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 * Primitive Numerics:: Primitive numeric functions.
188 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
189 * Random:: Random number generation.
193 @node Numerical Tower
194 @subsubsection Scheme's Numerical ``Tower''
197 Scheme's numerical ``tower'' consists of the following categories of
202 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
205 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
206 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
207 pi (an irrational number) doesn't. These include integers
211 The set of numbers that describes all possible positions along a
212 one-dimensional line. This includes rationals as well as irrational
215 @item complex numbers
216 The set of numbers that describes all possible positions in a two
217 dimensional space. This includes real as well as imaginary numbers
218 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
219 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
223 It is called a tower because each category ``sits on'' the one that
224 follows it, in the sense that every integer is also a rational, every
225 rational is also real, and every real number is also a complex number
226 (but with zero imaginary part).
228 In addition to the classification into integers, rationals, reals and
229 complex numbers, Scheme also distinguishes between whether a number is
230 represented exactly or not. For example, the result of
231 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
232 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
233 Instead, it stores an inexact approximation, using the C type
236 Guile can represent exact rationals of any magnitude, inexact
237 rationals that fit into a C @code{double}, and inexact complex numbers
238 with @code{double} real and imaginary parts.
240 The @code{number?} predicate may be applied to any Scheme value to
241 discover whether the value is any of the supported numerical types.
243 @deffn {Scheme Procedure} number? obj
244 @deffnx {C Function} scm_number_p (obj)
245 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
254 (number? "hello there!")
257 (define pi 3.141592654)
262 @deftypefn {C Function} int scm_is_number (SCM obj)
263 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
266 The next few subsections document each of Guile's numerical data types
270 @subsubsection Integers
272 @tpindex Integer numbers
276 Integers are whole numbers, that is numbers with no fractional part,
277 such as 2, 83, and @minus{}3789.
279 Integers in Guile can be arbitrarily big, as shown by the following
283 (define (factorial n)
284 (let loop ((n n) (product 1))
287 (loop (- n 1) (* product n)))))
293 @result{} 2432902008176640000
296 @result{} -119622220865480194561963161495657715064383733760000000000
299 Readers whose background is in programming languages where integers are
300 limited by the need to fit into just 4 or 8 bytes of memory may find
301 this surprising, or suspect that Guile's representation of integers is
302 inefficient. In fact, Guile achieves a near optimal balance of
303 convenience and efficiency by using the host computer's native
304 representation of integers where possible, and a more general
305 representation where the required number does not fit in the native
306 form. Conversion between these two representations is automatic and
307 completely invisible to the Scheme level programmer.
309 The infinities @samp{+inf.0} and @samp{-inf.0} are considered to be
310 inexact integers. They are explained in detail in the next section,
311 together with reals and rationals.
313 C has a host of different integer types, and Guile offers a host of
314 functions to convert between them and the @code{SCM} representation.
315 For example, a C @code{int} can be handled with @code{scm_to_int} and
316 @code{scm_from_int}. Guile also defines a few C integer types of its
317 own, to help with differences between systems.
319 C integer types that are not covered can be handled with the generic
320 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
321 signed types, or with @code{scm_to_unsigned_integer} and
322 @code{scm_from_unsigned_integer} for unsigned types.
324 Scheme integers can be exact and inexact. For example, a number
325 written as @code{3.0} with an explicit decimal-point is inexact, but
326 it is also an integer. The functions @code{integer?} and
327 @code{scm_is_integer} report true for such a number, but the functions
328 @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only
329 allow exact integers and thus report false. Likewise, the conversion
330 functions like @code{scm_to_signed_integer} only accept exact
333 The motivation for this behavior is that the inexactness of a number
334 should not be lost silently. If you want to allow inexact integers,
335 you can explicitly insert a call to @code{inexact->exact} or to its C
336 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
337 be converted by this call into exact integers; inexact non-integers
338 will become exact fractions.)
340 @deffn {Scheme Procedure} integer? x
341 @deffnx {C Function} scm_integer_p (x)
342 Return @code{#t} if @var{x} is an exact or inexact integer number, else
360 @deftypefn {C Function} int scm_is_integer (SCM x)
361 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
364 @defvr {C Type} scm_t_int8
365 @defvrx {C Type} scm_t_uint8
366 @defvrx {C Type} scm_t_int16
367 @defvrx {C Type} scm_t_uint16
368 @defvrx {C Type} scm_t_int32
369 @defvrx {C Type} scm_t_uint32
370 @defvrx {C Type} scm_t_int64
371 @defvrx {C Type} scm_t_uint64
372 @defvrx {C Type} scm_t_intmax
373 @defvrx {C Type} scm_t_uintmax
374 The C types are equivalent to the corresponding ISO C types but are
375 defined on all platforms, with the exception of @code{scm_t_int64} and
376 @code{scm_t_uint64}, which are only defined when a 64-bit type is
377 available. For example, @code{scm_t_int8} is equivalent to
380 You can regard these definitions as a stop-gap measure until all
381 platforms provide these types. If you know that all the platforms
382 that you are interested in already provide these types, it is better
383 to use them directly instead of the types provided by Guile.
386 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
387 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
388 Return @code{1} when @var{x} represents an exact integer that is
389 between @var{min} and @var{max}, inclusive.
391 These functions can be used to check whether a @code{SCM} value will
392 fit into a given range, such as the range of a given C integer type.
393 If you just want to convert a @code{SCM} value to a given C integer
394 type, use one of the conversion functions directly.
397 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
398 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
399 When @var{x} represents an exact integer that is between @var{min} and
400 @var{max} inclusive, return that integer. Else signal an error,
401 either a `wrong-type' error when @var{x} is not an exact integer, or
402 an `out-of-range' error when it doesn't fit the given range.
405 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
406 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
407 Return the @code{SCM} value that represents the integer @var{x}. This
408 function will always succeed and will always return an exact number.
411 @deftypefn {C Function} char scm_to_char (SCM x)
412 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
413 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
414 @deftypefnx {C Function} short scm_to_short (SCM x)
415 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
416 @deftypefnx {C Function} int scm_to_int (SCM x)
417 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
418 @deftypefnx {C Function} long scm_to_long (SCM x)
419 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
420 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
421 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
422 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
423 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
424 @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x)
425 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
426 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
427 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
428 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
429 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
430 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
431 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
432 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
433 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
434 When @var{x} represents an exact integer that fits into the indicated
435 C type, return that integer. Else signal an error, either a
436 `wrong-type' error when @var{x} is not an exact integer, or an
437 `out-of-range' error when it doesn't fit the given range.
439 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
440 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
441 the corresponding types are.
444 @deftypefn {C Function} SCM scm_from_char (char x)
445 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
446 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
447 @deftypefnx {C Function} SCM scm_from_short (short x)
448 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
449 @deftypefnx {C Function} SCM scm_from_int (int x)
450 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
451 @deftypefnx {C Function} SCM scm_from_long (long x)
452 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
453 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
454 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
455 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
456 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
457 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
458 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
459 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
460 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
461 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
462 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
463 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
464 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
465 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
466 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
467 Return the @code{SCM} value that represents the integer @var{x}.
468 These functions will always succeed and will always return an exact
472 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
473 Assign @var{val} to the multiple precision integer @var{rop}.
474 @var{val} must be an exact integer, otherwise an error will be
475 signalled. @var{rop} must have been initialized with @code{mpz_init}
476 before this function is called. When @var{rop} is no longer needed
477 the occupied space must be freed with @code{mpz_clear}.
478 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
481 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
482 Return the @code{SCM} value that represents @var{val}.
485 @node Reals and Rationals
486 @subsubsection Real and Rational Numbers
487 @tpindex Real numbers
488 @tpindex Rational numbers
493 Mathematically, the real numbers are the set of numbers that describe
494 all possible points along a continuous, infinite, one-dimensional line.
495 The rational numbers are the set of all numbers that can be written as
496 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
497 All rational numbers are also real, but there are real numbers that
498 are not rational, for example @m{\sqrt2, the square root of 2}, and
501 Guile can represent both exact and inexact rational numbers, but it
502 can not represent irrational numbers. Exact rationals are represented
503 by storing the numerator and denominator as two exact integers.
504 Inexact rationals are stored as floating point numbers using the C
507 Exact rationals are written as a fraction of integers. There must be
508 no whitespace around the slash:
515 Even though the actual encoding of inexact rationals is in binary, it
516 may be helpful to think of it as a decimal number with a limited
517 number of significant figures and a decimal point somewhere, since
518 this corresponds to the standard notation for non-whole numbers. For
524 -5648394822220000000000.0
528 The limited precision of Guile's encoding means that any ``real'' number
529 in Guile can be written in a rational form, by multiplying and then dividing
530 by sufficient powers of 10 (or in fact, 2). For example,
531 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided by
532 100000000000000000. In Guile's current incarnation, therefore, the
533 @code{rational?} and @code{real?} predicates are equivalent.
536 Dividing by an exact zero leads to a error message, as one might
537 expect. However, dividing by an inexact zero does not produce an
538 error. Instead, the result of the division is either plus or minus
539 infinity, depending on the sign of the divided number.
541 The infinities are written @samp{+inf.0} and @samp{-inf.0},
542 respectivly. This syntax is also recognized by @code{read} as an
543 extension to the usual Scheme syntax.
545 Dividing zero by zero yields something that is not a number at all:
546 @samp{+nan.0}. This is the special `not a number' value.
548 On platforms that follow @acronym{IEEE} 754 for their floating point
549 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
550 are implemented using the corresponding @acronym{IEEE} 754 values.
551 They behave in arithmetic operations like @acronym{IEEE} 754 describes
552 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
554 The infinities are inexact integers and are considered to be both even
555 and odd. While @samp{+nan.0} is not @code{=} to itself, it is
556 @code{eqv?} to itself.
558 To test for the special values, use the functions @code{inf?} and
561 @deffn {Scheme Procedure} real? obj
562 @deffnx {C Function} scm_real_p (obj)
563 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
564 that the sets of integer and rational values form subsets of the set
565 of real numbers, so the predicate will also be fulfilled if @var{obj}
566 is an integer number or a rational number.
569 @deffn {Scheme Procedure} rational? x
570 @deffnx {C Function} scm_rational_p (x)
571 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
572 Note that the set of integer values forms a subset of the set of
573 rational numbers, i. e. the predicate will also be fulfilled if
574 @var{x} is an integer number.
576 Since Guile can not represent irrational numbers, every number
577 satisfying @code{real?} also satisfies @code{rational?} in Guile.
580 @deffn {Scheme Procedure} rationalize x eps
581 @deffnx {C Function} scm_rationalize (x, eps)
582 Returns the @emph{simplest} rational number differing
583 from @var{x} by no more than @var{eps}.
585 As required by @acronym{R5RS}, @code{rationalize} only returns an
586 exact result when both its arguments are exact. Thus, you might need
587 to use @code{inexact->exact} on the arguments.
590 (rationalize (inexact->exact 1.2) 1/100)
596 @deffn {Scheme Procedure} inf? x
597 @deffnx {C Function} scm_inf_p (x)
598 Return @code{#t} if @var{x} is either @samp{+inf.0} or @samp{-inf.0},
602 @deffn {Scheme Procedure} nan? x
603 @deffnx {C Function} scm_nan_p (x)
604 Return @code{#t} if @var{x} is @samp{+nan.0}, @code{#f} otherwise.
607 @deffn {Scheme Procedure} nan
608 @deffnx {C Function} scm_nan ()
612 @deffn {Scheme Procedure} inf
613 @deffnx {C Function} scm_inf ()
617 @deffn {Scheme Procedure} numerator x
618 @deffnx {C Function} scm_numerator (x)
619 Return the numerator of the rational number @var{x}.
622 @deffn {Scheme Procedure} denominator x
623 @deffnx {C Function} scm_denominator (x)
624 Return the denominator of the rational number @var{x}.
627 @deftypefn {C Function} int scm_is_real (SCM val)
628 @deftypefnx {C Function} int scm_is_rational (SCM val)
629 Equivalent to @code{scm_is_true (scm_real_p (val))} and
630 @code{scm_is_true (scm_rational_p (val))}, respectively.
633 @deftypefn {C Function} double scm_to_double (SCM val)
634 Returns the number closest to @var{val} that is representable as a
635 @code{double}. Returns infinity for a @var{val} that is too large in
636 magnitude. The argument @var{val} must be a real number.
639 @deftypefn {C Function} SCM scm_from_double (double val)
640 Return the @code{SCM} value that representats @var{val}. The returned
641 value is inexact according to the predicate @code{inexact?}, but it
642 will be exactly equal to @var{val}.
645 @node Complex Numbers
646 @subsubsection Complex Numbers
647 @tpindex Complex numbers
651 Complex numbers are the set of numbers that describe all possible points
652 in a two-dimensional space. The two coordinates of a particular point
653 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
654 the complex number that describes that point.
656 In Guile, complex numbers are written in rectangular form as the sum of
657 their real and imaginary parts, using the symbol @code{i} to indicate
672 Polar form can also be used, with an @samp{@@} between magnitude and
676 1@@3.141592 @result{} -1.0 (approx)
677 -1@@1.57079 @result{} 0.0-1.0i (approx)
680 Guile represents a complex number with a non-zero imaginary part as a
681 pair of inexact rationals, so the real and imaginary parts of a
682 complex number have the same properties of inexactness and limited
683 precision as single inexact rational numbers. Guile can not represent
684 exact complex numbers with non-zero imaginary parts.
686 @deffn {Scheme Procedure} complex? z
687 @deffnx {C Function} scm_complex_p (z)
688 Return @code{#t} if @var{x} is a complex number, @code{#f}
689 otherwise. Note that the sets of real, rational and integer
690 values form subsets of the set of complex numbers, i. e. the
691 predicate will also be fulfilled if @var{x} is a real,
692 rational or integer number.
695 @deftypefn {C Function} int scm_is_complex (SCM val)
696 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
700 @subsubsection Exact and Inexact Numbers
701 @tpindex Exact numbers
702 @tpindex Inexact numbers
706 @rnindex exact->inexact
707 @rnindex inexact->exact
709 R5RS requires that a calculation involving inexact numbers always
710 produces an inexact result. To meet this requirement, Guile
711 distinguishes between an exact integer value such as @samp{5} and the
712 corresponding inexact real value which, to the limited precision
713 available, has no fractional part, and is printed as @samp{5.0}. Guile
714 will only convert the latter value to the former when forced to do so by
715 an invocation of the @code{inexact->exact} procedure.
717 @deffn {Scheme Procedure} exact? z
718 @deffnx {C Function} scm_exact_p (z)
719 Return @code{#t} if the number @var{z} is exact, @code{#f}
735 @deffn {Scheme Procedure} inexact? z
736 @deffnx {C Function} scm_inexact_p (z)
737 Return @code{#t} if the number @var{z} is inexact, @code{#f}
741 @deffn {Scheme Procedure} inexact->exact z
742 @deffnx {C Function} scm_inexact_to_exact (z)
743 Return an exact number that is numerically closest to @var{z}, when
744 there is one. For inexact rationals, Guile returns the exact rational
745 that is numerically equal to the inexact rational. Inexact complex
746 numbers with a non-zero imaginary part can not be made exact.
753 The following happens because 12/10 is not exactly representable as a
754 @code{double} (on most platforms). However, when reading a decimal
755 number that has been marked exact with the ``#e'' prefix, Guile is
756 able to represent it correctly.
760 @result{} 5404319552844595/4503599627370496
768 @c begin (texi-doc-string "guile" "exact->inexact")
769 @deffn {Scheme Procedure} exact->inexact z
770 @deffnx {C Function} scm_exact_to_inexact (z)
771 Convert the number @var{z} to its inexact representation.
776 @subsubsection Read Syntax for Numerical Data
778 The read syntax for integers is a string of digits, optionally
779 preceded by a minus or plus character, a code indicating the
780 base in which the integer is encoded, and a code indicating whether
781 the number is exact or inexact. The supported base codes are:
786 the integer is written in binary (base 2)
790 the integer is written in octal (base 8)
794 the integer is written in decimal (base 10)
798 the integer is written in hexadecimal (base 16)
801 If the base code is omitted, the integer is assumed to be decimal. The
802 following examples show how these base codes are used.
821 The codes for indicating exactness (which can, incidentally, be applied
822 to all numerical values) are:
831 the number is inexact.
834 If the exactness indicator is omitted, the number is exact unless it
835 contains a radix point. Since Guile can not represent exact complex
836 numbers, an error is signalled when asking for them.
846 ERROR: Wrong type argument
849 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
850 plus and minus infinity, respectively. The value must be written
851 exactly as shown, that is, they always must have a sign and exactly
852 one zero digit after the decimal point. It also understands
853 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
854 The sign is ignored for `not-a-number' and the value is always printed
857 @node Integer Operations
858 @subsubsection Operations on Integer Values
867 @deffn {Scheme Procedure} odd? n
868 @deffnx {C Function} scm_odd_p (n)
869 Return @code{#t} if @var{n} is an odd number, @code{#f}
873 @deffn {Scheme Procedure} even? n
874 @deffnx {C Function} scm_even_p (n)
875 Return @code{#t} if @var{n} is an even number, @code{#f}
879 @c begin (texi-doc-string "guile" "quotient")
880 @c begin (texi-doc-string "guile" "remainder")
881 @deffn {Scheme Procedure} quotient n d
882 @deffnx {Scheme Procedure} remainder n d
883 @deffnx {C Function} scm_quotient (n, d)
884 @deffnx {C Function} scm_remainder (n, d)
885 Return the quotient or remainder from @var{n} divided by @var{d}. The
886 quotient is rounded towards zero, and the remainder will have the same
887 sign as @var{n}. In all cases quotient and remainder satisfy
888 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
891 (remainder 13 4) @result{} 1
892 (remainder -13 4) @result{} -1
896 @c begin (texi-doc-string "guile" "modulo")
897 @deffn {Scheme Procedure} modulo n d
898 @deffnx {C Function} scm_modulo (n, d)
899 Return the remainder from @var{n} divided by @var{d}, with the same
903 (modulo 13 4) @result{} 1
904 (modulo -13 4) @result{} 3
905 (modulo 13 -4) @result{} -3
906 (modulo -13 -4) @result{} -1
910 @c begin (texi-doc-string "guile" "gcd")
911 @deffn {Scheme Procedure} gcd x@dots{}
912 @deffnx {C Function} scm_gcd (x, y)
913 Return the greatest common divisor of all arguments.
914 If called without arguments, 0 is returned.
916 The C function @code{scm_gcd} always takes two arguments, while the
917 Scheme function can take an arbitrary number.
920 @c begin (texi-doc-string "guile" "lcm")
921 @deffn {Scheme Procedure} lcm x@dots{}
922 @deffnx {C Function} scm_lcm (x, y)
923 Return the least common multiple of the arguments.
924 If called without arguments, 1 is returned.
926 The C function @code{scm_lcm} always takes two arguments, while the
927 Scheme function can take an arbitrary number.
930 @deffn {Scheme Procedure} modulo-expt n k m
931 @deffnx {C Function} scm_modulo_expt (n, k, m)
932 Return @var{n} raised to the integer exponent
933 @var{k}, modulo @var{m}.
942 @subsubsection Comparison Predicates
947 The C comparison functions below always takes two arguments, while the
948 Scheme functions can take an arbitrary number. Also keep in mind that
949 the C functions return one of the Scheme boolean values
950 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
951 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
952 y))} when testing the two Scheme numbers @code{x} and @code{y} for
953 equality, for example.
955 @c begin (texi-doc-string "guile" "=")
956 @deffn {Scheme Procedure} =
957 @deffnx {C Function} scm_num_eq_p (x, y)
958 Return @code{#t} if all parameters are numerically equal.
961 @c begin (texi-doc-string "guile" "<")
962 @deffn {Scheme Procedure} <
963 @deffnx {C Function} scm_less_p (x, y)
964 Return @code{#t} if the list of parameters is monotonically
968 @c begin (texi-doc-string "guile" ">")
969 @deffn {Scheme Procedure} >
970 @deffnx {C Function} scm_gr_p (x, y)
971 Return @code{#t} if the list of parameters is monotonically
975 @c begin (texi-doc-string "guile" "<=")
976 @deffn {Scheme Procedure} <=
977 @deffnx {C Function} scm_leq_p (x, y)
978 Return @code{#t} if the list of parameters is monotonically
982 @c begin (texi-doc-string "guile" ">=")
983 @deffn {Scheme Procedure} >=
984 @deffnx {C Function} scm_geq_p (x, y)
985 Return @code{#t} if the list of parameters is monotonically
989 @c begin (texi-doc-string "guile" "zero?")
990 @deffn {Scheme Procedure} zero? z
991 @deffnx {C Function} scm_zero_p (z)
992 Return @code{#t} if @var{z} is an exact or inexact number equal to
996 @c begin (texi-doc-string "guile" "positive?")
997 @deffn {Scheme Procedure} positive? x
998 @deffnx {C Function} scm_positive_p (x)
999 Return @code{#t} if @var{x} is an exact or inexact number greater than
1003 @c begin (texi-doc-string "guile" "negative?")
1004 @deffn {Scheme Procedure} negative? x
1005 @deffnx {C Function} scm_negative_p (x)
1006 Return @code{#t} if @var{x} is an exact or inexact number less than
1012 @subsubsection Converting Numbers To and From Strings
1013 @rnindex number->string
1014 @rnindex string->number
1016 The following procedures read and write numbers according to their
1017 external representation as defined by R5RS (@pxref{Lexical structure,
1018 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1019 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1020 i18n)} module}, for locale-dependent number parsing.
1022 @deffn {Scheme Procedure} number->string n [radix]
1023 @deffnx {C Function} scm_number_to_string (n, radix)
1024 Return a string holding the external representation of the
1025 number @var{n} in the given @var{radix}. If @var{n} is
1026 inexact, a radix of 10 will be used.
1029 @deffn {Scheme Procedure} string->number string [radix]
1030 @deffnx {C Function} scm_string_to_number (string, radix)
1031 Return a number of the maximally precise representation
1032 expressed by the given @var{string}. @var{radix} must be an
1033 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1034 is a default radix that may be overridden by an explicit radix
1035 prefix in @var{string} (e.g. "#o177"). If @var{radix} is not
1036 supplied, then the default radix is 10. If string is not a
1037 syntactically valid notation for a number, then
1038 @code{string->number} returns @code{#f}.
1041 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1042 As per @code{string->number} above, but taking a C string, as pointer
1043 and length. The string characters should be in the current locale
1044 encoding (@code{locale} in the name refers only to that, there's no
1045 locale-dependent parsing).
1050 @subsubsection Complex Number Operations
1051 @rnindex make-rectangular
1058 @deffn {Scheme Procedure} make-rectangular real imaginary
1059 @deffnx {C Function} scm_make_rectangular (real, imaginary)
1060 Return a complex number constructed of the given @var{real} and
1061 @var{imaginary} parts.
1064 @deffn {Scheme Procedure} make-polar x y
1065 @deffnx {C Function} scm_make_polar (x, y)
1067 Return the complex number @var{x} * e^(i * @var{y}).
1070 @c begin (texi-doc-string "guile" "real-part")
1071 @deffn {Scheme Procedure} real-part z
1072 @deffnx {C Function} scm_real_part (z)
1073 Return the real part of the number @var{z}.
1076 @c begin (texi-doc-string "guile" "imag-part")
1077 @deffn {Scheme Procedure} imag-part z
1078 @deffnx {C Function} scm_imag_part (z)
1079 Return the imaginary part of the number @var{z}.
1082 @c begin (texi-doc-string "guile" "magnitude")
1083 @deffn {Scheme Procedure} magnitude z
1084 @deffnx {C Function} scm_magnitude (z)
1085 Return the magnitude of the number @var{z}. This is the same as
1086 @code{abs} for real arguments, but also allows complex numbers.
1089 @c begin (texi-doc-string "guile" "angle")
1090 @deffn {Scheme Procedure} angle z
1091 @deffnx {C Function} scm_angle (z)
1092 Return the angle of the complex number @var{z}.
1095 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1096 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1097 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1098 respectively, but these functions take @code{double}s as their
1102 @deftypefn {C Function} double scm_c_real_part (z)
1103 @deftypefnx {C Function} double scm_c_imag_part (z)
1104 Returns the real or imaginary part of @var{z} as a @code{double}.
1107 @deftypefn {C Function} double scm_c_magnitude (z)
1108 @deftypefnx {C Function} double scm_c_angle (z)
1109 Returns the magnitude or angle of @var{z} as a @code{double}.
1114 @subsubsection Arithmetic Functions
1129 The C arithmetic functions below always takes two arguments, while the
1130 Scheme functions can take an arbitrary number. When you need to
1131 invoke them with just one argument, for example to compute the
1132 equivalent od @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1133 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1135 @c begin (texi-doc-string "guile" "+")
1136 @deffn {Scheme Procedure} + z1 @dots{}
1137 @deffnx {C Function} scm_sum (z1, z2)
1138 Return the sum of all parameter values. Return 0 if called without any
1142 @c begin (texi-doc-string "guile" "-")
1143 @deffn {Scheme Procedure} - z1 z2 @dots{}
1144 @deffnx {C Function} scm_difference (z1, z2)
1145 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1146 the sum of all but the first argument are subtracted from the first
1150 @c begin (texi-doc-string "guile" "*")
1151 @deffn {Scheme Procedure} * z1 @dots{}
1152 @deffnx {C Function} scm_product (z1, z2)
1153 Return the product of all arguments. If called without arguments, 1 is
1157 @c begin (texi-doc-string "guile" "/")
1158 @deffn {Scheme Procedure} / z1 z2 @dots{}
1159 @deffnx {C Function} scm_divide (z1, z2)
1160 Divide the first argument by the product of the remaining arguments. If
1161 called with one argument @var{z1}, 1/@var{z1} is returned.
1164 @deffn {Scheme Procedure} 1+ z
1165 @deffnx {C Function} scm_oneplus (z)
1166 Return @math{@var{z} + 1}.
1169 @deffn {Scheme Procedure} 1- z
1170 @deffnx {C function} scm_oneminus (z)
1171 Return @math{@var{z} - 1}.
1174 @c begin (texi-doc-string "guile" "abs")
1175 @deffn {Scheme Procedure} abs x
1176 @deffnx {C Function} scm_abs (x)
1177 Return the absolute value of @var{x}.
1179 @var{x} must be a number with zero imaginary part. To calculate the
1180 magnitude of a complex number, use @code{magnitude} instead.
1183 @c begin (texi-doc-string "guile" "max")
1184 @deffn {Scheme Procedure} max x1 x2 @dots{}
1185 @deffnx {C Function} scm_max (x1, x2)
1186 Return the maximum of all parameter values.
1189 @c begin (texi-doc-string "guile" "min")
1190 @deffn {Scheme Procedure} min x1 x2 @dots{}
1191 @deffnx {C Function} scm_min (x1, x2)
1192 Return the minimum of all parameter values.
1195 @c begin (texi-doc-string "guile" "truncate")
1196 @deffn {Scheme Procedure} truncate x
1197 @deffnx {C Function} scm_truncate_number (x)
1198 Round the inexact number @var{x} towards zero.
1201 @c begin (texi-doc-string "guile" "round")
1202 @deffn {Scheme Procedure} round x
1203 @deffnx {C Function} scm_round_number (x)
1204 Round the inexact number @var{x} to the nearest integer. When exactly
1205 halfway between two integers, round to the even one.
1208 @c begin (texi-doc-string "guile" "floor")
1209 @deffn {Scheme Procedure} floor x
1210 @deffnx {C Function} scm_floor (x)
1211 Round the number @var{x} towards minus infinity.
1214 @c begin (texi-doc-string "guile" "ceiling")
1215 @deffn {Scheme Procedure} ceiling x
1216 @deffnx {C Function} scm_ceiling (x)
1217 Round the number @var{x} towards infinity.
1220 @deftypefn {C Function} double scm_c_truncate (double x)
1221 @deftypefnx {C Function} double scm_c_round (double x)
1222 Like @code{scm_truncate_number} or @code{scm_round_number},
1223 respectively, but these functions take and return @code{double}
1228 @subsubsection Scientific Functions
1230 The following procedures accept any kind of number as arguments,
1231 including complex numbers.
1234 @c begin (texi-doc-string "guile" "sqrt")
1235 @deffn {Scheme Procedure} sqrt z
1236 Return the square root of @var{z}. Of the two possible roots
1237 (positive and negative), the one with the a positive real part is
1238 returned, or if that's zero then a positive imaginary part. Thus,
1241 (sqrt 9.0) @result{} 3.0
1242 (sqrt -9.0) @result{} 0.0+3.0i
1243 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1244 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1249 @c begin (texi-doc-string "guile" "expt")
1250 @deffn {Scheme Procedure} expt z1 z2
1251 Return @var{z1} raised to the power of @var{z2}.
1255 @c begin (texi-doc-string "guile" "sin")
1256 @deffn {Scheme Procedure} sin z
1257 Return the sine of @var{z}.
1261 @c begin (texi-doc-string "guile" "cos")
1262 @deffn {Scheme Procedure} cos z
1263 Return the cosine of @var{z}.
1267 @c begin (texi-doc-string "guile" "tan")
1268 @deffn {Scheme Procedure} tan z
1269 Return the tangent of @var{z}.
1273 @c begin (texi-doc-string "guile" "asin")
1274 @deffn {Scheme Procedure} asin z
1275 Return the arcsine of @var{z}.
1279 @c begin (texi-doc-string "guile" "acos")
1280 @deffn {Scheme Procedure} acos z
1281 Return the arccosine of @var{z}.
1285 @c begin (texi-doc-string "guile" "atan")
1286 @deffn {Scheme Procedure} atan z
1287 @deffnx {Scheme Procedure} atan y x
1288 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1292 @c begin (texi-doc-string "guile" "exp")
1293 @deffn {Scheme Procedure} exp z
1294 Return e to the power of @var{z}, where e is the base of natural
1295 logarithms (2.71828@dots{}).
1299 @c begin (texi-doc-string "guile" "log")
1300 @deffn {Scheme Procedure} log z
1301 Return the natural logarithm of @var{z}.
1304 @c begin (texi-doc-string "guile" "log10")
1305 @deffn {Scheme Procedure} log10 z
1306 Return the base 10 logarithm of @var{z}.
1309 @c begin (texi-doc-string "guile" "sinh")
1310 @deffn {Scheme Procedure} sinh z
1311 Return the hyperbolic sine of @var{z}.
1314 @c begin (texi-doc-string "guile" "cosh")
1315 @deffn {Scheme Procedure} cosh z
1316 Return the hyperbolic cosine of @var{z}.
1319 @c begin (texi-doc-string "guile" "tanh")
1320 @deffn {Scheme Procedure} tanh z
1321 Return the hyperbolic tangent of @var{z}.
1324 @c begin (texi-doc-string "guile" "asinh")
1325 @deffn {Scheme Procedure} asinh z
1326 Return the hyperbolic arcsine of @var{z}.
1329 @c begin (texi-doc-string "guile" "acosh")
1330 @deffn {Scheme Procedure} acosh z
1331 Return the hyperbolic arccosine of @var{z}.
1334 @c begin (texi-doc-string "guile" "atanh")
1335 @deffn {Scheme Procedure} atanh z
1336 Return the hyperbolic arctangent of @var{z}.
1340 @node Primitive Numerics
1341 @subsubsection Primitive Numeric Functions
1343 Many of Guile's numeric procedures which accept any kind of numbers as
1344 arguments, including complex numbers, are implemented as Scheme
1345 procedures that use the following real number-based primitives. These
1346 primitives signal an error if they are called with complex arguments.
1348 @c begin (texi-doc-string "guile" "$abs")
1349 @deffn {Scheme Procedure} $abs x
1350 Return the absolute value of @var{x}.
1353 @c begin (texi-doc-string "guile" "$sqrt")
1354 @deffn {Scheme Procedure} $sqrt x
1355 Return the square root of @var{x}.
1358 @deffn {Scheme Procedure} $expt x y
1359 @deffnx {C Function} scm_sys_expt (x, y)
1360 Return @var{x} raised to the power of @var{y}. This
1361 procedure does not accept complex arguments.
1364 @c begin (texi-doc-string "guile" "$sin")
1365 @deffn {Scheme Procedure} $sin x
1366 Return the sine of @var{x}.
1369 @c begin (texi-doc-string "guile" "$cos")
1370 @deffn {Scheme Procedure} $cos x
1371 Return the cosine of @var{x}.
1374 @c begin (texi-doc-string "guile" "$tan")
1375 @deffn {Scheme Procedure} $tan x
1376 Return the tangent of @var{x}.
1379 @c begin (texi-doc-string "guile" "$asin")
1380 @deffn {Scheme Procedure} $asin x
1381 Return the arcsine of @var{x}.
1384 @c begin (texi-doc-string "guile" "$acos")
1385 @deffn {Scheme Procedure} $acos x
1386 Return the arccosine of @var{x}.
1389 @c begin (texi-doc-string "guile" "$atan")
1390 @deffn {Scheme Procedure} $atan x
1391 Return the arctangent of @var{x} in the range @minus{}@math{PI/2} to
1395 @deffn {Scheme Procedure} $atan2 x y
1396 @deffnx {C Function} scm_sys_atan2 (x, y)
1397 Return the arc tangent of the two arguments @var{x} and
1398 @var{y}. This is similar to calculating the arc tangent of
1399 @var{x} / @var{y}, except that the signs of both arguments
1400 are used to determine the quadrant of the result. This
1401 procedure does not accept complex arguments.
1404 @c begin (texi-doc-string "guile" "$exp")
1405 @deffn {Scheme Procedure} $exp x
1406 Return e to the power of @var{x}, where e is the base of natural
1407 logarithms (2.71828@dots{}).
1410 @c begin (texi-doc-string "guile" "$log")
1411 @deffn {Scheme Procedure} $log x
1412 Return the natural logarithm of @var{x}.
1415 @c begin (texi-doc-string "guile" "$sinh")
1416 @deffn {Scheme Procedure} $sinh x
1417 Return the hyperbolic sine of @var{x}.
1420 @c begin (texi-doc-string "guile" "$cosh")
1421 @deffn {Scheme Procedure} $cosh x
1422 Return the hyperbolic cosine of @var{x}.
1425 @c begin (texi-doc-string "guile" "$tanh")
1426 @deffn {Scheme Procedure} $tanh x
1427 Return the hyperbolic tangent of @var{x}.
1430 @c begin (texi-doc-string "guile" "$asinh")
1431 @deffn {Scheme Procedure} $asinh x
1432 Return the hyperbolic arcsine of @var{x}.
1435 @c begin (texi-doc-string "guile" "$acosh")
1436 @deffn {Scheme Procedure} $acosh x
1437 Return the hyperbolic arccosine of @var{x}.
1440 @c begin (texi-doc-string "guile" "$atanh")
1441 @deffn {Scheme Procedure} $atanh x
1442 Return the hyperbolic arctangent of @var{x}.
1445 C functions for the above are provided by the standard mathematics
1446 library. Naturally these expect and return @code{double} arguments
1447 (@pxref{Mathematics,,, libc, GNU C Library Reference Manual}).
1449 @multitable {xx} {Scheme Procedure} {C Function}
1450 @item @tab Scheme Procedure @tab C Function
1452 @item @tab @code{$abs} @tab @code{fabs}
1453 @item @tab @code{$sqrt} @tab @code{sqrt}
1454 @item @tab @code{$sin} @tab @code{sin}
1455 @item @tab @code{$cos} @tab @code{cos}
1456 @item @tab @code{$tan} @tab @code{tan}
1457 @item @tab @code{$asin} @tab @code{asin}
1458 @item @tab @code{$acos} @tab @code{acos}
1459 @item @tab @code{$atan} @tab @code{atan}
1460 @item @tab @code{$atan2} @tab @code{atan2}
1461 @item @tab @code{$exp} @tab @code{exp}
1462 @item @tab @code{$expt} @tab @code{pow}
1463 @item @tab @code{$log} @tab @code{log}
1464 @item @tab @code{$sinh} @tab @code{sinh}
1465 @item @tab @code{$cosh} @tab @code{cosh}
1466 @item @tab @code{$tanh} @tab @code{tanh}
1467 @item @tab @code{$asinh} @tab @code{asinh}
1468 @item @tab @code{$acosh} @tab @code{acosh}
1469 @item @tab @code{$atanh} @tab @code{atanh}
1472 @code{asinh}, @code{acosh} and @code{atanh} are C99 standard but might
1473 not be available on older systems. Guile provides the following
1474 equivalents (on all systems).
1476 @deftypefn {C Function} double scm_asinh (double x)
1477 @deftypefnx {C Function} double scm_acosh (double x)
1478 @deftypefnx {C Function} double scm_atanh (double x)
1479 Return the hyperbolic arcsine, arccosine or arctangent of @var{x}
1484 @node Bitwise Operations
1485 @subsubsection Bitwise Operations
1487 For the following bitwise functions, negative numbers are treated as
1488 infinite precision twos-complements. For instance @math{-6} is bits
1489 @math{@dots{}111010}, with infinitely many ones on the left. It can
1490 be seen that adding 6 (binary 110) to such a bit pattern gives all
1493 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1494 @deffnx {C Function} scm_logand (n1, n2)
1495 Return the bitwise @sc{and} of the integer arguments.
1498 (logand) @result{} -1
1499 (logand 7) @result{} 7
1500 (logand #b111 #b011 #b001) @result{} 1
1504 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1505 @deffnx {C Function} scm_logior (n1, n2)
1506 Return the bitwise @sc{or} of the integer arguments.
1509 (logior) @result{} 0
1510 (logior 7) @result{} 7
1511 (logior #b000 #b001 #b011) @result{} 3
1515 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1516 @deffnx {C Function} scm_loxor (n1, n2)
1517 Return the bitwise @sc{xor} of the integer arguments. A bit is
1518 set in the result if it is set in an odd number of arguments.
1521 (logxor) @result{} 0
1522 (logxor 7) @result{} 7
1523 (logxor #b000 #b001 #b011) @result{} 2
1524 (logxor #b000 #b001 #b011 #b011) @result{} 1
1528 @deffn {Scheme Procedure} lognot n
1529 @deffnx {C Function} scm_lognot (n)
1530 Return the integer which is the ones-complement of the integer
1531 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1534 (number->string (lognot #b10000000) 2)
1535 @result{} "-10000001"
1536 (number->string (lognot #b0) 2)
1541 @deffn {Scheme Procedure} logtest j k
1542 @deffnx {C Function} scm_logtest (j, k)
1543 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1544 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1545 calculating the @code{logand}, just testing for non-zero.
1548 (logtest #b0100 #b1011) @result{} #f
1549 (logtest #b0100 #b0111) @result{} #t
1553 @deffn {Scheme Procedure} logbit? index j
1554 @deffnx {C Function} scm_logbit_p (index, j)
1555 Test whether bit number @var{index} in @var{j} is set. @var{index}
1556 starts from 0 for the least significant bit.
1559 (logbit? 0 #b1101) @result{} #t
1560 (logbit? 1 #b1101) @result{} #f
1561 (logbit? 2 #b1101) @result{} #t
1562 (logbit? 3 #b1101) @result{} #t
1563 (logbit? 4 #b1101) @result{} #f
1567 @deffn {Scheme Procedure} ash n cnt
1568 @deffnx {C Function} scm_ash (n, cnt)
1569 Return @var{n} shifted left by @var{cnt} bits, or shifted right if
1570 @var{cnt} is negative. This is an ``arithmetic'' shift.
1572 This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and
1573 when @var{cnt} is negative it's a division, rounded towards negative
1574 infinity. (Note that this is not the same rounding as @code{quotient}
1577 With @var{n} viewed as an infinite precision twos complement,
1578 @code{ash} means a left shift introducing zero bits, or a right shift
1582 (number->string (ash #b1 3) 2) @result{} "1000"
1583 (number->string (ash #b1010 -1) 2) @result{} "101"
1585 ;; -23 is bits ...11101001, -6 is bits ...111010
1586 (ash -23 -2) @result{} -6
1590 @deffn {Scheme Procedure} logcount n
1591 @deffnx {C Function} scm_logcount (n)
1592 Return the number of bits in integer @var{n}. If @var{n} is
1593 positive, the 1-bits in its binary representation are counted.
1594 If negative, the 0-bits in its two's-complement binary
1595 representation are counted. If zero, 0 is returned.
1598 (logcount #b10101010)
1607 @deffn {Scheme Procedure} integer-length n
1608 @deffnx {C Function} scm_integer_length (n)
1609 Return the number of bits necessary to represent @var{n}.
1611 For positive @var{n} this is how many bits to the most significant one
1612 bit. For negative @var{n} it's how many bits to the most significant
1613 zero bit in twos complement form.
1616 (integer-length #b10101010) @result{} 8
1617 (integer-length #b1111) @result{} 4
1618 (integer-length 0) @result{} 0
1619 (integer-length -1) @result{} 0
1620 (integer-length -256) @result{} 8
1621 (integer-length -257) @result{} 9
1625 @deffn {Scheme Procedure} integer-expt n k
1626 @deffnx {C Function} scm_integer_expt (n, k)
1627 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1628 integer, @var{n} can be any number.
1630 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1631 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1635 (integer-expt 2 5) @result{} 32
1636 (integer-expt -3 3) @result{} -27
1637 (integer-expt 5 -3) @result{} 1/125
1638 (integer-expt 0 0) @result{} 1
1642 @deffn {Scheme Procedure} bit-extract n start end
1643 @deffnx {C Function} scm_bit_extract (n, start, end)
1644 Return the integer composed of the @var{start} (inclusive)
1645 through @var{end} (exclusive) bits of @var{n}. The
1646 @var{start}th bit becomes the 0-th bit in the result.
1649 (number->string (bit-extract #b1101101010 0 4) 2)
1651 (number->string (bit-extract #b1101101010 4 9) 2)
1658 @subsubsection Random Number Generation
1660 Pseudo-random numbers are generated from a random state object, which
1661 can be created with @code{seed->random-state}. The @var{state}
1662 parameter to the various functions below is optional, it defaults to
1663 the state object in the @code{*random-state*} variable.
1665 @deffn {Scheme Procedure} copy-random-state [state]
1666 @deffnx {C Function} scm_copy_random_state (state)
1667 Return a copy of the random state @var{state}.
1670 @deffn {Scheme Procedure} random n [state]
1671 @deffnx {C Function} scm_random (n, state)
1672 Return a number in [0, @var{n}).
1674 Accepts a positive integer or real n and returns a
1675 number of the same type between zero (inclusive) and
1676 @var{n} (exclusive). The values returned have a uniform
1680 @deffn {Scheme Procedure} random:exp [state]
1681 @deffnx {C Function} scm_random_exp (state)
1682 Return an inexact real in an exponential distribution with mean
1683 1. For an exponential distribution with mean @var{u} use @code{(*
1684 @var{u} (random:exp))}.
1687 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1688 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1689 Fills @var{vect} with inexact real random numbers the sum of whose
1690 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1691 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1692 the coordinates are uniformly distributed over the surface of the unit
1696 @deffn {Scheme Procedure} random:normal [state]
1697 @deffnx {C Function} scm_random_normal (state)
1698 Return an inexact real in a normal distribution. The distribution
1699 used has mean 0 and standard deviation 1. For a normal distribution
1700 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1701 (* @var{d} (random:normal)))}.
1704 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1705 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1706 Fills @var{vect} with inexact real random numbers that are
1707 independent and standard normally distributed
1708 (i.e., with mean 0 and variance 1).
1711 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1712 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1713 Fills @var{vect} with inexact real random numbers the sum of whose
1714 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1715 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1716 the coordinates are uniformly distributed within the unit
1718 @c FIXME: What does this mean, particularly the n-sphere part?
1721 @deffn {Scheme Procedure} random:uniform [state]
1722 @deffnx {C Function} scm_random_uniform (state)
1723 Return a uniformly distributed inexact real random number in
1727 @deffn {Scheme Procedure} seed->random-state seed
1728 @deffnx {C Function} scm_seed_to_random_state (seed)
1729 Return a new random state using @var{seed}.
1732 @defvar *random-state*
1733 The global random state used by the above functions when the
1734 @var{state} parameter is not given.
1737 Note that the initial value of @code{*random-state*} is the same every
1738 time Guile starts up. Therefore, if you don't pass a @var{state}
1739 parameter to the above procedures, and you don't set
1740 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1741 @code{your-seed} is something that @emph{isn't} the same every time,
1742 you'll get the same sequence of ``random'' numbers on every run.
1744 For example, unless the relevant source code has changed, @code{(map
1745 random (cdr (iota 30)))}, if the first use of random numbers since
1746 Guile started up, will always give:
1749 (map random (cdr (iota 19)))
1751 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1754 To use the time of day as the random seed, you can use code like this:
1757 (let ((time (gettimeofday)))
1758 (set! *random-state*
1759 (seed->random-state (+ (car time)
1764 And then (depending on the time of day, of course):
1767 (map random (cdr (iota 19)))
1769 (0 0 1 0 2 4 5 4 5 5 9 3 10 1 8 3 14 17)
1772 For security applications, such as password generation, you should use
1773 more bits of seed. Otherwise an open source password generator could
1774 be attacked by guessing the seed@dots{} but that's a subject for
1779 @subsection Characters
1782 In Scheme, a character literal is written as @code{#\@var{name}} where
1783 @var{name} is the name of the character that you want. Printable
1784 characters have their usual single character name; for example,
1785 @code{#\a} is a lower case @code{a}.
1787 Most of the ``control characters'' (those below codepoint 32) in the
1788 @acronym{ASCII} character set, as well as the space, may be referred
1789 to by longer names: for example, @code{#\tab}, @code{#\esc},
1790 @code{#\stx}, and so on. The following table describes the
1791 @acronym{ASCII} names for each character.
1793 @multitable @columnfractions .25 .25 .25 .25
1794 @item 0 = @code{#\nul}
1795 @tab 1 = @code{#\soh}
1796 @tab 2 = @code{#\stx}
1797 @tab 3 = @code{#\etx}
1798 @item 4 = @code{#\eot}
1799 @tab 5 = @code{#\enq}
1800 @tab 6 = @code{#\ack}
1801 @tab 7 = @code{#\bel}
1802 @item 8 = @code{#\bs}
1803 @tab 9 = @code{#\ht}
1804 @tab 10 = @code{#\nl}
1805 @tab 11 = @code{#\vt}
1806 @item 12 = @code{#\np}
1807 @tab 13 = @code{#\cr}
1808 @tab 14 = @code{#\so}
1809 @tab 15 = @code{#\si}
1810 @item 16 = @code{#\dle}
1811 @tab 17 = @code{#\dc1}
1812 @tab 18 = @code{#\dc2}
1813 @tab 19 = @code{#\dc3}
1814 @item 20 = @code{#\dc4}
1815 @tab 21 = @code{#\nak}
1816 @tab 22 = @code{#\syn}
1817 @tab 23 = @code{#\etb}
1818 @item 24 = @code{#\can}
1819 @tab 25 = @code{#\em}
1820 @tab 26 = @code{#\sub}
1821 @tab 27 = @code{#\esc}
1822 @item 28 = @code{#\fs}
1823 @tab 29 = @code{#\gs}
1824 @tab 30 = @code{#\rs}
1825 @tab 31 = @code{#\us}
1826 @item 32 = @code{#\sp}
1829 The ``delete'' character (octal 177) may be referred to with the name
1832 Several characters have more than one name:
1834 @multitable {@code{#\backspace}} {Original}
1835 @item Alias @tab Original
1836 @item @code{#\space} @tab @code{#\sp}
1837 @item @code{#\newline} @tab @code{#\nl}
1838 @item @code{#\tab} @tab @code{#\ht}
1839 @item @code{#\backspace} @tab @code{#\bs}
1840 @item @code{#\return} @tab @code{#\cr}
1841 @item @code{#\page} @tab @code{#\np}
1842 @item @code{#\null} @tab @code{#\nul}
1846 @deffn {Scheme Procedure} char? x
1847 @deffnx {C Function} scm_char_p (x)
1848 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1852 @deffn {Scheme Procedure} char=? x y
1853 Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}.
1857 @deffn {Scheme Procedure} char<? x y
1858 Return @code{#t} iff @var{x} is less than @var{y} in the @acronym{ASCII} sequence,
1863 @deffn {Scheme Procedure} char<=? x y
1864 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1865 @acronym{ASCII} sequence, else @code{#f}.
1869 @deffn {Scheme Procedure} char>? x y
1870 Return @code{#t} iff @var{x} is greater than @var{y} in the @acronym{ASCII}
1871 sequence, else @code{#f}.
1875 @deffn {Scheme Procedure} char>=? x y
1876 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1877 @acronym{ASCII} sequence, else @code{#f}.
1881 @deffn {Scheme Procedure} char-ci=? x y
1882 Return @code{#t} iff @var{x} is the same character as @var{y} ignoring
1883 case, else @code{#f}.
1887 @deffn {Scheme Procedure} char-ci<? x y
1888 Return @code{#t} iff @var{x} is less than @var{y} in the @acronym{ASCII} sequence
1889 ignoring case, else @code{#f}.
1893 @deffn {Scheme Procedure} char-ci<=? x y
1894 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1895 @acronym{ASCII} sequence ignoring case, else @code{#f}.
1899 @deffn {Scheme Procedure} char-ci>? x y
1900 Return @code{#t} iff @var{x} is greater than @var{y} in the @acronym{ASCII}
1901 sequence ignoring case, else @code{#f}.
1905 @deffn {Scheme Procedure} char-ci>=? x y
1906 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1907 @acronym{ASCII} sequence ignoring case, else @code{#f}.
1910 @rnindex char-alphabetic?
1911 @deffn {Scheme Procedure} char-alphabetic? chr
1912 @deffnx {C Function} scm_char_alphabetic_p (chr)
1913 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1916 @rnindex char-numeric?
1917 @deffn {Scheme Procedure} char-numeric? chr
1918 @deffnx {C Function} scm_char_numeric_p (chr)
1919 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1922 @rnindex char-whitespace?
1923 @deffn {Scheme Procedure} char-whitespace? chr
1924 @deffnx {C Function} scm_char_whitespace_p (chr)
1925 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1928 @rnindex char-upper-case?
1929 @deffn {Scheme Procedure} char-upper-case? chr
1930 @deffnx {C Function} scm_char_upper_case_p (chr)
1931 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1934 @rnindex char-lower-case?
1935 @deffn {Scheme Procedure} char-lower-case? chr
1936 @deffnx {C Function} scm_char_lower_case_p (chr)
1937 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1940 @deffn {Scheme Procedure} char-is-both? chr
1941 @deffnx {C Function} scm_char_is_both_p (chr)
1942 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
1946 @rnindex char->integer
1947 @deffn {Scheme Procedure} char->integer chr
1948 @deffnx {C Function} scm_char_to_integer (chr)
1949 Return the number corresponding to ordinal position of @var{chr} in the
1950 @acronym{ASCII} sequence.
1953 @rnindex integer->char
1954 @deffn {Scheme Procedure} integer->char n
1955 @deffnx {C Function} scm_integer_to_char (n)
1956 Return the character at position @var{n} in the @acronym{ASCII} sequence.
1959 @rnindex char-upcase
1960 @deffn {Scheme Procedure} char-upcase chr
1961 @deffnx {C Function} scm_char_upcase (chr)
1962 Return the uppercase character version of @var{chr}.
1965 @rnindex char-downcase
1966 @deffn {Scheme Procedure} char-downcase chr
1967 @deffnx {C Function} scm_char_downcase (chr)
1968 Return the lowercase character version of @var{chr}.
1971 @node Character Sets
1972 @subsection Character Sets
1974 The features described in this section correspond directly to SRFI-14.
1976 The data type @dfn{charset} implements sets of characters
1977 (@pxref{Characters}). Because the internal representation of
1978 character sets is not visible to the user, a lot of procedures for
1979 handling them are provided.
1981 Character sets can be created, extended, tested for the membership of a
1982 characters and be compared to other character sets.
1984 The Guile implementation of character sets currently deals only with
1985 8-bit characters. In the future, when Guile gets support for
1986 international character sets, this will change, but the functions
1987 provided here will always then be able to efficiently cope with very
1988 large character sets.
1991 * Character Set Predicates/Comparison::
1992 * Iterating Over Character Sets:: Enumerate charset elements.
1993 * Creating Character Sets:: Making new charsets.
1994 * Querying Character Sets:: Test charsets for membership etc.
1995 * Character-Set Algebra:: Calculating new charsets.
1996 * Standard Character Sets:: Variables containing predefined charsets.
1999 @node Character Set Predicates/Comparison
2000 @subsubsection Character Set Predicates/Comparison
2002 Use these procedures for testing whether an object is a character set,
2003 or whether several character sets are equal or subsets of each other.
2004 @code{char-set-hash} can be used for calculating a hash value, maybe for
2005 usage in fast lookup procedures.
2007 @deffn {Scheme Procedure} char-set? obj
2008 @deffnx {C Function} scm_char_set_p (obj)
2009 Return @code{#t} if @var{obj} is a character set, @code{#f}
2013 @deffn {Scheme Procedure} char-set= . char_sets
2014 @deffnx {C Function} scm_char_set_eq (char_sets)
2015 Return @code{#t} if all given character sets are equal.
2018 @deffn {Scheme Procedure} char-set<= . char_sets
2019 @deffnx {C Function} scm_char_set_leq (char_sets)
2020 Return @code{#t} if every character set @var{cs}i is a subset
2021 of character set @var{cs}i+1.
2024 @deffn {Scheme Procedure} char-set-hash cs [bound]
2025 @deffnx {C Function} scm_char_set_hash (cs, bound)
2026 Compute a hash value for the character set @var{cs}. If
2027 @var{bound} is given and non-zero, it restricts the
2028 returned value to the range 0 @dots{} @var{bound - 1}.
2031 @c ===================================================================
2033 @node Iterating Over Character Sets
2034 @subsubsection Iterating Over Character Sets
2036 Character set cursors are a means for iterating over the members of a
2037 character sets. After creating a character set cursor with
2038 @code{char-set-cursor}, a cursor can be dereferenced with
2039 @code{char-set-ref}, advanced to the next member with
2040 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2041 element of the set can be checked with @code{end-of-char-set?}.
2043 Additionally, mapping and (un-)folding procedures for character sets are
2046 @deffn {Scheme Procedure} char-set-cursor cs
2047 @deffnx {C Function} scm_char_set_cursor (cs)
2048 Return a cursor into the character set @var{cs}.
2051 @deffn {Scheme Procedure} char-set-ref cs cursor
2052 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2053 Return the character at the current cursor position
2054 @var{cursor} in the character set @var{cs}. It is an error to
2055 pass a cursor for which @code{end-of-char-set?} returns true.
2058 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2059 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2060 Advance the character set cursor @var{cursor} to the next
2061 character in the character set @var{cs}. It is an error if the
2062 cursor given satisfies @code{end-of-char-set?}.
2065 @deffn {Scheme Procedure} end-of-char-set? cursor
2066 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2067 Return @code{#t} if @var{cursor} has reached the end of a
2068 character set, @code{#f} otherwise.
2071 @deffn {Scheme Procedure} char-set-fold kons knil cs
2072 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2073 Fold the procedure @var{kons} over the character set @var{cs},
2074 initializing it with @var{knil}.
2077 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2078 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2079 This is a fundamental constructor for character sets.
2081 @item @var{g} is used to generate a series of ``seed'' values
2082 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2083 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2084 @item @var{p} tells us when to stop -- when it returns true
2085 when applied to one of the seed values.
2086 @item @var{f} maps each seed value to a character. These
2087 characters are added to the base character set @var{base_cs} to
2088 form the result; @var{base_cs} defaults to the empty set.
2092 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2093 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2094 This is a fundamental constructor for character sets.
2096 @item @var{g} is used to generate a series of ``seed'' values
2097 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2098 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2099 @item @var{p} tells us when to stop -- when it returns true
2100 when applied to one of the seed values.
2101 @item @var{f} maps each seed value to a character. These
2102 characters are added to the base character set @var{base_cs} to
2103 form the result; @var{base_cs} defaults to the empty set.
2107 @deffn {Scheme Procedure} char-set-for-each proc cs
2108 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2109 Apply @var{proc} to every character in the character set
2110 @var{cs}. The return value is not specified.
2113 @deffn {Scheme Procedure} char-set-map proc cs
2114 @deffnx {C Function} scm_char_set_map (proc, cs)
2115 Map the procedure @var{proc} over every character in @var{cs}.
2116 @var{proc} must be a character -> character procedure.
2119 @c ===================================================================
2121 @node Creating Character Sets
2122 @subsubsection Creating Character Sets
2124 New character sets are produced with these procedures.
2126 @deffn {Scheme Procedure} char-set-copy cs
2127 @deffnx {C Function} scm_char_set_copy (cs)
2128 Return a newly allocated character set containing all
2129 characters in @var{cs}.
2132 @deffn {Scheme Procedure} char-set . rest
2133 @deffnx {C Function} scm_char_set (rest)
2134 Return a character set containing all given characters.
2137 @deffn {Scheme Procedure} list->char-set list [base_cs]
2138 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2139 Convert the character list @var{list} to a character set. If
2140 the character set @var{base_cs} is given, the character in this
2141 set are also included in the result.
2144 @deffn {Scheme Procedure} list->char-set! list base_cs
2145 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2146 Convert the character list @var{list} to a character set. The
2147 characters are added to @var{base_cs} and @var{base_cs} is
2151 @deffn {Scheme Procedure} string->char-set str [base_cs]
2152 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2153 Convert the string @var{str} to a character set. If the
2154 character set @var{base_cs} is given, the characters in this
2155 set are also included in the result.
2158 @deffn {Scheme Procedure} string->char-set! str base_cs
2159 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2160 Convert the string @var{str} to a character set. The
2161 characters from the string are added to @var{base_cs}, and
2162 @var{base_cs} is returned.
2165 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2166 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2167 Return a character set containing every character from @var{cs}
2168 so that it satisfies @var{pred}. If provided, the characters
2169 from @var{base_cs} are added to the result.
2172 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2173 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2174 Return a character set containing every character from @var{cs}
2175 so that it satisfies @var{pred}. The characters are added to
2176 @var{base_cs} and @var{base_cs} is returned.
2179 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2180 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2181 Return a character set containing all characters whose
2182 character codes lie in the half-open range
2183 [@var{lower},@var{upper}).
2185 If @var{error} is a true value, an error is signalled if the
2186 specified range contains characters which are not contained in
2187 the implemented character range. If @var{error} is @code{#f},
2188 these characters are silently left out of the resultung
2191 The characters in @var{base_cs} are added to the result, if
2195 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2196 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2197 Return a character set containing all characters whose
2198 character codes lie in the half-open range
2199 [@var{lower},@var{upper}).
2201 If @var{error} is a true value, an error is signalled if the
2202 specified range contains characters which are not contained in
2203 the implemented character range. If @var{error} is @code{#f},
2204 these characters are silently left out of the resultung
2207 The characters are added to @var{base_cs} and @var{base_cs} is
2211 @deffn {Scheme Procedure} ->char-set x
2212 @deffnx {C Function} scm_to_char_set (x)
2213 Coerces x into a char-set. @var{x} may be a string, character or char-set. A string is converted to the set of its constituent characters; a character is converted to a singleton set; a char-set is returned as-is.
2216 @c ===================================================================
2218 @node Querying Character Sets
2219 @subsubsection Querying Character Sets
2221 Access the elements and other information of a character set with these
2224 @deffn {Scheme Procedure} char-set-size cs
2225 @deffnx {C Function} scm_char_set_size (cs)
2226 Return the number of elements in character set @var{cs}.
2229 @deffn {Scheme Procedure} char-set-count pred cs
2230 @deffnx {C Function} scm_char_set_count (pred, cs)
2231 Return the number of the elements int the character set
2232 @var{cs} which satisfy the predicate @var{pred}.
2235 @deffn {Scheme Procedure} char-set->list cs
2236 @deffnx {C Function} scm_char_set_to_list (cs)
2237 Return a list containing the elements of the character set
2241 @deffn {Scheme Procedure} char-set->string cs
2242 @deffnx {C Function} scm_char_set_to_string (cs)
2243 Return a string containing the elements of the character set
2244 @var{cs}. The order in which the characters are placed in the
2245 string is not defined.
2248 @deffn {Scheme Procedure} char-set-contains? cs ch
2249 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2250 Return @code{#t} iff the character @var{ch} is contained in the
2251 character set @var{cs}.
2254 @deffn {Scheme Procedure} char-set-every pred cs
2255 @deffnx {C Function} scm_char_set_every (pred, cs)
2256 Return a true value if every character in the character set
2257 @var{cs} satisfies the predicate @var{pred}.
2260 @deffn {Scheme Procedure} char-set-any pred cs
2261 @deffnx {C Function} scm_char_set_any (pred, cs)
2262 Return a true value if any character in the character set
2263 @var{cs} satisfies the predicate @var{pred}.
2266 @c ===================================================================
2268 @node Character-Set Algebra
2269 @subsubsection Character-Set Algebra
2271 Character sets can be manipulated with the common set algebra operation,
2272 such as union, complement, intersection etc. All of these procedures
2273 provide side-effecting variants, which modify their character set
2276 @deffn {Scheme Procedure} char-set-adjoin cs . rest
2277 @deffnx {C Function} scm_char_set_adjoin (cs, rest)
2278 Add all character arguments to the first argument, which must
2282 @deffn {Scheme Procedure} char-set-delete cs . rest
2283 @deffnx {C Function} scm_char_set_delete (cs, rest)
2284 Delete all character arguments from the first argument, which
2285 must be a character set.
2288 @deffn {Scheme Procedure} char-set-adjoin! cs . rest
2289 @deffnx {C Function} scm_char_set_adjoin_x (cs, rest)
2290 Add all character arguments to the first argument, which must
2294 @deffn {Scheme Procedure} char-set-delete! cs . rest
2295 @deffnx {C Function} scm_char_set_delete_x (cs, rest)
2296 Delete all character arguments from the first argument, which
2297 must be a character set.
2300 @deffn {Scheme Procedure} char-set-complement cs
2301 @deffnx {C Function} scm_char_set_complement (cs)
2302 Return the complement of the character set @var{cs}.
2305 @deffn {Scheme Procedure} char-set-union . rest
2306 @deffnx {C Function} scm_char_set_union (rest)
2307 Return the union of all argument character sets.
2310 @deffn {Scheme Procedure} char-set-intersection . rest
2311 @deffnx {C Function} scm_char_set_intersection (rest)
2312 Return the intersection of all argument character sets.
2315 @deffn {Scheme Procedure} char-set-difference cs1 . rest
2316 @deffnx {C Function} scm_char_set_difference (cs1, rest)
2317 Return the difference of all argument character sets.
2320 @deffn {Scheme Procedure} char-set-xor . rest
2321 @deffnx {C Function} scm_char_set_xor (rest)
2322 Return the exclusive-or of all argument character sets.
2325 @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest
2326 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest)
2327 Return the difference and the intersection of all argument
2331 @deffn {Scheme Procedure} char-set-complement! cs
2332 @deffnx {C Function} scm_char_set_complement_x (cs)
2333 Return the complement of the character set @var{cs}.
2336 @deffn {Scheme Procedure} char-set-union! cs1 . rest
2337 @deffnx {C Function} scm_char_set_union_x (cs1, rest)
2338 Return the union of all argument character sets.
2341 @deffn {Scheme Procedure} char-set-intersection! cs1 . rest
2342 @deffnx {C Function} scm_char_set_intersection_x (cs1, rest)
2343 Return the intersection of all argument character sets.
2346 @deffn {Scheme Procedure} char-set-difference! cs1 . rest
2347 @deffnx {C Function} scm_char_set_difference_x (cs1, rest)
2348 Return the difference of all argument character sets.
2351 @deffn {Scheme Procedure} char-set-xor! cs1 . rest
2352 @deffnx {C Function} scm_char_set_xor_x (cs1, rest)
2353 Return the exclusive-or of all argument character sets.
2356 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest
2357 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest)
2358 Return the difference and the intersection of all argument
2362 @c ===================================================================
2364 @node Standard Character Sets
2365 @subsubsection Standard Character Sets
2367 In order to make the use of the character set data type and procedures
2368 useful, several predefined character set variables exist.
2374 Currently, the contents of these character sets are recomputed upon a
2375 successful @code{setlocale} call (@pxref{Locales}) in order to reflect
2376 the characters available in the current locale's codeset. For
2377 instance, @code{char-set:letter} contains 52 characters under an ASCII
2378 locale (e.g., the default @code{C} locale) and 117 characters under an
2379 ISO-8859-1 (``Latin-1'') locale.
2381 @defvr {Scheme Variable} char-set:lower-case
2382 @defvrx {C Variable} scm_char_set_lower_case
2383 All lower-case characters.
2386 @defvr {Scheme Variable} char-set:upper-case
2387 @defvrx {C Variable} scm_char_set_upper_case
2388 All upper-case characters.
2391 @defvr {Scheme Variable} char-set:title-case
2392 @defvrx {C Variable} scm_char_set_title_case
2393 This is empty, because ASCII has no titlecase characters.
2396 @defvr {Scheme Variable} char-set:letter
2397 @defvrx {C Variable} scm_char_set_letter
2398 All letters, e.g. the union of @code{char-set:lower-case} and
2399 @code{char-set:upper-case}.
2402 @defvr {Scheme Variable} char-set:digit
2403 @defvrx {C Variable} scm_char_set_digit
2407 @defvr {Scheme Variable} char-set:letter+digit
2408 @defvrx {C Variable} scm_char_set_letter_and_digit
2409 The union of @code{char-set:letter} and @code{char-set:digit}.
2412 @defvr {Scheme Variable} char-set:graphic
2413 @defvrx {C Variable} scm_char_set_graphic
2414 All characters which would put ink on the paper.
2417 @defvr {Scheme Variable} char-set:printing
2418 @defvrx {C Variable} scm_char_set_printing
2419 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2422 @defvr {Scheme Variable} char-set:whitespace
2423 @defvrx {C Variable} scm_char_set_whitespace
2424 All whitespace characters.
2427 @defvr {Scheme Variable} char-set:blank
2428 @defvrx {C Variable} scm_char_set_blank
2429 All horizontal whitespace characters, that is @code{#\space} and
2433 @defvr {Scheme Variable} char-set:iso-control
2434 @defvrx {C Variable} scm_char_set_iso_control
2435 The ISO control characters with the codes 0--31 and 127.
2438 @defvr {Scheme Variable} char-set:punctuation
2439 @defvrx {C Variable} scm_char_set_punctuation
2440 The characters @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2443 @defvr {Scheme Variable} char-set:symbol
2444 @defvrx {C Variable} scm_char_set_symbol
2445 The characters @code{$+<=>^`|~}.
2448 @defvr {Scheme Variable} char-set:hex-digit
2449 @defvrx {C Variable} scm_char_set_hex_digit
2450 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2453 @defvr {Scheme Variable} char-set:ascii
2454 @defvrx {C Variable} scm_char_set_ascii
2455 All ASCII characters.
2458 @defvr {Scheme Variable} char-set:empty
2459 @defvrx {C Variable} scm_char_set_empty
2460 The empty character set.
2463 @defvr {Scheme Variable} char-set:full
2464 @defvrx {C Variable} scm_char_set_full
2465 This character set contains all possible characters.
2472 Strings are fixed-length sequences of characters. They can be created
2473 by calling constructor procedures, but they can also literally get
2474 entered at the @acronym{REPL} or in Scheme source files.
2476 @c Guile provides a rich set of string processing procedures, because text
2477 @c handling is very important when Guile is used as a scripting language.
2479 Strings always carry the information about how many characters they are
2480 composed of with them, so there is no special end-of-string character,
2481 like in C. That means that Scheme strings can contain any character,
2482 even the @samp{#\nul} character @samp{\0}.
2484 To use strings efficiently, you need to know a bit about how Guile
2485 implements them. In Guile, a string consists of two parts, a head and
2486 the actual memory where the characters are stored. When a string (or
2487 a substring of it) is copied, only a new head gets created, the memory
2488 is usually not copied. The two heads start out pointing to the same
2491 When one of these two strings is modified, as with @code{string-set!},
2492 their common memory does get copied so that each string has its own
2493 memory and modifying one does not accidently modify the other as well.
2494 Thus, Guile's strings are `copy on write'; the actual copying of their
2495 memory is delayed until one string is written to.
2497 This implementation makes functions like @code{substring} very
2498 efficient in the common case that no modifications are done to the
2501 If you do know that your strings are getting modified right away, you
2502 can use @code{substring/copy} instead of @code{substring}. This
2503 function performs the copy immediately at the time of creation. This
2504 is more efficient, especially in a multi-threaded program. Also,
2505 @code{substring/copy} can avoid the problem that a short substring
2506 holds on to the memory of a very large original string that could
2507 otherwise be recycled.
2509 If you want to avoid the copy altogether, so that modifications of one
2510 string show up in the other, you can use @code{substring/shared}. The
2511 strings created by this procedure are called @dfn{mutation sharing
2512 substrings} since the substring and the original string share
2513 modifications to each other.
2515 If you want to prevent modifications, use @code{substring/read-only}.
2517 Guile provides all procedures of SRFI-13 and a few more.
2520 * String Syntax:: Read syntax for strings.
2521 * String Predicates:: Testing strings for certain properties.
2522 * String Constructors:: Creating new string objects.
2523 * List/String Conversion:: Converting from/to lists of characters.
2524 * String Selection:: Select portions from strings.
2525 * String Modification:: Modify parts or whole strings.
2526 * String Comparison:: Lexicographic ordering predicates.
2527 * String Searching:: Searching in strings.
2528 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2529 * Reversing and Appending Strings:: Appending strings to form a new string.
2530 * Mapping Folding and Unfolding:: Iterating over strings.
2531 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2532 * Conversion to/from C::
2536 @subsubsection String Read Syntax
2538 @c In the following @code is used to get a good font in TeX etc, but
2539 @c is omitted for Info format, so as not to risk any confusion over
2540 @c whether surrounding ` ' quotes are part of the escape or are
2541 @c special in a string (they're not).
2543 The read syntax for strings is an arbitrarily long sequence of
2544 characters enclosed in double quotes (@nicode{"}).
2546 Backslash is an escape character and can be used to insert the
2547 following special characters. @nicode{\"} and @nicode{\\} are R5RS
2548 standard, the rest are Guile extensions, notice they follow C string
2553 Backslash character.
2556 Double quote character (an unescaped @nicode{"} is otherwise the end
2560 NUL character (ASCII 0).
2563 Bell character (ASCII 7).
2566 Formfeed character (ASCII 12).
2569 Newline character (ASCII 10).
2572 Carriage return character (ASCII 13).
2575 Tab character (ASCII 9).
2578 Vertical tab character (ASCII 11).
2581 Character code given by two hexadecimal digits. For example
2582 @nicode{\x7f} for an ASCII DEL (127).
2586 The following are examples of string literals:
2596 @node String Predicates
2597 @subsubsection String Predicates
2599 The following procedures can be used to check whether a given string
2600 fulfills some specified property.
2603 @deffn {Scheme Procedure} string? obj
2604 @deffnx {C Function} scm_string_p (obj)
2605 Return @code{#t} if @var{obj} is a string, else @code{#f}.
2608 @deftypefn {C Function} int scm_is_string (SCM obj)
2609 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
2612 @deffn {Scheme Procedure} string-null? str
2613 @deffnx {C Function} scm_string_null_p (str)
2614 Return @code{#t} if @var{str}'s length is zero, and
2615 @code{#f} otherwise.
2617 (string-null? "") @result{} #t
2619 (string-null? y) @result{} #f
2623 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
2624 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
2625 Check if @var{char_pred} is true for any character in string @var{s}.
2627 @var{char_pred} can be a character to check for any equal to that, or
2628 a character set (@pxref{Character Sets}) to check for any in that set,
2629 or a predicate procedure to call.
2631 For a procedure, calls @code{(@var{char_pred} c)} are made
2632 successively on the characters from @var{start} to @var{end}. If
2633 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
2634 stops and that return value is the return from @code{string-any}. The
2635 call on the last character (ie.@: at @math{@var{end}-1}), if that
2636 point is reached, is a tail call.
2638 If there are no characters in @var{s} (ie.@: @var{start} equals
2639 @var{end}) then the return is @code{#f}.
2642 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
2643 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
2644 Check if @var{char_pred} is true for every character in string
2647 @var{char_pred} can be a character to check for every character equal
2648 to that, or a character set (@pxref{Character Sets}) to check for
2649 every character being in that set, or a predicate procedure to call.
2651 For a procedure, calls @code{(@var{char_pred} c)} are made
2652 successively on the characters from @var{start} to @var{end}. If
2653 @var{char_pred} returns @code{#f}, @code{string-every} stops and
2654 returns @code{#f}. The call on the last character (ie.@: at
2655 @math{@var{end}-1}), if that point is reached, is a tail call and the
2656 return from that call is the return from @code{string-every}.
2658 If there are no characters in @var{s} (ie.@: @var{start} equals
2659 @var{end}) then the return is @code{#t}.
2662 @node String Constructors
2663 @subsubsection String Constructors
2665 The string constructor procedures create new string objects, possibly
2666 initializing them with some specified character data. See also
2667 @xref{String Selection}, for ways to create strings from existing
2670 @c FIXME::martin: list->string belongs into `List/String Conversion'
2672 @deffn {Scheme Procedure} string char@dots{}
2674 Return a newly allocated string made from the given character
2678 (string #\x #\y #\z) @result{} "xyz"
2679 (string) @result{} ""
2683 @deffn {Scheme Procedure} list->string lst
2684 @deffnx {C Function} scm_string (lst)
2685 @rnindex list->string
2686 Return a newly allocated string made from a list of characters.
2689 (list->string '(#\a #\b #\c)) @result{} "abc"
2693 @deffn {Scheme Procedure} reverse-list->string lst
2694 @deffnx {C Function} scm_reverse_list_to_string (lst)
2695 Return a newly allocated string made from a list of characters, in
2699 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
2703 @rnindex make-string
2704 @deffn {Scheme Procedure} make-string k [chr]
2705 @deffnx {C Function} scm_make_string (k, chr)
2706 Return a newly allocated string of
2707 length @var{k}. If @var{chr} is given, then all elements of
2708 the string are initialized to @var{chr}, otherwise the contents
2709 of the @var{string} are unspecified.
2712 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
2713 Like @code{scm_make_string}, but expects the length as a
2717 @deffn {Scheme Procedure} string-tabulate proc len
2718 @deffnx {C Function} scm_string_tabulate (proc, len)
2719 @var{proc} is an integer->char procedure. Construct a string
2720 of size @var{len} by applying @var{proc} to each index to
2721 produce the corresponding string element. The order in which
2722 @var{proc} is applied to the indices is not specified.
2725 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
2726 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
2727 Append the string in the string list @var{ls}, using the string
2728 @var{delim} as a delimiter between the elements of @var{ls}.
2729 @var{grammar} is a symbol which specifies how the delimiter is
2730 placed between the strings, and defaults to the symbol
2735 Insert the separator between list elements. An empty string
2736 will produce an empty list.
2738 Like @code{infix}, but will raise an error if given the empty
2741 Insert the separator after every list element.
2743 Insert the separator before each list element.
2747 @node List/String Conversion
2748 @subsubsection List/String conversion
2750 When processing strings, it is often convenient to first convert them
2751 into a list representation by using the procedure @code{string->list},
2752 work with the resulting list, and then convert it back into a string.
2753 These procedures are useful for similar tasks.
2755 @rnindex string->list
2756 @deffn {Scheme Procedure} string->list str [start [end]]
2757 @deffnx {C Function} scm_substring_to_list (str, start, end)
2758 @deffnx {C Function} scm_string_to_list (str)
2759 Convert the string @var{str} into a list of characters.
2762 @deffn {Scheme Procedure} string-split str chr
2763 @deffnx {C Function} scm_string_split (str, chr)
2764 Split the string @var{str} into the a list of the substrings delimited
2765 by appearances of the character @var{chr}. Note that an empty substring
2766 between separator characters will result in an empty string in the
2770 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
2772 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
2774 (string-split "::" #\:)
2778 (string-split "" #\:)
2785 @node String Selection
2786 @subsubsection String Selection
2788 Portions of strings can be extracted by these procedures.
2789 @code{string-ref} delivers individual characters whereas
2790 @code{substring} can be used to extract substrings from longer strings.
2792 @rnindex string-length
2793 @deffn {Scheme Procedure} string-length string
2794 @deffnx {C Function} scm_string_length (string)
2795 Return the number of characters in @var{string}.
2798 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
2799 Return the number of characters in @var{str} as a @code{size_t}.
2803 @deffn {Scheme Procedure} string-ref str k
2804 @deffnx {C Function} scm_string_ref (str, k)
2805 Return character @var{k} of @var{str} using zero-origin
2806 indexing. @var{k} must be a valid index of @var{str}.
2809 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
2810 Return character @var{k} of @var{str} using zero-origin
2811 indexing. @var{k} must be a valid index of @var{str}.
2814 @rnindex string-copy
2815 @deffn {Scheme Procedure} string-copy str [start [end]]
2816 @deffnx {C Function} scm_substring_copy (str, start, end)
2817 @deffnx {C Function} scm_string_copy (str)
2818 Return a copy of the given string @var{str}.
2820 The returned string shares storage with @var{str} initially, but it is
2821 copied as soon as one of the two strings is modified.
2825 @deffn {Scheme Procedure} substring str start [end]
2826 @deffnx {C Function} scm_substring (str, start, end)
2827 Return a new string formed from the characters
2828 of @var{str} beginning with index @var{start} (inclusive) and
2829 ending with index @var{end} (exclusive).
2830 @var{str} must be a string, @var{start} and @var{end} must be
2831 exact integers satisfying:
2833 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
2835 The returned string shares storage with @var{str} initially, but it is
2836 copied as soon as one of the two strings is modified.
2839 @deffn {Scheme Procedure} substring/shared str start [end]
2840 @deffnx {C Function} scm_substring_shared (str, start, end)
2841 Like @code{substring}, but the strings continue to share their storage
2842 even if they are modified. Thus, modifications to @var{str} show up
2843 in the new string, and vice versa.
2846 @deffn {Scheme Procedure} substring/copy str start [end]
2847 @deffnx {C Function} scm_substring_copy (str, start, end)
2848 Like @code{substring}, but the storage for the new string is copied
2852 @deffn {Scheme Procedure} substring/read-only str start [end]
2853 @deffnx {C Function} scm_substring_read_only (str, start, end)
2854 Like @code{substring}, but the resulting string can not be modified.
2857 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
2858 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
2859 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
2860 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
2861 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
2864 @deffn {Scheme Procedure} string-take s n
2865 @deffnx {C Function} scm_string_take (s, n)
2866 Return the @var{n} first characters of @var{s}.
2869 @deffn {Scheme Procedure} string-drop s n
2870 @deffnx {C Function} scm_string_drop (s, n)
2871 Return all but the first @var{n} characters of @var{s}.
2874 @deffn {Scheme Procedure} string-take-right s n
2875 @deffnx {C Function} scm_string_take_right (s, n)
2876 Return the @var{n} last characters of @var{s}.
2879 @deffn {Scheme Procedure} string-drop-right s n
2880 @deffnx {C Function} scm_string_drop_right (s, n)
2881 Return all but the last @var{n} characters of @var{s}.
2884 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
2885 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
2886 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
2887 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
2888 Take characters @var{start} to @var{end} from the string @var{s} and
2889 either pad with @var{char} or truncate them to give @var{len}
2892 @code{string-pad} pads or truncates on the left, so for example
2895 (string-pad "x" 3) @result{} " x"
2896 (string-pad "abcde" 3) @result{} "cde"
2899 @code{string-pad-right} pads or truncates on the right, so for example
2902 (string-pad-right "x" 3) @result{} "x "
2903 (string-pad-right "abcde" 3) @result{} "abc"
2907 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
2908 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
2909 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
2910 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
2911 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
2912 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
2913 Trim occurrances of @var{char_pred} from the ends of @var{s}.
2915 @code{string-trim} trims @var{char_pred} characters from the left
2916 (start) of the string, @code{string-trim-right} trims them from the
2917 right (end) of the string, @code{string-trim-both} trims from both
2920 @var{char_pred} can be a character, a character set, or a predicate
2921 procedure to call on each character. If @var{char_pred} is not given
2922 the default is whitespace as per @code{char-set:whitespace}
2923 (@pxref{Standard Character Sets}).
2926 (string-trim " x ") @result{} "x "
2927 (string-trim-right "banana" #\a) @result{} "banan"
2928 (string-trim-both ".,xy:;" char-set:punctuation)
2930 (string-trim-both "xyzzy" (lambda (c)
2937 @node String Modification
2938 @subsubsection String Modification
2940 These procedures are for modifying strings in-place. This means that the
2941 result of the operation is not a new string; instead, the original string's
2942 memory representation is modified.
2944 @rnindex string-set!
2945 @deffn {Scheme Procedure} string-set! str k chr
2946 @deffnx {C Function} scm_string_set_x (str, k, chr)
2947 Store @var{chr} in element @var{k} of @var{str} and return
2948 an unspecified value. @var{k} must be a valid index of
2952 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
2953 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
2956 @rnindex string-fill!
2957 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
2958 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
2959 @deffnx {C Function} scm_string_fill_x (str, chr)
2960 Stores @var{chr} in every element of the given @var{str} and
2961 returns an unspecified value.
2964 @deffn {Scheme Procedure} substring-fill! str start end fill
2965 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
2966 Change every character in @var{str} between @var{start} and
2967 @var{end} to @var{fill}.
2970 (define y "abcdefg")
2971 (substring-fill! y 1 3 #\r)
2977 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
2978 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
2979 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
2980 into @var{str2} beginning at position @var{start2}.
2981 @var{str1} and @var{str2} can be the same string.
2984 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
2985 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
2986 Copy the sequence of characters from index range [@var{start},
2987 @var{end}) in string @var{s} to string @var{target}, beginning
2988 at index @var{tstart}. The characters are copied left-to-right
2989 or right-to-left as needed -- the copy is guaranteed to work,
2990 even if @var{target} and @var{s} are the same string. It is an
2991 error if the copy operation runs off the end of the target
2996 @node String Comparison
2997 @subsubsection String Comparison
2999 The procedures in this section are similar to the character ordering
3000 predicates (@pxref{Characters}), but are defined on character sequences.
3002 The first set is specified in R5RS and has names that end in @code{?}.
3003 The second set is specified in SRFI-13 and the names have no ending
3004 @code{?}. The predicates ending in @code{-ci} ignore the character case
3005 when comparing strings. @xref{Text Collation, the @code{(ice-9
3006 i18n)} module}, for locale-dependent string comparison.
3009 @deffn {Scheme Procedure} string=? s1 s2
3010 Lexicographic equality predicate; return @code{#t} if the two
3011 strings are the same length and contain the same characters in
3012 the same positions, otherwise return @code{#f}.
3014 The procedure @code{string-ci=?} treats upper and lower case
3015 letters as though they were the same character, but
3016 @code{string=?} treats upper and lower case as distinct
3021 @deffn {Scheme Procedure} string<? s1 s2
3022 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3023 is lexicographically less than @var{s2}.
3027 @deffn {Scheme Procedure} string<=? s1 s2
3028 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3029 is lexicographically less than or equal to @var{s2}.
3033 @deffn {Scheme Procedure} string>? s1 s2
3034 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3035 is lexicographically greater than @var{s2}.
3039 @deffn {Scheme Procedure} string>=? s1 s2
3040 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3041 is lexicographically greater than or equal to @var{s2}.
3044 @rnindex string-ci=?
3045 @deffn {Scheme Procedure} string-ci=? s1 s2
3046 Case-insensitive string equality predicate; return @code{#t} if
3047 the two strings are the same length and their component
3048 characters match (ignoring case) at each position; otherwise
3052 @rnindex string-ci<?
3053 @deffn {Scheme Procedure} string-ci<? s1 s2
3054 Case insensitive lexicographic ordering predicate; return
3055 @code{#t} if @var{s1} is lexicographically less than @var{s2}
3060 @deffn {Scheme Procedure} string-ci<=? s1 s2
3061 Case insensitive lexicographic ordering predicate; return
3062 @code{#t} if @var{s1} is lexicographically less than or equal
3063 to @var{s2} regardless of case.
3066 @rnindex string-ci>?
3067 @deffn {Scheme Procedure} string-ci>? s1 s2
3068 Case insensitive lexicographic ordering predicate; return
3069 @code{#t} if @var{s1} is lexicographically greater than
3070 @var{s2} regardless of case.
3073 @rnindex string-ci>=?
3074 @deffn {Scheme Procedure} string-ci>=? s1 s2
3075 Case insensitive lexicographic ordering predicate; return
3076 @code{#t} if @var{s1} is lexicographically greater than or
3077 equal to @var{s2} regardless of case.
3080 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3081 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3082 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3083 mismatch index, depending upon whether @var{s1} is less than,
3084 equal to, or greater than @var{s2}. The mismatch index is the
3085 largest index @var{i} such that for every 0 <= @var{j} <
3086 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3087 @var{i} is the first position that does not match.
3090 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3091 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3092 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3093 mismatch index, depending upon whether @var{s1} is less than,
3094 equal to, or greater than @var{s2}. The mismatch index is the
3095 largest index @var{i} such that for every 0 <= @var{j} <
3096 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3097 @var{i} is the first position that does not match. The
3098 character comparison is done case-insensitively.
3101 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3102 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3103 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3107 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3108 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3109 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3113 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3114 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3115 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3116 true value otherwise.
3119 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3120 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3121 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3122 true value otherwise.
3125 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3126 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3127 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3131 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3132 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3133 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3137 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3138 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3139 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3140 value otherwise. The character comparison is done
3144 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3145 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3146 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3147 value otherwise. The character comparison is done
3151 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3152 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3153 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3154 true value otherwise. The character comparison is done
3158 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3159 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3160 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3161 true value otherwise. The character comparison is done
3165 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3166 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3167 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3168 value otherwise. The character comparison is done
3172 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3173 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3174 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3175 otherwise. The character comparison is done
3179 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3180 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3181 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).
3184 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3185 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3186 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).
3189 @node String Searching
3190 @subsubsection String Searching
3192 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3193 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3194 Search through the string @var{s} from left to right, returning
3195 the index of the first occurence of a character which
3199 equals @var{char_pred}, if it is character,
3202 satisifies the predicate @var{char_pred}, if it is a procedure,
3205 is in the set @var{char_pred}, if it is a character set.
3209 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3210 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3211 Search through the string @var{s} from right to left, returning
3212 the index of the last occurence of a character which
3216 equals @var{char_pred}, if it is character,
3219 satisifies the predicate @var{char_pred}, if it is a procedure,
3222 is in the set if @var{char_pred} is a character set.
3226 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3227 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3228 Return the length of the longest common prefix of the two
3232 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3233 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3234 Return the length of the longest common prefix of the two
3235 strings, ignoring character case.
3238 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3239 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3240 Return the length of the longest common suffix of the two
3244 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3245 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3246 Return the length of the longest common suffix of the two
3247 strings, ignoring character case.
3250 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3251 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3252 Is @var{s1} a prefix of @var{s2}?
3255 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3256 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3257 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3260 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3261 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3262 Is @var{s1} a suffix of @var{s2}?
3265 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3266 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3267 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3270 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3271 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3272 Search through the string @var{s} from right to left, returning
3273 the index of the last occurence of a character which
3277 equals @var{char_pred}, if it is character,
3280 satisifies the predicate @var{char_pred}, if it is a procedure,
3283 is in the set if @var{char_pred} is a character set.
3287 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3288 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3289 Search through the string @var{s} from left to right, returning
3290 the index of the first occurence of a character which
3294 does not equal @var{char_pred}, if it is character,
3297 does not satisify the predicate @var{char_pred}, if it is a
3301 is not in the set if @var{char_pred} is a character set.
3305 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3306 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3307 Search through the string @var{s} from right to left, returning
3308 the index of the last occurence of a character which
3312 does not equal @var{char_pred}, if it is character,
3315 does not satisfy the predicate @var{char_pred}, if it is a
3319 is not in the set if @var{char_pred} is a character set.
3323 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3324 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3325 Return the count of the number of characters in the string
3330 equals @var{char_pred}, if it is character,
3333 satisifies the predicate @var{char_pred}, if it is a procedure.
3336 is in the set @var{char_pred}, if it is a character set.
3340 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3341 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3342 Does string @var{s1} contain string @var{s2}? Return the index
3343 in @var{s1} where @var{s2} occurs as a substring, or false.
3344 The optional start/end indices restrict the operation to the
3345 indicated substrings.
3348 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3349 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3350 Does string @var{s1} contain string @var{s2}? Return the index
3351 in @var{s1} where @var{s2} occurs as a substring, or false.
3352 The optional start/end indices restrict the operation to the
3353 indicated substrings. Character comparison is done
3357 @node Alphabetic Case Mapping
3358 @subsubsection Alphabetic Case Mapping
3360 These are procedures for mapping strings to their upper- or lower-case
3361 equivalents, respectively, or for capitalizing strings.
3363 @deffn {Scheme Procedure} string-upcase str [start [end]]
3364 @deffnx {C Function} scm_substring_upcase (str, start, end)
3365 @deffnx {C Function} scm_string_upcase (str)
3366 Upcase every character in @code{str}.
3369 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3370 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3371 @deffnx {C Function} scm_string_upcase_x (str)
3372 Destructively upcase every character in @code{str}.
3382 @deffn {Scheme Procedure} string-downcase str [start [end]]
3383 @deffnx {C Function} scm_substring_downcase (str, start, end)
3384 @deffnx {C Function} scm_string_downcase (str)
3385 Downcase every character in @var{str}.
3388 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3389 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3390 @deffnx {C Function} scm_string_downcase_x (str)
3391 Destructively downcase every character in @var{str}.
3396 (string-downcase! y)
3403 @deffn {Scheme Procedure} string-capitalize str
3404 @deffnx {C Function} scm_string_capitalize (str)
3405 Return a freshly allocated string with the characters in
3406 @var{str}, where the first character of every word is
3410 @deffn {Scheme Procedure} string-capitalize! str
3411 @deffnx {C Function} scm_string_capitalize_x (str)
3412 Upcase the first character of every word in @var{str}
3413 destructively and return @var{str}.
3416 y @result{} "hello world"
3417 (string-capitalize! y) @result{} "Hello World"
3418 y @result{} "Hello World"
3422 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3423 @deffnx {C Function} scm_string_titlecase (str, start, end)
3424 Titlecase every first character in a word in @var{str}.
3427 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3428 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3429 Destructively titlecase every first character in a word in
3433 @node Reversing and Appending Strings
3434 @subsubsection Reversing and Appending Strings
3436 @deffn {Scheme Procedure} string-reverse str [start [end]]
3437 @deffnx {C Function} scm_string_reverse (str, start, end)
3438 Reverse the string @var{str}. The optional arguments
3439 @var{start} and @var{end} delimit the region of @var{str} to
3443 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3444 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3445 Reverse the string @var{str} in-place. The optional arguments
3446 @var{start} and @var{end} delimit the region of @var{str} to
3447 operate on. The return value is unspecified.
3450 @rnindex string-append
3451 @deffn {Scheme Procedure} string-append . args
3452 @deffnx {C Function} scm_string_append (args)
3453 Return a newly allocated string whose characters form the
3454 concatenation of the given strings, @var{args}.
3458 (string-append h "world"))
3459 @result{} "hello world"
3463 @deffn {Scheme Procedure} string-append/shared . ls
3464 @deffnx {C Function} scm_string_append_shared (ls)
3465 Like @code{string-append}, but the result may share memory
3466 with the argument strings.
3469 @deffn {Scheme Procedure} string-concatenate ls
3470 @deffnx {C Function} scm_string_concatenate (ls)
3471 Append the elements of @var{ls} (which must be strings)
3472 together into a single string. Guaranteed to return a freshly
3476 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3477 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3478 Without optional arguments, this procedure is equivalent to
3481 (string-concatenate (reverse ls))
3484 If the optional argument @var{final_string} is specified, it is
3485 consed onto the beginning to @var{ls} before performing the
3486 list-reverse and string-concatenate operations. If @var{end}
3487 is given, only the characters of @var{final_string} up to index
3490 Guaranteed to return a freshly allocated string.
3493 @deffn {Scheme Procedure} string-concatenate/shared ls
3494 @deffnx {C Function} scm_string_concatenate_shared (ls)
3495 Like @code{string-concatenate}, but the result may share memory
3496 with the strings in the list @var{ls}.
3499 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3500 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3501 Like @code{string-concatenate-reverse}, but the result may
3502 share memory with the the strings in the @var{ls} arguments.
3505 @node Mapping Folding and Unfolding
3506 @subsubsection Mapping, Folding, and Unfolding
3508 @deffn {Scheme Procedure} string-map proc s [start [end]]
3509 @deffnx {C Function} scm_string_map (proc, s, start, end)
3510 @var{proc} is a char->char procedure, it is mapped over
3511 @var{s}. The order in which the procedure is applied to the
3512 string elements is not specified.
3515 @deffn {Scheme Procedure} string-map! proc s [start [end]]
3516 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
3517 @var{proc} is a char->char procedure, it is mapped over
3518 @var{s}. The order in which the procedure is applied to the
3519 string elements is not specified. The string @var{s} is
3520 modified in-place, the return value is not specified.
3523 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
3524 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
3525 @var{proc} is mapped over @var{s} in left-to-right order. The
3526 return value is not specified.
3529 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
3530 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
3531 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
3534 For example, to change characters to alternately upper and lower case,
3537 (define str (string-copy "studly"))
3538 (string-for-each-index (lambda (i)
3540 ((if (even? i) char-upcase char-downcase)
3541 (string-ref str i))))
3543 str @result{} "StUdLy"
3547 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
3548 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
3549 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3550 as the terminating element, from left to right. @var{kons}
3551 must expect two arguments: The actual character and the last
3552 result of @var{kons}' application.
3555 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
3556 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
3557 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3558 as the terminating element, from right to left. @var{kons}
3559 must expect two arguments: The actual character and the last
3560 result of @var{kons}' application.
3563 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
3564 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
3566 @item @var{g} is used to generate a series of @emph{seed}
3567 values from the initial @var{seed}: @var{seed}, (@var{g}
3568 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3570 @item @var{p} tells us when to stop -- when it returns true
3571 when applied to one of these seed values.
3572 @item @var{f} maps each seed value to the corresponding
3573 character in the result string. These chars are assembled
3574 into the string in a left-to-right order.
3575 @item @var{base} is the optional initial/leftmost portion
3576 of the constructed string; it default to the empty
3578 @item @var{make_final} is applied to the terminal seed
3579 value (on which @var{p} returns true) to produce
3580 the final/rightmost portion of the constructed string.
3581 The default is nothing extra.
3585 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
3586 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
3588 @item @var{g} is used to generate a series of @emph{seed}
3589 values from the initial @var{seed}: @var{seed}, (@var{g}
3590 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3592 @item @var{p} tells us when to stop -- when it returns true
3593 when applied to one of these seed values.
3594 @item @var{f} maps each seed value to the corresponding
3595 character in the result string. These chars are assembled
3596 into the string in a right-to-left order.
3597 @item @var{base} is the optional initial/rightmost portion
3598 of the constructed string; it default to the empty
3600 @item @var{make_final} is applied to the terminal seed
3601 value (on which @var{p} returns true) to produce
3602 the final/leftmost portion of the constructed string.
3603 It defaults to @code{(lambda (x) )}.
3607 @node Miscellaneous String Operations
3608 @subsubsection Miscellaneous String Operations
3610 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
3611 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
3612 This is the @emph{extended substring} procedure that implements
3613 replicated copying of a substring of some string.
3615 @var{s} is a string, @var{start} and @var{end} are optional
3616 arguments that demarcate a substring of @var{s}, defaulting to
3617 0 and the length of @var{s}. Replicate this substring up and
3618 down index space, in both the positive and negative directions.
3619 @code{xsubstring} returns the substring of this string
3620 beginning at index @var{from}, and ending at @var{to}, which
3621 defaults to @var{from} + (@var{end} - @var{start}).
3624 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
3625 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
3626 Exactly the same as @code{xsubstring}, but the extracted text
3627 is written into the string @var{target} starting at index
3628 @var{tstart}. The operation is not defined if @code{(eq?
3629 @var{target} @var{s})} or these arguments share storage -- you
3630 cannot copy a string on top of itself.
3633 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
3634 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
3635 Return the string @var{s1}, but with the characters
3636 @var{start1} @dots{} @var{end1} replaced by the characters
3637 @var{start2} @dots{} @var{end2} from @var{s2}.
3640 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
3641 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
3642 Split the string @var{s} into a list of substrings, where each
3643 substring is a maximal non-empty contiguous sequence of
3644 characters from the character set @var{token_set}, which
3645 defaults to @code{char-set:graphic}.
3646 If @var{start} or @var{end} indices are provided, they restrict
3647 @code{string-tokenize} to operating on the indicated substring
3651 @deffn {Scheme Procedure} string-filter s char_pred [start [end]]
3652 @deffnx {C Function} scm_string_filter (s, char_pred, start, end)
3653 Filter the string @var{s}, retaining only those characters which
3654 satisfy @var{char_pred}.
3656 If @var{char_pred} is a procedure, it is applied to each character as
3657 a predicate, if it is a character, it is tested for equality and if it
3658 is a character set, it is tested for membership.
3661 @deffn {Scheme Procedure} string-delete s char_pred [start [end]]
3662 @deffnx {C Function} scm_string_delete (s, char_pred, start, end)
3663 Delete characters satisfying @var{char_pred} from @var{s}.
3665 If @var{char_pred} is a procedure, it is applied to each character as
3666 a predicate, if it is a character, it is tested for equality and if it
3667 is a character set, it is tested for membership.
3670 @node Conversion to/from C
3671 @subsubsection Conversion to/from C
3673 When creating a Scheme string from a C string or when converting a
3674 Scheme string to a C string, the concept of character encoding becomes
3677 In C, a string is just a sequence of bytes, and the character encoding
3678 describes the relation between these bytes and the actual characters
3679 that make up the string. For Scheme strings, character encoding is
3680 not an issue (most of the time), since in Scheme you never get to see
3681 the bytes, only the characters.
3683 Well, ideally, anyway. Right now, Guile simply equates Scheme
3684 characters and bytes, ignoring the possibility of multi-byte encodings
3685 completely. This will change in the future, where Guile will use
3686 Unicode codepoints as its characters and UTF-8 or some other encoding
3687 as its internal encoding. When you exclusively use the functions
3688 listed in this section, you are `future-proof'.
3690 Converting a Scheme string to a C string will often allocate fresh
3691 memory to hold the result. You must take care that this memory is
3692 properly freed eventually. In many cases, this can be achieved by
3693 using @code{scm_dynwind_free} inside an appropriate dynwind context,
3694 @xref{Dynamic Wind}.
3696 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
3697 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
3698 Creates a new Scheme string that has the same contents as @var{str}
3699 when interpreted in the current locale character encoding.
3701 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
3703 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
3704 @var{str} in bytes, and @var{str} does not need to be null-terminated.
3705 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
3706 null-terminated and the real length will be found with @code{strlen}.
3709 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
3710 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
3711 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
3712 respectively, but also frees @var{str} with @code{free} eventually.
3713 Thus, you can use this function when you would free @var{str} anyway
3714 immediately after creating the Scheme string. In certain cases, Guile
3715 can then use @var{str} directly as its internal representation.
3718 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
3719 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
3720 Returns a C string in the current locale encoding with the same
3721 contents as @var{str}. The C string must be freed with @code{free}
3722 eventually, maybe by using @code{scm_dynwind_free}, @xref{Dynamic
3725 For @code{scm_to_locale_string}, the returned string is
3726 null-terminated and an error is signalled when @var{str} contains
3727 @code{#\nul} characters.
3729 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
3730 @var{str} might contain @code{#\nul} characters and the length of the
3731 returned string in bytes is stored in @code{*@var{lenp}}. The
3732 returned string will not be null-terminated in this case. If
3733 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
3734 @code{scm_to_locale_string}.
3737 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
3738 Puts @var{str} as a C string in the current locale encoding into the
3739 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
3740 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
3741 more than that. No terminating @code{'\0'} will be stored.
3743 The return value of @code{scm_to_locale_stringbuf} is the number of
3744 bytes that are needed for all of @var{str}, regardless of whether
3745 @var{buf} was large enough to hold them. Thus, when the return value
3746 is larger than @var{max_len}, only @var{max_len} bytes have been
3747 stored and you probably need to try again with a larger buffer.
3751 @subsection Bytevectors
3756 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevector)}
3757 module provides the programming interface specified by the
3758 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
3759 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
3760 interpret their contents in a number of ways: bytevector contents can be
3761 accessed as signed or unsigned integer of various sizes and endianness,
3762 as IEEE-754 floating point numbers, or as strings. It is a useful tool
3763 to encode and decode binary data.
3765 The R6RS (Section 4.3.4) specifies an external representation for
3766 bytevectors, whereby the octets (integers in the range 0--255) contained
3767 in the bytevector are represented as a list prefixed by @code{#vu8}:
3773 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
3774 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
3775 they do not need to be quoted:
3779 @result{} #vu8(1 53 204)
3782 Bytevectors can be used with the binary input/output primitives of the
3783 R6RS (@pxref{R6RS I/O Ports}).
3786 * Bytevector Endianness:: Dealing with byte order.
3787 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
3788 * Bytevectors as Integers:: Interpreting bytes as integers.
3789 * Bytevectors and Integer Lists:: Converting to/from an integer list.
3790 * Bytevectors as Floats:: Interpreting bytes as real numbers.
3791 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
3792 * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API.
3795 @node Bytevector Endianness
3796 @subsubsection Endianness
3802 Some of the following procedures take an @var{endianness} parameter.
3803 The @dfn{endianness} is defined as the order of bytes in multi-byte
3804 numbers: numbers encoded in @dfn{big endian} have their most
3805 significant bytes written first, whereas numbers encoded in
3806 @dfn{little endian} have their least significant bytes
3807 first@footnote{Big-endian and little-endian are the most common
3808 ``endiannesses'', but others do exist. For instance, the GNU MP
3809 library allows @dfn{word order} to be specified independently of
3810 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
3811 Multiple Precision Arithmetic Library Manual}).}.
3813 Little-endian is the native endianness of the IA32 architecture and
3814 its derivatives, while big-endian is native to SPARC and PowerPC,
3815 among others. The @code{native-endianness} procedure returns the
3816 native endianness of the machine it runs on.
3818 @deffn {Scheme Procedure} native-endianness
3819 @deffnx {C Function} scm_native_endianness ()
3820 Return a value denoting the native endianness of the host machine.
3823 @deffn {Scheme Macro} endianness symbol
3824 Return an object denoting the endianness specified by @var{symbol}. If
3825 @var{symbol} is neither @code{big} nor @code{little} then an error is
3826 raised at expand-time.
3829 @defvr {C Variable} scm_endianness_big
3830 @defvrx {C Variable} scm_endianness_little
3831 The objects denoting big- and little-endianness, respectively.
3835 @node Bytevector Manipulation
3836 @subsubsection Manipulating Bytevectors
3838 Bytevectors can be created, copied, and analyzed with the following
3839 procedures and C functions.
3841 @deffn {Scheme Procedure} make-bytevector len [fill]
3842 @deffnx {C Function} scm_make_bytevector (len, fill)
3843 @deffnx {C Function} scm_c_make_bytevector (size_t len)
3844 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
3845 is given, fill it with @var{fill}; @var{fill} must be in the range
3849 @deffn {Scheme Procedure} bytevector? obj
3850 @deffnx {C Function} scm_bytevector_p (obj)
3851 Return true if @var{obj} is a bytevector.
3854 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
3855 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
3858 @deffn {Scheme Procedure} bytevector-length bv
3859 @deffnx {C Function} scm_bytevector_length (bv)
3860 Return the length in bytes of bytevector @var{bv}.
3863 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
3864 Likewise, return the length in bytes of bytevector @var{bv}.
3867 @deffn {Scheme Procedure} bytevector=? bv1 bv2
3868 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
3869 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
3870 length and contents.
3873 @deffn {Scheme Procedure} bytevector-fill! bv fill
3874 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
3875 Fill bytevector @var{bv} with @var{fill}, a byte.
3878 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
3879 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
3880 Copy @var{len} bytes from @var{source} into @var{target}, starting
3881 reading from @var{source-start} (a positive index within @var{source})
3882 and start writing at @var{target-start}.
3885 @deffn {Scheme Procedure} bytevector-copy bv
3886 @deffnx {C Function} scm_bytevector_copy (bv)
3887 Return a newly allocated copy of @var{bv}.
3890 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
3891 Return the byte at @var{index} in bytevector @var{bv}.
3894 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
3895 Set the byte at @var{index} in @var{bv} to @var{value}.
3898 Low-level C macros are available. They do not perform any
3899 type-checking; as such they should be used with care.
3901 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
3902 Return the length in bytes of bytevector @var{bv}.
3905 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
3906 Return a pointer to the contents of bytevector @var{bv}.
3910 @node Bytevectors as Integers
3911 @subsubsection Interpreting Bytevector Contents as Integers
3913 The contents of a bytevector can be interpreted as a sequence of
3914 integers of any given size, sign, and endianness.
3917 (let ((bv (make-bytevector 4)))
3918 (bytevector-u8-set! bv 0 #x12)
3919 (bytevector-u8-set! bv 1 #x34)
3920 (bytevector-u8-set! bv 2 #x56)
3921 (bytevector-u8-set! bv 3 #x78)
3923 (map (lambda (number)
3924 (number->string number 16))
3925 (list (bytevector-u8-ref bv 0)
3926 (bytevector-u16-ref bv 0 (endianness big))
3927 (bytevector-u32-ref bv 0 (endianness little)))))
3929 @result{} ("12" "1234" "78563412")
3932 The most generic procedures to interpret bytevector contents as integers
3933 are described below.
3935 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
3936 @deffnx {Scheme Procedure} bytevector-sint-ref bv index endianness size
3937 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
3938 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
3939 Return the @var{size}-byte long unsigned (resp. signed) integer at
3940 index @var{index} in @var{bv}, decoded according to @var{endianness}.
3943 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
3944 @deffnx {Scheme Procedure} bytevector-sint-set! bv index value endianness size
3945 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
3946 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
3947 Set the @var{size}-byte long unsigned (resp. signed) integer at
3948 @var{index} to @var{value}, encoded according to @var{endianness}.
3951 The following procedures are similar to the ones above, but specialized
3952 to a given integer size:
3954 @deffn {Scheme Procedure} bytevector-u8-ref bv index
3955 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
3956 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
3957 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
3958 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
3959 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
3960 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
3961 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
3962 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
3963 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
3964 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
3965 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
3966 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
3967 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
3968 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
3969 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
3970 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
3971 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
3975 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
3976 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
3977 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
3978 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
3979 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
3980 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
3981 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
3982 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
3983 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
3984 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
3985 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
3986 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
3987 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
3988 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
3989 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
3990 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
3991 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
3992 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
3996 Finally, a variant specialized for the host's endianness is available
3997 for each of these functions (with the exception of the @code{u8}
3998 accessors, for obvious reasons):
4000 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4001 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4002 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4003 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4004 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4005 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4006 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4007 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4008 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4009 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4010 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4011 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4012 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4013 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4014 host's native endianness.
4017 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4018 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4019 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4020 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4021 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4022 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4023 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4024 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4025 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4026 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4027 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4028 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4029 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4030 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4031 host's native endianness.
4035 @node Bytevectors and Integer Lists
4036 @subsubsection Converting Bytevectors to/from Integer Lists
4038 Bytevector contents can readily be converted to/from lists of signed or
4042 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4043 (endianness little) 2)
4047 @deffn {Scheme Procedure} bytevector->u8-list bv
4048 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4049 Return a newly allocated list of unsigned 8-bit integers from the
4050 contents of @var{bv}.
4053 @deffn {Scheme Procedure} u8-list->bytevector lst
4054 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4055 Return a newly allocated bytevector consisting of the unsigned 8-bit
4056 integers listed in @var{lst}.
4059 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4060 @deffnx {Scheme Procedure} bytevector->sint-list bv endianness size
4061 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4062 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4063 Return a list of unsigned (resp. signed) integers of @var{size} bytes
4064 representing the contents of @var{bv}, decoded according to
4068 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4069 @deffnx {Scheme Procedure} sint-list->bytevector lst endianness size
4070 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4071 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4072 Return a new bytevector containing the unsigned (resp. signed) integers
4073 listed in @var{lst} and encoded on @var{size} bytes according to
4077 @node Bytevectors as Floats
4078 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4080 @cindex IEEE-754 floating point numbers
4082 Bytevector contents can also be accessed as IEEE-754 single- or
4083 double-precision floating point numbers (respectively 32 and 64-bit
4084 long) using the procedures described here.
4086 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4087 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4088 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4089 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4090 Return the IEEE-754 single-precision floating point number from @var{bv}
4091 at @var{index} according to @var{endianness}.
4094 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4095 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4096 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4097 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4098 Store real number @var{value} in @var{bv} at @var{index} according to
4102 Specialized procedures are also available:
4104 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4105 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4106 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4107 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4108 Return the IEEE-754 single-precision floating point number from @var{bv}
4109 at @var{index} according to the host's native endianness.
4112 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4113 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4114 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4115 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4116 Store real number @var{value} in @var{bv} at @var{index} according to
4117 the host's native endianness.
4121 @node Bytevectors as Strings
4122 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4124 @cindex Unicode string encoding
4126 Bytevector contents can also be interpreted as Unicode strings encoded
4127 in one of the most commonly available encoding formats@footnote{Guile
4128 1.8 does @emph{not} support Unicode strings. Therefore, the procedures
4129 described here assume that Guile strings are internally encoded
4130 according to the current locale. For instance, if @code{$LC_CTYPE} is
4131 @code{fr_FR.ISO-8859-1}, then @code{string->utf-8} @i{et al.} will
4132 assume that Guile strings are Latin-1-encoded.}.
4135 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4138 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4139 @result{} #vu8(99 97 102 195 169)
4142 @deffn {Scheme Procedure} string->utf8 str
4143 @deffnx {Scheme Procedure} string->utf16 str
4144 @deffnx {Scheme Procedure} string->utf32 str
4145 @deffnx {C Function} scm_string_to_utf8 (str)
4146 @deffnx {C Function} scm_string_to_utf16 (str)
4147 @deffnx {C Function} scm_string_to_utf32 (str)
4148 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4149 UTF-32 (aka. UCS-4) encoding of @var{str}.
4152 @deffn {Scheme Procedure} utf8->string utf
4153 @deffnx {Scheme Procedure} utf16->string utf
4154 @deffnx {Scheme Procedure} utf32->string utf
4155 @deffnx {C Function} scm_utf8_to_string (utf)
4156 @deffnx {C Function} scm_utf16_to_string (utf)
4157 @deffnx {C Function} scm_utf32_to_string (utf)
4158 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4159 or UTF-32-decoded contents of bytevector @var{utf}.
4162 @node Bytevectors as Generalized Vectors
4163 @subsubsection Accessing Bytevectors with the Generalized Vector API
4165 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4166 with the @dfn{generalized vector} procedures (@pxref{Generalized
4167 Vectors}). This also allows bytevectors to be accessed using the
4168 generic @dfn{array} procedures (@pxref{Array Procedures}). When using
4169 these APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4172 (define bv #vu8(0 1 2 3))
4174 (generalized-vector? bv)
4177 (generalized-vector-ref bv 2)
4180 (generalized-vector-set! bv 2 77)
4189 @node Regular Expressions
4190 @subsection Regular Expressions
4191 @tpindex Regular expressions
4193 @cindex regular expressions
4195 @cindex emacs regexp
4197 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
4198 describes a whole class of strings. A full description of regular
4199 expressions and their syntax is beyond the scope of this manual;
4200 an introduction can be found in the Emacs manual (@pxref{Regexps,
4201 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}), or
4202 in many general Unix reference books.
4204 If your system does not include a POSIX regular expression library,
4205 and you have not linked Guile with a third-party regexp library such
4206 as Rx, these functions will not be available. You can tell whether
4207 your Guile installation includes regular expression support by
4208 checking whether @code{(provided? 'regex)} returns true.
4210 The following regexp and string matching features are provided by the
4211 @code{(ice-9 regex)} module. Before using the described functions,
4212 you should load this module by executing @code{(use-modules (ice-9
4216 * Regexp Functions:: Functions that create and match regexps.
4217 * Match Structures:: Finding what was matched by a regexp.
4218 * Backslash Escapes:: Removing the special meaning of regexp
4223 @node Regexp Functions
4224 @subsubsection Regexp Functions
4226 By default, Guile supports POSIX extended regular expressions.
4227 That means that the characters @samp{(}, @samp{)}, @samp{+} and
4228 @samp{?} are special, and must be escaped if you wish to match the
4231 This regular expression interface was modeled after that
4232 implemented by SCSH, the Scheme Shell. It is intended to be
4233 upwardly compatible with SCSH regular expressions.
4235 Zero bytes (@code{#\nul}) cannot be used in regex patterns or input
4236 strings, since the underlying C functions treat that as the end of
4237 string. If there's a zero byte an error is thrown.
4239 Patterns and input strings are treated as being in the locale
4240 character set if @code{setlocale} has been called (@pxref{Locales}),
4241 and in a multibyte locale this includes treating multi-byte sequences
4242 as a single character. (Guile strings are currently merely bytes,
4243 though this may change in the future, @xref{Conversion to/from C}.)
4245 @deffn {Scheme Procedure} string-match pattern str [start]
4246 Compile the string @var{pattern} into a regular expression and compare
4247 it with @var{str}. The optional numeric argument @var{start} specifies
4248 the position of @var{str} at which to begin matching.
4250 @code{string-match} returns a @dfn{match structure} which
4251 describes what, if anything, was matched by the regular
4252 expression. @xref{Match Structures}. If @var{str} does not match
4253 @var{pattern} at all, @code{string-match} returns @code{#f}.
4256 Two examples of a match follow. In the first example, the pattern
4257 matches the four digits in the match string. In the second, the pattern
4261 (string-match "[0-9][0-9][0-9][0-9]" "blah2002")
4262 @result{} #("blah2002" (4 . 8))
4264 (string-match "[A-Za-z]" "123456")
4268 Each time @code{string-match} is called, it must compile its
4269 @var{pattern} argument into a regular expression structure. This
4270 operation is expensive, which makes @code{string-match} inefficient if
4271 the same regular expression is used several times (for example, in a
4272 loop). For better performance, you can compile a regular expression in
4273 advance and then match strings against the compiled regexp.
4275 @deffn {Scheme Procedure} make-regexp pat flag@dots{}
4276 @deffnx {C Function} scm_make_regexp (pat, flaglst)
4277 Compile the regular expression described by @var{pat}, and
4278 return the compiled regexp structure. If @var{pat} does not
4279 describe a legal regular expression, @code{make-regexp} throws
4280 a @code{regular-expression-syntax} error.
4282 The @var{flag} arguments change the behavior of the compiled
4283 regular expression. The following values may be supplied:
4285 @defvar regexp/icase
4286 Consider uppercase and lowercase letters to be the same when
4290 @defvar regexp/newline
4291 If a newline appears in the target string, then permit the
4292 @samp{^} and @samp{$} operators to match immediately after or
4293 immediately before the newline, respectively. Also, the
4294 @samp{.} and @samp{[^...]} operators will never match a newline
4295 character. The intent of this flag is to treat the target
4296 string as a buffer containing many lines of text, and the
4297 regular expression as a pattern that may match a single one of
4301 @defvar regexp/basic
4302 Compile a basic (``obsolete'') regexp instead of the extended
4303 (``modern'') regexps that are the default. Basic regexps do
4304 not consider @samp{|}, @samp{+} or @samp{?} to be special
4305 characters, and require the @samp{@{...@}} and @samp{(...)}
4306 metacharacters to be backslash-escaped (@pxref{Backslash
4307 Escapes}). There are several other differences between basic
4308 and extended regular expressions, but these are the most
4312 @defvar regexp/extended
4313 Compile an extended regular expression rather than a basic
4314 regexp. This is the default behavior; this flag will not
4315 usually be needed. If a call to @code{make-regexp} includes
4316 both @code{regexp/basic} and @code{regexp/extended} flags, the
4317 one which comes last will override the earlier one.
4321 @deffn {Scheme Procedure} regexp-exec rx str [start [flags]]
4322 @deffnx {C Function} scm_regexp_exec (rx, str, start, flags)
4323 Match the compiled regular expression @var{rx} against
4324 @code{str}. If the optional integer @var{start} argument is
4325 provided, begin matching from that position in the string.
4326 Return a match structure describing the results of the match,
4327 or @code{#f} if no match could be found.
4329 The @var{flags} argument changes the matching behavior. The following
4330 flag values may be supplied, use @code{logior} (@pxref{Bitwise
4331 Operations}) to combine them,
4333 @defvar regexp/notbol
4334 Consider that the @var{start} offset into @var{str} is not the
4335 beginning of a line and should not match operator @samp{^}.
4337 If @var{rx} was created with the @code{regexp/newline} option above,
4338 @samp{^} will still match after a newline in @var{str}.
4341 @defvar regexp/noteol
4342 Consider that the end of @var{str} is not the end of a line and should
4343 not match operator @samp{$}.
4345 If @var{rx} was created with the @code{regexp/newline} option above,
4346 @samp{$} will still match before a newline in @var{str}.
4351 ;; Regexp to match uppercase letters
4352 (define r (make-regexp "[A-Z]*"))
4354 ;; Regexp to match letters, ignoring case
4355 (define ri (make-regexp "[A-Z]*" regexp/icase))
4357 ;; Search for bob using regexp r
4358 (match:substring (regexp-exec r "bob"))
4359 @result{} "" ; no match
4361 ;; Search for bob using regexp ri
4362 (match:substring (regexp-exec ri "Bob"))
4363 @result{} "Bob" ; matched case insensitive
4366 @deffn {Scheme Procedure} regexp? obj
4367 @deffnx {C Function} scm_regexp_p (obj)
4368 Return @code{#t} if @var{obj} is a compiled regular expression,
4369 or @code{#f} otherwise.
4373 @deffn {Scheme Procedure} list-matches regexp str [flags]
4374 Return a list of match structures which are the non-overlapping
4375 matches of @var{regexp} in @var{str}. @var{regexp} can be either a
4376 pattern string or a compiled regexp. The @var{flags} argument is as
4377 per @code{regexp-exec} above.
4380 (map match:substring (list-matches "[a-z]+" "abc 42 def 78"))
4381 @result{} ("abc" "def")
4385 @deffn {Scheme Procedure} fold-matches regexp str init proc [flags]
4386 Apply @var{proc} to the non-overlapping matches of @var{regexp} in
4387 @var{str}, to build a result. @var{regexp} can be either a pattern
4388 string or a compiled regexp. The @var{flags} argument is as per
4389 @code{regexp-exec} above.
4391 @var{proc} is called as @code{(@var{proc} match prev)} where
4392 @var{match} is a match structure and @var{prev} is the previous return
4393 from @var{proc}. For the first call @var{prev} is the given
4394 @var{init} parameter. @code{fold-matches} returns the final value
4397 For example to count matches,
4400 (fold-matches "[a-z][0-9]" "abc x1 def y2" 0
4401 (lambda (match count)
4408 Regular expressions are commonly used to find patterns in one string
4409 and replace them with the contents of another string. The following
4410 functions are convenient ways to do this.
4412 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4413 @deffn {Scheme Procedure} regexp-substitute port match [item@dots{}]
4414 Write to @var{port} selected parts of the match structure @var{match}.
4415 Or if @var{port} is @code{#f} then form a string from those parts and
4418 Each @var{item} specifies a part to be written, and may be one of the
4423 A string. String arguments are written out verbatim.
4426 An integer. The submatch with that number is written
4427 (@code{match:substring}). Zero is the entire match.
4430 The symbol @samp{pre}. The portion of the matched string preceding
4431 the regexp match is written (@code{match:prefix}).
4434 The symbol @samp{post}. The portion of the matched string following
4435 the regexp match is written (@code{match:suffix}).
4438 For example, changing a match and retaining the text before and after,
4441 (regexp-substitute #f (string-match "[0-9]+" "number 25 is good")
4443 @result{} "number 37 is good"
4446 Or matching a @sc{yyyymmdd} format date such as @samp{20020828} and
4447 re-ordering and hyphenating the fields.
4450 (define date-regex "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4451 (define s "Date 20020429 12am.")
4452 (regexp-substitute #f (string-match date-regex s)
4453 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4454 @result{} "Date 04-29-2002 12am. (20020429)"
4459 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4460 @deffn {Scheme Procedure} regexp-substitute/global port regexp target [item@dots{}]
4461 @cindex search and replace
4462 Write to @var{port} selected parts of matches of @var{regexp} in
4463 @var{target}. If @var{port} is @code{#f} then form a string from
4464 those parts and return that. @var{regexp} can be a string or a
4467 This is similar to @code{regexp-substitute}, but allows global
4468 substitutions on @var{target}. Each @var{item} behaves as per
4469 @code{regexp-substitute}, with the following differences,
4473 A function. Called as @code{(@var{item} match)} with the match
4474 structure for the @var{regexp} match, it should return a string to be
4475 written to @var{port}.
4478 The symbol @samp{post}. This doesn't output anything, but instead
4479 causes @code{regexp-substitute/global} to recurse on the unmatched
4480 portion of @var{target}.
4482 This @emph{must} be supplied to perform a global search and replace on
4483 @var{target}; without it @code{regexp-substitute/global} returns after
4484 a single match and output.
4487 For example, to collapse runs of tabs and spaces to a single hyphen
4491 (regexp-substitute/global #f "[ \t]+" "this is the text"
4493 @result{} "this-is-the-text"
4496 Or using a function to reverse the letters in each word,
4499 (regexp-substitute/global #f "[a-z]+" "to do and not-do"
4500 'pre (lambda (m) (string-reverse (match:substring m))) 'post)
4501 @result{} "ot od dna ton-od"
4504 Without the @code{post} symbol, just one regexp match is made. For
4505 example the following is the date example from
4506 @code{regexp-substitute} above, without the need for the separate
4507 @code{string-match} call.
4510 (define date-regex "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4511 (define s "Date 20020429 12am.")
4512 (regexp-substitute/global #f date-regex s
4513 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4515 @result{} "Date 04-29-2002 12am. (20020429)"
4520 @node Match Structures
4521 @subsubsection Match Structures
4523 @cindex match structures
4525 A @dfn{match structure} is the object returned by @code{string-match} and
4526 @code{regexp-exec}. It describes which portion of a string, if any,
4527 matched the given regular expression. Match structures include: a
4528 reference to the string that was checked for matches; the starting and
4529 ending positions of the regexp match; and, if the regexp included any
4530 parenthesized subexpressions, the starting and ending positions of each
4533 In each of the regexp match functions described below, the @code{match}
4534 argument must be a match structure returned by a previous call to
4535 @code{string-match} or @code{regexp-exec}. Most of these functions
4536 return some information about the original target string that was
4537 matched against a regular expression; we will call that string
4538 @var{target} for easy reference.
4540 @c begin (scm-doc-string "regex.scm" "regexp-match?")
4541 @deffn {Scheme Procedure} regexp-match? obj
4542 Return @code{#t} if @var{obj} is a match structure returned by a
4543 previous call to @code{regexp-exec}, or @code{#f} otherwise.
4546 @c begin (scm-doc-string "regex.scm" "match:substring")
4547 @deffn {Scheme Procedure} match:substring match [n]
4548 Return the portion of @var{target} matched by subexpression number
4549 @var{n}. Submatch 0 (the default) represents the entire regexp match.
4550 If the regular expression as a whole matched, but the subexpression
4551 number @var{n} did not match, return @code{#f}.
4555 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4559 ;; match starting at offset 6 in the string
4561 (string-match "[0-9][0-9][0-9][0-9]" "blah987654" 6))
4565 @c begin (scm-doc-string "regex.scm" "match:start")
4566 @deffn {Scheme Procedure} match:start match [n]
4567 Return the starting position of submatch number @var{n}.
4570 In the following example, the result is 4, since the match starts at
4574 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4579 @c begin (scm-doc-string "regex.scm" "match:end")
4580 @deffn {Scheme Procedure} match:end match [n]
4581 Return the ending position of submatch number @var{n}.
4584 In the following example, the result is 8, since the match runs between
4585 characters 4 and 8 (i.e. the ``2002'').
4588 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4593 @c begin (scm-doc-string "regex.scm" "match:prefix")
4594 @deffn {Scheme Procedure} match:prefix match
4595 Return the unmatched portion of @var{target} preceding the regexp match.
4598 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4604 @c begin (scm-doc-string "regex.scm" "match:suffix")
4605 @deffn {Scheme Procedure} match:suffix match
4606 Return the unmatched portion of @var{target} following the regexp match.
4610 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4615 @c begin (scm-doc-string "regex.scm" "match:count")
4616 @deffn {Scheme Procedure} match:count match
4617 Return the number of parenthesized subexpressions from @var{match}.
4618 Note that the entire regular expression match itself counts as a
4619 subexpression, and failed submatches are included in the count.
4622 @c begin (scm-doc-string "regex.scm" "match:string")
4623 @deffn {Scheme Procedure} match:string match
4624 Return the original @var{target} string.
4628 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4630 @result{} "blah2002foo"
4634 @node Backslash Escapes
4635 @subsubsection Backslash Escapes
4637 Sometimes you will want a regexp to match characters like @samp{*} or
4638 @samp{$} exactly. For example, to check whether a particular string
4639 represents a menu entry from an Info node, it would be useful to match
4640 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
4641 because the asterisk is a metacharacter, it won't match the @samp{*} at
4642 the beginning of the string. In this case, we want to make the first
4645 You can do this by preceding the metacharacter with a backslash
4646 character @samp{\}. (This is also called @dfn{quoting} the
4647 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
4648 sees a backslash in a regular expression, it considers the following
4649 glyph to be an ordinary character, no matter what special meaning it
4650 would ordinarily have. Therefore, we can make the above example work by
4651 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
4652 the regular expression engine to match only a single asterisk in the
4655 Since the backslash is itself a metacharacter, you may force a regexp to
4656 match a backslash in the target string by preceding the backslash with
4657 itself. For example, to find variable references in a @TeX{} program,
4658 you might want to find occurrences of the string @samp{\let\} followed
4659 by any number of alphabetic characters. The regular expression
4660 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
4661 regexp each match a single backslash in the target string.
4663 @c begin (scm-doc-string "regex.scm" "regexp-quote")
4664 @deffn {Scheme Procedure} regexp-quote str
4665 Quote each special character found in @var{str} with a backslash, and
4666 return the resulting string.
4669 @strong{Very important:} Using backslash escapes in Guile source code
4670 (as in Emacs Lisp or C) can be tricky, because the backslash character
4671 has special meaning for the Guile reader. For example, if Guile
4672 encounters the character sequence @samp{\n} in the middle of a string
4673 while processing Scheme code, it replaces those characters with a
4674 newline character. Similarly, the character sequence @samp{\t} is
4675 replaced by a horizontal tab. Several of these @dfn{escape sequences}
4676 are processed by the Guile reader before your code is executed.
4677 Unrecognized escape sequences are ignored: if the characters @samp{\*}
4678 appear in a string, they will be translated to the single character
4681 This translation is obviously undesirable for regular expressions, since
4682 we want to be able to include backslashes in a string in order to
4683 escape regexp metacharacters. Therefore, to make sure that a backslash
4684 is preserved in a string in your Guile program, you must use @emph{two}
4685 consecutive backslashes:
4688 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
4691 The string in this example is preprocessed by the Guile reader before
4692 any code is executed. The resulting argument to @code{make-regexp} is
4693 the string @samp{^\* [^:]*}, which is what we really want.
4695 This also means that in order to write a regular expression that matches
4696 a single backslash character, the regular expression string in the
4697 source code must include @emph{four} backslashes. Each consecutive pair
4698 of backslashes gets translated by the Guile reader to a single
4699 backslash, and the resulting double-backslash is interpreted by the
4700 regexp engine as matching a single backslash character. Hence:
4703 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
4706 The reason for the unwieldiness of this syntax is historical. Both
4707 regular expression pattern matchers and Unix string processing systems
4708 have traditionally used backslashes with the special meanings
4709 described above. The POSIX regular expression specification and ANSI C
4710 standard both require these semantics. Attempting to abandon either
4711 convention would cause other kinds of compatibility problems, possibly
4712 more severe ones. Therefore, without extending the Scheme reader to
4713 support strings with different quoting conventions (an ungainly and
4714 confusing extension when implemented in other languages), we must adhere
4715 to this cumbersome escape syntax.
4722 Symbols in Scheme are widely used in three ways: as items of discrete
4723 data, as lookup keys for alists and hash tables, and to denote variable
4726 A @dfn{symbol} is similar to a string in that it is defined by a
4727 sequence of characters. The sequence of characters is known as the
4728 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4729 name doesn't include any characters that could be confused with other
4730 elements of Scheme syntax --- a symbol is written in a Scheme program by
4731 writing the sequence of characters that make up the name, @emph{without}
4732 any quotation marks or other special syntax. For example, the symbol
4733 whose name is ``multiply-by-2'' is written, simply:
4739 Notice how this differs from a @emph{string} with contents
4740 ``multiply-by-2'', which is written with double quotation marks, like
4747 Looking beyond how they are written, symbols are different from strings
4748 in two important respects.
4750 The first important difference is uniqueness. If the same-looking
4751 string is read twice from two different places in a program, the result
4752 is two @emph{different} string objects whose contents just happen to be
4753 the same. If, on the other hand, the same-looking symbol is read twice
4754 from two different places in a program, the result is the @emph{same}
4755 symbol object both times.
4757 Given two read symbols, you can use @code{eq?} to test whether they are
4758 the same (that is, have the same name). @code{eq?} is the most
4759 efficient comparison operator in Scheme, and comparing two symbols like
4760 this is as fast as comparing, for example, two numbers. Given two
4761 strings, on the other hand, you must use @code{equal?} or
4762 @code{string=?}, which are much slower comparison operators, to
4763 determine whether the strings have the same contents.
4766 (define sym1 (quote hello))
4767 (define sym2 (quote hello))
4768 (eq? sym1 sym2) @result{} #t
4770 (define str1 "hello")
4771 (define str2 "hello")
4772 (eq? str1 str2) @result{} #f
4773 (equal? str1 str2) @result{} #t
4776 The second important difference is that symbols, unlike strings, are not
4777 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
4778 example above: @code{(quote hello)} evaluates to the symbol named
4779 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
4780 symbol named "hello" and evaluated as a variable reference @dots{} about
4781 which more below (@pxref{Symbol Variables}).
4784 * Symbol Data:: Symbols as discrete data.
4785 * Symbol Keys:: Symbols as lookup keys.
4786 * Symbol Variables:: Symbols as denoting variables.
4787 * Symbol Primitives:: Operations related to symbols.
4788 * Symbol Props:: Function slots and property lists.
4789 * Symbol Read Syntax:: Extended read syntax for symbols.
4790 * Symbol Uninterned:: Uninterned symbols.
4795 @subsubsection Symbols as Discrete Data
4797 Numbers and symbols are similar to the extent that they both lend
4798 themselves to @code{eq?} comparison. But symbols are more descriptive
4799 than numbers, because a symbol's name can be used directly to describe
4800 the concept for which that symbol stands.
4802 For example, imagine that you need to represent some colours in a
4803 computer program. Using numbers, you would have to choose arbitrarily
4804 some mapping between numbers and colours, and then take care to use that
4805 mapping consistently:
4808 ;; 1=red, 2=green, 3=purple
4810 (if (eq? (colour-of car) 1)
4815 You can make the mapping more explicit and the code more readable by
4823 (if (eq? (colour-of car) red)
4828 But the simplest and clearest approach is not to use numbers at all, but
4829 symbols whose names specify the colours that they refer to:
4832 (if (eq? (colour-of car) 'red)
4836 The descriptive advantages of symbols over numbers increase as the set
4837 of concepts that you want to describe grows. Suppose that a car object
4838 can have other properties as well, such as whether it has or uses:
4842 automatic or manual transmission
4844 leaded or unleaded fuel
4846 power steering (or not).
4850 Then a car's combined property set could be naturally represented and
4851 manipulated as a list of symbols:
4854 (properties-of car1)
4856 (red manual unleaded power-steering)
4858 (if (memq 'power-steering (properties-of car1))
4859 (display "Unfit people can drive this car.\n")
4860 (display "You'll need strong arms to drive this car!\n"))
4862 Unfit people can drive this car.
4865 Remember, the fundamental property of symbols that we are relying on
4866 here is that an occurrence of @code{'red} in one part of a program is an
4867 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
4868 another part of a program; this means that symbols can usefully be
4869 compared using @code{eq?}. At the same time, symbols have naturally
4870 descriptive names. This combination of efficiency and descriptive power
4871 makes them ideal for use as discrete data.
4875 @subsubsection Symbols as Lookup Keys
4877 Given their efficiency and descriptive power, it is natural to use
4878 symbols as the keys in an association list or hash table.
4880 To illustrate this, consider a more structured representation of the car
4881 properties example from the preceding subsection. Rather than
4882 mixing all the properties up together in a flat list, we could use an
4883 association list like this:
4886 (define car1-properties '((colour . red)
4887 (transmission . manual)
4889 (steering . power-assisted)))
4892 Notice how this structure is more explicit and extensible than the flat
4893 list. For example it makes clear that @code{manual} refers to the
4894 transmission rather than, say, the windows or the locking of the car.
4895 It also allows further properties to use the same symbols among their
4896 possible values without becoming ambiguous:
4899 (define car1-properties '((colour . red)
4900 (transmission . manual)
4902 (steering . power-assisted)
4904 (locking . manual)))
4907 With a representation like this, it is easy to use the efficient
4908 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
4909 extract or change individual pieces of information:
4912 (assq-ref car1-properties 'fuel) @result{} unleaded
4913 (assq-ref car1-properties 'transmission) @result{} manual
4915 (assq-set! car1-properties 'seat-colour 'black)
4918 (transmission . manual)
4920 (steering . power-assisted)
4921 (seat-colour . black)
4922 (locking . manual)))
4925 Hash tables also have keys, and exactly the same arguments apply to the
4926 use of symbols in hash tables as in association lists. The hash value
4927 that Guile uses to decide where to add a symbol-keyed entry to a hash
4928 table can be obtained by calling the @code{symbol-hash} procedure:
4930 @deffn {Scheme Procedure} symbol-hash symbol
4931 @deffnx {C Function} scm_symbol_hash (symbol)
4932 Return a hash value for @var{symbol}.
4935 See @ref{Hash Tables} for information about hash tables in general, and
4936 for why you might choose to use a hash table rather than an association
4940 @node Symbol Variables
4941 @subsubsection Symbols as Denoting Variables
4943 When an unquoted symbol in a Scheme program is evaluated, it is
4944 interpreted as a variable reference, and the result of the evaluation is
4945 the appropriate variable's value.
4947 For example, when the expression @code{(string-length "abcd")} is read
4948 and evaluated, the sequence of characters @code{string-length} is read
4949 as the symbol whose name is "string-length". This symbol is associated
4950 with a variable whose value is the procedure that implements string
4951 length calculation. Therefore evaluation of the @code{string-length}
4952 symbol results in that procedure.
4954 The details of the connection between an unquoted symbol and the
4955 variable to which it refers are explained elsewhere. See @ref{Binding
4956 Constructs}, for how associations between symbols and variables are
4957 created, and @ref{Modules}, for how those associations are affected by
4958 Guile's module system.
4961 @node Symbol Primitives
4962 @subsubsection Operations Related to Symbols
4964 Given any Scheme value, you can determine whether it is a symbol using
4965 the @code{symbol?} primitive:
4968 @deffn {Scheme Procedure} symbol? obj
4969 @deffnx {C Function} scm_symbol_p (obj)
4970 Return @code{#t} if @var{obj} is a symbol, otherwise return
4974 @deftypefn {C Function} int scm_is_symbol (SCM val)
4975 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
4978 Once you know that you have a symbol, you can obtain its name as a
4979 string by calling @code{symbol->string}. Note that Guile differs by
4980 default from R5RS on the details of @code{symbol->string} as regards
4983 @rnindex symbol->string
4984 @deffn {Scheme Procedure} symbol->string s
4985 @deffnx {C Function} scm_symbol_to_string (s)
4986 Return the name of symbol @var{s} as a string. By default, Guile reads
4987 symbols case-sensitively, so the string returned will have the same case
4988 variation as the sequence of characters that caused @var{s} to be
4991 If Guile is set to read symbols case-insensitively (as specified by
4992 R5RS), and @var{s} comes into being as part of a literal expression
4993 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
4994 by a call to the @code{read} or @code{string-ci->symbol} procedures,
4995 Guile converts any alphabetic characters in the symbol's name to
4996 lower case before creating the symbol object, so the string returned
4997 here will be in lower case.
4999 If @var{s} was created by @code{string->symbol}, the case of characters
5000 in the string returned will be the same as that in the string that was
5001 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5002 setting at the time @var{s} was created.
5004 It is an error to apply mutation procedures like @code{string-set!} to
5005 strings returned by this procedure.
5008 Most symbols are created by writing them literally in code. However it
5009 is also possible to create symbols programmatically using the following
5010 @code{string->symbol} and @code{string-ci->symbol} procedures:
5012 @rnindex string->symbol
5013 @deffn {Scheme Procedure} string->symbol string
5014 @deffnx {C Function} scm_string_to_symbol (string)
5015 Return the symbol whose name is @var{string}. This procedure can create
5016 symbols with names containing special characters or letters in the
5017 non-standard case, but it is usually a bad idea to create such symbols
5018 because in some implementations of Scheme they cannot be read as
5022 @deffn {Scheme Procedure} string-ci->symbol str
5023 @deffnx {C Function} scm_string_ci_to_symbol (str)
5024 Return the symbol whose name is @var{str}. If Guile is currently
5025 reading symbols case-insensitively, @var{str} is converted to lowercase
5026 before the returned symbol is looked up or created.
5029 The following examples illustrate Guile's detailed behaviour as regards
5030 the case-sensitivity of symbols:
5033 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5035 (symbol->string 'flying-fish) @result{} "flying-fish"
5036 (symbol->string 'Martin) @result{} "martin"
5038 (string->symbol "Malvina")) @result{} "Malvina"
5040 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5041 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5042 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5044 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5045 (string=? "K. Harper, M.D."
5047 (string->symbol "K. Harper, M.D."))) @result{} #t
5049 (read-disable 'case-insensitive) ; Guile default behaviour
5051 (symbol->string 'flying-fish) @result{} "flying-fish"
5052 (symbol->string 'Martin) @result{} "Martin"
5054 (string->symbol "Malvina")) @result{} "Malvina"
5056 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5057 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5058 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5060 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5061 (string=? "K. Harper, M.D."
5063 (string->symbol "K. Harper, M.D."))) @result{} #t
5066 From C, there are lower level functions that construct a Scheme symbol
5067 from a C string in the current locale encoding.
5069 When you want to do more from C, you should convert between symbols
5070 and strings using @code{scm_symbol_to_string} and
5071 @code{scm_string_to_symbol} and work with the strings.
5073 @deffn {C Function} scm_from_locale_symbol (const char *name)
5074 @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
5075 Construct and return a Scheme symbol whose name is specified by
5076 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5077 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5078 specified explicitly by @var{len}.
5081 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5082 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5083 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5084 respectively, but also frees @var{str} with @code{free} eventually.
5085 Thus, you can use this function when you would free @var{str} anyway
5086 immediately after creating the Scheme string. In certain cases, Guile
5087 can then use @var{str} directly as its internal representation.
5090 The size of a symbol can also be obtained from C:
5092 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5093 Return the number of characters in @var{sym}.
5096 Finally, some applications, especially those that generate new Scheme
5097 code dynamically, need to generate symbols for use in the generated
5098 code. The @code{gensym} primitive meets this need:
5100 @deffn {Scheme Procedure} gensym [prefix]
5101 @deffnx {C Function} scm_gensym (prefix)
5102 Create a new symbol with a name constructed from a prefix and a counter
5103 value. The string @var{prefix} can be specified as an optional
5104 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5105 at each call. There is no provision for resetting the counter.
5108 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5109 since their names begin with a space and it is only otherwise possible
5110 to generate such symbols if a programmer goes out of their way to do
5111 so. Uniqueness can be guaranteed by instead using uninterned symbols
5112 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5117 @subsubsection Function Slots and Property Lists
5119 In traditional Lisp dialects, symbols are often understood as having
5120 three kinds of value at once:
5124 a @dfn{variable} value, which is used when the symbol appears in
5125 code in a variable reference context
5128 a @dfn{function} value, which is used when the symbol appears in
5129 code in a function name position (i.e. as the first element in an
5133 a @dfn{property list} value, which is used when the symbol is given as
5134 the first argument to Lisp's @code{put} or @code{get} functions.
5137 Although Scheme (as one of its simplifications with respect to Lisp)
5138 does away with the distinction between variable and function namespaces,
5139 Guile currently retains some elements of the traditional structure in
5140 case they turn out to be useful when implementing translators for other
5141 languages, in particular Emacs Lisp.
5143 Specifically, Guile symbols have two extra slots. for a symbol's
5144 property list, and for its ``function value.'' The following procedures
5145 are provided to access these slots.
5147 @deffn {Scheme Procedure} symbol-fref symbol
5148 @deffnx {C Function} scm_symbol_fref (symbol)
5149 Return the contents of @var{symbol}'s @dfn{function slot}.
5152 @deffn {Scheme Procedure} symbol-fset! symbol value
5153 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5154 Set the contents of @var{symbol}'s function slot to @var{value}.
5157 @deffn {Scheme Procedure} symbol-pref symbol
5158 @deffnx {C Function} scm_symbol_pref (symbol)
5159 Return the @dfn{property list} currently associated with @var{symbol}.
5162 @deffn {Scheme Procedure} symbol-pset! symbol value
5163 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5164 Set @var{symbol}'s property list to @var{value}.
5167 @deffn {Scheme Procedure} symbol-property sym prop
5168 From @var{sym}'s property list, return the value for property
5169 @var{prop}. The assumption is that @var{sym}'s property list is an
5170 association list whose keys are distinguished from each other using
5171 @code{equal?}; @var{prop} should be one of the keys in that list. If
5172 the property list has no entry for @var{prop}, @code{symbol-property}
5176 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5177 In @var{sym}'s property list, set the value for property @var{prop} to
5178 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5179 none already exists. For the structure of the property list, see
5180 @code{symbol-property}.
5183 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5184 From @var{sym}'s property list, remove the entry for property
5185 @var{prop}, if there is one. For the structure of the property list,
5186 see @code{symbol-property}.
5189 Support for these extra slots may be removed in a future release, and it
5190 is probably better to avoid using them. For a more modern and Schemely
5191 approach to properties, see @ref{Object Properties}.
5194 @node Symbol Read Syntax
5195 @subsubsection Extended Read Syntax for Symbols
5197 The read syntax for a symbol is a sequence of letters, digits, and
5198 @dfn{extended alphabetic characters}, beginning with a character that
5199 cannot begin a number. In addition, the special cases of @code{+},
5200 @code{-}, and @code{...} are read as symbols even though numbers can
5201 begin with @code{+}, @code{-} or @code{.}.
5203 Extended alphabetic characters may be used within identifiers as if
5204 they were letters. The set of extended alphabetic characters is:
5207 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5210 In addition to the standard read syntax defined above (which is taken
5211 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5212 Scheme})), Guile provides an extended symbol read syntax that allows the
5213 inclusion of unusual characters such as space characters, newlines and
5214 parentheses. If (for whatever reason) you need to write a symbol
5215 containing characters not mentioned above, you can do so as follows.
5219 Begin the symbol with the characters @code{#@{},
5222 write the characters of the symbol and
5225 finish the symbol with the characters @code{@}#}.
5228 Here are a few examples of this form of read syntax. The first symbol
5229 needs to use extended syntax because it contains a space character, the
5230 second because it contains a line break, and the last because it looks
5242 Although Guile provides this extended read syntax for symbols,
5243 widespread usage of it is discouraged because it is not portable and not
5247 @node Symbol Uninterned
5248 @subsubsection Uninterned Symbols
5250 What makes symbols useful is that they are automatically kept unique.
5251 There are no two symbols that are distinct objects but have the same
5252 name. But of course, there is no rule without exception. In addition
5253 to the normal symbols that have been discussed up to now, you can also
5254 create special @dfn{uninterned} symbols that behave slightly
5257 To understand what is different about them and why they might be useful,
5258 we look at how normal symbols are actually kept unique.
5260 Whenever Guile wants to find the symbol with a specific name, for
5261 example during @code{read} or when executing @code{string->symbol}, it
5262 first looks into a table of all existing symbols to find out whether a
5263 symbol with the given name already exists. When this is the case, Guile
5264 just returns that symbol. When not, a new symbol with the name is
5265 created and entered into the table so that it can be found later.
5267 Sometimes you might want to create a symbol that is guaranteed `fresh',
5268 i.e. a symbol that did not exist previously. You might also want to
5269 somehow guarantee that no one else will ever unintentionally stumble
5270 across your symbol in the future. These properties of a symbol are
5271 often needed when generating code during macro expansion. When
5272 introducing new temporary variables, you want to guarantee that they
5273 don't conflict with variables in other people's code.
5275 The simplest way to arrange for this is to create a new symbol but
5276 not enter it into the global table of all symbols. That way, no one
5277 will ever get access to your symbol by chance. Symbols that are not in
5278 the table are called @dfn{uninterned}. Of course, symbols that
5279 @emph{are} in the table are called @dfn{interned}.
5281 You create new uninterned symbols with the function @code{make-symbol}.
5282 You can test whether a symbol is interned or not with
5283 @code{symbol-interned?}.
5285 Uninterned symbols break the rule that the name of a symbol uniquely
5286 identifies the symbol object. Because of this, they can not be written
5287 out and read back in like interned symbols. Currently, Guile has no
5288 support for reading uninterned symbols. Note that the function
5289 @code{gensym} does not return uninterned symbols for this reason.
5291 @deffn {Scheme Procedure} make-symbol name
5292 @deffnx {C Function} scm_make_symbol (name)
5293 Return a new uninterned symbol with the name @var{name}. The returned
5294 symbol is guaranteed to be unique and future calls to
5295 @code{string->symbol} will not return it.
5298 @deffn {Scheme Procedure} symbol-interned? symbol
5299 @deffnx {C Function} scm_symbol_interned_p (symbol)
5300 Return @code{#t} if @var{symbol} is interned, otherwise return
5307 (define foo-1 (string->symbol "foo"))
5308 (define foo-2 (string->symbol "foo"))
5309 (define foo-3 (make-symbol "foo"))
5310 (define foo-4 (make-symbol "foo"))
5314 ; Two interned symbols with the same name are the same object,
5318 ; but a call to make-symbol with the same name returns a
5323 ; A call to make-symbol always returns a new object, even for
5327 @result{} #<uninterned-symbol foo 8085290>
5328 ; Uninterned symbols print differently from interned symbols,
5332 ; but they are still symbols,
5334 (symbol-interned? foo-3)
5336 ; just not interned.
5341 @subsection Keywords
5344 Keywords are self-evaluating objects with a convenient read syntax that
5345 makes them easy to type.
5347 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5348 syntax extension to permit keywords to begin with @code{:} as well as
5349 @code{#:}, or to end with @code{:}.
5352 * Why Use Keywords?:: Motivation for keyword usage.
5353 * Coding With Keywords:: How to use keywords.
5354 * Keyword Read Syntax:: Read syntax for keywords.
5355 * Keyword Procedures:: Procedures for dealing with keywords.
5358 @node Why Use Keywords?
5359 @subsubsection Why Use Keywords?
5361 Keywords are useful in contexts where a program or procedure wants to be
5362 able to accept a large number of optional arguments without making its
5363 interface unmanageable.
5365 To illustrate this, consider a hypothetical @code{make-window}
5366 procedure, which creates a new window on the screen for drawing into
5367 using some graphical toolkit. There are many parameters that the caller
5368 might like to specify, but which could also be sensibly defaulted, for
5373 color depth -- Default: the color depth for the screen
5376 background color -- Default: white
5379 width -- Default: 600
5382 height -- Default: 400
5385 If @code{make-window} did not use keywords, the caller would have to
5386 pass in a value for each possible argument, remembering the correct
5387 argument order and using a special value to indicate the default value
5391 (make-window 'default ;; Color depth
5392 'default ;; Background color
5395 @dots{}) ;; More make-window arguments
5398 With keywords, on the other hand, defaulted arguments are omitted, and
5399 non-default arguments are clearly tagged by the appropriate keyword. As
5400 a result, the invocation becomes much clearer:
5403 (make-window #:width 800 #:height 100)
5406 On the other hand, for a simpler procedure with few arguments, the use
5407 of keywords would be a hindrance rather than a help. The primitive
5408 procedure @code{cons}, for example, would not be improved if it had to
5412 (cons #:car x #:cdr y)
5415 So the decision whether to use keywords or not is purely pragmatic: use
5416 them if they will clarify the procedure invocation at point of call.
5418 @node Coding With Keywords
5419 @subsubsection Coding With Keywords
5421 If a procedure wants to support keywords, it should take a rest argument
5422 and then use whatever means is convenient to extract keywords and their
5423 corresponding arguments from the contents of that rest argument.
5425 The following example illustrates the principle: the code for
5426 @code{make-window} uses a helper procedure called
5427 @code{get-keyword-value} to extract individual keyword arguments from
5431 (define (get-keyword-value args keyword default)
5432 (let ((kv (memq keyword args)))
5433 (if (and kv (>= (length kv) 2))
5437 (define (make-window . args)
5438 (let ((depth (get-keyword-value args #:depth screen-depth))
5439 (bg (get-keyword-value args #:bg "white"))
5440 (width (get-keyword-value args #:width 800))
5441 (height (get-keyword-value args #:height 100))
5446 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5447 optargs)} module provides a set of powerful macros that you can use to
5448 implement keyword-supporting procedures like this:
5451 (use-modules (ice-9 optargs))
5453 (define (make-window . args)
5454 (let-keywords args #f ((depth screen-depth)
5462 Or, even more economically, like this:
5465 (use-modules (ice-9 optargs))
5467 (define* (make-window #:key (depth screen-depth)
5474 For further details on @code{let-keywords}, @code{define*} and other
5475 facilities provided by the @code{(ice-9 optargs)} module, see
5476 @ref{Optional Arguments}.
5479 @node Keyword Read Syntax
5480 @subsubsection Keyword Read Syntax
5482 Guile, by default, only recognizes a keyword syntax that is compatible
5483 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5484 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5485 external representation of the keyword named @code{NAME}. Keyword
5486 objects print using this syntax as well, so values containing keyword
5487 objects can be read back into Guile. When used in an expression,
5488 keywords are self-quoting objects.
5490 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5491 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5492 of the form @code{:NAME} are read as symbols, as required by R5RS.
5494 @cindex SRFI-88 keyword syntax
5496 If the @code{keyword} read option is set to @code{'postfix}, Guile
5497 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5498 Otherwise, tokens of this form are read as symbols.
5500 To enable and disable the alternative non-R5RS keyword syntax, you use
5501 the @code{read-set!} procedure documented in @ref{User level options
5502 interfaces} and @ref{Reader options}. Note that the @code{prefix} and
5503 @code{postfix} syntax are mutually exclusive.
5506 (read-set! keywords 'prefix)
5516 (read-set! keywords 'postfix)
5526 (read-set! keywords #f)
5534 ERROR: In expression :type:
5535 ERROR: Unbound variable: :type
5536 ABORT: (unbound-variable)
5539 @node Keyword Procedures
5540 @subsubsection Keyword Procedures
5542 @deffn {Scheme Procedure} keyword? obj
5543 @deffnx {C Function} scm_keyword_p (obj)
5544 Return @code{#t} if the argument @var{obj} is a keyword, else
5548 @deffn {Scheme Procedure} keyword->symbol keyword
5549 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5550 Return the symbol with the same name as @var{keyword}.
5553 @deffn {Scheme Procedure} symbol->keyword symbol
5554 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5555 Return the keyword with the same name as @var{symbol}.
5558 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5559 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5562 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *str)
5563 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *str, size_t len)
5564 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5565 (@var{str}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5566 (@var{str}, @var{len}))}, respectively.
5570 @subsection ``Functionality-Centric'' Data Types
5572 Procedures and macros are documented in their own chapter: see
5573 @ref{Procedures and Macros}.
5575 Variable objects are documented as part of the description of Guile's
5576 module system: see @ref{Variables}.
5578 Asyncs, dynamic roots and fluids are described in the chapter on
5579 scheduling: see @ref{Scheduling}.
5581 Hooks are documented in the chapter on general utility functions: see
5584 Ports are described in the chapter on I/O: see @ref{Input and Output}.
5588 @c TeX-master: "guile.texi"