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2 | @node Simple Data Types |
3 | @chapter Simple Generic Data Types | |
a0e07ba4 | 4 | |
4c731ece | 5 | This chapter describes those of Guile's simple data types which are |
801892e7 | 6 | primarily used for their role as items of generic data. By |
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7 | @dfn{simple} we mean data types that are not primarily used as |
8 | containers to hold other data --- i.e. pairs, lists, vectors and so on. | |
9 | For the documentation of such @dfn{compound} data types, see | |
10 | @ref{Compound Data Types}. | |
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11 | |
12 | One of the great strengths of Scheme is that there is no straightforward | |
13 | distinction between ``data'' and ``functionality''. For example, | |
14 | Guile's support for dynamic linking could be described | |
15 | ||
16 | @itemize @bullet | |
17 | @item | |
18 | either in a ``data-centric'' way, as the behaviour and properties of the | |
19 | ``dynamically linked object'' data type, and the operations that may be | |
20 | applied to instances of this type | |
21 | ||
22 | @item | |
23 | or in a ``functionality-centric'' way, as the set of procedures that | |
24 | constitute Guile's support for dynamic linking, in the context of the | |
25 | module system. | |
26 | @end itemize | |
27 | ||
85a9b4ed | 28 | The contents of this chapter are, therefore, a matter of judgment. By |
4c731ece | 29 | @dfn{generic}, we mean to select those data types whose typical use as |
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30 | @emph{data} in a wide variety of programming contexts is more important |
31 | than their use in the implementation of a particular piece of | |
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32 | @emph{functionality}. The last section of this chapter provides |
33 | references for all the data types that are documented not here but in a | |
34 | ``functionality-centric'' way elsewhere in the manual. | |
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35 | |
36 | @menu | |
37 | * Booleans:: True/false values. | |
38 | * Numbers:: Numerical data types. | |
39 | * Characters:: New character names. | |
40 | * Strings:: Special things about strings. | |
41 | * Regular Expressions:: Pattern matching and substitution. | |
2a946b44 | 42 | * Symbols:: Symbols. |
a0e07ba4 | 43 | * Keywords:: Self-quoting, customizable display keywords. |
4c731ece | 44 | * Other Types:: "Functionality-centric" data types. |
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45 | @end menu |
46 | ||
47 | ||
48 | @node Booleans | |
49 | @section Booleans | |
50 | @tpindex Booleans | |
51 | ||
52 | The two boolean values are @code{#t} for true and @code{#f} for false. | |
53 | ||
54 | Boolean values are returned by predicate procedures, such as the general | |
55 | equality predicates @code{eq?}, @code{eqv?} and @code{equal?} | |
56 | (@pxref{Equality}) and numerical and string comparison operators like | |
57 | @code{string=?} (@pxref{String Comparison}) and @code{<=} | |
58 | (@pxref{Comparison}). | |
59 | ||
60 | @lisp | |
61 | (<= 3 8) | |
62 | @result{} | |
63 | #t | |
64 | ||
65 | (<= 3 -3) | |
66 | @result{} | |
67 | #f | |
68 | ||
69 | (equal? "house" "houses") | |
70 | @result{} | |
71 | #f | |
72 | ||
73 | (eq? #f #f) | |
74 | @result{} | |
75 | #t | |
76 | @end lisp | |
77 | ||
78 | In test condition contexts like @code{if} and @code{cond} (@pxref{if | |
79 | cond case}), where a group of subexpressions will be evaluated only if a | |
80 | @var{condition} expression evaluates to ``true'', ``true'' means any | |
81 | value at all except @code{#f}. | |
82 | ||
83 | @lisp | |
84 | (if #t "yes" "no") | |
85 | @result{} | |
86 | "yes" | |
87 | ||
88 | (if 0 "yes" "no") | |
89 | @result{} | |
90 | "yes" | |
91 | ||
92 | (if #f "yes" "no") | |
93 | @result{} | |
94 | "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 | The @code{not} procedure returns the boolean inverse of its argument: | |
108 | ||
109 | @rnindex not | |
8f85c0c6 NJ |
110 | @deffn {Scheme Procedure} not x |
111 | @deffnx {C Function} scm_not (x) | |
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112 | Return @code{#t} iff @var{x} is @code{#f}, else return @code{#f}. |
113 | @end deffn | |
114 | ||
115 | The @code{boolean?} procedure is a predicate that returns @code{#t} if | |
116 | its argument is one of the boolean values, otherwise @code{#f}. | |
117 | ||
118 | @rnindex boolean? | |
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119 | @deffn {Scheme Procedure} boolean? obj |
120 | @deffnx {C Function} scm_boolean_p (obj) | |
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121 | Return @code{#t} iff @var{obj} is either @code{#t} or @code{#f}. |
122 | @end deffn | |
123 | ||
124 | ||
125 | @node Numbers | |
126 | @section Numerical data types | |
127 | @tpindex Numbers | |
128 | ||
129 | Guile supports a rich ``tower'' of numerical types --- integer, | |
130 | rational, real and complex --- and provides an extensive set of | |
131 | mathematical and scientific functions for operating on numerical | |
132 | data. This section of the manual documents those types and functions. | |
133 | ||
134 | You may also find it illuminating to read R5RS's presentation of numbers | |
135 | in Scheme, which is particularly clear and accessible: see | |
136 | @xref{Numbers,,,r5rs}. | |
137 | ||
138 | @menu | |
139 | * Numerical Tower:: Scheme's numerical "tower". | |
140 | * Integers:: Whole numbers. | |
141 | * Reals and Rationals:: Real and rational numbers. | |
142 | * Complex Numbers:: Complex numbers. | |
143 | * Exactness:: Exactness and inexactness. | |
144 | * Number Syntax:: Read syntax for numerical data. | |
145 | * Integer Operations:: Operations on integer values. | |
146 | * Comparison:: Comparison predicates. | |
147 | * Conversion:: Converting numbers to and from strings. | |
148 | * Complex:: Complex number operations. | |
149 | * Arithmetic:: Arithmetic functions. | |
150 | * Scientific:: Scientific functions. | |
151 | * Primitive Numerics:: Primitive numeric functions. | |
152 | * Bitwise Operations:: Logical AND, OR, NOT, and so on. | |
153 | * Random:: Random number generation. | |
154 | @end menu | |
155 | ||
156 | ||
157 | @node Numerical Tower | |
158 | @subsection Scheme's Numerical ``Tower'' | |
159 | @rnindex number? | |
160 | ||
161 | Scheme's numerical ``tower'' consists of the following categories of | |
162 | numbers: | |
163 | ||
164 | @itemize @bullet | |
165 | @item | |
166 | integers (whole numbers) | |
167 | ||
168 | @item | |
169 | rationals (the set of numbers that can be expressed as P/Q where P and Q | |
170 | are integers) | |
171 | ||
172 | @item | |
173 | real numbers (the set of numbers that describes all possible positions | |
174 | along a one dimensional line) | |
175 | ||
176 | @item | |
177 | complex numbers (the set of numbers that describes all possible | |
178 | positions in a two dimensional space) | |
179 | @end itemize | |
180 | ||
181 | It is called a tower because each category ``sits on'' the one that | |
182 | follows it, in the sense that every integer is also a rational, every | |
183 | rational is also real, and every real number is also a complex number | |
184 | (but with zero imaginary part). | |
185 | ||
186 | Of these, Guile implements integers, reals and complex numbers as | |
187 | distinct types. Rationals are implemented as regards the read syntax | |
188 | for rational numbers that is specified by R5RS, but are immediately | |
189 | converted by Guile to the corresponding real number. | |
190 | ||
191 | The @code{number?} predicate may be applied to any Scheme value to | |
192 | discover whether the value is any of the supported numerical types. | |
193 | ||
8f85c0c6 NJ |
194 | @deffn {Scheme Procedure} number? obj |
195 | @deffnx {C Function} scm_number_p (obj) | |
801892e7 | 196 | Return @code{#t} if @var{obj} is any kind of number, else @code{#f}. |
a0e07ba4 NJ |
197 | @end deffn |
198 | ||
199 | For example: | |
200 | ||
201 | @lisp | |
202 | (number? 3) | |
203 | @result{} | |
204 | #t | |
205 | ||
206 | (number? "hello there!") | |
207 | @result{} | |
208 | #f | |
209 | ||
210 | (define pi 3.141592654) | |
211 | (number? pi) | |
212 | @result{} | |
213 | #t | |
214 | @end lisp | |
215 | ||
216 | The next few subsections document each of Guile's numerical data types | |
217 | in detail. | |
218 | ||
219 | @node Integers | |
220 | @subsection Integers | |
221 | ||
222 | @tpindex Integer numbers | |
223 | ||
224 | @rnindex integer? | |
225 | ||
226 | Integers are whole numbers, that is numbers with no fractional part, | |
227 | such as 2, 83 and -3789. | |
228 | ||
229 | Integers in Guile can be arbitrarily big, as shown by the following | |
230 | example. | |
231 | ||
232 | @lisp | |
233 | (define (factorial n) | |
234 | (let loop ((n n) (product 1)) | |
235 | (if (= n 0) | |
236 | product | |
237 | (loop (- n 1) (* product n))))) | |
238 | ||
239 | (factorial 3) | |
240 | @result{} | |
241 | 6 | |
242 | ||
243 | (factorial 20) | |
244 | @result{} | |
245 | 2432902008176640000 | |
246 | ||
247 | (- (factorial 45)) | |
248 | @result{} | |
249 | -119622220865480194561963161495657715064383733760000000000 | |
250 | @end lisp | |
251 | ||
252 | Readers whose background is in programming languages where integers are | |
253 | limited by the need to fit into just 4 or 8 bytes of memory may find | |
254 | this surprising, or suspect that Guile's representation of integers is | |
255 | inefficient. In fact, Guile achieves a near optimal balance of | |
256 | convenience and efficiency by using the host computer's native | |
257 | representation of integers where possible, and a more general | |
258 | representation where the required number does not fit in the native | |
259 | form. Conversion between these two representations is automatic and | |
260 | completely invisible to the Scheme level programmer. | |
261 | ||
35a3c69c MV |
262 | The infinities @code{+inf.0} and @code{-inf.0} are considered to be |
263 | inexact integers. They are explained in detail in the next section, | |
264 | together with reals and rationals. | |
265 | ||
a0e07ba4 NJ |
266 | @c REFFIXME Maybe point here to discussion of handling immediates/bignums |
267 | @c on the C level, where the conversion is not so automatic - NJ | |
268 | ||
8f85c0c6 NJ |
269 | @deffn {Scheme Procedure} integer? x |
270 | @deffnx {C Function} scm_integer_p (x) | |
801892e7 | 271 | Return @code{#t} if @var{x} is an integer number, else @code{#f}. |
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272 | |
273 | @lisp | |
274 | (integer? 487) | |
275 | @result{} | |
276 | #t | |
277 | ||
278 | (integer? -3.4) | |
279 | @result{} | |
280 | #f | |
35a3c69c MV |
281 | |
282 | (integer? +inf.0) | |
283 | @result{} | |
284 | #t | |
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285 | @end lisp |
286 | @end deffn | |
287 | ||
288 | ||
289 | @node Reals and Rationals | |
290 | @subsection Real and Rational Numbers | |
291 | @tpindex Real numbers | |
292 | @tpindex Rational numbers | |
293 | ||
294 | @rnindex real? | |
295 | @rnindex rational? | |
296 | ||
297 | Mathematically, the real numbers are the set of numbers that describe | |
298 | all possible points along a continuous, infinite, one-dimensional line. | |
299 | The rational numbers are the set of all numbers that can be written as | |
300 | fractions P/Q, where P and Q are integers. All rational numbers are | |
301 | also real, but there are real numbers that are not rational, for example | |
302 | the square root of 2, and pi. | |
303 | ||
304 | Guile represents both real and rational numbers approximately using a | |
305 | floating point encoding with limited precision. Even though the actual | |
306 | encoding is in binary, it may be helpful to think of it as a decimal | |
307 | number with a limited number of significant figures and a decimal point | |
308 | somewhere, since this corresponds to the standard notation for non-whole | |
309 | numbers. For example: | |
310 | ||
311 | @lisp | |
312 | 0.34 | |
313 | -0.00000142857931198 | |
314 | -5648394822220000000000.0 | |
315 | 4.0 | |
316 | @end lisp | |
317 | ||
318 | The limited precision of Guile's encoding means that any ``real'' number | |
319 | in Guile can be written in a rational form, by multiplying and then dividing | |
320 | by sufficient powers of 10 (or in fact, 2). For example, | |
321 | @code{-0.00000142857931198} is the same as @code{142857931198} divided by | |
322 | @code{100000000000000000}. In Guile's current incarnation, therefore, | |
323 | the @code{rational?} and @code{real?} predicates are equivalent. | |
324 | ||
325 | Another aspect of this equivalence is that Guile currently does not | |
326 | preserve the exactness that is possible with rational arithmetic. | |
327 | If such exactness is needed, it is of course possible to implement | |
328 | exact rational arithmetic at the Scheme level using Guile's arbitrary | |
329 | size integers. | |
330 | ||
331 | A planned future revision of Guile's numerical tower will make it | |
332 | possible to implement exact representations and arithmetic for both | |
333 | rational numbers and real irrational numbers such as square roots, | |
334 | and in such a way that the new kinds of number integrate seamlessly | |
335 | with those that are already implemented. | |
336 | ||
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337 | Dividing by an exact zero leads to a error message, as one might |
338 | expect. However, dividing by an inexact zero does not produce an | |
339 | error. Instead, the result of the division is either plus or minus | |
340 | infinity, depending on the sign of the divided number. | |
341 | ||
342 | The infinities are written @samp{+inf.0} and @samp{-inf.0}, | |
343 | respectibly. This syntax is also recognized by @code{read} as an | |
344 | extension to the usual Scheme syntax. | |
345 | ||
346 | Dividing zero by zero yields something that is not a number at all: | |
347 | @samp{+nan.0}. This is the special 'not a number' value. | |
348 | ||
349 | On platforms that follow IEEE 754 for their floating point arithmetic, | |
350 | the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values are | |
351 | implemented using the corresponding IEEE 754 values. They behave in | |
352 | arithmetic operations like IEEE 754 describes it, i.e., @code{(= | |
353 | +nan.0 +nan.0) @result{#f}}. | |
354 | ||
355 | The infinities are inexact integers and are considered to be both even | |
356 | and odd. While @samp{+nan.0} is not @code{=} to itself, it is | |
357 | @code{eqv?} to itself. | |
358 | ||
359 | To test for the special values, use the functions @code{inf?} and | |
360 | @code{nan?}. | |
361 | ||
8f85c0c6 NJ |
362 | @deffn {Scheme Procedure} real? obj |
363 | @deffnx {C Function} scm_real_p (obj) | |
801892e7 | 364 | Return @code{#t} if @var{obj} is a real number, else @code{#f}. |
a0e07ba4 NJ |
365 | Note that the sets of integer and rational values form subsets |
366 | of the set of real numbers, so the predicate will also be fulfilled | |
367 | if @var{obj} is an integer number or a rational number. | |
368 | @end deffn | |
369 | ||
8f85c0c6 NJ |
370 | @deffn {Scheme Procedure} rational? x |
371 | @deffnx {C Function} scm_real_p (x) | |
a0e07ba4 | 372 | Return @code{#t} if @var{x} is a rational number, @code{#f} |
198586ed | 373 | otherwise. Note that the set of integer values forms a subset of |
a0e07ba4 NJ |
374 | the set of rational numbers, i. e. the predicate will also be |
375 | fulfilled if @var{x} is an integer number. Real numbers | |
376 | will also satisfy this predicate, because of their limited | |
377 | precision. | |
378 | @end deffn | |
379 | ||
35a3c69c MV |
380 | @deffn {Scheme Procedure} inf? x |
381 | Return @code{#t} if @var{x} is either @samp{+inf.0} or @samp{-inf.0}, | |
23de7b97 | 382 | @code{#f} otherwise. |
35a3c69c MV |
383 | @end deffn |
384 | ||
385 | @deffn {Scheme Procedure} nan? x | |
23de7b97 | 386 | Return @code{#t} if @var{x} is @samp{+nan.0}, @code{#f} otherwise. |
35a3c69c | 387 | @end deffn |
a0e07ba4 NJ |
388 | |
389 | @node Complex Numbers | |
390 | @subsection Complex Numbers | |
391 | @tpindex Complex numbers | |
392 | ||
393 | @rnindex complex? | |
394 | ||
395 | Complex numbers are the set of numbers that describe all possible points | |
396 | in a two-dimensional space. The two coordinates of a particular point | |
397 | in this space are known as the @dfn{real} and @dfn{imaginary} parts of | |
398 | the complex number that describes that point. | |
399 | ||
400 | In Guile, complex numbers are written in rectangular form as the sum of | |
401 | their real and imaginary parts, using the symbol @code{i} to indicate | |
402 | the imaginary part. | |
403 | ||
404 | @lisp | |
405 | 3+4i | |
406 | @result{} | |
407 | 3.0+4.0i | |
408 | ||
409 | (* 3-8i 2.3+0.3i) | |
410 | @result{} | |
411 | 9.3-17.5i | |
412 | @end lisp | |
413 | ||
414 | Guile represents a complex number as a pair of numbers both of which are | |
415 | real, so the real and imaginary parts of a complex number have the same | |
416 | properties of inexactness and limited precision as single real numbers. | |
417 | ||
8f85c0c6 NJ |
418 | @deffn {Scheme Procedure} complex? x |
419 | @deffnx {C Function} scm_number_p (x) | |
a0e07ba4 | 420 | Return @code{#t} if @var{x} is a complex number, @code{#f} |
198586ed | 421 | otherwise. Note that the sets of real, rational and integer |
a0e07ba4 NJ |
422 | values form subsets of the set of complex numbers, i. e. the |
423 | predicate will also be fulfilled if @var{x} is a real, | |
424 | rational or integer number. | |
425 | @end deffn | |
426 | ||
427 | ||
428 | @node Exactness | |
429 | @subsection Exact and Inexact Numbers | |
430 | @tpindex Exact numbers | |
431 | @tpindex Inexact numbers | |
432 | ||
433 | @rnindex exact? | |
434 | @rnindex inexact? | |
435 | @rnindex exact->inexact | |
436 | @rnindex inexact->exact | |
437 | ||
438 | R5RS requires that a calculation involving inexact numbers always | |
439 | produces an inexact result. To meet this requirement, Guile | |
440 | distinguishes between an exact integer value such as @code{5} and the | |
441 | corresponding inexact real value which, to the limited precision | |
442 | available, has no fractional part, and is printed as @code{5.0}. Guile | |
443 | will only convert the latter value to the former when forced to do so by | |
444 | an invocation of the @code{inexact->exact} procedure. | |
445 | ||
8f85c0c6 NJ |
446 | @deffn {Scheme Procedure} exact? x |
447 | @deffnx {C Function} scm_exact_p (x) | |
a0e07ba4 NJ |
448 | Return @code{#t} if @var{x} is an exact number, @code{#f} |
449 | otherwise. | |
450 | @end deffn | |
451 | ||
8f85c0c6 NJ |
452 | @deffn {Scheme Procedure} inexact? x |
453 | @deffnx {C Function} scm_inexact_p (x) | |
a0e07ba4 NJ |
454 | Return @code{#t} if @var{x} is an inexact number, @code{#f} |
455 | else. | |
456 | @end deffn | |
457 | ||
8f85c0c6 NJ |
458 | @deffn {Scheme Procedure} inexact->exact z |
459 | @deffnx {C Function} scm_inexact_to_exact (z) | |
a0e07ba4 NJ |
460 | Return an exact number that is numerically closest to @var{z}. |
461 | @end deffn | |
462 | ||
463 | @c begin (texi-doc-string "guile" "exact->inexact") | |
8f85c0c6 | 464 | @deffn {Scheme Procedure} exact->inexact z |
a0e07ba4 NJ |
465 | Convert the number @var{z} to its inexact representation. |
466 | @end deffn | |
467 | ||
468 | ||
469 | @node Number Syntax | |
470 | @subsection Read Syntax for Numerical Data | |
471 | ||
472 | The read syntax for integers is a string of digits, optionally | |
473 | preceded by a minus or plus character, a code indicating the | |
474 | base in which the integer is encoded, and a code indicating whether | |
475 | the number is exact or inexact. The supported base codes are: | |
476 | ||
477 | @itemize @bullet | |
478 | @item | |
479 | @code{#b}, @code{#B} --- the integer is written in binary (base 2) | |
480 | ||
481 | @item | |
482 | @code{#o}, @code{#O} --- the integer is written in octal (base 8) | |
483 | ||
484 | @item | |
485 | @code{#d}, @code{#D} --- the integer is written in decimal (base 10) | |
486 | ||
487 | @item | |
488 | @code{#x}, @code{#X} --- the integer is written in hexadecimal (base 16). | |
489 | @end itemize | |
490 | ||
491 | If the base code is omitted, the integer is assumed to be decimal. The | |
492 | following examples show how these base codes are used. | |
493 | ||
494 | @lisp | |
495 | -13 | |
496 | @result{} | |
497 | -13 | |
498 | ||
499 | #d-13 | |
500 | @result{} | |
501 | -13 | |
502 | ||
503 | #x-13 | |
504 | @result{} | |
505 | -19 | |
506 | ||
507 | #b+1101 | |
508 | @result{} | |
509 | 13 | |
510 | ||
511 | #o377 | |
512 | @result{} | |
513 | 255 | |
514 | @end lisp | |
515 | ||
516 | The codes for indicating exactness (which can, incidentally, be applied | |
517 | to all numerical values) are: | |
518 | ||
519 | @itemize @bullet | |
520 | @item | |
521 | @code{#e}, @code{#E} --- the number is exact | |
522 | ||
523 | @item | |
524 | @code{#i}, @code{#I} --- the number is inexact. | |
525 | @end itemize | |
526 | ||
527 | If the exactness indicator is omitted, the integer is assumed to be exact, | |
528 | since Guile's internal representation for integers is always exact. | |
529 | Real numbers have limited precision similar to the precision of the | |
530 | @code{double} type in C. A consequence of the limited precision is that | |
531 | all real numbers in Guile are also rational, since any number R with a | |
532 | limited number of decimal places, say N, can be made into an integer by | |
533 | multiplying by 10^N. | |
534 | ||
35a3c69c MV |
535 | Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for |
536 | plus and minus infinity, respectively. The value must be written | |
537 | exactly as shown, that is, the always must have a sign and exactly one | |
538 | zero digit after the decimal point. It also understands @samp{+nan.0} | |
539 | and @samp{-nan.0} for the special 'not-a-number' value. The sign is | |
540 | ignored for 'not-a-number' and the value is always printed as @samp{+nan.0}. | |
a0e07ba4 NJ |
541 | |
542 | @node Integer Operations | |
543 | @subsection Operations on Integer Values | |
544 | @rnindex odd? | |
545 | @rnindex even? | |
546 | @rnindex quotient | |
547 | @rnindex remainder | |
548 | @rnindex modulo | |
549 | @rnindex gcd | |
550 | @rnindex lcm | |
551 | ||
8f85c0c6 NJ |
552 | @deffn {Scheme Procedure} odd? n |
553 | @deffnx {C Function} scm_odd_p (n) | |
a0e07ba4 NJ |
554 | Return @code{#t} if @var{n} is an odd number, @code{#f} |
555 | otherwise. | |
556 | @end deffn | |
557 | ||
8f85c0c6 NJ |
558 | @deffn {Scheme Procedure} even? n |
559 | @deffnx {C Function} scm_even_p (n) | |
a0e07ba4 NJ |
560 | Return @code{#t} if @var{n} is an even number, @code{#f} |
561 | otherwise. | |
562 | @end deffn | |
563 | ||
564 | @c begin (texi-doc-string "guile" "quotient") | |
8f85c0c6 | 565 | @deffn {Scheme Procedure} quotient |
a0e07ba4 NJ |
566 | Return the quotient of the numbers @var{x} and @var{y}. |
567 | @end deffn | |
568 | ||
569 | @c begin (texi-doc-string "guile" "remainder") | |
8f85c0c6 | 570 | @deffn {Scheme Procedure} remainder |
a0e07ba4 NJ |
571 | Return the remainder of the numbers @var{x} and @var{y}. |
572 | @lisp | |
573 | (remainder 13 4) @result{} 1 | |
574 | (remainder -13 4) @result{} -1 | |
575 | @end lisp | |
576 | @end deffn | |
577 | ||
578 | @c begin (texi-doc-string "guile" "modulo") | |
8f85c0c6 | 579 | @deffn {Scheme Procedure} modulo |
a0e07ba4 NJ |
580 | Return the modulo of the numbers @var{x} and @var{y}. |
581 | @lisp | |
582 | (modulo 13 4) @result{} 1 | |
583 | (modulo -13 4) @result{} 3 | |
584 | @end lisp | |
585 | @end deffn | |
586 | ||
587 | @c begin (texi-doc-string "guile" "gcd") | |
8f85c0c6 | 588 | @deffn {Scheme Procedure} gcd |
a0e07ba4 NJ |
589 | Return the greatest common divisor of all arguments. |
590 | If called without arguments, 0 is returned. | |
591 | @end deffn | |
592 | ||
593 | @c begin (texi-doc-string "guile" "lcm") | |
8f85c0c6 | 594 | @deffn {Scheme Procedure} lcm |
a0e07ba4 NJ |
595 | Return the least common multiple of the arguments. |
596 | If called without arguments, 1 is returned. | |
597 | @end deffn | |
598 | ||
599 | ||
600 | @node Comparison | |
601 | @subsection Comparison Predicates | |
602 | @rnindex zero? | |
603 | @rnindex positive? | |
604 | @rnindex negative? | |
605 | ||
606 | @c begin (texi-doc-string "guile" "=") | |
8f85c0c6 | 607 | @deffn {Scheme Procedure} = |
a0e07ba4 NJ |
608 | Return @code{#t} if all parameters are numerically equal. |
609 | @end deffn | |
610 | ||
611 | @c begin (texi-doc-string "guile" "<") | |
8f85c0c6 | 612 | @deffn {Scheme Procedure} < |
a0e07ba4 NJ |
613 | Return @code{#t} if the list of parameters is monotonically |
614 | increasing. | |
615 | @end deffn | |
616 | ||
617 | @c begin (texi-doc-string "guile" ">") | |
8f85c0c6 | 618 | @deffn {Scheme Procedure} > |
a0e07ba4 NJ |
619 | Return @code{#t} if the list of parameters is monotonically |
620 | decreasing. | |
621 | @end deffn | |
622 | ||
623 | @c begin (texi-doc-string "guile" "<=") | |
8f85c0c6 | 624 | @deffn {Scheme Procedure} <= |
a0e07ba4 NJ |
625 | Return @code{#t} if the list of parameters is monotonically |
626 | non-decreasing. | |
627 | @end deffn | |
628 | ||
629 | @c begin (texi-doc-string "guile" ">=") | |
8f85c0c6 | 630 | @deffn {Scheme Procedure} >= |
a0e07ba4 NJ |
631 | Return @code{#t} if the list of parameters is monotonically |
632 | non-increasing. | |
633 | @end deffn | |
634 | ||
635 | @c begin (texi-doc-string "guile" "zero?") | |
8f85c0c6 | 636 | @deffn {Scheme Procedure} zero? |
a0e07ba4 NJ |
637 | Return @code{#t} if @var{z} is an exact or inexact number equal to |
638 | zero. | |
639 | @end deffn | |
640 | ||
641 | @c begin (texi-doc-string "guile" "positive?") | |
8f85c0c6 | 642 | @deffn {Scheme Procedure} positive? |
a0e07ba4 NJ |
643 | Return @code{#t} if @var{x} is an exact or inexact number greater than |
644 | zero. | |
645 | @end deffn | |
646 | ||
647 | @c begin (texi-doc-string "guile" "negative?") | |
8f85c0c6 | 648 | @deffn {Scheme Procedure} negative? |
a0e07ba4 NJ |
649 | Return @code{#t} if @var{x} is an exact or inexact number less than |
650 | zero. | |
651 | @end deffn | |
652 | ||
653 | ||
654 | @node Conversion | |
655 | @subsection Converting Numbers To and From Strings | |
656 | @rnindex number->string | |
657 | @rnindex string->number | |
658 | ||
8f85c0c6 NJ |
659 | @deffn {Scheme Procedure} number->string n [radix] |
660 | @deffnx {C Function} scm_number_to_string (n, radix) | |
a0e07ba4 NJ |
661 | Return a string holding the external representation of the |
662 | number @var{n} in the given @var{radix}. If @var{n} is | |
663 | inexact, a radix of 10 will be used. | |
664 | @end deffn | |
665 | ||
8f85c0c6 NJ |
666 | @deffn {Scheme Procedure} string->number string [radix] |
667 | @deffnx {C Function} scm_string_to_number (string, radix) | |
a0e07ba4 NJ |
668 | Return a number of the maximally precise representation |
669 | expressed by the given @var{string}. @var{radix} must be an | |
670 | exact integer, either 2, 8, 10, or 16. If supplied, @var{radix} | |
671 | is a default radix that may be overridden by an explicit radix | |
672 | prefix in @var{string} (e.g. "#o177"). If @var{radix} is not | |
673 | supplied, then the default radix is 10. If string is not a | |
674 | syntactically valid notation for a number, then | |
675 | @code{string->number} returns @code{#f}. | |
676 | @end deffn | |
677 | ||
678 | ||
679 | @node Complex | |
680 | @subsection Complex Number Operations | |
681 | @rnindex make-rectangular | |
682 | @rnindex make-polar | |
683 | @rnindex real-part | |
684 | @rnindex imag-part | |
685 | @rnindex magnitude | |
686 | @rnindex angle | |
687 | ||
8f85c0c6 NJ |
688 | @deffn {Scheme Procedure} make-rectangular real imaginary |
689 | @deffnx {C Function} scm_make_rectangular (real, imaginary) | |
a0e07ba4 NJ |
690 | Return a complex number constructed of the given @var{real} and |
691 | @var{imaginary} parts. | |
692 | @end deffn | |
693 | ||
8f85c0c6 NJ |
694 | @deffn {Scheme Procedure} make-polar x y |
695 | @deffnx {C Function} scm_make_polar (x, y) | |
a0e07ba4 NJ |
696 | Return the complex number @var{x} * e^(i * @var{y}). |
697 | @end deffn | |
698 | ||
699 | @c begin (texi-doc-string "guile" "real-part") | |
8f85c0c6 | 700 | @deffn {Scheme Procedure} real-part |
a0e07ba4 NJ |
701 | Return the real part of the number @var{z}. |
702 | @end deffn | |
703 | ||
704 | @c begin (texi-doc-string "guile" "imag-part") | |
8f85c0c6 | 705 | @deffn {Scheme Procedure} imag-part |
a0e07ba4 NJ |
706 | Return the imaginary part of the number @var{z}. |
707 | @end deffn | |
708 | ||
709 | @c begin (texi-doc-string "guile" "magnitude") | |
8f85c0c6 | 710 | @deffn {Scheme Procedure} magnitude |
a0e07ba4 NJ |
711 | Return the magnitude of the number @var{z}. This is the same as |
712 | @code{abs} for real arguments, but also allows complex numbers. | |
713 | @end deffn | |
714 | ||
715 | @c begin (texi-doc-string "guile" "angle") | |
8f85c0c6 | 716 | @deffn {Scheme Procedure} angle |
a0e07ba4 NJ |
717 | Return the angle of the complex number @var{z}. |
718 | @end deffn | |
719 | ||
720 | ||
721 | @node Arithmetic | |
722 | @subsection Arithmetic Functions | |
723 | @rnindex max | |
724 | @rnindex min | |
725 | @rnindex + | |
726 | @rnindex * | |
727 | @rnindex - | |
728 | @rnindex / | |
729 | @rnindex abs | |
730 | @rnindex floor | |
731 | @rnindex ceiling | |
732 | @rnindex truncate | |
733 | @rnindex round | |
734 | ||
735 | @c begin (texi-doc-string "guile" "+") | |
8f85c0c6 | 736 | @deffn {Scheme Procedure} + z1 @dots{} |
a0e07ba4 NJ |
737 | Return the sum of all parameter values. Return 0 if called without any |
738 | parameters. | |
739 | @end deffn | |
740 | ||
741 | @c begin (texi-doc-string "guile" "-") | |
8f85c0c6 | 742 | @deffn {Scheme Procedure} - z1 z2 @dots{} |
a0e07ba4 NJ |
743 | If called with one argument @var{z1}, -@var{z1} is returned. Otherwise |
744 | the sum of all but the first argument are subtracted from the first | |
745 | argument. | |
746 | @end deffn | |
747 | ||
748 | @c begin (texi-doc-string "guile" "*") | |
8f85c0c6 | 749 | @deffn {Scheme Procedure} * z1 @dots{} |
a0e07ba4 NJ |
750 | Return the product of all arguments. If called without arguments, 1 is |
751 | returned. | |
752 | @end deffn | |
753 | ||
754 | @c begin (texi-doc-string "guile" "/") | |
8f85c0c6 | 755 | @deffn {Scheme Procedure} / z1 z2 @dots{} |
a0e07ba4 NJ |
756 | Divide the first argument by the product of the remaining arguments. If |
757 | called with one argument @var{z1}, 1/@var{z1} is returned. | |
758 | @end deffn | |
759 | ||
760 | @c begin (texi-doc-string "guile" "abs") | |
8f85c0c6 | 761 | @deffn {Scheme Procedure} abs x |
387d418c | 762 | @deffnx {C Function} scm_abs (x) |
a0e07ba4 | 763 | Return the absolute value of @var{x}. |
387d418c NJ |
764 | |
765 | @var{x} must be a number with zero imaginary part. To calculate the | |
766 | magnitude of a complex number, use @code{magnitude} instead. | |
a0e07ba4 NJ |
767 | @end deffn |
768 | ||
769 | @c begin (texi-doc-string "guile" "max") | |
8f85c0c6 | 770 | @deffn {Scheme Procedure} max x1 x2 @dots{} |
a0e07ba4 NJ |
771 | Return the maximum of all parameter values. |
772 | @end deffn | |
773 | ||
774 | @c begin (texi-doc-string "guile" "min") | |
8f85c0c6 | 775 | @deffn {Scheme Procedure} min x1 x2 @dots{} |
85a9b4ed | 776 | Return the minimum of all parameter values. |
a0e07ba4 NJ |
777 | @end deffn |
778 | ||
779 | @c begin (texi-doc-string "guile" "truncate") | |
8f85c0c6 | 780 | @deffn {Scheme Procedure} truncate |
a0e07ba4 NJ |
781 | Round the inexact number @var{x} towards zero. |
782 | @end deffn | |
783 | ||
784 | @c begin (texi-doc-string "guile" "round") | |
8f85c0c6 | 785 | @deffn {Scheme Procedure} round x |
a0e07ba4 NJ |
786 | Round the inexact number @var{x} towards zero. |
787 | @end deffn | |
788 | ||
789 | @c begin (texi-doc-string "guile" "floor") | |
8f85c0c6 | 790 | @deffn {Scheme Procedure} floor x |
a0e07ba4 NJ |
791 | Round the number @var{x} towards minus infinity. |
792 | @end deffn | |
793 | ||
794 | @c begin (texi-doc-string "guile" "ceiling") | |
8f85c0c6 | 795 | @deffn {Scheme Procedure} ceiling x |
a0e07ba4 NJ |
796 | Round the number @var{x} towards infinity. |
797 | @end deffn | |
798 | ||
387d418c NJ |
799 | For the @code{truncate} and @code{round} procedures, the Guile library |
800 | exports equivalent C functions, but taking and returning arguments of | |
801 | type @code{double} rather than the usual @code{SCM}. | |
802 | ||
803 | @deftypefn {C Function} double scm_truncate (double x) | |
804 | @deftypefnx {C Function} double scm_round (double x) | |
805 | @end deftypefn | |
806 | ||
807 | For @code{floor} and @code{ceiling}, the equivalent C functions are | |
808 | @code{floor} and @code{ceil} from the standard mathematics library | |
809 | (which also take and return @code{double} arguments). | |
810 | ||
a0e07ba4 NJ |
811 | |
812 | @node Scientific | |
813 | @subsection Scientific Functions | |
814 | ||
815 | The following procedures accept any kind of number as arguments, | |
816 | including complex numbers. | |
817 | ||
818 | @rnindex sqrt | |
819 | @c begin (texi-doc-string "guile" "sqrt") | |
8f85c0c6 | 820 | @deffn {Scheme Procedure} sqrt z |
a0e07ba4 NJ |
821 | Return the square root of @var{z}. |
822 | @end deffn | |
823 | ||
824 | @rnindex expt | |
825 | @c begin (texi-doc-string "guile" "expt") | |
8f85c0c6 | 826 | @deffn {Scheme Procedure} expt z1 z2 |
a0e07ba4 NJ |
827 | Return @var{z1} raised to the power of @var{z2}. |
828 | @end deffn | |
829 | ||
830 | @rnindex sin | |
831 | @c begin (texi-doc-string "guile" "sin") | |
8f85c0c6 | 832 | @deffn {Scheme Procedure} sin z |
a0e07ba4 NJ |
833 | Return the sine of @var{z}. |
834 | @end deffn | |
835 | ||
836 | @rnindex cos | |
837 | @c begin (texi-doc-string "guile" "cos") | |
8f85c0c6 | 838 | @deffn {Scheme Procedure} cos z |
a0e07ba4 NJ |
839 | Return the cosine of @var{z}. |
840 | @end deffn | |
841 | ||
842 | @rnindex tan | |
843 | @c begin (texi-doc-string "guile" "tan") | |
8f85c0c6 | 844 | @deffn {Scheme Procedure} tan z |
a0e07ba4 NJ |
845 | Return the tangent of @var{z}. |
846 | @end deffn | |
847 | ||
848 | @rnindex asin | |
849 | @c begin (texi-doc-string "guile" "asin") | |
8f85c0c6 | 850 | @deffn {Scheme Procedure} asin z |
a0e07ba4 NJ |
851 | Return the arcsine of @var{z}. |
852 | @end deffn | |
853 | ||
854 | @rnindex acos | |
855 | @c begin (texi-doc-string "guile" "acos") | |
8f85c0c6 | 856 | @deffn {Scheme Procedure} acos z |
a0e07ba4 NJ |
857 | Return the arccosine of @var{z}. |
858 | @end deffn | |
859 | ||
860 | @rnindex atan | |
861 | @c begin (texi-doc-string "guile" "atan") | |
8f85c0c6 | 862 | @deffn {Scheme Procedure} atan z |
a0e07ba4 NJ |
863 | Return the arctangent of @var{z}. |
864 | @end deffn | |
865 | ||
866 | @rnindex exp | |
867 | @c begin (texi-doc-string "guile" "exp") | |
8f85c0c6 | 868 | @deffn {Scheme Procedure} exp z |
a0e07ba4 NJ |
869 | Return e to the power of @var{z}, where e is the base of natural |
870 | logarithms (2.71828@dots{}). | |
871 | @end deffn | |
872 | ||
873 | @rnindex log | |
874 | @c begin (texi-doc-string "guile" "log") | |
8f85c0c6 | 875 | @deffn {Scheme Procedure} log z |
a0e07ba4 NJ |
876 | Return the natural logarithm of @var{z}. |
877 | @end deffn | |
878 | ||
879 | @c begin (texi-doc-string "guile" "log10") | |
8f85c0c6 | 880 | @deffn {Scheme Procedure} log10 z |
a0e07ba4 NJ |
881 | Return the base 10 logarithm of @var{z}. |
882 | @end deffn | |
883 | ||
884 | @c begin (texi-doc-string "guile" "sinh") | |
8f85c0c6 | 885 | @deffn {Scheme Procedure} sinh z |
a0e07ba4 NJ |
886 | Return the hyperbolic sine of @var{z}. |
887 | @end deffn | |
888 | ||
889 | @c begin (texi-doc-string "guile" "cosh") | |
8f85c0c6 | 890 | @deffn {Scheme Procedure} cosh z |
a0e07ba4 NJ |
891 | Return the hyperbolic cosine of @var{z}. |
892 | @end deffn | |
893 | ||
894 | @c begin (texi-doc-string "guile" "tanh") | |
8f85c0c6 | 895 | @deffn {Scheme Procedure} tanh z |
a0e07ba4 NJ |
896 | Return the hyperbolic tangent of @var{z}. |
897 | @end deffn | |
898 | ||
899 | @c begin (texi-doc-string "guile" "asinh") | |
8f85c0c6 | 900 | @deffn {Scheme Procedure} asinh z |
a0e07ba4 NJ |
901 | Return the hyperbolic arcsine of @var{z}. |
902 | @end deffn | |
903 | ||
904 | @c begin (texi-doc-string "guile" "acosh") | |
8f85c0c6 | 905 | @deffn {Scheme Procedure} acosh z |
a0e07ba4 NJ |
906 | Return the hyperbolic arccosine of @var{z}. |
907 | @end deffn | |
908 | ||
909 | @c begin (texi-doc-string "guile" "atanh") | |
8f85c0c6 | 910 | @deffn {Scheme Procedure} atanh z |
a0e07ba4 NJ |
911 | Return the hyperbolic arctangent of @var{z}. |
912 | @end deffn | |
913 | ||
914 | ||
915 | @node Primitive Numerics | |
916 | @subsection Primitive Numeric Functions | |
917 | ||
918 | Many of Guile's numeric procedures which accept any kind of numbers as | |
919 | arguments, including complex numbers, are implemented as Scheme | |
920 | procedures that use the following real number-based primitives. These | |
921 | primitives signal an error if they are called with complex arguments. | |
922 | ||
923 | @c begin (texi-doc-string "guile" "$abs") | |
8f85c0c6 | 924 | @deffn {Scheme Procedure} $abs x |
a0e07ba4 NJ |
925 | Return the absolute value of @var{x}. |
926 | @end deffn | |
927 | ||
928 | @c begin (texi-doc-string "guile" "$sqrt") | |
8f85c0c6 | 929 | @deffn {Scheme Procedure} $sqrt x |
a0e07ba4 NJ |
930 | Return the square root of @var{x}. |
931 | @end deffn | |
932 | ||
8f85c0c6 NJ |
933 | @deffn {Scheme Procedure} $expt x y |
934 | @deffnx {C Function} scm_sys_expt (x, y) | |
a0e07ba4 NJ |
935 | Return @var{x} raised to the power of @var{y}. This |
936 | procedure does not accept complex arguments. | |
937 | @end deffn | |
938 | ||
939 | @c begin (texi-doc-string "guile" "$sin") | |
8f85c0c6 | 940 | @deffn {Scheme Procedure} $sin x |
a0e07ba4 NJ |
941 | Return the sine of @var{x}. |
942 | @end deffn | |
943 | ||
944 | @c begin (texi-doc-string "guile" "$cos") | |
8f85c0c6 | 945 | @deffn {Scheme Procedure} $cos x |
a0e07ba4 NJ |
946 | Return the cosine of @var{x}. |
947 | @end deffn | |
948 | ||
949 | @c begin (texi-doc-string "guile" "$tan") | |
8f85c0c6 | 950 | @deffn {Scheme Procedure} $tan x |
a0e07ba4 NJ |
951 | Return the tangent of @var{x}. |
952 | @end deffn | |
953 | ||
954 | @c begin (texi-doc-string "guile" "$asin") | |
8f85c0c6 | 955 | @deffn {Scheme Procedure} $asin x |
a0e07ba4 NJ |
956 | Return the arcsine of @var{x}. |
957 | @end deffn | |
958 | ||
959 | @c begin (texi-doc-string "guile" "$acos") | |
8f85c0c6 | 960 | @deffn {Scheme Procedure} $acos x |
a0e07ba4 NJ |
961 | Return the arccosine of @var{x}. |
962 | @end deffn | |
963 | ||
964 | @c begin (texi-doc-string "guile" "$atan") | |
8f85c0c6 | 965 | @deffn {Scheme Procedure} $atan x |
a0e07ba4 NJ |
966 | Return the arctangent of @var{x} in the range -PI/2 to PI/2. |
967 | @end deffn | |
968 | ||
8f85c0c6 NJ |
969 | @deffn {Scheme Procedure} $atan2 x y |
970 | @deffnx {C Function} scm_sys_atan2 (x, y) | |
a0e07ba4 NJ |
971 | Return the arc tangent of the two arguments @var{x} and |
972 | @var{y}. This is similar to calculating the arc tangent of | |
973 | @var{x} / @var{y}, except that the signs of both arguments | |
974 | are used to determine the quadrant of the result. This | |
975 | procedure does not accept complex arguments. | |
976 | @end deffn | |
977 | ||
978 | @c begin (texi-doc-string "guile" "$exp") | |
8f85c0c6 | 979 | @deffn {Scheme Procedure} $exp x |
a0e07ba4 NJ |
980 | Return e to the power of @var{x}, where e is the base of natural |
981 | logarithms (2.71828@dots{}). | |
982 | @end deffn | |
983 | ||
984 | @c begin (texi-doc-string "guile" "$log") | |
8f85c0c6 | 985 | @deffn {Scheme Procedure} $log x |
a0e07ba4 NJ |
986 | Return the natural logarithm of @var{x}. |
987 | @end deffn | |
988 | ||
989 | @c begin (texi-doc-string "guile" "$sinh") | |
8f85c0c6 | 990 | @deffn {Scheme Procedure} $sinh x |
a0e07ba4 NJ |
991 | Return the hyperbolic sine of @var{x}. |
992 | @end deffn | |
993 | ||
994 | @c begin (texi-doc-string "guile" "$cosh") | |
8f85c0c6 | 995 | @deffn {Scheme Procedure} $cosh x |
a0e07ba4 NJ |
996 | Return the hyperbolic cosine of @var{x}. |
997 | @end deffn | |
998 | ||
999 | @c begin (texi-doc-string "guile" "$tanh") | |
8f85c0c6 | 1000 | @deffn {Scheme Procedure} $tanh x |
a0e07ba4 NJ |
1001 | Return the hyperbolic tangent of @var{x}. |
1002 | @end deffn | |
1003 | ||
1004 | @c begin (texi-doc-string "guile" "$asinh") | |
8f85c0c6 | 1005 | @deffn {Scheme Procedure} $asinh x |
a0e07ba4 NJ |
1006 | Return the hyperbolic arcsine of @var{x}. |
1007 | @end deffn | |
1008 | ||
1009 | @c begin (texi-doc-string "guile" "$acosh") | |
8f85c0c6 | 1010 | @deffn {Scheme Procedure} $acosh x |
a0e07ba4 NJ |
1011 | Return the hyperbolic arccosine of @var{x}. |
1012 | @end deffn | |
1013 | ||
1014 | @c begin (texi-doc-string "guile" "$atanh") | |
8f85c0c6 | 1015 | @deffn {Scheme Procedure} $atanh x |
a0e07ba4 NJ |
1016 | Return the hyperbolic arctangent of @var{x}. |
1017 | @end deffn | |
1018 | ||
387d418c NJ |
1019 | For the hyperbolic arc-functions, the Guile library exports C functions |
1020 | corresponding to these Scheme procedures, but taking and returning | |
1021 | arguments of type @code{double} rather than the usual @code{SCM}. | |
1022 | ||
1023 | @deftypefn {C Function} double scm_asinh (double x) | |
1024 | @deftypefnx {C Function} double scm_acosh (double x) | |
1025 | @deftypefnx {C Function} double scm_atanh (double x) | |
1026 | Return the hyperbolic arcsine, arccosine or arctangent of @var{x} | |
1027 | respectively. | |
1028 | @end deftypefn | |
1029 | ||
1030 | For all the other Scheme procedures above, except @code{expt} and | |
1031 | @code{atan2} (whose entries specifically mention an equivalent C | |
1032 | function), the equivalent C functions are those provided by the standard | |
1033 | mathematics library. The mapping is as follows. | |
1034 | ||
1035 | @multitable {xx} {Scheme Procedure} {C Function} | |
1036 | @item @tab Scheme Procedure @tab C Function | |
1037 | ||
1038 | @item @tab @code{$abs} @tab @code{fabs} | |
1039 | @item @tab @code{$sqrt} @tab @code{sqrt} | |
1040 | @item @tab @code{$sin} @tab @code{sin} | |
1041 | @item @tab @code{$cos} @tab @code{cos} | |
1042 | @item @tab @code{$tan} @tab @code{tan} | |
1043 | @item @tab @code{$asin} @tab @code{asin} | |
1044 | @item @tab @code{$acos} @tab @code{acos} | |
1045 | @item @tab @code{$atan} @tab @code{atan} | |
1046 | @item @tab @code{$exp} @tab @code{exp} | |
1047 | @item @tab @code{$log} @tab @code{log} | |
1048 | @item @tab @code{$sinh} @tab @code{sinh} | |
1049 | @item @tab @code{$cosh} @tab @code{cosh} | |
1050 | @item @tab @code{$tanh} @tab @code{tanh} | |
1051 | @end multitable | |
1052 | ||
1053 | @noindent | |
1054 | Naturally, these C functions expect and return @code{double} arguments. | |
1055 | ||
a0e07ba4 NJ |
1056 | |
1057 | @node Bitwise Operations | |
1058 | @subsection Bitwise Operations | |
1059 | ||
8f85c0c6 | 1060 | @deffn {Scheme Procedure} logand n1 n2 |
9401323e | 1061 | Return the bitwise AND of the integer arguments. |
a0e07ba4 NJ |
1062 | |
1063 | @lisp | |
9401323e NJ |
1064 | (logand) @result{} -1 |
1065 | (logand 7) @result{} 7 | |
1066 | (logand #b111 #b011 #b001) @result{} 1 | |
a0e07ba4 NJ |
1067 | @end lisp |
1068 | @end deffn | |
1069 | ||
8f85c0c6 | 1070 | @deffn {Scheme Procedure} logior n1 n2 |
9401323e | 1071 | Return the bitwise OR of the integer arguments. |
a0e07ba4 NJ |
1072 | |
1073 | @lisp | |
9401323e NJ |
1074 | (logior) @result{} 0 |
1075 | (logior 7) @result{} 7 | |
1076 | (logior #b000 #b001 #b011) @result{} 3 | |
a0e07ba4 NJ |
1077 | @end lisp |
1078 | @end deffn | |
1079 | ||
8f85c0c6 | 1080 | @deffn {Scheme Procedure} logxor n1 n2 |
9401323e NJ |
1081 | Return the bitwise XOR of the integer arguments. A bit is |
1082 | set in the result if it is set in an odd number of arguments. | |
a0e07ba4 | 1083 | @lisp |
9401323e NJ |
1084 | (logxor) @result{} 0 |
1085 | (logxor 7) @result{} 7 | |
1086 | (logxor #b000 #b001 #b011) @result{} 2 | |
1087 | (logxor #b000 #b001 #b011 #b011) @result{} 1 | |
a0e07ba4 NJ |
1088 | @end lisp |
1089 | @end deffn | |
1090 | ||
8f85c0c6 NJ |
1091 | @deffn {Scheme Procedure} lognot n |
1092 | @deffnx {C Function} scm_lognot (n) | |
a0e07ba4 NJ |
1093 | Return the integer which is the 2s-complement of the integer |
1094 | argument. | |
1095 | ||
1096 | @lisp | |
1097 | (number->string (lognot #b10000000) 2) | |
1098 | @result{} "-10000001" | |
1099 | (number->string (lognot #b0) 2) | |
1100 | @result{} "-1" | |
1101 | @end lisp | |
1102 | @end deffn | |
1103 | ||
8f85c0c6 NJ |
1104 | @deffn {Scheme Procedure} logtest j k |
1105 | @deffnx {C Function} scm_logtest (j, k) | |
a0e07ba4 NJ |
1106 | @lisp |
1107 | (logtest j k) @equiv{} (not (zero? (logand j k))) | |
1108 | ||
1109 | (logtest #b0100 #b1011) @result{} #f | |
1110 | (logtest #b0100 #b0111) @result{} #t | |
1111 | @end lisp | |
1112 | @end deffn | |
1113 | ||
8f85c0c6 NJ |
1114 | @deffn {Scheme Procedure} logbit? index j |
1115 | @deffnx {C Function} scm_logbit_p (index, j) | |
a0e07ba4 NJ |
1116 | @lisp |
1117 | (logbit? index j) @equiv{} (logtest (integer-expt 2 index) j) | |
1118 | ||
1119 | (logbit? 0 #b1101) @result{} #t | |
1120 | (logbit? 1 #b1101) @result{} #f | |
1121 | (logbit? 2 #b1101) @result{} #t | |
1122 | (logbit? 3 #b1101) @result{} #t | |
1123 | (logbit? 4 #b1101) @result{} #f | |
1124 | @end lisp | |
1125 | @end deffn | |
1126 | ||
8f85c0c6 NJ |
1127 | @deffn {Scheme Procedure} ash n cnt |
1128 | @deffnx {C Function} scm_ash (n, cnt) | |
a0e07ba4 NJ |
1129 | The function ash performs an arithmetic shift left by @var{cnt} |
1130 | bits (or shift right, if @var{cnt} is negative). 'Arithmetic' | |
1131 | means, that the function does not guarantee to keep the bit | |
1132 | structure of @var{n}, but rather guarantees that the result | |
1133 | will always be rounded towards minus infinity. Therefore, the | |
1134 | results of ash and a corresponding bitwise shift will differ if | |
1135 | @var{n} is negative. | |
1136 | ||
1137 | Formally, the function returns an integer equivalent to | |
1138 | @code{(inexact->exact (floor (* @var{n} (expt 2 @var{cnt}))))}. | |
1139 | ||
1140 | @lisp | |
1141 | (number->string (ash #b1 3) 2) @result{} "1000" | |
1142 | (number->string (ash #b1010 -1) 2) @result{} "101" | |
1143 | @end lisp | |
1144 | @end deffn | |
1145 | ||
8f85c0c6 NJ |
1146 | @deffn {Scheme Procedure} logcount n |
1147 | @deffnx {C Function} scm_logcount (n) | |
a0e07ba4 NJ |
1148 | Return the number of bits in integer @var{n}. If integer is |
1149 | positive, the 1-bits in its binary representation are counted. | |
1150 | If negative, the 0-bits in its two's-complement binary | |
1151 | representation are counted. If 0, 0 is returned. | |
1152 | ||
1153 | @lisp | |
1154 | (logcount #b10101010) | |
1155 | @result{} 4 | |
1156 | (logcount 0) | |
1157 | @result{} 0 | |
1158 | (logcount -2) | |
1159 | @result{} 1 | |
1160 | @end lisp | |
1161 | @end deffn | |
1162 | ||
8f85c0c6 NJ |
1163 | @deffn {Scheme Procedure} integer-length n |
1164 | @deffnx {C Function} scm_integer_length (n) | |
85a9b4ed | 1165 | Return the number of bits necessary to represent @var{n}. |
a0e07ba4 NJ |
1166 | |
1167 | @lisp | |
1168 | (integer-length #b10101010) | |
1169 | @result{} 8 | |
1170 | (integer-length 0) | |
1171 | @result{} 0 | |
1172 | (integer-length #b1111) | |
1173 | @result{} 4 | |
1174 | @end lisp | |
1175 | @end deffn | |
1176 | ||
8f85c0c6 NJ |
1177 | @deffn {Scheme Procedure} integer-expt n k |
1178 | @deffnx {C Function} scm_integer_expt (n, k) | |
a0e07ba4 NJ |
1179 | Return @var{n} raised to the non-negative integer exponent |
1180 | @var{k}. | |
1181 | ||
1182 | @lisp | |
1183 | (integer-expt 2 5) | |
1184 | @result{} 32 | |
1185 | (integer-expt -3 3) | |
1186 | @result{} -27 | |
1187 | @end lisp | |
1188 | @end deffn | |
1189 | ||
8f85c0c6 NJ |
1190 | @deffn {Scheme Procedure} bit-extract n start end |
1191 | @deffnx {C Function} scm_bit_extract (n, start, end) | |
a0e07ba4 NJ |
1192 | Return the integer composed of the @var{start} (inclusive) |
1193 | through @var{end} (exclusive) bits of @var{n}. The | |
1194 | @var{start}th bit becomes the 0-th bit in the result. | |
1195 | ||
1196 | @lisp | |
1197 | (number->string (bit-extract #b1101101010 0 4) 2) | |
1198 | @result{} "1010" | |
1199 | (number->string (bit-extract #b1101101010 4 9) 2) | |
1200 | @result{} "10110" | |
1201 | @end lisp | |
1202 | @end deffn | |
1203 | ||
1204 | ||
1205 | @node Random | |
1206 | @subsection Random Number Generation | |
1207 | ||
8f85c0c6 NJ |
1208 | @deffn {Scheme Procedure} copy-random-state [state] |
1209 | @deffnx {C Function} scm_copy_random_state (state) | |
a0e07ba4 NJ |
1210 | Return a copy of the random state @var{state}. |
1211 | @end deffn | |
1212 | ||
8f85c0c6 NJ |
1213 | @deffn {Scheme Procedure} random n [state] |
1214 | @deffnx {C Function} scm_random (n, state) | |
f631e15e | 1215 | Return a number in [0, N). |
a0e07ba4 NJ |
1216 | |
1217 | Accepts a positive integer or real n and returns a | |
1218 | number of the same type between zero (inclusive) and | |
1219 | N (exclusive). The values returned have a uniform | |
1220 | distribution. | |
1221 | ||
1222 | The optional argument @var{state} must be of the type produced | |
1223 | by @code{seed->random-state}. It defaults to the value of the | |
1224 | variable @var{*random-state*}. This object is used to maintain | |
1225 | the state of the pseudo-random-number generator and is altered | |
1226 | as a side effect of the random operation. | |
1227 | @end deffn | |
1228 | ||
8f85c0c6 NJ |
1229 | @deffn {Scheme Procedure} random:exp [state] |
1230 | @deffnx {C Function} scm_random_exp (state) | |
a0e07ba4 NJ |
1231 | Return an inexact real in an exponential distribution with mean |
1232 | 1. For an exponential distribution with mean u use (* u | |
1233 | (random:exp)). | |
1234 | @end deffn | |
1235 | ||
8f85c0c6 NJ |
1236 | @deffn {Scheme Procedure} random:hollow-sphere! v [state] |
1237 | @deffnx {C Function} scm_random_hollow_sphere_x (v, state) | |
a0e07ba4 NJ |
1238 | Fills vect with inexact real random numbers |
1239 | the sum of whose squares is equal to 1.0. | |
1240 | Thinking of vect as coordinates in space of | |
1241 | dimension n = (vector-length vect), the coordinates | |
1242 | are uniformly distributed over the surface of the | |
6c997de2 | 1243 | unit n-sphere. |
a0e07ba4 NJ |
1244 | @end deffn |
1245 | ||
8f85c0c6 NJ |
1246 | @deffn {Scheme Procedure} random:normal [state] |
1247 | @deffnx {C Function} scm_random_normal (state) | |
a0e07ba4 NJ |
1248 | Return an inexact real in a normal distribution. The |
1249 | distribution used has mean 0 and standard deviation 1. For a | |
1250 | normal distribution with mean m and standard deviation d use | |
1251 | @code{(+ m (* d (random:normal)))}. | |
1252 | @end deffn | |
1253 | ||
8f85c0c6 NJ |
1254 | @deffn {Scheme Procedure} random:normal-vector! v [state] |
1255 | @deffnx {C Function} scm_random_normal_vector_x (v, state) | |
a0e07ba4 NJ |
1256 | Fills vect with inexact real random numbers that are |
1257 | independent and standard normally distributed | |
1258 | (i.e., with mean 0 and variance 1). | |
1259 | @end deffn | |
1260 | ||
8f85c0c6 NJ |
1261 | @deffn {Scheme Procedure} random:solid-sphere! v [state] |
1262 | @deffnx {C Function} scm_random_solid_sphere_x (v, state) | |
a0e07ba4 NJ |
1263 | Fills vect with inexact real random numbers |
1264 | the sum of whose squares is less than 1.0. | |
1265 | Thinking of vect as coordinates in space of | |
1266 | dimension n = (vector-length vect), the coordinates | |
6c997de2 | 1267 | are uniformly distributed within the unit n-sphere. |
a0e07ba4 NJ |
1268 | The sum of the squares of the numbers is returned. |
1269 | @end deffn | |
1270 | ||
8f85c0c6 NJ |
1271 | @deffn {Scheme Procedure} random:uniform [state] |
1272 | @deffnx {C Function} scm_random_uniform (state) | |
a0e07ba4 NJ |
1273 | Return a uniformly distributed inexact real random number in |
1274 | [0,1). | |
1275 | @end deffn | |
1276 | ||
8f85c0c6 NJ |
1277 | @deffn {Scheme Procedure} seed->random-state seed |
1278 | @deffnx {C Function} scm_seed_to_random_state (seed) | |
a0e07ba4 NJ |
1279 | Return a new random state using @var{seed}. |
1280 | @end deffn | |
1281 | ||
1282 | ||
1283 | @node Characters | |
1284 | @section Characters | |
1285 | @tpindex Characters | |
1286 | ||
1287 | Most of the characters in the ASCII character set may be referred to by | |
1288 | name: for example, @code{#\tab}, @code{#\esc}, @code{#\stx}, and so on. | |
1289 | The following table describes the ASCII names for each character. | |
1290 | ||
1291 | @multitable @columnfractions .25 .25 .25 .25 | |
1292 | @item 0 = @code{#\nul} | |
1293 | @tab 1 = @code{#\soh} | |
1294 | @tab 2 = @code{#\stx} | |
1295 | @tab 3 = @code{#\etx} | |
1296 | @item 4 = @code{#\eot} | |
1297 | @tab 5 = @code{#\enq} | |
1298 | @tab 6 = @code{#\ack} | |
1299 | @tab 7 = @code{#\bel} | |
1300 | @item 8 = @code{#\bs} | |
1301 | @tab 9 = @code{#\ht} | |
1302 | @tab 10 = @code{#\nl} | |
1303 | @tab 11 = @code{#\vt} | |
1304 | @item 12 = @code{#\np} | |
1305 | @tab 13 = @code{#\cr} | |
1306 | @tab 14 = @code{#\so} | |
1307 | @tab 15 = @code{#\si} | |
1308 | @item 16 = @code{#\dle} | |
1309 | @tab 17 = @code{#\dc1} | |
1310 | @tab 18 = @code{#\dc2} | |
1311 | @tab 19 = @code{#\dc3} | |
1312 | @item 20 = @code{#\dc4} | |
1313 | @tab 21 = @code{#\nak} | |
1314 | @tab 22 = @code{#\syn} | |
1315 | @tab 23 = @code{#\etb} | |
1316 | @item 24 = @code{#\can} | |
1317 | @tab 25 = @code{#\em} | |
1318 | @tab 26 = @code{#\sub} | |
1319 | @tab 27 = @code{#\esc} | |
1320 | @item 28 = @code{#\fs} | |
1321 | @tab 29 = @code{#\gs} | |
1322 | @tab 30 = @code{#\rs} | |
1323 | @tab 31 = @code{#\us} | |
1324 | @item 32 = @code{#\sp} | |
1325 | @end multitable | |
1326 | ||
1327 | The @code{delete} character (octal 177) may be referred to with the name | |
1328 | @code{#\del}. | |
1329 | ||
1330 | Several characters have more than one name: | |
1331 | ||
1332 | @itemize @bullet | |
1333 | @item | |
1334 | @code{#\space}, @code{#\sp} | |
1335 | @item | |
1336 | @code{#\newline}, @code{#\nl} | |
1337 | @item | |
1338 | @code{#\tab}, @code{#\ht} | |
1339 | @item | |
1340 | @code{#\backspace}, @code{#\bs} | |
1341 | @item | |
1342 | @code{#\return}, @code{#\cr} | |
1343 | @item | |
1344 | @code{#\page}, @code{#\np} | |
1345 | @item | |
1346 | @code{#\null}, @code{#\nul} | |
1347 | @end itemize | |
1348 | ||
1349 | @rnindex char? | |
8f85c0c6 NJ |
1350 | @deffn {Scheme Procedure} char? x |
1351 | @deffnx {C Function} scm_char_p (x) | |
a0e07ba4 NJ |
1352 | Return @code{#t} iff @var{x} is a character, else @code{#f}. |
1353 | @end deffn | |
1354 | ||
1355 | @rnindex char=? | |
8f85c0c6 | 1356 | @deffn {Scheme Procedure} char=? x y |
a0e07ba4 NJ |
1357 | Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}. |
1358 | @end deffn | |
1359 | ||
1360 | @rnindex char<? | |
8f85c0c6 | 1361 | @deffn {Scheme Procedure} char<? x y |
a0e07ba4 NJ |
1362 | Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence, |
1363 | else @code{#f}. | |
1364 | @end deffn | |
1365 | ||
1366 | @rnindex char<=? | |
8f85c0c6 | 1367 | @deffn {Scheme Procedure} char<=? x y |
a0e07ba4 NJ |
1368 | Return @code{#t} iff @var{x} is less than or equal to @var{y} in the |
1369 | ASCII sequence, else @code{#f}. | |
1370 | @end deffn | |
1371 | ||
1372 | @rnindex char>? | |
8f85c0c6 | 1373 | @deffn {Scheme Procedure} char>? x y |
a0e07ba4 NJ |
1374 | Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII |
1375 | sequence, else @code{#f}. | |
1376 | @end deffn | |
1377 | ||
1378 | @rnindex char>=? | |
8f85c0c6 | 1379 | @deffn {Scheme Procedure} char>=? x y |
a0e07ba4 NJ |
1380 | Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the |
1381 | ASCII sequence, else @code{#f}. | |
1382 | @end deffn | |
1383 | ||
1384 | @rnindex char-ci=? | |
8f85c0c6 | 1385 | @deffn {Scheme Procedure} char-ci=? x y |
a0e07ba4 NJ |
1386 | Return @code{#t} iff @var{x} is the same character as @var{y} ignoring |
1387 | case, else @code{#f}. | |
1388 | @end deffn | |
1389 | ||
1390 | @rnindex char-ci<? | |
8f85c0c6 | 1391 | @deffn {Scheme Procedure} char-ci<? x y |
a0e07ba4 NJ |
1392 | Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence |
1393 | ignoring case, else @code{#f}. | |
1394 | @end deffn | |
1395 | ||
1396 | @rnindex char-ci<=? | |
8f85c0c6 | 1397 | @deffn {Scheme Procedure} char-ci<=? x y |
a0e07ba4 NJ |
1398 | Return @code{#t} iff @var{x} is less than or equal to @var{y} in the |
1399 | ASCII sequence ignoring case, else @code{#f}. | |
1400 | @end deffn | |
1401 | ||
1402 | @rnindex char-ci>? | |
8f85c0c6 | 1403 | @deffn {Scheme Procedure} char-ci>? x y |
a0e07ba4 NJ |
1404 | Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII |
1405 | sequence ignoring case, else @code{#f}. | |
1406 | @end deffn | |
1407 | ||
1408 | @rnindex char-ci>=? | |
8f85c0c6 | 1409 | @deffn {Scheme Procedure} char-ci>=? x y |
a0e07ba4 NJ |
1410 | Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the |
1411 | ASCII sequence ignoring case, else @code{#f}. | |
1412 | @end deffn | |
1413 | ||
1414 | @rnindex char-alphabetic? | |
8f85c0c6 NJ |
1415 | @deffn {Scheme Procedure} char-alphabetic? chr |
1416 | @deffnx {C Function} scm_char_alphabetic_p (chr) | |
a0e07ba4 NJ |
1417 | Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}. |
1418 | Alphabetic means the same thing as the isalpha C library function. | |
1419 | @end deffn | |
1420 | ||
1421 | @rnindex char-numeric? | |
8f85c0c6 NJ |
1422 | @deffn {Scheme Procedure} char-numeric? chr |
1423 | @deffnx {C Function} scm_char_numeric_p (chr) | |
a0e07ba4 NJ |
1424 | Return @code{#t} iff @var{chr} is numeric, else @code{#f}. |
1425 | Numeric means the same thing as the isdigit C library function. | |
1426 | @end deffn | |
1427 | ||
1428 | @rnindex char-whitespace? | |
8f85c0c6 NJ |
1429 | @deffn {Scheme Procedure} char-whitespace? chr |
1430 | @deffnx {C Function} scm_char_whitespace_p (chr) | |
a0e07ba4 NJ |
1431 | Return @code{#t} iff @var{chr} is whitespace, else @code{#f}. |
1432 | Whitespace means the same thing as the isspace C library function. | |
1433 | @end deffn | |
1434 | ||
1435 | @rnindex char-upper-case? | |
8f85c0c6 NJ |
1436 | @deffn {Scheme Procedure} char-upper-case? chr |
1437 | @deffnx {C Function} scm_char_upper_case_p (chr) | |
a0e07ba4 NJ |
1438 | Return @code{#t} iff @var{chr} is uppercase, else @code{#f}. |
1439 | Uppercase means the same thing as the isupper C library function. | |
1440 | @end deffn | |
1441 | ||
1442 | @rnindex char-lower-case? | |
8f85c0c6 NJ |
1443 | @deffn {Scheme Procedure} char-lower-case? chr |
1444 | @deffnx {C Function} scm_char_lower_case_p (chr) | |
a0e07ba4 NJ |
1445 | Return @code{#t} iff @var{chr} is lowercase, else @code{#f}. |
1446 | Lowercase means the same thing as the islower C library function. | |
1447 | @end deffn | |
1448 | ||
8f85c0c6 NJ |
1449 | @deffn {Scheme Procedure} char-is-both? chr |
1450 | @deffnx {C Function} scm_char_is_both_p (chr) | |
a0e07ba4 NJ |
1451 | Return @code{#t} iff @var{chr} is either uppercase or lowercase, else @code{#f}. |
1452 | Uppercase and lowercase are as defined by the isupper and islower | |
1453 | C library functions. | |
1454 | @end deffn | |
1455 | ||
1456 | @rnindex char->integer | |
8f85c0c6 NJ |
1457 | @deffn {Scheme Procedure} char->integer chr |
1458 | @deffnx {C Function} scm_char_to_integer (chr) | |
a0e07ba4 NJ |
1459 | Return the number corresponding to ordinal position of @var{chr} in the |
1460 | ASCII sequence. | |
1461 | @end deffn | |
1462 | ||
1463 | @rnindex integer->char | |
8f85c0c6 NJ |
1464 | @deffn {Scheme Procedure} integer->char n |
1465 | @deffnx {C Function} scm_integer_to_char (n) | |
a0e07ba4 NJ |
1466 | Return the character at position @var{n} in the ASCII sequence. |
1467 | @end deffn | |
1468 | ||
1469 | @rnindex char-upcase | |
8f85c0c6 NJ |
1470 | @deffn {Scheme Procedure} char-upcase chr |
1471 | @deffnx {C Function} scm_char_upcase (chr) | |
a0e07ba4 NJ |
1472 | Return the uppercase character version of @var{chr}. |
1473 | @end deffn | |
1474 | ||
1475 | @rnindex char-downcase | |
8f85c0c6 NJ |
1476 | @deffn {Scheme Procedure} char-downcase chr |
1477 | @deffnx {C Function} scm_char_downcase (chr) | |
a0e07ba4 NJ |
1478 | Return the lowercase character version of @var{chr}. |
1479 | @end deffn | |
1480 | ||
1481 | ||
1482 | @node Strings | |
1483 | @section Strings | |
1484 | @tpindex Strings | |
1485 | ||
1486 | Strings are fixed-length sequences of characters. They can be created | |
1487 | by calling constructor procedures, but they can also literally get | |
1488 | entered at the REPL or in Scheme source files. | |
1489 | ||
1490 | Guile provides a rich set of string processing procedures, because text | |
1491 | handling is very important when Guile is used as a scripting language. | |
1492 | ||
1493 | Strings always carry the information about how many characters they are | |
1494 | composed of with them, so there is no special end-of-string character, | |
1495 | like in C. That means that Scheme strings can contain any character, | |
1496 | even the NUL character @code{'\0'}. But note: Since most operating | |
1497 | system calls dealing with strings (such as for file operations) expect | |
1498 | strings to be zero-terminated, they might do unexpected things when | |
85a9b4ed | 1499 | called with string containing unusual characters. |
a0e07ba4 NJ |
1500 | |
1501 | @menu | |
1502 | * String Syntax:: Read syntax for strings. | |
1503 | * String Predicates:: Testing strings for certain properties. | |
1504 | * String Constructors:: Creating new string objects. | |
1505 | * List/String Conversion:: Converting from/to lists of characters. | |
1506 | * String Selection:: Select portions from strings. | |
1507 | * String Modification:: Modify parts or whole strings. | |
1508 | * String Comparison:: Lexicographic ordering predicates. | |
1509 | * String Searching:: Searching in strings. | |
1510 | * Alphabetic Case Mapping:: Convert the alphabetic case of strings. | |
1511 | * Appending Strings:: Appending strings to form a new string. | |
a0e07ba4 NJ |
1512 | @end menu |
1513 | ||
1514 | @node String Syntax | |
1515 | @subsection String Read Syntax | |
1516 | ||
1517 | The read syntax for strings is an arbitrarily long sequence of | |
1518 | characters enclosed in double quotes (@code{"}). @footnote{Actually, the | |
1519 | current implementation restricts strings to a length of 2^24 | |
1520 | characters.} If you want to insert a double quote character into a | |
1521 | string literal, it must be prefixed with a backslash @code{\} character | |
6c997de2 | 1522 | (called an @dfn{escape character}). |
a0e07ba4 NJ |
1523 | |
1524 | The following are examples of string literals: | |
1525 | ||
1526 | @lisp | |
1527 | "foo" | |
1528 | "bar plonk" | |
1529 | "Hello World" | |
1530 | "\"Hi\", he said." | |
1531 | @end lisp | |
1532 | ||
1533 | @c FIXME::martin: What about escape sequences like \r, \n etc.? | |
1534 | ||
1535 | @node String Predicates | |
1536 | @subsection String Predicates | |
1537 | ||
1538 | The following procedures can be used to check whether a given string | |
1539 | fulfills some specified property. | |
1540 | ||
1541 | @rnindex string? | |
8f85c0c6 NJ |
1542 | @deffn {Scheme Procedure} string? obj |
1543 | @deffnx {C Function} scm_string_p (obj) | |
198586ed | 1544 | Return @code{#t} if @var{obj} is a string, else @code{#f}. |
a0e07ba4 NJ |
1545 | @end deffn |
1546 | ||
8f85c0c6 NJ |
1547 | @deffn {Scheme Procedure} string-null? str |
1548 | @deffnx {C Function} scm_string_null_p (str) | |
b56b5983 | 1549 | Return @code{#t} if @var{str}'s length is zero, and |
a0e07ba4 NJ |
1550 | @code{#f} otherwise. |
1551 | @lisp | |
1552 | (string-null? "") @result{} #t | |
1553 | y @result{} "foo" | |
1554 | (string-null? y) @result{} #f | |
1555 | @end lisp | |
1556 | @end deffn | |
1557 | ||
1558 | @node String Constructors | |
1559 | @subsection String Constructors | |
1560 | ||
1561 | The string constructor procedures create new string objects, possibly | |
1562 | initializing them with some specified character data. | |
1563 | ||
1564 | @c FIXME::martin: list->string belongs into `List/String Conversion' | |
1565 | ||
1566 | @rnindex string | |
1567 | @rnindex list->string | |
8f85c0c6 NJ |
1568 | @deffn {Scheme Procedure} string . chrs |
1569 | @deffnx {Scheme Procedure} list->string chrs | |
1570 | @deffnx {C Function} scm_string (chrs) | |
a0e07ba4 NJ |
1571 | Return a newly allocated string composed of the arguments, |
1572 | @var{chrs}. | |
1573 | @end deffn | |
1574 | ||
1575 | @rnindex make-string | |
8f85c0c6 NJ |
1576 | @deffn {Scheme Procedure} make-string k [chr] |
1577 | @deffnx {C Function} scm_make_string (k, chr) | |
a0e07ba4 NJ |
1578 | Return a newly allocated string of |
1579 | length @var{k}. If @var{chr} is given, then all elements of | |
1580 | the string are initialized to @var{chr}, otherwise the contents | |
1581 | of the @var{string} are unspecified. | |
1582 | @end deffn | |
1583 | ||
1584 | @node List/String Conversion | |
1585 | @subsection List/String conversion | |
1586 | ||
1587 | When processing strings, it is often convenient to first convert them | |
1588 | into a list representation by using the procedure @code{string->list}, | |
1589 | work with the resulting list, and then convert it back into a string. | |
1590 | These procedures are useful for similar tasks. | |
1591 | ||
1592 | @rnindex string->list | |
8f85c0c6 NJ |
1593 | @deffn {Scheme Procedure} string->list str |
1594 | @deffnx {C Function} scm_string_to_list (str) | |
a0e07ba4 NJ |
1595 | Return a newly allocated list of the characters that make up |
1596 | the given string @var{str}. @code{string->list} and | |
1597 | @code{list->string} are inverses as far as @samp{equal?} is | |
1598 | concerned. | |
1599 | @end deffn | |
1600 | ||
8f85c0c6 NJ |
1601 | @deffn {Scheme Procedure} string-split str chr |
1602 | @deffnx {C Function} scm_string_split (str, chr) | |
a0e07ba4 NJ |
1603 | Split the string @var{str} into the a list of the substrings delimited |
1604 | by appearances of the character @var{chr}. Note that an empty substring | |
1605 | between separator characters will result in an empty string in the | |
1606 | result list. | |
9401323e | 1607 | |
a0e07ba4 | 1608 | @lisp |
72dd0a03 | 1609 | (string-split "root:x:0:0:root:/root:/bin/bash" #\:) |
a0e07ba4 NJ |
1610 | @result{} |
1611 | ("root" "x" "0" "0" "root" "/root" "/bin/bash") | |
1612 | ||
72dd0a03 | 1613 | (string-split "::" #\:) |
a0e07ba4 NJ |
1614 | @result{} |
1615 | ("" "" "") | |
1616 | ||
72dd0a03 | 1617 | (string-split "" #\:) |
a0e07ba4 NJ |
1618 | @result{} |
1619 | ("") | |
1620 | @end lisp | |
1621 | @end deffn | |
1622 | ||
1623 | ||
1624 | @node String Selection | |
1625 | @subsection String Selection | |
1626 | ||
1627 | Portions of strings can be extracted by these procedures. | |
1628 | @code{string-ref} delivers individual characters whereas | |
1629 | @code{substring} can be used to extract substrings from longer strings. | |
1630 | ||
1631 | @rnindex string-length | |
8f85c0c6 NJ |
1632 | @deffn {Scheme Procedure} string-length string |
1633 | @deffnx {C Function} scm_string_length (string) | |
a0e07ba4 NJ |
1634 | Return the number of characters in @var{string}. |
1635 | @end deffn | |
1636 | ||
1637 | @rnindex string-ref | |
8f85c0c6 NJ |
1638 | @deffn {Scheme Procedure} string-ref str k |
1639 | @deffnx {C Function} scm_string_ref (str, k) | |
a0e07ba4 NJ |
1640 | Return character @var{k} of @var{str} using zero-origin |
1641 | indexing. @var{k} must be a valid index of @var{str}. | |
1642 | @end deffn | |
1643 | ||
1644 | @rnindex string-copy | |
8f85c0c6 NJ |
1645 | @deffn {Scheme Procedure} string-copy str |
1646 | @deffnx {C Function} scm_string_copy (str) | |
a0e07ba4 NJ |
1647 | Return a newly allocated copy of the given @var{string}. |
1648 | @end deffn | |
1649 | ||
1650 | @rnindex substring | |
8f85c0c6 NJ |
1651 | @deffn {Scheme Procedure} substring str start [end] |
1652 | @deffnx {C Function} scm_substring (str, start, end) | |
a0e07ba4 NJ |
1653 | Return a newly allocated string formed from the characters |
1654 | of @var{str} beginning with index @var{start} (inclusive) and | |
1655 | ending with index @var{end} (exclusive). | |
1656 | @var{str} must be a string, @var{start} and @var{end} must be | |
1657 | exact integers satisfying: | |
1658 | ||
1659 | 0 <= @var{start} <= @var{end} <= (string-length @var{str}). | |
1660 | @end deffn | |
1661 | ||
1662 | @node String Modification | |
1663 | @subsection String Modification | |
1664 | ||
6c997de2 NJ |
1665 | These procedures are for modifying strings in-place. This means that the |
1666 | result of the operation is not a new string; instead, the original string's | |
1667 | memory representation is modified. | |
a0e07ba4 NJ |
1668 | |
1669 | @rnindex string-set! | |
8f85c0c6 NJ |
1670 | @deffn {Scheme Procedure} string-set! str k chr |
1671 | @deffnx {C Function} scm_string_set_x (str, k, chr) | |
a0e07ba4 NJ |
1672 | Store @var{chr} in element @var{k} of @var{str} and return |
1673 | an unspecified value. @var{k} must be a valid index of | |
1674 | @var{str}. | |
1675 | @end deffn | |
1676 | ||
1677 | @rnindex string-fill! | |
8f85c0c6 NJ |
1678 | @deffn {Scheme Procedure} string-fill! str chr |
1679 | @deffnx {C Function} scm_string_fill_x (str, chr) | |
a0e07ba4 NJ |
1680 | Store @var{char} in every element of the given @var{string} and |
1681 | return an unspecified value. | |
1682 | @end deffn | |
1683 | ||
8f85c0c6 NJ |
1684 | @deffn {Scheme Procedure} substring-fill! str start end fill |
1685 | @deffnx {C Function} scm_substring_fill_x (str, start, end, fill) | |
a0e07ba4 NJ |
1686 | Change every character in @var{str} between @var{start} and |
1687 | @var{end} to @var{fill}. | |
1688 | ||
1689 | @lisp | |
1690 | (define y "abcdefg") | |
1691 | (substring-fill! y 1 3 #\r) | |
1692 | y | |
1693 | @result{} "arrdefg" | |
1694 | @end lisp | |
1695 | @end deffn | |
1696 | ||
8f85c0c6 NJ |
1697 | @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2 |
1698 | @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2) | |
a0e07ba4 | 1699 | Copy the substring of @var{str1} bounded by @var{start1} and @var{end1} |
9401323e | 1700 | into @var{str2} beginning at position @var{start2}. |
8f85c0c6 | 1701 | @var{str1} and @var{str2} can be the same string. |
a0e07ba4 NJ |
1702 | @end deffn |
1703 | ||
1704 | ||
1705 | @node String Comparison | |
1706 | @subsection String Comparison | |
1707 | ||
1708 | The procedures in this section are similar to the character ordering | |
1709 | predicates (@pxref{Characters}), but are defined on character sequences. | |
1710 | They all return @code{#t} on success and @code{#f} on failure. The | |
1711 | predicates ending in @code{-ci} ignore the character case when comparing | |
1712 | strings. | |
1713 | ||
1714 | ||
1715 | @rnindex string=? | |
8f85c0c6 | 1716 | @deffn {Scheme Procedure} string=? s1 s2 |
a0e07ba4 NJ |
1717 | Lexicographic equality predicate; return @code{#t} if the two |
1718 | strings are the same length and contain the same characters in | |
1719 | the same positions, otherwise return @code{#f}. | |
1720 | ||
1721 | The procedure @code{string-ci=?} treats upper and lower case | |
1722 | letters as though they were the same character, but | |
1723 | @code{string=?} treats upper and lower case as distinct | |
1724 | characters. | |
1725 | @end deffn | |
1726 | ||
1727 | @rnindex string<? | |
8f85c0c6 | 1728 | @deffn {Scheme Procedure} string<? s1 s2 |
a0e07ba4 NJ |
1729 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
1730 | is lexicographically less than @var{s2}. | |
1731 | @end deffn | |
1732 | ||
1733 | @rnindex string<=? | |
8f85c0c6 | 1734 | @deffn {Scheme Procedure} string<=? s1 s2 |
a0e07ba4 NJ |
1735 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
1736 | is lexicographically less than or equal to @var{s2}. | |
1737 | @end deffn | |
1738 | ||
1739 | @rnindex string>? | |
8f85c0c6 | 1740 | @deffn {Scheme Procedure} string>? s1 s2 |
a0e07ba4 NJ |
1741 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
1742 | is lexicographically greater than @var{s2}. | |
1743 | @end deffn | |
1744 | ||
1745 | @rnindex string>=? | |
8f85c0c6 | 1746 | @deffn {Scheme Procedure} string>=? s1 s2 |
a0e07ba4 NJ |
1747 | Lexicographic ordering predicate; return @code{#t} if @var{s1} |
1748 | is lexicographically greater than or equal to @var{s2}. | |
1749 | @end deffn | |
1750 | ||
1751 | @rnindex string-ci=? | |
8f85c0c6 | 1752 | @deffn {Scheme Procedure} string-ci=? s1 s2 |
a0e07ba4 NJ |
1753 | Case-insensitive string equality predicate; return @code{#t} if |
1754 | the two strings are the same length and their component | |
1755 | characters match (ignoring case) at each position; otherwise | |
1756 | return @code{#f}. | |
1757 | @end deffn | |
1758 | ||
1759 | @rnindex string-ci< | |
8f85c0c6 | 1760 | @deffn {Scheme Procedure} string-ci<? s1 s2 |
a0e07ba4 NJ |
1761 | Case insensitive lexicographic ordering predicate; return |
1762 | @code{#t} if @var{s1} is lexicographically less than @var{s2} | |
1763 | regardless of case. | |
1764 | @end deffn | |
1765 | ||
1766 | @rnindex string<=? | |
8f85c0c6 | 1767 | @deffn {Scheme Procedure} string-ci<=? s1 s2 |
a0e07ba4 NJ |
1768 | Case insensitive lexicographic ordering predicate; return |
1769 | @code{#t} if @var{s1} is lexicographically less than or equal | |
1770 | to @var{s2} regardless of case. | |
1771 | @end deffn | |
1772 | ||
1773 | @rnindex string-ci>? | |
8f85c0c6 | 1774 | @deffn {Scheme Procedure} string-ci>? s1 s2 |
a0e07ba4 NJ |
1775 | Case insensitive lexicographic ordering predicate; return |
1776 | @code{#t} if @var{s1} is lexicographically greater than | |
1777 | @var{s2} regardless of case. | |
1778 | @end deffn | |
1779 | ||
1780 | @rnindex string-ci>=? | |
8f85c0c6 | 1781 | @deffn {Scheme Procedure} string-ci>=? s1 s2 |
a0e07ba4 NJ |
1782 | Case insensitive lexicographic ordering predicate; return |
1783 | @code{#t} if @var{s1} is lexicographically greater than or | |
1784 | equal to @var{s2} regardless of case. | |
1785 | @end deffn | |
1786 | ||
1787 | ||
1788 | @node String Searching | |
1789 | @subsection String Searching | |
1790 | ||
b56b5983 NJ |
1791 | When searching for the index of a character in a string, these |
1792 | procedures can be used. | |
a0e07ba4 | 1793 | |
8f85c0c6 NJ |
1794 | @deffn {Scheme Procedure} string-index str chr [frm [to]] |
1795 | @deffnx {C Function} scm_string_index (str, chr, frm, to) | |
a0e07ba4 NJ |
1796 | Return the index of the first occurrence of @var{chr} in |
1797 | @var{str}. The optional integer arguments @var{frm} and | |
1798 | @var{to} limit the search to a portion of the string. This | |
1799 | procedure essentially implements the @code{index} or | |
1800 | @code{strchr} functions from the C library. | |
1801 | ||
1802 | @lisp | |
1803 | (string-index "weiner" #\e) | |
1804 | @result{} 1 | |
1805 | ||
1806 | (string-index "weiner" #\e 2) | |
1807 | @result{} 4 | |
1808 | ||
1809 | (string-index "weiner" #\e 2 4) | |
1810 | @result{} #f | |
1811 | @end lisp | |
1812 | @end deffn | |
1813 | ||
8f85c0c6 NJ |
1814 | @deffn {Scheme Procedure} string-rindex str chr [frm [to]] |
1815 | @deffnx {C Function} scm_string_rindex (str, chr, frm, to) | |
a0e07ba4 NJ |
1816 | Like @code{string-index}, but search from the right of the |
1817 | string rather than from the left. This procedure essentially | |
1818 | implements the @code{rindex} or @code{strrchr} functions from | |
1819 | the C library. | |
1820 | ||
1821 | @lisp | |
1822 | (string-rindex "weiner" #\e) | |
1823 | @result{} 4 | |
1824 | ||
1825 | (string-rindex "weiner" #\e 2 4) | |
1826 | @result{} #f | |
1827 | ||
1828 | (string-rindex "weiner" #\e 2 5) | |
1829 | @result{} 4 | |
1830 | @end lisp | |
1831 | @end deffn | |
1832 | ||
1833 | @node Alphabetic Case Mapping | |
1834 | @subsection Alphabetic Case Mapping | |
1835 | ||
1836 | These are procedures for mapping strings to their upper- or lower-case | |
1837 | equivalents, respectively, or for capitalizing strings. | |
1838 | ||
8f85c0c6 NJ |
1839 | @deffn {Scheme Procedure} string-upcase str |
1840 | @deffnx {C Function} scm_string_upcase (str) | |
a0e07ba4 NJ |
1841 | Return a freshly allocated string containing the characters of |
1842 | @var{str} in upper case. | |
1843 | @end deffn | |
1844 | ||
8f85c0c6 NJ |
1845 | @deffn {Scheme Procedure} string-upcase! str |
1846 | @deffnx {C Function} scm_string_upcase_x (str) | |
a0e07ba4 NJ |
1847 | Destructively upcase every character in @var{str} and return |
1848 | @var{str}. | |
1849 | @lisp | |
1850 | y @result{} "arrdefg" | |
1851 | (string-upcase! y) @result{} "ARRDEFG" | |
1852 | y @result{} "ARRDEFG" | |
1853 | @end lisp | |
1854 | @end deffn | |
1855 | ||
8f85c0c6 NJ |
1856 | @deffn {Scheme Procedure} string-downcase str |
1857 | @deffnx {C Function} scm_string_downcase (str) | |
a0e07ba4 NJ |
1858 | Return a freshly allocation string containing the characters in |
1859 | @var{str} in lower case. | |
1860 | @end deffn | |
1861 | ||
8f85c0c6 NJ |
1862 | @deffn {Scheme Procedure} string-downcase! str |
1863 | @deffnx {C Function} scm_string_downcase_x (str) | |
a0e07ba4 NJ |
1864 | Destructively downcase every character in @var{str} and return |
1865 | @var{str}. | |
1866 | @lisp | |
1867 | y @result{} "ARRDEFG" | |
1868 | (string-downcase! y) @result{} "arrdefg" | |
1869 | y @result{} "arrdefg" | |
1870 | @end lisp | |
1871 | @end deffn | |
1872 | ||
8f85c0c6 NJ |
1873 | @deffn {Scheme Procedure} string-capitalize str |
1874 | @deffnx {C Function} scm_string_capitalize (str) | |
a0e07ba4 NJ |
1875 | Return a freshly allocated string with the characters in |
1876 | @var{str}, where the first character of every word is | |
1877 | capitalized. | |
1878 | @end deffn | |
1879 | ||
8f85c0c6 NJ |
1880 | @deffn {Scheme Procedure} string-capitalize! str |
1881 | @deffnx {C Function} scm_string_capitalize_x (str) | |
a0e07ba4 NJ |
1882 | Upcase the first character of every word in @var{str} |
1883 | destructively and return @var{str}. | |
1884 | ||
1885 | @lisp | |
1886 | y @result{} "hello world" | |
1887 | (string-capitalize! y) @result{} "Hello World" | |
1888 | y @result{} "Hello World" | |
1889 | @end lisp | |
1890 | @end deffn | |
1891 | ||
1892 | ||
1893 | @node Appending Strings | |
1894 | @subsection Appending Strings | |
1895 | ||
1896 | The procedure @code{string-append} appends several strings together to | |
1897 | form a longer result string. | |
1898 | ||
1899 | @rnindex string-append | |
8f85c0c6 NJ |
1900 | @deffn {Scheme Procedure} string-append . args |
1901 | @deffnx {C Function} scm_string_append (args) | |
a0e07ba4 | 1902 | Return a newly allocated string whose characters form the |
8f85c0c6 | 1903 | concatenation of the given strings, @var{args}. |
a0e07ba4 NJ |
1904 | @end deffn |
1905 | ||
1906 | ||
a0e07ba4 NJ |
1907 | @node Regular Expressions |
1908 | @section Regular Expressions | |
1909 | @tpindex Regular expressions | |
1910 | ||
1911 | @cindex regular expressions | |
1912 | @cindex regex | |
1913 | @cindex emacs regexp | |
1914 | ||
1915 | A @dfn{regular expression} (or @dfn{regexp}) is a pattern that | |
1916 | describes a whole class of strings. A full description of regular | |
1917 | expressions and their syntax is beyond the scope of this manual; | |
1918 | an introduction can be found in the Emacs manual (@pxref{Regexps, | |
6c997de2 | 1919 | , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}), or |
a0e07ba4 NJ |
1920 | in many general Unix reference books. |
1921 | ||
1922 | If your system does not include a POSIX regular expression library, and | |
1923 | you have not linked Guile with a third-party regexp library such as Rx, | |
1924 | these functions will not be available. You can tell whether your Guile | |
1925 | installation includes regular expression support by checking whether the | |
1926 | @code{*features*} list includes the @code{regex} symbol. | |
1927 | ||
1928 | @menu | |
1929 | * Regexp Functions:: Functions that create and match regexps. | |
1930 | * Match Structures:: Finding what was matched by a regexp. | |
85a9b4ed TTN |
1931 | * Backslash Escapes:: Removing the special meaning of regexp |
1932 | meta-characters. | |
a0e07ba4 NJ |
1933 | @end menu |
1934 | ||
1935 | [FIXME: it may be useful to include an Examples section. Parts of this | |
1936 | interface are bewildering on first glance.] | |
1937 | ||
1938 | @node Regexp Functions | |
1939 | @subsection Regexp Functions | |
1940 | ||
1941 | By default, Guile supports POSIX extended regular expressions. | |
1942 | That means that the characters @samp{(}, @samp{)}, @samp{+} and | |
1943 | @samp{?} are special, and must be escaped if you wish to match the | |
1944 | literal characters. | |
1945 | ||
1946 | This regular expression interface was modeled after that | |
1947 | implemented by SCSH, the Scheme Shell. It is intended to be | |
1948 | upwardly compatible with SCSH regular expressions. | |
1949 | ||
1950 | @c begin (scm-doc-string "regex.scm" "string-match") | |
8f85c0c6 | 1951 | @deffn {Scheme Procedure} string-match pattern str [start] |
a0e07ba4 NJ |
1952 | Compile the string @var{pattern} into a regular expression and compare |
1953 | it with @var{str}. The optional numeric argument @var{start} specifies | |
1954 | the position of @var{str} at which to begin matching. | |
1955 | ||
1956 | @code{string-match} returns a @dfn{match structure} which | |
1957 | describes what, if anything, was matched by the regular | |
1958 | expression. @xref{Match Structures}. If @var{str} does not match | |
1959 | @var{pattern} at all, @code{string-match} returns @code{#f}. | |
1960 | @end deffn | |
1961 | ||
1962 | Each time @code{string-match} is called, it must compile its | |
1963 | @var{pattern} argument into a regular expression structure. This | |
1964 | operation is expensive, which makes @code{string-match} inefficient if | |
1965 | the same regular expression is used several times (for example, in a | |
1966 | loop). For better performance, you can compile a regular expression in | |
1967 | advance and then match strings against the compiled regexp. | |
1968 | ||
8f85c0c6 NJ |
1969 | @deffn {Scheme Procedure} make-regexp pat . flags |
1970 | @deffnx {C Function} scm_make_regexp (pat, flags) | |
a0e07ba4 NJ |
1971 | Compile the regular expression described by @var{pat}, and |
1972 | return the compiled regexp structure. If @var{pat} does not | |
1973 | describe a legal regular expression, @code{make-regexp} throws | |
1974 | a @code{regular-expression-syntax} error. | |
1975 | ||
1976 | The @var{flags} arguments change the behavior of the compiled | |
1977 | regular expression. The following flags may be supplied: | |
1978 | ||
1979 | @table @code | |
1980 | @item regexp/icase | |
1981 | Consider uppercase and lowercase letters to be the same when | |
1982 | matching. | |
1983 | @item regexp/newline | |
1984 | If a newline appears in the target string, then permit the | |
1985 | @samp{^} and @samp{$} operators to match immediately after or | |
1986 | immediately before the newline, respectively. Also, the | |
1987 | @samp{.} and @samp{[^...]} operators will never match a newline | |
1988 | character. The intent of this flag is to treat the target | |
1989 | string as a buffer containing many lines of text, and the | |
1990 | regular expression as a pattern that may match a single one of | |
1991 | those lines. | |
1992 | @item regexp/basic | |
1993 | Compile a basic (``obsolete'') regexp instead of the extended | |
1994 | (``modern'') regexps that are the default. Basic regexps do | |
1995 | not consider @samp{|}, @samp{+} or @samp{?} to be special | |
1996 | characters, and require the @samp{@{...@}} and @samp{(...)} | |
1997 | metacharacters to be backslash-escaped (@pxref{Backslash | |
1998 | Escapes}). There are several other differences between basic | |
1999 | and extended regular expressions, but these are the most | |
2000 | significant. | |
2001 | @item regexp/extended | |
2002 | Compile an extended regular expression rather than a basic | |
2003 | regexp. This is the default behavior; this flag will not | |
2004 | usually be needed. If a call to @code{make-regexp} includes | |
2005 | both @code{regexp/basic} and @code{regexp/extended} flags, the | |
2006 | one which comes last will override the earlier one. | |
2007 | @end table | |
2008 | @end deffn | |
2009 | ||
8f85c0c6 NJ |
2010 | @deffn {Scheme Procedure} regexp-exec rx str [start [flags]] |
2011 | @deffnx {C Function} scm_regexp_exec (rx, str, start, flags) | |
a0e07ba4 NJ |
2012 | Match the compiled regular expression @var{rx} against |
2013 | @code{str}. If the optional integer @var{start} argument is | |
2014 | provided, begin matching from that position in the string. | |
2015 | Return a match structure describing the results of the match, | |
2016 | or @code{#f} if no match could be found. | |
9401323e NJ |
2017 | |
2018 | The @var{flags} arguments change the matching behavior. | |
2019 | The following flags may be supplied: | |
2020 | ||
2021 | @table @code | |
2022 | @item regexp/notbol | |
2023 | Operator @samp{^} always fails (unless @code{regexp/newline} | |
2024 | is used). Use this when the beginning of the string should | |
2025 | not be considered the beginning of a line. | |
2026 | @item regexp/noteol | |
2027 | Operator @samp{$} always fails (unless @code{regexp/newline} | |
2028 | is used). Use this when the end of the string should not be | |
2029 | considered the end of a line. | |
2030 | @end table | |
a0e07ba4 NJ |
2031 | @end deffn |
2032 | ||
8f85c0c6 NJ |
2033 | @deffn {Scheme Procedure} regexp? obj |
2034 | @deffnx {C Function} scm_regexp_p (obj) | |
a0e07ba4 NJ |
2035 | Return @code{#t} if @var{obj} is a compiled regular expression, |
2036 | or @code{#f} otherwise. | |
2037 | @end deffn | |
2038 | ||
2039 | Regular expressions are commonly used to find patterns in one string and | |
2040 | replace them with the contents of another string. | |
2041 | ||
2042 | @c begin (scm-doc-string "regex.scm" "regexp-substitute") | |
8f85c0c6 | 2043 | @deffn {Scheme Procedure} regexp-substitute port match [item@dots{}] |
a0e07ba4 NJ |
2044 | Write to the output port @var{port} selected contents of the match |
2045 | structure @var{match}. Each @var{item} specifies what should be | |
2046 | written, and may be one of the following arguments: | |
2047 | ||
2048 | @itemize @bullet | |
2049 | @item | |
2050 | A string. String arguments are written out verbatim. | |
2051 | ||
2052 | @item | |
2053 | An integer. The submatch with that number is written. | |
2054 | ||
2055 | @item | |
2056 | The symbol @samp{pre}. The portion of the matched string preceding | |
2057 | the regexp match is written. | |
2058 | ||
2059 | @item | |
2060 | The symbol @samp{post}. The portion of the matched string following | |
2061 | the regexp match is written. | |
2062 | @end itemize | |
2063 | ||
2064 | @var{port} may be @code{#f}, in which case nothing is written; instead, | |
2065 | @code{regexp-substitute} constructs a string from the specified | |
2066 | @var{item}s and returns that. | |
2067 | @end deffn | |
2068 | ||
2069 | @c begin (scm-doc-string "regex.scm" "regexp-substitute") | |
8f85c0c6 | 2070 | @deffn {Scheme Procedure} regexp-substitute/global port regexp target [item@dots{}] |
a0e07ba4 NJ |
2071 | Similar to @code{regexp-substitute}, but can be used to perform global |
2072 | substitutions on @var{str}. Instead of taking a match structure as an | |
2073 | argument, @code{regexp-substitute/global} takes two string arguments: a | |
2074 | @var{regexp} string describing a regular expression, and a @var{target} | |
2075 | string which should be matched against this regular expression. | |
2076 | ||
2077 | Each @var{item} behaves as in @var{regexp-substitute}, with the | |
2078 | following exceptions: | |
2079 | ||
2080 | @itemize @bullet | |
2081 | @item | |
2082 | A function may be supplied. When this function is called, it will be | |
2083 | passed one argument: a match structure for a given regular expression | |
2084 | match. It should return a string to be written out to @var{port}. | |
2085 | ||
2086 | @item | |
2087 | The @samp{post} symbol causes @code{regexp-substitute/global} to recurse | |
2088 | on the unmatched portion of @var{str}. This @emph{must} be supplied in | |
2089 | order to perform global search-and-replace on @var{str}; if it is not | |
2090 | present among the @var{item}s, then @code{regexp-substitute/global} will | |
2091 | return after processing a single match. | |
2092 | @end itemize | |
2093 | @end deffn | |
2094 | ||
2095 | @node Match Structures | |
2096 | @subsection Match Structures | |
2097 | ||
2098 | @cindex match structures | |
2099 | ||
2100 | A @dfn{match structure} is the object returned by @code{string-match} and | |
2101 | @code{regexp-exec}. It describes which portion of a string, if any, | |
2102 | matched the given regular expression. Match structures include: a | |
2103 | reference to the string that was checked for matches; the starting and | |
2104 | ending positions of the regexp match; and, if the regexp included any | |
2105 | parenthesized subexpressions, the starting and ending positions of each | |
2106 | submatch. | |
2107 | ||
2108 | In each of the regexp match functions described below, the @code{match} | |
2109 | argument must be a match structure returned by a previous call to | |
2110 | @code{string-match} or @code{regexp-exec}. Most of these functions | |
2111 | return some information about the original target string that was | |
2112 | matched against a regular expression; we will call that string | |
2113 | @var{target} for easy reference. | |
2114 | ||
2115 | @c begin (scm-doc-string "regex.scm" "regexp-match?") | |
8f85c0c6 | 2116 | @deffn {Scheme Procedure} regexp-match? obj |
a0e07ba4 NJ |
2117 | Return @code{#t} if @var{obj} is a match structure returned by a |
2118 | previous call to @code{regexp-exec}, or @code{#f} otherwise. | |
2119 | @end deffn | |
2120 | ||
2121 | @c begin (scm-doc-string "regex.scm" "match:substring") | |
8f85c0c6 | 2122 | @deffn {Scheme Procedure} match:substring match [n] |
a0e07ba4 NJ |
2123 | Return the portion of @var{target} matched by subexpression number |
2124 | @var{n}. Submatch 0 (the default) represents the entire regexp match. | |
2125 | If the regular expression as a whole matched, but the subexpression | |
2126 | number @var{n} did not match, return @code{#f}. | |
2127 | @end deffn | |
2128 | ||
2129 | @c begin (scm-doc-string "regex.scm" "match:start") | |
8f85c0c6 | 2130 | @deffn {Scheme Procedure} match:start match [n] |
a0e07ba4 NJ |
2131 | Return the starting position of submatch number @var{n}. |
2132 | @end deffn | |
2133 | ||
2134 | @c begin (scm-doc-string "regex.scm" "match:end") | |
8f85c0c6 | 2135 | @deffn {Scheme Procedure} match:end match [n] |
a0e07ba4 NJ |
2136 | Return the ending position of submatch number @var{n}. |
2137 | @end deffn | |
2138 | ||
2139 | @c begin (scm-doc-string "regex.scm" "match:prefix") | |
8f85c0c6 | 2140 | @deffn {Scheme Procedure} match:prefix match |
a0e07ba4 NJ |
2141 | Return the unmatched portion of @var{target} preceding the regexp match. |
2142 | @end deffn | |
2143 | ||
2144 | @c begin (scm-doc-string "regex.scm" "match:suffix") | |
8f85c0c6 | 2145 | @deffn {Scheme Procedure} match:suffix match |
a0e07ba4 NJ |
2146 | Return the unmatched portion of @var{target} following the regexp match. |
2147 | @end deffn | |
2148 | ||
2149 | @c begin (scm-doc-string "regex.scm" "match:count") | |
8f85c0c6 | 2150 | @deffn {Scheme Procedure} match:count match |
a0e07ba4 NJ |
2151 | Return the number of parenthesized subexpressions from @var{match}. |
2152 | Note that the entire regular expression match itself counts as a | |
2153 | subexpression, and failed submatches are included in the count. | |
2154 | @end deffn | |
2155 | ||
2156 | @c begin (scm-doc-string "regex.scm" "match:string") | |
8f85c0c6 | 2157 | @deffn {Scheme Procedure} match:string match |
a0e07ba4 NJ |
2158 | Return the original @var{target} string. |
2159 | @end deffn | |
2160 | ||
2161 | @node Backslash Escapes | |
2162 | @subsection Backslash Escapes | |
2163 | ||
2164 | Sometimes you will want a regexp to match characters like @samp{*} or | |
2165 | @samp{$} exactly. For example, to check whether a particular string | |
2166 | represents a menu entry from an Info node, it would be useful to match | |
2167 | it against a regexp like @samp{^* [^:]*::}. However, this won't work; | |
2168 | because the asterisk is a metacharacter, it won't match the @samp{*} at | |
2169 | the beginning of the string. In this case, we want to make the first | |
2170 | asterisk un-magic. | |
2171 | ||
2172 | You can do this by preceding the metacharacter with a backslash | |
2173 | character @samp{\}. (This is also called @dfn{quoting} the | |
2174 | metacharacter, and is known as a @dfn{backslash escape}.) When Guile | |
2175 | sees a backslash in a regular expression, it considers the following | |
2176 | glyph to be an ordinary character, no matter what special meaning it | |
2177 | would ordinarily have. Therefore, we can make the above example work by | |
2178 | changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells | |
2179 | the regular expression engine to match only a single asterisk in the | |
2180 | target string. | |
2181 | ||
2182 | Since the backslash is itself a metacharacter, you may force a regexp to | |
2183 | match a backslash in the target string by preceding the backslash with | |
2184 | itself. For example, to find variable references in a @TeX{} program, | |
2185 | you might want to find occurrences of the string @samp{\let\} followed | |
2186 | by any number of alphabetic characters. The regular expression | |
2187 | @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the | |
2188 | regexp each match a single backslash in the target string. | |
2189 | ||
2190 | @c begin (scm-doc-string "regex.scm" "regexp-quote") | |
8f85c0c6 | 2191 | @deffn {Scheme Procedure} regexp-quote str |
a0e07ba4 NJ |
2192 | Quote each special character found in @var{str} with a backslash, and |
2193 | return the resulting string. | |
2194 | @end deffn | |
2195 | ||
2196 | @strong{Very important:} Using backslash escapes in Guile source code | |
2197 | (as in Emacs Lisp or C) can be tricky, because the backslash character | |
2198 | has special meaning for the Guile reader. For example, if Guile | |
2199 | encounters the character sequence @samp{\n} in the middle of a string | |
2200 | while processing Scheme code, it replaces those characters with a | |
2201 | newline character. Similarly, the character sequence @samp{\t} is | |
2202 | replaced by a horizontal tab. Several of these @dfn{escape sequences} | |
2203 | are processed by the Guile reader before your code is executed. | |
2204 | Unrecognized escape sequences are ignored: if the characters @samp{\*} | |
2205 | appear in a string, they will be translated to the single character | |
2206 | @samp{*}. | |
2207 | ||
2208 | This translation is obviously undesirable for regular expressions, since | |
2209 | we want to be able to include backslashes in a string in order to | |
2210 | escape regexp metacharacters. Therefore, to make sure that a backslash | |
2211 | is preserved in a string in your Guile program, you must use @emph{two} | |
2212 | consecutive backslashes: | |
2213 | ||
2214 | @lisp | |
2215 | (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*")) | |
2216 | @end lisp | |
2217 | ||
2218 | The string in this example is preprocessed by the Guile reader before | |
2219 | any code is executed. The resulting argument to @code{make-regexp} is | |
2220 | the string @samp{^\* [^:]*}, which is what we really want. | |
2221 | ||
2222 | This also means that in order to write a regular expression that matches | |
2223 | a single backslash character, the regular expression string in the | |
2224 | source code must include @emph{four} backslashes. Each consecutive pair | |
2225 | of backslashes gets translated by the Guile reader to a single | |
2226 | backslash, and the resulting double-backslash is interpreted by the | |
2227 | regexp engine as matching a single backslash character. Hence: | |
2228 | ||
2229 | @lisp | |
2230 | (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*")) | |
2231 | @end lisp | |
2232 | ||
2233 | The reason for the unwieldiness of this syntax is historical. Both | |
2234 | regular expression pattern matchers and Unix string processing systems | |
2235 | have traditionally used backslashes with the special meanings | |
2236 | described above. The POSIX regular expression specification and ANSI C | |
2237 | standard both require these semantics. Attempting to abandon either | |
2238 | convention would cause other kinds of compatibility problems, possibly | |
2239 | more severe ones. Therefore, without extending the Scheme reader to | |
2240 | support strings with different quoting conventions (an ungainly and | |
2241 | confusing extension when implemented in other languages), we must adhere | |
2242 | to this cumbersome escape syntax. | |
2243 | ||
a0e07ba4 | 2244 | |
2a946b44 NJ |
2245 | @node Symbols |
2246 | @section Symbols | |
2247 | @tpindex Symbols | |
a0e07ba4 | 2248 | |
755de645 NJ |
2249 | Symbols in Scheme are widely used in three ways: as items of discrete |
2250 | data, as lookup keys for alists and hash tables, and to denote variable | |
2251 | references. | |
a0e07ba4 | 2252 | |
755de645 NJ |
2253 | A @dfn{symbol} is similar to a string in that it is defined by a |
2254 | sequence of characters. The sequence of characters is known as the | |
2255 | symbol's @dfn{name}. In the usual case --- that is, where the symbol's | |
2256 | name doesn't include any characters that could be confused with other | |
2257 | elements of Scheme syntax --- a symbol is written in a Scheme program by | |
2258 | writing the sequence of characters that make up the name, @emph{without} | |
2259 | any quotation marks or other special syntax. For example, the symbol | |
2260 | whose name is ``multiply-by-2'' is written, simply: | |
a0e07ba4 | 2261 | |
2a946b44 NJ |
2262 | @lisp |
2263 | multiply-by-2 | |
2264 | @end lisp | |
a0e07ba4 | 2265 | |
755de645 NJ |
2266 | Notice how this differs from a @emph{string} with contents |
2267 | ``multiply-by-2'', which is written with double quotation marks, like | |
2268 | this: | |
a0e07ba4 | 2269 | |
2a946b44 | 2270 | @lisp |
755de645 NJ |
2271 | "multiply-by-2" |
2272 | @end lisp | |
2273 | ||
2274 | Looking beyond how they are written, symbols are different from strings | |
2275 | in two important respects. | |
a0e07ba4 | 2276 | |
755de645 NJ |
2277 | The first important difference is uniqueness. If the same-looking |
2278 | string is read twice from two different places in a program, the result | |
2279 | is two @emph{different} string objects whose contents just happen to be | |
2280 | the same. If, on the other hand, the same-looking symbol is read twice | |
2281 | from two different places in a program, the result is the @emph{same} | |
2282 | symbol object both times. | |
2283 | ||
2284 | Given two read symbols, you can use @code{eq?} to test whether they are | |
2285 | the same (that is, have the same name). @code{eq?} is the most | |
2286 | efficient comparison operator in Scheme, and comparing two symbols like | |
2287 | this is as fast as comparing, for example, two numbers. Given two | |
2288 | strings, on the other hand, you must use @code{equal?} or | |
2289 | @code{string=?}, which are much slower comparison operators, to | |
2290 | determine whether the strings have the same contents. | |
2291 | ||
2292 | @lisp | |
2a946b44 NJ |
2293 | (define sym1 (quote hello)) |
2294 | (define sym2 (quote hello)) | |
2295 | (eq? sym1 sym2) @result{} #t | |
755de645 NJ |
2296 | |
2297 | (define str1 "hello") | |
2298 | (define str2 "hello") | |
2299 | (eq? str1 str2) @result{} #f | |
2300 | (equal? str1 str2) @result{} #t | |
2a946b44 | 2301 | @end lisp |
a0e07ba4 | 2302 | |
2a946b44 | 2303 | The second important difference is that symbols, unlike strings, are not |
755de645 NJ |
2304 | self-evaluating. This is why we need the @code{(quote @dots{})}s in the |
2305 | example above: @code{(quote hello)} evaluates to the symbol named | |
2306 | "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the | |
2307 | symbol named "hello" and evaluated as a variable reference @dots{} about | |
2308 | which more below (@pxref{Symbol Variables}). | |
a0e07ba4 NJ |
2309 | |
2310 | @menu | |
755de645 NJ |
2311 | * Symbol Data:: Symbols as discrete data. |
2312 | * Symbol Keys:: Symbols as lookup keys. | |
2313 | * Symbol Variables:: Symbols as denoting variables. | |
2a946b44 | 2314 | * Symbol Primitives:: Operations related to symbols. |
2a946b44 | 2315 | * Symbol Props:: Function slots and property lists. |
755de645 | 2316 | * Symbol Read Syntax:: Extended read syntax for symbols. |
3933a786 | 2317 | * Symbol Uninterned:: Uninterned symbols. |
a0e07ba4 NJ |
2318 | @end menu |
2319 | ||
a0e07ba4 | 2320 | |
755de645 NJ |
2321 | @node Symbol Data |
2322 | @subsection Symbols as Discrete Data | |
a0e07ba4 | 2323 | |
755de645 NJ |
2324 | Numbers and symbols are similar to the extent that they both lend |
2325 | themselves to @code{eq?} comparison. But symbols are more descriptive | |
2326 | than numbers, because a symbol's name can be used directly to describe | |
2327 | the concept for which that symbol stands. | |
a0e07ba4 | 2328 | |
755de645 NJ |
2329 | For example, imagine that you need to represent some colours in a |
2330 | computer program. Using numbers, you would have to choose arbitrarily | |
2331 | some mapping between numbers and colours, and then take care to use that | |
2332 | mapping consistently: | |
a0e07ba4 | 2333 | |
755de645 NJ |
2334 | @lisp |
2335 | ;; 1=red, 2=green, 3=purple | |
a0e07ba4 | 2336 | |
755de645 NJ |
2337 | (if (eq? (colour-of car) 1) |
2338 | ...) | |
2339 | @end lisp | |
2340 | ||
2341 | @noindent | |
2342 | You can make the mapping more explicit and the code more readable by | |
2343 | defining constants: | |
2344 | ||
2345 | @lisp | |
2346 | (define red 1) | |
2347 | (define green 2) | |
2348 | (define purple 3) | |
2349 | ||
2350 | (if (eq? (colour-of car) red) | |
2351 | ...) | |
2352 | @end lisp | |
2353 | ||
2354 | @noindent | |
2355 | But the simplest and clearest approach is not to use numbers at all, but | |
2356 | symbols whose names specify the colours that they refer to: | |
2357 | ||
2358 | @lisp | |
2359 | (if (eq? (colour-of car) 'red) | |
2360 | ...) | |
2361 | @end lisp | |
2362 | ||
2363 | The descriptive advantages of symbols over numbers increase as the set | |
2364 | of concepts that you want to describe grows. Suppose that a car object | |
2365 | can have other properties as well, such as whether it has or uses: | |
a0e07ba4 NJ |
2366 | |
2367 | @itemize @bullet | |
2368 | @item | |
755de645 | 2369 | automatic or manual transmission |
a0e07ba4 | 2370 | @item |
755de645 | 2371 | leaded or unleaded fuel |
a0e07ba4 | 2372 | @item |
755de645 | 2373 | power steering (or not). |
a0e07ba4 NJ |
2374 | @end itemize |
2375 | ||
755de645 NJ |
2376 | @noindent |
2377 | Then a car's combined property set could be naturally represented and | |
2378 | manipulated as a list of symbols: | |
a0e07ba4 NJ |
2379 | |
2380 | @lisp | |
755de645 NJ |
2381 | (properties-of car1) |
2382 | @result{} | |
2383 | (red manual unleaded power-steering) | |
2a946b44 | 2384 | |
755de645 NJ |
2385 | (if (memq 'power-steering (properties-of car1)) |
2386 | (display "Unfit people can drive this car.\n") | |
2387 | (display "You'll need strong arms to drive this car!\n")) | |
2388 | @print{} | |
2389 | Unfit people can drive this car. | |
2390 | @end lisp | |
2a946b44 | 2391 | |
755de645 NJ |
2392 | Remember, the fundamental property of symbols that we are relying on |
2393 | here is that an occurrence of @code{'red} in one part of a program is an | |
2394 | @emph{indistinguishable} symbol from an occurrence of @code{'red} in | |
2395 | another part of a program; this means that symbols can usefully be | |
2396 | compared using @code{eq?}. At the same time, symbols have naturally | |
2397 | descriptive names. This combination of efficiency and descriptive power | |
2398 | makes them ideal for use as discrete data. | |
2399 | ||
2400 | ||
2401 | @node Symbol Keys | |
2402 | @subsection Symbols as Lookup Keys | |
2403 | ||
2404 | Given their efficiency and descriptive power, it is natural to use | |
2405 | symbols as the keys in an association list or hash table. | |
2406 | ||
2407 | To illustrate this, consider a more structured representation of the car | |
2408 | properties example from the preceding subsection. Rather than | |
2409 | mixing all the properties up together in a flat list, we could use an | |
2410 | association list like this: | |
2411 | ||
2412 | @lisp | |
2413 | (define car1-properties '((colour . red) | |
2414 | (transmission . manual) | |
2415 | (fuel . unleaded) | |
2416 | (steering . power-assisted))) | |
a0e07ba4 NJ |
2417 | @end lisp |
2418 | ||
755de645 NJ |
2419 | Notice how this structure is more explicit and extensible than the flat |
2420 | list. For example it makes clear that @code{manual} refers to the | |
2421 | transmission rather than, say, the windows or the locking of the car. | |
2422 | It also allows further properties to use the same symbols among their | |
2423 | possible values without becoming ambiguous: | |
2424 | ||
2425 | @lisp | |
2426 | (define car1-properties '((colour . red) | |
2427 | (transmission . manual) | |
2428 | (fuel . unleaded) | |
2429 | (steering . power-assisted) | |
2430 | (seat-colour . red) | |
2431 | (locking . manual))) | |
2432 | @end lisp | |
2433 | ||
2434 | With a representation like this, it is easy to use the efficient | |
2435 | @code{assq-XXX} family of procedures (@pxref{Association Lists}) to | |
2436 | extract or change individual pieces of information: | |
2437 | ||
2438 | @lisp | |
2439 | (assq-ref car1-properties 'fuel) @result{} unleaded | |
2440 | (assq-ref car1-properties 'transmission) @result{} manual | |
2441 | ||
2442 | (assq-set! car1-properties 'seat-colour 'black) | |
2443 | @result{} | |
2444 | ((colour . red) | |
2445 | (transmission . manual) | |
2446 | (fuel . unleaded) | |
2447 | (steering . power-assisted) | |
2448 | (seat-colour . black) | |
2449 | (locking . manual))) | |
2450 | @end lisp | |
2451 | ||
2452 | Hash tables also have keys, and exactly the same arguments apply to the | |
2453 | use of symbols in hash tables as in association lists. The hash value | |
2454 | that Guile uses to decide where to add a symbol-keyed entry to a hash | |
2455 | table can be obtained by calling the @code{symbol-hash} procedure: | |
2456 | ||
2457 | @deffn {Scheme Procedure} symbol-hash symbol | |
2458 | @deffnx {C Function} scm_symbol_hash (symbol) | |
2459 | Return a hash value for @var{symbol}. | |
2460 | @end deffn | |
2461 | ||
2462 | See @ref{Hash Tables} for information about hash tables in general, and | |
2463 | for why you might choose to use a hash table rather than an association | |
2464 | list. | |
2465 | ||
2466 | ||
2467 | @node Symbol Variables | |
2468 | @subsection Symbols as Denoting Variables | |
2469 | ||
2470 | When an unquoted symbol in a Scheme program is evaluated, it is | |
2471 | interpreted as a variable reference, and the result of the evaluation is | |
2472 | the appropriate variable's value. | |
2473 | ||
2474 | For example, when the expression @code{(string-length "abcd")} is read | |
2475 | and evaluated, the sequence of characters @code{string-length} is read | |
2476 | as the symbol whose name is "string-length". This symbol is associated | |
2477 | with a variable whose value is the procedure that implements string | |
2478 | length calculation. Therefore evaluation of the @code{string-length} | |
2479 | symbol results in that procedure. | |
2480 | ||
2481 | The details of the connection between an unquoted symbol and the | |
2482 | variable to which it refers are explained elsewhere. See @ref{Binding | |
2483 | Constructs}, for how associations between symbols and variables are | |
2484 | created, and @ref{Modules}, for how those associations are affected by | |
2485 | Guile's module system. | |
2a946b44 NJ |
2486 | |
2487 | ||
2488 | @node Symbol Primitives | |
2489 | @subsection Operations Related to Symbols | |
a0e07ba4 | 2490 | |
755de645 NJ |
2491 | Given any Scheme value, you can determine whether it is a symbol using |
2492 | the @code{symbol?} primitive: | |
2493 | ||
a0e07ba4 | 2494 | @rnindex symbol? |
8f85c0c6 NJ |
2495 | @deffn {Scheme Procedure} symbol? obj |
2496 | @deffnx {C Function} scm_symbol_p (obj) | |
a0e07ba4 NJ |
2497 | Return @code{#t} if @var{obj} is a symbol, otherwise return |
2498 | @code{#f}. | |
2499 | @end deffn | |
2500 | ||
755de645 NJ |
2501 | Once you know that you have a symbol, you can obtain its name as a |
2502 | string by calling @code{symbol->string}. Note that Guile differs by | |
2503 | default from R5RS on the details of @code{symbol->string} as regards | |
2504 | case-sensitivity: | |
2505 | ||
2506 | @rnindex symbol->string | |
2507 | @deffn {Scheme Procedure} symbol->string s | |
2508 | @deffnx {C Function} scm_symbol_to_string (s) | |
2509 | Return the name of symbol @var{s} as a string. By default, Guile reads | |
2510 | symbols case-sensitively, so the string returned will have the same case | |
2511 | variation as the sequence of characters that caused @var{s} to be | |
2512 | created. | |
2513 | ||
2514 | If Guile is set to read symbols case-insensitively (as specified by | |
2515 | R5RS), and @var{s} comes into being as part of a literal expression | |
2516 | (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or | |
2517 | by a call to the @code{read} or @code{string-ci->symbol} procedures, | |
2518 | Guile converts any alphabetic characters in the symbol's name to | |
2519 | lower case before creating the symbol object, so the string returned | |
2520 | here will be in lower case. | |
2521 | ||
2522 | If @var{s} was created by @code{string->symbol}, the case of characters | |
2523 | in the string returned will be the same as that in the string that was | |
2524 | passed to @code{string->symbol}, regardless of Guile's case-sensitivity | |
2525 | setting at the time @var{s} was created. | |
2526 | ||
2527 | It is an error to apply mutation procedures like @code{string-set!} to | |
2528 | strings returned by this procedure. | |
2529 | @end deffn | |
2530 | ||
2531 | Most symbols are created by writing them literally in code. However it | |
2532 | is also possible to create symbols programmatically using the following | |
2533 | @code{string->symbol} and @code{string-ci->symbol} procedures: | |
2534 | ||
a0e07ba4 | 2535 | @rnindex string->symbol |
8f85c0c6 NJ |
2536 | @deffn {Scheme Procedure} string->symbol string |
2537 | @deffnx {C Function} scm_string_to_symbol (string) | |
755de645 NJ |
2538 | Return the symbol whose name is @var{string}. This procedure can create |
2539 | symbols with names containing special characters or letters in the | |
2540 | non-standard case, but it is usually a bad idea to create such symbols | |
2541 | because in some implementations of Scheme they cannot be read as | |
2542 | themselves. | |
2543 | @end deffn | |
a0e07ba4 | 2544 | |
755de645 NJ |
2545 | @deffn {Scheme Procedure} string-ci->symbol str |
2546 | @deffnx {C Function} scm_string_ci_to_symbol (str) | |
2547 | Return the symbol whose name is @var{str}. If Guile is currently | |
2548 | reading symbols case-insensitively, @var{str} is converted to lowercase | |
2549 | before the returned symbol is looked up or created. | |
2550 | @end deffn | |
2551 | ||
2552 | The following examples illustrate Guile's detailed behaviour as regards | |
2553 | the case-sensitivity of symbols: | |
a0e07ba4 NJ |
2554 | |
2555 | @lisp | |
755de645 NJ |
2556 | (read-enable 'case-insensitive) ; R5RS compliant behaviour |
2557 | ||
2558 | (symbol->string 'flying-fish) @result{} "flying-fish" | |
2559 | (symbol->string 'Martin) @result{} "martin" | |
2560 | (symbol->string | |
2561 | (string->symbol "Malvina")) @result{} "Malvina" | |
2562 | ||
2563 | (eq? 'mISSISSIppi 'mississippi) @result{} #t | |
2564 | (string->symbol "mISSISSIppi") @result{} mISSISSIppi | |
a0e07ba4 | 2565 | (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f |
801892e7 NJ |
2566 | (eq? 'LolliPop |
2567 | (string->symbol (symbol->string 'LolliPop))) @result{} #t | |
a0e07ba4 NJ |
2568 | (string=? "K. Harper, M.D." |
2569 | (symbol->string | |
755de645 | 2570 | (string->symbol "K. Harper, M.D."))) @result{} #t |
2a946b44 | 2571 | |
755de645 | 2572 | (read-disable 'case-insensitive) ; Guile default behaviour |
a0e07ba4 | 2573 | |
a0e07ba4 | 2574 | (symbol->string 'flying-fish) @result{} "flying-fish" |
755de645 | 2575 | (symbol->string 'Martin) @result{} "Martin" |
a0e07ba4 | 2576 | (symbol->string |
755de645 | 2577 | (string->symbol "Malvina")) @result{} "Malvina" |
801892e7 | 2578 | |
755de645 NJ |
2579 | (eq? 'mISSISSIppi 'mississippi) @result{} #f |
2580 | (string->symbol "mISSISSIppi") @result{} mISSISSIppi | |
2581 | (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t | |
2582 | (eq? 'LolliPop | |
2583 | (string->symbol (symbol->string 'LolliPop))) @result{} #t | |
2584 | (string=? "K. Harper, M.D." | |
2585 | (symbol->string | |
2586 | (string->symbol "K. Harper, M.D."))) @result{} #t | |
2587 | @end lisp | |
801892e7 | 2588 | |
755de645 NJ |
2589 | Finally, some applications, especially those that generate new Scheme |
2590 | code dynamically, need to generate symbols for use in the generated | |
2591 | code. The @code{gensym} primitive meets this need: | |
a0e07ba4 | 2592 | |
8f85c0c6 NJ |
2593 | @deffn {Scheme Procedure} gensym [prefix] |
2594 | @deffnx {C Function} scm_gensym (prefix) | |
755de645 NJ |
2595 | Create a new symbol with a name constructed from a prefix and a counter |
2596 | value. The string @var{prefix} can be specified as an optional | |
2597 | argument. Default prefix is @samp{ g}. The counter is increased by 1 | |
2598 | at each call. There is no provision for resetting the counter. | |
a0e07ba4 NJ |
2599 | @end deffn |
2600 | ||
755de645 NJ |
2601 | The symbols generated by @code{gensym} are @emph{likely} to be unique, |
2602 | since their names begin with a space and it is only otherwise possible | |
2603 | to generate such symbols if a programmer goes out of their way to do | |
2604 | so. The 1.8 release of Guile will include a way of creating | |
2605 | symbols that are @emph{guaranteed} to be unique. | |
801892e7 | 2606 | |
a0e07ba4 | 2607 | |
755de645 NJ |
2608 | @node Symbol Props |
2609 | @subsection Function Slots and Property Lists | |
a0e07ba4 | 2610 | |
755de645 NJ |
2611 | In traditional Lisp dialects, symbols are often understood as having |
2612 | three kinds of value at once: | |
a0e07ba4 | 2613 | |
755de645 NJ |
2614 | @itemize @bullet |
2615 | @item | |
2616 | a @dfn{variable} value, which is used when the symbol appears in | |
2617 | code in a variable reference context | |
a0e07ba4 | 2618 | |
755de645 NJ |
2619 | @item |
2620 | a @dfn{function} value, which is used when the symbol appears in | |
2621 | code in a function name position (i.e. as the first element in an | |
2622 | unquoted list) | |
2a946b44 | 2623 | |
755de645 NJ |
2624 | @item |
2625 | a @dfn{property list} value, which is used when the symbol is given as | |
2626 | the first argument to Lisp's @code{put} or @code{get} functions. | |
2627 | @end itemize | |
2628 | ||
2629 | Although Scheme (as one of its simplifications with respect to Lisp) | |
2630 | does away with the distinction between variable and function namespaces, | |
2631 | Guile currently retains some elements of the traditional structure in | |
2632 | case they turn out to be useful when implementing translators for other | |
2633 | languages, in particular Emacs Lisp. | |
2634 | ||
2635 | Specifically, Guile symbols have two extra slots. for a symbol's | |
2636 | property list, and for its ``function value.'' The following procedures | |
2637 | are provided to access these slots. | |
a0e07ba4 | 2638 | |
8f85c0c6 NJ |
2639 | @deffn {Scheme Procedure} symbol-fref symbol |
2640 | @deffnx {C Function} scm_symbol_fref (symbol) | |
a0e07ba4 NJ |
2641 | Return the contents of @var{symbol}'s @dfn{function slot}. |
2642 | @end deffn | |
2643 | ||
8f85c0c6 NJ |
2644 | @deffn {Scheme Procedure} symbol-fset! symbol value |
2645 | @deffnx {C Function} scm_symbol_fset_x (symbol, value) | |
755de645 | 2646 | Set the contents of @var{symbol}'s function slot to @var{value}. |
801892e7 NJ |
2647 | @end deffn |
2648 | ||
8f85c0c6 NJ |
2649 | @deffn {Scheme Procedure} symbol-pref symbol |
2650 | @deffnx {C Function} scm_symbol_pref (symbol) | |
a0e07ba4 NJ |
2651 | Return the @dfn{property list} currently associated with @var{symbol}. |
2652 | @end deffn | |
2653 | ||
8f85c0c6 NJ |
2654 | @deffn {Scheme Procedure} symbol-pset! symbol value |
2655 | @deffnx {C Function} scm_symbol_pset_x (symbol, value) | |
755de645 NJ |
2656 | Set @var{symbol}'s property list to @var{value}. |
2657 | @end deffn | |
2658 | ||
2659 | @deffn {Scheme Procedure} symbol-property sym prop | |
2660 | From @var{sym}'s property list, return the value for property | |
2661 | @var{prop}. The assumption is that @var{sym}'s property list is an | |
2662 | association list whose keys are distinguished from each other using | |
2663 | @code{equal?}; @var{prop} should be one of the keys in that list. If | |
2664 | the property list has no entry for @var{prop}, @code{symbol-property} | |
2665 | returns @code{#f}. | |
2666 | @end deffn | |
2667 | ||
2668 | @deffn {Scheme Procedure} set-symbol-property sym prop val | |
2669 | In @var{sym}'s property list, set the value for property @var{prop} to | |
2670 | @var{val}, or add a new entry for @var{prop}, with value @var{val}, if | |
2671 | none already exists. For the structure of the property list, see | |
2672 | @code{symbol-property}. | |
2673 | @end deffn | |
2674 | ||
2675 | @deffn {Scheme Procedure} symbol-property-remove! sym prop | |
2676 | From @var{sym}'s property list, remove the entry for property | |
2677 | @var{prop}, if there is one. For the structure of the property list, | |
2678 | see @code{symbol-property}. | |
a0e07ba4 NJ |
2679 | @end deffn |
2680 | ||
755de645 NJ |
2681 | Support for these extra slots may be removed in a future release, and it |
2682 | is probably better to avoid using them. (In release 1.6, Guile itself | |
2683 | uses the property list slot sparingly, and the function slot not at | |
2684 | all.) For a more modern and Schemely approach to properties, see | |
2685 | @ref{Object Properties}. | |
2686 | ||
2687 | ||
2688 | @node Symbol Read Syntax | |
2689 | @subsection Extended Read Syntax for Symbols | |
2690 | ||
2691 | The read syntax for a symbol is a sequence of letters, digits, and | |
2692 | @dfn{extended alphabetic characters}, beginning with a character that | |
2693 | cannot begin a number. In addition, the special cases of @code{+}, | |
2694 | @code{-}, and @code{...} are read as symbols even though numbers can | |
2695 | begin with @code{+}, @code{-} or @code{.}. | |
2696 | ||
2697 | Extended alphabetic characters may be used within identifiers as if | |
2698 | they were letters. The set of extended alphabetic characters is: | |
2699 | ||
2700 | @example | |
2701 | ! $ % & * + - . / : < = > ? @@ ^ _ ~ | |
2702 | @end example | |
2703 | ||
2704 | In addition to the standard read syntax defined above (which is taken | |
2705 | from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on | |
2706 | Scheme})), Guile provides an extended symbol read syntax that allows the | |
2707 | inclusion of unusual characters such as space characters, newlines and | |
2708 | parentheses. If (for whatever reason) you need to write a symbol | |
2709 | containing characters not mentioned above, you can do so as follows. | |
2710 | ||
2711 | @itemize @bullet | |
2712 | @item | |
2713 | Begin the symbol with the characters @code{#@{}, | |
2714 | ||
2715 | @item | |
2716 | write the characters of the symbol and | |
2717 | ||
2718 | @item | |
2719 | finish the symbol with the characters @code{@}#}. | |
2720 | @end itemize | |
2721 | ||
2722 | Here are a few examples of this form of read syntax. The first symbol | |
2723 | needs to use extended syntax because it contains a space character, the | |
2724 | second because it contains a line break, and the last because it looks | |
2725 | like a number. | |
2726 | ||
2727 | @lisp | |
2728 | #@{foo bar@}# | |
2729 | ||
2730 | #@{what | |
2731 | ever@}# | |
2732 | ||
2733 | #@{4242@}# | |
2734 | @end lisp | |
2735 | ||
2736 | Although Guile provides this extended read syntax for symbols, | |
2737 | widespread usage of it is discouraged because it is not portable and not | |
2738 | very readable. | |
801892e7 NJ |
2739 | |
2740 | ||
3933a786 MV |
2741 | @node Symbol Uninterned |
2742 | @subsection Uninterned Symbols | |
2743 | ||
2744 | What makes symbols useful is that they are automatically kept unique. | |
2745 | There are no two symbols that are distinct objects but have the same | |
2746 | name. But of course, there is no rule without exception. In addition | |
755de645 | 2747 | to the normal symbols that have been discussed up to now, you can also |
3933a786 MV |
2748 | create special @dfn{uninterned} symbols that behave slightly |
2749 | differently. | |
2750 | ||
2751 | To understand what is different about them and why they might be useful, | |
2752 | we look at how normal symbols are actually kept unique. | |
2753 | ||
2754 | Whenever Guile wants to find the symbol with a specific name, for | |
2755 | example during @code{read} or when executing @code{string->symbol}, it | |
2756 | first looks into a table of all existing symbols to find out whether a | |
2757 | symbol with the given name already exists. When this is the case, Guile | |
2758 | just returns that symbol. When not, a new symbol with the name is | |
2759 | created and entered into the table so that it can be found later. | |
2760 | ||
2761 | Sometimes you might want to create a symbol that is guaranteed `fresh', | |
801892e7 | 2762 | i.e. a symbol that did not exist previously. You might also want to |
3933a786 MV |
2763 | somehow guarantee that no one else will ever unintentionally stumble |
2764 | across your symbol in the future. These properties of a symbol are | |
2765 | often needed when generating code during macro expansion. When | |
2766 | introducing new temporary variables, you want to guarantee that they | |
801892e7 | 2767 | don't conflict with variables in other people's code. |
3933a786 | 2768 | |
801892e7 | 2769 | The simplest way to arrange for this is to create a new symbol but |
3933a786 MV |
2770 | not enter it into the global table of all symbols. That way, no one |
2771 | will ever get access to your symbol by chance. Symbols that are not in | |
2772 | the table are called @dfn{uninterned}. Of course, symbols that | |
2773 | @emph{are} in the table are called @dfn{interned}. | |
2774 | ||
2775 | You create new uninterned symbols with the function @code{make-symbol}. | |
2776 | You can test whether a symbol is interned or not with | |
2777 | @code{symbol-interned?}. | |
2778 | ||
2779 | Uninterned symbols break the rule that the name of a symbol uniquely | |
2780 | identifies the symbol object. Because of this, they can not be written | |
2781 | out and read back in like interned symbols. Currently, Guile has no | |
2782 | support for reading uninterned symbols. Note that the function | |
2783 | @code{gensym} does not return uninterned symbols for this reason. | |
2784 | ||
2785 | @deffn {Scheme Procedure} make-symbol name | |
2786 | @deffnx {C Function} scm_make_symbol (name) | |
2787 | Return a new uninterned symbol with the name @var{name}. The returned | |
2788 | symbol is guaranteed to be unique and future calls to | |
2789 | @code{string->symbol} will not return it. | |
2790 | @end deffn | |
2791 | ||
2792 | @deffn {Scheme Procedure} symbol-interned? symbol | |
2793 | @deffnx {C Function} scm_symbol_interned_p (symbol) | |
2794 | Return @code{#t} if @var{symbol} is interned, otherwise return | |
2795 | @code{#f}. | |
2796 | @end deffn | |
2797 | ||
2798 | For example: | |
2799 | ||
2800 | @lisp | |
2801 | (define foo-1 (string->symbol "foo")) | |
2802 | (define foo-2 (string->symbol "foo")) | |
2803 | (define foo-3 (make-symbol "foo")) | |
2804 | (define foo-4 (make-symbol "foo")) | |
2805 | ||
2806 | (eq? foo-1 foo-2) | |
755de645 NJ |
2807 | @result{} #t |
2808 | ; Two interned symbols with the same name are the same object, | |
3933a786 MV |
2809 | |
2810 | (eq? foo-1 foo-3) | |
755de645 NJ |
2811 | @result{} #f |
2812 | ; but a call to make-symbol with the same name returns a | |
2813 | ; distinct object. | |
3933a786 MV |
2814 | |
2815 | (eq? foo-3 foo-4) | |
755de645 NJ |
2816 | @result{} #f |
2817 | ; A call to make-symbol always returns a new object, even for | |
2818 | ; the same name. | |
3933a786 MV |
2819 | |
2820 | foo-3 | |
755de645 NJ |
2821 | @result{} #<uninterned-symbol foo 8085290> |
2822 | ; Uninterned symbols print differently from interned symbols, | |
2823 | ||
3933a786 | 2824 | (symbol? foo-3) |
755de645 NJ |
2825 | @result{} #t |
2826 | ; but they are still symbols, | |
3933a786 MV |
2827 | |
2828 | (symbol-interned? foo-3) | |
755de645 NJ |
2829 | @result{} #f |
2830 | ; just not interned. | |
3933a786 | 2831 | @end lisp |
a0e07ba4 | 2832 | |
801892e7 | 2833 | |
a0e07ba4 NJ |
2834 | @node Keywords |
2835 | @section Keywords | |
2836 | @tpindex Keywords | |
2837 | ||
2838 | Keywords are self-evaluating objects with a convenient read syntax that | |
2839 | makes them easy to type. | |
2840 | ||
2841 | Guile's keyword support conforms to R5RS, and adds a (switchable) read | |
2842 | syntax extension to permit keywords to begin with @code{:} as well as | |
2843 | @code{#:}. | |
2844 | ||
2845 | @menu | |
2846 | * Why Use Keywords?:: Motivation for keyword usage. | |
2847 | * Coding With Keywords:: How to use keywords. | |
2848 | * Keyword Read Syntax:: Read syntax for keywords. | |
2849 | * Keyword Procedures:: Procedures for dealing with keywords. | |
2850 | * Keyword Primitives:: The underlying primitive procedures. | |
2851 | @end menu | |
2852 | ||
2853 | @node Why Use Keywords? | |
2854 | @subsection Why Use Keywords? | |
2855 | ||
2856 | Keywords are useful in contexts where a program or procedure wants to be | |
2857 | able to accept a large number of optional arguments without making its | |
2858 | interface unmanageable. | |
2859 | ||
2860 | To illustrate this, consider a hypothetical @code{make-window} | |
2861 | procedure, which creates a new window on the screen for drawing into | |
2862 | using some graphical toolkit. There are many parameters that the caller | |
2863 | might like to specify, but which could also be sensibly defaulted, for | |
2864 | example: | |
2865 | ||
2866 | @itemize @bullet | |
2867 | @item | |
85a9b4ed | 2868 | color depth -- Default: the color depth for the screen |
a0e07ba4 NJ |
2869 | |
2870 | @item | |
85a9b4ed | 2871 | background color -- Default: white |
a0e07ba4 NJ |
2872 | |
2873 | @item | |
2874 | width -- Default: 600 | |
2875 | ||
2876 | @item | |
2877 | height -- Default: 400 | |
2878 | @end itemize | |
2879 | ||
2880 | If @code{make-window} did not use keywords, the caller would have to | |
2881 | pass in a value for each possible argument, remembering the correct | |
2882 | argument order and using a special value to indicate the default value | |
2883 | for that argument: | |
2884 | ||
2885 | @lisp | |
85a9b4ed TTN |
2886 | (make-window 'default ;; Color depth |
2887 | 'default ;; Background color | |
a0e07ba4 NJ |
2888 | 800 ;; Width |
2889 | 100 ;; Height | |
2890 | @dots{}) ;; More make-window arguments | |
2891 | @end lisp | |
2892 | ||
2893 | With keywords, on the other hand, defaulted arguments are omitted, and | |
2894 | non-default arguments are clearly tagged by the appropriate keyword. As | |
2895 | a result, the invocation becomes much clearer: | |
2896 | ||
2897 | @lisp | |
2898 | (make-window #:width 800 #:height 100) | |
2899 | @end lisp | |
2900 | ||
2901 | On the other hand, for a simpler procedure with few arguments, the use | |
2902 | of keywords would be a hindrance rather than a help. The primitive | |
2903 | procedure @code{cons}, for example, would not be improved if it had to | |
2904 | be invoked as | |
2905 | ||
2906 | @lisp | |
2907 | (cons #:car x #:cdr y) | |
2908 | @end lisp | |
2909 | ||
2910 | So the decision whether to use keywords or not is purely pragmatic: use | |
2911 | them if they will clarify the procedure invocation at point of call. | |
2912 | ||
2913 | @node Coding With Keywords | |
2914 | @subsection Coding With Keywords | |
2915 | ||
2916 | If a procedure wants to support keywords, it should take a rest argument | |
2917 | and then use whatever means is convenient to extract keywords and their | |
2918 | corresponding arguments from the contents of that rest argument. | |
2919 | ||
2920 | The following example illustrates the principle: the code for | |
2921 | @code{make-window} uses a helper procedure called | |
2922 | @code{get-keyword-value} to extract individual keyword arguments from | |
2923 | the rest argument. | |
2924 | ||
2925 | @lisp | |
2926 | (define (get-keyword-value args keyword default) | |
2927 | (let ((kv (memq keyword args))) | |
2928 | (if (and kv (>= (length kv) 2)) | |
2929 | (cadr kv) | |
2930 | default))) | |
2931 | ||
2932 | (define (make-window . args) | |
2933 | (let ((depth (get-keyword-value args #:depth screen-depth)) | |
2934 | (bg (get-keyword-value args #:bg "white")) | |
2935 | (width (get-keyword-value args #:width 800)) | |
2936 | (height (get-keyword-value args #:height 100)) | |
2937 | @dots{}) | |
2938 | @dots{})) | |
2939 | @end lisp | |
2940 | ||
2941 | But you don't need to write @code{get-keyword-value}. The @code{(ice-9 | |
2942 | optargs)} module provides a set of powerful macros that you can use to | |
2943 | implement keyword-supporting procedures like this: | |
2944 | ||
2945 | @lisp | |
2946 | (use-modules (ice-9 optargs)) | |
2947 | ||
2948 | (define (make-window . args) | |
2949 | (let-keywords args #f ((depth screen-depth) | |
2950 | (bg "white") | |
2951 | (width 800) | |
2952 | (height 100)) | |
2953 | ...)) | |
2954 | @end lisp | |
2955 | ||
2956 | @noindent | |
2957 | Or, even more economically, like this: | |
2958 | ||
2959 | @lisp | |
2960 | (use-modules (ice-9 optargs)) | |
2961 | ||
2962 | (define* (make-window #:key (depth screen-depth) | |
2963 | (bg "white") | |
2964 | (width 800) | |
2965 | (height 100)) | |
2966 | ...) | |
2967 | @end lisp | |
2968 | ||
2969 | For further details on @code{let-keywords}, @code{define*} and other | |
2a946b44 NJ |
2970 | facilities provided by the @code{(ice-9 optargs)} module, see |
2971 | @ref{Optional Arguments}. | |
a0e07ba4 NJ |
2972 | |
2973 | ||
2974 | @node Keyword Read Syntax | |
2975 | @subsection Keyword Read Syntax | |
2976 | ||
2977 | Guile, by default, only recognizes the keyword syntax specified by R5RS. | |
2978 | A token of the form @code{#:NAME}, where @code{NAME} has the same syntax | |
2a946b44 NJ |
2979 | as a Scheme symbol (@pxref{Symbol Read Syntax}), is the external |
2980 | representation of the keyword named @code{NAME}. Keyword objects print | |
2981 | using this syntax as well, so values containing keyword objects can be | |
2982 | read back into Guile. When used in an expression, keywords are | |
2983 | self-quoting objects. | |
a0e07ba4 NJ |
2984 | |
2985 | If the @code{keyword} read option is set to @code{'prefix}, Guile also | |
2986 | recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens | |
2987 | of the form @code{:NAME} are read as symbols, as required by R5RS. | |
2988 | ||
2989 | To enable and disable the alternative non-R5RS keyword syntax, you use | |
2990 | the @code{read-options} procedure documented in @ref{General option | |
2991 | interface} and @ref{Reader options}. | |
2992 | ||
2993 | @smalllisp | |
2994 | (read-set! keywords 'prefix) | |
2995 | ||
2996 | #:type | |
2997 | @result{} | |
2998 | #:type | |
2999 | ||
3000 | :type | |
3001 | @result{} | |
3002 | #:type | |
3003 | ||
3004 | (read-set! keywords #f) | |
3005 | ||
3006 | #:type | |
3007 | @result{} | |
3008 | #:type | |
3009 | ||
3010 | :type | |
2a946b44 | 3011 | @print{} |
a0e07ba4 NJ |
3012 | ERROR: In expression :type: |
3013 | ERROR: Unbound variable: :type | |
3014 | ABORT: (unbound-variable) | |
3015 | @end smalllisp | |
3016 | ||
3017 | @node Keyword Procedures | |
3018 | @subsection Keyword Procedures | |
3019 | ||
a0e07ba4 NJ |
3020 | The following procedures can be used for converting symbols to keywords |
3021 | and back. | |
3022 | ||
8f85c0c6 | 3023 | @deffn {Scheme Procedure} symbol->keyword sym |
a0e07ba4 NJ |
3024 | Return a keyword with the same characters as in @var{sym}. |
3025 | @end deffn | |
3026 | ||
8f85c0c6 | 3027 | @deffn {Scheme Procedure} keyword->symbol kw |
a0e07ba4 NJ |
3028 | Return a symbol with the same characters as in @var{kw}. |
3029 | @end deffn | |
3030 | ||
3031 | ||
3032 | @node Keyword Primitives | |
3033 | @subsection Keyword Primitives | |
3034 | ||
3035 | Internally, a keyword is implemented as something like a tagged symbol, | |
3036 | where the tag identifies the keyword as being self-evaluating, and the | |
3037 | symbol, known as the keyword's @dfn{dash symbol} has the same name as | |
3038 | the keyword name but prefixed by a single dash. For example, the | |
3039 | keyword @code{#:name} has the corresponding dash symbol @code{-name}. | |
3040 | ||
3041 | Most keyword objects are constructed automatically by the reader when it | |
3042 | reads a token beginning with @code{#:}. However, if you need to | |
3043 | construct a keyword object programmatically, you can do so by calling | |
3044 | @code{make-keyword-from-dash-symbol} with the corresponding dash symbol | |
3045 | (as the reader does). The dash symbol for a keyword object can be | |
3046 | retrieved using the @code{keyword-dash-symbol} procedure. | |
3047 | ||
8f85c0c6 NJ |
3048 | @deffn {Scheme Procedure} make-keyword-from-dash-symbol symbol |
3049 | @deffnx {C Function} scm_make_keyword_from_dash_symbol (symbol) | |
a0e07ba4 NJ |
3050 | Make a keyword object from a @var{symbol} that starts with a dash. |
3051 | @end deffn | |
3052 | ||
8f85c0c6 NJ |
3053 | @deffn {Scheme Procedure} keyword? obj |
3054 | @deffnx {C Function} scm_keyword_p (obj) | |
a0e07ba4 NJ |
3055 | Return @code{#t} if the argument @var{obj} is a keyword, else |
3056 | @code{#f}. | |
3057 | @end deffn | |
3058 | ||
8f85c0c6 NJ |
3059 | @deffn {Scheme Procedure} keyword-dash-symbol keyword |
3060 | @deffnx {C Function} scm_keyword_dash_symbol (keyword) | |
a0e07ba4 NJ |
3061 | Return the dash symbol for @var{keyword}. |
3062 | This is the inverse of @code{make-keyword-from-dash-symbol}. | |
3063 | @end deffn | |
3064 | ||
a0e07ba4 | 3065 | |
4c731ece NJ |
3066 | @node Other Types |
3067 | @section ``Functionality-Centric'' Data Types | |
a0e07ba4 | 3068 | |
4c731ece NJ |
3069 | Procedures and macros are documented in their own chapter: see |
3070 | @ref{Procedures and Macros}. | |
a0e07ba4 | 3071 | |
4c731ece NJ |
3072 | Variable objects are documented as part of the description of Guile's |
3073 | module system: see @ref{Variables}. | |
a0e07ba4 | 3074 | |
4c731ece NJ |
3075 | Asyncs, dynamic roots and fluids are described in the chapter on |
3076 | scheduling: see @ref{Scheduling}. | |
a0e07ba4 | 3077 | |
4c731ece NJ |
3078 | Hooks are documented in the chapter on general utility functions: see |
3079 | @ref{Hooks}. | |
a0e07ba4 | 3080 | |
4c731ece | 3081 | Ports are described in the chapter on I/O: see @ref{Input and Output}. |
a0e07ba4 | 3082 | |
a0e07ba4 NJ |
3083 | |
3084 | @c Local Variables: | |
3085 | @c TeX-master: "guile.texi" | |
3086 | @c End: |