Procedure} char-set-map proc cs | |
2409 | @deffnx {C Function} scm_char_set_map (proc, cs) | |
2410 | Map the procedure @var{proc} over every character in @var{cs}. | |
2411 | @var{proc} must be a character -> character procedure. | |
2412 | @end deffn | |
2413 | ||
2414 | @c =================================================================== | |
2415 | ||
2416 | @node Creating Character Sets | |
2417 | @subsubsection Creating Character Sets | |
2418 | ||
2419 | New character sets are produced with these procedures. | |
2420 | ||
2421 | @deffn {Scheme Procedure} char-set-copy cs | |
2422 | @deffnx {C Function} scm_char_set_copy (cs) | |
2423 | Return a newly allocated character set containing all | |
2424 | characters in @var{cs}. | |
2425 | @end deffn | |
2426 | ||
2427 | @deffn {Scheme Procedure} char-set . rest | |
2428 | @deffnx {C Function} scm_char_set (rest) | |
2429 | Return a character set containing all given characters. | |
2430 | @end deffn | |
2431 | ||
2432 | @deffn {Scheme Procedure} list->char-set list [base_cs] | |
2433 | @deffnx {C Function} scm_list_to_char_set (list, base_cs) | |
2434 | Convert the character list @var{list} to a character set. If | |
2435 | the character set @var{base_cs} is given, the character in this | |
2436 | set are also included in the result. | |
2437 | @end deffn | |
2438 | ||
2439 | @deffn {Scheme Procedure} list->char-set! list base_cs | |
2440 | @deffnx {C Function} scm_list_to_char_set_x (list, base_cs) | |
2441 | Convert the character list @var{list} to a character set. The | |
2442 | characters are added to @var{base_cs} and @var{base_cs} is | |
2443 | returned. | |
2444 | @end deffn | |
2445 | ||
2446 | @deffn {Scheme Procedure} string->char-set str [base_cs] | |
2447 | @deffnx {C Function} scm_string_to_char_set (str, base_cs) | |
2448 | Convert the string @var{str} to a character set. If the | |
2449 | character set @var{base_cs} is given, the characters in this | |
2450 | set are also included in the result. | |
2451 | @end deffn | |
2452 | ||
2453 | @deffn {Scheme Procedure} string->char-set! str base_cs | |
2454 | @deffnx {C Function} scm_string_to_char_set_x (str, base_cs) | |
2455 | Convert the string @var{str} to a character set. The | |
2456 | characters from the string are added to @var{base_cs}, and | |
2457 | @var{base_cs} is returned. | |
2458 | @end deffn | |
2459 | ||
2460 | @deffn {Scheme Procedure} char-set-filter pred cs [base_cs] | |
2461 | @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs) | |
2462 | Return a character set containing every character from @var{cs} | |
2463 | so that it satisfies @var{pred}. If provided, the characters | |
2464 | from @var{base_cs} are added to the result. | |
2465 | @end deffn | |
2466 | ||
2467 | @deffn {Scheme Procedure} char-set-filter! pred cs base_cs | |
2468 | @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs) | |
2469 | Return a character set containing every character from @var{cs} | |
2470 | so that it satisfies @var{pred}. The characters are added to | |
2471 | @var{base_cs} and @var{base_cs} is returned. | |
2472 | @end deffn | |
2473 | ||
2474 | @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]] | |
2475 | @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs) | |
2476 | Return a character set containing all characters whose | |
2477 | character codes lie in the half-open range | |
2478 | [@var{lower},@var{upper}). | |
2479 | ||
2480 | If @var{error} is a true value, an error is signalled if the | |
2481 | specified range contains characters which are not contained in | |
2482 | the implemented character range. If @var{error} is @code{#f}, | |
be3eb25c | 2483 | these characters are silently left out of the resulting |
050ab45f MV |
2484 | character set. |
2485 | ||
2486 | The characters in @var{base_cs} are added to the result, if | |
2487 | given. | |
2488 | @end deffn | |
2489 | ||
2490 | @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs | |
2491 | @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs) | |
2492 | Return a character set containing all characters whose | |
2493 | character codes lie in the half-open range | |
2494 | [@var{lower},@var{upper}). | |
2495 | ||
2496 | If @var{error} is a true value, an error is signalled if the | |
2497 | specified range contains characters which are not contained in | |
2498 | the implemented character range. If @var{error} is @code{#f}, | |
be3eb25c | 2499 | these characters are silently left out of the resulting |
050ab45f MV |
2500 | character set. |
2501 | ||
2502 | The characters are added to @var{base_cs} and @var{base_cs} is | |
2503 | returned. | |
2504 | @end deffn | |
2505 | ||
2506 | @deffn {Scheme Procedure} ->char-set x | |
2507 | @deffnx {C Function} scm_to_char_set (x) | |
be3eb25c MG |
2508 | Coerces x into a char-set. @var{x} may be a string, character or |
2509 | char-set. A string is converted to the set of its constituent | |
2510 | characters; a character is converted to a singleton set; a char-set is | |
2511 | returned as-is. | |
050ab45f MV |
2512 | @end deffn |
2513 | ||
2514 | @c =================================================================== | |
2515 | ||
2516 | @node Querying Character Sets | |
2517 | @subsubsection Querying Character Sets | |
2518 | ||
2519 | Access the elements and other information of a character set with these | |
2520 | procedures. | |
2521 | ||
be3eb25c MG |
2522 | @deffn {Scheme Procedure} %char-set-dump cs |
2523 | Returns an association list containing debugging information | |
2524 | for @var{cs}. The association list has the following entries. | |
2525 | @table @code | |
2526 | @item char-set | |
2527 | The char-set itself | |
2528 | @item len | |
2529 | The number of groups of contiguous code points the char-set | |
2530 | contains | |
2531 | @item ranges | |
2532 | A list of lists where each sublist is a range of code points | |
2533 | and their associated characters | |
2534 | @end table | |
2535 | The return value of this function cannot be relied upon to be | |
2536 | consistent between versions of Guile and should not be used in code. | |
2537 | @end deffn | |
2538 | ||
050ab45f MV |
2539 | @deffn {Scheme Procedure} char-set-size cs |
2540 | @deffnx {C Function} scm_char_set_size (cs) | |
2541 | Return the number of elements in character set @var{cs}. | |
2542 | @end deffn | |
2543 | ||
2544 | @deffn {Scheme Procedure} char-set-count pred cs | |
2545 | @deffnx {C Function} scm_char_set_count (pred, cs) | |
2546 | Return the number of the elements int the character set | |
2547 | @var{cs} which satisfy the predicate @var{pred}. | |
2548 | @end deffn | |
2549 | ||
2550 | @deffn {Scheme Procedure} char-set->list cs | |
2551 | @deffnx {C Function} scm_char_set_to_list (cs) | |
2552 | Return a list containing the elements of the character set | |
2553 | @var{cs}. | |
2554 | @end deffn | |
2555 | ||
2556 | @deffn {Scheme Procedure} char-set->string cs | |
2557 | @deffnx {C Function} scm_char_set_to_string (cs) | |
2558 | Return a string containing the elements of the character set | |
2559 | @var{cs}. The order in which the characters are placed in the | |
2560 | string is not defined. | |
2561 | @end deffn | |
2562 | ||
2563 | @deffn {Scheme Procedure} char-set-contains? cs ch | |
2564 | @deffnx {C Function} scm_char_set_contains_p (cs, ch) | |
2565 | Return @code{#t} iff the character @var{ch} is contained in the | |
2566 | character set @var{cs}. | |
2567 | @end deffn | |
2568 | ||
2569 | @deffn {Scheme Procedure} char-set-every pred cs | |
2570 | @deffnx {C Function} scm_char_set_every (pred, cs) | |
2571 | Return a true value if every character in the character set | |
2572 | @var{cs} satisfies the predicate @var{pred}. | |
2573 | @end deffn | |
2574 | ||
2575 | @deffn {Scheme Procedure} char-set-any pred cs | |
2576 | @deffnx {C Function} scm_char_set_any (pred, cs) | |
2577 | Return a true value if any character in the character set | |
2578 | @var{cs} satisfies the predicate @var{pred}. | |
2579 | @end deffn | |
2580 | ||
2581 | @c =================================================================== | |
2582 | ||
2583 | @node Character-Set Algebra | |
2584 | @subsubsection Character-Set Algebra | |
2585 | ||
2586 | Character sets can be manipulated with the common set algebra operation, | |
2587 | such as union, complement, intersection etc. All of these procedures | |
2588 | provide side-effecting variants, which modify their character set | |
2589 | argument(s). | |
2590 | ||
2591 | @deffn {Scheme Procedure} char-set-adjoin cs . rest | |
2592 | @deffnx {C Function} scm_char_set_adjoin (cs, rest) | |
2593 | Add all character arguments to the first argument, which must | |
2594 | be a character set. | |
2595 | @end deffn | |
2596 | ||
2597 | @deffn {Scheme Procedure} char-set-delete cs . rest | |
2598 | @deffnx {C Function} scm_char_set_delete (cs, rest) | |
2599 | Delete all character arguments from the first argument, which | |
2600 | must be a character set. | |
2601 | @end deffn | |
2602 | ||
2603 | @deffn {Scheme Procedure} char-set-adjoin! cs . rest | |
2604 | @deffnx {C Function} scm_char_set_adjoin_x (cs, rest) | |
2605 | Add all character arguments to the first argument, which must | |
2606 | be a character set. | |
2607 | @end deffn | |
2608 | ||
2609 | @deffn {Scheme Procedure} char-set-delete! cs . rest | |
2610 | @deffnx {C Function} scm_char_set_delete_x (cs, rest) | |
2611 | Delete all character arguments from the first argument, which | |
2612 | must be a character set. | |
2613 | @end deffn | |
2614 | ||
2615 | @deffn {Scheme Procedure} char-set-complement cs | |
2616 | @deffnx {C Function} scm_char_set_complement (cs) | |
2617 | Return the complement of the character set @var{cs}. | |
2618 | @end deffn | |
2619 | ||
be3eb25c MG |
2620 | Note that the complement of a character set is likely to contain many |
2621 | reserved code points (code points that are not associated with | |
2622 | characters). It may be helpful to modify the output of | |
2623 | @code{char-set-complement} by computing its intersection with the set | |
2624 | of designated code points, @code{char-set:designated}. | |
2625 | ||
050ab45f MV |
2626 | @deffn {Scheme Procedure} char-set-union . rest |
2627 | @deffnx {C Function} scm_char_set_union (rest) | |
2628 | Return the union of all argument character sets. | |
2629 | @end deffn | |
2630 | ||
2631 | @deffn {Scheme Procedure} char-set-intersection . rest | |
2632 | @deffnx {C Function} scm_char_set_intersection (rest) | |
2633 | Return the intersection of all argument character sets. | |
2634 | @end deffn | |
2635 | ||
2636 | @deffn {Scheme Procedure} char-set-difference cs1 . rest | |
2637 | @deffnx {C Function} scm_char_set_difference (cs1, rest) | |
2638 | Return the difference of all argument character sets. | |
2639 | @end deffn | |
2640 | ||
2641 | @deffn {Scheme Procedure} char-set-xor . rest | |
2642 | @deffnx {C Function} scm_char_set_xor (rest) | |
2643 | Return the exclusive-or of all argument character sets. | |
2644 | @end deffn | |
2645 | ||
2646 | @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest | |
2647 | @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest) | |
2648 | Return the difference and the intersection of all argument | |
2649 | character sets. | |
2650 | @end deffn | |
2651 | ||
2652 | @deffn {Scheme Procedure} char-set-complement! cs | |
2653 | @deffnx {C Function} scm_char_set_complement_x (cs) | |
2654 | Return the complement of the character set @var{cs}. | |
2655 | @end deffn | |
2656 | ||
2657 | @deffn {Scheme Procedure} char-set-union! cs1 . rest | |
2658 | @deffnx {C Function} scm_char_set_union_x (cs1, rest) | |
2659 | Return the union of all argument character sets. | |
2660 | @end deffn | |
2661 | ||
2662 | @deffn {Scheme Procedure} char-set-intersection! cs1 . rest | |
2663 | @deffnx {C Function} scm_char_set_intersection_x (cs1, rest) | |
2664 | Return the intersection of all argument character sets. | |
2665 | @end deffn | |
2666 | ||
2667 | @deffn {Scheme Procedure} char-set-difference! cs1 . rest | |
2668 | @deffnx {C Function} scm_char_set_difference_x (cs1, rest) | |
2669 | Return the difference of all argument character sets. | |
2670 | @end deffn | |
2671 | ||
2672 | @deffn {Scheme Procedure} char-set-xor! cs1 . rest | |
2673 | @deffnx {C Function} scm_char_set_xor_x (cs1, rest) | |
2674 | Return the exclusive-or of all argument character sets. | |
2675 | @end deffn | |
2676 | ||
2677 | @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest | |
2678 | @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest) | |
2679 | Return the difference and the intersection of all argument | |
2680 | character sets. | |
2681 | @end deffn | |
2682 | ||
2683 | @c =================================================================== | |
2684 | ||
2685 | @node Standard Character Sets | |
2686 | @subsubsection Standard Character Sets | |
2687 | ||
2688 | In order to make the use of the character set data type and procedures | |
2689 | useful, several predefined character set variables exist. | |
2690 | ||
49dec04b LC |
2691 | @cindex codeset |
2692 | @cindex charset | |
2693 | @cindex locale | |
2694 | ||
be3eb25c MG |
2695 | These character sets are locale independent and are not recomputed |
2696 | upon a @code{setlocale} call. They contain characters from the whole | |
2697 | range of Unicode code points. For instance, @code{char-set:letter} | |
2698 | contains about 94,000 characters. | |
49dec04b | 2699 | |
c9dc8c6c MV |
2700 | @defvr {Scheme Variable} char-set:lower-case |
2701 | @defvrx {C Variable} scm_char_set_lower_case | |
050ab45f | 2702 | All lower-case characters. |
c9dc8c6c | 2703 | @end defvr |
050ab45f | 2704 | |
c9dc8c6c MV |
2705 | @defvr {Scheme Variable} char-set:upper-case |
2706 | @defvrx {C Variable} scm_char_set_upper_case | |
050ab45f | 2707 | All upper-case characters. |
c9dc8c6c | 2708 | @end defvr |
050ab45f | 2709 | |
c9dc8c6c MV |
2710 | @defvr {Scheme Variable} char-set:title-case |
2711 | @defvrx {C Variable} scm_char_set_title_case | |
be3eb25c MG |
2712 | All single characters that function as if they were an upper-case |
2713 | letter followed by a lower-case letter. | |
c9dc8c6c | 2714 | @end defvr |
050ab45f | 2715 | |
c9dc8c6c MV |
2716 | @defvr {Scheme Variable} char-set:letter |
2717 | @defvrx {C Variable} scm_char_set_letter | |
be3eb25c MG |
2718 | All letters. This includes @code{char-set:lower-case}, |
2719 | @code{char-set:upper-case}, @code{char-set:title-case}, and many | |
2720 | letters that have no case at all. For example, Chinese and Japanese | |
2721 | characters typically have no concept of case. | |
c9dc8c6c | 2722 | @end defvr |
050ab45f | 2723 | |
c9dc8c6c MV |
2724 | @defvr {Scheme Variable} char-set:digit |
2725 | @defvrx {C Variable} scm_char_set_digit | |
050ab45f | 2726 | All digits. |
c9dc8c6c | 2727 | @end defvr |
050ab45f | 2728 | |
c9dc8c6c MV |
2729 | @defvr {Scheme Variable} char-set:letter+digit |
2730 | @defvrx {C Variable} scm_char_set_letter_and_digit | |
050ab45f | 2731 | The union of @code{char-set:letter} and @code{char-set:digit}. |
c9dc8c6c | 2732 | @end defvr |
050ab45f | 2733 | |
c9dc8c6c MV |
2734 | @defvr {Scheme Variable} char-set:graphic |
2735 | @defvrx {C Variable} scm_char_set_graphic | |
050ab45f | 2736 | All characters which would put ink on the paper. |
c9dc8c6c | 2737 | @end defvr |
050ab45f | 2738 | |
c9dc8c6c MV |
2739 | @defvr {Scheme Variable} char-set:printing |
2740 | @defvrx {C Variable} scm_char_set_printing | |
050ab45f | 2741 | The union of @code{char-set:graphic} and @code{char-set:whitespace}. |
c9dc8c6c | 2742 | @end defvr |
050ab45f | 2743 | |
c9dc8c6c MV |
2744 | @defvr {Scheme Variable} char-set:whitespace |
2745 | @defvrx {C Variable} scm_char_set_whitespace | |
050ab45f | 2746 | All whitespace characters. |
c9dc8c6c | 2747 | @end defvr |
050ab45f | 2748 | |
c9dc8c6c MV |
2749 | @defvr {Scheme Variable} char-set:blank |
2750 | @defvrx {C Variable} scm_char_set_blank | |
be3eb25c MG |
2751 | All horizontal whitespace characters, which notably includes |
2752 | @code{#\space} and @code{#\tab}. | |
c9dc8c6c | 2753 | @end defvr |
050ab45f | 2754 | |
c9dc8c6c MV |
2755 | @defvr {Scheme Variable} char-set:iso-control |
2756 | @defvrx {C Variable} scm_char_set_iso_control | |
be3eb25c MG |
2757 | The ISO control characters are the C0 control characters (U+0000 to |
2758 | U+001F), delete (U+007F), and the C1 control characters (U+0080 to | |
2759 | U+009F). | |
c9dc8c6c | 2760 | @end defvr |
050ab45f | 2761 | |
c9dc8c6c MV |
2762 | @defvr {Scheme Variable} char-set:punctuation |
2763 | @defvrx {C Variable} scm_char_set_punctuation | |
be3eb25c MG |
2764 | All punctuation characters, such as the characters |
2765 | @code{!"#%&'()*,-./:;?@@[\\]_@{@}} | |
c9dc8c6c | 2766 | @end defvr |
050ab45f | 2767 | |
c9dc8c6c MV |
2768 | @defvr {Scheme Variable} char-set:symbol |
2769 | @defvrx {C Variable} scm_char_set_symbol | |
be3eb25c | 2770 | All symbol characters, such as the characters @code{$+<=>^`|~}. |
c9dc8c6c | 2771 | @end defvr |
050ab45f | 2772 | |
c9dc8c6c MV |
2773 | @defvr {Scheme Variable} char-set:hex-digit |
2774 | @defvrx {C Variable} scm_char_set_hex_digit | |
050ab45f | 2775 | The hexadecimal digits @code{0123456789abcdefABCDEF}. |
c9dc8c6c | 2776 | @end defvr |
050ab45f | 2777 | |
c9dc8c6c MV |
2778 | @defvr {Scheme Variable} char-set:ascii |
2779 | @defvrx {C Variable} scm_char_set_ascii | |
050ab45f | 2780 | All ASCII characters. |
c9dc8c6c | 2781 | @end defvr |
050ab45f | 2782 | |
c9dc8c6c MV |
2783 | @defvr {Scheme Variable} char-set:empty |
2784 | @defvrx {C Variable} scm_char_set_empty | |
050ab45f | 2785 | The empty character set. |
c9dc8c6c | 2786 | @end defvr |
050ab45f | 2787 | |
be3eb25c MG |
2788 | @defvr {Scheme Variable} char-set:designated |
2789 | @defvrx {C Variable} scm_char_set_designated | |
2790 | This character set contains all designated code points. This includes | |
2791 | all the code points to which Unicode has assigned a character or other | |
2792 | meaning. | |
2793 | @end defvr | |
2794 | ||
c9dc8c6c MV |
2795 | @defvr {Scheme Variable} char-set:full |
2796 | @defvrx {C Variable} scm_char_set_full | |
be3eb25c MG |
2797 | This character set contains all possible code points. This includes |
2798 | both designated and reserved code points. | |
c9dc8c6c | 2799 | @end defvr |
07d83abe MV |
2800 | |
2801 | @node Strings | |
2802 | @subsection Strings | |
2803 | @tpindex Strings | |
2804 | ||
2805 | Strings are fixed-length sequences of characters. They can be created | |
2806 | by calling constructor procedures, but they can also literally get | |
2807 | entered at the @acronym{REPL} or in Scheme source files. | |
2808 | ||
2809 | @c Guile provides a rich set of string processing procedures, because text | |
2810 | @c handling is very important when Guile is used as a scripting language. | |
2811 | ||
2812 | Strings always carry the information about how many characters they are | |
2813 | composed of with them, so there is no special end-of-string character, | |
2814 | like in C. That means that Scheme strings can contain any character, | |
c48c62d0 MV |
2815 | even the @samp{#\nul} character @samp{\0}. |
2816 | ||
2817 | To use strings efficiently, you need to know a bit about how Guile | |
2818 | implements them. In Guile, a string consists of two parts, a head and | |
2819 | the actual memory where the characters are stored. When a string (or | |
2820 | a substring of it) is copied, only a new head gets created, the memory | |
2821 | is usually not copied. The two heads start out pointing to the same | |
2822 | memory. | |
2823 | ||
2824 | When one of these two strings is modified, as with @code{string-set!}, | |
2825 | their common memory does get copied so that each string has its own | |
be3eb25c | 2826 | memory and modifying one does not accidentally modify the other as well. |
c48c62d0 MV |
2827 | Thus, Guile's strings are `copy on write'; the actual copying of their |
2828 | memory is delayed until one string is written to. | |
2829 | ||
2830 | This implementation makes functions like @code{substring} very | |
2831 | efficient in the common case that no modifications are done to the | |
2832 | involved strings. | |
2833 | ||
2834 | If you do know that your strings are getting modified right away, you | |
2835 | can use @code{substring/copy} instead of @code{substring}. This | |
2836 | function performs the copy immediately at the time of creation. This | |
2837 | is more efficient, especially in a multi-threaded program. Also, | |
2838 | @code{substring/copy} can avoid the problem that a short substring | |
2839 | holds on to the memory of a very large original string that could | |
2840 | otherwise be recycled. | |
2841 | ||
2842 | If you want to avoid the copy altogether, so that modifications of one | |
2843 | string show up in the other, you can use @code{substring/shared}. The | |
2844 | strings created by this procedure are called @dfn{mutation sharing | |
2845 | substrings} since the substring and the original string share | |
2846 | modifications to each other. | |
07d83abe | 2847 | |
05256760 MV |
2848 | If you want to prevent modifications, use @code{substring/read-only}. |
2849 | ||
c9dc8c6c MV |
2850 | Guile provides all procedures of SRFI-13 and a few more. |
2851 | ||
07d83abe | 2852 | @menu |
5676b4fa MV |
2853 | * String Syntax:: Read syntax for strings. |
2854 | * String Predicates:: Testing strings for certain properties. | |
2855 | * String Constructors:: Creating new string objects. | |
2856 | * List/String Conversion:: Converting from/to lists of characters. | |
2857 | * String Selection:: Select portions from strings. | |
2858 | * String Modification:: Modify parts or whole strings. | |
2859 | * String Comparison:: Lexicographic ordering predicates. | |
2860 | * String Searching:: Searching in strings. | |
2861 | * Alphabetic Case Mapping:: Convert the alphabetic case of strings. | |
2862 | * Reversing and Appending Strings:: Appending strings to form a new string. | |
2863 | * Mapping Folding and Unfolding:: Iterating over strings. | |
2864 | * Miscellaneous String Operations:: Replicating, insertion, parsing, ... | |
67af975c | 2865 | * Conversion to/from C:: |
5b6b22e8 | 2866 | * String Internals:: The storage strategy for strings. |
07d83abe MV |
2867 | @end menu |
2868 | ||
2869 | @node String Syntax | |
2870 | @subsubsection String Read Syntax | |
2871 | ||
2872 | @c In the following @code is used to get a good font in TeX etc, but | |
2873 | @c is omitted for Info format, so as not to risk any confusion over | |
2874 | @c whether surrounding ` ' quotes are part of the escape or are | |
2875 | @c special in a string (they're not). | |
2876 | ||
2877 | The read syntax for strings is an arbitrarily long sequence of | |
c48c62d0 | 2878 | characters enclosed in double quotes (@nicode{"}). |
07d83abe | 2879 | |
67af975c MG |
2880 | Backslash is an escape character and can be used to insert the following |
2881 | special characters. @nicode{\"} and @nicode{\\} are R5RS standard, the | |
2882 | next seven are R6RS standard --- notice they follow C syntax --- and the | |
2883 | remaining four are Guile extensions. | |
07d83abe MV |
2884 | |
2885 | @table @asis | |
2886 | @item @nicode{\\} | |
2887 | Backslash character. | |
2888 | ||
2889 | @item @nicode{\"} | |
2890 | Double quote character (an unescaped @nicode{"} is otherwise the end | |
2891 | of the string). | |
2892 | ||
07d83abe MV |
2893 | @item @nicode{\a} |
2894 | Bell character (ASCII 7). | |
2895 | ||
2896 | @item @nicode{\f} | |
2897 | Formfeed character (ASCII 12). | |
2898 | ||
2899 | @item @nicode{\n} | |
2900 | Newline character (ASCII 10). | |
2901 | ||
2902 | @item @nicode{\r} | |
2903 | Carriage return character (ASCII 13). | |
2904 | ||
2905 | @item @nicode{\t} | |
2906 | Tab character (ASCII 9). | |
2907 | ||
2908 | @item @nicode{\v} | |
2909 | Vertical tab character (ASCII 11). | |
2910 | ||
67a4a16d MG |
2911 | @item @nicode{\b} |
2912 | Backspace character (ASCII 8). | |
2913 | ||
67af975c MG |
2914 | @item @nicode{\0} |
2915 | NUL character (ASCII 0). | |
2916 | ||
c869f0c1 AW |
2917 | @item @nicode{\} followed by newline (ASCII 10) |
2918 | Nothing. This way if @nicode{\} is the last character in a line, the | |
2919 | string will continue with the first character from the next line, | |
2920 | without a line break. | |
2921 | ||
2922 | If the @code{hungry-eol-escapes} reader option is enabled, which is not | |
2923 | the case by default, leading whitespace on the next line is discarded. | |
2924 | ||
2925 | @lisp | |
2926 | "foo\ | |
2927 | bar" | |
2928 | @result{} "foo bar" | |
2929 | (read-enable 'hungry-eol-escapes) | |
2930 | "foo\ | |
2931 | bar" | |
2932 | @result{} "foobar" | |
2933 | @end lisp | |
07d83abe MV |
2934 | @item @nicode{\xHH} |
2935 | Character code given by two hexadecimal digits. For example | |
2936 | @nicode{\x7f} for an ASCII DEL (127). | |
28cc8dac MG |
2937 | |
2938 | @item @nicode{\uHHHH} | |
2939 | Character code given by four hexadecimal digits. For example | |
2940 | @nicode{\u0100} for a capital A with macron (U+0100). | |
2941 | ||
2942 | @item @nicode{\UHHHHHH} | |
2943 | Character code given by six hexadecimal digits. For example | |
2944 | @nicode{\U010402}. | |
07d83abe MV |
2945 | @end table |
2946 | ||
2947 | @noindent | |
2948 | The following are examples of string literals: | |
2949 | ||
2950 | @lisp | |
2951 | "foo" | |
2952 | "bar plonk" | |
2953 | "Hello World" | |
2954 | "\"Hi\", he said." | |
2955 | @end lisp | |
2956 | ||
6ea30487 MG |
2957 | The three escape sequences @code{\xHH}, @code{\uHHHH} and @code{\UHHHHHH} were |
2958 | chosen to not break compatibility with code written for previous versions of | |
2959 | Guile. The R6RS specification suggests a different, incompatible syntax for hex | |
2960 | escapes: @code{\xHHHH;} -- a character code followed by one to eight hexadecimal | |
2961 | digits terminated with a semicolon. If this escape format is desired instead, | |
2962 | it can be enabled with the reader option @code{r6rs-hex-escapes}. | |
2963 | ||
2964 | @lisp | |
2965 | (read-enable 'r6rs-hex-escapes) | |
2966 | @end lisp | |
2967 | ||
1518f649 | 2968 | For more on reader options, @xref{Scheme Read}. |
07d83abe MV |
2969 | |
2970 | @node String Predicates | |
2971 | @subsubsection String Predicates | |
2972 | ||
2973 | The following procedures can be used to check whether a given string | |
2974 | fulfills some specified property. | |
2975 | ||
2976 | @rnindex string? | |
2977 | @deffn {Scheme Procedure} string? obj | |
2978 | @deffnx {C Function} scm_string_p (obj) | |
2979 | Return @code{#t} if @var{obj} is a string, else @code{#f}. | |
2980 | @end deffn | |
2981 | ||
91210d62 MV |
2982 | @deftypefn {C Function} int scm_is_string (SCM obj) |
2983 | Returns @code{1} if @var{obj} is a string, @code{0} otherwise. | |
2984 | @end deftypefn | |
2985 | ||
07d83abe MV |
2986 | @deffn {Scheme Procedure} string-null? str |
2987 | @deffnx {C Function} scm_string_null_p (str) | |
2988 | Return @code{#t} if @var{str}'s length is zero, and | |
2989 | @code{#f} otherwise. | |
2990 | @lisp | |
2991 | (string-null? "") @result{} #t | |
2992 | y @result{} "foo" | |
2993 | (string-null? y) @result{} #f | |
2994 | @end lisp | |
2995 | @end deffn | |
2996 | ||
5676b4fa MV |
2997 | @deffn {Scheme Procedure} string-any char_pred s [start [end]] |
2998 | @deffnx {C Function} scm_string_any (char_pred, s, start, end) | |
c100a12c | 2999 | Check if @var{char_pred} is true for any character in string @var{s}. |
5676b4fa | 3000 | |
c100a12c KR |
3001 | @var{char_pred} can be a character to check for any equal to that, or |
3002 | a character set (@pxref{Character Sets}) to check for any in that set, | |
3003 | or a predicate procedure to call. | |
5676b4fa | 3004 | |
c100a12c KR |
3005 | For a procedure, calls @code{(@var{char_pred} c)} are made |
3006 | successively on the characters from @var{start} to @var{end}. If | |
3007 | @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any} | |
3008 | stops and that return value is the return from @code{string-any}. The | |
3009 | call on the last character (ie.@: at @math{@var{end}-1}), if that | |
3010 | point is reached, is a tail call. | |
3011 | ||
3012 | If there are no characters in @var{s} (ie.@: @var{start} equals | |
3013 | @var{end}) then the return is @code{#f}. | |
5676b4fa MV |
3014 | @end deffn |
3015 | ||
3016 | @deffn {Scheme Procedure} string-every char_pred s [start [end]] | |
3017 | @deffnx {C Function} scm_string_every (char_pred, s, start, end) | |
c100a12c KR |
3018 | Check if @var{char_pred} is true for every character in string |
3019 | @var{s}. | |
5676b4fa | 3020 | |
c100a12c KR |
3021 | @var{char_pred} can be a character to check for every character equal |
3022 | to that, or a character set (@pxref{Character Sets}) to check for | |
3023 | every character being in that set, or a predicate procedure to call. | |
3024 | ||
3025 | For a procedure, calls @code{(@var{char_pred} c)} are made | |
3026 | successively on the characters from @var{start} to @var{end}. If | |
3027 | @var{char_pred} returns @code{#f}, @code{string-every} stops and | |
3028 | returns @code{#f}. The call on the last character (ie.@: at | |
3029 | @math{@var{end}-1}), if that point is reached, is a tail call and the | |
3030 | return from that call is the return from @code{string-every}. | |
5676b4fa MV |
3031 | |
3032 | If there are no characters in @var{s} (ie.@: @var{start} equals | |
3033 | @var{end}) then the return is @code{#t}. | |
5676b4fa MV |
3034 | @end deffn |
3035 | ||
07d83abe MV |
3036 | @node String Constructors |
3037 | @subsubsection String Constructors | |
3038 | ||
3039 | The string constructor procedures create new string objects, possibly | |
c48c62d0 MV |
3040 | initializing them with some specified character data. See also |
3041 | @xref{String Selection}, for ways to create strings from existing | |
3042 | strings. | |
07d83abe MV |
3043 | |
3044 | @c FIXME::martin: list->string belongs into `List/String Conversion' | |
3045 | ||
bba26c32 | 3046 | @deffn {Scheme Procedure} string char@dots{} |
07d83abe | 3047 | @rnindex string |
bba26c32 KR |
3048 | Return a newly allocated string made from the given character |
3049 | arguments. | |
3050 | ||
3051 | @example | |
3052 | (string #\x #\y #\z) @result{} "xyz" | |
3053 | (string) @result{} "" | |
3054 | @end example | |
3055 | @end deffn | |
3056 | ||
3057 | @deffn {Scheme Procedure} list->string lst | |
3058 | @deffnx {C Function} scm_string (lst) | |
07d83abe | 3059 | @rnindex list->string |
bba26c32 KR |
3060 | Return a newly allocated string made from a list of characters. |
3061 | ||
3062 | @example | |
3063 | (list->string '(#\a #\b #\c)) @result{} "abc" | |
3064 | @end example | |
3065 | @end deffn | |
3066 | ||
3067 | @deffn {Scheme Procedure} reverse-list->string lst | |
3068 | @deffnx {C Function} scm_reverse_list_to_string (lst) | |
3069 | Return a newly allocated string made from a list of characters, in | |
3070 | reverse order. | |
3071 | ||
3072 | @example | |
3073 | (reverse-list->string '(#\a #\B #\c)) @result{} "cBa" | |
3074 | @end example | |
07d83abe MV |
3075 | @end deffn |
3076 | ||
3077 | @rnindex make-string | |
3078 | @deffn {Scheme Procedure} make-string k [chr] | |
3079 | @deffnx {C Function} scm_make_string (k, chr) | |
3080 | Return a newly allocated string of | |
3081 | length @var{k}. If @var{chr} is given, then all elements of | |
3082 | the string are initialized to @var{chr}, otherwise the contents | |
3083 | of the @var{string} are unspecified. | |
3084 | @end deffn | |
3085 | ||
c48c62d0 MV |
3086 | @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr) |
3087 | Like @code{scm_make_string}, but expects the length as a | |
3088 | @code{size_t}. | |
3089 | @end deftypefn | |
3090 | ||
5676b4fa MV |
3091 | @deffn {Scheme Procedure} string-tabulate proc len |
3092 | @deffnx {C Function} scm_string_tabulate (proc, len) | |
3093 | @var{proc} is an integer->char procedure. Construct a string | |
3094 | of size @var{len} by applying @var{proc} to each index to | |
3095 | produce the corresponding string element. The order in which | |
3096 | @var{proc} is applied to the indices is not specified. | |
3097 | @end deffn | |
3098 | ||
5676b4fa MV |
3099 | @deffn {Scheme Procedure} string-join ls [delimiter [grammar]] |
3100 | @deffnx {C Function} scm_string_join (ls, delimiter, grammar) | |
3101 | Append the string in the string list @var{ls}, using the string | |
3102 | @var{delim} as a delimiter between the elements of @var{ls}. | |
3103 | @var{grammar} is a symbol which specifies how the delimiter is | |
3104 | placed between the strings, and defaults to the symbol | |
3105 | @code{infix}. | |
3106 | ||
3107 | @table @code | |
3108 | @item infix | |
3109 | Insert the separator between list elements. An empty string | |
3110 | will produce an empty list. | |
3111 | @item string-infix | |
3112 | Like @code{infix}, but will raise an error if given the empty | |
3113 | list. | |
3114 | @item suffix | |
3115 | Insert the separator after every list element. | |
3116 | @item prefix | |
3117 | Insert the separator before each list element. | |
3118 | @end table | |
3119 | @end deffn | |
3120 | ||
07d83abe MV |
3121 | @node List/String Conversion |
3122 | @subsubsection List/String conversion | |
3123 | ||
3124 | When processing strings, it is often convenient to first convert them | |
3125 | into a list representation by using the procedure @code{string->list}, | |
3126 | work with the resulting list, and then convert it back into a string. | |
3127 | These procedures are useful for similar tasks. | |
3128 | ||
3129 | @rnindex string->list | |
5676b4fa MV |
3130 | @deffn {Scheme Procedure} string->list str [start [end]] |
3131 | @deffnx {C Function} scm_substring_to_list (str, start, end) | |
07d83abe | 3132 | @deffnx {C Function} scm_string_to_list (str) |
5676b4fa | 3133 | Convert the string @var{str} into a list of characters. |
07d83abe MV |
3134 | @end deffn |
3135 | ||
3136 | @deffn {Scheme Procedure} string-split str chr | |
3137 | @deffnx {C Function} scm_string_split (str, chr) | |
ecb87335 | 3138 | Split the string @var{str} into a list of substrings delimited |
07d83abe MV |
3139 | by appearances of the character @var{chr}. Note that an empty substring |
3140 | between separator characters will result in an empty string in the | |
3141 | result list. | |
3142 | ||
3143 | @lisp | |
3144 | (string-split "root:x:0:0:root:/root:/bin/bash" #\:) | |
3145 | @result{} | |
3146 | ("root" "x" "0" "0" "root" "/root" "/bin/bash") | |
3147 | ||
3148 | (string-split "::" #\:) | |
3149 | @result{} | |
3150 | ("" "" "") | |
3151 | ||
3152 | (string-split "" #\:) | |
3153 | @result{} | |
3154 | ("") | |
3155 | @end lisp | |
3156 | @end deffn | |
3157 | ||
3158 | ||
3159 | @node String Selection | |
3160 | @subsubsection String Selection | |
3161 | ||
3162 | Portions of strings can be extracted by these procedures. | |
3163 | @code{string-ref} delivers individual characters whereas | |
3164 | @code{substring} can be used to extract substrings from longer strings. | |
3165 | ||
3166 | @rnindex string-length | |
3167 | @deffn {Scheme Procedure} string-length string | |
3168 | @deffnx {C Function} scm_string_length (string) | |
3169 | Return the number of characters in @var{string}. | |
3170 | @end deffn | |
3171 | ||
c48c62d0 MV |
3172 | @deftypefn {C Function} size_t scm_c_string_length (SCM str) |
3173 | Return the number of characters in @var{str} as a @code{size_t}. | |
3174 | @end deftypefn | |
3175 | ||
07d83abe MV |
3176 | @rnindex string-ref |
3177 | @deffn {Scheme Procedure} string-ref str k | |
3178 | @deffnx {C Function} scm_string_ref (str, k) | |
3179 | Return character @var{k} of @var{str} using zero-origin | |
3180 | indexing. @var{k} must be a valid index of @var{str}. | |
3181 | @end deffn | |
3182 | ||
c48c62d0 MV |
3183 | @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k) |
3184 | Return character @var{k} of @var{str} using zero-origin | |
3185 | indexing. @var{k} must be a valid index of @var{str}. | |
3186 | @end deftypefn | |
3187 | ||
07d83abe | 3188 | @rnindex string-copy |
5676b4fa MV |
3189 | @deffn {Scheme Procedure} string-copy str [start [end]] |
3190 | @deffnx {C Function} scm_substring_copy (str, start, end) | |
07d83abe | 3191 | @deffnx {C Function} scm_string_copy (str) |
5676b4fa | 3192 | Return a copy of the given string @var{str}. |
c48c62d0 MV |
3193 | |
3194 | The returned string shares storage with @var{str} initially, but it is | |
3195 | copied as soon as one of the two strings is modified. | |
07d83abe MV |
3196 | @end deffn |
3197 | ||
3198 | @rnindex substring | |
3199 | @deffn {Scheme Procedure} substring str start [end] | |
3200 | @deffnx {C Function} scm_substring (str, start, end) | |
c48c62d0 | 3201 | Return a new string formed from the characters |
07d83abe MV |
3202 | of @var{str} beginning with index @var{start} (inclusive) and |
3203 | ending with index @var{end} (exclusive). | |
3204 | @var{str} must be a string, @var{start} and @var{end} must be | |
3205 | exact integers satisfying: | |
3206 | ||
3207 | 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}. | |
c48c62d0 MV |
3208 | |
3209 | The returned string shares storage with @var{str} initially, but it is | |
3210 | copied as soon as one of the two strings is modified. | |
3211 | @end deffn | |
3212 | ||
3213 | @deffn {Scheme Procedure} substring/shared str start [end] | |
3214 | @deffnx {C Function} scm_substring_shared (str, start, end) | |
3215 | Like @code{substring}, but the strings continue to share their storage | |
3216 | even if they are modified. Thus, modifications to @var{str} show up | |
3217 | in the new string, and vice versa. | |
3218 | @end deffn | |
3219 | ||
3220 | @deffn {Scheme Procedure} substring/copy str start [end] | |
3221 | @deffnx {C Function} scm_substring_copy (str, start, end) | |
3222 | Like @code{substring}, but the storage for the new string is copied | |
3223 | immediately. | |
07d83abe MV |
3224 | @end deffn |
3225 | ||
05256760 MV |
3226 | @deffn {Scheme Procedure} substring/read-only str start [end] |
3227 | @deffnx {C Function} scm_substring_read_only (str, start, end) | |
3228 | Like @code{substring}, but the resulting string can not be modified. | |
3229 | @end deffn | |
3230 | ||
c48c62d0 MV |
3231 | @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end) |
3232 | @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end) | |
3233 | @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end) | |
05256760 | 3234 | @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end) |
c48c62d0 MV |
3235 | Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}. |
3236 | @end deftypefn | |
3237 | ||
5676b4fa MV |
3238 | @deffn {Scheme Procedure} string-take s n |
3239 | @deffnx {C Function} scm_string_take (s, n) | |
3240 | Return the @var{n} first characters of @var{s}. | |
3241 | @end deffn | |
3242 | ||
3243 | @deffn {Scheme Procedure} string-drop s n | |
3244 | @deffnx {C Function} scm_string_drop (s, n) | |
3245 | Return all but the first @var{n} characters of @var{s}. | |
3246 | @end deffn | |
3247 | ||
3248 | @deffn {Scheme Procedure} string-take-right s n | |
3249 | @deffnx {C Function} scm_string_take_right (s, n) | |
3250 | Return the @var{n} last characters of @var{s}. | |
3251 | @end deffn | |
3252 | ||
3253 | @deffn {Scheme Procedure} string-drop-right s n | |
3254 | @deffnx {C Function} scm_string_drop_right (s, n) | |
3255 | Return all but the last @var{n} characters of @var{s}. | |
3256 | @end deffn | |
3257 | ||
3258 | @deffn {Scheme Procedure} string-pad s len [chr [start [end]]] | |
6337e7fb | 3259 | @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]] |
5676b4fa | 3260 | @deffnx {C Function} scm_string_pad (s, len, chr, start, end) |
5676b4fa | 3261 | @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end) |
6337e7fb KR |
3262 | Take characters @var{start} to @var{end} from the string @var{s} and |
3263 | either pad with @var{char} or truncate them to give @var{len} | |
3264 | characters. | |
3265 | ||
3266 | @code{string-pad} pads or truncates on the left, so for example | |
3267 | ||
3268 | @example | |
3269 | (string-pad "x" 3) @result{} " x" | |
3270 | (string-pad "abcde" 3) @result{} "cde" | |
3271 | @end example | |
3272 | ||
3273 | @code{string-pad-right} pads or truncates on the right, so for example | |
3274 | ||
3275 | @example | |
3276 | (string-pad-right "x" 3) @result{} "x " | |
3277 | (string-pad-right "abcde" 3) @result{} "abc" | |
3278 | @end example | |
5676b4fa MV |
3279 | @end deffn |
3280 | ||
3281 | @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]] | |
dc297bb7 KR |
3282 | @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]] |
3283 | @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]] | |
5676b4fa | 3284 | @deffnx {C Function} scm_string_trim (s, char_pred, start, end) |
5676b4fa | 3285 | @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end) |
5676b4fa | 3286 | @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end) |
be3eb25c | 3287 | Trim occurrences of @var{char_pred} from the ends of @var{s}. |
5676b4fa | 3288 | |
dc297bb7 KR |
3289 | @code{string-trim} trims @var{char_pred} characters from the left |
3290 | (start) of the string, @code{string-trim-right} trims them from the | |
3291 | right (end) of the string, @code{string-trim-both} trims from both | |
3292 | ends. | |
5676b4fa | 3293 | |
dc297bb7 KR |
3294 | @var{char_pred} can be a character, a character set, or a predicate |
3295 | procedure to call on each character. If @var{char_pred} is not given | |
3296 | the default is whitespace as per @code{char-set:whitespace} | |
3297 | (@pxref{Standard Character Sets}). | |
5676b4fa | 3298 | |
dc297bb7 KR |
3299 | @example |
3300 | (string-trim " x ") @result{} "x " | |
3301 | (string-trim-right "banana" #\a) @result{} "banan" | |
3302 | (string-trim-both ".,xy:;" char-set:punctuation) | |
3303 | @result{} "xy" | |
3304 | (string-trim-both "xyzzy" (lambda (c) | |
3305 | (or (eqv? c #\x) | |
3306 | (eqv? c #\y)))) | |
3307 | @result{} "zz" | |
3308 | @end example | |
5676b4fa MV |
3309 | @end deffn |
3310 | ||
07d83abe MV |
3311 | @node String Modification |
3312 | @subsubsection String Modification | |
3313 | ||
3314 | These procedures are for modifying strings in-place. This means that the | |
3315 | result of the operation is not a new string; instead, the original string's | |
3316 | memory representation is modified. | |
3317 | ||
3318 | @rnindex string-set! | |
3319 | @deffn {Scheme Procedure} string-set! str k chr | |
3320 | @deffnx {C Function} scm_string_set_x (str, k, chr) | |
3321 | Store @var{chr} in element @var{k} of @var{str} and return | |
3322 | an unspecified value. @var{k} must be a valid index of | |
3323 | @var{str}. | |
3324 | @end deffn | |
3325 | ||
c48c62d0 MV |
3326 | @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr) |
3327 | Like @code{scm_string_set_x}, but the index is given as a @code{size_t}. | |
3328 | @end deftypefn | |
3329 | ||
07d83abe | 3330 | @rnindex string-fill! |
5676b4fa MV |
3331 | @deffn {Scheme Procedure} string-fill! str chr [start [end]] |
3332 | @deffnx {C Function} scm_substring_fill_x (str, chr, start, end) | |
07d83abe | 3333 | @deffnx {C Function} scm_string_fill_x (str, chr) |
5676b4fa MV |
3334 | Stores @var{chr} in every element of the given @var{str} and |
3335 | returns an unspecified value. | |
07d83abe MV |
3336 | @end deffn |
3337 | ||
3338 | @deffn {Scheme Procedure} substring-fill! str start end fill | |
3339 | @deffnx {C Function} scm_substring_fill_x (str, start, end, fill) | |
3340 | Change every character in @var{str} between @var{start} and | |
3341 | @var{end} to @var{fill}. | |
3342 | ||
3343 | @lisp | |
3344 | (define y "abcdefg") | |
3345 | (substring-fill! y 1 3 #\r) | |
3346 | y | |
3347 | @result{} "arrdefg" | |
3348 | @end lisp | |
3349 | @end deffn | |
3350 | ||
3351 | @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2 | |
3352 | @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2) | |
3353 | Copy the substring of @var{str1} bounded by @var{start1} and @var{end1} | |
3354 | into @var{str2} beginning at position @var{start2}. | |
3355 | @var{str1} and @var{str2} can be the same string. | |
3356 | @end deffn | |
3357 | ||
5676b4fa MV |
3358 | @deffn {Scheme Procedure} string-copy! target tstart s [start [end]] |
3359 | @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end) | |
3360 | Copy the sequence of characters from index range [@var{start}, | |
3361 | @var{end}) in string @var{s} to string @var{target}, beginning | |
3362 | at index @var{tstart}. The characters are copied left-to-right | |
3363 | or right-to-left as needed -- the copy is guaranteed to work, | |
3364 | even if @var{target} and @var{s} are the same string. It is an | |
3365 | error if the copy operation runs off the end of the target | |
3366 | string. | |
3367 | @end deffn | |
3368 | ||
07d83abe MV |
3369 | |
3370 | @node String Comparison | |
3371 | @subsubsection String Comparison | |
3372 | ||
3373 | The procedures in this section are similar to the character ordering | |
3374 | predicates (@pxref{Characters}), but are defined on character sequences. | |
07d83abe | 3375 | |
5676b4fa | 3376 | The first set is specified in R5RS and has names that end in @code{?}. |
28cc8dac | 3377 | The second set is specified in SRFI-13 and the names have not ending |
67af975c | 3378 | @code{?}. |
28cc8dac MG |
3379 | |
3380 | The predicates ending in @code{-ci} ignore the character case | |
3381 | when comparing strings. For now, case-insensitive comparison is done | |
3382 | using the R5RS rules, where every lower-case character that has a | |
3383 | single character upper-case form is converted to uppercase before | |
3384 | comparison. See @xref{Text Collation, the @code{(ice-9 | |
b89c4943 | 3385 | i18n)} module}, for locale-dependent string comparison. |
07d83abe MV |
3386 | |
3387 | @rnindex string=? | |
3323ec06 NJ |
3388 | @deffn {Scheme Procedure} string=? [s1 [s2 . rest]] |
3389 | @deffnx {C Function} scm_i_string_equal_p (s1, s2, rest) | |
07d83abe MV |
3390 | Lexicographic equality predicate; return @code{#t} if the two |
3391 | strings are the same length and contain the same characters in | |
3392 | the same positions, otherwise return @code{#f}. | |
3393 | ||
3394 | The procedure @code{string-ci=?} treats upper and lower case | |
3395 | letters as though they were the same character, but | |
3396 | @code{string=?} treats upper and lower case as distinct | |
3397 | characters. | |
3398 | @end deffn | |
3399 | ||
3400 | @rnindex string<? | |
3323ec06 NJ |
3401 | @deffn {Scheme Procedure} string<? [s1 [s2 . rest]] |
3402 | @deffnx {C Function} scm_i_string_less_p (s1, s2, rest) | |
07d83abe MV |
3403 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
3404 | is lexicographically less than @var{s2}. | |
3405 | @end deffn | |
3406 | ||
3407 | @rnindex string<=? | |
3323ec06 NJ |
3408 | @deffn {Scheme Procedure} string<=? [s1 [s2 . rest]] |
3409 | @deffnx {C Function} scm_i_string_leq_p (s1, s2, rest) | |
07d83abe MV |
3410 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
3411 | is lexicographically less than or equal to @var{s2}. | |
3412 | @end deffn | |
3413 | ||
3414 | @rnindex string>? | |
3323ec06 NJ |
3415 | @deffn {Scheme Procedure} string>? [s1 [s2 . rest]] |
3416 | @deffnx {C Function} scm_i_string_gr_p (s1, s2, rest) | |
07d83abe MV |
3417 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
3418 | is lexicographically greater than @var{s2}. | |
3419 | @end deffn | |
3420 | ||
3421 | @rnindex string>=? | |
3323ec06 NJ |
3422 | @deffn {Scheme Procedure} string>=? [s1 [s2 . rest]] |
3423 | @deffnx {C Function} scm_i_string_geq_p (s1, s2, rest) | |
07d83abe MV |
3424 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
3425 | is lexicographically greater than or equal to @var{s2}. | |
3426 | @end deffn | |
3427 | ||
3428 | @rnindex string-ci=? | |
3323ec06 NJ |
3429 | @deffn {Scheme Procedure} string-ci=? [s1 [s2 . rest]] |
3430 | @deffnx {C Function} scm_i_string_ci_equal_p (s1, s2, rest) | |
07d83abe MV |
3431 | Case-insensitive string equality predicate; return @code{#t} if |
3432 | the two strings are the same length and their component | |
3433 | characters match (ignoring case) at each position; otherwise | |
3434 | return @code{#f}. | |
3435 | @end deffn | |
3436 | ||
5676b4fa | 3437 | @rnindex string-ci<? |
3323ec06 NJ |
3438 | @deffn {Scheme Procedure} string-ci<? [s1 [s2 . rest]] |
3439 | @deffnx {C Function} scm_i_string_ci_less_p (s1, s2, rest) | |
07d83abe MV |
3440 | Case insensitive lexicographic ordering predicate; return |
3441 | @code{#t} if @var{s1} is lexicographically less than @var{s2} | |
3442 | regardless of case. | |
3443 | @end deffn | |
3444 | ||
3445 | @rnindex string<=? | |
3323ec06 NJ |
3446 | @deffn {Scheme Procedure} string-ci<=? [s1 [s2 . rest]] |
3447 | @deffnx {C Function} scm_i_string_ci_leq_p (s1, s2, rest) | |
07d83abe MV |
3448 | Case insensitive lexicographic ordering predicate; return |
3449 | @code{#t} if @var{s1} is lexicographically less than or equal | |
3450 | to @var{s2} regardless of case. | |
3451 | @end deffn | |
3452 | ||
3453 | @rnindex string-ci>? | |
3323ec06 NJ |
3454 | @deffn {Scheme Procedure} string-ci>? [s1 [s2 . rest]] |
3455 | @deffnx {C Function} scm_i_string_ci_gr_p (s1, s2, rest) | |
07d83abe MV |
3456 | Case insensitive lexicographic ordering predicate; return |
3457 | @code{#t} if @var{s1} is lexicographically greater than | |
3458 | @var{s2} regardless of case. | |
3459 | @end deffn | |
3460 | ||
3461 | @rnindex string-ci>=? | |
3323ec06 NJ |
3462 | @deffn {Scheme Procedure} string-ci>=? [s1 [s2 . rest]] |
3463 | @deffnx {C Function} scm_i_string_ci_geq_p (s1, s2, rest) | |
07d83abe MV |
3464 | Case insensitive lexicographic ordering predicate; return |
3465 | @code{#t} if @var{s1} is lexicographically greater than or | |
3466 | equal to @var{s2} regardless of case. | |
3467 | @end deffn | |
3468 | ||
5676b4fa MV |
3469 | @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]] |
3470 | @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2) | |
3471 | Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the | |
3472 | mismatch index, depending upon whether @var{s1} is less than, | |
3473 | equal to, or greater than @var{s2}. The mismatch index is the | |
3474 | largest index @var{i} such that for every 0 <= @var{j} < | |
3475 | @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is, | |
3476 | @var{i} is the first position that does not match. | |
3477 | @end deffn | |
3478 | ||
3479 | @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]] | |
3480 | @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2) | |
3481 | Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the | |
3482 | mismatch index, depending upon whether @var{s1} is less than, | |
3483 | equal to, or greater than @var{s2}. The mismatch index is the | |
3484 | largest index @var{i} such that for every 0 <= @var{j} < | |
3485 | @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is, | |
3323ec06 NJ |
3486 | @var{i} is the first position where the lowercased letters |
3487 | do not match. | |
3488 | ||
5676b4fa MV |
3489 | @end deffn |
3490 | ||
3491 | @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3492 | @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2) | |
3493 | Return @code{#f} if @var{s1} and @var{s2} are not equal, a true | |
3494 | value otherwise. | |
3495 | @end deffn | |
3496 | ||
3497 | @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]] | |
3498 | @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2) | |
3499 | Return @code{#f} if @var{s1} and @var{s2} are equal, a true | |
3500 | value otherwise. | |
3501 | @end deffn | |
3502 | ||
3503 | @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]] | |
3504 | @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2) | |
3505 | Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a | |
3506 | true value otherwise. | |
3507 | @end deffn | |
3508 | ||
3509 | @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]] | |
3510 | @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2) | |
3511 | Return @code{#f} if @var{s1} is less or equal to @var{s2}, a | |
3512 | true value otherwise. | |
3513 | @end deffn | |
3514 | ||
3515 | @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3516 | @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2) | |
3517 | Return @code{#f} if @var{s1} is greater to @var{s2}, a true | |
3518 | value otherwise. | |
3519 | @end deffn | |
3520 | ||
3521 | @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3522 | @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2) | |
3523 | Return @code{#f} if @var{s1} is less to @var{s2}, a true value | |
3524 | otherwise. | |
3525 | @end deffn | |
3526 | ||
3527 | @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3528 | @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2) | |
3529 | Return @code{#f} if @var{s1} and @var{s2} are not equal, a true | |
3530 | value otherwise. The character comparison is done | |
3531 | case-insensitively. | |
3532 | @end deffn | |
3533 | ||
3534 | @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]] | |
3535 | @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2) | |
3536 | Return @code{#f} if @var{s1} and @var{s2} are equal, a true | |
3537 | value otherwise. The character comparison is done | |
3538 | case-insensitively. | |
3539 | @end deffn | |
3540 | ||
3541 | @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]] | |
3542 | @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2) | |
3543 | Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a | |
3544 | true value otherwise. The character comparison is done | |
3545 | case-insensitively. | |
3546 | @end deffn | |
3547 | ||
3548 | @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]] | |
3549 | @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2) | |
3550 | Return @code{#f} if @var{s1} is less or equal to @var{s2}, a | |
3551 | true value otherwise. The character comparison is done | |
3552 | case-insensitively. | |
3553 | @end deffn | |
3554 | ||
3555 | @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3556 | @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2) | |
3557 | Return @code{#f} if @var{s1} is greater to @var{s2}, a true | |
3558 | value otherwise. The character comparison is done | |
3559 | case-insensitively. | |
3560 | @end deffn | |
3561 | ||
3562 | @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]] | |
3563 | @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2) | |
3564 | Return @code{#f} if @var{s1} is less to @var{s2}, a true value | |
3565 | otherwise. The character comparison is done | |
3566 | case-insensitively. | |
3567 | @end deffn | |
3568 | ||
3569 | @deffn {Scheme Procedure} string-hash s [bound [start [end]]] | |
3570 | @deffnx {C Function} scm_substring_hash (s, bound, start, end) | |
ecb87335 | 3571 | Compute a hash value for @var{S}. The optional argument @var{bound} is a non-negative exact integer specifying the range of the hash function. A positive value restricts the return value to the range [0,bound). |
5676b4fa MV |
3572 | @end deffn |
3573 | ||
3574 | @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]] | |
3575 | @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end) | |
ecb87335 | 3576 | Compute a hash value for @var{S}. The optional argument @var{bound} is a non-negative exact integer specifying the range of the hash function. A positive value restricts the return value to the range [0,bound). |
5676b4fa | 3577 | @end deffn |
07d83abe | 3578 | |
edb7bb47 JG |
3579 | Because the same visual appearance of an abstract Unicode character can |
3580 | be obtained via multiple sequences of Unicode characters, even the | |
3581 | case-insensitive string comparison functions described above may return | |
3582 | @code{#f} when presented with strings containing different | |
3583 | representations of the same character. For example, the Unicode | |
3584 | character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be | |
3585 | represented with a single character (U+1E69) or by the character ``LATIN | |
3586 | SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING | |
3587 | DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307). | |
3588 | ||
3589 | For this reason, it is often desirable to ensure that the strings | |
3590 | to be compared are using a mutually consistent representation for every | |
3591 | character. The Unicode standard defines two methods of normalizing the | |
3592 | contents of strings: Decomposition, which breaks composite characters | |
3593 | into a set of constituent characters with an ordering defined by the | |
3594 | Unicode Standard; and composition, which performs the converse. | |
3595 | ||
3596 | There are two decomposition operations. ``Canonical decomposition'' | |
3597 | produces character sequences that share the same visual appearance as | |
ecb87335 | 3598 | the original characters, while ``compatibility decomposition'' produces |
edb7bb47 JG |
3599 | ones whose visual appearances may differ from the originals but which |
3600 | represent the same abstract character. | |
3601 | ||
3602 | These operations are encapsulated in the following set of normalization | |
3603 | forms: | |
3604 | ||
3605 | @table @dfn | |
3606 | @item NFD | |
3607 | Characters are decomposed to their canonical forms. | |
3608 | ||
3609 | @item NFKD | |
3610 | Characters are decomposed to their compatibility forms. | |
3611 | ||
3612 | @item NFC | |
3613 | Characters are decomposed to their canonical forms, then composed. | |
3614 | ||
3615 | @item NFKC | |
3616 | Characters are decomposed to their compatibility forms, then composed. | |
3617 | ||
3618 | @end table | |
3619 | ||
3620 | The functions below put their arguments into one of the forms described | |
3621 | above. | |
3622 | ||
3623 | @deffn {Scheme Procedure} string-normalize-nfd s | |
3624 | @deffnx {C Function} scm_string_normalize_nfd (s) | |
3625 | Return the @code{NFD} normalized form of @var{s}. | |
3626 | @end deffn | |
3627 | ||
3628 | @deffn {Scheme Procedure} string-normalize-nfkd s | |
3629 | @deffnx {C Function} scm_string_normalize_nfkd (s) | |
3630 | Return the @code{NFKD} normalized form of @var{s}. | |
3631 | @end deffn | |
3632 | ||
3633 | @deffn {Scheme Procedure} string-normalize-nfc s | |
3634 | @deffnx {C Function} scm_string_normalize_nfc (s) | |
3635 | Return the @code{NFC} normalized form of @var{s}. | |
3636 | @end deffn | |
3637 | ||
3638 | @deffn {Scheme Procedure} string-normalize-nfkc s | |
3639 | @deffnx {C Function} scm_string_normalize_nfkc (s) | |
3640 | Return the @code{NFKC} normalized form of @var{s}. | |
3641 | @end deffn | |
3642 | ||
07d83abe MV |
3643 | @node String Searching |
3644 | @subsubsection String Searching | |
3645 | ||
5676b4fa MV |
3646 | @deffn {Scheme Procedure} string-index s char_pred [start [end]] |
3647 | @deffnx {C Function} scm_string_index (s, char_pred, start, end) | |
3648 | Search through the string @var{s} from left to right, returning | |
be3eb25c | 3649 | the index of the first occurrence of a character which |
07d83abe | 3650 | |
5676b4fa MV |
3651 | @itemize @bullet |
3652 | @item | |
3653 | equals @var{char_pred}, if it is character, | |
07d83abe | 3654 | |
5676b4fa | 3655 | @item |
be3eb25c | 3656 | satisfies the predicate @var{char_pred}, if it is a procedure, |
07d83abe | 3657 | |
5676b4fa MV |
3658 | @item |
3659 | is in the set @var{char_pred}, if it is a character set. | |
3660 | @end itemize | |
bf7c2e96 LC |
3661 | |
3662 | Return @code{#f} if no match is found. | |
5676b4fa | 3663 | @end deffn |
07d83abe | 3664 | |
5676b4fa MV |
3665 | @deffn {Scheme Procedure} string-rindex s char_pred [start [end]] |
3666 | @deffnx {C Function} scm_string_rindex (s, char_pred, start, end) | |
3667 | Search through the string @var{s} from right to left, returning | |
be3eb25c | 3668 | the index of the last occurrence of a character which |
5676b4fa MV |
3669 | |
3670 | @itemize @bullet | |
3671 | @item | |
3672 | equals @var{char_pred}, if it is character, | |
3673 | ||
3674 | @item | |
be3eb25c | 3675 | satisfies the predicate @var{char_pred}, if it is a procedure, |
5676b4fa MV |
3676 | |
3677 | @item | |
3678 | is in the set if @var{char_pred} is a character set. | |
3679 | @end itemize | |
bf7c2e96 LC |
3680 | |
3681 | Return @code{#f} if no match is found. | |
07d83abe MV |
3682 | @end deffn |
3683 | ||
5676b4fa MV |
3684 | @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]] |
3685 | @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2) | |
3686 | Return the length of the longest common prefix of the two | |
3687 | strings. | |
3688 | @end deffn | |
07d83abe | 3689 | |
5676b4fa MV |
3690 | @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]] |
3691 | @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2) | |
3692 | Return the length of the longest common prefix of the two | |
3693 | strings, ignoring character case. | |
3694 | @end deffn | |
07d83abe | 3695 | |
5676b4fa MV |
3696 | @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]] |
3697 | @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2) | |
3698 | Return the length of the longest common suffix of the two | |
3699 | strings. | |
3700 | @end deffn | |
07d83abe | 3701 | |
5676b4fa MV |
3702 | @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]] |
3703 | @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2) | |
3704 | Return the length of the longest common suffix of the two | |
3705 | strings, ignoring character case. | |
3706 | @end deffn | |
3707 | ||
3708 | @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]] | |
3709 | @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2) | |
3710 | Is @var{s1} a prefix of @var{s2}? | |
3711 | @end deffn | |
3712 | ||
3713 | @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]] | |
3714 | @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2) | |
3715 | Is @var{s1} a prefix of @var{s2}, ignoring character case? | |
3716 | @end deffn | |
3717 | ||
3718 | @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]] | |
3719 | @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2) | |
3720 | Is @var{s1} a suffix of @var{s2}? | |
3721 | @end deffn | |
3722 | ||
3723 | @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]] | |
3724 | @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2) | |
3725 | Is @var{s1} a suffix of @var{s2}, ignoring character case? | |
3726 | @end deffn | |
3727 | ||
3728 | @deffn {Scheme Procedure} string-index-right s char_pred [start [end]] | |
3729 | @deffnx {C Function} scm_string_index_right (s, char_pred, start, end) | |
3730 | Search through the string @var{s} from right to left, returning | |
be3eb25c | 3731 | the index of the last occurrence of a character which |
5676b4fa MV |
3732 | |
3733 | @itemize @bullet | |
3734 | @item | |
3735 | equals @var{char_pred}, if it is character, | |
3736 | ||
3737 | @item | |
be3eb25c | 3738 | satisfies the predicate @var{char_pred}, if it is a procedure, |
5676b4fa MV |
3739 | |
3740 | @item | |
3741 | is in the set if @var{char_pred} is a character set. | |
3742 | @end itemize | |
bf7c2e96 LC |
3743 | |
3744 | Return @code{#f} if no match is found. | |
5676b4fa MV |
3745 | @end deffn |
3746 | ||
3747 | @deffn {Scheme Procedure} string-skip s char_pred [start [end]] | |
3748 | @deffnx {C Function} scm_string_skip (s, char_pred, start, end) | |
3749 | Search through the string @var{s} from left to right, returning | |
be3eb25c | 3750 | the index of the first occurrence of a character which |
5676b4fa MV |
3751 | |
3752 | @itemize @bullet | |
3753 | @item | |
3754 | does not equal @var{char_pred}, if it is character, | |
3755 | ||
3756 | @item | |
be3eb25c | 3757 | does not satisfy the predicate @var{char_pred}, if it is a |
5676b4fa MV |
3758 | procedure, |
3759 | ||
3760 | @item | |
3761 | is not in the set if @var{char_pred} is a character set. | |
3762 | @end itemize | |
3763 | @end deffn | |
3764 | ||
3765 | @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]] | |
3766 | @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end) | |
3767 | Search through the string @var{s} from right to left, returning | |
be3eb25c | 3768 | the index of the last occurrence of a character which |
5676b4fa MV |
3769 | |
3770 | @itemize @bullet | |
3771 | @item | |
3772 | does not equal @var{char_pred}, if it is character, | |
3773 | ||
3774 | @item | |
3775 | does not satisfy the predicate @var{char_pred}, if it is a | |
3776 | procedure, | |
3777 | ||
3778 | @item | |
3779 | is not in the set if @var{char_pred} is a character set. | |
3780 | @end itemize | |
3781 | @end deffn | |
3782 | ||
3783 | @deffn {Scheme Procedure} string-count s char_pred [start [end]] | |
3784 | @deffnx {C Function} scm_string_count (s, char_pred, start, end) | |
3785 | Return the count of the number of characters in the string | |
3786 | @var{s} which | |
3787 | ||
3788 | @itemize @bullet | |
3789 | @item | |
3790 | equals @var{char_pred}, if it is character, | |
3791 | ||
3792 | @item | |
be3eb25c | 3793 | satisfies the predicate @var{char_pred}, if it is a procedure. |
5676b4fa MV |
3794 | |
3795 | @item | |
3796 | is in the set @var{char_pred}, if it is a character set. | |
3797 | @end itemize | |
3798 | @end deffn | |
3799 | ||
3800 | @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]] | |
3801 | @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2) | |
3802 | Does string @var{s1} contain string @var{s2}? Return the index | |
3803 | in @var{s1} where @var{s2} occurs as a substring, or false. | |
3804 | The optional start/end indices restrict the operation to the | |
3805 | indicated substrings. | |
3806 | @end deffn | |
3807 | ||
3808 | @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]] | |
3809 | @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2) | |
3810 | Does string @var{s1} contain string @var{s2}? Return the index | |
3811 | in @var{s1} where @var{s2} occurs as a substring, or false. | |
3812 | The optional start/end indices restrict the operation to the | |
3813 | indicated substrings. Character comparison is done | |
3814 | case-insensitively. | |
07d83abe MV |
3815 | @end deffn |
3816 | ||
3817 | @node Alphabetic Case Mapping | |
3818 | @subsubsection Alphabetic Case Mapping | |
3819 | ||
3820 | These are procedures for mapping strings to their upper- or lower-case | |
3821 | equivalents, respectively, or for capitalizing strings. | |
3822 | ||
67af975c MG |
3823 | They use the basic case mapping rules for Unicode characters. No |
3824 | special language or context rules are considered. The resulting strings | |
3825 | are guaranteed to be the same length as the input strings. | |
3826 | ||
3827 | @xref{Character Case Mapping, the @code{(ice-9 | |
3828 | i18n)} module}, for locale-dependent case conversions. | |
3829 | ||
5676b4fa MV |
3830 | @deffn {Scheme Procedure} string-upcase str [start [end]] |
3831 | @deffnx {C Function} scm_substring_upcase (str, start, end) | |
07d83abe | 3832 | @deffnx {C Function} scm_string_upcase (str) |
5676b4fa | 3833 | Upcase every character in @code{str}. |
07d83abe MV |
3834 | @end deffn |
3835 | ||
5676b4fa MV |
3836 | @deffn {Scheme Procedure} string-upcase! str [start [end]] |
3837 | @deffnx {C Function} scm_substring_upcase_x (str, start, end) | |
07d83abe | 3838 | @deffnx {C Function} scm_string_upcase_x (str) |
5676b4fa MV |
3839 | Destructively upcase every character in @code{str}. |
3840 | ||
07d83abe | 3841 | @lisp |
5676b4fa MV |
3842 | (string-upcase! y) |
3843 | @result{} "ARRDEFG" | |
3844 | y | |
3845 | @result{} "ARRDEFG" | |
07d83abe MV |
3846 | @end lisp |
3847 | @end deffn | |
3848 | ||
5676b4fa MV |
3849 | @deffn {Scheme Procedure} string-downcase str [start [end]] |
3850 | @deffnx {C Function} scm_substring_downcase (str, start, end) | |
07d83abe | 3851 | @deffnx {C Function} scm_string_downcase (str) |
5676b4fa | 3852 | Downcase every character in @var{str}. |
07d83abe MV |
3853 | @end deffn |
3854 | ||
5676b4fa MV |
3855 | @deffn {Scheme Procedure} string-downcase! str [start [end]] |
3856 | @deffnx {C Function} scm_substring_downcase_x (str, start, end) | |
07d83abe | 3857 | @deffnx {C Function} scm_string_downcase_x (str) |
5676b4fa MV |
3858 | Destructively downcase every character in @var{str}. |
3859 | ||
07d83abe | 3860 | @lisp |
5676b4fa MV |
3861 | y |
3862 | @result{} "ARRDEFG" | |
3863 | (string-downcase! y) | |
3864 | @result{} "arrdefg" | |
3865 | y | |
3866 | @result{} "arrdefg" | |
07d83abe MV |
3867 | @end lisp |
3868 | @end deffn | |
3869 | ||
3870 | @deffn {Scheme Procedure} string-capitalize str | |
3871 | @deffnx {C Function} scm_string_capitalize (str) | |
3872 | Return a freshly allocated string with the characters in | |
3873 | @var{str}, where the first character of every word is | |
3874 | capitalized. | |
3875 | @end deffn | |
3876 | ||
3877 | @deffn {Scheme Procedure} string-capitalize! str | |
3878 | @deffnx {C Function} scm_string_capitalize_x (str) | |
3879 | Upcase the first character of every word in @var{str} | |
3880 | destructively and return @var{str}. | |
3881 | ||
3882 | @lisp | |
3883 | y @result{} "hello world" | |
3884 | (string-capitalize! y) @result{} "Hello World" | |
3885 | y @result{} "Hello World" | |
3886 | @end lisp | |
3887 | @end deffn | |
3888 | ||
5676b4fa MV |
3889 | @deffn {Scheme Procedure} string-titlecase str [start [end]] |
3890 | @deffnx {C Function} scm_string_titlecase (str, start, end) | |
3891 | Titlecase every first character in a word in @var{str}. | |
3892 | @end deffn | |
07d83abe | 3893 | |
5676b4fa MV |
3894 | @deffn {Scheme Procedure} string-titlecase! str [start [end]] |
3895 | @deffnx {C Function} scm_string_titlecase_x (str, start, end) | |
3896 | Destructively titlecase every first character in a word in | |
3897 | @var{str}. | |
3898 | @end deffn | |
3899 | ||
3900 | @node Reversing and Appending Strings | |
3901 | @subsubsection Reversing and Appending Strings | |
07d83abe | 3902 | |
5676b4fa MV |
3903 | @deffn {Scheme Procedure} string-reverse str [start [end]] |
3904 | @deffnx {C Function} scm_string_reverse (str, start, end) | |
3905 | Reverse the string @var{str}. The optional arguments | |
3906 | @var{start} and @var{end} delimit the region of @var{str} to | |
3907 | operate on. | |
3908 | @end deffn | |
3909 | ||
3910 | @deffn {Scheme Procedure} string-reverse! str [start [end]] | |
3911 | @deffnx {C Function} scm_string_reverse_x (str, start, end) | |
3912 | Reverse the string @var{str} in-place. The optional arguments | |
3913 | @var{start} and @var{end} delimit the region of @var{str} to | |
3914 | operate on. The return value is unspecified. | |
3915 | @end deffn | |
07d83abe MV |
3916 | |
3917 | @rnindex string-append | |
3918 | @deffn {Scheme Procedure} string-append . args | |
3919 | @deffnx {C Function} scm_string_append (args) | |
3920 | Return a newly allocated string whose characters form the | |
3921 | concatenation of the given strings, @var{args}. | |
3922 | ||
3923 | @example | |
3924 | (let ((h "hello ")) | |
3925 | (string-append h "world")) | |
3926 | @result{} "hello world" | |
3927 | @end example | |
3928 | @end deffn | |
3929 | ||
3323ec06 NJ |
3930 | @deffn {Scheme Procedure} string-append/shared . rest |
3931 | @deffnx {C Function} scm_string_append_shared (rest) | |
5676b4fa MV |
3932 | Like @code{string-append}, but the result may share memory |
3933 | with the argument strings. | |
3934 | @end deffn | |
3935 | ||
3936 | @deffn {Scheme Procedure} string-concatenate ls | |
3937 | @deffnx {C Function} scm_string_concatenate (ls) | |
3938 | Append the elements of @var{ls} (which must be strings) | |
3939 | together into a single string. Guaranteed to return a freshly | |
3940 | allocated string. | |
3941 | @end deffn | |
3942 | ||
3943 | @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]] | |
3944 | @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end) | |
3945 | Without optional arguments, this procedure is equivalent to | |
3946 | ||
aba0dff5 | 3947 | @lisp |
5676b4fa | 3948 | (string-concatenate (reverse ls)) |
aba0dff5 | 3949 | @end lisp |
5676b4fa MV |
3950 | |
3951 | If the optional argument @var{final_string} is specified, it is | |
3952 | consed onto the beginning to @var{ls} before performing the | |
3953 | list-reverse and string-concatenate operations. If @var{end} | |
3954 | is given, only the characters of @var{final_string} up to index | |
3955 | @var{end} are used. | |
3956 | ||
3957 | Guaranteed to return a freshly allocated string. | |
3958 | @end deffn | |
3959 | ||
3960 | @deffn {Scheme Procedure} string-concatenate/shared ls | |
3961 | @deffnx {C Function} scm_string_concatenate_shared (ls) | |
3962 | Like @code{string-concatenate}, but the result may share memory | |
3963 | with the strings in the list @var{ls}. | |
3964 | @end deffn | |
3965 | ||
3966 | @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]] | |
3967 | @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end) | |
3968 | Like @code{string-concatenate-reverse}, but the result may | |
72b3aa56 | 3969 | share memory with the strings in the @var{ls} arguments. |
5676b4fa MV |
3970 | @end deffn |
3971 | ||
3972 | @node Mapping Folding and Unfolding | |
3973 | @subsubsection Mapping, Folding, and Unfolding | |
3974 | ||
3975 | @deffn {Scheme Procedure} string-map proc s [start [end]] | |
3976 | @deffnx {C Function} scm_string_map (proc, s, start, end) | |
3977 | @var{proc} is a char->char procedure, it is mapped over | |
3978 | @var{s}. The order in which the procedure is applied to the | |
3979 | string elements is not specified. | |
3980 | @end deffn | |
3981 | ||
3982 | @deffn {Scheme Procedure} string-map! proc s [start [end]] | |
3983 | @deffnx {C Function} scm_string_map_x (proc, s, start, end) | |
3984 | @var{proc} is a char->char procedure, it is mapped over | |
3985 | @var{s}. The order in which the procedure is applied to the | |
3986 | string elements is not specified. The string @var{s} is | |
3987 | modified in-place, the return value is not specified. | |
3988 | @end deffn | |
3989 | ||
3990 | @deffn {Scheme Procedure} string-for-each proc s [start [end]] | |
3991 | @deffnx {C Function} scm_string_for_each (proc, s, start, end) | |
3992 | @var{proc} is mapped over @var{s} in left-to-right order. The | |
3993 | return value is not specified. | |
3994 | @end deffn | |
3995 | ||
3996 | @deffn {Scheme Procedure} string-for-each-index proc s [start [end]] | |
3997 | @deffnx {C Function} scm_string_for_each_index (proc, s, start, end) | |
2a7820f2 KR |
3998 | Call @code{(@var{proc} i)} for each index i in @var{s}, from left to |
3999 | right. | |
4000 | ||
4001 | For example, to change characters to alternately upper and lower case, | |
4002 | ||
4003 | @example | |
4004 | (define str (string-copy "studly")) | |
45867c2a NJ |
4005 | (string-for-each-index |
4006 | (lambda (i) | |
4007 | (string-set! str i | |
4008 | ((if (even? i) char-upcase char-downcase) | |
4009 | (string-ref str i)))) | |
4010 | str) | |
2a7820f2 KR |
4011 | str @result{} "StUdLy" |
4012 | @end example | |
5676b4fa MV |
4013 | @end deffn |
4014 | ||
4015 | @deffn {Scheme Procedure} string-fold kons knil s [start [end]] | |
4016 | @deffnx {C Function} scm_string_fold (kons, knil, s, start, end) | |
4017 | Fold @var{kons} over the characters of @var{s}, with @var{knil} | |
4018 | as the terminating element, from left to right. @var{kons} | |
4019 | must expect two arguments: The actual character and the last | |
4020 | result of @var{kons}' application. | |
4021 | @end deffn | |
4022 | ||
4023 | @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]] | |
4024 | @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end) | |
4025 | Fold @var{kons} over the characters of @var{s}, with @var{knil} | |
4026 | as the terminating element, from right to left. @var{kons} | |
4027 | must expect two arguments: The actual character and the last | |
4028 | result of @var{kons}' application. | |
4029 | @end deffn | |
4030 | ||
4031 | @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]] | |
4032 | @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final) | |
4033 | @itemize @bullet | |
4034 | @item @var{g} is used to generate a series of @emph{seed} | |
4035 | values from the initial @var{seed}: @var{seed}, (@var{g} | |
4036 | @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), | |
4037 | @dots{} | |
4038 | @item @var{p} tells us when to stop -- when it returns true | |
4039 | when applied to one of these seed values. | |
4040 | @item @var{f} maps each seed value to the corresponding | |
4041 | character in the result string. These chars are assembled | |
4042 | into the string in a left-to-right order. | |
4043 | @item @var{base} is the optional initial/leftmost portion | |
4044 | of the constructed string; it default to the empty | |
4045 | string. | |
4046 | @item @var{make_final} is applied to the terminal seed | |
4047 | value (on which @var{p} returns true) to produce | |
4048 | the final/rightmost portion of the constructed string. | |
9a18d8d4 | 4049 | The default is nothing extra. |
5676b4fa MV |
4050 | @end itemize |
4051 | @end deffn | |
4052 | ||
4053 | @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]] | |
4054 | @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final) | |
4055 | @itemize @bullet | |
4056 | @item @var{g} is used to generate a series of @emph{seed} | |
4057 | values from the initial @var{seed}: @var{seed}, (@var{g} | |
4058 | @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), | |
4059 | @dots{} | |
4060 | @item @var{p} tells us when to stop -- when it returns true | |
4061 | when applied to one of these seed values. | |
4062 | @item @var{f} maps each seed value to the corresponding | |
4063 | character in the result string. These chars are assembled | |
4064 | into the string in a right-to-left order. | |
4065 | @item @var{base} is the optional initial/rightmost portion | |
4066 | of the constructed string; it default to the empty | |
4067 | string. | |
4068 | @item @var{make_final} is applied to the terminal seed | |
4069 | value (on which @var{p} returns true) to produce | |
4070 | the final/leftmost portion of the constructed string. | |
4071 | It defaults to @code{(lambda (x) )}. | |
4072 | @end itemize | |
4073 | @end deffn | |
4074 | ||
4075 | @node Miscellaneous String Operations | |
4076 | @subsubsection Miscellaneous String Operations | |
4077 | ||
4078 | @deffn {Scheme Procedure} xsubstring s from [to [start [end]]] | |
4079 | @deffnx {C Function} scm_xsubstring (s, from, to, start, end) | |
4080 | This is the @emph{extended substring} procedure that implements | |
4081 | replicated copying of a substring of some string. | |
4082 | ||
4083 | @var{s} is a string, @var{start} and @var{end} are optional | |
4084 | arguments that demarcate a substring of @var{s}, defaulting to | |
4085 | 0 and the length of @var{s}. Replicate this substring up and | |
4086 | down index space, in both the positive and negative directions. | |
4087 | @code{xsubstring} returns the substring of this string | |
4088 | beginning at index @var{from}, and ending at @var{to}, which | |
4089 | defaults to @var{from} + (@var{end} - @var{start}). | |
4090 | @end deffn | |
4091 | ||
4092 | @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]] | |
4093 | @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end) | |
4094 | Exactly the same as @code{xsubstring}, but the extracted text | |
4095 | is written into the string @var{target} starting at index | |
4096 | @var{tstart}. The operation is not defined if @code{(eq? | |
4097 | @var{target} @var{s})} or these arguments share storage -- you | |
4098 | cannot copy a string on top of itself. | |
4099 | @end deffn | |
4100 | ||
4101 | @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]] | |
4102 | @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2) | |
4103 | Return the string @var{s1}, but with the characters | |
4104 | @var{start1} @dots{} @var{end1} replaced by the characters | |
4105 | @var{start2} @dots{} @var{end2} from @var{s2}. | |
4106 | @end deffn | |
4107 | ||
4108 | @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]] | |
4109 | @deffnx {C Function} scm_string_tokenize (s, token_set, start, end) | |
4110 | Split the string @var{s} into a list of substrings, where each | |
4111 | substring is a maximal non-empty contiguous sequence of | |
4112 | characters from the character set @var{token_set}, which | |
4113 | defaults to @code{char-set:graphic}. | |
4114 | If @var{start} or @var{end} indices are provided, they restrict | |
4115 | @code{string-tokenize} to operating on the indicated substring | |
4116 | of @var{s}. | |
4117 | @end deffn | |
4118 | ||
9fe717e2 AW |
4119 | @deffn {Scheme Procedure} string-filter char_pred s [start [end]] |
4120 | @deffnx {C Function} scm_string_filter (char_pred, s, start, end) | |
08de3e24 | 4121 | Filter the string @var{s}, retaining only those characters which |
a88e2a96 | 4122 | satisfy @var{char_pred}. |
08de3e24 KR |
4123 | |
4124 | If @var{char_pred} is a procedure, it is applied to each character as | |
4125 | a predicate, if it is a character, it is tested for equality and if it | |
4126 | is a character set, it is tested for membership. | |
5676b4fa MV |
4127 | @end deffn |
4128 | ||
9fe717e2 AW |
4129 | @deffn {Scheme Procedure} string-delete char_pred s [start [end]] |
4130 | @deffnx {C Function} scm_string_delete (char_pred, s, start, end) | |
a88e2a96 | 4131 | Delete characters satisfying @var{char_pred} from @var{s}. |
08de3e24 KR |
4132 | |
4133 | If @var{char_pred} is a procedure, it is applied to each character as | |
4134 | a predicate, if it is a character, it is tested for equality and if it | |
4135 | is a character set, it is tested for membership. | |
5676b4fa MV |
4136 | @end deffn |
4137 | ||
91210d62 MV |
4138 | @node Conversion to/from C |
4139 | @subsubsection Conversion to/from C | |
4140 | ||
4141 | When creating a Scheme string from a C string or when converting a | |
4142 | Scheme string to a C string, the concept of character encoding becomes | |
4143 | important. | |
4144 | ||
4145 | In C, a string is just a sequence of bytes, and the character encoding | |
4146 | describes the relation between these bytes and the actual characters | |
c88453e8 MV |
4147 | that make up the string. For Scheme strings, character encoding is |
4148 | not an issue (most of the time), since in Scheme you never get to see | |
4149 | the bytes, only the characters. | |
91210d62 | 4150 | |
67af975c MG |
4151 | Converting to C and converting from C each have their own challenges. |
4152 | ||
4153 | When converting from C to Scheme, it is important that the sequence of | |
4154 | bytes in the C string be valid with respect to its encoding. ASCII | |
4155 | strings, for example, can't have any bytes greater than 127. An ASCII | |
4156 | byte greater than 127 is considered @emph{ill-formed} and cannot be | |
4157 | converted into a Scheme character. | |
4158 | ||
4159 | Problems can occur in the reverse operation as well. Not all character | |
4160 | encodings can hold all possible Scheme characters. Some encodings, like | |
4161 | ASCII for example, can only describe a small subset of all possible | |
4162 | characters. So, when converting to C, one must first decide what to do | |
4163 | with Scheme characters that can't be represented in the C string. | |
91210d62 | 4164 | |
c88453e8 MV |
4165 | Converting a Scheme string to a C string will often allocate fresh |
4166 | memory to hold the result. You must take care that this memory is | |
4167 | properly freed eventually. In many cases, this can be achieved by | |
661ae7ab MV |
4168 | using @code{scm_dynwind_free} inside an appropriate dynwind context, |
4169 | @xref{Dynamic Wind}. | |
91210d62 MV |
4170 | |
4171 | @deftypefn {C Function} SCM scm_from_locale_string (const char *str) | |
4172 | @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len) | |
67af975c MG |
4173 | Creates a new Scheme string that has the same contents as @var{str} when |
4174 | interpreted in the locale character encoding of the | |
4175 | @code{current-input-port}. | |
91210d62 MV |
4176 | |
4177 | For @code{scm_from_locale_string}, @var{str} must be null-terminated. | |
4178 | ||
4179 | For @code{scm_from_locale_stringn}, @var{len} specifies the length of | |
4180 | @var{str} in bytes, and @var{str} does not need to be null-terminated. | |
4181 | If @var{len} is @code{(size_t)-1}, then @var{str} does need to be | |
4182 | null-terminated and the real length will be found with @code{strlen}. | |
67af975c MG |
4183 | |
4184 | If the C string is ill-formed, an error will be raised. | |
ce3ce21c MW |
4185 | |
4186 | Note that these functions should @emph{not} be used to convert C string | |
4187 | constants, because there is no guarantee that the current locale will | |
4188 | match that of the source code. To convert C string constants, use | |
4189 | @code{scm_from_latin1_string}, @code{scm_from_utf8_string} or | |
4190 | @code{scm_from_utf32_string}. | |
91210d62 MV |
4191 | @end deftypefn |
4192 | ||
4193 | @deftypefn {C Function} SCM scm_take_locale_string (char *str) | |
4194 | @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len) | |
4195 | Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn}, | |
4196 | respectively, but also frees @var{str} with @code{free} eventually. | |
4197 | Thus, you can use this function when you would free @var{str} anyway | |
4198 | immediately after creating the Scheme string. In certain cases, Guile | |
4199 | can then use @var{str} directly as its internal representation. | |
4200 | @end deftypefn | |
4201 | ||
4846ae2c KR |
4202 | @deftypefn {C Function} {char *} scm_to_locale_string (SCM str) |
4203 | @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp) | |
67af975c MG |
4204 | Returns a C string with the same contents as @var{str} in the locale |
4205 | encoding of the @code{current-output-port}. The C string must be freed | |
4206 | with @code{free} eventually, maybe by using @code{scm_dynwind_free}, | |
4207 | @xref{Dynamic Wind}. | |
91210d62 MV |
4208 | |
4209 | For @code{scm_to_locale_string}, the returned string is | |
4210 | null-terminated and an error is signalled when @var{str} contains | |
4211 | @code{#\nul} characters. | |
4212 | ||
4213 | For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL}, | |
4214 | @var{str} might contain @code{#\nul} characters and the length of the | |
4215 | returned string in bytes is stored in @code{*@var{lenp}}. The | |
4216 | returned string will not be null-terminated in this case. If | |
4217 | @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like | |
4218 | @code{scm_to_locale_string}. | |
67af975c MG |
4219 | |
4220 | If a character in @var{str} cannot be represented in the locale encoding | |
4221 | of the current output port, the port conversion strategy of the current | |
4222 | output port will determine the result, @xref{Ports}. If output port's | |
4223 | conversion strategy is @code{error}, an error will be raised. If it is | |
ecb87335 | 4224 | @code{substitute}, a replacement character, such as a question mark, will |
67af975c MG |
4225 | be inserted in its place. If it is @code{escape}, a hex escape will be |
4226 | inserted in its place. | |
91210d62 MV |
4227 | @end deftypefn |
4228 | ||
4229 | @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len) | |
4230 | Puts @var{str} as a C string in the current locale encoding into the | |
4231 | memory pointed to by @var{buf}. The buffer at @var{buf} has room for | |
4232 | @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store | |
4233 | more than that. No terminating @code{'\0'} will be stored. | |
4234 | ||
4235 | The return value of @code{scm_to_locale_stringbuf} is the number of | |
4236 | bytes that are needed for all of @var{str}, regardless of whether | |
4237 | @var{buf} was large enough to hold them. Thus, when the return value | |
4238 | is larger than @var{max_len}, only @var{max_len} bytes have been | |
4239 | stored and you probably need to try again with a larger buffer. | |
4240 | @end deftypefn | |
cf313a94 MG |
4241 | |
4242 | For most situations, string conversion should occur using the current | |
4243 | locale, such as with the functions above. But there may be cases where | |
4244 | one wants to convert strings from a character encoding other than the | |
4245 | locale's character encoding. For these cases, the lower-level functions | |
4246 | @code{scm_to_stringn} and @code{scm_from_stringn} are provided. These | |
4247 | functions should seldom be necessary if one is properly using locales. | |
4248 | ||
4249 | @deftp {C Type} scm_t_string_failed_conversion_handler | |
4250 | This is an enumerated type that can take one of three values: | |
4251 | @code{SCM_FAILED_CONVERSION_ERROR}, | |
4252 | @code{SCM_FAILED_CONVERSION_QUESTION_MARK}, and | |
4253 | @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}. They are used to indicate | |
4254 | a strategy for handling characters that cannot be converted to or from a | |
4255 | given character encoding. @code{SCM_FAILED_CONVERSION_ERROR} indicates | |
4256 | that a conversion should throw an error if some characters cannot be | |
4257 | converted. @code{SCM_FAILED_CONVERSION_QUESTION_MARK} indicates that a | |
4258 | conversion should replace unconvertable characters with the question | |
4259 | mark character. And, @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE} | |
4260 | requests that a conversion should replace an unconvertable character | |
4261 | with an escape sequence. | |
4262 | ||
4263 | While all three strategies apply when converting Scheme strings to C, | |
4264 | only @code{SCM_FAILED_CONVERSION_ERROR} and | |
4265 | @code{SCM_FAILED_CONVERSION_QUESTION_MARK} can be used when converting C | |
4266 | strings to Scheme. | |
4267 | @end deftp | |
4268 | ||
4269 | @deftypefn {C Function} char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding, scm_t_string_failed_conversion_handler handler) | |
4270 | This function returns a newly allocated C string from the Guile string | |
4271 | @var{str}. The length of the string will be returned in @var{lenp}. | |
4272 | The character encoding of the C string is passed as the ASCII, | |
4273 | null-terminated C string @var{encoding}. The @var{handler} parameter | |
4274 | gives a strategy for dealing with characters that cannot be converted | |
4275 | into @var{encoding}. | |
4276 | ||
4277 | If @var{lenp} is NULL, this function will return a null-terminated C | |
4278 | string. It will throw an error if the string contains a null | |
4279 | character. | |
4280 | @end deftypefn | |
4281 | ||
4282 | @deftypefn {C Function} SCM scm_from_stringn (const char *str, size_t len, const char *encoding, scm_t_string_failed_conversion_handler handler) | |
4283 | This function returns a scheme string from the C string @var{str}. The | |
4284 | length of the C string is input as @var{len}. The encoding of the C | |
4285 | string is passed as the ASCII, null-terminated C string @code{encoding}. | |
4286 | The @var{handler} parameters suggests a strategy for dealing with | |
4287 | unconvertable characters. | |
4288 | @end deftypefn | |
4289 | ||
ce3ce21c MW |
4290 | The following conversion functions are provided as a convenience for the |
4291 | most commonly used encodings. | |
4292 | ||
4293 | @deftypefn {C Function} SCM scm_from_latin1_string (const char *str) | |
4294 | @deftypefnx {C Function} SCM scm_from_utf8_string (const char *str) | |
4295 | @deftypefnx {C Function} SCM scm_from_utf32_string (const scm_t_wchar *str) | |
4296 | Return a scheme string from the null-terminated C string @var{str}, | |
4297 | which is ISO-8859-1-, UTF-8-, or UTF-32-encoded. These functions should | |
4298 | be used to convert hard-coded C string constants into Scheme strings. | |
4299 | @end deftypefn | |
cf313a94 MG |
4300 | |
4301 | @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len) | |
647dc1ac LC |
4302 | @deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len) |
4303 | @deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len) | |
4304 | Return a scheme string from C string @var{str}, which is ISO-8859-1-, | |
4305 | UTF-8-, or UTF-32-encoded, of length @var{len}. @var{len} is the number | |
4306 | of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and | |
4307 | @code{scm_from_utf8_stringn}; it is the number of elements (code points) | |
4308 | in @var{str} in the case of @code{scm_from_utf32_stringn}. | |
cf313a94 MG |
4309 | @end deftypefn |
4310 | ||
647dc1ac LC |
4311 | @deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp) |
4312 | @deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp) | |
4313 | @deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp) | |
4314 | Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string | |
4315 | from Scheme string @var{str}. An error is thrown when @var{str} | |
4316 | string cannot be converted to the specified encoding. If @var{lenp} is | |
cf313a94 MG |
4317 | @code{NULL}, the returned C string will be null terminated, and an error |
4318 | will be thrown if the C string would otherwise contain null | |
4319 | characters. If @var{lenp} is not NULL, the length of the string is | |
4320 | returned in @var{lenp}, and the string is not null terminated. | |
4321 | @end deftypefn | |
07d83abe | 4322 | |
5b6b22e8 MG |
4323 | @node String Internals |
4324 | @subsubsection String Internals | |
4325 | ||
4326 | Guile stores each string in memory as a contiguous array of Unicode code | |
4327 | points along with an associated set of attributes. If all of the code | |
4328 | points of a string have an integer range between 0 and 255 inclusive, | |
4329 | the code point array is stored as one byte per code point: it is stored | |
4330 | as an ISO-8859-1 (aka Latin-1) string. If any of the code points of the | |
4331 | string has an integer value greater that 255, the code point array is | |
4332 | stored as four bytes per code point: it is stored as a UTF-32 string. | |
4333 | ||
4334 | Conversion between the one-byte-per-code-point and | |
4335 | four-bytes-per-code-point representations happens automatically as | |
4336 | necessary. | |
4337 | ||
4338 | No API is provided to set the internal representation of strings; | |
4339 | however, there are pair of procedures available to query it. These are | |
4340 | debugging procedures. Using them in production code is discouraged, | |
4341 | since the details of Guile's internal representation of strings may | |
4342 | change from release to release. | |
4343 | ||
4344 | @deffn {Scheme Procedure} string-bytes-per-char str | |
4345 | @deffnx {C Function} scm_string_bytes_per_char (str) | |
4346 | Return the number of bytes used to encode a Unicode code point in string | |
4347 | @var{str}. The result is one or four. | |
4348 | @end deffn | |
4349 | ||
4350 | @deffn {Scheme Procedure} %string-dump str | |
4351 | @deffnx {C Function} scm_sys_string_dump (str) | |
4352 | Returns an association list containing debugging information for | |
4353 | @var{str}. The association list has the following entries. | |
4354 | @table @code | |
4355 | ||
4356 | @item string | |
4357 | The string itself. | |
4358 | ||
4359 | @item start | |
4360 | The start index of the string into its stringbuf | |
4361 | ||
4362 | @item length | |
4363 | The length of the string | |
4364 | ||
4365 | @item shared | |
4366 | If this string is a substring, it returns its | |
4367 | parent string. Otherwise, it returns @code{#f} | |
4368 | ||
4369 | @item read-only | |
4370 | @code{#t} if the string is read-only | |
4371 | ||
4372 | @item stringbuf-chars | |
4373 | A new string containing this string's stringbuf's characters | |
4374 | ||
4375 | @item stringbuf-length | |
4376 | The number of characters in this stringbuf | |
4377 | ||
4378 | @item stringbuf-shared | |
4379 | @code{#t} if this stringbuf is shared | |
4380 | ||
4381 | @item stringbuf-wide | |
4382 | @code{#t} if this stringbuf's characters are stored in a 32-bit buffer, | |
4383 | or @code{#f} if they are stored in an 8-bit buffer | |
4384 | @end table | |
4385 | @end deffn | |
4386 | ||
4387 | ||
b242715b LC |
4388 | @node Bytevectors |
4389 | @subsection Bytevectors | |
4390 | ||
4391 | @cindex bytevector | |
4392 | @cindex R6RS | |
4393 | ||
07d22c02 | 4394 | A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevectors)} |
b242715b | 4395 | module provides the programming interface specified by the |
5fa2deb3 | 4396 | @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language |
b242715b LC |
4397 | Scheme (R6RS)}. It contains procedures to manipulate bytevectors and |
4398 | interpret their contents in a number of ways: bytevector contents can be | |
4399 | accessed as signed or unsigned integer of various sizes and endianness, | |
4400 | as IEEE-754 floating point numbers, or as strings. It is a useful tool | |
4401 | to encode and decode binary data. | |
4402 | ||
4403 | The R6RS (Section 4.3.4) specifies an external representation for | |
4404 | bytevectors, whereby the octets (integers in the range 0--255) contained | |
4405 | in the bytevector are represented as a list prefixed by @code{#vu8}: | |
4406 | ||
4407 | @lisp | |
4408 | #vu8(1 53 204) | |
4409 | @end lisp | |
4410 | ||
4411 | denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like | |
4412 | string literals, booleans, etc., bytevectors are ``self-quoting'', i.e., | |
4413 | they do not need to be quoted: | |
4414 | ||
4415 | @lisp | |
4416 | #vu8(1 53 204) | |
4417 | @result{} #vu8(1 53 204) | |
4418 | @end lisp | |
4419 | ||
4420 | Bytevectors can be used with the binary input/output primitives of the | |
4421 | R6RS (@pxref{R6RS I/O Ports}). | |
4422 | ||
4423 | @menu | |
4424 | * Bytevector Endianness:: Dealing with byte order. | |
4425 | * Bytevector Manipulation:: Creating, copying, manipulating bytevectors. | |
4426 | * Bytevectors as Integers:: Interpreting bytes as integers. | |
4427 | * Bytevectors and Integer Lists:: Converting to/from an integer list. | |
4428 | * Bytevectors as Floats:: Interpreting bytes as real numbers. | |
4429 | * Bytevectors as Strings:: Interpreting bytes as Unicode strings. | |
438974d0 | 4430 | * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API. |
27219b32 | 4431 | * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4. |
b242715b LC |
4432 | @end menu |
4433 | ||
4434 | @node Bytevector Endianness | |
4435 | @subsubsection Endianness | |
4436 | ||
4437 | @cindex endianness | |
4438 | @cindex byte order | |
4439 | @cindex word order | |
4440 | ||
4441 | Some of the following procedures take an @var{endianness} parameter. | |
5fa2deb3 AW |
4442 | The @dfn{endianness} is defined as the order of bytes in multi-byte |
4443 | numbers: numbers encoded in @dfn{big endian} have their most | |
4444 | significant bytes written first, whereas numbers encoded in | |
4445 | @dfn{little endian} have their least significant bytes | |
4446 | first@footnote{Big-endian and little-endian are the most common | |
4447 | ``endiannesses'', but others do exist. For instance, the GNU MP | |
4448 | library allows @dfn{word order} to be specified independently of | |
4449 | @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU | |
4450 | Multiple Precision Arithmetic Library Manual}).}. | |
4451 | ||
4452 | Little-endian is the native endianness of the IA32 architecture and | |
4453 | its derivatives, while big-endian is native to SPARC and PowerPC, | |
4454 | among others. The @code{native-endianness} procedure returns the | |
4455 | native endianness of the machine it runs on. | |
b242715b LC |
4456 | |
4457 | @deffn {Scheme Procedure} native-endianness | |
4458 | @deffnx {C Function} scm_native_endianness () | |
4459 | Return a value denoting the native endianness of the host machine. | |
4460 | @end deffn | |
4461 | ||
4462 | @deffn {Scheme Macro} endianness symbol | |
4463 | Return an object denoting the endianness specified by @var{symbol}. If | |
5fa2deb3 AW |
4464 | @var{symbol} is neither @code{big} nor @code{little} then an error is |
4465 | raised at expand-time. | |
b242715b LC |
4466 | @end deffn |
4467 | ||
4468 | @defvr {C Variable} scm_endianness_big | |
4469 | @defvrx {C Variable} scm_endianness_little | |
5fa2deb3 | 4470 | The objects denoting big- and little-endianness, respectively. |
b242715b LC |
4471 | @end defvr |
4472 | ||
4473 | ||
4474 | @node Bytevector Manipulation | |
4475 | @subsubsection Manipulating Bytevectors | |
4476 | ||
4477 | Bytevectors can be created, copied, and analyzed with the following | |
404bb5f8 | 4478 | procedures and C functions. |
b242715b LC |
4479 | |
4480 | @deffn {Scheme Procedure} make-bytevector len [fill] | |
4481 | @deffnx {C Function} scm_make_bytevector (len, fill) | |
2d34e924 | 4482 | @deffnx {C Function} scm_c_make_bytevector (size_t len) |
b242715b | 4483 | Return a new bytevector of @var{len} bytes. Optionally, if @var{fill} |
d64fc8b0 LC |
4484 | is given, fill it with @var{fill}; @var{fill} must be in the range |
4485 | [-128,255]. | |
b242715b LC |
4486 | @end deffn |
4487 | ||
4488 | @deffn {Scheme Procedure} bytevector? obj | |
4489 | @deffnx {C Function} scm_bytevector_p (obj) | |
4490 | Return true if @var{obj} is a bytevector. | |
4491 | @end deffn | |
4492 | ||
404bb5f8 LC |
4493 | @deftypefn {C Function} int scm_is_bytevector (SCM obj) |
4494 | Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}. | |
4495 | @end deftypefn | |
4496 | ||
b242715b LC |
4497 | @deffn {Scheme Procedure} bytevector-length bv |
4498 | @deffnx {C Function} scm_bytevector_length (bv) | |
4499 | Return the length in bytes of bytevector @var{bv}. | |
4500 | @end deffn | |
4501 | ||
404bb5f8 LC |
4502 | @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv) |
4503 | Likewise, return the length in bytes of bytevector @var{bv}. | |
4504 | @end deftypefn | |
4505 | ||
b242715b LC |
4506 | @deffn {Scheme Procedure} bytevector=? bv1 bv2 |
4507 | @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2) | |
4508 | Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same | |
4509 | length and contents. | |
4510 | @end deffn | |
4511 | ||
4512 | @deffn {Scheme Procedure} bytevector-fill! bv fill | |
4513 | @deffnx {C Function} scm_bytevector_fill_x (bv, fill) | |
4514 | Fill bytevector @var{bv} with @var{fill}, a byte. | |
4515 | @end deffn | |
4516 | ||
4517 | @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len | |
4518 | @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len) | |
4519 | Copy @var{len} bytes from @var{source} into @var{target}, starting | |
4520 | reading from @var{source-start} (a positive index within @var{source}) | |
4521 | and start writing at @var{target-start}. | |
4522 | @end deffn | |
4523 | ||
4524 | @deffn {Scheme Procedure} bytevector-copy bv | |
4525 | @deffnx {C Function} scm_bytevector_copy (bv) | |
4526 | Return a newly allocated copy of @var{bv}. | |
4527 | @end deffn | |
4528 | ||
404bb5f8 LC |
4529 | @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index) |
4530 | Return the byte at @var{index} in bytevector @var{bv}. | |
4531 | @end deftypefn | |
4532 | ||
4533 | @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value) | |
4534 | Set the byte at @var{index} in @var{bv} to @var{value}. | |
4535 | @end deftypefn | |
4536 | ||
b242715b LC |
4537 | Low-level C macros are available. They do not perform any |
4538 | type-checking; as such they should be used with care. | |
4539 | ||
4540 | @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv) | |
4541 | Return the length in bytes of bytevector @var{bv}. | |
4542 | @end deftypefn | |
4543 | ||
4544 | @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv) | |
4545 | Return a pointer to the contents of bytevector @var{bv}. | |
4546 | @end deftypefn | |
4547 | ||
4548 | ||
4549 | @node Bytevectors as Integers | |
4550 | @subsubsection Interpreting Bytevector Contents as Integers | |
4551 | ||
4552 | The contents of a bytevector can be interpreted as a sequence of | |
4553 | integers of any given size, sign, and endianness. | |
4554 | ||
4555 | @lisp | |
4556 | (let ((bv (make-bytevector 4))) | |
4557 | (bytevector-u8-set! bv 0 #x12) | |
4558 | (bytevector-u8-set! bv 1 #x34) | |
4559 | (bytevector-u8-set! bv 2 #x56) | |
4560 | (bytevector-u8-set! bv 3 #x78) | |
4561 | ||
4562 | (map (lambda (number) | |
4563 | (number->string number 16)) | |
4564 | (list (bytevector-u8-ref bv 0) | |
4565 | (bytevector-u16-ref bv 0 (endianness big)) | |
4566 | (bytevector-u32-ref bv 0 (endianness little))))) | |
4567 | ||
4568 | @result{} ("12" "1234" "78563412") | |
4569 | @end lisp | |
4570 | ||
4571 | The most generic procedures to interpret bytevector contents as integers | |
4572 | are described below. | |
4573 | ||
4574 | @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size | |
b242715b | 4575 | @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size) |
4827afeb NJ |
4576 | Return the @var{size}-byte long unsigned integer at index @var{index} in |
4577 | @var{bv}, decoded according to @var{endianness}. | |
4578 | @end deffn | |
4579 | ||
4580 | @deffn {Scheme Procedure} bytevector-sint-ref bv index endianness size | |
b242715b | 4581 | @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size) |
4827afeb NJ |
4582 | Return the @var{size}-byte long signed integer at index @var{index} in |
4583 | @var{bv}, decoded according to @var{endianness}. | |
b242715b LC |
4584 | @end deffn |
4585 | ||
4586 | @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size | |
b242715b | 4587 | @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size) |
4827afeb NJ |
4588 | Set the @var{size}-byte long unsigned integer at @var{index} to |
4589 | @var{value}, encoded according to @var{endianness}. | |
4590 | @end deffn | |
4591 | ||
4592 | @deffn {Scheme Procedure} bytevector-sint-set! bv index value endianness size | |
b242715b | 4593 | @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size) |
4827afeb NJ |
4594 | Set the @var{size}-byte long signed integer at @var{index} to |
4595 | @var{value}, encoded according to @var{endianness}. | |
b242715b LC |
4596 | @end deffn |
4597 | ||
4598 | The following procedures are similar to the ones above, but specialized | |
4599 | to a given integer size: | |
4600 | ||
4601 | @deffn {Scheme Procedure} bytevector-u8-ref bv index | |
4602 | @deffnx {Scheme Procedure} bytevector-s8-ref bv index | |
4603 | @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness | |
4604 | @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness | |
4605 | @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness | |
4606 | @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness | |
4607 | @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness | |
4608 | @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness | |
4609 | @deffnx {C Function} scm_bytevector_u8_ref (bv, index) | |
4610 | @deffnx {C Function} scm_bytevector_s8_ref (bv, index) | |
4611 | @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness) | |
4612 | @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness) | |
4613 | @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness) | |
4614 | @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness) | |
4615 | @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness) | |
4616 | @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness) | |
4617 | Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8, | |
4618 | 16, 32 or 64) from @var{bv} at @var{index}, decoded according to | |
4619 | @var{endianness}. | |
4620 | @end deffn | |
4621 | ||
4622 | @deffn {Scheme Procedure} bytevector-u8-set! bv index value | |
4623 | @deffnx {Scheme Procedure} bytevector-s8-set! bv index value | |
4624 | @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness | |
4625 | @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness | |
4626 | @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness | |
4627 | @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness | |
4628 | @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness | |
4629 | @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness | |
4630 | @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value) | |
4631 | @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value) | |
4632 | @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness) | |
4633 | @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness) | |
4634 | @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness) | |
4635 | @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness) | |
4636 | @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness) | |
4637 | @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness) | |
4638 | Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is | |
4639 | 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to | |
4640 | @var{endianness}. | |
4641 | @end deffn | |
4642 | ||
4643 | Finally, a variant specialized for the host's endianness is available | |
4644 | for each of these functions (with the exception of the @code{u8} | |
4645 | accessors, for obvious reasons): | |
4646 | ||
4647 | @deffn {Scheme Procedure} bytevector-u16-native-ref bv index | |
4648 | @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index | |
4649 | @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index | |
4650 | @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index | |
4651 | @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index | |
4652 | @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index | |
4653 | @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index) | |
4654 | @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index) | |
4655 | @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index) | |
4656 | @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index) | |
4657 | @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index) | |
4658 | @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index) | |
4659 | Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8, | |
4660 | 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the | |
4661 | host's native endianness. | |
4662 | @end deffn | |
4663 | ||
4664 | @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value | |
4665 | @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value | |
4666 | @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value | |
4667 | @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value | |
4668 | @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value | |
4669 | @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value | |
4670 | @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value) | |
4671 | @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value) | |
4672 | @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value) | |
4673 | @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value) | |
4674 | @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value) | |
4675 | @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value) | |
4676 | Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is | |
4677 | 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the | |
4678 | host's native endianness. | |
4679 | @end deffn | |
4680 | ||
4681 | ||
4682 | @node Bytevectors and Integer Lists | |
4683 | @subsubsection Converting Bytevectors to/from Integer Lists | |
4684 | ||
4685 | Bytevector contents can readily be converted to/from lists of signed or | |
4686 | unsigned integers: | |
4687 | ||
4688 | @lisp | |
4689 | (bytevector->sint-list (u8-list->bytevector (make-list 4 255)) | |
4690 | (endianness little) 2) | |
4691 | @result{} (-1 -1) | |
4692 | @end lisp | |
4693 | ||
4694 | @deffn {Scheme Procedure} bytevector->u8-list bv | |
4695 | @deffnx {C Function} scm_bytevector_to_u8_list (bv) | |
4696 | Return a newly allocated list of unsigned 8-bit integers from the | |
4697 | contents of @var{bv}. | |
4698 | @end deffn | |
4699 | ||
4700 | @deffn {Scheme Procedure} u8-list->bytevector lst | |
4701 | @deffnx {C Function} scm_u8_list_to_bytevector (lst) | |
4702 | Return a newly allocated bytevector consisting of the unsigned 8-bit | |
4703 | integers listed in @var{lst}. | |
4704 | @end deffn | |
4705 | ||
4706 | @deffn {Scheme Procedure} bytevector->uint-list bv endianness size | |
b242715b | 4707 | @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size) |
4827afeb NJ |
4708 | Return a list of unsigned integers of @var{size} bytes representing the |
4709 | contents of @var{bv}, decoded according to @var{endianness}. | |
4710 | @end deffn | |
4711 | ||
4712 | @deffn {Scheme Procedure} bytevector->sint-list bv endianness size | |
b242715b | 4713 | @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size) |
4827afeb NJ |
4714 | Return a list of signed integers of @var{size} bytes representing the |
4715 | contents of @var{bv}, decoded according to @var{endianness}. | |
b242715b LC |
4716 | @end deffn |
4717 | ||
4718 | @deffn {Scheme Procedure} uint-list->bytevector lst endianness size | |
b242715b | 4719 | @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size) |
4827afeb NJ |
4720 | Return a new bytevector containing the unsigned integers listed in |
4721 | @var{lst} and encoded on @var{size} bytes according to @var{endianness}. | |
4722 | @end deffn | |
4723 | ||
4724 | @deffn {Scheme Procedure} sint-list->bytevector lst endianness size | |
b242715b | 4725 | @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size) |
4827afeb NJ |
4726 | Return a new bytevector containing the signed integers listed in |
4727 | @var{lst} and encoded on @var{size} bytes according to @var{endianness}. | |
b242715b LC |
4728 | @end deffn |
4729 | ||
4730 | @node Bytevectors as Floats | |
4731 | @subsubsection Interpreting Bytevector Contents as Floating Point Numbers | |
4732 | ||
4733 | @cindex IEEE-754 floating point numbers | |
4734 | ||
4735 | Bytevector contents can also be accessed as IEEE-754 single- or | |
4736 | double-precision floating point numbers (respectively 32 and 64-bit | |
4737 | long) using the procedures described here. | |
4738 | ||
4739 | @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness | |
4740 | @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness | |
4741 | @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness) | |
4742 | @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness) | |
4743 | Return the IEEE-754 single-precision floating point number from @var{bv} | |
4744 | at @var{index} according to @var{endianness}. | |
4745 | @end deffn | |
4746 | ||
4747 | @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness | |
4748 | @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness | |
4749 | @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness) | |
4750 | @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness) | |
4751 | Store real number @var{value} in @var{bv} at @var{index} according to | |
4752 | @var{endianness}. | |
4753 | @end deffn | |
4754 | ||
4755 | Specialized procedures are also available: | |
4756 | ||
4757 | @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index | |
4758 | @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index | |
4759 | @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index) | |
4760 | @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index) | |
4761 | Return the IEEE-754 single-precision floating point number from @var{bv} | |
4762 | at @var{index} according to the host's native endianness. | |
4763 | @end deffn | |
4764 | ||
4765 | @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value | |
4766 | @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value | |
4767 | @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value) | |
4768 | @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value) | |
4769 | Store real number @var{value} in @var{bv} at @var{index} according to | |
4770 | the host's native endianness. | |
4771 | @end deffn | |
4772 | ||
4773 | ||
4774 | @node Bytevectors as Strings | |
4775 | @subsubsection Interpreting Bytevector Contents as Unicode Strings | |
4776 | ||
4777 | @cindex Unicode string encoding | |
4778 | ||
4779 | Bytevector contents can also be interpreted as Unicode strings encoded | |
d3b5628c | 4780 | in one of the most commonly available encoding formats. |
b242715b LC |
4781 | |
4782 | @lisp | |
4783 | (utf8->string (u8-list->bytevector '(99 97 102 101))) | |
4784 | @result{} "cafe" | |
4785 | ||
4786 | (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT | |
4787 | @result{} #vu8(99 97 102 195 169) | |
4788 | @end lisp | |
4789 | ||
4790 | @deffn {Scheme Procedure} string->utf8 str | |
524aa8ae LC |
4791 | @deffnx {Scheme Procedure} string->utf16 str [endianness] |
4792 | @deffnx {Scheme Procedure} string->utf32 str [endianness] | |
b242715b | 4793 | @deffnx {C Function} scm_string_to_utf8 (str) |
524aa8ae LC |
4794 | @deffnx {C Function} scm_string_to_utf16 (str, endianness) |
4795 | @deffnx {C Function} scm_string_to_utf32 (str, endianness) | |
b242715b | 4796 | Return a newly allocated bytevector that contains the UTF-8, UTF-16, or |
524aa8ae LC |
4797 | UTF-32 (aka. UCS-4) encoding of @var{str}. For UTF-16 and UTF-32, |
4798 | @var{endianness} should be the symbol @code{big} or @code{little}; when omitted, | |
4799 | it defaults to big endian. | |
b242715b LC |
4800 | @end deffn |
4801 | ||
4802 | @deffn {Scheme Procedure} utf8->string utf | |
524aa8ae LC |
4803 | @deffnx {Scheme Procedure} utf16->string utf [endianness] |
4804 | @deffnx {Scheme Procedure} utf32->string utf [endianness] | |
b242715b | 4805 | @deffnx {C Function} scm_utf8_to_string (utf) |
524aa8ae LC |
4806 | @deffnx {C Function} scm_utf16_to_string (utf, endianness) |
4807 | @deffnx {C Function} scm_utf32_to_string (utf, endianness) | |
b242715b | 4808 | Return a newly allocated string that contains from the UTF-8-, UTF-16-, |
524aa8ae LC |
4809 | or UTF-32-decoded contents of bytevector @var{utf}. For UTF-16 and UTF-32, |
4810 | @var{endianness} should be the symbol @code{big} or @code{little}; when omitted, | |
4811 | it defaults to big endian. | |
b242715b LC |
4812 | @end deffn |
4813 | ||
438974d0 LC |
4814 | @node Bytevectors as Generalized Vectors |
4815 | @subsubsection Accessing Bytevectors with the Generalized Vector API | |
4816 | ||
4817 | As an extension to the R6RS, Guile allows bytevectors to be manipulated | |
4818 | with the @dfn{generalized vector} procedures (@pxref{Generalized | |
4819 | Vectors}). This also allows bytevectors to be accessed using the | |
4820 | generic @dfn{array} procedures (@pxref{Array Procedures}). When using | |
4821 | these APIs, bytes are accessed one at a time as 8-bit unsigned integers: | |
4822 | ||
4823 | @example | |
4824 | (define bv #vu8(0 1 2 3)) | |
4825 | ||
4826 | (generalized-vector? bv) | |
4827 | @result{} #t | |
4828 | ||
4829 | (generalized-vector-ref bv 2) | |
4830 | @result{} 2 | |
4831 | ||
4832 | (generalized-vector-set! bv 2 77) | |
4833 | (array-ref bv 2) | |
4834 | @result{} 77 | |
4835 | ||
4836 | (array-type bv) | |
4837 | @result{} vu8 | |
4838 | @end example | |
4839 | ||
b242715b | 4840 | |
27219b32 AW |
4841 | @node Bytevectors as Uniform Vectors |
4842 | @subsubsection Accessing Bytevectors with the SRFI-4 API | |
4843 | ||
4844 | Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and | |
4845 | Bytevectors}, for more information. | |
4846 | ||
4847 | ||
07d83abe MV |
4848 | @node Symbols |
4849 | @subsection Symbols | |
4850 | @tpindex Symbols | |
4851 | ||
4852 | Symbols in Scheme are widely used in three ways: as items of discrete | |
4853 | data, as lookup keys for alists and hash tables, and to denote variable | |
4854 | references. | |
4855 | ||
4856 | A @dfn{symbol} is similar to a string in that it is defined by a | |
4857 | sequence of characters. The sequence of characters is known as the | |
4858 | symbol's @dfn{name}. In the usual case --- that is, where the symbol's | |
4859 | name doesn't include any characters that could be confused with other | |
4860 | elements of Scheme syntax --- a symbol is written in a Scheme program by | |
4861 | writing the sequence of characters that make up the name, @emph{without} | |
4862 | any quotation marks or other special syntax. For example, the symbol | |
4863 | whose name is ``multiply-by-2'' is written, simply: | |
4864 | ||
4865 | @lisp | |
4866 | multiply-by-2 | |
4867 | @end lisp | |
4868 | ||
4869 | Notice how this differs from a @emph{string} with contents | |
4870 | ``multiply-by-2'', which is written with double quotation marks, like | |
4871 | this: | |
4872 | ||
4873 | @lisp | |
4874 | "multiply-by-2" | |
4875 | @end lisp | |
4876 | ||
4877 | Looking beyond how they are written, symbols are different from strings | |
4878 | in two important respects. | |
4879 | ||
4880 | The first important difference is uniqueness. If the same-looking | |
4881 | string is read twice from two different places in a program, the result | |
4882 | is two @emph{different} string objects whose contents just happen to be | |
4883 | the same. If, on the other hand, the same-looking symbol is read twice | |
4884 | from two different places in a program, the result is the @emph{same} | |
4885 | symbol object both times. | |
4886 | ||
4887 | Given two read symbols, you can use @code{eq?} to test whether they are | |
4888 | the same (that is, have the same name). @code{eq?} is the most | |
4889 | efficient comparison operator in Scheme, and comparing two symbols like | |
4890 | this is as fast as comparing, for example, two numbers. Given two | |
4891 | strings, on the other hand, you must use @code{equal?} or | |
4892 | @code{string=?}, which are much slower comparison operators, to | |
4893 | determine whether the strings have the same contents. | |
4894 | ||
4895 | @lisp | |
4896 | (define sym1 (quote hello)) | |
4897 | (define sym2 (quote hello)) | |
4898 | (eq? sym1 sym2) @result{} #t | |
4899 | ||
4900 | (define str1 "hello") | |
4901 | (define str2 "hello") | |
4902 | (eq? str1 str2) @result{} #f | |
4903 | (equal? str1 str2) @result{} #t | |
4904 | @end lisp | |
4905 | ||
4906 | The second important difference is that symbols, unlike strings, are not | |
4907 | self-evaluating. This is why we need the @code{(quote @dots{})}s in the | |
4908 | example above: @code{(quote hello)} evaluates to the symbol named | |
4909 | "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the | |
4910 | symbol named "hello" and evaluated as a variable reference @dots{} about | |
4911 | which more below (@pxref{Symbol Variables}). | |
4912 | ||
4913 | @menu | |
4914 | * Symbol Data:: Symbols as discrete data. | |
4915 | * Symbol Keys:: Symbols as lookup keys. | |
4916 | * Symbol Variables:: Symbols as denoting variables. | |
4917 | * Symbol Primitives:: Operations related to symbols. | |
4918 | * Symbol Props:: Function slots and property lists. | |
4919 | * Symbol Read Syntax:: Extended read syntax for symbols. | |
4920 | * Symbol Uninterned:: Uninterned symbols. | |
4921 | @end menu | |
4922 | ||
4923 | ||
4924 | @node Symbol Data | |
4925 | @subsubsection Symbols as Discrete Data | |
4926 | ||
4927 | Numbers and symbols are similar to the extent that they both lend | |
4928 | themselves to @code{eq?} comparison. But symbols are more descriptive | |
4929 | than numbers, because a symbol's name can be used directly to describe | |
4930 | the concept for which that symbol stands. | |
4931 | ||
4932 | For example, imagine that you need to represent some colours in a | |
4933 | computer program. Using numbers, you would have to choose arbitrarily | |
4934 | some mapping between numbers and colours, and then take care to use that | |
4935 | mapping consistently: | |
4936 | ||
4937 | @lisp | |
4938 | ;; 1=red, 2=green, 3=purple | |
4939 | ||
4940 | (if (eq? (colour-of car) 1) | |
4941 | ...) | |
4942 | @end lisp | |
4943 | ||
4944 | @noindent | |
4945 | You can make the mapping more explicit and the code more readable by | |
4946 | defining constants: | |
4947 | ||
4948 | @lisp | |
4949 | (define red 1) | |
4950 | (define green 2) | |
4951 | (define purple 3) | |
4952 | ||
4953 | (if (eq? (colour-of car) red) | |
4954 | ...) | |
4955 | @end lisp | |
4956 | ||
4957 | @noindent | |
4958 | But the simplest and clearest approach is not to use numbers at all, but | |
4959 | symbols whose names specify the colours that they refer to: | |
4960 | ||
4961 | @lisp | |
4962 | (if (eq? (colour-of car) 'red) | |
4963 | ...) | |
4964 | @end lisp | |
4965 | ||
4966 | The descriptive advantages of symbols over numbers increase as the set | |
4967 | of concepts that you want to describe grows. Suppose that a car object | |
4968 | can have other properties as well, such as whether it has or uses: | |
4969 | ||
4970 | @itemize @bullet | |
4971 | @item | |
4972 | automatic or manual transmission | |
4973 | @item | |
4974 | leaded or unleaded fuel | |
4975 | @item | |
4976 | power steering (or not). | |
4977 | @end itemize | |
4978 | ||
4979 | @noindent | |
4980 | Then a car's combined property set could be naturally represented and | |
4981 | manipulated as a list of symbols: | |
4982 | ||
4983 | @lisp | |
4984 | (properties-of car1) | |
4985 | @result{} | |
4986 | (red manual unleaded power-steering) | |
4987 | ||
4988 | (if (memq 'power-steering (properties-of car1)) | |
4989 | (display "Unfit people can drive this car.\n") | |
4990 | (display "You'll need strong arms to drive this car!\n")) | |
4991 | @print{} | |
4992 | Unfit people can drive this car. | |
4993 | @end lisp | |
4994 | ||
4995 | Remember, the fundamental property of symbols that we are relying on | |
4996 | here is that an occurrence of @code{'red} in one part of a program is an | |
4997 | @emph{indistinguishable} symbol from an occurrence of @code{'red} in | |
4998 | another part of a program; this means that symbols can usefully be | |
4999 | compared using @code{eq?}. At the same time, symbols have naturally | |
5000 | descriptive names. This combination of efficiency and descriptive power | |
5001 | makes them ideal for use as discrete data. | |
5002 | ||
5003 | ||
5004 | @node Symbol Keys | |
5005 | @subsubsection Symbols as Lookup Keys | |
5006 | ||
5007 | Given their efficiency and descriptive power, it is natural to use | |
5008 | symbols as the keys in an association list or hash table. | |
5009 | ||
5010 | To illustrate this, consider a more structured representation of the car | |
5011 | properties example from the preceding subsection. Rather than | |
5012 | mixing all the properties up together in a flat list, we could use an | |
5013 | association list like this: | |
5014 | ||
5015 | @lisp | |
5016 | (define car1-properties '((colour . red) | |
5017 | (transmission . manual) | |
5018 | (fuel . unleaded) | |
5019 | (steering . power-assisted))) | |
5020 | @end lisp | |
5021 | ||
5022 | Notice how this structure is more explicit and extensible than the flat | |
5023 | list. For example it makes clear that @code{manual} refers to the | |
5024 | transmission rather than, say, the windows or the locking of the car. | |
5025 | It also allows further properties to use the same symbols among their | |
5026 | possible values without becoming ambiguous: | |
5027 | ||
5028 | @lisp | |
5029 | (define car1-properties '((colour . red) | |
5030 | (transmission . manual) | |
5031 | (fuel . unleaded) | |
5032 | (steering . power-assisted) | |
5033 | (seat-colour . red) | |
5034 | (locking . manual))) | |
5035 | @end lisp | |
5036 | ||
5037 | With a representation like this, it is easy to use the efficient | |
5038 | @code{assq-XXX} family of procedures (@pxref{Association Lists}) to | |
5039 | extract or change individual pieces of information: | |
5040 | ||
5041 | @lisp | |
5042 | (assq-ref car1-properties 'fuel) @result{} unleaded | |
5043 | (assq-ref car1-properties 'transmission) @result{} manual | |
5044 | ||
5045 | (assq-set! car1-properties 'seat-colour 'black) | |
5046 | @result{} | |
5047 | ((colour . red) | |
5048 | (transmission . manual) | |
5049 | (fuel . unleaded) | |
5050 | (steering . power-assisted) | |
5051 | (seat-colour . black) | |
5052 | (locking . manual))) | |
5053 | @end lisp | |
5054 | ||
5055 | Hash tables also have keys, and exactly the same arguments apply to the | |
5056 | use of symbols in hash tables as in association lists. The hash value | |
5057 | that Guile uses to decide where to add a symbol-keyed entry to a hash | |
5058 | table can be obtained by calling the @code{symbol-hash} procedure: | |
5059 | ||
5060 | @deffn {Scheme Procedure} symbol-hash symbol | |
5061 | @deffnx {C Function} scm_symbol_hash (symbol) | |
5062 | Return a hash value for @var{symbol}. | |
5063 | @end deffn | |
5064 | ||
5065 | See @ref{Hash Tables} for information about hash tables in general, and | |
5066 | for why you might choose to use a hash table rather than an association | |
5067 | list. | |
5068 | ||
5069 | ||
5070 | @node Symbol Variables | |
5071 | @subsubsection Symbols as Denoting Variables | |
5072 | ||
5073 | When an unquoted symbol in a Scheme program is evaluated, it is | |
5074 | interpreted as a variable reference, and the result of the evaluation is | |
5075 | the appropriate variable's value. | |
5076 | ||
5077 | For example, when the expression @code{(string-length "abcd")} is read | |
5078 | and evaluated, the sequence of characters @code{string-length} is read | |
5079 | as the symbol whose name is "string-length". This symbol is associated | |
5080 | with a variable whose value is the procedure that implements string | |
5081 | length calculation. Therefore evaluation of the @code{string-length} | |
5082 | symbol results in that procedure. | |
5083 | ||
5084 | The details of the connection between an unquoted symbol and the | |
5085 | variable to which it refers are explained elsewhere. See @ref{Binding | |
5086 | Constructs}, for how associations between symbols and variables are | |
5087 | created, and @ref{Modules}, for how those associations are affected by | |
5088 | Guile's module system. | |
5089 | ||
5090 | ||
5091 | @node Symbol Primitives | |
5092 | @subsubsection Operations Related to Symbols | |
5093 | ||
5094 | Given any Scheme value, you can determine whether it is a symbol using | |
5095 | the @code{symbol?} primitive: | |
5096 | ||
5097 | @rnindex symbol? | |
5098 | @deffn {Scheme Procedure} symbol? obj | |
5099 | @deffnx {C Function} scm_symbol_p (obj) | |
5100 | Return @code{#t} if @var{obj} is a symbol, otherwise return | |
5101 | @code{#f}. | |
5102 | @end deffn | |
5103 | ||
c9dc8c6c MV |
5104 | @deftypefn {C Function} int scm_is_symbol (SCM val) |
5105 | Equivalent to @code{scm_is_true (scm_symbol_p (val))}. | |
5106 | @end deftypefn | |
5107 | ||
07d83abe MV |
5108 | Once you know that you have a symbol, you can obtain its name as a |
5109 | string by calling @code{symbol->string}. Note that Guile differs by | |
5110 | default from R5RS on the details of @code{symbol->string} as regards | |
5111 | case-sensitivity: | |
5112 | ||
5113 | @rnindex symbol->string | |
5114 | @deffn {Scheme Procedure} symbol->string s | |
5115 | @deffnx {C Function} scm_symbol_to_string (s) | |
5116 | Return the name of symbol @var{s} as a string. By default, Guile reads | |
5117 | symbols case-sensitively, so the string returned will have the same case | |
5118 | variation as the sequence of characters that caused @var{s} to be | |
5119 | created. | |
5120 | ||
5121 | If Guile is set to read symbols case-insensitively (as specified by | |
5122 | R5RS), and @var{s} comes into being as part of a literal expression | |
5123 | (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or | |
5124 | by a call to the @code{read} or @code{string-ci->symbol} procedures, | |
5125 | Guile converts any alphabetic characters in the symbol's name to | |
5126 | lower case before creating the symbol object, so the string returned | |
5127 | here will be in lower case. | |
5128 | ||
5129 | If @var{s} was created by @code{string->symbol}, the case of characters | |
5130 | in the string returned will be the same as that in the string that was | |
5131 | passed to @code{string->symbol}, regardless of Guile's case-sensitivity | |
5132 | setting at the time @var{s} was created. | |
5133 | ||
5134 | It is an error to apply mutation procedures like @code{string-set!} to | |
5135 | strings returned by this procedure. | |
5136 | @end deffn | |
5137 | ||
5138 | Most symbols are created by writing them literally in code. However it | |
5139 | is also possible to create symbols programmatically using the following | |
c5fc8f8c JG |
5140 | procedures: |
5141 | ||
5142 | @deffn {Scheme Procedure} symbol char@dots{} | |
5143 | @rnindex symbol | |
5144 | Return a newly allocated symbol made from the given character arguments. | |
5145 | ||
5146 | @example | |
5147 | (symbol #\x #\y #\z) @result{} xyz | |
5148 | @end example | |
5149 | @end deffn | |
5150 | ||
5151 | @deffn {Scheme Procedure} list->symbol lst | |
5152 | @rnindex list->symbol | |
5153 | Return a newly allocated symbol made from a list of characters. | |
5154 | ||
5155 | @example | |
5156 | (list->symbol '(#\a #\b #\c)) @result{} abc | |
5157 | @end example | |
5158 | @end deffn | |
5159 | ||
5160 | @rnindex symbol-append | |
5161 | @deffn {Scheme Procedure} symbol-append . args | |
5162 | Return a newly allocated symbol whose characters form the | |
5163 | concatenation of the given symbols, @var{args}. | |
5164 | ||
5165 | @example | |
5166 | (let ((h 'hello)) | |
5167 | (symbol-append h 'world)) | |
5168 | @result{} helloworld | |
5169 | @end example | |
5170 | @end deffn | |
07d83abe MV |
5171 | |
5172 | @rnindex string->symbol | |
5173 | @deffn {Scheme Procedure} string->symbol string | |
5174 | @deffnx {C Function} scm_string_to_symbol (string) | |
5175 | Return the symbol whose name is @var{string}. This procedure can create | |
5176 | symbols with names containing special characters or letters in the | |
5177 | non-standard case, but it is usually a bad idea to create such symbols | |
5178 | because in some implementations of Scheme they cannot be read as | |
5179 | themselves. | |
5180 | @end deffn | |
5181 | ||
5182 | @deffn {Scheme Procedure} string-ci->symbol str | |
5183 | @deffnx {C Function} scm_string_ci_to_symbol (str) | |
5184 | Return the symbol whose name is @var{str}. If Guile is currently | |
5185 | reading symbols case-insensitively, @var{str} is converted to lowercase | |
5186 | before the returned symbol is looked up or created. | |
5187 | @end deffn | |
5188 | ||
5189 | The following examples illustrate Guile's detailed behaviour as regards | |
5190 | the case-sensitivity of symbols: | |
5191 | ||
5192 | @lisp | |
5193 | (read-enable 'case-insensitive) ; R5RS compliant behaviour | |
5194 | ||
5195 | (symbol->string 'flying-fish) @result{} "flying-fish" | |
5196 | (symbol->string 'Martin) @result{} "martin" | |
5197 | (symbol->string | |
5198 | (string->symbol "Malvina")) @result{} "Malvina" | |
5199 | ||
5200 | (eq? 'mISSISSIppi 'mississippi) @result{} #t | |
5201 | (string->symbol "mISSISSIppi") @result{} mISSISSIppi | |
5202 | (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f | |
5203 | (eq? 'LolliPop | |
5204 | (string->symbol (symbol->string 'LolliPop))) @result{} #t | |
5205 | (string=? "K. Harper, M.D." | |
5206 | (symbol->string | |
5207 | (string->symbol "K. Harper, M.D."))) @result{} #t | |
5208 | ||
5209 | (read-disable 'case-insensitive) ; Guile default behaviour | |
5210 | ||
5211 | (symbol->string 'flying-fish) @result{} "flying-fish" | |
5212 | (symbol->string 'Martin) @result{} "Martin" | |
5213 | (symbol->string | |
5214 | (string->symbol "Malvina")) @result{} "Malvina" | |
5215 | ||
5216 | (eq? 'mISSISSIppi 'mississippi) @result{} #f | |
5217 | (string->symbol "mISSISSIppi") @result{} mISSISSIppi | |
5218 | (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t | |
5219 | (eq? 'LolliPop | |
5220 | (string->symbol (symbol->string 'LolliPop))) @result{} #t | |
5221 | (string=? "K. Harper, M.D." | |
5222 | (symbol->string | |
5223 | (string->symbol "K. Harper, M.D."))) @result{} #t | |
5224 | @end lisp | |
5225 | ||
5226 | From C, there are lower level functions that construct a Scheme symbol | |
c48c62d0 MV |
5227 | from a C string in the current locale encoding. |
5228 | ||
5229 | When you want to do more from C, you should convert between symbols | |
5230 | and strings using @code{scm_symbol_to_string} and | |
5231 | @code{scm_string_to_symbol} and work with the strings. | |
07d83abe | 5232 | |
ce3ce21c MW |
5233 | @deffn {C Function} scm_from_latin1_symbol (const char *name) |
5234 | @deffnx {C Function} scm_from_utf8_symbol (const char *name) | |
5235 | Construct and return a Scheme symbol whose name is specified by the | |
5236 | null-terminated C string @var{name}. These are appropriate when | |
5237 | the C string is hard-coded in the source code. | |
5238 | @end deffn | |
5239 | ||
c48c62d0 MV |
5240 | @deffn {C Function} scm_from_locale_symbol (const char *name) |
5241 | @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len) | |
07d83abe | 5242 | Construct and return a Scheme symbol whose name is specified by |
c48c62d0 MV |
5243 | @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null |
5244 | terminated; for @code{scm_from_locale_symboln} the length of @var{name} is | |
07d83abe | 5245 | specified explicitly by @var{len}. |
ce3ce21c MW |
5246 | |
5247 | Note that these functions should @emph{not} be used when @var{name} is a | |
5248 | C string constant, because there is no guarantee that the current locale | |
5249 | will match that of the source code. In such cases, use | |
5250 | @code{scm_from_latin1_symbol} or @code{scm_from_utf8_symbol}. | |
07d83abe MV |
5251 | @end deffn |
5252 | ||
fd0a5bbc HWN |
5253 | @deftypefn {C Function} SCM scm_take_locale_symbol (char *str) |
5254 | @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len) | |
5255 | Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln}, | |
5256 | respectively, but also frees @var{str} with @code{free} eventually. | |
5257 | Thus, you can use this function when you would free @var{str} anyway | |
5258 | immediately after creating the Scheme string. In certain cases, Guile | |
5259 | can then use @var{str} directly as its internal representation. | |
5260 | @end deftypefn | |
5261 | ||
071bb6a8 LC |
5262 | The size of a symbol can also be obtained from C: |
5263 | ||
5264 | @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym) | |
5265 | Return the number of characters in @var{sym}. | |
5266 | @end deftypefn | |
fd0a5bbc | 5267 | |
07d83abe MV |
5268 | Finally, some applications, especially those that generate new Scheme |
5269 | code dynamically, need to generate symbols for use in the generated | |
5270 | code. The @code{gensym} primitive meets this need: | |
5271 | ||
5272 | @deffn {Scheme Procedure} gensym [prefix] | |
5273 | @deffnx {C Function} scm_gensym (prefix) | |
5274 | Create a new symbol with a name constructed from a prefix and a counter | |
5275 | value. The string @var{prefix} can be specified as an optional | |
5276 | argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1 | |
5277 | at each call. There is no provision for resetting the counter. | |
5278 | @end deffn | |
5279 | ||
5280 | The symbols generated by @code{gensym} are @emph{likely} to be unique, | |
5281 | since their names begin with a space and it is only otherwise possible | |
5282 | to generate such symbols if a programmer goes out of their way to do | |
5283 | so. Uniqueness can be guaranteed by instead using uninterned symbols | |
5284 | (@pxref{Symbol Uninterned}), though they can't be usefully written out | |
5285 | and read back in. | |
5286 | ||
5287 | ||
5288 | @node Symbol Props | |
5289 | @subsubsection Function Slots and Property Lists | |
5290 | ||
5291 | In traditional Lisp dialects, symbols are often understood as having | |
5292 | three kinds of value at once: | |
5293 | ||
5294 | @itemize @bullet | |
5295 | @item | |
5296 | a @dfn{variable} value, which is used when the symbol appears in | |
5297 | code in a variable reference context | |
5298 | ||
5299 | @item | |
5300 | a @dfn{function} value, which is used when the symbol appears in | |
679cceed | 5301 | code in a function name position (i.e.@: as the first element in an |
07d83abe MV |
5302 | unquoted list) |
5303 | ||
5304 | @item | |
5305 | a @dfn{property list} value, which is used when the symbol is given as | |
5306 | the first argument to Lisp's @code{put} or @code{get} functions. | |
5307 | @end itemize | |
5308 | ||
5309 | Although Scheme (as one of its simplifications with respect to Lisp) | |
5310 | does away with the distinction between variable and function namespaces, | |
5311 | Guile currently retains some elements of the traditional structure in | |
5312 | case they turn out to be useful when implementing translators for other | |
5313 | languages, in particular Emacs Lisp. | |
5314 | ||
ecb87335 RW |
5315 | Specifically, Guile symbols have two extra slots, one for a symbol's |
5316 | property list, and one for its ``function value.'' The following procedures | |
07d83abe MV |
5317 | are provided to access these slots. |
5318 | ||
5319 | @deffn {Scheme Procedure} symbol-fref symbol | |
5320 | @deffnx {C Function} scm_symbol_fref (symbol) | |
5321 | Return the contents of @var{symbol}'s @dfn{function slot}. | |
5322 | @end deffn | |
5323 | ||
5324 | @deffn {Scheme Procedure} symbol-fset! symbol value | |
5325 | @deffnx {C Function} scm_symbol_fset_x (symbol, value) | |
5326 | Set the contents of @var{symbol}'s function slot to @var{value}. | |
5327 | @end deffn | |
5328 | ||
5329 | @deffn {Scheme Procedure} symbol-pref symbol | |
5330 | @deffnx {C Function} scm_symbol_pref (symbol) | |
5331 | Return the @dfn{property list} currently associated with @var{symbol}. | |
5332 | @end deffn | |
5333 | ||
5334 | @deffn {Scheme Procedure} symbol-pset! symbol value | |
5335 | @deffnx {C Function} scm_symbol_pset_x (symbol, value) | |
5336 | Set @var{symbol}'s property list to @var{value}. | |
5337 | @end deffn | |
5338 | ||
5339 | @deffn {Scheme Procedure} symbol-property sym prop | |
5340 | From @var{sym}'s property list, return the value for property | |
5341 | @var{prop}. The assumption is that @var{sym}'s property list is an | |
5342 | association list whose keys are distinguished from each other using | |
5343 | @code{equal?}; @var{prop} should be one of the keys in that list. If | |
5344 | the property list has no entry for @var{prop}, @code{symbol-property} | |
5345 | returns @code{#f}. | |
5346 | @end deffn | |
5347 | ||
5348 | @deffn {Scheme Procedure} set-symbol-property! sym prop val | |
5349 | In @var{sym}'s property list, set the value for property @var{prop} to | |
5350 | @var{val}, or add a new entry for @var{prop}, with value @var{val}, if | |
5351 | none already exists. For the structure of the property list, see | |
5352 | @code{symbol-property}. | |
5353 | @end deffn | |
5354 | ||
5355 | @deffn {Scheme Procedure} symbol-property-remove! sym prop | |
5356 | From @var{sym}'s property list, remove the entry for property | |
5357 | @var{prop}, if there is one. For the structure of the property list, | |
5358 | see @code{symbol-property}. | |
5359 | @end deffn | |
5360 | ||
5361 | Support for these extra slots may be removed in a future release, and it | |
4695789c NJ |
5362 | is probably better to avoid using them. For a more modern and Schemely |
5363 | approach to properties, see @ref{Object Properties}. | |
07d83abe MV |
5364 | |
5365 | ||
5366 | @node Symbol Read Syntax | |
5367 | @subsubsection Extended Read Syntax for Symbols | |
5368 | ||
5369 | The read syntax for a symbol is a sequence of letters, digits, and | |
5370 | @dfn{extended alphabetic characters}, beginning with a character that | |
5371 | cannot begin a number. In addition, the special cases of @code{+}, | |
5372 | @code{-}, and @code{...} are read as symbols even though numbers can | |
5373 | begin with @code{+}, @code{-} or @code{.}. | |
5374 | ||
5375 | Extended alphabetic characters may be used within identifiers as if | |
5376 | they were letters. The set of extended alphabetic characters is: | |
5377 | ||
5378 | @example | |
5379 | ! $ % & * + - . / : < = > ? @@ ^ _ ~ | |
5380 | @end example | |
5381 | ||
5382 | In addition to the standard read syntax defined above (which is taken | |
5383 | from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on | |
5384 | Scheme})), Guile provides an extended symbol read syntax that allows the | |
5385 | inclusion of unusual characters such as space characters, newlines and | |
5386 | parentheses. If (for whatever reason) you need to write a symbol | |
5387 | containing characters not mentioned above, you can do so as follows. | |
5388 | ||
5389 | @itemize @bullet | |
5390 | @item | |
5391 | Begin the symbol with the characters @code{#@{}, | |
5392 | ||
5393 | @item | |
5394 | write the characters of the symbol and | |
5395 | ||
5396 | @item | |
5397 | finish the symbol with the characters @code{@}#}. | |
5398 | @end itemize | |
5399 | ||
5400 | Here are a few examples of this form of read syntax. The first symbol | |
5401 | needs to use extended syntax because it contains a space character, the | |
5402 | second because it contains a line break, and the last because it looks | |
5403 | like a number. | |
5404 | ||
5405 | @lisp | |
5406 | #@{foo bar@}# | |
5407 | ||
5408 | #@{what | |
5409 | ever@}# | |
5410 | ||
5411 | #@{4242@}# | |
5412 | @end lisp | |
5413 | ||
5414 | Although Guile provides this extended read syntax for symbols, | |
5415 | widespread usage of it is discouraged because it is not portable and not | |
5416 | very readable. | |
5417 | ||
5418 | ||
5419 | @node Symbol Uninterned | |
5420 | @subsubsection Uninterned Symbols | |
5421 | ||
5422 | What makes symbols useful is that they are automatically kept unique. | |
5423 | There are no two symbols that are distinct objects but have the same | |
5424 | name. But of course, there is no rule without exception. In addition | |
5425 | to the normal symbols that have been discussed up to now, you can also | |
5426 | create special @dfn{uninterned} symbols that behave slightly | |
5427 | differently. | |
5428 | ||
5429 | To understand what is different about them and why they might be useful, | |
5430 | we look at how normal symbols are actually kept unique. | |
5431 | ||
5432 | Whenever Guile wants to find the symbol with a specific name, for | |
5433 | example during @code{read} or when executing @code{string->symbol}, it | |
5434 | first looks into a table of all existing symbols to find out whether a | |
5435 | symbol with the given name already exists. When this is the case, Guile | |
5436 | just returns that symbol. When not, a new symbol with the name is | |
5437 | created and entered into the table so that it can be found later. | |
5438 | ||
5439 | Sometimes you might want to create a symbol that is guaranteed `fresh', | |
679cceed | 5440 | i.e.@: a symbol that did not exist previously. You might also want to |
07d83abe MV |
5441 | somehow guarantee that no one else will ever unintentionally stumble |
5442 | across your symbol in the future. These properties of a symbol are | |
5443 | often needed when generating code during macro expansion. When | |
5444 | introducing new temporary variables, you want to guarantee that they | |
5445 | don't conflict with variables in other people's code. | |
5446 | ||
5447 | The simplest way to arrange for this is to create a new symbol but | |
5448 | not enter it into the global table of all symbols. That way, no one | |
5449 | will ever get access to your symbol by chance. Symbols that are not in | |
5450 | the table are called @dfn{uninterned}. Of course, symbols that | |
5451 | @emph{are} in the table are called @dfn{interned}. | |
5452 | ||
5453 | You create new uninterned symbols with the function @code{make-symbol}. | |
5454 | You can test whether a symbol is interned or not with | |
5455 | @code{symbol-interned?}. | |
5456 | ||
5457 | Uninterned symbols break the rule that the name of a symbol uniquely | |
5458 | identifies the symbol object. Because of this, they can not be written | |
5459 | out and read back in like interned symbols. Currently, Guile has no | |
5460 | support for reading uninterned symbols. Note that the function | |
5461 | @code{gensym} does not return uninterned symbols for this reason. | |
5462 | ||
5463 | @deffn {Scheme Procedure} make-symbol name | |
5464 | @deffnx {C Function} scm_make_symbol (name) | |
5465 | Return a new uninterned symbol with the name @var{name}. The returned | |
5466 | symbol is guaranteed to be unique and future calls to | |
5467 | @code{string->symbol} will not return it. | |
5468 | @end deffn | |
5469 | ||
5470 | @deffn {Scheme Procedure} symbol-interned? symbol | |
5471 | @deffnx {C Function} scm_symbol_interned_p (symbol) | |
5472 | Return @code{#t} if @var{symbol} is interned, otherwise return | |
5473 | @code{#f}. | |
5474 | @end deffn | |
5475 | ||
5476 | For example: | |
5477 | ||
5478 | @lisp | |
5479 | (define foo-1 (string->symbol "foo")) | |
5480 | (define foo-2 (string->symbol "foo")) | |
5481 | (define foo-3 (make-symbol "foo")) | |
5482 | (define foo-4 (make-symbol "foo")) | |
5483 | ||
5484 | (eq? foo-1 foo-2) | |
5485 | @result{} #t | |
5486 | ; Two interned symbols with the same name are the same object, | |
5487 | ||
5488 | (eq? foo-1 foo-3) | |
5489 | @result{} #f | |
5490 | ; but a call to make-symbol with the same name returns a | |
5491 | ; distinct object. | |
5492 | ||
5493 | (eq? foo-3 foo-4) | |
5494 | @result{} #f | |
5495 | ; A call to make-symbol always returns a new object, even for | |
5496 | ; the same name. | |
5497 | ||
5498 | foo-3 | |
5499 | @result{} #<uninterned-symbol foo 8085290> | |
5500 | ; Uninterned symbols print differently from interned symbols, | |
5501 | ||
5502 | (symbol? foo-3) | |
5503 | @result{} #t | |
5504 | ; but they are still symbols, | |
5505 | ||
5506 | (symbol-interned? foo-3) | |
5507 | @result{} #f | |
5508 | ; just not interned. | |
5509 | @end lisp | |
5510 | ||
5511 | ||
5512 | @node Keywords | |
5513 | @subsection Keywords | |
5514 | @tpindex Keywords | |
5515 | ||
5516 | Keywords are self-evaluating objects with a convenient read syntax that | |
5517 | makes them easy to type. | |
5518 | ||
5519 | Guile's keyword support conforms to R5RS, and adds a (switchable) read | |
5520 | syntax extension to permit keywords to begin with @code{:} as well as | |
ef4cbc08 | 5521 | @code{#:}, or to end with @code{:}. |
07d83abe MV |
5522 | |
5523 | @menu | |
5524 | * Why Use Keywords?:: Motivation for keyword usage. | |
5525 | * Coding With Keywords:: How to use keywords. | |
5526 | * Keyword Read Syntax:: Read syntax for keywords. | |
5527 | * Keyword Procedures:: Procedures for dealing with keywords. | |
07d83abe MV |
5528 | @end menu |
5529 | ||
5530 | @node Why Use Keywords? | |
5531 | @subsubsection Why Use Keywords? | |
5532 | ||
5533 | Keywords are useful in contexts where a program or procedure wants to be | |
5534 | able to accept a large number of optional arguments without making its | |
5535 | interface unmanageable. | |
5536 | ||
5537 | To illustrate this, consider a hypothetical @code{make-window} | |
5538 | procedure, which creates a new window on the screen for drawing into | |
5539 | using some graphical toolkit. There are many parameters that the caller | |
5540 | might like to specify, but which could also be sensibly defaulted, for | |
5541 | example: | |
5542 | ||
5543 | @itemize @bullet | |
5544 | @item | |
5545 | color depth -- Default: the color depth for the screen | |
5546 | ||
5547 | @item | |
5548 | background color -- Default: white | |
5549 | ||
5550 | @item | |
5551 | width -- Default: 600 | |
5552 | ||
5553 | @item | |
5554 | height -- Default: 400 | |
5555 | @end itemize | |
5556 | ||
5557 | If @code{make-window} did not use keywords, the caller would have to | |
5558 | pass in a value for each possible argument, remembering the correct | |
5559 | argument order and using a special value to indicate the default value | |
5560 | for that argument: | |
5561 | ||
5562 | @lisp | |
5563 | (make-window 'default ;; Color depth | |
5564 | 'default ;; Background color | |
5565 | 800 ;; Width | |
5566 | 100 ;; Height | |
5567 | @dots{}) ;; More make-window arguments | |
5568 | @end lisp | |
5569 | ||
5570 | With keywords, on the other hand, defaulted arguments are omitted, and | |
5571 | non-default arguments are clearly tagged by the appropriate keyword. As | |
5572 | a result, the invocation becomes much clearer: | |
5573 | ||
5574 | @lisp | |
5575 | (make-window #:width 800 #:height 100) | |
5576 | @end lisp | |
5577 | ||
5578 | On the other hand, for a simpler procedure with few arguments, the use | |
5579 | of keywords would be a hindrance rather than a help. The primitive | |
5580 | procedure @code{cons}, for example, would not be improved if it had to | |
5581 | be invoked as | |
5582 | ||
5583 | @lisp | |
5584 | (cons #:car x #:cdr y) | |
5585 | @end lisp | |
5586 | ||
5587 | So the decision whether to use keywords or not is purely pragmatic: use | |
5588 | them if they will clarify the procedure invocation at point of call. | |
5589 | ||
5590 | @node Coding With Keywords | |
5591 | @subsubsection Coding With Keywords | |
5592 | ||
5593 | If a procedure wants to support keywords, it should take a rest argument | |
5594 | and then use whatever means is convenient to extract keywords and their | |
5595 | corresponding arguments from the contents of that rest argument. | |
5596 | ||
5597 | The following example illustrates the principle: the code for | |
5598 | @code{make-window} uses a helper procedure called | |
5599 | @code{get-keyword-value} to extract individual keyword arguments from | |
5600 | the rest argument. | |
5601 | ||
5602 | @lisp | |
5603 | (define (get-keyword-value args keyword default) | |
5604 | (let ((kv (memq keyword args))) | |
5605 | (if (and kv (>= (length kv) 2)) | |
5606 | (cadr kv) | |
5607 | default))) | |
5608 | ||
5609 | (define (make-window . args) | |
5610 | (let ((depth (get-keyword-value args #:depth screen-depth)) | |
5611 | (bg (get-keyword-value args #:bg "white")) | |
5612 | (width (get-keyword-value args #:width 800)) | |
5613 | (height (get-keyword-value args #:height 100)) | |
5614 | @dots{}) | |
5615 | @dots{})) | |
5616 | @end lisp | |
5617 | ||
5618 | But you don't need to write @code{get-keyword-value}. The @code{(ice-9 | |
5619 | optargs)} module provides a set of powerful macros that you can use to | |
5620 | implement keyword-supporting procedures like this: | |
5621 | ||
5622 | @lisp | |
5623 | (use-modules (ice-9 optargs)) | |
5624 | ||
5625 | (define (make-window . args) | |
5626 | (let-keywords args #f ((depth screen-depth) | |
5627 | (bg "white") | |
5628 | (width 800) | |
5629 | (height 100)) | |
5630 | ...)) | |
5631 | @end lisp | |
5632 | ||
5633 | @noindent | |
5634 | Or, even more economically, like this: | |
5635 | ||
5636 | @lisp | |
5637 | (use-modules (ice-9 optargs)) | |
5638 | ||
5639 | (define* (make-window #:key (depth screen-depth) | |
5640 | (bg "white") | |
5641 | (width 800) | |
5642 | (height 100)) | |
5643 | ...) | |
5644 | @end lisp | |
5645 | ||
5646 | For further details on @code{let-keywords}, @code{define*} and other | |
5647 | facilities provided by the @code{(ice-9 optargs)} module, see | |
5648 | @ref{Optional Arguments}. | |
5649 | ||
5650 | ||
5651 | @node Keyword Read Syntax | |
5652 | @subsubsection Keyword Read Syntax | |
5653 | ||
7719ef22 MV |
5654 | Guile, by default, only recognizes a keyword syntax that is compatible |
5655 | with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the | |
5656 | same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the | |
5657 | external representation of the keyword named @code{NAME}. Keyword | |
5658 | objects print using this syntax as well, so values containing keyword | |
5659 | objects can be read back into Guile. When used in an expression, | |
5660 | keywords are self-quoting objects. | |
07d83abe MV |
5661 | |
5662 | If the @code{keyword} read option is set to @code{'prefix}, Guile also | |
5663 | recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens | |
5664 | of the form @code{:NAME} are read as symbols, as required by R5RS. | |
5665 | ||
ef4cbc08 LC |
5666 | @cindex SRFI-88 keyword syntax |
5667 | ||
5668 | If the @code{keyword} read option is set to @code{'postfix}, Guile | |
189681f5 LC |
5669 | recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}). |
5670 | Otherwise, tokens of this form are read as symbols. | |
ef4cbc08 | 5671 | |
07d83abe | 5672 | To enable and disable the alternative non-R5RS keyword syntax, you use |
1518f649 AW |
5673 | the @code{read-set!} procedure documented @ref{Scheme Read}. Note that |
5674 | the @code{prefix} and @code{postfix} syntax are mutually exclusive. | |
07d83abe | 5675 | |
aba0dff5 | 5676 | @lisp |
07d83abe MV |
5677 | (read-set! keywords 'prefix) |
5678 | ||
5679 | #:type | |
5680 | @result{} | |
5681 | #:type | |
5682 | ||
5683 | :type | |
5684 | @result{} | |
5685 | #:type | |
5686 | ||
ef4cbc08 LC |
5687 | (read-set! keywords 'postfix) |
5688 | ||
5689 | type: | |
5690 | @result{} | |
5691 | #:type | |
5692 | ||
5693 | :type | |
5694 | @result{} | |
5695 | :type | |
5696 | ||
07d83abe MV |
5697 | (read-set! keywords #f) |
5698 | ||
5699 | #:type | |
5700 | @result{} | |
5701 | #:type | |
5702 | ||
5703 | :type | |
5704 | @print{} | |
5705 | ERROR: In expression :type: | |
5706 | ERROR: Unbound variable: :type | |
5707 | ABORT: (unbound-variable) | |
aba0dff5 | 5708 | @end lisp |
07d83abe MV |
5709 | |
5710 | @node Keyword Procedures | |
5711 | @subsubsection Keyword Procedures | |
5712 | ||
07d83abe MV |
5713 | @deffn {Scheme Procedure} keyword? obj |
5714 | @deffnx {C Function} scm_keyword_p (obj) | |
5715 | Return @code{#t} if the argument @var{obj} is a keyword, else | |
5716 | @code{#f}. | |
5717 | @end deffn | |
5718 | ||
7719ef22 MV |
5719 | @deffn {Scheme Procedure} keyword->symbol keyword |
5720 | @deffnx {C Function} scm_keyword_to_symbol (keyword) | |
5721 | Return the symbol with the same name as @var{keyword}. | |
07d83abe MV |
5722 | @end deffn |
5723 | ||
7719ef22 MV |
5724 | @deffn {Scheme Procedure} symbol->keyword symbol |
5725 | @deffnx {C Function} scm_symbol_to_keyword (symbol) | |
5726 | Return the keyword with the same name as @var{symbol}. | |
5727 | @end deffn | |
07d83abe | 5728 | |
7719ef22 MV |
5729 | @deftypefn {C Function} int scm_is_keyword (SCM obj) |
5730 | Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}. | |
07d83abe MV |
5731 | @end deftypefn |
5732 | ||
7719ef22 MV |
5733 | @deftypefn {C Function} SCM scm_from_locale_keyword (const char *str) |
5734 | @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *str, size_t len) | |
5735 | Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol | |
5736 | (@var{str}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln | |
5737 | (@var{str}, @var{len}))}, respectively. | |
5738 | @end deftypefn | |
07d83abe MV |
5739 | |
5740 | @node Other Types | |
5741 | @subsection ``Functionality-Centric'' Data Types | |
5742 | ||
a136ada6 | 5743 | Procedures and macros are documented in their own sections: see |
e4955559 | 5744 | @ref{Procedures} and @ref{Macros}. |
07d83abe MV |
5745 | |
5746 | Variable objects are documented as part of the description of Guile's | |
5747 | module system: see @ref{Variables}. | |
5748 | ||
a136ada6 | 5749 | Asyncs, dynamic roots and fluids are described in the section on |
07d83abe MV |
5750 | scheduling: see @ref{Scheduling}. |
5751 | ||
a136ada6 | 5752 | Hooks are documented in the section on general utility functions: see |
07d83abe MV |
5753 | @ref{Hooks}. |
5754 | ||
a136ada6 | 5755 | Ports are described in the section on I/O: see @ref{Input and Output}. |
07d83abe | 5756 | |
a136ada6 NJ |
5757 | Regular expressions are described in their own section: see @ref{Regular |
5758 | Expressions}. | |
07d83abe MV |
5759 | |
5760 | @c Local Variables: | |
5761 | @c TeX-master: "guile.texi" | |
5762 | @c End: |