2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @node Simple Data Types
9 @section Simple Generic Data Types
11 This chapter describes those of Guile's simple data types which are
12 primarily used for their role as items of generic data. By
13 @dfn{simple} we mean data types that are not primarily used as
14 containers to hold other data --- i.e.@: pairs, lists, vectors and so on.
15 For the documentation of such @dfn{compound} data types, see
16 @ref{Compound Data Types}.
18 @c One of the great strengths of Scheme is that there is no straightforward
19 @c distinction between ``data'' and ``functionality''. For example,
20 @c Guile's support for dynamic linking could be described:
24 @c either in a ``data-centric'' way, as the behaviour and properties of the
25 @c ``dynamically linked object'' data type, and the operations that may be
26 @c applied to instances of this type
29 @c or in a ``functionality-centric'' way, as the set of procedures that
30 @c constitute Guile's support for dynamic linking, in the context of the
34 @c The contents of this chapter are, therefore, a matter of judgment. By
35 @c @dfn{generic}, we mean to select those data types whose typical use as
36 @c @emph{data} in a wide variety of programming contexts is more important
37 @c than their use in the implementation of a particular piece of
38 @c @emph{functionality}. The last section of this chapter provides
39 @c references for all the data types that are documented not here but in a
40 @c ``functionality-centric'' way elsewhere in the manual.
43 * Booleans:: True/false values.
44 * Numbers:: Numerical data types.
45 * Characters:: Single characters.
46 * Character Sets:: Sets of characters.
47 * Strings:: Sequences of characters.
48 * Bytevectors:: Sequences of bytes.
49 * Regular Expressions:: Pattern matching and substitution.
51 * Keywords:: Self-quoting, customizable display keywords.
52 * Other Types:: "Functionality-centric" data types.
60 The two boolean values are @code{#t} for true and @code{#f} for false.
62 Boolean values are returned by predicate procedures, such as the general
63 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
64 (@pxref{Equality}) and numerical and string comparison operators like
65 @code{string=?} (@pxref{String Comparison}) and @code{<=}
75 (equal? "house" "houses")
83 In test condition contexts like @code{if} and @code{cond} (@pxref{if
84 cond case}), where a group of subexpressions will be evaluated only if a
85 @var{condition} expression evaluates to ``true'', ``true'' means any
86 value at all except @code{#f}.
99 A result of this asymmetry is that typical Scheme source code more often
100 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
101 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
102 not necessary to represent an @code{if} or @code{cond} true value.
104 It is important to note that @code{#f} is @strong{not} equivalent to any
105 other Scheme value. In particular, @code{#f} is not the same as the
106 number 0 (like in C and C++), and not the same as the ``empty list''
107 (like in some Lisp dialects).
109 In C, the two Scheme boolean values are available as the two constants
110 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
111 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
112 false when used in C conditionals. In order to test for it, use
113 @code{scm_is_false} or @code{scm_is_true}.
116 @deffn {Scheme Procedure} not x
117 @deffnx {C Function} scm_not (x)
118 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
122 @deffn {Scheme Procedure} boolean? obj
123 @deffnx {C Function} scm_boolean_p (obj)
124 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
128 @deftypevr {C Macro} SCM SCM_BOOL_T
129 The @code{SCM} representation of the Scheme object @code{#t}.
132 @deftypevr {C Macro} SCM SCM_BOOL_F
133 The @code{SCM} representation of the Scheme object @code{#f}.
136 @deftypefn {C Function} int scm_is_true (SCM obj)
137 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
140 @deftypefn {C Function} int scm_is_false (SCM obj)
141 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
144 @deftypefn {C Function} int scm_is_bool (SCM obj)
145 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
149 @deftypefn {C Function} SCM scm_from_bool (int val)
150 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
153 @deftypefn {C Function} int scm_to_bool (SCM val)
154 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
155 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
157 You should probably use @code{scm_is_true} instead of this function
158 when you just want to test a @code{SCM} value for trueness.
162 @subsection Numerical data types
165 Guile supports a rich ``tower'' of numerical types --- integer,
166 rational, real and complex --- and provides an extensive set of
167 mathematical and scientific functions for operating on numerical
168 data. This section of the manual documents those types and functions.
170 You may also find it illuminating to read R5RS's presentation of numbers
171 in Scheme, which is particularly clear and accessible: see
172 @ref{Numbers,,,r5rs,R5RS}.
175 * Numerical Tower:: Scheme's numerical "tower".
176 * Integers:: Whole numbers.
177 * Reals and Rationals:: Real and rational numbers.
178 * Complex Numbers:: Complex numbers.
179 * Exactness:: Exactness and inexactness.
180 * Number Syntax:: Read syntax for numerical data.
181 * Integer Operations:: Operations on integer values.
182 * Comparison:: Comparison predicates.
183 * Conversion:: Converting numbers to and from strings.
184 * Complex:: Complex number operations.
185 * Arithmetic:: Arithmetic functions.
186 * Scientific:: Scientific functions.
187 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
188 * Random:: Random number generation.
192 @node Numerical Tower
193 @subsubsection Scheme's Numerical ``Tower''
196 Scheme's numerical ``tower'' consists of the following categories of
201 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
204 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
205 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
206 pi (an irrational number) doesn't. These include integers
210 The set of numbers that describes all possible positions along a
211 one-dimensional line. This includes rationals as well as irrational
214 @item complex numbers
215 The set of numbers that describes all possible positions in a two
216 dimensional space. This includes real as well as imaginary numbers
217 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
218 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
222 It is called a tower because each category ``sits on'' the one that
223 follows it, in the sense that every integer is also a rational, every
224 rational is also real, and every real number is also a complex number
225 (but with zero imaginary part).
227 In addition to the classification into integers, rationals, reals and
228 complex numbers, Scheme also distinguishes between whether a number is
229 represented exactly or not. For example, the result of
230 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
231 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
232 Instead, it stores an inexact approximation, using the C type
235 Guile can represent exact rationals of any magnitude, inexact
236 rationals that fit into a C @code{double}, and inexact complex numbers
237 with @code{double} real and imaginary parts.
239 The @code{number?} predicate may be applied to any Scheme value to
240 discover whether the value is any of the supported numerical types.
242 @deffn {Scheme Procedure} number? obj
243 @deffnx {C Function} scm_number_p (obj)
244 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
253 (number? "hello there!")
256 (define pi 3.141592654)
261 @deftypefn {C Function} int scm_is_number (SCM obj)
262 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
265 The next few subsections document each of Guile's numerical data types
269 @subsubsection Integers
271 @tpindex Integer numbers
275 Integers are whole numbers, that is numbers with no fractional part,
276 such as 2, 83, and @minus{}3789.
278 Integers in Guile can be arbitrarily big, as shown by the following
282 (define (factorial n)
283 (let loop ((n n) (product 1))
286 (loop (- n 1) (* product n)))))
292 @result{} 2432902008176640000
295 @result{} -119622220865480194561963161495657715064383733760000000000
298 Readers whose background is in programming languages where integers are
299 limited by the need to fit into just 4 or 8 bytes of memory may find
300 this surprising, or suspect that Guile's representation of integers is
301 inefficient. In fact, Guile achieves a near optimal balance of
302 convenience and efficiency by using the host computer's native
303 representation of integers where possible, and a more general
304 representation where the required number does not fit in the native
305 form. Conversion between these two representations is automatic and
306 completely invisible to the Scheme level programmer.
308 The infinities @samp{+inf.0} and @samp{-inf.0} are considered to be
309 inexact integers. They are explained in detail in the next section,
310 together with reals and rationals.
312 C has a host of different integer types, and Guile offers a host of
313 functions to convert between them and the @code{SCM} representation.
314 For example, a C @code{int} can be handled with @code{scm_to_int} and
315 @code{scm_from_int}. Guile also defines a few C integer types of its
316 own, to help with differences between systems.
318 C integer types that are not covered can be handled with the generic
319 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
320 signed types, or with @code{scm_to_unsigned_integer} and
321 @code{scm_from_unsigned_integer} for unsigned types.
323 Scheme integers can be exact and inexact. For example, a number
324 written as @code{3.0} with an explicit decimal-point is inexact, but
325 it is also an integer. The functions @code{integer?} and
326 @code{scm_is_integer} report true for such a number, but the functions
327 @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only
328 allow exact integers and thus report false. Likewise, the conversion
329 functions like @code{scm_to_signed_integer} only accept exact
332 The motivation for this behavior is that the inexactness of a number
333 should not be lost silently. If you want to allow inexact integers,
334 you can explicitly insert a call to @code{inexact->exact} or to its C
335 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
336 be converted by this call into exact integers; inexact non-integers
337 will become exact fractions.)
339 @deffn {Scheme Procedure} integer? x
340 @deffnx {C Function} scm_integer_p (x)
341 Return @code{#t} if @var{x} is an exact or inexact integer number, else
359 @deftypefn {C Function} int scm_is_integer (SCM x)
360 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
363 @defvr {C Type} scm_t_int8
364 @defvrx {C Type} scm_t_uint8
365 @defvrx {C Type} scm_t_int16
366 @defvrx {C Type} scm_t_uint16
367 @defvrx {C Type} scm_t_int32
368 @defvrx {C Type} scm_t_uint32
369 @defvrx {C Type} scm_t_int64
370 @defvrx {C Type} scm_t_uint64
371 @defvrx {C Type} scm_t_intmax
372 @defvrx {C Type} scm_t_uintmax
373 The C types are equivalent to the corresponding ISO C types but are
374 defined on all platforms, with the exception of @code{scm_t_int64} and
375 @code{scm_t_uint64}, which are only defined when a 64-bit type is
376 available. For example, @code{scm_t_int8} is equivalent to
379 You can regard these definitions as a stop-gap measure until all
380 platforms provide these types. If you know that all the platforms
381 that you are interested in already provide these types, it is better
382 to use them directly instead of the types provided by Guile.
385 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
386 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
387 Return @code{1} when @var{x} represents an exact integer that is
388 between @var{min} and @var{max}, inclusive.
390 These functions can be used to check whether a @code{SCM} value will
391 fit into a given range, such as the range of a given C integer type.
392 If you just want to convert a @code{SCM} value to a given C integer
393 type, use one of the conversion functions directly.
396 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
397 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
398 When @var{x} represents an exact integer that is between @var{min} and
399 @var{max} inclusive, return that integer. Else signal an error,
400 either a `wrong-type' error when @var{x} is not an exact integer, or
401 an `out-of-range' error when it doesn't fit the given range.
404 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
405 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
406 Return the @code{SCM} value that represents the integer @var{x}. This
407 function will always succeed and will always return an exact number.
410 @deftypefn {C Function} char scm_to_char (SCM x)
411 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
412 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
413 @deftypefnx {C Function} short scm_to_short (SCM x)
414 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
415 @deftypefnx {C Function} int scm_to_int (SCM x)
416 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
417 @deftypefnx {C Function} long scm_to_long (SCM x)
418 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
419 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
420 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
421 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
422 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
423 @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x)
424 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
425 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
426 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
427 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
428 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
429 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
430 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
431 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
432 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
433 When @var{x} represents an exact integer that fits into the indicated
434 C type, return that integer. Else signal an error, either a
435 `wrong-type' error when @var{x} is not an exact integer, or an
436 `out-of-range' error when it doesn't fit the given range.
438 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
439 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
440 the corresponding types are.
443 @deftypefn {C Function} SCM scm_from_char (char x)
444 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
445 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
446 @deftypefnx {C Function} SCM scm_from_short (short x)
447 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
448 @deftypefnx {C Function} SCM scm_from_int (int x)
449 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
450 @deftypefnx {C Function} SCM scm_from_long (long x)
451 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
452 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
453 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
454 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
455 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
456 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
457 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
458 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
459 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
460 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
461 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
462 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
463 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
464 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
465 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
466 Return the @code{SCM} value that represents the integer @var{x}.
467 These functions will always succeed and will always return an exact
471 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
472 Assign @var{val} to the multiple precision integer @var{rop}.
473 @var{val} must be an exact integer, otherwise an error will be
474 signalled. @var{rop} must have been initialized with @code{mpz_init}
475 before this function is called. When @var{rop} is no longer needed
476 the occupied space must be freed with @code{mpz_clear}.
477 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
480 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
481 Return the @code{SCM} value that represents @var{val}.
484 @node Reals and Rationals
485 @subsubsection Real and Rational Numbers
486 @tpindex Real numbers
487 @tpindex Rational numbers
492 Mathematically, the real numbers are the set of numbers that describe
493 all possible points along a continuous, infinite, one-dimensional line.
494 The rational numbers are the set of all numbers that can be written as
495 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
496 All rational numbers are also real, but there are real numbers that
497 are not rational, for example @m{\sqrt2, the square root of 2}, and
500 Guile can represent both exact and inexact rational numbers, but it
501 can not represent irrational numbers. Exact rationals are represented
502 by storing the numerator and denominator as two exact integers.
503 Inexact rationals are stored as floating point numbers using the C
506 Exact rationals are written as a fraction of integers. There must be
507 no whitespace around the slash:
514 Even though the actual encoding of inexact rationals is in binary, it
515 may be helpful to think of it as a decimal number with a limited
516 number of significant figures and a decimal point somewhere, since
517 this corresponds to the standard notation for non-whole numbers. For
523 -5648394822220000000000.0
527 The limited precision of Guile's encoding means that any ``real'' number
528 in Guile can be written in a rational form, by multiplying and then dividing
529 by sufficient powers of 10 (or in fact, 2). For example,
530 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided by
531 100000000000000000. In Guile's current incarnation, therefore, the
532 @code{rational?} and @code{real?} predicates are equivalent.
535 Dividing by an exact zero leads to a error message, as one might
536 expect. However, dividing by an inexact zero does not produce an
537 error. Instead, the result of the division is either plus or minus
538 infinity, depending on the sign of the divided number.
540 The infinities are written @samp{+inf.0} and @samp{-inf.0},
541 respectively. This syntax is also recognized by @code{read} as an
542 extension to the usual Scheme syntax.
544 Dividing zero by zero yields something that is not a number at all:
545 @samp{+nan.0}. This is the special `not a number' value.
547 On platforms that follow @acronym{IEEE} 754 for their floating point
548 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
549 are implemented using the corresponding @acronym{IEEE} 754 values.
550 They behave in arithmetic operations like @acronym{IEEE} 754 describes
551 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
553 The infinities are inexact integers and are considered to be both even
554 and odd. While @samp{+nan.0} is not @code{=} to itself, it is
555 @code{eqv?} to itself.
557 To test for the special values, use the functions @code{inf?} and
560 @deffn {Scheme Procedure} real? obj
561 @deffnx {C Function} scm_real_p (obj)
562 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
563 that the sets of integer and rational values form subsets of the set
564 of real numbers, so the predicate will also be fulfilled if @var{obj}
565 is an integer number or a rational number.
568 @deffn {Scheme Procedure} rational? x
569 @deffnx {C Function} scm_rational_p (x)
570 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
571 Note that the set of integer values forms a subset of the set of
572 rational numbers, i. e. the predicate will also be fulfilled if
573 @var{x} is an integer number.
575 Since Guile can not represent irrational numbers, every number
576 satisfying @code{real?} also satisfies @code{rational?} in Guile.
579 @deffn {Scheme Procedure} rationalize x eps
580 @deffnx {C Function} scm_rationalize (x, eps)
581 Returns the @emph{simplest} rational number differing
582 from @var{x} by no more than @var{eps}.
584 As required by @acronym{R5RS}, @code{rationalize} only returns an
585 exact result when both its arguments are exact. Thus, you might need
586 to use @code{inexact->exact} on the arguments.
589 (rationalize (inexact->exact 1.2) 1/100)
595 @deffn {Scheme Procedure} inf? x
596 @deffnx {C Function} scm_inf_p (x)
597 Return @code{#t} if @var{x} is either @samp{+inf.0} or @samp{-inf.0},
601 @deffn {Scheme Procedure} nan? x
602 @deffnx {C Function} scm_nan_p (x)
603 Return @code{#t} if @var{x} is @samp{+nan.0}, @code{#f} otherwise.
606 @deffn {Scheme Procedure} nan
607 @deffnx {C Function} scm_nan ()
611 @deffn {Scheme Procedure} inf
612 @deffnx {C Function} scm_inf ()
616 @deffn {Scheme Procedure} numerator x
617 @deffnx {C Function} scm_numerator (x)
618 Return the numerator of the rational number @var{x}.
621 @deffn {Scheme Procedure} denominator x
622 @deffnx {C Function} scm_denominator (x)
623 Return the denominator of the rational number @var{x}.
626 @deftypefn {C Function} int scm_is_real (SCM val)
627 @deftypefnx {C Function} int scm_is_rational (SCM val)
628 Equivalent to @code{scm_is_true (scm_real_p (val))} and
629 @code{scm_is_true (scm_rational_p (val))}, respectively.
632 @deftypefn {C Function} double scm_to_double (SCM val)
633 Returns the number closest to @var{val} that is representable as a
634 @code{double}. Returns infinity for a @var{val} that is too large in
635 magnitude. The argument @var{val} must be a real number.
638 @deftypefn {C Function} SCM scm_from_double (double val)
639 Return the @code{SCM} value that represents @var{val}. The returned
640 value is inexact according to the predicate @code{inexact?}, but it
641 will be exactly equal to @var{val}.
644 @node Complex Numbers
645 @subsubsection Complex Numbers
646 @tpindex Complex numbers
650 Complex numbers are the set of numbers that describe all possible points
651 in a two-dimensional space. The two coordinates of a particular point
652 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
653 the complex number that describes that point.
655 In Guile, complex numbers are written in rectangular form as the sum of
656 their real and imaginary parts, using the symbol @code{i} to indicate
671 Polar form can also be used, with an @samp{@@} between magnitude and
675 1@@3.141592 @result{} -1.0 (approx)
676 -1@@1.57079 @result{} 0.0-1.0i (approx)
679 Guile represents a complex number with a non-zero imaginary part as a
680 pair of inexact rationals, so the real and imaginary parts of a
681 complex number have the same properties of inexactness and limited
682 precision as single inexact rational numbers. Guile can not represent
683 exact complex numbers with non-zero imaginary parts.
685 @deffn {Scheme Procedure} complex? z
686 @deffnx {C Function} scm_complex_p (z)
687 Return @code{#t} if @var{x} is a complex number, @code{#f}
688 otherwise. Note that the sets of real, rational and integer
689 values form subsets of the set of complex numbers, i. e. the
690 predicate will also be fulfilled if @var{x} is a real,
691 rational or integer number.
694 @deftypefn {C Function} int scm_is_complex (SCM val)
695 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
699 @subsubsection Exact and Inexact Numbers
700 @tpindex Exact numbers
701 @tpindex Inexact numbers
705 @rnindex exact->inexact
706 @rnindex inexact->exact
708 R5RS requires that a calculation involving inexact numbers always
709 produces an inexact result. To meet this requirement, Guile
710 distinguishes between an exact integer value such as @samp{5} and the
711 corresponding inexact real value which, to the limited precision
712 available, has no fractional part, and is printed as @samp{5.0}. Guile
713 will only convert the latter value to the former when forced to do so by
714 an invocation of the @code{inexact->exact} procedure.
716 @deffn {Scheme Procedure} exact? z
717 @deffnx {C Function} scm_exact_p (z)
718 Return @code{#t} if the number @var{z} is exact, @code{#f}
734 @deffn {Scheme Procedure} inexact? z
735 @deffnx {C Function} scm_inexact_p (z)
736 Return @code{#t} if the number @var{z} is inexact, @code{#f}
740 @deffn {Scheme Procedure} inexact->exact z
741 @deffnx {C Function} scm_inexact_to_exact (z)
742 Return an exact number that is numerically closest to @var{z}, when
743 there is one. For inexact rationals, Guile returns the exact rational
744 that is numerically equal to the inexact rational. Inexact complex
745 numbers with a non-zero imaginary part can not be made exact.
752 The following happens because 12/10 is not exactly representable as a
753 @code{double} (on most platforms). However, when reading a decimal
754 number that has been marked exact with the ``#e'' prefix, Guile is
755 able to represent it correctly.
759 @result{} 5404319552844595/4503599627370496
767 @c begin (texi-doc-string "guile" "exact->inexact")
768 @deffn {Scheme Procedure} exact->inexact z
769 @deffnx {C Function} scm_exact_to_inexact (z)
770 Convert the number @var{z} to its inexact representation.
775 @subsubsection Read Syntax for Numerical Data
777 The read syntax for integers is a string of digits, optionally
778 preceded by a minus or plus character, a code indicating the
779 base in which the integer is encoded, and a code indicating whether
780 the number is exact or inexact. The supported base codes are:
785 the integer is written in binary (base 2)
789 the integer is written in octal (base 8)
793 the integer is written in decimal (base 10)
797 the integer is written in hexadecimal (base 16)
800 If the base code is omitted, the integer is assumed to be decimal. The
801 following examples show how these base codes are used.
820 The codes for indicating exactness (which can, incidentally, be applied
821 to all numerical values) are:
830 the number is inexact.
833 If the exactness indicator is omitted, the number is exact unless it
834 contains a radix point. Since Guile can not represent exact complex
835 numbers, an error is signalled when asking for them.
845 ERROR: Wrong type argument
848 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
849 plus and minus infinity, respectively. The value must be written
850 exactly as shown, that is, they always must have a sign and exactly
851 one zero digit after the decimal point. It also understands
852 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
853 The sign is ignored for `not-a-number' and the value is always printed
856 @node Integer Operations
857 @subsubsection Operations on Integer Values
866 @deffn {Scheme Procedure} odd? n
867 @deffnx {C Function} scm_odd_p (n)
868 Return @code{#t} if @var{n} is an odd number, @code{#f}
872 @deffn {Scheme Procedure} even? n
873 @deffnx {C Function} scm_even_p (n)
874 Return @code{#t} if @var{n} is an even number, @code{#f}
878 @c begin (texi-doc-string "guile" "quotient")
879 @c begin (texi-doc-string "guile" "remainder")
880 @deffn {Scheme Procedure} quotient n d
881 @deffnx {Scheme Procedure} remainder n d
882 @deffnx {C Function} scm_quotient (n, d)
883 @deffnx {C Function} scm_remainder (n, d)
884 Return the quotient or remainder from @var{n} divided by @var{d}. The
885 quotient is rounded towards zero, and the remainder will have the same
886 sign as @var{n}. In all cases quotient and remainder satisfy
887 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
890 (remainder 13 4) @result{} 1
891 (remainder -13 4) @result{} -1
895 @c begin (texi-doc-string "guile" "modulo")
896 @deffn {Scheme Procedure} modulo n d
897 @deffnx {C Function} scm_modulo (n, d)
898 Return the remainder from @var{n} divided by @var{d}, with the same
902 (modulo 13 4) @result{} 1
903 (modulo -13 4) @result{} 3
904 (modulo 13 -4) @result{} -3
905 (modulo -13 -4) @result{} -1
909 @c begin (texi-doc-string "guile" "gcd")
910 @deffn {Scheme Procedure} gcd x@dots{}
911 @deffnx {C Function} scm_gcd (x, y)
912 Return the greatest common divisor of all arguments.
913 If called without arguments, 0 is returned.
915 The C function @code{scm_gcd} always takes two arguments, while the
916 Scheme function can take an arbitrary number.
919 @c begin (texi-doc-string "guile" "lcm")
920 @deffn {Scheme Procedure} lcm x@dots{}
921 @deffnx {C Function} scm_lcm (x, y)
922 Return the least common multiple of the arguments.
923 If called without arguments, 1 is returned.
925 The C function @code{scm_lcm} always takes two arguments, while the
926 Scheme function can take an arbitrary number.
929 @deffn {Scheme Procedure} modulo-expt n k m
930 @deffnx {C Function} scm_modulo_expt (n, k, m)
931 Return @var{n} raised to the integer exponent
932 @var{k}, modulo @var{m}.
941 @subsubsection Comparison Predicates
946 The C comparison functions below always takes two arguments, while the
947 Scheme functions can take an arbitrary number. Also keep in mind that
948 the C functions return one of the Scheme boolean values
949 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
950 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
951 y))} when testing the two Scheme numbers @code{x} and @code{y} for
952 equality, for example.
954 @c begin (texi-doc-string "guile" "=")
955 @deffn {Scheme Procedure} =
956 @deffnx {C Function} scm_num_eq_p (x, y)
957 Return @code{#t} if all parameters are numerically equal.
960 @c begin (texi-doc-string "guile" "<")
961 @deffn {Scheme Procedure} <
962 @deffnx {C Function} scm_less_p (x, y)
963 Return @code{#t} if the list of parameters is monotonically
967 @c begin (texi-doc-string "guile" ">")
968 @deffn {Scheme Procedure} >
969 @deffnx {C Function} scm_gr_p (x, y)
970 Return @code{#t} if the list of parameters is monotonically
974 @c begin (texi-doc-string "guile" "<=")
975 @deffn {Scheme Procedure} <=
976 @deffnx {C Function} scm_leq_p (x, y)
977 Return @code{#t} if the list of parameters is monotonically
981 @c begin (texi-doc-string "guile" ">=")
982 @deffn {Scheme Procedure} >=
983 @deffnx {C Function} scm_geq_p (x, y)
984 Return @code{#t} if the list of parameters is monotonically
988 @c begin (texi-doc-string "guile" "zero?")
989 @deffn {Scheme Procedure} zero? z
990 @deffnx {C Function} scm_zero_p (z)
991 Return @code{#t} if @var{z} is an exact or inexact number equal to
995 @c begin (texi-doc-string "guile" "positive?")
996 @deffn {Scheme Procedure} positive? x
997 @deffnx {C Function} scm_positive_p (x)
998 Return @code{#t} if @var{x} is an exact or inexact number greater than
1002 @c begin (texi-doc-string "guile" "negative?")
1003 @deffn {Scheme Procedure} negative? x
1004 @deffnx {C Function} scm_negative_p (x)
1005 Return @code{#t} if @var{x} is an exact or inexact number less than
1011 @subsubsection Converting Numbers To and From Strings
1012 @rnindex number->string
1013 @rnindex string->number
1015 The following procedures read and write numbers according to their
1016 external representation as defined by R5RS (@pxref{Lexical structure,
1017 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1018 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1019 i18n)} module}, for locale-dependent number parsing.
1021 @deffn {Scheme Procedure} number->string n [radix]
1022 @deffnx {C Function} scm_number_to_string (n, radix)
1023 Return a string holding the external representation of the
1024 number @var{n} in the given @var{radix}. If @var{n} is
1025 inexact, a radix of 10 will be used.
1028 @deffn {Scheme Procedure} string->number string [radix]
1029 @deffnx {C Function} scm_string_to_number (string, radix)
1030 Return a number of the maximally precise representation
1031 expressed by the given @var{string}. @var{radix} must be an
1032 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1033 is a default radix that may be overridden by an explicit radix
1034 prefix in @var{string} (e.g. "#o177"). If @var{radix} is not
1035 supplied, then the default radix is 10. If string is not a
1036 syntactically valid notation for a number, then
1037 @code{string->number} returns @code{#f}.
1040 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1041 As per @code{string->number} above, but taking a C string, as pointer
1042 and length. The string characters should be in the current locale
1043 encoding (@code{locale} in the name refers only to that, there's no
1044 locale-dependent parsing).
1049 @subsubsection Complex Number Operations
1050 @rnindex make-rectangular
1057 @deffn {Scheme Procedure} make-rectangular real imaginary
1058 @deffnx {C Function} scm_make_rectangular (real, imaginary)
1059 Return a complex number constructed of the given @var{real} and
1060 @var{imaginary} parts.
1063 @deffn {Scheme Procedure} make-polar x y
1064 @deffnx {C Function} scm_make_polar (x, y)
1066 Return the complex number @var{x} * e^(i * @var{y}).
1069 @c begin (texi-doc-string "guile" "real-part")
1070 @deffn {Scheme Procedure} real-part z
1071 @deffnx {C Function} scm_real_part (z)
1072 Return the real part of the number @var{z}.
1075 @c begin (texi-doc-string "guile" "imag-part")
1076 @deffn {Scheme Procedure} imag-part z
1077 @deffnx {C Function} scm_imag_part (z)
1078 Return the imaginary part of the number @var{z}.
1081 @c begin (texi-doc-string "guile" "magnitude")
1082 @deffn {Scheme Procedure} magnitude z
1083 @deffnx {C Function} scm_magnitude (z)
1084 Return the magnitude of the number @var{z}. This is the same as
1085 @code{abs} for real arguments, but also allows complex numbers.
1088 @c begin (texi-doc-string "guile" "angle")
1089 @deffn {Scheme Procedure} angle z
1090 @deffnx {C Function} scm_angle (z)
1091 Return the angle of the complex number @var{z}.
1094 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1095 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1096 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1097 respectively, but these functions take @code{double}s as their
1101 @deftypefn {C Function} double scm_c_real_part (z)
1102 @deftypefnx {C Function} double scm_c_imag_part (z)
1103 Returns the real or imaginary part of @var{z} as a @code{double}.
1106 @deftypefn {C Function} double scm_c_magnitude (z)
1107 @deftypefnx {C Function} double scm_c_angle (z)
1108 Returns the magnitude or angle of @var{z} as a @code{double}.
1113 @subsubsection Arithmetic Functions
1128 The C arithmetic functions below always takes two arguments, while the
1129 Scheme functions can take an arbitrary number. When you need to
1130 invoke them with just one argument, for example to compute the
1131 equivalent od @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1132 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1134 @c begin (texi-doc-string "guile" "+")
1135 @deffn {Scheme Procedure} + z1 @dots{}
1136 @deffnx {C Function} scm_sum (z1, z2)
1137 Return the sum of all parameter values. Return 0 if called without any
1141 @c begin (texi-doc-string "guile" "-")
1142 @deffn {Scheme Procedure} - z1 z2 @dots{}
1143 @deffnx {C Function} scm_difference (z1, z2)
1144 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1145 the sum of all but the first argument are subtracted from the first
1149 @c begin (texi-doc-string "guile" "*")
1150 @deffn {Scheme Procedure} * z1 @dots{}
1151 @deffnx {C Function} scm_product (z1, z2)
1152 Return the product of all arguments. If called without arguments, 1 is
1156 @c begin (texi-doc-string "guile" "/")
1157 @deffn {Scheme Procedure} / z1 z2 @dots{}
1158 @deffnx {C Function} scm_divide (z1, z2)
1159 Divide the first argument by the product of the remaining arguments. If
1160 called with one argument @var{z1}, 1/@var{z1} is returned.
1163 @deffn {Scheme Procedure} 1+ z
1164 @deffnx {C Function} scm_oneplus (z)
1165 Return @math{@var{z} + 1}.
1168 @deffn {Scheme Procedure} 1- z
1169 @deffnx {C function} scm_oneminus (z)
1170 Return @math{@var{z} - 1}.
1173 @c begin (texi-doc-string "guile" "abs")
1174 @deffn {Scheme Procedure} abs x
1175 @deffnx {C Function} scm_abs (x)
1176 Return the absolute value of @var{x}.
1178 @var{x} must be a number with zero imaginary part. To calculate the
1179 magnitude of a complex number, use @code{magnitude} instead.
1182 @c begin (texi-doc-string "guile" "max")
1183 @deffn {Scheme Procedure} max x1 x2 @dots{}
1184 @deffnx {C Function} scm_max (x1, x2)
1185 Return the maximum of all parameter values.
1188 @c begin (texi-doc-string "guile" "min")
1189 @deffn {Scheme Procedure} min x1 x2 @dots{}
1190 @deffnx {C Function} scm_min (x1, x2)
1191 Return the minimum of all parameter values.
1194 @c begin (texi-doc-string "guile" "truncate")
1195 @deffn {Scheme Procedure} truncate x
1196 @deffnx {C Function} scm_truncate_number (x)
1197 Round the inexact number @var{x} towards zero.
1200 @c begin (texi-doc-string "guile" "round")
1201 @deffn {Scheme Procedure} round x
1202 @deffnx {C Function} scm_round_number (x)
1203 Round the inexact number @var{x} to the nearest integer. When exactly
1204 halfway between two integers, round to the even one.
1207 @c begin (texi-doc-string "guile" "floor")
1208 @deffn {Scheme Procedure} floor x
1209 @deffnx {C Function} scm_floor (x)
1210 Round the number @var{x} towards minus infinity.
1213 @c begin (texi-doc-string "guile" "ceiling")
1214 @deffn {Scheme Procedure} ceiling x
1215 @deffnx {C Function} scm_ceiling (x)
1216 Round the number @var{x} towards infinity.
1219 @deftypefn {C Function} double scm_c_truncate (double x)
1220 @deftypefnx {C Function} double scm_c_round (double x)
1221 Like @code{scm_truncate_number} or @code{scm_round_number},
1222 respectively, but these functions take and return @code{double}
1227 @subsubsection Scientific Functions
1229 The following procedures accept any kind of number as arguments,
1230 including complex numbers.
1233 @c begin (texi-doc-string "guile" "sqrt")
1234 @deffn {Scheme Procedure} sqrt z
1235 Return the square root of @var{z}. Of the two possible roots
1236 (positive and negative), the one with the a positive real part is
1237 returned, or if that's zero then a positive imaginary part. Thus,
1240 (sqrt 9.0) @result{} 3.0
1241 (sqrt -9.0) @result{} 0.0+3.0i
1242 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1243 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1248 @c begin (texi-doc-string "guile" "expt")
1249 @deffn {Scheme Procedure} expt z1 z2
1250 Return @var{z1} raised to the power of @var{z2}.
1254 @c begin (texi-doc-string "guile" "sin")
1255 @deffn {Scheme Procedure} sin z
1256 Return the sine of @var{z}.
1260 @c begin (texi-doc-string "guile" "cos")
1261 @deffn {Scheme Procedure} cos z
1262 Return the cosine of @var{z}.
1266 @c begin (texi-doc-string "guile" "tan")
1267 @deffn {Scheme Procedure} tan z
1268 Return the tangent of @var{z}.
1272 @c begin (texi-doc-string "guile" "asin")
1273 @deffn {Scheme Procedure} asin z
1274 Return the arcsine of @var{z}.
1278 @c begin (texi-doc-string "guile" "acos")
1279 @deffn {Scheme Procedure} acos z
1280 Return the arccosine of @var{z}.
1284 @c begin (texi-doc-string "guile" "atan")
1285 @deffn {Scheme Procedure} atan z
1286 @deffnx {Scheme Procedure} atan y x
1287 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1291 @c begin (texi-doc-string "guile" "exp")
1292 @deffn {Scheme Procedure} exp z
1293 Return e to the power of @var{z}, where e is the base of natural
1294 logarithms (2.71828@dots{}).
1298 @c begin (texi-doc-string "guile" "log")
1299 @deffn {Scheme Procedure} log z
1300 Return the natural logarithm of @var{z}.
1303 @c begin (texi-doc-string "guile" "log10")
1304 @deffn {Scheme Procedure} log10 z
1305 Return the base 10 logarithm of @var{z}.
1308 @c begin (texi-doc-string "guile" "sinh")
1309 @deffn {Scheme Procedure} sinh z
1310 Return the hyperbolic sine of @var{z}.
1313 @c begin (texi-doc-string "guile" "cosh")
1314 @deffn {Scheme Procedure} cosh z
1315 Return the hyperbolic cosine of @var{z}.
1318 @c begin (texi-doc-string "guile" "tanh")
1319 @deffn {Scheme Procedure} tanh z
1320 Return the hyperbolic tangent of @var{z}.
1323 @c begin (texi-doc-string "guile" "asinh")
1324 @deffn {Scheme Procedure} asinh z
1325 Return the hyperbolic arcsine of @var{z}.
1328 @c begin (texi-doc-string "guile" "acosh")
1329 @deffn {Scheme Procedure} acosh z
1330 Return the hyperbolic arccosine of @var{z}.
1333 @c begin (texi-doc-string "guile" "atanh")
1334 @deffn {Scheme Procedure} atanh z
1335 Return the hyperbolic arctangent of @var{z}.
1339 @node Bitwise Operations
1340 @subsubsection Bitwise Operations
1342 For the following bitwise functions, negative numbers are treated as
1343 infinite precision twos-complements. For instance @math{-6} is bits
1344 @math{@dots{}111010}, with infinitely many ones on the left. It can
1345 be seen that adding 6 (binary 110) to such a bit pattern gives all
1348 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1349 @deffnx {C Function} scm_logand (n1, n2)
1350 Return the bitwise @sc{and} of the integer arguments.
1353 (logand) @result{} -1
1354 (logand 7) @result{} 7
1355 (logand #b111 #b011 #b001) @result{} 1
1359 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1360 @deffnx {C Function} scm_logior (n1, n2)
1361 Return the bitwise @sc{or} of the integer arguments.
1364 (logior) @result{} 0
1365 (logior 7) @result{} 7
1366 (logior #b000 #b001 #b011) @result{} 3
1370 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1371 @deffnx {C Function} scm_loxor (n1, n2)
1372 Return the bitwise @sc{xor} of the integer arguments. A bit is
1373 set in the result if it is set in an odd number of arguments.
1376 (logxor) @result{} 0
1377 (logxor 7) @result{} 7
1378 (logxor #b000 #b001 #b011) @result{} 2
1379 (logxor #b000 #b001 #b011 #b011) @result{} 1
1383 @deffn {Scheme Procedure} lognot n
1384 @deffnx {C Function} scm_lognot (n)
1385 Return the integer which is the ones-complement of the integer
1386 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1389 (number->string (lognot #b10000000) 2)
1390 @result{} "-10000001"
1391 (number->string (lognot #b0) 2)
1396 @deffn {Scheme Procedure} logtest j k
1397 @deffnx {C Function} scm_logtest (j, k)
1398 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1399 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1400 calculating the @code{logand}, just testing for non-zero.
1403 (logtest #b0100 #b1011) @result{} #f
1404 (logtest #b0100 #b0111) @result{} #t
1408 @deffn {Scheme Procedure} logbit? index j
1409 @deffnx {C Function} scm_logbit_p (index, j)
1410 Test whether bit number @var{index} in @var{j} is set. @var{index}
1411 starts from 0 for the least significant bit.
1414 (logbit? 0 #b1101) @result{} #t
1415 (logbit? 1 #b1101) @result{} #f
1416 (logbit? 2 #b1101) @result{} #t
1417 (logbit? 3 #b1101) @result{} #t
1418 (logbit? 4 #b1101) @result{} #f
1422 @deffn {Scheme Procedure} ash n cnt
1423 @deffnx {C Function} scm_ash (n, cnt)
1424 Return @var{n} shifted left by @var{cnt} bits, or shifted right if
1425 @var{cnt} is negative. This is an ``arithmetic'' shift.
1427 This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and
1428 when @var{cnt} is negative it's a division, rounded towards negative
1429 infinity. (Note that this is not the same rounding as @code{quotient}
1432 With @var{n} viewed as an infinite precision twos complement,
1433 @code{ash} means a left shift introducing zero bits, or a right shift
1437 (number->string (ash #b1 3) 2) @result{} "1000"
1438 (number->string (ash #b1010 -1) 2) @result{} "101"
1440 ;; -23 is bits ...11101001, -6 is bits ...111010
1441 (ash -23 -2) @result{} -6
1445 @deffn {Scheme Procedure} logcount n
1446 @deffnx {C Function} scm_logcount (n)
1447 Return the number of bits in integer @var{n}. If @var{n} is
1448 positive, the 1-bits in its binary representation are counted.
1449 If negative, the 0-bits in its two's-complement binary
1450 representation are counted. If zero, 0 is returned.
1453 (logcount #b10101010)
1462 @deffn {Scheme Procedure} integer-length n
1463 @deffnx {C Function} scm_integer_length (n)
1464 Return the number of bits necessary to represent @var{n}.
1466 For positive @var{n} this is how many bits to the most significant one
1467 bit. For negative @var{n} it's how many bits to the most significant
1468 zero bit in twos complement form.
1471 (integer-length #b10101010) @result{} 8
1472 (integer-length #b1111) @result{} 4
1473 (integer-length 0) @result{} 0
1474 (integer-length -1) @result{} 0
1475 (integer-length -256) @result{} 8
1476 (integer-length -257) @result{} 9
1480 @deffn {Scheme Procedure} integer-expt n k
1481 @deffnx {C Function} scm_integer_expt (n, k)
1482 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1483 integer, @var{n} can be any number.
1485 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1486 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1490 (integer-expt 2 5) @result{} 32
1491 (integer-expt -3 3) @result{} -27
1492 (integer-expt 5 -3) @result{} 1/125
1493 (integer-expt 0 0) @result{} 1
1497 @deffn {Scheme Procedure} bit-extract n start end
1498 @deffnx {C Function} scm_bit_extract (n, start, end)
1499 Return the integer composed of the @var{start} (inclusive)
1500 through @var{end} (exclusive) bits of @var{n}. The
1501 @var{start}th bit becomes the 0-th bit in the result.
1504 (number->string (bit-extract #b1101101010 0 4) 2)
1506 (number->string (bit-extract #b1101101010 4 9) 2)
1513 @subsubsection Random Number Generation
1515 Pseudo-random numbers are generated from a random state object, which
1516 can be created with @code{seed->random-state}. The @var{state}
1517 parameter to the various functions below is optional, it defaults to
1518 the state object in the @code{*random-state*} variable.
1520 @deffn {Scheme Procedure} copy-random-state [state]
1521 @deffnx {C Function} scm_copy_random_state (state)
1522 Return a copy of the random state @var{state}.
1525 @deffn {Scheme Procedure} random n [state]
1526 @deffnx {C Function} scm_random (n, state)
1527 Return a number in [0, @var{n}).
1529 Accepts a positive integer or real n and returns a
1530 number of the same type between zero (inclusive) and
1531 @var{n} (exclusive). The values returned have a uniform
1535 @deffn {Scheme Procedure} random:exp [state]
1536 @deffnx {C Function} scm_random_exp (state)
1537 Return an inexact real in an exponential distribution with mean
1538 1. For an exponential distribution with mean @var{u} use @code{(*
1539 @var{u} (random:exp))}.
1542 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1543 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1544 Fills @var{vect} with inexact real random numbers the sum of whose
1545 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1546 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1547 the coordinates are uniformly distributed over the surface of the unit
1551 @deffn {Scheme Procedure} random:normal [state]
1552 @deffnx {C Function} scm_random_normal (state)
1553 Return an inexact real in a normal distribution. The distribution
1554 used has mean 0 and standard deviation 1. For a normal distribution
1555 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1556 (* @var{d} (random:normal)))}.
1559 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1560 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1561 Fills @var{vect} with inexact real random numbers that are
1562 independent and standard normally distributed
1563 (i.e., with mean 0 and variance 1).
1566 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1567 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1568 Fills @var{vect} with inexact real random numbers the sum of whose
1569 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1570 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1571 the coordinates are uniformly distributed within the unit
1573 @c FIXME: What does this mean, particularly the n-sphere part?
1576 @deffn {Scheme Procedure} random:uniform [state]
1577 @deffnx {C Function} scm_random_uniform (state)
1578 Return a uniformly distributed inexact real random number in
1582 @deffn {Scheme Procedure} seed->random-state seed
1583 @deffnx {C Function} scm_seed_to_random_state (seed)
1584 Return a new random state using @var{seed}.
1587 @defvar *random-state*
1588 The global random state used by the above functions when the
1589 @var{state} parameter is not given.
1592 Note that the initial value of @code{*random-state*} is the same every
1593 time Guile starts up. Therefore, if you don't pass a @var{state}
1594 parameter to the above procedures, and you don't set
1595 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1596 @code{your-seed} is something that @emph{isn't} the same every time,
1597 you'll get the same sequence of ``random'' numbers on every run.
1599 For example, unless the relevant source code has changed, @code{(map
1600 random (cdr (iota 30)))}, if the first use of random numbers since
1601 Guile started up, will always give:
1604 (map random (cdr (iota 19)))
1606 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1609 To use the time of day as the random seed, you can use code like this:
1612 (let ((time (gettimeofday)))
1613 (set! *random-state*
1614 (seed->random-state (+ (car time)
1619 And then (depending on the time of day, of course):
1622 (map random (cdr (iota 19)))
1624 (0 0 1 0 2 4 5 4 5 5 9 3 10 1 8 3 14 17)
1627 For security applications, such as password generation, you should use
1628 more bits of seed. Otherwise an open source password generator could
1629 be attacked by guessing the seed@dots{} but that's a subject for
1634 @subsection Characters
1637 In Scheme, there is a data type to describe a single character.
1639 Defining what exactly a character @emph{is} can be more complicated
1640 than it seems. Guile follows the advice of R6RS and uses The Unicode
1641 Standard to help define what a character is. So, for Guile, a
1642 character is anything in the Unicode Character Database.
1645 @cindex Unicode code point
1647 The Unicode Character Database is basically a table of characters
1648 indexed using integers called 'code points'. Valid code points are in
1649 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1650 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1652 @cindex designated code point
1653 @cindex code point, designated
1655 Any code point that has been assigned to a character or that has
1656 otherwise been given a meaning by Unicode is called a 'designated code
1657 point'. Most of the designated code points, about 200,000 of them,
1658 indicate characters, accents or other combining marks that modify
1659 other characters, symbols, whitespace, and control characters. Some
1660 are not characters but indicators that suggest how to format or
1661 display neighboring characters.
1663 @cindex reserved code point
1664 @cindex code point, reserved
1666 If a code point is not a designated code point -- if it has not been
1667 assigned to a character by The Unicode Standard -- it is a 'reserved
1668 code point', meaning that they are reserved for future use. Most of
1669 the code points, about 800,000, are 'reserved code points'.
1671 By convention, a Unicode code point is written as
1672 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1673 this convenient notation is not valid code. Guile does not interpret
1674 ``U+XXXX'' as a character.
1676 In Scheme, a character literal is written as @code{#\@var{name}} where
1677 @var{name} is the name of the character that you want. Printable
1678 characters have their usual single character name; for example,
1679 @code{#\a} is a lower case @code{a}.
1681 Some of the code points are 'combining characters' that are not meant
1682 to be printed by themselves but are instead meant to modify the
1683 appearance of the previous character. For combining characters, an
1684 alternate form of the character literal is @code{#\} followed by
1685 U+25CC (a small, dotted circle), followed by the combining character.
1686 This allows the combining character to be drawn on the circle, not on
1687 the backslash of @code{#\}.
1689 Many of the non-printing characters, such as whitespace characters and
1690 control characters, also have names.
1692 The most commonly used non-printing characters are space and
1693 newline. Their character names are @code{#\space} and
1694 @code{#\newline}. There are also names for all of the ``C0 control
1695 characters'' (those with code points below 32). The following table
1696 describes the names for each character.
1698 @multitable @columnfractions .25 .25 .25 .25
1699 @item 0 = @code{#\nul}
1700 @tab 1 = @code{#\soh}
1701 @tab 2 = @code{#\stx}
1702 @tab 3 = @code{#\etx}
1703 @item 4 = @code{#\eot}
1704 @tab 5 = @code{#\enq}
1705 @tab 6 = @code{#\ack}
1706 @tab 7 = @code{#\bel}
1707 @item 8 = @code{#\bs}
1708 @tab 9 = @code{#\ht}
1709 @tab 10 = @code{#\lf}
1710 @tab 11 = @code{#\vt}
1711 @item 12 = @code{#\ff}
1712 @tab 13 = @code{#\cr}
1713 @tab 14 = @code{#\so}
1714 @tab 15 = @code{#\si}
1715 @item 16 = @code{#\dle}
1716 @tab 17 = @code{#\dc1}
1717 @tab 18 = @code{#\dc2}
1718 @tab 19 = @code{#\dc3}
1719 @item 20 = @code{#\dc4}
1720 @tab 21 = @code{#\nak}
1721 @tab 22 = @code{#\syn}
1722 @tab 23 = @code{#\etb}
1723 @item 24 = @code{#\can}
1724 @tab 25 = @code{#\em}
1725 @tab 26 = @code{#\sub}
1726 @tab 27 = @code{#\esc}
1727 @item 28 = @code{#\fs}
1728 @tab 29 = @code{#\gs}
1729 @tab 30 = @code{#\rs}
1730 @tab 31 = @code{#\us}
1731 @item 32 = @code{#\sp}
1734 The ``delete'' character (code point U+007F) may be referred to with the
1737 One might note that the space character has two names --
1738 @code{#\space} and @code{#\sp} -- as does the newline character.
1739 Several other non-printing characters have more than one name, for the
1740 sake of compatibility with previous versions.
1742 @multitable {@code{#\backspace}} {Preferred}
1743 @item Alternate @tab Standard
1744 @item @code{#\sp} @tab @code{#\space}
1745 @item @code{#\nl} @tab @code{#\newline}
1746 @item @code{#\lf} @tab @code{#\newline}
1747 @item @code{#\tab} @tab @code{#\ht}
1748 @item @code{#\backspace} @tab @code{#\bs}
1749 @item @code{#\return} @tab @code{#\cr}
1750 @item @code{#\page} @tab @code{#\ff}
1751 @item @code{#\np} @tab @code{#\ff}
1752 @item @code{#\null} @tab @code{#\nul}
1755 Characters may also be written using their code point values. They can
1756 be written with as an octal number, such as @code{#\10} for
1757 @code{#\bs} or @code{#\177} for @code{#\del}.
1760 @deffn {Scheme Procedure} char? x
1761 @deffnx {C Function} scm_char_p (x)
1762 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1765 Fundamentally, the character comparison operations below are
1766 numeric comparisons of the character's code points.
1769 @deffn {Scheme Procedure} char=? x y
1770 Return @code{#t} iff code point of @var{x} is equal to the code point
1771 of @var{y}, else @code{#f}.
1775 @deffn {Scheme Procedure} char<? x y
1776 Return @code{#t} iff the code point of @var{x} is less than the code
1777 point of @var{y}, else @code{#f}.
1781 @deffn {Scheme Procedure} char<=? x y
1782 Return @code{#t} iff the code point of @var{x} is less than or equal
1783 to the code point of @var{y}, else @code{#f}.
1787 @deffn {Scheme Procedure} char>? x y
1788 Return @code{#t} iff the code point of @var{x} is greater than the
1789 code point of @var{y}, else @code{#f}.
1793 @deffn {Scheme Procedure} char>=? x y
1794 Return @code{#t} iff the code point of @var{x} is greater than or
1795 equal to the code point of @var{y}, else @code{#f}.
1798 @cindex case folding
1800 Case-insensitive character comparisons use @emph{Unicode case
1801 folding}. In case folding comparisons, if a character is lowercase
1802 and has an uppercase form that can be expressed as a single character,
1803 it is converted to uppercase before comparison. All other characters
1804 undergo no conversion before the comparison occurs. This includes the
1805 German sharp S (Eszett) which is not uppercased before conversion
1806 because its uppercase form has two characters. Unicode case folding
1807 is language independent: it uses rules that are generally true, but,
1808 it cannot cover all cases for all languages.
1811 @deffn {Scheme Procedure} char-ci=? x y
1812 Return @code{#t} iff the case-folded code point of @var{x} is the same
1813 as the case-folded code point of @var{y}, else @code{#f}.
1817 @deffn {Scheme Procedure} char-ci<? x y
1818 Return @code{#t} iff the case-folded code point of @var{x} is less
1819 than the case-folded code point of @var{y}, else @code{#f}.
1823 @deffn {Scheme Procedure} char-ci<=? x y
1824 Return @code{#t} iff the case-folded code point of @var{x} is less
1825 than or equal to the case-folded code point of @var{y}, else
1830 @deffn {Scheme Procedure} char-ci>? x y
1831 Return @code{#t} iff the case-folded code point of @var{x} is greater
1832 than the case-folded code point of @var{y}, else @code{#f}.
1836 @deffn {Scheme Procedure} char-ci>=? x y
1837 Return @code{#t} iff the case-folded code point of @var{x} is greater
1838 than or equal to the case-folded code point of @var{y}, else
1842 @rnindex char-alphabetic?
1843 @deffn {Scheme Procedure} char-alphabetic? chr
1844 @deffnx {C Function} scm_char_alphabetic_p (chr)
1845 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1848 @rnindex char-numeric?
1849 @deffn {Scheme Procedure} char-numeric? chr
1850 @deffnx {C Function} scm_char_numeric_p (chr)
1851 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1854 @rnindex char-whitespace?
1855 @deffn {Scheme Procedure} char-whitespace? chr
1856 @deffnx {C Function} scm_char_whitespace_p (chr)
1857 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1860 @rnindex char-upper-case?
1861 @deffn {Scheme Procedure} char-upper-case? chr
1862 @deffnx {C Function} scm_char_upper_case_p (chr)
1863 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1866 @rnindex char-lower-case?
1867 @deffn {Scheme Procedure} char-lower-case? chr
1868 @deffnx {C Function} scm_char_lower_case_p (chr)
1869 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1872 @deffn {Scheme Procedure} char-is-both? chr
1873 @deffnx {C Function} scm_char_is_both_p (chr)
1874 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
1878 @rnindex char->integer
1879 @deffn {Scheme Procedure} char->integer chr
1880 @deffnx {C Function} scm_char_to_integer (chr)
1881 Return the code point of @var{chr}.
1884 @rnindex integer->char
1885 @deffn {Scheme Procedure} integer->char n
1886 @deffnx {C Function} scm_integer_to_char (n)
1887 Return the character that has code point @var{n}. The integer @var{n}
1888 must be a valid code point. Valid code points are in the ranges 0 to
1889 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
1892 @rnindex char-upcase
1893 @deffn {Scheme Procedure} char-upcase chr
1894 @deffnx {C Function} scm_char_upcase (chr)
1895 Return the uppercase character version of @var{chr}.
1898 @rnindex char-downcase
1899 @deffn {Scheme Procedure} char-downcase chr
1900 @deffnx {C Function} scm_char_downcase (chr)
1901 Return the lowercase character version of @var{chr}.
1904 @rnindex char-titlecase
1905 @deffn {Scheme Procedure} char-titlecase chr
1906 @deffnx {C Function} scm_char_titlecase (chr)
1907 Return the titlecase character version of @var{chr} if one exists;
1908 otherwise return the uppercase version.
1910 For most characters these will be the same, but the Unicode Standard
1911 includes certain digraph compatibility characters, such as @code{U+01F3}
1912 ``dz'', for which the uppercase and titlecase characters are different
1913 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
1917 @node Character Sets
1918 @subsection Character Sets
1920 The features described in this section correspond directly to SRFI-14.
1922 The data type @dfn{charset} implements sets of characters
1923 (@pxref{Characters}). Because the internal representation of
1924 character sets is not visible to the user, a lot of procedures for
1925 handling them are provided.
1927 Character sets can be created, extended, tested for the membership of a
1928 characters and be compared to other character sets.
1931 * Character Set Predicates/Comparison::
1932 * Iterating Over Character Sets:: Enumerate charset elements.
1933 * Creating Character Sets:: Making new charsets.
1934 * Querying Character Sets:: Test charsets for membership etc.
1935 * Character-Set Algebra:: Calculating new charsets.
1936 * Standard Character Sets:: Variables containing predefined charsets.
1939 @node Character Set Predicates/Comparison
1940 @subsubsection Character Set Predicates/Comparison
1942 Use these procedures for testing whether an object is a character set,
1943 or whether several character sets are equal or subsets of each other.
1944 @code{char-set-hash} can be used for calculating a hash value, maybe for
1945 usage in fast lookup procedures.
1947 @deffn {Scheme Procedure} char-set? obj
1948 @deffnx {C Function} scm_char_set_p (obj)
1949 Return @code{#t} if @var{obj} is a character set, @code{#f}
1953 @deffn {Scheme Procedure} char-set= . char_sets
1954 @deffnx {C Function} scm_char_set_eq (char_sets)
1955 Return @code{#t} if all given character sets are equal.
1958 @deffn {Scheme Procedure} char-set<= . char_sets
1959 @deffnx {C Function} scm_char_set_leq (char_sets)
1960 Return @code{#t} if every character set @var{cs}i is a subset
1961 of character set @var{cs}i+1.
1964 @deffn {Scheme Procedure} char-set-hash cs [bound]
1965 @deffnx {C Function} scm_char_set_hash (cs, bound)
1966 Compute a hash value for the character set @var{cs}. If
1967 @var{bound} is given and non-zero, it restricts the
1968 returned value to the range 0 @dots{} @var{bound - 1}.
1971 @c ===================================================================
1973 @node Iterating Over Character Sets
1974 @subsubsection Iterating Over Character Sets
1976 Character set cursors are a means for iterating over the members of a
1977 character sets. After creating a character set cursor with
1978 @code{char-set-cursor}, a cursor can be dereferenced with
1979 @code{char-set-ref}, advanced to the next member with
1980 @code{char-set-cursor-next}. Whether a cursor has passed past the last
1981 element of the set can be checked with @code{end-of-char-set?}.
1983 Additionally, mapping and (un-)folding procedures for character sets are
1986 @deffn {Scheme Procedure} char-set-cursor cs
1987 @deffnx {C Function} scm_char_set_cursor (cs)
1988 Return a cursor into the character set @var{cs}.
1991 @deffn {Scheme Procedure} char-set-ref cs cursor
1992 @deffnx {C Function} scm_char_set_ref (cs, cursor)
1993 Return the character at the current cursor position
1994 @var{cursor} in the character set @var{cs}. It is an error to
1995 pass a cursor for which @code{end-of-char-set?} returns true.
1998 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
1999 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2000 Advance the character set cursor @var{cursor} to the next
2001 character in the character set @var{cs}. It is an error if the
2002 cursor given satisfies @code{end-of-char-set?}.
2005 @deffn {Scheme Procedure} end-of-char-set? cursor
2006 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2007 Return @code{#t} if @var{cursor} has reached the end of a
2008 character set, @code{#f} otherwise.
2011 @deffn {Scheme Procedure} char-set-fold kons knil cs
2012 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2013 Fold the procedure @var{kons} over the character set @var{cs},
2014 initializing it with @var{knil}.
2017 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2018 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2019 This is a fundamental constructor for character sets.
2021 @item @var{g} is used to generate a series of ``seed'' values
2022 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2023 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2024 @item @var{p} tells us when to stop -- when it returns true
2025 when applied to one of the seed values.
2026 @item @var{f} maps each seed value to a character. These
2027 characters are added to the base character set @var{base_cs} to
2028 form the result; @var{base_cs} defaults to the empty set.
2032 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2033 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2034 This is a fundamental constructor for character sets.
2036 @item @var{g} is used to generate a series of ``seed'' values
2037 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2038 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2039 @item @var{p} tells us when to stop -- when it returns true
2040 when applied to one of the seed values.
2041 @item @var{f} maps each seed value to a character. These
2042 characters are added to the base character set @var{base_cs} to
2043 form the result; @var{base_cs} defaults to the empty set.
2047 @deffn {Scheme Procedure} char-set-for-each proc cs
2048 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2049 Apply @var{proc} to every character in the character set
2050 @var{cs}. The return value is not specified.
2053 @deffn {Scheme Procedure} char-set-map proc cs
2054 @deffnx {C Function} scm_char_set_map (proc, cs)
2055 Map the procedure @var{proc} over every character in @var{cs}.
2056 @var{proc} must be a character -> character procedure.
2059 @c ===================================================================
2061 @node Creating Character Sets
2062 @subsubsection Creating Character Sets
2064 New character sets are produced with these procedures.
2066 @deffn {Scheme Procedure} char-set-copy cs
2067 @deffnx {C Function} scm_char_set_copy (cs)
2068 Return a newly allocated character set containing all
2069 characters in @var{cs}.
2072 @deffn {Scheme Procedure} char-set . rest
2073 @deffnx {C Function} scm_char_set (rest)
2074 Return a character set containing all given characters.
2077 @deffn {Scheme Procedure} list->char-set list [base_cs]
2078 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2079 Convert the character list @var{list} to a character set. If
2080 the character set @var{base_cs} is given, the character in this
2081 set are also included in the result.
2084 @deffn {Scheme Procedure} list->char-set! list base_cs
2085 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2086 Convert the character list @var{list} to a character set. The
2087 characters are added to @var{base_cs} and @var{base_cs} is
2091 @deffn {Scheme Procedure} string->char-set str [base_cs]
2092 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2093 Convert the string @var{str} to a character set. If the
2094 character set @var{base_cs} is given, the characters in this
2095 set are also included in the result.
2098 @deffn {Scheme Procedure} string->char-set! str base_cs
2099 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2100 Convert the string @var{str} to a character set. The
2101 characters from the string are added to @var{base_cs}, and
2102 @var{base_cs} is returned.
2105 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2106 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2107 Return a character set containing every character from @var{cs}
2108 so that it satisfies @var{pred}. If provided, the characters
2109 from @var{base_cs} are added to the result.
2112 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2113 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2114 Return a character set containing every character from @var{cs}
2115 so that it satisfies @var{pred}. The characters are added to
2116 @var{base_cs} and @var{base_cs} is returned.
2119 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2120 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2121 Return a character set containing all characters whose
2122 character codes lie in the half-open range
2123 [@var{lower},@var{upper}).
2125 If @var{error} is a true value, an error is signalled if the
2126 specified range contains characters which are not contained in
2127 the implemented character range. If @var{error} is @code{#f},
2128 these characters are silently left out of the resulting
2131 The characters in @var{base_cs} are added to the result, if
2135 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2136 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2137 Return a character set containing all characters whose
2138 character codes lie in the half-open range
2139 [@var{lower},@var{upper}).
2141 If @var{error} is a true value, an error is signalled if the
2142 specified range contains characters which are not contained in
2143 the implemented character range. If @var{error} is @code{#f},
2144 these characters are silently left out of the resulting
2147 The characters are added to @var{base_cs} and @var{base_cs} is
2151 @deffn {Scheme Procedure} ->char-set x
2152 @deffnx {C Function} scm_to_char_set (x)
2153 Coerces x into a char-set. @var{x} may be a string, character or
2154 char-set. A string is converted to the set of its constituent
2155 characters; a character is converted to a singleton set; a char-set is
2159 @c ===================================================================
2161 @node Querying Character Sets
2162 @subsubsection Querying Character Sets
2164 Access the elements and other information of a character set with these
2167 @deffn {Scheme Procedure} %char-set-dump cs
2168 Returns an association list containing debugging information
2169 for @var{cs}. The association list has the following entries.
2174 The number of groups of contiguous code points the char-set
2177 A list of lists where each sublist is a range of code points
2178 and their associated characters
2180 The return value of this function cannot be relied upon to be
2181 consistent between versions of Guile and should not be used in code.
2184 @deffn {Scheme Procedure} char-set-size cs
2185 @deffnx {C Function} scm_char_set_size (cs)
2186 Return the number of elements in character set @var{cs}.
2189 @deffn {Scheme Procedure} char-set-count pred cs
2190 @deffnx {C Function} scm_char_set_count (pred, cs)
2191 Return the number of the elements int the character set
2192 @var{cs} which satisfy the predicate @var{pred}.
2195 @deffn {Scheme Procedure} char-set->list cs
2196 @deffnx {C Function} scm_char_set_to_list (cs)
2197 Return a list containing the elements of the character set
2201 @deffn {Scheme Procedure} char-set->string cs
2202 @deffnx {C Function} scm_char_set_to_string (cs)
2203 Return a string containing the elements of the character set
2204 @var{cs}. The order in which the characters are placed in the
2205 string is not defined.
2208 @deffn {Scheme Procedure} char-set-contains? cs ch
2209 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2210 Return @code{#t} iff the character @var{ch} is contained in the
2211 character set @var{cs}.
2214 @deffn {Scheme Procedure} char-set-every pred cs
2215 @deffnx {C Function} scm_char_set_every (pred, cs)
2216 Return a true value if every character in the character set
2217 @var{cs} satisfies the predicate @var{pred}.
2220 @deffn {Scheme Procedure} char-set-any pred cs
2221 @deffnx {C Function} scm_char_set_any (pred, cs)
2222 Return a true value if any character in the character set
2223 @var{cs} satisfies the predicate @var{pred}.
2226 @c ===================================================================
2228 @node Character-Set Algebra
2229 @subsubsection Character-Set Algebra
2231 Character sets can be manipulated with the common set algebra operation,
2232 such as union, complement, intersection etc. All of these procedures
2233 provide side-effecting variants, which modify their character set
2236 @deffn {Scheme Procedure} char-set-adjoin cs . rest
2237 @deffnx {C Function} scm_char_set_adjoin (cs, rest)
2238 Add all character arguments to the first argument, which must
2242 @deffn {Scheme Procedure} char-set-delete cs . rest
2243 @deffnx {C Function} scm_char_set_delete (cs, rest)
2244 Delete all character arguments from the first argument, which
2245 must be a character set.
2248 @deffn {Scheme Procedure} char-set-adjoin! cs . rest
2249 @deffnx {C Function} scm_char_set_adjoin_x (cs, rest)
2250 Add all character arguments to the first argument, which must
2254 @deffn {Scheme Procedure} char-set-delete! cs . rest
2255 @deffnx {C Function} scm_char_set_delete_x (cs, rest)
2256 Delete all character arguments from the first argument, which
2257 must be a character set.
2260 @deffn {Scheme Procedure} char-set-complement cs
2261 @deffnx {C Function} scm_char_set_complement (cs)
2262 Return the complement of the character set @var{cs}.
2265 Note that the complement of a character set is likely to contain many
2266 reserved code points (code points that are not associated with
2267 characters). It may be helpful to modify the output of
2268 @code{char-set-complement} by computing its intersection with the set
2269 of designated code points, @code{char-set:designated}.
2271 @deffn {Scheme Procedure} char-set-union . rest
2272 @deffnx {C Function} scm_char_set_union (rest)
2273 Return the union of all argument character sets.
2276 @deffn {Scheme Procedure} char-set-intersection . rest
2277 @deffnx {C Function} scm_char_set_intersection (rest)
2278 Return the intersection of all argument character sets.
2281 @deffn {Scheme Procedure} char-set-difference cs1 . rest
2282 @deffnx {C Function} scm_char_set_difference (cs1, rest)
2283 Return the difference of all argument character sets.
2286 @deffn {Scheme Procedure} char-set-xor . rest
2287 @deffnx {C Function} scm_char_set_xor (rest)
2288 Return the exclusive-or of all argument character sets.
2291 @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest
2292 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest)
2293 Return the difference and the intersection of all argument
2297 @deffn {Scheme Procedure} char-set-complement! cs
2298 @deffnx {C Function} scm_char_set_complement_x (cs)
2299 Return the complement of the character set @var{cs}.
2302 @deffn {Scheme Procedure} char-set-union! cs1 . rest
2303 @deffnx {C Function} scm_char_set_union_x (cs1, rest)
2304 Return the union of all argument character sets.
2307 @deffn {Scheme Procedure} char-set-intersection! cs1 . rest
2308 @deffnx {C Function} scm_char_set_intersection_x (cs1, rest)
2309 Return the intersection of all argument character sets.
2312 @deffn {Scheme Procedure} char-set-difference! cs1 . rest
2313 @deffnx {C Function} scm_char_set_difference_x (cs1, rest)
2314 Return the difference of all argument character sets.
2317 @deffn {Scheme Procedure} char-set-xor! cs1 . rest
2318 @deffnx {C Function} scm_char_set_xor_x (cs1, rest)
2319 Return the exclusive-or of all argument character sets.
2322 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest
2323 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest)
2324 Return the difference and the intersection of all argument
2328 @c ===================================================================
2330 @node Standard Character Sets
2331 @subsubsection Standard Character Sets
2333 In order to make the use of the character set data type and procedures
2334 useful, several predefined character set variables exist.
2340 These character sets are locale independent and are not recomputed
2341 upon a @code{setlocale} call. They contain characters from the whole
2342 range of Unicode code points. For instance, @code{char-set:letter}
2343 contains about 94,000 characters.
2345 @defvr {Scheme Variable} char-set:lower-case
2346 @defvrx {C Variable} scm_char_set_lower_case
2347 All lower-case characters.
2350 @defvr {Scheme Variable} char-set:upper-case
2351 @defvrx {C Variable} scm_char_set_upper_case
2352 All upper-case characters.
2355 @defvr {Scheme Variable} char-set:title-case
2356 @defvrx {C Variable} scm_char_set_title_case
2357 All single characters that function as if they were an upper-case
2358 letter followed by a lower-case letter.
2361 @defvr {Scheme Variable} char-set:letter
2362 @defvrx {C Variable} scm_char_set_letter
2363 All letters. This includes @code{char-set:lower-case},
2364 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2365 letters that have no case at all. For example, Chinese and Japanese
2366 characters typically have no concept of case.
2369 @defvr {Scheme Variable} char-set:digit
2370 @defvrx {C Variable} scm_char_set_digit
2374 @defvr {Scheme Variable} char-set:letter+digit
2375 @defvrx {C Variable} scm_char_set_letter_and_digit
2376 The union of @code{char-set:letter} and @code{char-set:digit}.
2379 @defvr {Scheme Variable} char-set:graphic
2380 @defvrx {C Variable} scm_char_set_graphic
2381 All characters which would put ink on the paper.
2384 @defvr {Scheme Variable} char-set:printing
2385 @defvrx {C Variable} scm_char_set_printing
2386 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2389 @defvr {Scheme Variable} char-set:whitespace
2390 @defvrx {C Variable} scm_char_set_whitespace
2391 All whitespace characters.
2394 @defvr {Scheme Variable} char-set:blank
2395 @defvrx {C Variable} scm_char_set_blank
2396 All horizontal whitespace characters, which notably includes
2397 @code{#\space} and @code{#\tab}.
2400 @defvr {Scheme Variable} char-set:iso-control
2401 @defvrx {C Variable} scm_char_set_iso_control
2402 The ISO control characters are the C0 control characters (U+0000 to
2403 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2407 @defvr {Scheme Variable} char-set:punctuation
2408 @defvrx {C Variable} scm_char_set_punctuation
2409 All punctuation characters, such as the characters
2410 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2413 @defvr {Scheme Variable} char-set:symbol
2414 @defvrx {C Variable} scm_char_set_symbol
2415 All symbol characters, such as the characters @code{$+<=>^`|~}.
2418 @defvr {Scheme Variable} char-set:hex-digit
2419 @defvrx {C Variable} scm_char_set_hex_digit
2420 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2423 @defvr {Scheme Variable} char-set:ascii
2424 @defvrx {C Variable} scm_char_set_ascii
2425 All ASCII characters.
2428 @defvr {Scheme Variable} char-set:empty
2429 @defvrx {C Variable} scm_char_set_empty
2430 The empty character set.
2433 @defvr {Scheme Variable} char-set:designated
2434 @defvrx {C Variable} scm_char_set_designated
2435 This character set contains all designated code points. This includes
2436 all the code points to which Unicode has assigned a character or other
2440 @defvr {Scheme Variable} char-set:full
2441 @defvrx {C Variable} scm_char_set_full
2442 This character set contains all possible code points. This includes
2443 both designated and reserved code points.
2450 Strings are fixed-length sequences of characters. They can be created
2451 by calling constructor procedures, but they can also literally get
2452 entered at the @acronym{REPL} or in Scheme source files.
2454 @c Guile provides a rich set of string processing procedures, because text
2455 @c handling is very important when Guile is used as a scripting language.
2457 Strings always carry the information about how many characters they are
2458 composed of with them, so there is no special end-of-string character,
2459 like in C. That means that Scheme strings can contain any character,
2460 even the @samp{#\nul} character @samp{\0}.
2462 To use strings efficiently, you need to know a bit about how Guile
2463 implements them. In Guile, a string consists of two parts, a head and
2464 the actual memory where the characters are stored. When a string (or
2465 a substring of it) is copied, only a new head gets created, the memory
2466 is usually not copied. The two heads start out pointing to the same
2469 When one of these two strings is modified, as with @code{string-set!},
2470 their common memory does get copied so that each string has its own
2471 memory and modifying one does not accidentally modify the other as well.
2472 Thus, Guile's strings are `copy on write'; the actual copying of their
2473 memory is delayed until one string is written to.
2475 This implementation makes functions like @code{substring} very
2476 efficient in the common case that no modifications are done to the
2479 If you do know that your strings are getting modified right away, you
2480 can use @code{substring/copy} instead of @code{substring}. This
2481 function performs the copy immediately at the time of creation. This
2482 is more efficient, especially in a multi-threaded program. Also,
2483 @code{substring/copy} can avoid the problem that a short substring
2484 holds on to the memory of a very large original string that could
2485 otherwise be recycled.
2487 If you want to avoid the copy altogether, so that modifications of one
2488 string show up in the other, you can use @code{substring/shared}. The
2489 strings created by this procedure are called @dfn{mutation sharing
2490 substrings} since the substring and the original string share
2491 modifications to each other.
2493 If you want to prevent modifications, use @code{substring/read-only}.
2495 Guile provides all procedures of SRFI-13 and a few more.
2498 * String Syntax:: Read syntax for strings.
2499 * String Predicates:: Testing strings for certain properties.
2500 * String Constructors:: Creating new string objects.
2501 * List/String Conversion:: Converting from/to lists of characters.
2502 * String Selection:: Select portions from strings.
2503 * String Modification:: Modify parts or whole strings.
2504 * String Comparison:: Lexicographic ordering predicates.
2505 * String Searching:: Searching in strings.
2506 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2507 * Reversing and Appending Strings:: Appending strings to form a new string.
2508 * Mapping Folding and Unfolding:: Iterating over strings.
2509 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2510 * Conversion to/from C::
2514 @subsubsection String Read Syntax
2516 @c In the following @code is used to get a good font in TeX etc, but
2517 @c is omitted for Info format, so as not to risk any confusion over
2518 @c whether surrounding ` ' quotes are part of the escape or are
2519 @c special in a string (they're not).
2521 The read syntax for strings is an arbitrarily long sequence of
2522 characters enclosed in double quotes (@nicode{"}).
2524 Backslash is an escape character and can be used to insert the
2525 following special characters. @nicode{\"} and @nicode{\\} are R5RS
2526 standard, the rest are Guile extensions, notice they follow C string
2531 Backslash character.
2534 Double quote character (an unescaped @nicode{"} is otherwise the end
2538 NUL character (ASCII 0).
2541 Bell character (ASCII 7).
2544 Formfeed character (ASCII 12).
2547 Newline character (ASCII 10).
2550 Carriage return character (ASCII 13).
2553 Tab character (ASCII 9).
2556 Vertical tab character (ASCII 11).
2559 Character code given by two hexadecimal digits. For example
2560 @nicode{\x7f} for an ASCII DEL (127).
2562 @item @nicode{\uHHHH}
2563 Character code given by four hexadecimal digits. For example
2564 @nicode{\u0100} for a capital A with macron (U+0100).
2566 @item @nicode{\UHHHHHH}
2567 Character code given by six hexadecimal digits. For example
2572 The following are examples of string literals:
2582 @node String Predicates
2583 @subsubsection String Predicates
2585 The following procedures can be used to check whether a given string
2586 fulfills some specified property.
2589 @deffn {Scheme Procedure} string? obj
2590 @deffnx {C Function} scm_string_p (obj)
2591 Return @code{#t} if @var{obj} is a string, else @code{#f}.
2594 @deftypefn {C Function} int scm_is_string (SCM obj)
2595 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
2598 @deffn {Scheme Procedure} string-null? str
2599 @deffnx {C Function} scm_string_null_p (str)
2600 Return @code{#t} if @var{str}'s length is zero, and
2601 @code{#f} otherwise.
2603 (string-null? "") @result{} #t
2605 (string-null? y) @result{} #f
2609 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
2610 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
2611 Check if @var{char_pred} is true for any character in string @var{s}.
2613 @var{char_pred} can be a character to check for any equal to that, or
2614 a character set (@pxref{Character Sets}) to check for any in that set,
2615 or a predicate procedure to call.
2617 For a procedure, calls @code{(@var{char_pred} c)} are made
2618 successively on the characters from @var{start} to @var{end}. If
2619 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
2620 stops and that return value is the return from @code{string-any}. The
2621 call on the last character (ie.@: at @math{@var{end}-1}), if that
2622 point is reached, is a tail call.
2624 If there are no characters in @var{s} (ie.@: @var{start} equals
2625 @var{end}) then the return is @code{#f}.
2628 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
2629 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
2630 Check if @var{char_pred} is true for every character in string
2633 @var{char_pred} can be a character to check for every character equal
2634 to that, or a character set (@pxref{Character Sets}) to check for
2635 every character being in that set, or a predicate procedure to call.
2637 For a procedure, calls @code{(@var{char_pred} c)} are made
2638 successively on the characters from @var{start} to @var{end}. If
2639 @var{char_pred} returns @code{#f}, @code{string-every} stops and
2640 returns @code{#f}. The call on the last character (ie.@: at
2641 @math{@var{end}-1}), if that point is reached, is a tail call and the
2642 return from that call is the return from @code{string-every}.
2644 If there are no characters in @var{s} (ie.@: @var{start} equals
2645 @var{end}) then the return is @code{#t}.
2648 @node String Constructors
2649 @subsubsection String Constructors
2651 The string constructor procedures create new string objects, possibly
2652 initializing them with some specified character data. See also
2653 @xref{String Selection}, for ways to create strings from existing
2656 @c FIXME::martin: list->string belongs into `List/String Conversion'
2658 @deffn {Scheme Procedure} string char@dots{}
2660 Return a newly allocated string made from the given character
2664 (string #\x #\y #\z) @result{} "xyz"
2665 (string) @result{} ""
2669 @deffn {Scheme Procedure} list->string lst
2670 @deffnx {C Function} scm_string (lst)
2671 @rnindex list->string
2672 Return a newly allocated string made from a list of characters.
2675 (list->string '(#\a #\b #\c)) @result{} "abc"
2679 @deffn {Scheme Procedure} reverse-list->string lst
2680 @deffnx {C Function} scm_reverse_list_to_string (lst)
2681 Return a newly allocated string made from a list of characters, in
2685 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
2689 @rnindex make-string
2690 @deffn {Scheme Procedure} make-string k [chr]
2691 @deffnx {C Function} scm_make_string (k, chr)
2692 Return a newly allocated string of
2693 length @var{k}. If @var{chr} is given, then all elements of
2694 the string are initialized to @var{chr}, otherwise the contents
2695 of the @var{string} are unspecified.
2698 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
2699 Like @code{scm_make_string}, but expects the length as a
2703 @deffn {Scheme Procedure} string-tabulate proc len
2704 @deffnx {C Function} scm_string_tabulate (proc, len)
2705 @var{proc} is an integer->char procedure. Construct a string
2706 of size @var{len} by applying @var{proc} to each index to
2707 produce the corresponding string element. The order in which
2708 @var{proc} is applied to the indices is not specified.
2711 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
2712 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
2713 Append the string in the string list @var{ls}, using the string
2714 @var{delim} as a delimiter between the elements of @var{ls}.
2715 @var{grammar} is a symbol which specifies how the delimiter is
2716 placed between the strings, and defaults to the symbol
2721 Insert the separator between list elements. An empty string
2722 will produce an empty list.
2724 Like @code{infix}, but will raise an error if given the empty
2727 Insert the separator after every list element.
2729 Insert the separator before each list element.
2733 @node List/String Conversion
2734 @subsubsection List/String conversion
2736 When processing strings, it is often convenient to first convert them
2737 into a list representation by using the procedure @code{string->list},
2738 work with the resulting list, and then convert it back into a string.
2739 These procedures are useful for similar tasks.
2741 @rnindex string->list
2742 @deffn {Scheme Procedure} string->list str [start [end]]
2743 @deffnx {C Function} scm_substring_to_list (str, start, end)
2744 @deffnx {C Function} scm_string_to_list (str)
2745 Convert the string @var{str} into a list of characters.
2748 @deffn {Scheme Procedure} string-split str chr
2749 @deffnx {C Function} scm_string_split (str, chr)
2750 Split the string @var{str} into the a list of the substrings delimited
2751 by appearances of the character @var{chr}. Note that an empty substring
2752 between separator characters will result in an empty string in the
2756 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
2758 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
2760 (string-split "::" #\:)
2764 (string-split "" #\:)
2771 @node String Selection
2772 @subsubsection String Selection
2774 Portions of strings can be extracted by these procedures.
2775 @code{string-ref} delivers individual characters whereas
2776 @code{substring} can be used to extract substrings from longer strings.
2778 @rnindex string-length
2779 @deffn {Scheme Procedure} string-length string
2780 @deffnx {C Function} scm_string_length (string)
2781 Return the number of characters in @var{string}.
2784 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
2785 Return the number of characters in @var{str} as a @code{size_t}.
2789 @deffn {Scheme Procedure} string-ref str k
2790 @deffnx {C Function} scm_string_ref (str, k)
2791 Return character @var{k} of @var{str} using zero-origin
2792 indexing. @var{k} must be a valid index of @var{str}.
2795 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
2796 Return character @var{k} of @var{str} using zero-origin
2797 indexing. @var{k} must be a valid index of @var{str}.
2800 @rnindex string-copy
2801 @deffn {Scheme Procedure} string-copy str [start [end]]
2802 @deffnx {C Function} scm_substring_copy (str, start, end)
2803 @deffnx {C Function} scm_string_copy (str)
2804 Return a copy of the given string @var{str}.
2806 The returned string shares storage with @var{str} initially, but it is
2807 copied as soon as one of the two strings is modified.
2811 @deffn {Scheme Procedure} substring str start [end]
2812 @deffnx {C Function} scm_substring (str, start, end)
2813 Return a new string formed from the characters
2814 of @var{str} beginning with index @var{start} (inclusive) and
2815 ending with index @var{end} (exclusive).
2816 @var{str} must be a string, @var{start} and @var{end} must be
2817 exact integers satisfying:
2819 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
2821 The returned string shares storage with @var{str} initially, but it is
2822 copied as soon as one of the two strings is modified.
2825 @deffn {Scheme Procedure} substring/shared str start [end]
2826 @deffnx {C Function} scm_substring_shared (str, start, end)
2827 Like @code{substring}, but the strings continue to share their storage
2828 even if they are modified. Thus, modifications to @var{str} show up
2829 in the new string, and vice versa.
2832 @deffn {Scheme Procedure} substring/copy str start [end]
2833 @deffnx {C Function} scm_substring_copy (str, start, end)
2834 Like @code{substring}, but the storage for the new string is copied
2838 @deffn {Scheme Procedure} substring/read-only str start [end]
2839 @deffnx {C Function} scm_substring_read_only (str, start, end)
2840 Like @code{substring}, but the resulting string can not be modified.
2843 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
2844 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
2845 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
2846 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
2847 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
2850 @deffn {Scheme Procedure} string-take s n
2851 @deffnx {C Function} scm_string_take (s, n)
2852 Return the @var{n} first characters of @var{s}.
2855 @deffn {Scheme Procedure} string-drop s n
2856 @deffnx {C Function} scm_string_drop (s, n)
2857 Return all but the first @var{n} characters of @var{s}.
2860 @deffn {Scheme Procedure} string-take-right s n
2861 @deffnx {C Function} scm_string_take_right (s, n)
2862 Return the @var{n} last characters of @var{s}.
2865 @deffn {Scheme Procedure} string-drop-right s n
2866 @deffnx {C Function} scm_string_drop_right (s, n)
2867 Return all but the last @var{n} characters of @var{s}.
2870 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
2871 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
2872 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
2873 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
2874 Take characters @var{start} to @var{end} from the string @var{s} and
2875 either pad with @var{char} or truncate them to give @var{len}
2878 @code{string-pad} pads or truncates on the left, so for example
2881 (string-pad "x" 3) @result{} " x"
2882 (string-pad "abcde" 3) @result{} "cde"
2885 @code{string-pad-right} pads or truncates on the right, so for example
2888 (string-pad-right "x" 3) @result{} "x "
2889 (string-pad-right "abcde" 3) @result{} "abc"
2893 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
2894 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
2895 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
2896 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
2897 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
2898 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
2899 Trim occurrences of @var{char_pred} from the ends of @var{s}.
2901 @code{string-trim} trims @var{char_pred} characters from the left
2902 (start) of the string, @code{string-trim-right} trims them from the
2903 right (end) of the string, @code{string-trim-both} trims from both
2906 @var{char_pred} can be a character, a character set, or a predicate
2907 procedure to call on each character. If @var{char_pred} is not given
2908 the default is whitespace as per @code{char-set:whitespace}
2909 (@pxref{Standard Character Sets}).
2912 (string-trim " x ") @result{} "x "
2913 (string-trim-right "banana" #\a) @result{} "banan"
2914 (string-trim-both ".,xy:;" char-set:punctuation)
2916 (string-trim-both "xyzzy" (lambda (c)
2923 @node String Modification
2924 @subsubsection String Modification
2926 These procedures are for modifying strings in-place. This means that the
2927 result of the operation is not a new string; instead, the original string's
2928 memory representation is modified.
2930 @rnindex string-set!
2931 @deffn {Scheme Procedure} string-set! str k chr
2932 @deffnx {C Function} scm_string_set_x (str, k, chr)
2933 Store @var{chr} in element @var{k} of @var{str} and return
2934 an unspecified value. @var{k} must be a valid index of
2938 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
2939 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
2942 @rnindex string-fill!
2943 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
2944 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
2945 @deffnx {C Function} scm_string_fill_x (str, chr)
2946 Stores @var{chr} in every element of the given @var{str} and
2947 returns an unspecified value.
2950 @deffn {Scheme Procedure} substring-fill! str start end fill
2951 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
2952 Change every character in @var{str} between @var{start} and
2953 @var{end} to @var{fill}.
2956 (define y "abcdefg")
2957 (substring-fill! y 1 3 #\r)
2963 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
2964 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
2965 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
2966 into @var{str2} beginning at position @var{start2}.
2967 @var{str1} and @var{str2} can be the same string.
2970 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
2971 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
2972 Copy the sequence of characters from index range [@var{start},
2973 @var{end}) in string @var{s} to string @var{target}, beginning
2974 at index @var{tstart}. The characters are copied left-to-right
2975 or right-to-left as needed -- the copy is guaranteed to work,
2976 even if @var{target} and @var{s} are the same string. It is an
2977 error if the copy operation runs off the end of the target
2982 @node String Comparison
2983 @subsubsection String Comparison
2985 The procedures in this section are similar to the character ordering
2986 predicates (@pxref{Characters}), but are defined on character sequences.
2988 The first set is specified in R5RS and has names that end in @code{?}.
2989 The second set is specified in SRFI-13 and the names have not ending
2992 The predicates ending in @code{-ci} ignore the character case
2993 when comparing strings. For now, case-insensitive comparison is done
2994 using the R5RS rules, where every lower-case character that has a
2995 single character upper-case form is converted to uppercase before
2996 comparison. See @xref{Text Collation, the @code{(ice-9
2997 i18n)} module}, for locale-dependent string comparison.
3000 @deffn {Scheme Procedure} string=? s1 s2
3001 Lexicographic equality predicate; return @code{#t} if the two
3002 strings are the same length and contain the same characters in
3003 the same positions, otherwise return @code{#f}.
3005 The procedure @code{string-ci=?} treats upper and lower case
3006 letters as though they were the same character, but
3007 @code{string=?} treats upper and lower case as distinct
3012 @deffn {Scheme Procedure} string<? s1 s2
3013 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3014 is lexicographically less than @var{s2}.
3018 @deffn {Scheme Procedure} string<=? s1 s2
3019 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3020 is lexicographically less than or equal to @var{s2}.
3024 @deffn {Scheme Procedure} string>? s1 s2
3025 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3026 is lexicographically greater than @var{s2}.
3030 @deffn {Scheme Procedure} string>=? s1 s2
3031 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3032 is lexicographically greater than or equal to @var{s2}.
3035 @rnindex string-ci=?
3036 @deffn {Scheme Procedure} string-ci=? s1 s2
3037 Case-insensitive string equality predicate; return @code{#t} if
3038 the two strings are the same length and their component
3039 characters match (ignoring case) at each position; otherwise
3043 @rnindex string-ci<?
3044 @deffn {Scheme Procedure} string-ci<? s1 s2
3045 Case insensitive lexicographic ordering predicate; return
3046 @code{#t} if @var{s1} is lexicographically less than @var{s2}
3051 @deffn {Scheme Procedure} string-ci<=? s1 s2
3052 Case insensitive lexicographic ordering predicate; return
3053 @code{#t} if @var{s1} is lexicographically less than or equal
3054 to @var{s2} regardless of case.
3057 @rnindex string-ci>?
3058 @deffn {Scheme Procedure} string-ci>? s1 s2
3059 Case insensitive lexicographic ordering predicate; return
3060 @code{#t} if @var{s1} is lexicographically greater than
3061 @var{s2} regardless of case.
3064 @rnindex string-ci>=?
3065 @deffn {Scheme Procedure} string-ci>=? s1 s2
3066 Case insensitive lexicographic ordering predicate; return
3067 @code{#t} if @var{s1} is lexicographically greater than or
3068 equal to @var{s2} regardless of case.
3071 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3072 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3073 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3074 mismatch index, depending upon whether @var{s1} is less than,
3075 equal to, or greater than @var{s2}. The mismatch index is the
3076 largest index @var{i} such that for every 0 <= @var{j} <
3077 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3078 @var{i} is the first position that does not match.
3081 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3082 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3083 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3084 mismatch index, depending upon whether @var{s1} is less than,
3085 equal to, or greater than @var{s2}. The mismatch index is the
3086 largest index @var{i} such that for every 0 <= @var{j} <
3087 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3088 @var{i} is the first position that does not match. The
3089 character comparison is done case-insensitively.
3092 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3093 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3094 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3098 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3099 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3100 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3104 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3105 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3106 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3107 true value otherwise.
3110 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3111 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3112 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3113 true value otherwise.
3116 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3117 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3118 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3122 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3123 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3124 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3128 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3129 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3130 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3131 value otherwise. The character comparison is done
3135 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3136 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3137 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3138 value otherwise. The character comparison is done
3142 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3143 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3144 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3145 true value otherwise. The character comparison is done
3149 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3150 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3151 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3152 true value otherwise. The character comparison is done
3156 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3157 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3158 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3159 value otherwise. The character comparison is done
3163 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3164 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3165 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3166 otherwise. The character comparison is done
3170 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3171 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3172 Compute a hash value for @var{S}. the optional argument @var{bound} is a non-negative exact integer specifying the range of the hash function. A positive value restricts the return value to the range [0,bound).
3175 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3176 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3177 Compute a hash value for @var{S}. the optional argument @var{bound} is a non-negative exact integer specifying the range of the hash function. A positive value restricts the return value to the range [0,bound).
3180 @node String Searching
3181 @subsubsection String Searching
3183 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3184 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3185 Search through the string @var{s} from left to right, returning
3186 the index of the first occurrence of a character which
3190 equals @var{char_pred}, if it is character,
3193 satisfies the predicate @var{char_pred}, if it is a procedure,
3196 is in the set @var{char_pred}, if it is a character set.
3200 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3201 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3202 Search through the string @var{s} from right to left, returning
3203 the index of the last occurrence of a character which
3207 equals @var{char_pred}, if it is character,
3210 satisfies the predicate @var{char_pred}, if it is a procedure,
3213 is in the set if @var{char_pred} is a character set.
3217 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3218 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3219 Return the length of the longest common prefix of the two
3223 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3224 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3225 Return the length of the longest common prefix of the two
3226 strings, ignoring character case.
3229 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3230 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3231 Return the length of the longest common suffix of the two
3235 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3236 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3237 Return the length of the longest common suffix of the two
3238 strings, ignoring character case.
3241 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3242 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3243 Is @var{s1} a prefix of @var{s2}?
3246 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3247 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3248 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3251 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3252 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3253 Is @var{s1} a suffix of @var{s2}?
3256 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3257 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3258 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3261 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3262 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3263 Search through the string @var{s} from right to left, returning
3264 the index of the last occurrence of a character which
3268 equals @var{char_pred}, if it is character,
3271 satisfies the predicate @var{char_pred}, if it is a procedure,
3274 is in the set if @var{char_pred} is a character set.
3278 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3279 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3280 Search through the string @var{s} from left to right, returning
3281 the index of the first occurrence of a character which
3285 does not equal @var{char_pred}, if it is character,
3288 does not satisfy the predicate @var{char_pred}, if it is a
3292 is not in the set if @var{char_pred} is a character set.
3296 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3297 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3298 Search through the string @var{s} from right to left, returning
3299 the index of the last occurrence of a character which
3303 does not equal @var{char_pred}, if it is character,
3306 does not satisfy the predicate @var{char_pred}, if it is a
3310 is not in the set if @var{char_pred} is a character set.
3314 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3315 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3316 Return the count of the number of characters in the string
3321 equals @var{char_pred}, if it is character,
3324 satisfies the predicate @var{char_pred}, if it is a procedure.
3327 is in the set @var{char_pred}, if it is a character set.
3331 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3332 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3333 Does string @var{s1} contain string @var{s2}? Return the index
3334 in @var{s1} where @var{s2} occurs as a substring, or false.
3335 The optional start/end indices restrict the operation to the
3336 indicated substrings.
3339 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3340 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3341 Does string @var{s1} contain string @var{s2}? Return the index
3342 in @var{s1} where @var{s2} occurs as a substring, or false.
3343 The optional start/end indices restrict the operation to the
3344 indicated substrings. Character comparison is done
3348 @node Alphabetic Case Mapping
3349 @subsubsection Alphabetic Case Mapping
3351 These are procedures for mapping strings to their upper- or lower-case
3352 equivalents, respectively, or for capitalizing strings.
3354 @deffn {Scheme Procedure} string-upcase str [start [end]]
3355 @deffnx {C Function} scm_substring_upcase (str, start, end)
3356 @deffnx {C Function} scm_string_upcase (str)
3357 Upcase every character in @code{str}.
3360 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3361 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3362 @deffnx {C Function} scm_string_upcase_x (str)
3363 Destructively upcase every character in @code{str}.
3373 @deffn {Scheme Procedure} string-downcase str [start [end]]
3374 @deffnx {C Function} scm_substring_downcase (str, start, end)
3375 @deffnx {C Function} scm_string_downcase (str)
3376 Downcase every character in @var{str}.
3379 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3380 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3381 @deffnx {C Function} scm_string_downcase_x (str)
3382 Destructively downcase every character in @var{str}.
3387 (string-downcase! y)
3394 @deffn {Scheme Procedure} string-capitalize str
3395 @deffnx {C Function} scm_string_capitalize (str)
3396 Return a freshly allocated string with the characters in
3397 @var{str}, where the first character of every word is
3401 @deffn {Scheme Procedure} string-capitalize! str
3402 @deffnx {C Function} scm_string_capitalize_x (str)
3403 Upcase the first character of every word in @var{str}
3404 destructively and return @var{str}.
3407 y @result{} "hello world"
3408 (string-capitalize! y) @result{} "Hello World"
3409 y @result{} "Hello World"
3413 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3414 @deffnx {C Function} scm_string_titlecase (str, start, end)
3415 Titlecase every first character in a word in @var{str}.
3418 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3419 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3420 Destructively titlecase every first character in a word in
3424 @node Reversing and Appending Strings
3425 @subsubsection Reversing and Appending Strings
3427 @deffn {Scheme Procedure} string-reverse str [start [end]]
3428 @deffnx {C Function} scm_string_reverse (str, start, end)
3429 Reverse the string @var{str}. The optional arguments
3430 @var{start} and @var{end} delimit the region of @var{str} to
3434 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3435 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3436 Reverse the string @var{str} in-place. The optional arguments
3437 @var{start} and @var{end} delimit the region of @var{str} to
3438 operate on. The return value is unspecified.
3441 @rnindex string-append
3442 @deffn {Scheme Procedure} string-append . args
3443 @deffnx {C Function} scm_string_append (args)
3444 Return a newly allocated string whose characters form the
3445 concatenation of the given strings, @var{args}.
3449 (string-append h "world"))
3450 @result{} "hello world"
3454 @deffn {Scheme Procedure} string-append/shared . ls
3455 @deffnx {C Function} scm_string_append_shared (ls)
3456 Like @code{string-append}, but the result may share memory
3457 with the argument strings.
3460 @deffn {Scheme Procedure} string-concatenate ls
3461 @deffnx {C Function} scm_string_concatenate (ls)
3462 Append the elements of @var{ls} (which must be strings)
3463 together into a single string. Guaranteed to return a freshly
3467 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3468 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3469 Without optional arguments, this procedure is equivalent to
3472 (string-concatenate (reverse ls))
3475 If the optional argument @var{final_string} is specified, it is
3476 consed onto the beginning to @var{ls} before performing the
3477 list-reverse and string-concatenate operations. If @var{end}
3478 is given, only the characters of @var{final_string} up to index
3481 Guaranteed to return a freshly allocated string.
3484 @deffn {Scheme Procedure} string-concatenate/shared ls
3485 @deffnx {C Function} scm_string_concatenate_shared (ls)
3486 Like @code{string-concatenate}, but the result may share memory
3487 with the strings in the list @var{ls}.
3490 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3491 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3492 Like @code{string-concatenate-reverse}, but the result may
3493 share memory with the strings in the @var{ls} arguments.
3496 @node Mapping Folding and Unfolding
3497 @subsubsection Mapping, Folding, and Unfolding
3499 @deffn {Scheme Procedure} string-map proc s [start [end]]
3500 @deffnx {C Function} scm_string_map (proc, s, start, end)
3501 @var{proc} is a char->char procedure, it is mapped over
3502 @var{s}. The order in which the procedure is applied to the
3503 string elements is not specified.
3506 @deffn {Scheme Procedure} string-map! proc s [start [end]]
3507 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
3508 @var{proc} is a char->char procedure, it is mapped over
3509 @var{s}. The order in which the procedure is applied to the
3510 string elements is not specified. The string @var{s} is
3511 modified in-place, the return value is not specified.
3514 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
3515 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
3516 @var{proc} is mapped over @var{s} in left-to-right order. The
3517 return value is not specified.
3520 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
3521 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
3522 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
3525 For example, to change characters to alternately upper and lower case,
3528 (define str (string-copy "studly"))
3529 (string-for-each-index
3532 ((if (even? i) char-upcase char-downcase)
3533 (string-ref str i))))
3535 str @result{} "StUdLy"
3539 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
3540 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
3541 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3542 as the terminating element, from left to right. @var{kons}
3543 must expect two arguments: The actual character and the last
3544 result of @var{kons}' application.
3547 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
3548 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
3549 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3550 as the terminating element, from right to left. @var{kons}
3551 must expect two arguments: The actual character and the last
3552 result of @var{kons}' application.
3555 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
3556 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
3558 @item @var{g} is used to generate a series of @emph{seed}
3559 values from the initial @var{seed}: @var{seed}, (@var{g}
3560 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3562 @item @var{p} tells us when to stop -- when it returns true
3563 when applied to one of these seed values.
3564 @item @var{f} maps each seed value to the corresponding
3565 character in the result string. These chars are assembled
3566 into the string in a left-to-right order.
3567 @item @var{base} is the optional initial/leftmost portion
3568 of the constructed string; it default to the empty
3570 @item @var{make_final} is applied to the terminal seed
3571 value (on which @var{p} returns true) to produce
3572 the final/rightmost portion of the constructed string.
3573 The default is nothing extra.
3577 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
3578 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
3580 @item @var{g} is used to generate a series of @emph{seed}
3581 values from the initial @var{seed}: @var{seed}, (@var{g}
3582 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3584 @item @var{p} tells us when to stop -- when it returns true
3585 when applied to one of these seed values.
3586 @item @var{f} maps each seed value to the corresponding
3587 character in the result string. These chars are assembled
3588 into the string in a right-to-left order.
3589 @item @var{base} is the optional initial/rightmost portion
3590 of the constructed string; it default to the empty
3592 @item @var{make_final} is applied to the terminal seed
3593 value (on which @var{p} returns true) to produce
3594 the final/leftmost portion of the constructed string.
3595 It defaults to @code{(lambda (x) )}.
3599 @node Miscellaneous String Operations
3600 @subsubsection Miscellaneous String Operations
3602 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
3603 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
3604 This is the @emph{extended substring} procedure that implements
3605 replicated copying of a substring of some string.
3607 @var{s} is a string, @var{start} and @var{end} are optional
3608 arguments that demarcate a substring of @var{s}, defaulting to
3609 0 and the length of @var{s}. Replicate this substring up and
3610 down index space, in both the positive and negative directions.
3611 @code{xsubstring} returns the substring of this string
3612 beginning at index @var{from}, and ending at @var{to}, which
3613 defaults to @var{from} + (@var{end} - @var{start}).
3616 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
3617 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
3618 Exactly the same as @code{xsubstring}, but the extracted text
3619 is written into the string @var{target} starting at index
3620 @var{tstart}. The operation is not defined if @code{(eq?
3621 @var{target} @var{s})} or these arguments share storage -- you
3622 cannot copy a string on top of itself.
3625 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
3626 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
3627 Return the string @var{s1}, but with the characters
3628 @var{start1} @dots{} @var{end1} replaced by the characters
3629 @var{start2} @dots{} @var{end2} from @var{s2}.
3632 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
3633 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
3634 Split the string @var{s} into a list of substrings, where each
3635 substring is a maximal non-empty contiguous sequence of
3636 characters from the character set @var{token_set}, which
3637 defaults to @code{char-set:graphic}.
3638 If @var{start} or @var{end} indices are provided, they restrict
3639 @code{string-tokenize} to operating on the indicated substring
3643 @deffn {Scheme Procedure} string-filter s char_pred [start [end]]
3644 @deffnx {C Function} scm_string_filter (s, char_pred, start, end)
3645 Filter the string @var{s}, retaining only those characters which
3646 satisfy @var{char_pred}.
3648 If @var{char_pred} is a procedure, it is applied to each character as
3649 a predicate, if it is a character, it is tested for equality and if it
3650 is a character set, it is tested for membership.
3653 @deffn {Scheme Procedure} string-delete s char_pred [start [end]]
3654 @deffnx {C Function} scm_string_delete (s, char_pred, start, end)
3655 Delete characters satisfying @var{char_pred} from @var{s}.
3657 If @var{char_pred} is a procedure, it is applied to each character as
3658 a predicate, if it is a character, it is tested for equality and if it
3659 is a character set, it is tested for membership.
3662 @node Conversion to/from C
3663 @subsubsection Conversion to/from C
3665 When creating a Scheme string from a C string or when converting a
3666 Scheme string to a C string, the concept of character encoding becomes
3669 In C, a string is just a sequence of bytes, and the character encoding
3670 describes the relation between these bytes and the actual characters
3671 that make up the string. For Scheme strings, character encoding is
3672 not an issue (most of the time), since in Scheme you never get to see
3673 the bytes, only the characters.
3675 Well, ideally, anyway. Right now, Guile simply equates Scheme
3676 characters and bytes, ignoring the possibility of multi-byte encodings
3677 completely. This will change in the future, where Guile will use
3678 Unicode codepoints as its characters and UTF-8 or some other encoding
3679 as its internal encoding. When you exclusively use the functions
3680 listed in this section, you are `future-proof'.
3682 Converting a Scheme string to a C string will often allocate fresh
3683 memory to hold the result. You must take care that this memory is
3684 properly freed eventually. In many cases, this can be achieved by
3685 using @code{scm_dynwind_free} inside an appropriate dynwind context,
3686 @xref{Dynamic Wind}.
3688 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
3689 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
3690 Creates a new Scheme string that has the same contents as @var{str}
3691 when interpreted in the current locale character encoding.
3693 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
3695 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
3696 @var{str} in bytes, and @var{str} does not need to be null-terminated.
3697 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
3698 null-terminated and the real length will be found with @code{strlen}.
3701 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
3702 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
3703 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
3704 respectively, but also frees @var{str} with @code{free} eventually.
3705 Thus, you can use this function when you would free @var{str} anyway
3706 immediately after creating the Scheme string. In certain cases, Guile
3707 can then use @var{str} directly as its internal representation.
3710 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
3711 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
3712 Returns a C string in the current locale encoding with the same
3713 contents as @var{str}. The C string must be freed with @code{free}
3714 eventually, maybe by using @code{scm_dynwind_free}, @xref{Dynamic
3717 For @code{scm_to_locale_string}, the returned string is
3718 null-terminated and an error is signalled when @var{str} contains
3719 @code{#\nul} characters.
3721 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
3722 @var{str} might contain @code{#\nul} characters and the length of the
3723 returned string in bytes is stored in @code{*@var{lenp}}. The
3724 returned string will not be null-terminated in this case. If
3725 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
3726 @code{scm_to_locale_string}.
3729 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
3730 Puts @var{str} as a C string in the current locale encoding into the
3731 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
3732 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
3733 more than that. No terminating @code{'\0'} will be stored.
3735 The return value of @code{scm_to_locale_stringbuf} is the number of
3736 bytes that are needed for all of @var{str}, regardless of whether
3737 @var{buf} was large enough to hold them. Thus, when the return value
3738 is larger than @var{max_len}, only @var{max_len} bytes have been
3739 stored and you probably need to try again with a larger buffer.
3743 @subsection Bytevectors
3748 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevector)}
3749 module provides the programming interface specified by the
3750 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
3751 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
3752 interpret their contents in a number of ways: bytevector contents can be
3753 accessed as signed or unsigned integer of various sizes and endianness,
3754 as IEEE-754 floating point numbers, or as strings. It is a useful tool
3755 to encode and decode binary data.
3757 The R6RS (Section 4.3.4) specifies an external representation for
3758 bytevectors, whereby the octets (integers in the range 0--255) contained
3759 in the bytevector are represented as a list prefixed by @code{#vu8}:
3765 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
3766 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
3767 they do not need to be quoted:
3771 @result{} #vu8(1 53 204)
3774 Bytevectors can be used with the binary input/output primitives of the
3775 R6RS (@pxref{R6RS I/O Ports}).
3778 * Bytevector Endianness:: Dealing with byte order.
3779 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
3780 * Bytevectors as Integers:: Interpreting bytes as integers.
3781 * Bytevectors and Integer Lists:: Converting to/from an integer list.
3782 * Bytevectors as Floats:: Interpreting bytes as real numbers.
3783 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
3784 * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API.
3787 @node Bytevector Endianness
3788 @subsubsection Endianness
3794 Some of the following procedures take an @var{endianness} parameter.
3795 The @dfn{endianness} is defined as the order of bytes in multi-byte
3796 numbers: numbers encoded in @dfn{big endian} have their most
3797 significant bytes written first, whereas numbers encoded in
3798 @dfn{little endian} have their least significant bytes
3799 first@footnote{Big-endian and little-endian are the most common
3800 ``endiannesses'', but others do exist. For instance, the GNU MP
3801 library allows @dfn{word order} to be specified independently of
3802 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
3803 Multiple Precision Arithmetic Library Manual}).}.
3805 Little-endian is the native endianness of the IA32 architecture and
3806 its derivatives, while big-endian is native to SPARC and PowerPC,
3807 among others. The @code{native-endianness} procedure returns the
3808 native endianness of the machine it runs on.
3810 @deffn {Scheme Procedure} native-endianness
3811 @deffnx {C Function} scm_native_endianness ()
3812 Return a value denoting the native endianness of the host machine.
3815 @deffn {Scheme Macro} endianness symbol
3816 Return an object denoting the endianness specified by @var{symbol}. If
3817 @var{symbol} is neither @code{big} nor @code{little} then an error is
3818 raised at expand-time.
3821 @defvr {C Variable} scm_endianness_big
3822 @defvrx {C Variable} scm_endianness_little
3823 The objects denoting big- and little-endianness, respectively.
3827 @node Bytevector Manipulation
3828 @subsubsection Manipulating Bytevectors
3830 Bytevectors can be created, copied, and analyzed with the following
3831 procedures and C functions.
3833 @deffn {Scheme Procedure} make-bytevector len [fill]
3834 @deffnx {C Function} scm_make_bytevector (len, fill)
3835 @deffnx {C Function} scm_c_make_bytevector (size_t len)
3836 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
3837 is given, fill it with @var{fill}; @var{fill} must be in the range
3841 @deffn {Scheme Procedure} bytevector? obj
3842 @deffnx {C Function} scm_bytevector_p (obj)
3843 Return true if @var{obj} is a bytevector.
3846 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
3847 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
3850 @deffn {Scheme Procedure} bytevector-length bv
3851 @deffnx {C Function} scm_bytevector_length (bv)
3852 Return the length in bytes of bytevector @var{bv}.
3855 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
3856 Likewise, return the length in bytes of bytevector @var{bv}.
3859 @deffn {Scheme Procedure} bytevector=? bv1 bv2
3860 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
3861 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
3862 length and contents.
3865 @deffn {Scheme Procedure} bytevector-fill! bv fill
3866 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
3867 Fill bytevector @var{bv} with @var{fill}, a byte.
3870 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
3871 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
3872 Copy @var{len} bytes from @var{source} into @var{target}, starting
3873 reading from @var{source-start} (a positive index within @var{source})
3874 and start writing at @var{target-start}.
3877 @deffn {Scheme Procedure} bytevector-copy bv
3878 @deffnx {C Function} scm_bytevector_copy (bv)
3879 Return a newly allocated copy of @var{bv}.
3882 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
3883 Return the byte at @var{index} in bytevector @var{bv}.
3886 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
3887 Set the byte at @var{index} in @var{bv} to @var{value}.
3890 Low-level C macros are available. They do not perform any
3891 type-checking; as such they should be used with care.
3893 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
3894 Return the length in bytes of bytevector @var{bv}.
3897 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
3898 Return a pointer to the contents of bytevector @var{bv}.
3902 @node Bytevectors as Integers
3903 @subsubsection Interpreting Bytevector Contents as Integers
3905 The contents of a bytevector can be interpreted as a sequence of
3906 integers of any given size, sign, and endianness.
3909 (let ((bv (make-bytevector 4)))
3910 (bytevector-u8-set! bv 0 #x12)
3911 (bytevector-u8-set! bv 1 #x34)
3912 (bytevector-u8-set! bv 2 #x56)
3913 (bytevector-u8-set! bv 3 #x78)
3915 (map (lambda (number)
3916 (number->string number 16))
3917 (list (bytevector-u8-ref bv 0)
3918 (bytevector-u16-ref bv 0 (endianness big))
3919 (bytevector-u32-ref bv 0 (endianness little)))))
3921 @result{} ("12" "1234" "78563412")
3924 The most generic procedures to interpret bytevector contents as integers
3925 are described below.
3927 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
3928 @deffnx {Scheme Procedure} bytevector-sint-ref bv index endianness size
3929 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
3930 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
3931 Return the @var{size}-byte long unsigned (resp. signed) integer at
3932 index @var{index} in @var{bv}, decoded according to @var{endianness}.
3935 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
3936 @deffnx {Scheme Procedure} bytevector-sint-set! bv index value endianness size
3937 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
3938 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
3939 Set the @var{size}-byte long unsigned (resp. signed) integer at
3940 @var{index} to @var{value}, encoded according to @var{endianness}.
3943 The following procedures are similar to the ones above, but specialized
3944 to a given integer size:
3946 @deffn {Scheme Procedure} bytevector-u8-ref bv index
3947 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
3948 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
3949 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
3950 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
3951 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
3952 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
3953 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
3954 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
3955 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
3956 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
3957 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
3958 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
3959 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
3960 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
3961 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
3962 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
3963 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
3967 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
3968 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
3969 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
3970 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
3971 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
3972 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
3973 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
3974 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
3975 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
3976 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
3977 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
3978 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
3979 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
3980 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
3981 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
3982 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
3983 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
3984 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
3988 Finally, a variant specialized for the host's endianness is available
3989 for each of these functions (with the exception of the @code{u8}
3990 accessors, for obvious reasons):
3992 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
3993 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
3994 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
3995 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
3996 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
3997 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
3998 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
3999 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4000 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4001 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4002 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4003 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4004 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4005 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4006 host's native endianness.
4009 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4010 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4011 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4012 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4013 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4014 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4015 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4016 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4017 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4018 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4019 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4020 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4021 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4022 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4023 host's native endianness.
4027 @node Bytevectors and Integer Lists
4028 @subsubsection Converting Bytevectors to/from Integer Lists
4030 Bytevector contents can readily be converted to/from lists of signed or
4034 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4035 (endianness little) 2)
4039 @deffn {Scheme Procedure} bytevector->u8-list bv
4040 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4041 Return a newly allocated list of unsigned 8-bit integers from the
4042 contents of @var{bv}.
4045 @deffn {Scheme Procedure} u8-list->bytevector lst
4046 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4047 Return a newly allocated bytevector consisting of the unsigned 8-bit
4048 integers listed in @var{lst}.
4051 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4052 @deffnx {Scheme Procedure} bytevector->sint-list bv endianness size
4053 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4054 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4055 Return a list of unsigned (resp. signed) integers of @var{size} bytes
4056 representing the contents of @var{bv}, decoded according to
4060 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4061 @deffnx {Scheme Procedure} sint-list->bytevector lst endianness size
4062 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4063 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4064 Return a new bytevector containing the unsigned (resp. signed) integers
4065 listed in @var{lst} and encoded on @var{size} bytes according to
4069 @node Bytevectors as Floats
4070 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4072 @cindex IEEE-754 floating point numbers
4074 Bytevector contents can also be accessed as IEEE-754 single- or
4075 double-precision floating point numbers (respectively 32 and 64-bit
4076 long) using the procedures described here.
4078 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4079 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4080 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4081 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4082 Return the IEEE-754 single-precision floating point number from @var{bv}
4083 at @var{index} according to @var{endianness}.
4086 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4087 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4088 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4089 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4090 Store real number @var{value} in @var{bv} at @var{index} according to
4094 Specialized procedures are also available:
4096 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4097 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4098 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4099 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4100 Return the IEEE-754 single-precision floating point number from @var{bv}
4101 at @var{index} according to the host's native endianness.
4104 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4105 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4106 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4107 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4108 Store real number @var{value} in @var{bv} at @var{index} according to
4109 the host's native endianness.
4113 @node Bytevectors as Strings
4114 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4116 @cindex Unicode string encoding
4118 Bytevector contents can also be interpreted as Unicode strings encoded
4119 in one of the most commonly available encoding formats@footnote{Guile
4120 1.8 does @emph{not} support Unicode strings. Therefore, the procedures
4121 described here assume that Guile strings are internally encoded
4122 according to the current locale. For instance, if @code{$LC_CTYPE} is
4123 @code{fr_FR.ISO-8859-1}, then @code{string->utf-8} @i{et al.} will
4124 assume that Guile strings are Latin-1-encoded.}.
4127 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4130 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4131 @result{} #vu8(99 97 102 195 169)
4134 @deffn {Scheme Procedure} string->utf8 str
4135 @deffnx {Scheme Procedure} string->utf16 str
4136 @deffnx {Scheme Procedure} string->utf32 str
4137 @deffnx {C Function} scm_string_to_utf8 (str)
4138 @deffnx {C Function} scm_string_to_utf16 (str)
4139 @deffnx {C Function} scm_string_to_utf32 (str)
4140 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4141 UTF-32 (aka. UCS-4) encoding of @var{str}.
4144 @deffn {Scheme Procedure} utf8->string utf
4145 @deffnx {Scheme Procedure} utf16->string utf
4146 @deffnx {Scheme Procedure} utf32->string utf
4147 @deffnx {C Function} scm_utf8_to_string (utf)
4148 @deffnx {C Function} scm_utf16_to_string (utf)
4149 @deffnx {C Function} scm_utf32_to_string (utf)
4150 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4151 or UTF-32-decoded contents of bytevector @var{utf}.
4154 @node Bytevectors as Generalized Vectors
4155 @subsubsection Accessing Bytevectors with the Generalized Vector API
4157 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4158 with the @dfn{generalized vector} procedures (@pxref{Generalized
4159 Vectors}). This also allows bytevectors to be accessed using the
4160 generic @dfn{array} procedures (@pxref{Array Procedures}). When using
4161 these APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4164 (define bv #vu8(0 1 2 3))
4166 (generalized-vector? bv)
4169 (generalized-vector-ref bv 2)
4172 (generalized-vector-set! bv 2 77)
4181 @node Regular Expressions
4182 @subsection Regular Expressions
4183 @tpindex Regular expressions
4185 @cindex regular expressions
4187 @cindex emacs regexp
4189 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
4190 describes a whole class of strings. A full description of regular
4191 expressions and their syntax is beyond the scope of this manual;
4192 an introduction can be found in the Emacs manual (@pxref{Regexps,
4193 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}), or
4194 in many general Unix reference books.
4196 If your system does not include a POSIX regular expression library,
4197 and you have not linked Guile with a third-party regexp library such
4198 as Rx, these functions will not be available. You can tell whether
4199 your Guile installation includes regular expression support by
4200 checking whether @code{(provided? 'regex)} returns true.
4202 The following regexp and string matching features are provided by the
4203 @code{(ice-9 regex)} module. Before using the described functions,
4204 you should load this module by executing @code{(use-modules (ice-9
4208 * Regexp Functions:: Functions that create and match regexps.
4209 * Match Structures:: Finding what was matched by a regexp.
4210 * Backslash Escapes:: Removing the special meaning of regexp
4215 @node Regexp Functions
4216 @subsubsection Regexp Functions
4218 By default, Guile supports POSIX extended regular expressions.
4219 That means that the characters @samp{(}, @samp{)}, @samp{+} and
4220 @samp{?} are special, and must be escaped if you wish to match the
4223 This regular expression interface was modeled after that
4224 implemented by SCSH, the Scheme Shell. It is intended to be
4225 upwardly compatible with SCSH regular expressions.
4227 Zero bytes (@code{#\nul}) cannot be used in regex patterns or input
4228 strings, since the underlying C functions treat that as the end of
4229 string. If there's a zero byte an error is thrown.
4231 Patterns and input strings are treated as being in the locale
4232 character set if @code{setlocale} has been called (@pxref{Locales}),
4233 and in a multibyte locale this includes treating multi-byte sequences
4234 as a single character. (Guile strings are currently merely bytes,
4235 though this may change in the future, @xref{Conversion to/from C}.)
4237 @deffn {Scheme Procedure} string-match pattern str [start]
4238 Compile the string @var{pattern} into a regular expression and compare
4239 it with @var{str}. The optional numeric argument @var{start} specifies
4240 the position of @var{str} at which to begin matching.
4242 @code{string-match} returns a @dfn{match structure} which
4243 describes what, if anything, was matched by the regular
4244 expression. @xref{Match Structures}. If @var{str} does not match
4245 @var{pattern} at all, @code{string-match} returns @code{#f}.
4248 Two examples of a match follow. In the first example, the pattern
4249 matches the four digits in the match string. In the second, the pattern
4253 (string-match "[0-9][0-9][0-9][0-9]" "blah2002")
4254 @result{} #("blah2002" (4 . 8))
4256 (string-match "[A-Za-z]" "123456")
4260 Each time @code{string-match} is called, it must compile its
4261 @var{pattern} argument into a regular expression structure. This
4262 operation is expensive, which makes @code{string-match} inefficient if
4263 the same regular expression is used several times (for example, in a
4264 loop). For better performance, you can compile a regular expression in
4265 advance and then match strings against the compiled regexp.
4267 @deffn {Scheme Procedure} make-regexp pat flag@dots{}
4268 @deffnx {C Function} scm_make_regexp (pat, flaglst)
4269 Compile the regular expression described by @var{pat}, and
4270 return the compiled regexp structure. If @var{pat} does not
4271 describe a legal regular expression, @code{make-regexp} throws
4272 a @code{regular-expression-syntax} error.
4274 The @var{flag} arguments change the behavior of the compiled
4275 regular expression. The following values may be supplied:
4277 @defvar regexp/icase
4278 Consider uppercase and lowercase letters to be the same when
4282 @defvar regexp/newline
4283 If a newline appears in the target string, then permit the
4284 @samp{^} and @samp{$} operators to match immediately after or
4285 immediately before the newline, respectively. Also, the
4286 @samp{.} and @samp{[^...]} operators will never match a newline
4287 character. The intent of this flag is to treat the target
4288 string as a buffer containing many lines of text, and the
4289 regular expression as a pattern that may match a single one of
4293 @defvar regexp/basic
4294 Compile a basic (``obsolete'') regexp instead of the extended
4295 (``modern'') regexps that are the default. Basic regexps do
4296 not consider @samp{|}, @samp{+} or @samp{?} to be special
4297 characters, and require the @samp{@{...@}} and @samp{(...)}
4298 metacharacters to be backslash-escaped (@pxref{Backslash
4299 Escapes}). There are several other differences between basic
4300 and extended regular expressions, but these are the most
4304 @defvar regexp/extended
4305 Compile an extended regular expression rather than a basic
4306 regexp. This is the default behavior; this flag will not
4307 usually be needed. If a call to @code{make-regexp} includes
4308 both @code{regexp/basic} and @code{regexp/extended} flags, the
4309 one which comes last will override the earlier one.
4313 @deffn {Scheme Procedure} regexp-exec rx str [start [flags]]
4314 @deffnx {C Function} scm_regexp_exec (rx, str, start, flags)
4315 Match the compiled regular expression @var{rx} against
4316 @code{str}. If the optional integer @var{start} argument is
4317 provided, begin matching from that position in the string.
4318 Return a match structure describing the results of the match,
4319 or @code{#f} if no match could be found.
4321 The @var{flags} argument changes the matching behavior. The following
4322 flag values may be supplied, use @code{logior} (@pxref{Bitwise
4323 Operations}) to combine them,
4325 @defvar regexp/notbol
4326 Consider that the @var{start} offset into @var{str} is not the
4327 beginning of a line and should not match operator @samp{^}.
4329 If @var{rx} was created with the @code{regexp/newline} option above,
4330 @samp{^} will still match after a newline in @var{str}.
4333 @defvar regexp/noteol
4334 Consider that the end of @var{str} is not the end of a line and should
4335 not match operator @samp{$}.
4337 If @var{rx} was created with the @code{regexp/newline} option above,
4338 @samp{$} will still match before a newline in @var{str}.
4343 ;; Regexp to match uppercase letters
4344 (define r (make-regexp "[A-Z]*"))
4346 ;; Regexp to match letters, ignoring case
4347 (define ri (make-regexp "[A-Z]*" regexp/icase))
4349 ;; Search for bob using regexp r
4350 (match:substring (regexp-exec r "bob"))
4351 @result{} "" ; no match
4353 ;; Search for bob using regexp ri
4354 (match:substring (regexp-exec ri "Bob"))
4355 @result{} "Bob" ; matched case insensitive
4358 @deffn {Scheme Procedure} regexp? obj
4359 @deffnx {C Function} scm_regexp_p (obj)
4360 Return @code{#t} if @var{obj} is a compiled regular expression,
4361 or @code{#f} otherwise.
4365 @deffn {Scheme Procedure} list-matches regexp str [flags]
4366 Return a list of match structures which are the non-overlapping
4367 matches of @var{regexp} in @var{str}. @var{regexp} can be either a
4368 pattern string or a compiled regexp. The @var{flags} argument is as
4369 per @code{regexp-exec} above.
4372 (map match:substring (list-matches "[a-z]+" "abc 42 def 78"))
4373 @result{} ("abc" "def")
4377 @deffn {Scheme Procedure} fold-matches regexp str init proc [flags]
4378 Apply @var{proc} to the non-overlapping matches of @var{regexp} in
4379 @var{str}, to build a result. @var{regexp} can be either a pattern
4380 string or a compiled regexp. The @var{flags} argument is as per
4381 @code{regexp-exec} above.
4383 @var{proc} is called as @code{(@var{proc} match prev)} where
4384 @var{match} is a match structure and @var{prev} is the previous return
4385 from @var{proc}. For the first call @var{prev} is the given
4386 @var{init} parameter. @code{fold-matches} returns the final value
4389 For example to count matches,
4392 (fold-matches "[a-z][0-9]" "abc x1 def y2" 0
4393 (lambda (match count)
4400 Regular expressions are commonly used to find patterns in one string
4401 and replace them with the contents of another string. The following
4402 functions are convenient ways to do this.
4404 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4405 @deffn {Scheme Procedure} regexp-substitute port match [item@dots{}]
4406 Write to @var{port} selected parts of the match structure @var{match}.
4407 Or if @var{port} is @code{#f} then form a string from those parts and
4410 Each @var{item} specifies a part to be written, and may be one of the
4415 A string. String arguments are written out verbatim.
4418 An integer. The submatch with that number is written
4419 (@code{match:substring}). Zero is the entire match.
4422 The symbol @samp{pre}. The portion of the matched string preceding
4423 the regexp match is written (@code{match:prefix}).
4426 The symbol @samp{post}. The portion of the matched string following
4427 the regexp match is written (@code{match:suffix}).
4430 For example, changing a match and retaining the text before and after,
4433 (regexp-substitute #f (string-match "[0-9]+" "number 25 is good")
4435 @result{} "number 37 is good"
4438 Or matching a @sc{yyyymmdd} format date such as @samp{20020828} and
4439 re-ordering and hyphenating the fields.
4443 "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4444 (define s "Date 20020429 12am.")
4445 (regexp-substitute #f (string-match date-regex s)
4446 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4447 @result{} "Date 04-29-2002 12am. (20020429)"
4452 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4453 @deffn {Scheme Procedure} regexp-substitute/global port regexp target [item@dots{}]
4454 @cindex search and replace
4455 Write to @var{port} selected parts of matches of @var{regexp} in
4456 @var{target}. If @var{port} is @code{#f} then form a string from
4457 those parts and return that. @var{regexp} can be a string or a
4460 This is similar to @code{regexp-substitute}, but allows global
4461 substitutions on @var{target}. Each @var{item} behaves as per
4462 @code{regexp-substitute}, with the following differences,
4466 A function. Called as @code{(@var{item} match)} with the match
4467 structure for the @var{regexp} match, it should return a string to be
4468 written to @var{port}.
4471 The symbol @samp{post}. This doesn't output anything, but instead
4472 causes @code{regexp-substitute/global} to recurse on the unmatched
4473 portion of @var{target}.
4475 This @emph{must} be supplied to perform a global search and replace on
4476 @var{target}; without it @code{regexp-substitute/global} returns after
4477 a single match and output.
4480 For example, to collapse runs of tabs and spaces to a single hyphen
4484 (regexp-substitute/global #f "[ \t]+" "this is the text"
4486 @result{} "this-is-the-text"
4489 Or using a function to reverse the letters in each word,
4492 (regexp-substitute/global #f "[a-z]+" "to do and not-do"
4493 'pre (lambda (m) (string-reverse (match:substring m))) 'post)
4494 @result{} "ot od dna ton-od"
4497 Without the @code{post} symbol, just one regexp match is made. For
4498 example the following is the date example from
4499 @code{regexp-substitute} above, without the need for the separate
4500 @code{string-match} call.
4504 "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4505 (define s "Date 20020429 12am.")
4506 (regexp-substitute/global #f date-regex s
4507 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4509 @result{} "Date 04-29-2002 12am. (20020429)"
4514 @node Match Structures
4515 @subsubsection Match Structures
4517 @cindex match structures
4519 A @dfn{match structure} is the object returned by @code{string-match} and
4520 @code{regexp-exec}. It describes which portion of a string, if any,
4521 matched the given regular expression. Match structures include: a
4522 reference to the string that was checked for matches; the starting and
4523 ending positions of the regexp match; and, if the regexp included any
4524 parenthesized subexpressions, the starting and ending positions of each
4527 In each of the regexp match functions described below, the @code{match}
4528 argument must be a match structure returned by a previous call to
4529 @code{string-match} or @code{regexp-exec}. Most of these functions
4530 return some information about the original target string that was
4531 matched against a regular expression; we will call that string
4532 @var{target} for easy reference.
4534 @c begin (scm-doc-string "regex.scm" "regexp-match?")
4535 @deffn {Scheme Procedure} regexp-match? obj
4536 Return @code{#t} if @var{obj} is a match structure returned by a
4537 previous call to @code{regexp-exec}, or @code{#f} otherwise.
4540 @c begin (scm-doc-string "regex.scm" "match:substring")
4541 @deffn {Scheme Procedure} match:substring match [n]
4542 Return the portion of @var{target} matched by subexpression number
4543 @var{n}. Submatch 0 (the default) represents the entire regexp match.
4544 If the regular expression as a whole matched, but the subexpression
4545 number @var{n} did not match, return @code{#f}.
4549 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4553 ;; match starting at offset 6 in the string
4555 (string-match "[0-9][0-9][0-9][0-9]" "blah987654" 6))
4559 @c begin (scm-doc-string "regex.scm" "match:start")
4560 @deffn {Scheme Procedure} match:start match [n]
4561 Return the starting position of submatch number @var{n}.
4564 In the following example, the result is 4, since the match starts at
4568 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4573 @c begin (scm-doc-string "regex.scm" "match:end")
4574 @deffn {Scheme Procedure} match:end match [n]
4575 Return the ending position of submatch number @var{n}.
4578 In the following example, the result is 8, since the match runs between
4579 characters 4 and 8 (i.e. the ``2002'').
4582 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4587 @c begin (scm-doc-string "regex.scm" "match:prefix")
4588 @deffn {Scheme Procedure} match:prefix match
4589 Return the unmatched portion of @var{target} preceding the regexp match.
4592 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4598 @c begin (scm-doc-string "regex.scm" "match:suffix")
4599 @deffn {Scheme Procedure} match:suffix match
4600 Return the unmatched portion of @var{target} following the regexp match.
4604 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4609 @c begin (scm-doc-string "regex.scm" "match:count")
4610 @deffn {Scheme Procedure} match:count match
4611 Return the number of parenthesized subexpressions from @var{match}.
4612 Note that the entire regular expression match itself counts as a
4613 subexpression, and failed submatches are included in the count.
4616 @c begin (scm-doc-string "regex.scm" "match:string")
4617 @deffn {Scheme Procedure} match:string match
4618 Return the original @var{target} string.
4622 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4624 @result{} "blah2002foo"
4628 @node Backslash Escapes
4629 @subsubsection Backslash Escapes
4631 Sometimes you will want a regexp to match characters like @samp{*} or
4632 @samp{$} exactly. For example, to check whether a particular string
4633 represents a menu entry from an Info node, it would be useful to match
4634 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
4635 because the asterisk is a metacharacter, it won't match the @samp{*} at
4636 the beginning of the string. In this case, we want to make the first
4639 You can do this by preceding the metacharacter with a backslash
4640 character @samp{\}. (This is also called @dfn{quoting} the
4641 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
4642 sees a backslash in a regular expression, it considers the following
4643 glyph to be an ordinary character, no matter what special meaning it
4644 would ordinarily have. Therefore, we can make the above example work by
4645 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
4646 the regular expression engine to match only a single asterisk in the
4649 Since the backslash is itself a metacharacter, you may force a regexp to
4650 match a backslash in the target string by preceding the backslash with
4651 itself. For example, to find variable references in a @TeX{} program,
4652 you might want to find occurrences of the string @samp{\let\} followed
4653 by any number of alphabetic characters. The regular expression
4654 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
4655 regexp each match a single backslash in the target string.
4657 @c begin (scm-doc-string "regex.scm" "regexp-quote")
4658 @deffn {Scheme Procedure} regexp-quote str
4659 Quote each special character found in @var{str} with a backslash, and
4660 return the resulting string.
4663 @strong{Very important:} Using backslash escapes in Guile source code
4664 (as in Emacs Lisp or C) can be tricky, because the backslash character
4665 has special meaning for the Guile reader. For example, if Guile
4666 encounters the character sequence @samp{\n} in the middle of a string
4667 while processing Scheme code, it replaces those characters with a
4668 newline character. Similarly, the character sequence @samp{\t} is
4669 replaced by a horizontal tab. Several of these @dfn{escape sequences}
4670 are processed by the Guile reader before your code is executed.
4671 Unrecognized escape sequences are ignored: if the characters @samp{\*}
4672 appear in a string, they will be translated to the single character
4675 This translation is obviously undesirable for regular expressions, since
4676 we want to be able to include backslashes in a string in order to
4677 escape regexp metacharacters. Therefore, to make sure that a backslash
4678 is preserved in a string in your Guile program, you must use @emph{two}
4679 consecutive backslashes:
4682 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
4685 The string in this example is preprocessed by the Guile reader before
4686 any code is executed. The resulting argument to @code{make-regexp} is
4687 the string @samp{^\* [^:]*}, which is what we really want.
4689 This also means that in order to write a regular expression that matches
4690 a single backslash character, the regular expression string in the
4691 source code must include @emph{four} backslashes. Each consecutive pair
4692 of backslashes gets translated by the Guile reader to a single
4693 backslash, and the resulting double-backslash is interpreted by the
4694 regexp engine as matching a single backslash character. Hence:
4697 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
4700 The reason for the unwieldiness of this syntax is historical. Both
4701 regular expression pattern matchers and Unix string processing systems
4702 have traditionally used backslashes with the special meanings
4703 described above. The POSIX regular expression specification and ANSI C
4704 standard both require these semantics. Attempting to abandon either
4705 convention would cause other kinds of compatibility problems, possibly
4706 more severe ones. Therefore, without extending the Scheme reader to
4707 support strings with different quoting conventions (an ungainly and
4708 confusing extension when implemented in other languages), we must adhere
4709 to this cumbersome escape syntax.
4716 Symbols in Scheme are widely used in three ways: as items of discrete
4717 data, as lookup keys for alists and hash tables, and to denote variable
4720 A @dfn{symbol} is similar to a string in that it is defined by a
4721 sequence of characters. The sequence of characters is known as the
4722 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4723 name doesn't include any characters that could be confused with other
4724 elements of Scheme syntax --- a symbol is written in a Scheme program by
4725 writing the sequence of characters that make up the name, @emph{without}
4726 any quotation marks or other special syntax. For example, the symbol
4727 whose name is ``multiply-by-2'' is written, simply:
4733 Notice how this differs from a @emph{string} with contents
4734 ``multiply-by-2'', which is written with double quotation marks, like
4741 Looking beyond how they are written, symbols are different from strings
4742 in two important respects.
4744 The first important difference is uniqueness. If the same-looking
4745 string is read twice from two different places in a program, the result
4746 is two @emph{different} string objects whose contents just happen to be
4747 the same. If, on the other hand, the same-looking symbol is read twice
4748 from two different places in a program, the result is the @emph{same}
4749 symbol object both times.
4751 Given two read symbols, you can use @code{eq?} to test whether they are
4752 the same (that is, have the same name). @code{eq?} is the most
4753 efficient comparison operator in Scheme, and comparing two symbols like
4754 this is as fast as comparing, for example, two numbers. Given two
4755 strings, on the other hand, you must use @code{equal?} or
4756 @code{string=?}, which are much slower comparison operators, to
4757 determine whether the strings have the same contents.
4760 (define sym1 (quote hello))
4761 (define sym2 (quote hello))
4762 (eq? sym1 sym2) @result{} #t
4764 (define str1 "hello")
4765 (define str2 "hello")
4766 (eq? str1 str2) @result{} #f
4767 (equal? str1 str2) @result{} #t
4770 The second important difference is that symbols, unlike strings, are not
4771 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
4772 example above: @code{(quote hello)} evaluates to the symbol named
4773 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
4774 symbol named "hello" and evaluated as a variable reference @dots{} about
4775 which more below (@pxref{Symbol Variables}).
4778 * Symbol Data:: Symbols as discrete data.
4779 * Symbol Keys:: Symbols as lookup keys.
4780 * Symbol Variables:: Symbols as denoting variables.
4781 * Symbol Primitives:: Operations related to symbols.
4782 * Symbol Props:: Function slots and property lists.
4783 * Symbol Read Syntax:: Extended read syntax for symbols.
4784 * Symbol Uninterned:: Uninterned symbols.
4789 @subsubsection Symbols as Discrete Data
4791 Numbers and symbols are similar to the extent that they both lend
4792 themselves to @code{eq?} comparison. But symbols are more descriptive
4793 than numbers, because a symbol's name can be used directly to describe
4794 the concept for which that symbol stands.
4796 For example, imagine that you need to represent some colours in a
4797 computer program. Using numbers, you would have to choose arbitrarily
4798 some mapping between numbers and colours, and then take care to use that
4799 mapping consistently:
4802 ;; 1=red, 2=green, 3=purple
4804 (if (eq? (colour-of car) 1)
4809 You can make the mapping more explicit and the code more readable by
4817 (if (eq? (colour-of car) red)
4822 But the simplest and clearest approach is not to use numbers at all, but
4823 symbols whose names specify the colours that they refer to:
4826 (if (eq? (colour-of car) 'red)
4830 The descriptive advantages of symbols over numbers increase as the set
4831 of concepts that you want to describe grows. Suppose that a car object
4832 can have other properties as well, such as whether it has or uses:
4836 automatic or manual transmission
4838 leaded or unleaded fuel
4840 power steering (or not).
4844 Then a car's combined property set could be naturally represented and
4845 manipulated as a list of symbols:
4848 (properties-of car1)
4850 (red manual unleaded power-steering)
4852 (if (memq 'power-steering (properties-of car1))
4853 (display "Unfit people can drive this car.\n")
4854 (display "You'll need strong arms to drive this car!\n"))
4856 Unfit people can drive this car.
4859 Remember, the fundamental property of symbols that we are relying on
4860 here is that an occurrence of @code{'red} in one part of a program is an
4861 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
4862 another part of a program; this means that symbols can usefully be
4863 compared using @code{eq?}. At the same time, symbols have naturally
4864 descriptive names. This combination of efficiency and descriptive power
4865 makes them ideal for use as discrete data.
4869 @subsubsection Symbols as Lookup Keys
4871 Given their efficiency and descriptive power, it is natural to use
4872 symbols as the keys in an association list or hash table.
4874 To illustrate this, consider a more structured representation of the car
4875 properties example from the preceding subsection. Rather than
4876 mixing all the properties up together in a flat list, we could use an
4877 association list like this:
4880 (define car1-properties '((colour . red)
4881 (transmission . manual)
4883 (steering . power-assisted)))
4886 Notice how this structure is more explicit and extensible than the flat
4887 list. For example it makes clear that @code{manual} refers to the
4888 transmission rather than, say, the windows or the locking of the car.
4889 It also allows further properties to use the same symbols among their
4890 possible values without becoming ambiguous:
4893 (define car1-properties '((colour . red)
4894 (transmission . manual)
4896 (steering . power-assisted)
4898 (locking . manual)))
4901 With a representation like this, it is easy to use the efficient
4902 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
4903 extract or change individual pieces of information:
4906 (assq-ref car1-properties 'fuel) @result{} unleaded
4907 (assq-ref car1-properties 'transmission) @result{} manual
4909 (assq-set! car1-properties 'seat-colour 'black)
4912 (transmission . manual)
4914 (steering . power-assisted)
4915 (seat-colour . black)
4916 (locking . manual)))
4919 Hash tables also have keys, and exactly the same arguments apply to the
4920 use of symbols in hash tables as in association lists. The hash value
4921 that Guile uses to decide where to add a symbol-keyed entry to a hash
4922 table can be obtained by calling the @code{symbol-hash} procedure:
4924 @deffn {Scheme Procedure} symbol-hash symbol
4925 @deffnx {C Function} scm_symbol_hash (symbol)
4926 Return a hash value for @var{symbol}.
4929 See @ref{Hash Tables} for information about hash tables in general, and
4930 for why you might choose to use a hash table rather than an association
4934 @node Symbol Variables
4935 @subsubsection Symbols as Denoting Variables
4937 When an unquoted symbol in a Scheme program is evaluated, it is
4938 interpreted as a variable reference, and the result of the evaluation is
4939 the appropriate variable's value.
4941 For example, when the expression @code{(string-length "abcd")} is read
4942 and evaluated, the sequence of characters @code{string-length} is read
4943 as the symbol whose name is "string-length". This symbol is associated
4944 with a variable whose value is the procedure that implements string
4945 length calculation. Therefore evaluation of the @code{string-length}
4946 symbol results in that procedure.
4948 The details of the connection between an unquoted symbol and the
4949 variable to which it refers are explained elsewhere. See @ref{Binding
4950 Constructs}, for how associations between symbols and variables are
4951 created, and @ref{Modules}, for how those associations are affected by
4952 Guile's module system.
4955 @node Symbol Primitives
4956 @subsubsection Operations Related to Symbols
4958 Given any Scheme value, you can determine whether it is a symbol using
4959 the @code{symbol?} primitive:
4962 @deffn {Scheme Procedure} symbol? obj
4963 @deffnx {C Function} scm_symbol_p (obj)
4964 Return @code{#t} if @var{obj} is a symbol, otherwise return
4968 @deftypefn {C Function} int scm_is_symbol (SCM val)
4969 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
4972 Once you know that you have a symbol, you can obtain its name as a
4973 string by calling @code{symbol->string}. Note that Guile differs by
4974 default from R5RS on the details of @code{symbol->string} as regards
4977 @rnindex symbol->string
4978 @deffn {Scheme Procedure} symbol->string s
4979 @deffnx {C Function} scm_symbol_to_string (s)
4980 Return the name of symbol @var{s} as a string. By default, Guile reads
4981 symbols case-sensitively, so the string returned will have the same case
4982 variation as the sequence of characters that caused @var{s} to be
4985 If Guile is set to read symbols case-insensitively (as specified by
4986 R5RS), and @var{s} comes into being as part of a literal expression
4987 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
4988 by a call to the @code{read} or @code{string-ci->symbol} procedures,
4989 Guile converts any alphabetic characters in the symbol's name to
4990 lower case before creating the symbol object, so the string returned
4991 here will be in lower case.
4993 If @var{s} was created by @code{string->symbol}, the case of characters
4994 in the string returned will be the same as that in the string that was
4995 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
4996 setting at the time @var{s} was created.
4998 It is an error to apply mutation procedures like @code{string-set!} to
4999 strings returned by this procedure.
5002 Most symbols are created by writing them literally in code. However it
5003 is also possible to create symbols programmatically using the following
5004 @code{string->symbol} and @code{string-ci->symbol} procedures:
5006 @rnindex string->symbol
5007 @deffn {Scheme Procedure} string->symbol string
5008 @deffnx {C Function} scm_string_to_symbol (string)
5009 Return the symbol whose name is @var{string}. This procedure can create
5010 symbols with names containing special characters or letters in the
5011 non-standard case, but it is usually a bad idea to create such symbols
5012 because in some implementations of Scheme they cannot be read as
5016 @deffn {Scheme Procedure} string-ci->symbol str
5017 @deffnx {C Function} scm_string_ci_to_symbol (str)
5018 Return the symbol whose name is @var{str}. If Guile is currently
5019 reading symbols case-insensitively, @var{str} is converted to lowercase
5020 before the returned symbol is looked up or created.
5023 The following examples illustrate Guile's detailed behaviour as regards
5024 the case-sensitivity of symbols:
5027 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5029 (symbol->string 'flying-fish) @result{} "flying-fish"
5030 (symbol->string 'Martin) @result{} "martin"
5032 (string->symbol "Malvina")) @result{} "Malvina"
5034 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5035 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5036 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5038 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5039 (string=? "K. Harper, M.D."
5041 (string->symbol "K. Harper, M.D."))) @result{} #t
5043 (read-disable 'case-insensitive) ; Guile default behaviour
5045 (symbol->string 'flying-fish) @result{} "flying-fish"
5046 (symbol->string 'Martin) @result{} "Martin"
5048 (string->symbol "Malvina")) @result{} "Malvina"
5050 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5051 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5052 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5054 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5055 (string=? "K. Harper, M.D."
5057 (string->symbol "K. Harper, M.D."))) @result{} #t
5060 From C, there are lower level functions that construct a Scheme symbol
5061 from a C string in the current locale encoding.
5063 When you want to do more from C, you should convert between symbols
5064 and strings using @code{scm_symbol_to_string} and
5065 @code{scm_string_to_symbol} and work with the strings.
5067 @deffn {C Function} scm_from_locale_symbol (const char *name)
5068 @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
5069 Construct and return a Scheme symbol whose name is specified by
5070 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5071 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5072 specified explicitly by @var{len}.
5075 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5076 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5077 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5078 respectively, but also frees @var{str} with @code{free} eventually.
5079 Thus, you can use this function when you would free @var{str} anyway
5080 immediately after creating the Scheme string. In certain cases, Guile
5081 can then use @var{str} directly as its internal representation.
5084 The size of a symbol can also be obtained from C:
5086 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5087 Return the number of characters in @var{sym}.
5090 Finally, some applications, especially those that generate new Scheme
5091 code dynamically, need to generate symbols for use in the generated
5092 code. The @code{gensym} primitive meets this need:
5094 @deffn {Scheme Procedure} gensym [prefix]
5095 @deffnx {C Function} scm_gensym (prefix)
5096 Create a new symbol with a name constructed from a prefix and a counter
5097 value. The string @var{prefix} can be specified as an optional
5098 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5099 at each call. There is no provision for resetting the counter.
5102 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5103 since their names begin with a space and it is only otherwise possible
5104 to generate such symbols if a programmer goes out of their way to do
5105 so. Uniqueness can be guaranteed by instead using uninterned symbols
5106 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5111 @subsubsection Function Slots and Property Lists
5113 In traditional Lisp dialects, symbols are often understood as having
5114 three kinds of value at once:
5118 a @dfn{variable} value, which is used when the symbol appears in
5119 code in a variable reference context
5122 a @dfn{function} value, which is used when the symbol appears in
5123 code in a function name position (i.e. as the first element in an
5127 a @dfn{property list} value, which is used when the symbol is given as
5128 the first argument to Lisp's @code{put} or @code{get} functions.
5131 Although Scheme (as one of its simplifications with respect to Lisp)
5132 does away with the distinction between variable and function namespaces,
5133 Guile currently retains some elements of the traditional structure in
5134 case they turn out to be useful when implementing translators for other
5135 languages, in particular Emacs Lisp.
5137 Specifically, Guile symbols have two extra slots. for a symbol's
5138 property list, and for its ``function value.'' The following procedures
5139 are provided to access these slots.
5141 @deffn {Scheme Procedure} symbol-fref symbol
5142 @deffnx {C Function} scm_symbol_fref (symbol)
5143 Return the contents of @var{symbol}'s @dfn{function slot}.
5146 @deffn {Scheme Procedure} symbol-fset! symbol value
5147 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5148 Set the contents of @var{symbol}'s function slot to @var{value}.
5151 @deffn {Scheme Procedure} symbol-pref symbol
5152 @deffnx {C Function} scm_symbol_pref (symbol)
5153 Return the @dfn{property list} currently associated with @var{symbol}.
5156 @deffn {Scheme Procedure} symbol-pset! symbol value
5157 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5158 Set @var{symbol}'s property list to @var{value}.
5161 @deffn {Scheme Procedure} symbol-property sym prop
5162 From @var{sym}'s property list, return the value for property
5163 @var{prop}. The assumption is that @var{sym}'s property list is an
5164 association list whose keys are distinguished from each other using
5165 @code{equal?}; @var{prop} should be one of the keys in that list. If
5166 the property list has no entry for @var{prop}, @code{symbol-property}
5170 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5171 In @var{sym}'s property list, set the value for property @var{prop} to
5172 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5173 none already exists. For the structure of the property list, see
5174 @code{symbol-property}.
5177 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5178 From @var{sym}'s property list, remove the entry for property
5179 @var{prop}, if there is one. For the structure of the property list,
5180 see @code{symbol-property}.
5183 Support for these extra slots may be removed in a future release, and it
5184 is probably better to avoid using them. For a more modern and Schemely
5185 approach to properties, see @ref{Object Properties}.
5188 @node Symbol Read Syntax
5189 @subsubsection Extended Read Syntax for Symbols
5191 The read syntax for a symbol is a sequence of letters, digits, and
5192 @dfn{extended alphabetic characters}, beginning with a character that
5193 cannot begin a number. In addition, the special cases of @code{+},
5194 @code{-}, and @code{...} are read as symbols even though numbers can
5195 begin with @code{+}, @code{-} or @code{.}.
5197 Extended alphabetic characters may be used within identifiers as if
5198 they were letters. The set of extended alphabetic characters is:
5201 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5204 In addition to the standard read syntax defined above (which is taken
5205 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5206 Scheme})), Guile provides an extended symbol read syntax that allows the
5207 inclusion of unusual characters such as space characters, newlines and
5208 parentheses. If (for whatever reason) you need to write a symbol
5209 containing characters not mentioned above, you can do so as follows.
5213 Begin the symbol with the characters @code{#@{},
5216 write the characters of the symbol and
5219 finish the symbol with the characters @code{@}#}.
5222 Here are a few examples of this form of read syntax. The first symbol
5223 needs to use extended syntax because it contains a space character, the
5224 second because it contains a line break, and the last because it looks
5236 Although Guile provides this extended read syntax for symbols,
5237 widespread usage of it is discouraged because it is not portable and not
5241 @node Symbol Uninterned
5242 @subsubsection Uninterned Symbols
5244 What makes symbols useful is that they are automatically kept unique.
5245 There are no two symbols that are distinct objects but have the same
5246 name. But of course, there is no rule without exception. In addition
5247 to the normal symbols that have been discussed up to now, you can also
5248 create special @dfn{uninterned} symbols that behave slightly
5251 To understand what is different about them and why they might be useful,
5252 we look at how normal symbols are actually kept unique.
5254 Whenever Guile wants to find the symbol with a specific name, for
5255 example during @code{read} or when executing @code{string->symbol}, it
5256 first looks into a table of all existing symbols to find out whether a
5257 symbol with the given name already exists. When this is the case, Guile
5258 just returns that symbol. When not, a new symbol with the name is
5259 created and entered into the table so that it can be found later.
5261 Sometimes you might want to create a symbol that is guaranteed `fresh',
5262 i.e. a symbol that did not exist previously. You might also want to
5263 somehow guarantee that no one else will ever unintentionally stumble
5264 across your symbol in the future. These properties of a symbol are
5265 often needed when generating code during macro expansion. When
5266 introducing new temporary variables, you want to guarantee that they
5267 don't conflict with variables in other people's code.
5269 The simplest way to arrange for this is to create a new symbol but
5270 not enter it into the global table of all symbols. That way, no one
5271 will ever get access to your symbol by chance. Symbols that are not in
5272 the table are called @dfn{uninterned}. Of course, symbols that
5273 @emph{are} in the table are called @dfn{interned}.
5275 You create new uninterned symbols with the function @code{make-symbol}.
5276 You can test whether a symbol is interned or not with
5277 @code{symbol-interned?}.
5279 Uninterned symbols break the rule that the name of a symbol uniquely
5280 identifies the symbol object. Because of this, they can not be written
5281 out and read back in like interned symbols. Currently, Guile has no
5282 support for reading uninterned symbols. Note that the function
5283 @code{gensym} does not return uninterned symbols for this reason.
5285 @deffn {Scheme Procedure} make-symbol name
5286 @deffnx {C Function} scm_make_symbol (name)
5287 Return a new uninterned symbol with the name @var{name}. The returned
5288 symbol is guaranteed to be unique and future calls to
5289 @code{string->symbol} will not return it.
5292 @deffn {Scheme Procedure} symbol-interned? symbol
5293 @deffnx {C Function} scm_symbol_interned_p (symbol)
5294 Return @code{#t} if @var{symbol} is interned, otherwise return
5301 (define foo-1 (string->symbol "foo"))
5302 (define foo-2 (string->symbol "foo"))
5303 (define foo-3 (make-symbol "foo"))
5304 (define foo-4 (make-symbol "foo"))
5308 ; Two interned symbols with the same name are the same object,
5312 ; but a call to make-symbol with the same name returns a
5317 ; A call to make-symbol always returns a new object, even for
5321 @result{} #<uninterned-symbol foo 8085290>
5322 ; Uninterned symbols print differently from interned symbols,
5326 ; but they are still symbols,
5328 (symbol-interned? foo-3)
5330 ; just not interned.
5335 @subsection Keywords
5338 Keywords are self-evaluating objects with a convenient read syntax that
5339 makes them easy to type.
5341 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5342 syntax extension to permit keywords to begin with @code{:} as well as
5343 @code{#:}, or to end with @code{:}.
5346 * Why Use Keywords?:: Motivation for keyword usage.
5347 * Coding With Keywords:: How to use keywords.
5348 * Keyword Read Syntax:: Read syntax for keywords.
5349 * Keyword Procedures:: Procedures for dealing with keywords.
5352 @node Why Use Keywords?
5353 @subsubsection Why Use Keywords?
5355 Keywords are useful in contexts where a program or procedure wants to be
5356 able to accept a large number of optional arguments without making its
5357 interface unmanageable.
5359 To illustrate this, consider a hypothetical @code{make-window}
5360 procedure, which creates a new window on the screen for drawing into
5361 using some graphical toolkit. There are many parameters that the caller
5362 might like to specify, but which could also be sensibly defaulted, for
5367 color depth -- Default: the color depth for the screen
5370 background color -- Default: white
5373 width -- Default: 600
5376 height -- Default: 400
5379 If @code{make-window} did not use keywords, the caller would have to
5380 pass in a value for each possible argument, remembering the correct
5381 argument order and using a special value to indicate the default value
5385 (make-window 'default ;; Color depth
5386 'default ;; Background color
5389 @dots{}) ;; More make-window arguments
5392 With keywords, on the other hand, defaulted arguments are omitted, and
5393 non-default arguments are clearly tagged by the appropriate keyword. As
5394 a result, the invocation becomes much clearer:
5397 (make-window #:width 800 #:height 100)
5400 On the other hand, for a simpler procedure with few arguments, the use
5401 of keywords would be a hindrance rather than a help. The primitive
5402 procedure @code{cons}, for example, would not be improved if it had to
5406 (cons #:car x #:cdr y)
5409 So the decision whether to use keywords or not is purely pragmatic: use
5410 them if they will clarify the procedure invocation at point of call.
5412 @node Coding With Keywords
5413 @subsubsection Coding With Keywords
5415 If a procedure wants to support keywords, it should take a rest argument
5416 and then use whatever means is convenient to extract keywords and their
5417 corresponding arguments from the contents of that rest argument.
5419 The following example illustrates the principle: the code for
5420 @code{make-window} uses a helper procedure called
5421 @code{get-keyword-value} to extract individual keyword arguments from
5425 (define (get-keyword-value args keyword default)
5426 (let ((kv (memq keyword args)))
5427 (if (and kv (>= (length kv) 2))
5431 (define (make-window . args)
5432 (let ((depth (get-keyword-value args #:depth screen-depth))
5433 (bg (get-keyword-value args #:bg "white"))
5434 (width (get-keyword-value args #:width 800))
5435 (height (get-keyword-value args #:height 100))
5440 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5441 optargs)} module provides a set of powerful macros that you can use to
5442 implement keyword-supporting procedures like this:
5445 (use-modules (ice-9 optargs))
5447 (define (make-window . args)
5448 (let-keywords args #f ((depth screen-depth)
5456 Or, even more economically, like this:
5459 (use-modules (ice-9 optargs))
5461 (define* (make-window #:key (depth screen-depth)
5468 For further details on @code{let-keywords}, @code{define*} and other
5469 facilities provided by the @code{(ice-9 optargs)} module, see
5470 @ref{Optional Arguments}.
5473 @node Keyword Read Syntax
5474 @subsubsection Keyword Read Syntax
5476 Guile, by default, only recognizes a keyword syntax that is compatible
5477 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5478 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5479 external representation of the keyword named @code{NAME}. Keyword
5480 objects print using this syntax as well, so values containing keyword
5481 objects can be read back into Guile. When used in an expression,
5482 keywords are self-quoting objects.
5484 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5485 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5486 of the form @code{:NAME} are read as symbols, as required by R5RS.
5488 @cindex SRFI-88 keyword syntax
5490 If the @code{keyword} read option is set to @code{'postfix}, Guile
5491 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5492 Otherwise, tokens of this form are read as symbols.
5494 To enable and disable the alternative non-R5RS keyword syntax, you use
5495 the @code{read-set!} procedure documented in @ref{User level options
5496 interfaces} and @ref{Reader options}. Note that the @code{prefix} and
5497 @code{postfix} syntax are mutually exclusive.
5500 (read-set! keywords 'prefix)
5510 (read-set! keywords 'postfix)
5520 (read-set! keywords #f)
5528 ERROR: In expression :type:
5529 ERROR: Unbound variable: :type
5530 ABORT: (unbound-variable)
5533 @node Keyword Procedures
5534 @subsubsection Keyword Procedures
5536 @deffn {Scheme Procedure} keyword? obj
5537 @deffnx {C Function} scm_keyword_p (obj)
5538 Return @code{#t} if the argument @var{obj} is a keyword, else
5542 @deffn {Scheme Procedure} keyword->symbol keyword
5543 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5544 Return the symbol with the same name as @var{keyword}.
5547 @deffn {Scheme Procedure} symbol->keyword symbol
5548 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5549 Return the keyword with the same name as @var{symbol}.
5552 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5553 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5556 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *str)
5557 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *str, size_t len)
5558 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5559 (@var{str}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5560 (@var{str}, @var{len}))}, respectively.
5564 @subsection ``Functionality-Centric'' Data Types
5566 Procedures and macros are documented in their own chapter: see
5567 @ref{Procedures and Macros}.
5569 Variable objects are documented as part of the description of Guile's
5570 module system: see @ref{Variables}.
5572 Asyncs, dynamic roots and fluids are described in the chapter on
5573 scheduling: see @ref{Scheduling}.
5575 Hooks are documented in the chapter on general utility functions: see
5578 Ports are described in the chapter on I/O: see @ref{Input and Output}.
5582 @c TeX-master: "guile.texi"