2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007,
4 @c 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
7 @node Simple Data Types
8 @section Simple Generic Data Types
10 This chapter describes those of Guile's simple data types which are
11 primarily used for their role as items of generic data. By
12 @dfn{simple} we mean data types that are not primarily used as
13 containers to hold other data --- i.e.@: pairs, lists, vectors and so on.
14 For the documentation of such @dfn{compound} data types, see
15 @ref{Compound Data Types}.
17 @c One of the great strengths of Scheme is that there is no straightforward
18 @c distinction between ``data'' and ``functionality''. For example,
19 @c Guile's support for dynamic linking could be described:
23 @c either in a ``data-centric'' way, as the behaviour and properties of the
24 @c ``dynamically linked object'' data type, and the operations that may be
25 @c applied to instances of this type
28 @c or in a ``functionality-centric'' way, as the set of procedures that
29 @c constitute Guile's support for dynamic linking, in the context of the
33 @c The contents of this chapter are, therefore, a matter of judgment. By
34 @c @dfn{generic}, we mean to select those data types whose typical use as
35 @c @emph{data} in a wide variety of programming contexts is more important
36 @c than their use in the implementation of a particular piece of
37 @c @emph{functionality}. The last section of this chapter provides
38 @c references for all the data types that are documented not here but in a
39 @c ``functionality-centric'' way elsewhere in the manual.
42 * Booleans:: True/false values.
43 * Numbers:: Numerical data types.
44 * Characters:: Single characters.
45 * Character Sets:: Sets of characters.
46 * Strings:: Sequences of characters.
47 * Bytevectors:: Sequences of bytes.
49 * Keywords:: Self-quoting, customizable display keywords.
50 * Other Types:: "Functionality-centric" data types.
58 The two boolean values are @code{#t} for true and @code{#f} for false.
60 Boolean values are returned by predicate procedures, such as the general
61 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
62 (@pxref{Equality}) and numerical and string comparison operators like
63 @code{string=?} (@pxref{String Comparison}) and @code{<=}
73 (equal? "house" "houses")
81 In test condition contexts like @code{if} and @code{cond}
82 (@pxref{Conditionals}), where a group of subexpressions will be
83 evaluated only if a @var{condition} expression evaluates to ``true'',
84 ``true'' means any value at all except @code{#f}.
97 A result of this asymmetry is that typical Scheme source code more often
98 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
99 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
100 not necessary to represent an @code{if} or @code{cond} true value.
102 It is important to note that @code{#f} is @strong{not} equivalent to any
103 other Scheme value. In particular, @code{#f} is not the same as the
104 number 0 (like in C and C++), and not the same as the ``empty list''
105 (like in some Lisp dialects).
107 In C, the two Scheme boolean values are available as the two constants
108 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
109 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
110 false when used in C conditionals. In order to test for it, use
111 @code{scm_is_false} or @code{scm_is_true}.
114 @deffn {Scheme Procedure} not x
115 @deffnx {C Function} scm_not (x)
116 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
120 @deffn {Scheme Procedure} boolean? obj
121 @deffnx {C Function} scm_boolean_p (obj)
122 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
126 @deftypevr {C Macro} SCM SCM_BOOL_T
127 The @code{SCM} representation of the Scheme object @code{#t}.
130 @deftypevr {C Macro} SCM SCM_BOOL_F
131 The @code{SCM} representation of the Scheme object @code{#f}.
134 @deftypefn {C Function} int scm_is_true (SCM obj)
135 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
138 @deftypefn {C Function} int scm_is_false (SCM obj)
139 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
142 @deftypefn {C Function} int scm_is_bool (SCM obj)
143 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
147 @deftypefn {C Function} SCM scm_from_bool (int val)
148 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
151 @deftypefn {C Function} int scm_to_bool (SCM val)
152 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
153 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
155 You should probably use @code{scm_is_true} instead of this function
156 when you just want to test a @code{SCM} value for trueness.
160 @subsection Numerical data types
163 Guile supports a rich ``tower'' of numerical types --- integer,
164 rational, real and complex --- and provides an extensive set of
165 mathematical and scientific functions for operating on numerical
166 data. This section of the manual documents those types and functions.
168 You may also find it illuminating to read R5RS's presentation of numbers
169 in Scheme, which is particularly clear and accessible: see
170 @ref{Numbers,,,r5rs,R5RS}.
173 * Numerical Tower:: Scheme's numerical "tower".
174 * Integers:: Whole numbers.
175 * Reals and Rationals:: Real and rational numbers.
176 * Complex Numbers:: Complex numbers.
177 * Exactness:: Exactness and inexactness.
178 * Number Syntax:: Read syntax for numerical data.
179 * Integer Operations:: Operations on integer values.
180 * Comparison:: Comparison predicates.
181 * Conversion:: Converting numbers to and from strings.
182 * Complex:: Complex number operations.
183 * Arithmetic:: Arithmetic functions.
184 * Scientific:: Scientific functions.
185 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
186 * Random:: Random number generation.
190 @node Numerical Tower
191 @subsubsection Scheme's Numerical ``Tower''
194 Scheme's numerical ``tower'' consists of the following categories of
199 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
202 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
203 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
204 pi (an irrational number) doesn't. These include integers
208 The set of numbers that describes all possible positions along a
209 one-dimensional line. This includes rationals as well as irrational
212 @item complex numbers
213 The set of numbers that describes all possible positions in a two
214 dimensional space. This includes real as well as imaginary numbers
215 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
216 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
220 It is called a tower because each category ``sits on'' the one that
221 follows it, in the sense that every integer is also a rational, every
222 rational is also real, and every real number is also a complex number
223 (but with zero imaginary part).
225 In addition to the classification into integers, rationals, reals and
226 complex numbers, Scheme also distinguishes between whether a number is
227 represented exactly or not. For example, the result of
228 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
229 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
230 Instead, it stores an inexact approximation, using the C type
233 Guile can represent exact rationals of any magnitude, inexact
234 rationals that fit into a C @code{double}, and inexact complex numbers
235 with @code{double} real and imaginary parts.
237 The @code{number?} predicate may be applied to any Scheme value to
238 discover whether the value is any of the supported numerical types.
240 @deffn {Scheme Procedure} number? obj
241 @deffnx {C Function} scm_number_p (obj)
242 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
251 (number? "hello there!")
254 (define pi 3.141592654)
259 @deftypefn {C Function} int scm_is_number (SCM obj)
260 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
263 The next few subsections document each of Guile's numerical data types
267 @subsubsection Integers
269 @tpindex Integer numbers
273 Integers are whole numbers, that is numbers with no fractional part,
274 such as 2, 83, and @minus{}3789.
276 Integers in Guile can be arbitrarily big, as shown by the following
280 (define (factorial n)
281 (let loop ((n n) (product 1))
284 (loop (- n 1) (* product n)))))
290 @result{} 2432902008176640000
293 @result{} -119622220865480194561963161495657715064383733760000000000
296 Readers whose background is in programming languages where integers are
297 limited by the need to fit into just 4 or 8 bytes of memory may find
298 this surprising, or suspect that Guile's representation of integers is
299 inefficient. In fact, Guile achieves a near optimal balance of
300 convenience and efficiency by using the host computer's native
301 representation of integers where possible, and a more general
302 representation where the required number does not fit in the native
303 form. Conversion between these two representations is automatic and
304 completely invisible to the Scheme level programmer.
306 C has a host of different integer types, and Guile offers a host of
307 functions to convert between them and the @code{SCM} representation.
308 For example, a C @code{int} can be handled with @code{scm_to_int} and
309 @code{scm_from_int}. Guile also defines a few C integer types of its
310 own, to help with differences between systems.
312 C integer types that are not covered can be handled with the generic
313 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
314 signed types, or with @code{scm_to_unsigned_integer} and
315 @code{scm_from_unsigned_integer} for unsigned types.
317 Scheme integers can be exact and inexact. For example, a number
318 written as @code{3.0} with an explicit decimal-point is inexact, but
319 it is also an integer. The functions @code{integer?} and
320 @code{scm_is_integer} report true for such a number, but the functions
321 @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only
322 allow exact integers and thus report false. Likewise, the conversion
323 functions like @code{scm_to_signed_integer} only accept exact
326 The motivation for this behavior is that the inexactness of a number
327 should not be lost silently. If you want to allow inexact integers,
328 you can explicitly insert a call to @code{inexact->exact} or to its C
329 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
330 be converted by this call into exact integers; inexact non-integers
331 will become exact fractions.)
333 @deffn {Scheme Procedure} integer? x
334 @deffnx {C Function} scm_integer_p (x)
335 Return @code{#t} if @var{x} is an exact or inexact integer number, else
353 @deftypefn {C Function} int scm_is_integer (SCM x)
354 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
357 @defvr {C Type} scm_t_int8
358 @defvrx {C Type} scm_t_uint8
359 @defvrx {C Type} scm_t_int16
360 @defvrx {C Type} scm_t_uint16
361 @defvrx {C Type} scm_t_int32
362 @defvrx {C Type} scm_t_uint32
363 @defvrx {C Type} scm_t_int64
364 @defvrx {C Type} scm_t_uint64
365 @defvrx {C Type} scm_t_intmax
366 @defvrx {C Type} scm_t_uintmax
367 The C types are equivalent to the corresponding ISO C types but are
368 defined on all platforms, with the exception of @code{scm_t_int64} and
369 @code{scm_t_uint64}, which are only defined when a 64-bit type is
370 available. For example, @code{scm_t_int8} is equivalent to
373 You can regard these definitions as a stop-gap measure until all
374 platforms provide these types. If you know that all the platforms
375 that you are interested in already provide these types, it is better
376 to use them directly instead of the types provided by Guile.
379 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
380 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
381 Return @code{1} when @var{x} represents an exact integer that is
382 between @var{min} and @var{max}, inclusive.
384 These functions can be used to check whether a @code{SCM} value will
385 fit into a given range, such as the range of a given C integer type.
386 If you just want to convert a @code{SCM} value to a given C integer
387 type, use one of the conversion functions directly.
390 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
391 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
392 When @var{x} represents an exact integer that is between @var{min} and
393 @var{max} inclusive, return that integer. Else signal an error,
394 either a `wrong-type' error when @var{x} is not an exact integer, or
395 an `out-of-range' error when it doesn't fit the given range.
398 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
399 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
400 Return the @code{SCM} value that represents the integer @var{x}. This
401 function will always succeed and will always return an exact number.
404 @deftypefn {C Function} char scm_to_char (SCM x)
405 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
406 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
407 @deftypefnx {C Function} short scm_to_short (SCM x)
408 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
409 @deftypefnx {C Function} int scm_to_int (SCM x)
410 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
411 @deftypefnx {C Function} long scm_to_long (SCM x)
412 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
413 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
414 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
415 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
416 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
417 @deftypefnx {C Function} scm_t_ptrdiff scm_to_ptrdiff_t (SCM x)
418 @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x)
419 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
420 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
421 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
422 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
423 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
424 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
425 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
426 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
427 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
428 When @var{x} represents an exact integer that fits into the indicated
429 C type, return that integer. Else signal an error, either a
430 `wrong-type' error when @var{x} is not an exact integer, or an
431 `out-of-range' error when it doesn't fit the given range.
433 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
434 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
435 the corresponding types are.
438 @deftypefn {C Function} SCM scm_from_char (char x)
439 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
440 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
441 @deftypefnx {C Function} SCM scm_from_short (short x)
442 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
443 @deftypefnx {C Function} SCM scm_from_int (int x)
444 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
445 @deftypefnx {C Function} SCM scm_from_long (long x)
446 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
447 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
448 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
449 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
450 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
451 @deftypefnx {C Function} SCM scm_from_ptrdiff_t (scm_t_ptrdiff x)
452 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
453 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
454 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
455 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
456 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
457 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
458 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
459 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
460 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
461 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
462 Return the @code{SCM} value that represents the integer @var{x}.
463 These functions will always succeed and will always return an exact
467 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
468 Assign @var{val} to the multiple precision integer @var{rop}.
469 @var{val} must be an exact integer, otherwise an error will be
470 signalled. @var{rop} must have been initialized with @code{mpz_init}
471 before this function is called. When @var{rop} is no longer needed
472 the occupied space must be freed with @code{mpz_clear}.
473 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
476 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
477 Return the @code{SCM} value that represents @var{val}.
480 @node Reals and Rationals
481 @subsubsection Real and Rational Numbers
482 @tpindex Real numbers
483 @tpindex Rational numbers
488 Mathematically, the real numbers are the set of numbers that describe
489 all possible points along a continuous, infinite, one-dimensional line.
490 The rational numbers are the set of all numbers that can be written as
491 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
492 All rational numbers are also real, but there are real numbers that
493 are not rational, for example @m{\sqrt{2}, the square root of 2}, and
496 Guile can represent both exact and inexact rational numbers, but it
497 cannot represent precise finite irrational numbers. Exact rationals are
498 represented by storing the numerator and denominator as two exact
499 integers. Inexact rationals are stored as floating point numbers using
500 the C type @code{double}.
502 Exact rationals are written as a fraction of integers. There must be
503 no whitespace around the slash:
510 Even though the actual encoding of inexact rationals is in binary, it
511 may be helpful to think of it as a decimal number with a limited
512 number of significant figures and a decimal point somewhere, since
513 this corresponds to the standard notation for non-whole numbers. For
519 -5648394822220000000000.0
523 The limited precision of Guile's encoding means that any finite ``real''
524 number in Guile can be written in a rational form, by multiplying and
525 then dividing by sufficient powers of 10 (or in fact, 2). For example,
526 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided
527 by 100000000000000000. In Guile's current incarnation, therefore, the
528 @code{rational?} and @code{real?} predicates are equivalent for finite
532 Dividing by an exact zero leads to a error message, as one might expect.
533 However, dividing by an inexact zero does not produce an error.
534 Instead, the result of the division is either plus or minus infinity,
535 depending on the sign of the divided number and the sign of the zero
536 divisor (some platforms support signed zeroes @samp{-0.0} and
537 @samp{+0.0}; @samp{0.0} is the same as @samp{+0.0}).
539 Dividing zero by an inexact zero yields a @acronym{NaN} (`not a number')
540 value, although they are actually considered numbers by Scheme.
541 Attempts to compare a @acronym{NaN} value with any number (including
542 itself) using @code{=}, @code{<}, @code{>}, @code{<=} or @code{>=}
543 always returns @code{#f}. Although a @acronym{NaN} value is not
544 @code{=} to itself, it is both @code{eqv?} and @code{equal?} to itself
545 and other @acronym{NaN} values. However, the preferred way to test for
546 them is by using @code{nan?}.
548 The real @acronym{NaN} values and infinities are written @samp{+nan.0},
549 @samp{+inf.0} and @samp{-inf.0}. This syntax is also recognized by
550 @code{read} as an extension to the usual Scheme syntax. These special
551 values are considered by Scheme to be inexact real numbers but not
552 rational. Note that non-real complex numbers may also contain
553 infinities or @acronym{NaN} values in their real or imaginary parts. To
554 test a real number to see if it is infinite, a @acronym{NaN} value, or
555 neither, use @code{inf?}, @code{nan?}, or @code{finite?}, respectively.
556 Every real number in Scheme belongs to precisely one of those three
559 On platforms that follow @acronym{IEEE} 754 for their floating point
560 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
561 are implemented using the corresponding @acronym{IEEE} 754 values.
562 They behave in arithmetic operations like @acronym{IEEE} 754 describes
563 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
565 @deffn {Scheme Procedure} real? obj
566 @deffnx {C Function} scm_real_p (obj)
567 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
568 that the sets of integer and rational values form subsets of the set
569 of real numbers, so the predicate will also be fulfilled if @var{obj}
570 is an integer number or a rational number.
573 @deffn {Scheme Procedure} rational? x
574 @deffnx {C Function} scm_rational_p (x)
575 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
576 Note that the set of integer values forms a subset of the set of
577 rational numbers, i.e.@: the predicate will also be fulfilled if
578 @var{x} is an integer number.
581 @deffn {Scheme Procedure} rationalize x eps
582 @deffnx {C Function} scm_rationalize (x, eps)
583 Returns the @emph{simplest} rational number differing
584 from @var{x} by no more than @var{eps}.
586 As required by @acronym{R5RS}, @code{rationalize} only returns an
587 exact result when both its arguments are exact. Thus, you might need
588 to use @code{inexact->exact} on the arguments.
591 (rationalize (inexact->exact 1.2) 1/100)
597 @deffn {Scheme Procedure} inf? x
598 @deffnx {C Function} scm_inf_p (x)
599 Return @code{#t} if the real number @var{x} is @samp{+inf.0} or
600 @samp{-inf.0}. Otherwise return @code{#f}.
603 @deffn {Scheme Procedure} nan? x
604 @deffnx {C Function} scm_nan_p (x)
605 Return @code{#t} if the real number @var{x} is @samp{+nan.0}, or
609 @deffn {Scheme Procedure} finite? x
610 @deffnx {C Function} scm_finite_p (x)
611 Return @code{#t} if the real number @var{x} is neither infinite nor a
612 NaN, @code{#f} otherwise.
615 @deffn {Scheme Procedure} nan
616 @deffnx {C Function} scm_nan ()
617 Return @samp{+nan.0}, a @acronym{NaN} value.
620 @deffn {Scheme Procedure} inf
621 @deffnx {C Function} scm_inf ()
622 Return @samp{+inf.0}, positive infinity.
625 @deffn {Scheme Procedure} numerator x
626 @deffnx {C Function} scm_numerator (x)
627 Return the numerator of the rational number @var{x}.
630 @deffn {Scheme Procedure} denominator x
631 @deffnx {C Function} scm_denominator (x)
632 Return the denominator of the rational number @var{x}.
635 @deftypefn {C Function} int scm_is_real (SCM val)
636 @deftypefnx {C Function} int scm_is_rational (SCM val)
637 Equivalent to @code{scm_is_true (scm_real_p (val))} and
638 @code{scm_is_true (scm_rational_p (val))}, respectively.
641 @deftypefn {C Function} double scm_to_double (SCM val)
642 Returns the number closest to @var{val} that is representable as a
643 @code{double}. Returns infinity for a @var{val} that is too large in
644 magnitude. The argument @var{val} must be a real number.
647 @deftypefn {C Function} SCM scm_from_double (double val)
648 Return the @code{SCM} value that represents @var{val}. The returned
649 value is inexact according to the predicate @code{inexact?}, but it
650 will be exactly equal to @var{val}.
653 @node Complex Numbers
654 @subsubsection Complex Numbers
655 @tpindex Complex numbers
659 Complex numbers are the set of numbers that describe all possible points
660 in a two-dimensional space. The two coordinates of a particular point
661 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
662 the complex number that describes that point.
664 In Guile, complex numbers are written in rectangular form as the sum of
665 their real and imaginary parts, using the symbol @code{i} to indicate
680 Polar form can also be used, with an @samp{@@} between magnitude and
684 1@@3.141592 @result{} -1.0 (approx)
685 -1@@1.57079 @result{} 0.0-1.0i (approx)
688 Guile represents a complex number as a pair of inexact reals, so the
689 real and imaginary parts of a complex number have the same properties of
690 inexactness and limited precision as single inexact real numbers.
692 Note that each part of a complex number may contain any inexact real
693 value, including the special values @samp{+nan.0}, @samp{+inf.0} and
694 @samp{-inf.0}, as well as either of the signed zeroes @samp{0.0} or
698 @deffn {Scheme Procedure} complex? z
699 @deffnx {C Function} scm_complex_p (z)
700 Return @code{#t} if @var{z} is a complex number, @code{#f}
701 otherwise. Note that the sets of real, rational and integer
702 values form subsets of the set of complex numbers, i.e.@: the
703 predicate will also be fulfilled if @var{z} is a real,
704 rational or integer number.
707 @deftypefn {C Function} int scm_is_complex (SCM val)
708 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
712 @subsubsection Exact and Inexact Numbers
713 @tpindex Exact numbers
714 @tpindex Inexact numbers
718 @rnindex exact->inexact
719 @rnindex inexact->exact
721 R5RS requires that, with few exceptions, a calculation involving inexact
722 numbers always produces an inexact result. To meet this requirement,
723 Guile distinguishes between an exact integer value such as @samp{5} and
724 the corresponding inexact integer value which, to the limited precision
725 available, has no fractional part, and is printed as @samp{5.0}. Guile
726 will only convert the latter value to the former when forced to do so by
727 an invocation of the @code{inexact->exact} procedure.
729 The only exception to the above requirement is when the values of the
730 inexact numbers do not affect the result. For example @code{(expt n 0)}
731 is @samp{1} for any value of @code{n}, therefore @code{(expt 5.0 0)} is
732 permitted to return an exact @samp{1}.
734 @deffn {Scheme Procedure} exact? z
735 @deffnx {C Function} scm_exact_p (z)
736 Return @code{#t} if the number @var{z} is exact, @code{#f}
752 @deftypefn {C Function} int scm_is_exact (SCM z)
753 Return a @code{1} if the number @var{z} is exact, and @code{0}
754 otherwise. This is equivalent to @code{scm_is_true (scm_exact_p (z))}.
756 An alternate approch to testing the exactness of a number is to
757 use @code{scm_is_signed_integer} or @code{scm_is_unsigned_integer}.
760 @deffn {Scheme Procedure} inexact? z
761 @deffnx {C Function} scm_inexact_p (z)
762 Return @code{#t} if the number @var{z} is inexact, @code{#f}
766 @deftypefn {C Function} int scm_is_inexact (SCM z)
767 Return a @code{1} if the number @var{z} is inexact, and @code{0}
768 otherwise. This is equivalent to @code{scm_is_true (scm_inexact_p (z))}.
771 @deffn {Scheme Procedure} inexact->exact z
772 @deffnx {C Function} scm_inexact_to_exact (z)
773 Return an exact number that is numerically closest to @var{z}, when
774 there is one. For inexact rationals, Guile returns the exact rational
775 that is numerically equal to the inexact rational. Inexact complex
776 numbers with a non-zero imaginary part can not be made exact.
783 The following happens because 12/10 is not exactly representable as a
784 @code{double} (on most platforms). However, when reading a decimal
785 number that has been marked exact with the ``#e'' prefix, Guile is
786 able to represent it correctly.
790 @result{} 5404319552844595/4503599627370496
798 @c begin (texi-doc-string "guile" "exact->inexact")
799 @deffn {Scheme Procedure} exact->inexact z
800 @deffnx {C Function} scm_exact_to_inexact (z)
801 Convert the number @var{z} to its inexact representation.
806 @subsubsection Read Syntax for Numerical Data
808 The read syntax for integers is a string of digits, optionally
809 preceded by a minus or plus character, a code indicating the
810 base in which the integer is encoded, and a code indicating whether
811 the number is exact or inexact. The supported base codes are:
816 the integer is written in binary (base 2)
820 the integer is written in octal (base 8)
824 the integer is written in decimal (base 10)
828 the integer is written in hexadecimal (base 16)
831 If the base code is omitted, the integer is assumed to be decimal. The
832 following examples show how these base codes are used.
851 The codes for indicating exactness (which can, incidentally, be applied
852 to all numerical values) are:
861 the number is inexact.
864 If the exactness indicator is omitted, the number is exact unless it
865 contains a radix point. Since Guile can not represent exact complex
866 numbers, an error is signalled when asking for them.
876 ERROR: Wrong type argument
879 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
880 plus and minus infinity, respectively. The value must be written
881 exactly as shown, that is, they always must have a sign and exactly
882 one zero digit after the decimal point. It also understands
883 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
884 The sign is ignored for `not-a-number' and the value is always printed
887 @node Integer Operations
888 @subsubsection Operations on Integer Values
897 @deffn {Scheme Procedure} odd? n
898 @deffnx {C Function} scm_odd_p (n)
899 Return @code{#t} if @var{n} is an odd number, @code{#f}
903 @deffn {Scheme Procedure} even? n
904 @deffnx {C Function} scm_even_p (n)
905 Return @code{#t} if @var{n} is an even number, @code{#f}
909 @c begin (texi-doc-string "guile" "quotient")
910 @c begin (texi-doc-string "guile" "remainder")
911 @deffn {Scheme Procedure} quotient n d
912 @deffnx {Scheme Procedure} remainder n d
913 @deffnx {C Function} scm_quotient (n, d)
914 @deffnx {C Function} scm_remainder (n, d)
915 Return the quotient or remainder from @var{n} divided by @var{d}. The
916 quotient is rounded towards zero, and the remainder will have the same
917 sign as @var{n}. In all cases quotient and remainder satisfy
918 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
921 (remainder 13 4) @result{} 1
922 (remainder -13 4) @result{} -1
925 See also @code{truncate-quotient}, @code{truncate-remainder} and
926 related operations in @ref{Arithmetic}.
929 @c begin (texi-doc-string "guile" "modulo")
930 @deffn {Scheme Procedure} modulo n d
931 @deffnx {C Function} scm_modulo (n, d)
932 Return the remainder from @var{n} divided by @var{d}, with the same
936 (modulo 13 4) @result{} 1
937 (modulo -13 4) @result{} 3
938 (modulo 13 -4) @result{} -3
939 (modulo -13 -4) @result{} -1
942 See also @code{floor-quotient}, @code{floor-remainder} and
943 related operations in @ref{Arithmetic}.
946 @c begin (texi-doc-string "guile" "gcd")
947 @deffn {Scheme Procedure} gcd x@dots{}
948 @deffnx {C Function} scm_gcd (x, y)
949 Return the greatest common divisor of all arguments.
950 If called without arguments, 0 is returned.
952 The C function @code{scm_gcd} always takes two arguments, while the
953 Scheme function can take an arbitrary number.
956 @c begin (texi-doc-string "guile" "lcm")
957 @deffn {Scheme Procedure} lcm x@dots{}
958 @deffnx {C Function} scm_lcm (x, y)
959 Return the least common multiple of the arguments.
960 If called without arguments, 1 is returned.
962 The C function @code{scm_lcm} always takes two arguments, while the
963 Scheme function can take an arbitrary number.
966 @deffn {Scheme Procedure} modulo-expt n k m
967 @deffnx {C Function} scm_modulo_expt (n, k, m)
968 Return @var{n} raised to the integer exponent
969 @var{k}, modulo @var{m}.
977 @deftypefn {Scheme Procedure} {} exact-integer-sqrt @var{k}
978 @deftypefnx {C Function} void scm_exact_integer_sqrt (SCM @var{k}, SCM *@var{s}, SCM *@var{r})
979 Return two exact non-negative integers @var{s} and @var{r}
980 such that @math{@var{k} = @var{s}^2 + @var{r}} and
981 @math{@var{s}^2 <= @var{k} < (@var{s} + 1)^2}.
982 An error is raised if @var{k} is not an exact non-negative integer.
985 (exact-integer-sqrt 10) @result{} 3 and 1
990 @subsubsection Comparison Predicates
995 The C comparison functions below always takes two arguments, while the
996 Scheme functions can take an arbitrary number. Also keep in mind that
997 the C functions return one of the Scheme boolean values
998 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
999 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
1000 y))} when testing the two Scheme numbers @code{x} and @code{y} for
1001 equality, for example.
1003 @c begin (texi-doc-string "guile" "=")
1004 @deffn {Scheme Procedure} =
1005 @deffnx {C Function} scm_num_eq_p (x, y)
1006 Return @code{#t} if all parameters are numerically equal.
1009 @c begin (texi-doc-string "guile" "<")
1010 @deffn {Scheme Procedure} <
1011 @deffnx {C Function} scm_less_p (x, y)
1012 Return @code{#t} if the list of parameters is monotonically
1016 @c begin (texi-doc-string "guile" ">")
1017 @deffn {Scheme Procedure} >
1018 @deffnx {C Function} scm_gr_p (x, y)
1019 Return @code{#t} if the list of parameters is monotonically
1023 @c begin (texi-doc-string "guile" "<=")
1024 @deffn {Scheme Procedure} <=
1025 @deffnx {C Function} scm_leq_p (x, y)
1026 Return @code{#t} if the list of parameters is monotonically
1030 @c begin (texi-doc-string "guile" ">=")
1031 @deffn {Scheme Procedure} >=
1032 @deffnx {C Function} scm_geq_p (x, y)
1033 Return @code{#t} if the list of parameters is monotonically
1037 @c begin (texi-doc-string "guile" "zero?")
1038 @deffn {Scheme Procedure} zero? z
1039 @deffnx {C Function} scm_zero_p (z)
1040 Return @code{#t} if @var{z} is an exact or inexact number equal to
1044 @c begin (texi-doc-string "guile" "positive?")
1045 @deffn {Scheme Procedure} positive? x
1046 @deffnx {C Function} scm_positive_p (x)
1047 Return @code{#t} if @var{x} is an exact or inexact number greater than
1051 @c begin (texi-doc-string "guile" "negative?")
1052 @deffn {Scheme Procedure} negative? x
1053 @deffnx {C Function} scm_negative_p (x)
1054 Return @code{#t} if @var{x} is an exact or inexact number less than
1060 @subsubsection Converting Numbers To and From Strings
1061 @rnindex number->string
1062 @rnindex string->number
1064 The following procedures read and write numbers according to their
1065 external representation as defined by R5RS (@pxref{Lexical structure,
1066 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1067 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1068 i18n)} module}, for locale-dependent number parsing.
1070 @deffn {Scheme Procedure} number->string n [radix]
1071 @deffnx {C Function} scm_number_to_string (n, radix)
1072 Return a string holding the external representation of the
1073 number @var{n} in the given @var{radix}. If @var{n} is
1074 inexact, a radix of 10 will be used.
1077 @deffn {Scheme Procedure} string->number string [radix]
1078 @deffnx {C Function} scm_string_to_number (string, radix)
1079 Return a number of the maximally precise representation
1080 expressed by the given @var{string}. @var{radix} must be an
1081 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1082 is a default radix that may be overridden by an explicit radix
1083 prefix in @var{string} (e.g.@: "#o177"). If @var{radix} is not
1084 supplied, then the default radix is 10. If string is not a
1085 syntactically valid notation for a number, then
1086 @code{string->number} returns @code{#f}.
1089 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1090 As per @code{string->number} above, but taking a C string, as pointer
1091 and length. The string characters should be in the current locale
1092 encoding (@code{locale} in the name refers only to that, there's no
1093 locale-dependent parsing).
1098 @subsubsection Complex Number Operations
1099 @rnindex make-rectangular
1106 @deffn {Scheme Procedure} make-rectangular real_part imaginary_part
1107 @deffnx {C Function} scm_make_rectangular (real_part, imaginary_part)
1108 Return a complex number constructed of the given @var{real-part} and @var{imaginary-part} parts.
1111 @deffn {Scheme Procedure} make-polar mag ang
1112 @deffnx {C Function} scm_make_polar (mag, ang)
1114 Return the complex number @var{mag} * e^(i * @var{ang}).
1117 @c begin (texi-doc-string "guile" "real-part")
1118 @deffn {Scheme Procedure} real-part z
1119 @deffnx {C Function} scm_real_part (z)
1120 Return the real part of the number @var{z}.
1123 @c begin (texi-doc-string "guile" "imag-part")
1124 @deffn {Scheme Procedure} imag-part z
1125 @deffnx {C Function} scm_imag_part (z)
1126 Return the imaginary part of the number @var{z}.
1129 @c begin (texi-doc-string "guile" "magnitude")
1130 @deffn {Scheme Procedure} magnitude z
1131 @deffnx {C Function} scm_magnitude (z)
1132 Return the magnitude of the number @var{z}. This is the same as
1133 @code{abs} for real arguments, but also allows complex numbers.
1136 @c begin (texi-doc-string "guile" "angle")
1137 @deffn {Scheme Procedure} angle z
1138 @deffnx {C Function} scm_angle (z)
1139 Return the angle of the complex number @var{z}.
1142 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1143 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1144 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1145 respectively, but these functions take @code{double}s as their
1149 @deftypefn {C Function} double scm_c_real_part (z)
1150 @deftypefnx {C Function} double scm_c_imag_part (z)
1151 Returns the real or imaginary part of @var{z} as a @code{double}.
1154 @deftypefn {C Function} double scm_c_magnitude (z)
1155 @deftypefnx {C Function} double scm_c_angle (z)
1156 Returns the magnitude or angle of @var{z} as a @code{double}.
1161 @subsubsection Arithmetic Functions
1176 @rnindex euclidean-quotient
1177 @rnindex euclidean-remainder
1179 @rnindex floor-quotient
1180 @rnindex floor-remainder
1182 @rnindex ceiling-quotient
1183 @rnindex ceiling-remainder
1185 @rnindex truncate-quotient
1186 @rnindex truncate-remainder
1188 @rnindex centered-quotient
1189 @rnindex centered-remainder
1191 @rnindex round-quotient
1192 @rnindex round-remainder
1194 The C arithmetic functions below always takes two arguments, while the
1195 Scheme functions can take an arbitrary number. When you need to
1196 invoke them with just one argument, for example to compute the
1197 equivalent of @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1198 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1200 @c begin (texi-doc-string "guile" "+")
1201 @deffn {Scheme Procedure} + z1 @dots{}
1202 @deffnx {C Function} scm_sum (z1, z2)
1203 Return the sum of all parameter values. Return 0 if called without any
1207 @c begin (texi-doc-string "guile" "-")
1208 @deffn {Scheme Procedure} - z1 z2 @dots{}
1209 @deffnx {C Function} scm_difference (z1, z2)
1210 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1211 the sum of all but the first argument are subtracted from the first
1215 @c begin (texi-doc-string "guile" "*")
1216 @deffn {Scheme Procedure} * z1 @dots{}
1217 @deffnx {C Function} scm_product (z1, z2)
1218 Return the product of all arguments. If called without arguments, 1 is
1222 @c begin (texi-doc-string "guile" "/")
1223 @deffn {Scheme Procedure} / z1 z2 @dots{}
1224 @deffnx {C Function} scm_divide (z1, z2)
1225 Divide the first argument by the product of the remaining arguments. If
1226 called with one argument @var{z1}, 1/@var{z1} is returned.
1229 @deffn {Scheme Procedure} 1+ z
1230 @deffnx {C Function} scm_oneplus (z)
1231 Return @math{@var{z} + 1}.
1234 @deffn {Scheme Procedure} 1- z
1235 @deffnx {C function} scm_oneminus (z)
1236 Return @math{@var{z} - 1}.
1239 @c begin (texi-doc-string "guile" "abs")
1240 @deffn {Scheme Procedure} abs x
1241 @deffnx {C Function} scm_abs (x)
1242 Return the absolute value of @var{x}.
1244 @var{x} must be a number with zero imaginary part. To calculate the
1245 magnitude of a complex number, use @code{magnitude} instead.
1248 @c begin (texi-doc-string "guile" "max")
1249 @deffn {Scheme Procedure} max x1 x2 @dots{}
1250 @deffnx {C Function} scm_max (x1, x2)
1251 Return the maximum of all parameter values.
1254 @c begin (texi-doc-string "guile" "min")
1255 @deffn {Scheme Procedure} min x1 x2 @dots{}
1256 @deffnx {C Function} scm_min (x1, x2)
1257 Return the minimum of all parameter values.
1260 @c begin (texi-doc-string "guile" "truncate")
1261 @deffn {Scheme Procedure} truncate x
1262 @deffnx {C Function} scm_truncate_number (x)
1263 Round the inexact number @var{x} towards zero.
1266 @c begin (texi-doc-string "guile" "round")
1267 @deffn {Scheme Procedure} round x
1268 @deffnx {C Function} scm_round_number (x)
1269 Round the inexact number @var{x} to the nearest integer. When exactly
1270 halfway between two integers, round to the even one.
1273 @c begin (texi-doc-string "guile" "floor")
1274 @deffn {Scheme Procedure} floor x
1275 @deffnx {C Function} scm_floor (x)
1276 Round the number @var{x} towards minus infinity.
1279 @c begin (texi-doc-string "guile" "ceiling")
1280 @deffn {Scheme Procedure} ceiling x
1281 @deffnx {C Function} scm_ceiling (x)
1282 Round the number @var{x} towards infinity.
1285 @deftypefn {C Function} double scm_c_truncate (double x)
1286 @deftypefnx {C Function} double scm_c_round (double x)
1287 Like @code{scm_truncate_number} or @code{scm_round_number},
1288 respectively, but these functions take and return @code{double}
1292 @deftypefn {Scheme Procedure} {} euclidean/ @var{x} @var{y}
1293 @deftypefnx {Scheme Procedure} {} euclidean-quotient @var{x} @var{y}
1294 @deftypefnx {Scheme Procedure} {} euclidean-remainder @var{x} @var{y}
1295 @deftypefnx {C Function} void scm_euclidean_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1296 @deftypefnx {C Function} SCM scm_euclidean_quotient (SCM @var{x}, SCM @var{y})
1297 @deftypefnx {C Function} SCM scm_euclidean_remainder (SCM @var{x}, SCM @var{y})
1298 These procedures accept two real numbers @var{x} and @var{y}, where the
1299 divisor @var{y} must be non-zero. @code{euclidean-quotient} returns the
1300 integer @var{q} and @code{euclidean-remainder} returns the real number
1301 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1302 @math{0 <= @var{r} < |@var{y}|}. @code{euclidean/} returns both @var{q} and
1303 @var{r}, and is more efficient than computing each separately. Note
1304 that when @math{@var{y} > 0}, @code{euclidean-quotient} returns
1305 @math{floor(@var{x}/@var{y})}, otherwise it returns
1306 @math{ceiling(@var{x}/@var{y})}.
1308 Note that these operators are equivalent to the R6RS operators
1309 @code{div}, @code{mod}, and @code{div-and-mod}.
1312 (euclidean-quotient 123 10) @result{} 12
1313 (euclidean-remainder 123 10) @result{} 3
1314 (euclidean/ 123 10) @result{} 12 and 3
1315 (euclidean/ 123 -10) @result{} -12 and 3
1316 (euclidean/ -123 10) @result{} -13 and 7
1317 (euclidean/ -123 -10) @result{} 13 and 7
1318 (euclidean/ -123.2 -63.5) @result{} 2.0 and 3.8
1319 (euclidean/ 16/3 -10/7) @result{} -3 and 22/21
1323 @deftypefn {Scheme Procedure} {} floor/ @var{x} @var{y}
1324 @deftypefnx {Scheme Procedure} {} floor-quotient @var{x} @var{y}
1325 @deftypefnx {Scheme Procedure} {} floor-remainder @var{x} @var{y}
1326 @deftypefnx {C Function} void scm_floor_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1327 @deftypefnx {C Function} SCM scm_floor_quotient (@var{x}, @var{y})
1328 @deftypefnx {C Function} SCM scm_floor_remainder (@var{x}, @var{y})
1329 These procedures accept two real numbers @var{x} and @var{y}, where the
1330 divisor @var{y} must be non-zero. @code{floor-quotient} returns the
1331 integer @var{q} and @code{floor-remainder} returns the real number
1332 @var{r} such that @math{@var{q} = floor(@var{x}/@var{y})} and
1333 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{floor/} returns
1334 both @var{q} and @var{r}, and is more efficient than computing each
1335 separately. Note that @var{r}, if non-zero, will have the same sign
1338 When @var{x} and @var{y} are integers, @code{floor-remainder} is
1339 equivalent to the R5RS integer-only operator @code{modulo}.
1342 (floor-quotient 123 10) @result{} 12
1343 (floor-remainder 123 10) @result{} 3
1344 (floor/ 123 10) @result{} 12 and 3
1345 (floor/ 123 -10) @result{} -13 and -7
1346 (floor/ -123 10) @result{} -13 and 7
1347 (floor/ -123 -10) @result{} 12 and -3
1348 (floor/ -123.2 -63.5) @result{} 1.0 and -59.7
1349 (floor/ 16/3 -10/7) @result{} -4 and -8/21
1353 @deftypefn {Scheme Procedure} {} ceiling/ @var{x} @var{y}
1354 @deftypefnx {Scheme Procedure} {} ceiling-quotient @var{x} @var{y}
1355 @deftypefnx {Scheme Procedure} {} ceiling-remainder @var{x} @var{y}
1356 @deftypefnx {C Function} void scm_ceiling_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1357 @deftypefnx {C Function} SCM scm_ceiling_quotient (@var{x}, @var{y})
1358 @deftypefnx {C Function} SCM scm_ceiling_remainder (@var{x}, @var{y})
1359 These procedures accept two real numbers @var{x} and @var{y}, where the
1360 divisor @var{y} must be non-zero. @code{ceiling-quotient} returns the
1361 integer @var{q} and @code{ceiling-remainder} returns the real number
1362 @var{r} such that @math{@var{q} = ceiling(@var{x}/@var{y})} and
1363 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{ceiling/} returns
1364 both @var{q} and @var{r}, and is more efficient than computing each
1365 separately. Note that @var{r}, if non-zero, will have the opposite sign
1369 (ceiling-quotient 123 10) @result{} 13
1370 (ceiling-remainder 123 10) @result{} -7
1371 (ceiling/ 123 10) @result{} 13 and -7
1372 (ceiling/ 123 -10) @result{} -12 and 3
1373 (ceiling/ -123 10) @result{} -12 and -3
1374 (ceiling/ -123 -10) @result{} 13 and 7
1375 (ceiling/ -123.2 -63.5) @result{} 2.0 and 3.8
1376 (ceiling/ 16/3 -10/7) @result{} -3 and 22/21
1380 @deftypefn {Scheme Procedure} {} truncate/ @var{x} @var{y}
1381 @deftypefnx {Scheme Procedure} {} truncate-quotient @var{x} @var{y}
1382 @deftypefnx {Scheme Procedure} {} truncate-remainder @var{x} @var{y}
1383 @deftypefnx {C Function} void scm_truncate_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1384 @deftypefnx {C Function} SCM scm_truncate_quotient (@var{x}, @var{y})
1385 @deftypefnx {C Function} SCM scm_truncate_remainder (@var{x}, @var{y})
1386 These procedures accept two real numbers @var{x} and @var{y}, where the
1387 divisor @var{y} must be non-zero. @code{truncate-quotient} returns the
1388 integer @var{q} and @code{truncate-remainder} returns the real number
1389 @var{r} such that @var{q} is @math{@var{x}/@var{y}} rounded toward zero,
1390 and @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{truncate/} returns
1391 both @var{q} and @var{r}, and is more efficient than computing each
1392 separately. Note that @var{r}, if non-zero, will have the same sign
1395 When @var{x} and @var{y} are integers, these operators are
1396 equivalent to the R5RS integer-only operators @code{quotient} and
1400 (truncate-quotient 123 10) @result{} 12
1401 (truncate-remainder 123 10) @result{} 3
1402 (truncate/ 123 10) @result{} 12 and 3
1403 (truncate/ 123 -10) @result{} -12 and 3
1404 (truncate/ -123 10) @result{} -12 and -3
1405 (truncate/ -123 -10) @result{} 12 and -3
1406 (truncate/ -123.2 -63.5) @result{} 1.0 and -59.7
1407 (truncate/ 16/3 -10/7) @result{} -3 and 22/21
1411 @deftypefn {Scheme Procedure} {} centered/ @var{x} @var{y}
1412 @deftypefnx {Scheme Procedure} {} centered-quotient @var{x} @var{y}
1413 @deftypefnx {Scheme Procedure} {} centered-remainder @var{x} @var{y}
1414 @deftypefnx {C Function} void scm_centered_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1415 @deftypefnx {C Function} SCM scm_centered_quotient (SCM @var{x}, SCM @var{y})
1416 @deftypefnx {C Function} SCM scm_centered_remainder (SCM @var{x}, SCM @var{y})
1417 These procedures accept two real numbers @var{x} and @var{y}, where the
1418 divisor @var{y} must be non-zero. @code{centered-quotient} returns the
1419 integer @var{q} and @code{centered-remainder} returns the real number
1420 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1421 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}. @code{centered/}
1422 returns both @var{q} and @var{r}, and is more efficient than computing
1425 Note that @code{centered-quotient} returns @math{@var{x}/@var{y}}
1426 rounded to the nearest integer. When @math{@var{x}/@var{y}} lies
1427 exactly half-way between two integers, the tie is broken according to
1428 the sign of @var{y}. If @math{@var{y} > 0}, ties are rounded toward
1429 positive infinity, otherwise they are rounded toward negative infinity.
1430 This is a consequence of the requirement that
1431 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}.
1433 Note that these operators are equivalent to the R6RS operators
1434 @code{div0}, @code{mod0}, and @code{div0-and-mod0}.
1437 (centered-quotient 123 10) @result{} 12
1438 (centered-remainder 123 10) @result{} 3
1439 (centered/ 123 10) @result{} 12 and 3
1440 (centered/ 123 -10) @result{} -12 and 3
1441 (centered/ -123 10) @result{} -12 and -3
1442 (centered/ -123 -10) @result{} 12 and -3
1443 (centered/ 125 10) @result{} 13 and -5
1444 (centered/ 127 10) @result{} 13 and -3
1445 (centered/ 135 10) @result{} 14 and -5
1446 (centered/ -123.2 -63.5) @result{} 2.0 and 3.8
1447 (centered/ 16/3 -10/7) @result{} -4 and -8/21
1451 @deftypefn {Scheme Procedure} {} round/ @var{x} @var{y}
1452 @deftypefnx {Scheme Procedure} {} round-quotient @var{x} @var{y}
1453 @deftypefnx {Scheme Procedure} {} round-remainder @var{x} @var{y}
1454 @deftypefnx {C Function} void scm_round_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1455 @deftypefnx {C Function} SCM scm_round_quotient (@var{x}, @var{y})
1456 @deftypefnx {C Function} SCM scm_round_remainder (@var{x}, @var{y})
1457 These procedures accept two real numbers @var{x} and @var{y}, where the
1458 divisor @var{y} must be non-zero. @code{round-quotient} returns the
1459 integer @var{q} and @code{round-remainder} returns the real number
1460 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1461 @var{q} is @math{@var{x}/@var{y}} rounded to the nearest integer,
1462 with ties going to the nearest even integer. @code{round/}
1463 returns both @var{q} and @var{r}, and is more efficient than computing
1466 Note that @code{round/} and @code{centered/} are almost equivalent, but
1467 their behavior differs when @math{@var{x}/@var{y}} lies exactly half-way
1468 between two integers. In this case, @code{round/} chooses the nearest
1469 even integer, whereas @code{centered/} chooses in such a way to satisfy
1470 the constraint @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}, which
1471 is stronger than the corresponding constraint for @code{round/},
1472 @math{-|@var{y}/2| <= @var{r} <= |@var{y}/2|}. In particular,
1473 when @var{x} and @var{y} are integers, the number of possible remainders
1474 returned by @code{centered/} is @math{|@var{y}|}, whereas the number of
1475 possible remainders returned by @code{round/} is @math{|@var{y}|+1} when
1479 (round-quotient 123 10) @result{} 12
1480 (round-remainder 123 10) @result{} 3
1481 (round/ 123 10) @result{} 12 and 3
1482 (round/ 123 -10) @result{} -12 and 3
1483 (round/ -123 10) @result{} -12 and -3
1484 (round/ -123 -10) @result{} 12 and -3
1485 (round/ 125 10) @result{} 12 and 5
1486 (round/ 127 10) @result{} 13 and -3
1487 (round/ 135 10) @result{} 14 and -5
1488 (round/ -123.2 -63.5) @result{} 2.0 and 3.8
1489 (round/ 16/3 -10/7) @result{} -4 and -8/21
1494 @subsubsection Scientific Functions
1496 The following procedures accept any kind of number as arguments,
1497 including complex numbers.
1500 @c begin (texi-doc-string "guile" "sqrt")
1501 @deffn {Scheme Procedure} sqrt z
1502 Return the square root of @var{z}. Of the two possible roots
1503 (positive and negative), the one with a positive real part is
1504 returned, or if that's zero then a positive imaginary part. Thus,
1507 (sqrt 9.0) @result{} 3.0
1508 (sqrt -9.0) @result{} 0.0+3.0i
1509 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1510 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1515 @c begin (texi-doc-string "guile" "expt")
1516 @deffn {Scheme Procedure} expt z1 z2
1517 Return @var{z1} raised to the power of @var{z2}.
1521 @c begin (texi-doc-string "guile" "sin")
1522 @deffn {Scheme Procedure} sin z
1523 Return the sine of @var{z}.
1527 @c begin (texi-doc-string "guile" "cos")
1528 @deffn {Scheme Procedure} cos z
1529 Return the cosine of @var{z}.
1533 @c begin (texi-doc-string "guile" "tan")
1534 @deffn {Scheme Procedure} tan z
1535 Return the tangent of @var{z}.
1539 @c begin (texi-doc-string "guile" "asin")
1540 @deffn {Scheme Procedure} asin z
1541 Return the arcsine of @var{z}.
1545 @c begin (texi-doc-string "guile" "acos")
1546 @deffn {Scheme Procedure} acos z
1547 Return the arccosine of @var{z}.
1551 @c begin (texi-doc-string "guile" "atan")
1552 @deffn {Scheme Procedure} atan z
1553 @deffnx {Scheme Procedure} atan y x
1554 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1558 @c begin (texi-doc-string "guile" "exp")
1559 @deffn {Scheme Procedure} exp z
1560 Return e to the power of @var{z}, where e is the base of natural
1561 logarithms (2.71828@dots{}).
1565 @c begin (texi-doc-string "guile" "log")
1566 @deffn {Scheme Procedure} log z
1567 Return the natural logarithm of @var{z}.
1570 @c begin (texi-doc-string "guile" "log10")
1571 @deffn {Scheme Procedure} log10 z
1572 Return the base 10 logarithm of @var{z}.
1575 @c begin (texi-doc-string "guile" "sinh")
1576 @deffn {Scheme Procedure} sinh z
1577 Return the hyperbolic sine of @var{z}.
1580 @c begin (texi-doc-string "guile" "cosh")
1581 @deffn {Scheme Procedure} cosh z
1582 Return the hyperbolic cosine of @var{z}.
1585 @c begin (texi-doc-string "guile" "tanh")
1586 @deffn {Scheme Procedure} tanh z
1587 Return the hyperbolic tangent of @var{z}.
1590 @c begin (texi-doc-string "guile" "asinh")
1591 @deffn {Scheme Procedure} asinh z
1592 Return the hyperbolic arcsine of @var{z}.
1595 @c begin (texi-doc-string "guile" "acosh")
1596 @deffn {Scheme Procedure} acosh z
1597 Return the hyperbolic arccosine of @var{z}.
1600 @c begin (texi-doc-string "guile" "atanh")
1601 @deffn {Scheme Procedure} atanh z
1602 Return the hyperbolic arctangent of @var{z}.
1606 @node Bitwise Operations
1607 @subsubsection Bitwise Operations
1609 For the following bitwise functions, negative numbers are treated as
1610 infinite precision twos-complements. For instance @math{-6} is bits
1611 @math{@dots{}111010}, with infinitely many ones on the left. It can
1612 be seen that adding 6 (binary 110) to such a bit pattern gives all
1615 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1616 @deffnx {C Function} scm_logand (n1, n2)
1617 Return the bitwise @sc{and} of the integer arguments.
1620 (logand) @result{} -1
1621 (logand 7) @result{} 7
1622 (logand #b111 #b011 #b001) @result{} 1
1626 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1627 @deffnx {C Function} scm_logior (n1, n2)
1628 Return the bitwise @sc{or} of the integer arguments.
1631 (logior) @result{} 0
1632 (logior 7) @result{} 7
1633 (logior #b000 #b001 #b011) @result{} 3
1637 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1638 @deffnx {C Function} scm_loxor (n1, n2)
1639 Return the bitwise @sc{xor} of the integer arguments. A bit is
1640 set in the result if it is set in an odd number of arguments.
1643 (logxor) @result{} 0
1644 (logxor 7) @result{} 7
1645 (logxor #b000 #b001 #b011) @result{} 2
1646 (logxor #b000 #b001 #b011 #b011) @result{} 1
1650 @deffn {Scheme Procedure} lognot n
1651 @deffnx {C Function} scm_lognot (n)
1652 Return the integer which is the ones-complement of the integer
1653 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1656 (number->string (lognot #b10000000) 2)
1657 @result{} "-10000001"
1658 (number->string (lognot #b0) 2)
1663 @deffn {Scheme Procedure} logtest j k
1664 @deffnx {C Function} scm_logtest (j, k)
1665 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1666 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1667 calculating the @code{logand}, just testing for non-zero.
1670 (logtest #b0100 #b1011) @result{} #f
1671 (logtest #b0100 #b0111) @result{} #t
1675 @deffn {Scheme Procedure} logbit? index j
1676 @deffnx {C Function} scm_logbit_p (index, j)
1677 Test whether bit number @var{index} in @var{j} is set. @var{index}
1678 starts from 0 for the least significant bit.
1681 (logbit? 0 #b1101) @result{} #t
1682 (logbit? 1 #b1101) @result{} #f
1683 (logbit? 2 #b1101) @result{} #t
1684 (logbit? 3 #b1101) @result{} #t
1685 (logbit? 4 #b1101) @result{} #f
1689 @deffn {Scheme Procedure} ash n count
1690 @deffnx {C Function} scm_ash (n, count)
1691 Return @math{floor(n * 2^count)}.
1692 @var{n} and @var{count} must be exact integers.
1694 With @var{n} viewed as an infinite-precision twos-complement
1695 integer, @code{ash} means a left shift introducing zero bits
1696 when @var{count} is positive, or a right shift dropping bits
1697 when @var{count} is negative. This is an ``arithmetic'' shift.
1700 (number->string (ash #b1 3) 2) @result{} "1000"
1701 (number->string (ash #b1010 -1) 2) @result{} "101"
1703 ;; -23 is bits ...11101001, -6 is bits ...111010
1704 (ash -23 -2) @result{} -6
1708 @deffn {Scheme Procedure} round-ash n count
1709 @deffnx {C Function} scm_round_ash (n, count)
1710 Return @math{round(n * 2^count)}.
1711 @var{n} and @var{count} must be exact integers.
1713 With @var{n} viewed as an infinite-precision twos-complement
1714 integer, @code{round-ash} means a left shift introducing zero
1715 bits when @var{count} is positive, or a right shift rounding
1716 to the nearest integer (with ties going to the nearest even
1717 integer) when @var{count} is negative. This is a rounded
1718 ``arithmetic'' shift.
1721 (number->string (round-ash #b1 3) 2) @result{} \"1000\"
1722 (number->string (round-ash #b1010 -1) 2) @result{} \"101\"
1723 (number->string (round-ash #b1010 -2) 2) @result{} \"10\"
1724 (number->string (round-ash #b1011 -2) 2) @result{} \"11\"
1725 (number->string (round-ash #b1101 -2) 2) @result{} \"11\"
1726 (number->string (round-ash #b1110 -2) 2) @result{} \"100\"
1730 @deffn {Scheme Procedure} logcount n
1731 @deffnx {C Function} scm_logcount (n)
1732 Return the number of bits in integer @var{n}. If @var{n} is
1733 positive, the 1-bits in its binary representation are counted.
1734 If negative, the 0-bits in its two's-complement binary
1735 representation are counted. If zero, 0 is returned.
1738 (logcount #b10101010)
1747 @deffn {Scheme Procedure} integer-length n
1748 @deffnx {C Function} scm_integer_length (n)
1749 Return the number of bits necessary to represent @var{n}.
1751 For positive @var{n} this is how many bits to the most significant one
1752 bit. For negative @var{n} it's how many bits to the most significant
1753 zero bit in twos complement form.
1756 (integer-length #b10101010) @result{} 8
1757 (integer-length #b1111) @result{} 4
1758 (integer-length 0) @result{} 0
1759 (integer-length -1) @result{} 0
1760 (integer-length -256) @result{} 8
1761 (integer-length -257) @result{} 9
1765 @deffn {Scheme Procedure} integer-expt n k
1766 @deffnx {C Function} scm_integer_expt (n, k)
1767 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1768 integer, @var{n} can be any number.
1770 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1771 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1775 (integer-expt 2 5) @result{} 32
1776 (integer-expt -3 3) @result{} -27
1777 (integer-expt 5 -3) @result{} 1/125
1778 (integer-expt 0 0) @result{} 1
1782 @deffn {Scheme Procedure} bit-extract n start end
1783 @deffnx {C Function} scm_bit_extract (n, start, end)
1784 Return the integer composed of the @var{start} (inclusive)
1785 through @var{end} (exclusive) bits of @var{n}. The
1786 @var{start}th bit becomes the 0-th bit in the result.
1789 (number->string (bit-extract #b1101101010 0 4) 2)
1791 (number->string (bit-extract #b1101101010 4 9) 2)
1798 @subsubsection Random Number Generation
1800 Pseudo-random numbers are generated from a random state object, which
1801 can be created with @code{seed->random-state} or
1802 @code{datum->random-state}. An external representation (i.e.@: one
1803 which can written with @code{write} and read with @code{read}) of a
1804 random state object can be obtained via
1805 @code{random-state->datum}. The @var{state} parameter to the
1806 various functions below is optional, it defaults to the state object
1807 in the @code{*random-state*} variable.
1809 @deffn {Scheme Procedure} copy-random-state [state]
1810 @deffnx {C Function} scm_copy_random_state (state)
1811 Return a copy of the random state @var{state}.
1814 @deffn {Scheme Procedure} random n [state]
1815 @deffnx {C Function} scm_random (n, state)
1816 Return a number in [0, @var{n}).
1818 Accepts a positive integer or real n and returns a
1819 number of the same type between zero (inclusive) and
1820 @var{n} (exclusive). The values returned have a uniform
1824 @deffn {Scheme Procedure} random:exp [state]
1825 @deffnx {C Function} scm_random_exp (state)
1826 Return an inexact real in an exponential distribution with mean
1827 1. For an exponential distribution with mean @var{u} use @code{(*
1828 @var{u} (random:exp))}.
1831 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1832 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1833 Fills @var{vect} with inexact real random numbers the sum of whose
1834 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1835 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1836 the coordinates are uniformly distributed over the surface of the unit
1840 @deffn {Scheme Procedure} random:normal [state]
1841 @deffnx {C Function} scm_random_normal (state)
1842 Return an inexact real in a normal distribution. The distribution
1843 used has mean 0 and standard deviation 1. For a normal distribution
1844 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1845 (* @var{d} (random:normal)))}.
1848 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1849 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1850 Fills @var{vect} with inexact real random numbers that are
1851 independent and standard normally distributed
1852 (i.e., with mean 0 and variance 1).
1855 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1856 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1857 Fills @var{vect} with inexact real random numbers the sum of whose
1858 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1859 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1860 the coordinates are uniformly distributed within the unit
1862 @c FIXME: What does this mean, particularly the n-sphere part?
1865 @deffn {Scheme Procedure} random:uniform [state]
1866 @deffnx {C Function} scm_random_uniform (state)
1867 Return a uniformly distributed inexact real random number in
1871 @deffn {Scheme Procedure} seed->random-state seed
1872 @deffnx {C Function} scm_seed_to_random_state (seed)
1873 Return a new random state using @var{seed}.
1876 @deffn {Scheme Procedure} datum->random-state datum
1877 @deffnx {C Function} scm_datum_to_random_state (datum)
1878 Return a new random state from @var{datum}, which should have been
1879 obtained by @code{random-state->datum}.
1882 @deffn {Scheme Procedure} random-state->datum state
1883 @deffnx {C Function} scm_random_state_to_datum (state)
1884 Return a datum representation of @var{state} that may be written out and
1885 read back with the Scheme reader.
1888 @deffn {Scheme Procedure} random-state-from-platform
1889 @deffnx {C Function} scm_random_state_from_platform ()
1890 Construct a new random state seeded from a platform-specific source of
1891 entropy, appropriate for use in non-security-critical applications.
1892 Currently @file{/dev/urandom} is tried first, or else the seed is based
1893 on the time, date, process ID, an address from a freshly allocated heap
1894 cell, an address from the local stack frame, and a high-resolution timer
1898 @defvar *random-state*
1899 The global random state used by the above functions when the
1900 @var{state} parameter is not given.
1903 Note that the initial value of @code{*random-state*} is the same every
1904 time Guile starts up. Therefore, if you don't pass a @var{state}
1905 parameter to the above procedures, and you don't set
1906 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1907 @code{your-seed} is something that @emph{isn't} the same every time,
1908 you'll get the same sequence of ``random'' numbers on every run.
1910 For example, unless the relevant source code has changed, @code{(map
1911 random (cdr (iota 30)))}, if the first use of random numbers since
1912 Guile started up, will always give:
1915 (map random (cdr (iota 19)))
1917 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1920 To seed the random state in a sensible way for non-security-critical
1921 applications, do this during initialization of your program:
1924 (set! *random-state* (random-state-from-platform))
1929 @subsection Characters
1932 In Scheme, there is a data type to describe a single character.
1934 Defining what exactly a character @emph{is} can be more complicated
1935 than it seems. Guile follows the advice of R6RS and uses The Unicode
1936 Standard to help define what a character is. So, for Guile, a
1937 character is anything in the Unicode Character Database.
1940 @cindex Unicode code point
1942 The Unicode Character Database is basically a table of characters
1943 indexed using integers called 'code points'. Valid code points are in
1944 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1945 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1947 @cindex designated code point
1948 @cindex code point, designated
1950 Any code point that has been assigned to a character or that has
1951 otherwise been given a meaning by Unicode is called a 'designated code
1952 point'. Most of the designated code points, about 200,000 of them,
1953 indicate characters, accents or other combining marks that modify
1954 other characters, symbols, whitespace, and control characters. Some
1955 are not characters but indicators that suggest how to format or
1956 display neighboring characters.
1958 @cindex reserved code point
1959 @cindex code point, reserved
1961 If a code point is not a designated code point -- if it has not been
1962 assigned to a character by The Unicode Standard -- it is a 'reserved
1963 code point', meaning that they are reserved for future use. Most of
1964 the code points, about 800,000, are 'reserved code points'.
1966 By convention, a Unicode code point is written as
1967 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1968 this convenient notation is not valid code. Guile does not interpret
1969 ``U+XXXX'' as a character.
1971 In Scheme, a character literal is written as @code{#\@var{name}} where
1972 @var{name} is the name of the character that you want. Printable
1973 characters have their usual single character name; for example,
1974 @code{#\a} is a lower case @code{a}.
1976 Some of the code points are 'combining characters' that are not meant
1977 to be printed by themselves but are instead meant to modify the
1978 appearance of the previous character. For combining characters, an
1979 alternate form of the character literal is @code{#\} followed by
1980 U+25CC (a small, dotted circle), followed by the combining character.
1981 This allows the combining character to be drawn on the circle, not on
1982 the backslash of @code{#\}.
1984 Many of the non-printing characters, such as whitespace characters and
1985 control characters, also have names.
1987 The most commonly used non-printing characters have long character
1988 names, described in the table below.
1990 @multitable {@code{#\backspace}} {Preferred}
1991 @item Character Name @tab Codepoint
1992 @item @code{#\nul} @tab U+0000
1993 @item @code{#\alarm} @tab u+0007
1994 @item @code{#\backspace} @tab U+0008
1995 @item @code{#\tab} @tab U+0009
1996 @item @code{#\linefeed} @tab U+000A
1997 @item @code{#\newline} @tab U+000A
1998 @item @code{#\vtab} @tab U+000B
1999 @item @code{#\page} @tab U+000C
2000 @item @code{#\return} @tab U+000D
2001 @item @code{#\esc} @tab U+001B
2002 @item @code{#\space} @tab U+0020
2003 @item @code{#\delete} @tab U+007F
2006 There are also short names for all of the ``C0 control characters''
2007 (those with code points below 32). The following table lists the short
2008 name for each character.
2010 @multitable @columnfractions .25 .25 .25 .25
2011 @item 0 = @code{#\nul}
2012 @tab 1 = @code{#\soh}
2013 @tab 2 = @code{#\stx}
2014 @tab 3 = @code{#\etx}
2015 @item 4 = @code{#\eot}
2016 @tab 5 = @code{#\enq}
2017 @tab 6 = @code{#\ack}
2018 @tab 7 = @code{#\bel}
2019 @item 8 = @code{#\bs}
2020 @tab 9 = @code{#\ht}
2021 @tab 10 = @code{#\lf}
2022 @tab 11 = @code{#\vt}
2023 @item 12 = @code{#\ff}
2024 @tab 13 = @code{#\cr}
2025 @tab 14 = @code{#\so}
2026 @tab 15 = @code{#\si}
2027 @item 16 = @code{#\dle}
2028 @tab 17 = @code{#\dc1}
2029 @tab 18 = @code{#\dc2}
2030 @tab 19 = @code{#\dc3}
2031 @item 20 = @code{#\dc4}
2032 @tab 21 = @code{#\nak}
2033 @tab 22 = @code{#\syn}
2034 @tab 23 = @code{#\etb}
2035 @item 24 = @code{#\can}
2036 @tab 25 = @code{#\em}
2037 @tab 26 = @code{#\sub}
2038 @tab 27 = @code{#\esc}
2039 @item 28 = @code{#\fs}
2040 @tab 29 = @code{#\gs}
2041 @tab 30 = @code{#\rs}
2042 @tab 31 = @code{#\us}
2043 @item 32 = @code{#\sp}
2046 The short name for the ``delete'' character (code point U+007F) is
2049 There are also a few alternative names left over for compatibility with
2050 previous versions of Guile.
2052 @multitable {@code{#\backspace}} {Preferred}
2053 @item Alternate @tab Standard
2054 @item @code{#\nl} @tab @code{#\newline}
2055 @item @code{#\np} @tab @code{#\page}
2056 @item @code{#\null} @tab @code{#\nul}
2059 Characters may also be written using their code point values. They can
2060 be written with as an octal number, such as @code{#\10} for
2061 @code{#\bs} or @code{#\177} for @code{#\del}.
2063 If one prefers hex to octal, there is an additional syntax for character
2064 escapes: @code{#\xHHHH} -- the letter 'x' followed by a hexadecimal
2065 number of one to eight digits.
2068 @deffn {Scheme Procedure} char? x
2069 @deffnx {C Function} scm_char_p (x)
2070 Return @code{#t} if @var{x} is a character, else @code{#f}.
2073 Fundamentally, the character comparison operations below are
2074 numeric comparisons of the character's code points.
2077 @deffn {Scheme Procedure} char=? x y
2078 Return @code{#t} if code point of @var{x} is equal to the code point
2079 of @var{y}, else @code{#f}.
2083 @deffn {Scheme Procedure} char<? x y
2084 Return @code{#t} if the code point of @var{x} is less than the code
2085 point of @var{y}, else @code{#f}.
2089 @deffn {Scheme Procedure} char<=? x y
2090 Return @code{#t} if the code point of @var{x} is less than or equal
2091 to the code point of @var{y}, else @code{#f}.
2095 @deffn {Scheme Procedure} char>? x y
2096 Return @code{#t} if the code point of @var{x} is greater than the
2097 code point of @var{y}, else @code{#f}.
2101 @deffn {Scheme Procedure} char>=? x y
2102 Return @code{#t} if the code point of @var{x} is greater than or
2103 equal to the code point of @var{y}, else @code{#f}.
2106 @cindex case folding
2108 Case-insensitive character comparisons use @emph{Unicode case
2109 folding}. In case folding comparisons, if a character is lowercase
2110 and has an uppercase form that can be expressed as a single character,
2111 it is converted to uppercase before comparison. All other characters
2112 undergo no conversion before the comparison occurs. This includes the
2113 German sharp S (Eszett) which is not uppercased before conversion
2114 because its uppercase form has two characters. Unicode case folding
2115 is language independent: it uses rules that are generally true, but,
2116 it cannot cover all cases for all languages.
2119 @deffn {Scheme Procedure} char-ci=? x y
2120 Return @code{#t} if the case-folded code point of @var{x} is the same
2121 as the case-folded code point of @var{y}, else @code{#f}.
2125 @deffn {Scheme Procedure} char-ci<? x y
2126 Return @code{#t} if the case-folded code point of @var{x} is less
2127 than the case-folded code point of @var{y}, else @code{#f}.
2131 @deffn {Scheme Procedure} char-ci<=? x y
2132 Return @code{#t} if the case-folded code point of @var{x} is less
2133 than or equal to the case-folded code point of @var{y}, else
2138 @deffn {Scheme Procedure} char-ci>? x y
2139 Return @code{#t} if the case-folded code point of @var{x} is greater
2140 than the case-folded code point of @var{y}, else @code{#f}.
2144 @deffn {Scheme Procedure} char-ci>=? x y
2145 Return @code{#t} if the case-folded code point of @var{x} is greater
2146 than or equal to the case-folded code point of @var{y}, else
2150 @rnindex char-alphabetic?
2151 @deffn {Scheme Procedure} char-alphabetic? chr
2152 @deffnx {C Function} scm_char_alphabetic_p (chr)
2153 Return @code{#t} if @var{chr} is alphabetic, else @code{#f}.
2156 @rnindex char-numeric?
2157 @deffn {Scheme Procedure} char-numeric? chr
2158 @deffnx {C Function} scm_char_numeric_p (chr)
2159 Return @code{#t} if @var{chr} is numeric, else @code{#f}.
2162 @rnindex char-whitespace?
2163 @deffn {Scheme Procedure} char-whitespace? chr
2164 @deffnx {C Function} scm_char_whitespace_p (chr)
2165 Return @code{#t} if @var{chr} is whitespace, else @code{#f}.
2168 @rnindex char-upper-case?
2169 @deffn {Scheme Procedure} char-upper-case? chr
2170 @deffnx {C Function} scm_char_upper_case_p (chr)
2171 Return @code{#t} if @var{chr} is uppercase, else @code{#f}.
2174 @rnindex char-lower-case?
2175 @deffn {Scheme Procedure} char-lower-case? chr
2176 @deffnx {C Function} scm_char_lower_case_p (chr)
2177 Return @code{#t} if @var{chr} is lowercase, else @code{#f}.
2180 @deffn {Scheme Procedure} char-is-both? chr
2181 @deffnx {C Function} scm_char_is_both_p (chr)
2182 Return @code{#t} if @var{chr} is either uppercase or lowercase, else
2186 @deffn {Scheme Procedure} char-general-category chr
2187 @deffnx {C Function} scm_char_general_category (chr)
2188 Return a symbol giving the two-letter name of the Unicode general
2189 category assigned to @var{chr} or @code{#f} if no named category is
2190 assigned. The following table provides a list of category names along
2191 with their meanings.
2193 @multitable @columnfractions .1 .4 .1 .4
2195 @tab Uppercase letter
2197 @tab Final quote punctuation
2199 @tab Lowercase letter
2201 @tab Other punctuation
2203 @tab Titlecase letter
2207 @tab Modifier letter
2209 @tab Currency symbol
2213 @tab Modifier symbol
2215 @tab Non-spacing mark
2219 @tab Combining spacing mark
2221 @tab Space separator
2227 @tab Decimal digit number
2229 @tab Paragraph separator
2239 @tab Connector punctuation
2243 @tab Dash punctuation
2247 @tab Open punctuation
2251 @tab Close punctuation
2255 @tab Initial quote punctuation
2261 @rnindex char->integer
2262 @deffn {Scheme Procedure} char->integer chr
2263 @deffnx {C Function} scm_char_to_integer (chr)
2264 Return the code point of @var{chr}.
2267 @rnindex integer->char
2268 @deffn {Scheme Procedure} integer->char n
2269 @deffnx {C Function} scm_integer_to_char (n)
2270 Return the character that has code point @var{n}. The integer @var{n}
2271 must be a valid code point. Valid code points are in the ranges 0 to
2272 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
2275 @rnindex char-upcase
2276 @deffn {Scheme Procedure} char-upcase chr
2277 @deffnx {C Function} scm_char_upcase (chr)
2278 Return the uppercase character version of @var{chr}.
2281 @rnindex char-downcase
2282 @deffn {Scheme Procedure} char-downcase chr
2283 @deffnx {C Function} scm_char_downcase (chr)
2284 Return the lowercase character version of @var{chr}.
2287 @rnindex char-titlecase
2288 @deffn {Scheme Procedure} char-titlecase chr
2289 @deffnx {C Function} scm_char_titlecase (chr)
2290 Return the titlecase character version of @var{chr} if one exists;
2291 otherwise return the uppercase version.
2293 For most characters these will be the same, but the Unicode Standard
2294 includes certain digraph compatibility characters, such as @code{U+01F3}
2295 ``dz'', for which the uppercase and titlecase characters are different
2296 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
2301 @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c})
2302 @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c})
2303 @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c})
2305 These C functions take an integer representation of a Unicode
2306 codepoint and return the codepoint corresponding to its uppercase,
2307 lowercase, and titlecase forms respectively. The type
2308 @code{scm_t_wchar} is a signed, 32-bit integer.
2311 @node Character Sets
2312 @subsection Character Sets
2314 The features described in this section correspond directly to SRFI-14.
2316 The data type @dfn{charset} implements sets of characters
2317 (@pxref{Characters}). Because the internal representation of
2318 character sets is not visible to the user, a lot of procedures for
2319 handling them are provided.
2321 Character sets can be created, extended, tested for the membership of a
2322 characters and be compared to other character sets.
2325 * Character Set Predicates/Comparison::
2326 * Iterating Over Character Sets:: Enumerate charset elements.
2327 * Creating Character Sets:: Making new charsets.
2328 * Querying Character Sets:: Test charsets for membership etc.
2329 * Character-Set Algebra:: Calculating new charsets.
2330 * Standard Character Sets:: Variables containing predefined charsets.
2333 @node Character Set Predicates/Comparison
2334 @subsubsection Character Set Predicates/Comparison
2336 Use these procedures for testing whether an object is a character set,
2337 or whether several character sets are equal or subsets of each other.
2338 @code{char-set-hash} can be used for calculating a hash value, maybe for
2339 usage in fast lookup procedures.
2341 @deffn {Scheme Procedure} char-set? obj
2342 @deffnx {C Function} scm_char_set_p (obj)
2343 Return @code{#t} if @var{obj} is a character set, @code{#f}
2347 @deffn {Scheme Procedure} char-set= char_set @dots{}
2348 @deffnx {C Function} scm_char_set_eq (char_sets)
2349 Return @code{#t} if all given character sets are equal.
2352 @deffn {Scheme Procedure} char-set<= char_set @dots{}
2353 @deffnx {C Function} scm_char_set_leq (char_sets)
2354 Return @code{#t} if every character set @var{char_set}i is a subset
2355 of character set @var{char_set}i+1.
2358 @deffn {Scheme Procedure} char-set-hash cs [bound]
2359 @deffnx {C Function} scm_char_set_hash (cs, bound)
2360 Compute a hash value for the character set @var{cs}. If
2361 @var{bound} is given and non-zero, it restricts the
2362 returned value to the range 0 @dots{} @var{bound} - 1.
2365 @c ===================================================================
2367 @node Iterating Over Character Sets
2368 @subsubsection Iterating Over Character Sets
2370 Character set cursors are a means for iterating over the members of a
2371 character sets. After creating a character set cursor with
2372 @code{char-set-cursor}, a cursor can be dereferenced with
2373 @code{char-set-ref}, advanced to the next member with
2374 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2375 element of the set can be checked with @code{end-of-char-set?}.
2377 Additionally, mapping and (un-)folding procedures for character sets are
2380 @deffn {Scheme Procedure} char-set-cursor cs
2381 @deffnx {C Function} scm_char_set_cursor (cs)
2382 Return a cursor into the character set @var{cs}.
2385 @deffn {Scheme Procedure} char-set-ref cs cursor
2386 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2387 Return the character at the current cursor position
2388 @var{cursor} in the character set @var{cs}. It is an error to
2389 pass a cursor for which @code{end-of-char-set?} returns true.
2392 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2393 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2394 Advance the character set cursor @var{cursor} to the next
2395 character in the character set @var{cs}. It is an error if the
2396 cursor given satisfies @code{end-of-char-set?}.
2399 @deffn {Scheme Procedure} end-of-char-set? cursor
2400 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2401 Return @code{#t} if @var{cursor} has reached the end of a
2402 character set, @code{#f} otherwise.
2405 @deffn {Scheme Procedure} char-set-fold kons knil cs
2406 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2407 Fold the procedure @var{kons} over the character set @var{cs},
2408 initializing it with @var{knil}.
2411 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2412 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2413 This is a fundamental constructor for character sets.
2415 @item @var{g} is used to generate a series of ``seed'' values
2416 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2417 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2418 @item @var{p} tells us when to stop -- when it returns true
2419 when applied to one of the seed values.
2420 @item @var{f} maps each seed value to a character. These
2421 characters are added to the base character set @var{base_cs} to
2422 form the result; @var{base_cs} defaults to the empty set.
2426 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2427 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2428 This is a fundamental constructor for character sets.
2430 @item @var{g} is used to generate a series of ``seed'' values
2431 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2432 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2433 @item @var{p} tells us when to stop -- when it returns true
2434 when applied to one of the seed values.
2435 @item @var{f} maps each seed value to a character. These
2436 characters are added to the base character set @var{base_cs} to
2437 form the result; @var{base_cs} defaults to the empty set.
2441 @deffn {Scheme Procedure} char-set-for-each proc cs
2442 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2443 Apply @var{proc} to every character in the character set
2444 @var{cs}. The return value is not specified.
2447 @deffn {Scheme Procedure} char-set-map proc cs
2448 @deffnx {C Function} scm_char_set_map (proc, cs)
2449 Map the procedure @var{proc} over every character in @var{cs}.
2450 @var{proc} must be a character -> character procedure.
2453 @c ===================================================================
2455 @node Creating Character Sets
2456 @subsubsection Creating Character Sets
2458 New character sets are produced with these procedures.
2460 @deffn {Scheme Procedure} char-set-copy cs
2461 @deffnx {C Function} scm_char_set_copy (cs)
2462 Return a newly allocated character set containing all
2463 characters in @var{cs}.
2466 @deffn {Scheme Procedure} char-set chr @dots{}
2467 @deffnx {C Function} scm_char_set (chrs)
2468 Return a character set containing all given characters.
2471 @deffn {Scheme Procedure} list->char-set list [base_cs]
2472 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2473 Convert the character list @var{list} to a character set. If
2474 the character set @var{base_cs} is given, the character in this
2475 set are also included in the result.
2478 @deffn {Scheme Procedure} list->char-set! list base_cs
2479 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2480 Convert the character list @var{list} to a character set. The
2481 characters are added to @var{base_cs} and @var{base_cs} is
2485 @deffn {Scheme Procedure} string->char-set str [base_cs]
2486 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2487 Convert the string @var{str} to a character set. If the
2488 character set @var{base_cs} is given, the characters in this
2489 set are also included in the result.
2492 @deffn {Scheme Procedure} string->char-set! str base_cs
2493 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2494 Convert the string @var{str} to a character set. The
2495 characters from the string are added to @var{base_cs}, and
2496 @var{base_cs} is returned.
2499 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2500 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2501 Return a character set containing every character from @var{cs}
2502 so that it satisfies @var{pred}. If provided, the characters
2503 from @var{base_cs} are added to the result.
2506 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2507 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2508 Return a character set containing every character from @var{cs}
2509 so that it satisfies @var{pred}. The characters are added to
2510 @var{base_cs} and @var{base_cs} is returned.
2513 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2514 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2515 Return a character set containing all characters whose
2516 character codes lie in the half-open range
2517 [@var{lower},@var{upper}).
2519 If @var{error} is a true value, an error is signalled if the
2520 specified range contains characters which are not contained in
2521 the implemented character range. If @var{error} is @code{#f},
2522 these characters are silently left out of the resulting
2525 The characters in @var{base_cs} are added to the result, if
2529 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2530 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2531 Return a character set containing all characters whose
2532 character codes lie in the half-open range
2533 [@var{lower},@var{upper}).
2535 If @var{error} is a true value, an error is signalled if the
2536 specified range contains characters which are not contained in
2537 the implemented character range. If @var{error} is @code{#f},
2538 these characters are silently left out of the resulting
2541 The characters are added to @var{base_cs} and @var{base_cs} is
2545 @deffn {Scheme Procedure} ->char-set x
2546 @deffnx {C Function} scm_to_char_set (x)
2547 Coerces x into a char-set. @var{x} may be a string, character or
2548 char-set. A string is converted to the set of its constituent
2549 characters; a character is converted to a singleton set; a char-set is
2553 @c ===================================================================
2555 @node Querying Character Sets
2556 @subsubsection Querying Character Sets
2558 Access the elements and other information of a character set with these
2561 @deffn {Scheme Procedure} %char-set-dump cs
2562 Returns an association list containing debugging information
2563 for @var{cs}. The association list has the following entries.
2568 The number of groups of contiguous code points the char-set
2571 A list of lists where each sublist is a range of code points
2572 and their associated characters
2574 The return value of this function cannot be relied upon to be
2575 consistent between versions of Guile and should not be used in code.
2578 @deffn {Scheme Procedure} char-set-size cs
2579 @deffnx {C Function} scm_char_set_size (cs)
2580 Return the number of elements in character set @var{cs}.
2583 @deffn {Scheme Procedure} char-set-count pred cs
2584 @deffnx {C Function} scm_char_set_count (pred, cs)
2585 Return the number of the elements int the character set
2586 @var{cs} which satisfy the predicate @var{pred}.
2589 @deffn {Scheme Procedure} char-set->list cs
2590 @deffnx {C Function} scm_char_set_to_list (cs)
2591 Return a list containing the elements of the character set
2595 @deffn {Scheme Procedure} char-set->string cs
2596 @deffnx {C Function} scm_char_set_to_string (cs)
2597 Return a string containing the elements of the character set
2598 @var{cs}. The order in which the characters are placed in the
2599 string is not defined.
2602 @deffn {Scheme Procedure} char-set-contains? cs ch
2603 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2604 Return @code{#t} if the character @var{ch} is contained in the
2605 character set @var{cs}, or @code{#f} otherwise.
2608 @deffn {Scheme Procedure} char-set-every pred cs
2609 @deffnx {C Function} scm_char_set_every (pred, cs)
2610 Return a true value if every character in the character set
2611 @var{cs} satisfies the predicate @var{pred}.
2614 @deffn {Scheme Procedure} char-set-any pred cs
2615 @deffnx {C Function} scm_char_set_any (pred, cs)
2616 Return a true value if any character in the character set
2617 @var{cs} satisfies the predicate @var{pred}.
2620 @c ===================================================================
2622 @node Character-Set Algebra
2623 @subsubsection Character-Set Algebra
2625 Character sets can be manipulated with the common set algebra operation,
2626 such as union, complement, intersection etc. All of these procedures
2627 provide side-effecting variants, which modify their character set
2630 @deffn {Scheme Procedure} char-set-adjoin cs chr @dots{}
2631 @deffnx {C Function} scm_char_set_adjoin (cs, chrs)
2632 Add all character arguments to the first argument, which must
2636 @deffn {Scheme Procedure} char-set-delete cs chr @dots{}
2637 @deffnx {C Function} scm_char_set_delete (cs, chrs)
2638 Delete all character arguments from the first argument, which
2639 must be a character set.
2642 @deffn {Scheme Procedure} char-set-adjoin! cs chr @dots{}
2643 @deffnx {C Function} scm_char_set_adjoin_x (cs, chrs)
2644 Add all character arguments to the first argument, which must
2648 @deffn {Scheme Procedure} char-set-delete! cs chr @dots{}
2649 @deffnx {C Function} scm_char_set_delete_x (cs, chrs)
2650 Delete all character arguments from the first argument, which
2651 must be a character set.
2654 @deffn {Scheme Procedure} char-set-complement cs
2655 @deffnx {C Function} scm_char_set_complement (cs)
2656 Return the complement of the character set @var{cs}.
2659 Note that the complement of a character set is likely to contain many
2660 reserved code points (code points that are not associated with
2661 characters). It may be helpful to modify the output of
2662 @code{char-set-complement} by computing its intersection with the set
2663 of designated code points, @code{char-set:designated}.
2665 @deffn {Scheme Procedure} char-set-union cs @dots{}
2666 @deffnx {C Function} scm_char_set_union (char_sets)
2667 Return the union of all argument character sets.
2670 @deffn {Scheme Procedure} char-set-intersection cs @dots{}
2671 @deffnx {C Function} scm_char_set_intersection (char_sets)
2672 Return the intersection of all argument character sets.
2675 @deffn {Scheme Procedure} char-set-difference cs1 cs @dots{}
2676 @deffnx {C Function} scm_char_set_difference (cs1, char_sets)
2677 Return the difference of all argument character sets.
2680 @deffn {Scheme Procedure} char-set-xor cs @dots{}
2681 @deffnx {C Function} scm_char_set_xor (char_sets)
2682 Return the exclusive-or of all argument character sets.
2685 @deffn {Scheme Procedure} char-set-diff+intersection cs1 cs @dots{}
2686 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, char_sets)
2687 Return the difference and the intersection of all argument
2691 @deffn {Scheme Procedure} char-set-complement! cs
2692 @deffnx {C Function} scm_char_set_complement_x (cs)
2693 Return the complement of the character set @var{cs}.
2696 @deffn {Scheme Procedure} char-set-union! cs1 cs @dots{}
2697 @deffnx {C Function} scm_char_set_union_x (cs1, char_sets)
2698 Return the union of all argument character sets.
2701 @deffn {Scheme Procedure} char-set-intersection! cs1 cs @dots{}
2702 @deffnx {C Function} scm_char_set_intersection_x (cs1, char_sets)
2703 Return the intersection of all argument character sets.
2706 @deffn {Scheme Procedure} char-set-difference! cs1 cs @dots{}
2707 @deffnx {C Function} scm_char_set_difference_x (cs1, char_sets)
2708 Return the difference of all argument character sets.
2711 @deffn {Scheme Procedure} char-set-xor! cs1 cs @dots{}
2712 @deffnx {C Function} scm_char_set_xor_x (cs1, char_sets)
2713 Return the exclusive-or of all argument character sets.
2716 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 cs @dots{}
2717 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, char_sets)
2718 Return the difference and the intersection of all argument
2722 @c ===================================================================
2724 @node Standard Character Sets
2725 @subsubsection Standard Character Sets
2727 In order to make the use of the character set data type and procedures
2728 useful, several predefined character set variables exist.
2734 These character sets are locale independent and are not recomputed
2735 upon a @code{setlocale} call. They contain characters from the whole
2736 range of Unicode code points. For instance, @code{char-set:letter}
2737 contains about 100,000 characters.
2739 @defvr {Scheme Variable} char-set:lower-case
2740 @defvrx {C Variable} scm_char_set_lower_case
2741 All lower-case characters.
2744 @defvr {Scheme Variable} char-set:upper-case
2745 @defvrx {C Variable} scm_char_set_upper_case
2746 All upper-case characters.
2749 @defvr {Scheme Variable} char-set:title-case
2750 @defvrx {C Variable} scm_char_set_title_case
2751 All single characters that function as if they were an upper-case
2752 letter followed by a lower-case letter.
2755 @defvr {Scheme Variable} char-set:letter
2756 @defvrx {C Variable} scm_char_set_letter
2757 All letters. This includes @code{char-set:lower-case},
2758 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2759 letters that have no case at all. For example, Chinese and Japanese
2760 characters typically have no concept of case.
2763 @defvr {Scheme Variable} char-set:digit
2764 @defvrx {C Variable} scm_char_set_digit
2768 @defvr {Scheme Variable} char-set:letter+digit
2769 @defvrx {C Variable} scm_char_set_letter_and_digit
2770 The union of @code{char-set:letter} and @code{char-set:digit}.
2773 @defvr {Scheme Variable} char-set:graphic
2774 @defvrx {C Variable} scm_char_set_graphic
2775 All characters which would put ink on the paper.
2778 @defvr {Scheme Variable} char-set:printing
2779 @defvrx {C Variable} scm_char_set_printing
2780 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2783 @defvr {Scheme Variable} char-set:whitespace
2784 @defvrx {C Variable} scm_char_set_whitespace
2785 All whitespace characters.
2788 @defvr {Scheme Variable} char-set:blank
2789 @defvrx {C Variable} scm_char_set_blank
2790 All horizontal whitespace characters, which notably includes
2791 @code{#\space} and @code{#\tab}.
2794 @defvr {Scheme Variable} char-set:iso-control
2795 @defvrx {C Variable} scm_char_set_iso_control
2796 The ISO control characters are the C0 control characters (U+0000 to
2797 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2801 @defvr {Scheme Variable} char-set:punctuation
2802 @defvrx {C Variable} scm_char_set_punctuation
2803 All punctuation characters, such as the characters
2804 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2807 @defvr {Scheme Variable} char-set:symbol
2808 @defvrx {C Variable} scm_char_set_symbol
2809 All symbol characters, such as the characters @code{$+<=>^`|~}.
2812 @defvr {Scheme Variable} char-set:hex-digit
2813 @defvrx {C Variable} scm_char_set_hex_digit
2814 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2817 @defvr {Scheme Variable} char-set:ascii
2818 @defvrx {C Variable} scm_char_set_ascii
2819 All ASCII characters.
2822 @defvr {Scheme Variable} char-set:empty
2823 @defvrx {C Variable} scm_char_set_empty
2824 The empty character set.
2827 @defvr {Scheme Variable} char-set:designated
2828 @defvrx {C Variable} scm_char_set_designated
2829 This character set contains all designated code points. This includes
2830 all the code points to which Unicode has assigned a character or other
2834 @defvr {Scheme Variable} char-set:full
2835 @defvrx {C Variable} scm_char_set_full
2836 This character set contains all possible code points. This includes
2837 both designated and reserved code points.
2844 Strings are fixed-length sequences of characters. They can be created
2845 by calling constructor procedures, but they can also literally get
2846 entered at the @acronym{REPL} or in Scheme source files.
2848 @c Guile provides a rich set of string processing procedures, because text
2849 @c handling is very important when Guile is used as a scripting language.
2851 Strings always carry the information about how many characters they are
2852 composed of with them, so there is no special end-of-string character,
2853 like in C. That means that Scheme strings can contain any character,
2854 even the @samp{#\nul} character @samp{\0}.
2856 To use strings efficiently, you need to know a bit about how Guile
2857 implements them. In Guile, a string consists of two parts, a head and
2858 the actual memory where the characters are stored. When a string (or
2859 a substring of it) is copied, only a new head gets created, the memory
2860 is usually not copied. The two heads start out pointing to the same
2863 When one of these two strings is modified, as with @code{string-set!},
2864 their common memory does get copied so that each string has its own
2865 memory and modifying one does not accidentally modify the other as well.
2866 Thus, Guile's strings are `copy on write'; the actual copying of their
2867 memory is delayed until one string is written to.
2869 This implementation makes functions like @code{substring} very
2870 efficient in the common case that no modifications are done to the
2873 If you do know that your strings are getting modified right away, you
2874 can use @code{substring/copy} instead of @code{substring}. This
2875 function performs the copy immediately at the time of creation. This
2876 is more efficient, especially in a multi-threaded program. Also,
2877 @code{substring/copy} can avoid the problem that a short substring
2878 holds on to the memory of a very large original string that could
2879 otherwise be recycled.
2881 If you want to avoid the copy altogether, so that modifications of one
2882 string show up in the other, you can use @code{substring/shared}. The
2883 strings created by this procedure are called @dfn{mutation sharing
2884 substrings} since the substring and the original string share
2885 modifications to each other.
2887 If you want to prevent modifications, use @code{substring/read-only}.
2889 Guile provides all procedures of SRFI-13 and a few more.
2892 * String Syntax:: Read syntax for strings.
2893 * String Predicates:: Testing strings for certain properties.
2894 * String Constructors:: Creating new string objects.
2895 * List/String Conversion:: Converting from/to lists of characters.
2896 * String Selection:: Select portions from strings.
2897 * String Modification:: Modify parts or whole strings.
2898 * String Comparison:: Lexicographic ordering predicates.
2899 * String Searching:: Searching in strings.
2900 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2901 * Reversing and Appending Strings:: Appending strings to form a new string.
2902 * Mapping Folding and Unfolding:: Iterating over strings.
2903 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2904 * Representing Strings as Bytes:: Encoding and decoding strings.
2905 * Conversion to/from C::
2906 * String Internals:: The storage strategy for strings.
2910 @subsubsection String Read Syntax
2912 @c In the following @code is used to get a good font in TeX etc, but
2913 @c is omitted for Info format, so as not to risk any confusion over
2914 @c whether surrounding ` ' quotes are part of the escape or are
2915 @c special in a string (they're not).
2917 The read syntax for strings is an arbitrarily long sequence of
2918 characters enclosed in double quotes (@nicode{"}).
2920 Backslash is an escape character and can be used to insert the following
2921 special characters. @nicode{\"} and @nicode{\\} are R5RS standard, the
2922 next seven are R6RS standard --- notice they follow C syntax --- and the
2923 remaining four are Guile extensions.
2927 Backslash character.
2930 Double quote character (an unescaped @nicode{"} is otherwise the end
2934 Bell character (ASCII 7).
2937 Formfeed character (ASCII 12).
2940 Newline character (ASCII 10).
2943 Carriage return character (ASCII 13).
2946 Tab character (ASCII 9).
2949 Vertical tab character (ASCII 11).
2952 Backspace character (ASCII 8).
2955 NUL character (ASCII 0).
2957 @item @nicode{\} followed by newline (ASCII 10)
2958 Nothing. This way if @nicode{\} is the last character in a line, the
2959 string will continue with the first character from the next line,
2960 without a line break.
2962 If the @code{hungry-eol-escapes} reader option is enabled, which is not
2963 the case by default, leading whitespace on the next line is discarded.
2969 (read-enable 'hungry-eol-escapes)
2975 Character code given by two hexadecimal digits. For example
2976 @nicode{\x7f} for an ASCII DEL (127).
2978 @item @nicode{\uHHHH}
2979 Character code given by four hexadecimal digits. For example
2980 @nicode{\u0100} for a capital A with macron (U+0100).
2982 @item @nicode{\UHHHHHH}
2983 Character code given by six hexadecimal digits. For example
2988 The following are examples of string literals:
2997 The three escape sequences @code{\xHH}, @code{\uHHHH} and @code{\UHHHHHH} were
2998 chosen to not break compatibility with code written for previous versions of
2999 Guile. The R6RS specification suggests a different, incompatible syntax for hex
3000 escapes: @code{\xHHHH;} -- a character code followed by one to eight hexadecimal
3001 digits terminated with a semicolon. If this escape format is desired instead,
3002 it can be enabled with the reader option @code{r6rs-hex-escapes}.
3005 (read-enable 'r6rs-hex-escapes)
3008 For more on reader options, @xref{Scheme Read}.
3010 @node String Predicates
3011 @subsubsection String Predicates
3013 The following procedures can be used to check whether a given string
3014 fulfills some specified property.
3017 @deffn {Scheme Procedure} string? obj
3018 @deffnx {C Function} scm_string_p (obj)
3019 Return @code{#t} if @var{obj} is a string, else @code{#f}.
3022 @deftypefn {C Function} int scm_is_string (SCM obj)
3023 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
3026 @deffn {Scheme Procedure} string-null? str
3027 @deffnx {C Function} scm_string_null_p (str)
3028 Return @code{#t} if @var{str}'s length is zero, and
3029 @code{#f} otherwise.
3031 (string-null? "") @result{} #t
3033 (string-null? y) @result{} #f
3037 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
3038 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
3039 Check if @var{char_pred} is true for any character in string @var{s}.
3041 @var{char_pred} can be a character to check for any equal to that, or
3042 a character set (@pxref{Character Sets}) to check for any in that set,
3043 or a predicate procedure to call.
3045 For a procedure, calls @code{(@var{char_pred} c)} are made
3046 successively on the characters from @var{start} to @var{end}. If
3047 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
3048 stops and that return value is the return from @code{string-any}. The
3049 call on the last character (ie.@: at @math{@var{end}-1}), if that
3050 point is reached, is a tail call.
3052 If there are no characters in @var{s} (ie.@: @var{start} equals
3053 @var{end}) then the return is @code{#f}.
3056 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
3057 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
3058 Check if @var{char_pred} is true for every character in string
3061 @var{char_pred} can be a character to check for every character equal
3062 to that, or a character set (@pxref{Character Sets}) to check for
3063 every character being in that set, or a predicate procedure to call.
3065 For a procedure, calls @code{(@var{char_pred} c)} are made
3066 successively on the characters from @var{start} to @var{end}. If
3067 @var{char_pred} returns @code{#f}, @code{string-every} stops and
3068 returns @code{#f}. The call on the last character (ie.@: at
3069 @math{@var{end}-1}), if that point is reached, is a tail call and the
3070 return from that call is the return from @code{string-every}.
3072 If there are no characters in @var{s} (ie.@: @var{start} equals
3073 @var{end}) then the return is @code{#t}.
3076 @node String Constructors
3077 @subsubsection String Constructors
3079 The string constructor procedures create new string objects, possibly
3080 initializing them with some specified character data. See also
3081 @xref{String Selection}, for ways to create strings from existing
3084 @c FIXME::martin: list->string belongs into `List/String Conversion'
3086 @deffn {Scheme Procedure} string char@dots{}
3088 Return a newly allocated string made from the given character
3092 (string #\x #\y #\z) @result{} "xyz"
3093 (string) @result{} ""
3097 @deffn {Scheme Procedure} list->string lst
3098 @deffnx {C Function} scm_string (lst)
3099 @rnindex list->string
3100 Return a newly allocated string made from a list of characters.
3103 (list->string '(#\a #\b #\c)) @result{} "abc"
3107 @deffn {Scheme Procedure} reverse-list->string lst
3108 @deffnx {C Function} scm_reverse_list_to_string (lst)
3109 Return a newly allocated string made from a list of characters, in
3113 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
3117 @rnindex make-string
3118 @deffn {Scheme Procedure} make-string k [chr]
3119 @deffnx {C Function} scm_make_string (k, chr)
3120 Return a newly allocated string of
3121 length @var{k}. If @var{chr} is given, then all elements of
3122 the string are initialized to @var{chr}, otherwise the contents
3123 of the string are unspecified.
3126 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
3127 Like @code{scm_make_string}, but expects the length as a
3131 @deffn {Scheme Procedure} string-tabulate proc len
3132 @deffnx {C Function} scm_string_tabulate (proc, len)
3133 @var{proc} is an integer->char procedure. Construct a string
3134 of size @var{len} by applying @var{proc} to each index to
3135 produce the corresponding string element. The order in which
3136 @var{proc} is applied to the indices is not specified.
3139 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
3140 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
3141 Append the string in the string list @var{ls}, using the string
3142 @var{delimiter} as a delimiter between the elements of @var{ls}.
3143 @var{grammar} is a symbol which specifies how the delimiter is
3144 placed between the strings, and defaults to the symbol
3149 Insert the separator between list elements. An empty string
3150 will produce an empty list.
3152 Like @code{infix}, but will raise an error if given the empty
3155 Insert the separator after every list element.
3157 Insert the separator before each list element.
3161 @node List/String Conversion
3162 @subsubsection List/String conversion
3164 When processing strings, it is often convenient to first convert them
3165 into a list representation by using the procedure @code{string->list},
3166 work with the resulting list, and then convert it back into a string.
3167 These procedures are useful for similar tasks.
3169 @rnindex string->list
3170 @deffn {Scheme Procedure} string->list str [start [end]]
3171 @deffnx {C Function} scm_substring_to_list (str, start, end)
3172 @deffnx {C Function} scm_string_to_list (str)
3173 Convert the string @var{str} into a list of characters.
3176 @deffn {Scheme Procedure} string-split str char_pred
3177 @deffnx {C Function} scm_string_split (str, char_pred)
3178 Split the string @var{str} into a list of substrings delimited
3179 by appearances of characters that
3183 equal @var{char_pred}, if it is a character,
3186 satisfy the predicate @var{char_pred}, if it is a procedure,
3189 are in the set @var{char_pred}, if it is a character set.
3192 Note that an empty substring between separator characters will result in
3193 an empty string in the result list.
3196 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
3198 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
3200 (string-split "::" #\:)
3204 (string-split "" #\:)
3211 @node String Selection
3212 @subsubsection String Selection
3214 Portions of strings can be extracted by these procedures.
3215 @code{string-ref} delivers individual characters whereas
3216 @code{substring} can be used to extract substrings from longer strings.
3218 @rnindex string-length
3219 @deffn {Scheme Procedure} string-length string
3220 @deffnx {C Function} scm_string_length (string)
3221 Return the number of characters in @var{string}.
3224 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
3225 Return the number of characters in @var{str} as a @code{size_t}.
3229 @deffn {Scheme Procedure} string-ref str k
3230 @deffnx {C Function} scm_string_ref (str, k)
3231 Return character @var{k} of @var{str} using zero-origin
3232 indexing. @var{k} must be a valid index of @var{str}.
3235 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
3236 Return character @var{k} of @var{str} using zero-origin
3237 indexing. @var{k} must be a valid index of @var{str}.
3240 @rnindex string-copy
3241 @deffn {Scheme Procedure} string-copy str [start [end]]
3242 @deffnx {C Function} scm_substring_copy (str, start, end)
3243 @deffnx {C Function} scm_string_copy (str)
3244 Return a copy of the given string @var{str}.
3246 The returned string shares storage with @var{str} initially, but it is
3247 copied as soon as one of the two strings is modified.
3251 @deffn {Scheme Procedure} substring str start [end]
3252 @deffnx {C Function} scm_substring (str, start, end)
3253 Return a new string formed from the characters
3254 of @var{str} beginning with index @var{start} (inclusive) and
3255 ending with index @var{end} (exclusive).
3256 @var{str} must be a string, @var{start} and @var{end} must be
3257 exact integers satisfying:
3259 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
3261 The returned string shares storage with @var{str} initially, but it is
3262 copied as soon as one of the two strings is modified.
3265 @deffn {Scheme Procedure} substring/shared str start [end]
3266 @deffnx {C Function} scm_substring_shared (str, start, end)
3267 Like @code{substring}, but the strings continue to share their storage
3268 even if they are modified. Thus, modifications to @var{str} show up
3269 in the new string, and vice versa.
3272 @deffn {Scheme Procedure} substring/copy str start [end]
3273 @deffnx {C Function} scm_substring_copy (str, start, end)
3274 Like @code{substring}, but the storage for the new string is copied
3278 @deffn {Scheme Procedure} substring/read-only str start [end]
3279 @deffnx {C Function} scm_substring_read_only (str, start, end)
3280 Like @code{substring}, but the resulting string can not be modified.
3283 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
3284 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
3285 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
3286 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
3287 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
3290 @deffn {Scheme Procedure} string-take s n
3291 @deffnx {C Function} scm_string_take (s, n)
3292 Return the @var{n} first characters of @var{s}.
3295 @deffn {Scheme Procedure} string-drop s n
3296 @deffnx {C Function} scm_string_drop (s, n)
3297 Return all but the first @var{n} characters of @var{s}.
3300 @deffn {Scheme Procedure} string-take-right s n
3301 @deffnx {C Function} scm_string_take_right (s, n)
3302 Return the @var{n} last characters of @var{s}.
3305 @deffn {Scheme Procedure} string-drop-right s n
3306 @deffnx {C Function} scm_string_drop_right (s, n)
3307 Return all but the last @var{n} characters of @var{s}.
3310 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
3311 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
3312 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
3313 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
3314 Take characters @var{start} to @var{end} from the string @var{s} and
3315 either pad with @var{chr} or truncate them to give @var{len}
3318 @code{string-pad} pads or truncates on the left, so for example
3321 (string-pad "x" 3) @result{} " x"
3322 (string-pad "abcde" 3) @result{} "cde"
3325 @code{string-pad-right} pads or truncates on the right, so for example
3328 (string-pad-right "x" 3) @result{} "x "
3329 (string-pad-right "abcde" 3) @result{} "abc"
3333 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
3334 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
3335 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
3336 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
3337 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
3338 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
3339 Trim occurrences of @var{char_pred} from the ends of @var{s}.
3341 @code{string-trim} trims @var{char_pred} characters from the left
3342 (start) of the string, @code{string-trim-right} trims them from the
3343 right (end) of the string, @code{string-trim-both} trims from both
3346 @var{char_pred} can be a character, a character set, or a predicate
3347 procedure to call on each character. If @var{char_pred} is not given
3348 the default is whitespace as per @code{char-set:whitespace}
3349 (@pxref{Standard Character Sets}).
3352 (string-trim " x ") @result{} "x "
3353 (string-trim-right "banana" #\a) @result{} "banan"
3354 (string-trim-both ".,xy:;" char-set:punctuation)
3356 (string-trim-both "xyzzy" (lambda (c)
3363 @node String Modification
3364 @subsubsection String Modification
3366 These procedures are for modifying strings in-place. This means that the
3367 result of the operation is not a new string; instead, the original string's
3368 memory representation is modified.
3370 @rnindex string-set!
3371 @deffn {Scheme Procedure} string-set! str k chr
3372 @deffnx {C Function} scm_string_set_x (str, k, chr)
3373 Store @var{chr} in element @var{k} of @var{str} and return
3374 an unspecified value. @var{k} must be a valid index of
3378 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
3379 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
3382 @rnindex string-fill!
3383 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
3384 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
3385 @deffnx {C Function} scm_string_fill_x (str, chr)
3386 Stores @var{chr} in every element of the given @var{str} and
3387 returns an unspecified value.
3390 @deffn {Scheme Procedure} substring-fill! str start end fill
3391 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
3392 Change every character in @var{str} between @var{start} and
3393 @var{end} to @var{fill}.
3396 (define y (string-copy "abcdefg"))
3397 (substring-fill! y 1 3 #\r)
3403 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
3404 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
3405 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
3406 into @var{str2} beginning at position @var{start2}.
3407 @var{str1} and @var{str2} can be the same string.
3410 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
3411 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
3412 Copy the sequence of characters from index range [@var{start},
3413 @var{end}) in string @var{s} to string @var{target}, beginning
3414 at index @var{tstart}. The characters are copied left-to-right
3415 or right-to-left as needed -- the copy is guaranteed to work,
3416 even if @var{target} and @var{s} are the same string. It is an
3417 error if the copy operation runs off the end of the target
3422 @node String Comparison
3423 @subsubsection String Comparison
3425 The procedures in this section are similar to the character ordering
3426 predicates (@pxref{Characters}), but are defined on character sequences.
3428 The first set is specified in R5RS and has names that end in @code{?}.
3429 The second set is specified in SRFI-13 and the names have not ending
3432 The predicates ending in @code{-ci} ignore the character case
3433 when comparing strings. For now, case-insensitive comparison is done
3434 using the R5RS rules, where every lower-case character that has a
3435 single character upper-case form is converted to uppercase before
3436 comparison. See @xref{Text Collation, the @code{(ice-9
3437 i18n)} module}, for locale-dependent string comparison.
3440 @deffn {Scheme Procedure} string=? s1 s2 s3 @dots{}
3441 Lexicographic equality predicate; return @code{#t} if all strings are
3442 the same length and contain the same characters in the same positions,
3443 otherwise return @code{#f}.
3445 The procedure @code{string-ci=?} treats upper and lower case
3446 letters as though they were the same character, but
3447 @code{string=?} treats upper and lower case as distinct
3452 @deffn {Scheme Procedure} string<? s1 s2 s3 @dots{}
3453 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3454 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3455 lexicographically less than @var{str_i+1}.
3459 @deffn {Scheme Procedure} string<=? s1 s2 s3 @dots{}
3460 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3461 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3462 lexicographically less than or equal to @var{str_i+1}.
3466 @deffn {Scheme Procedure} string>? s1 s2 s3 @dots{}
3467 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3468 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3469 lexicographically greater than @var{str_i+1}.
3473 @deffn {Scheme Procedure} string>=? s1 s2 s3 @dots{}
3474 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3475 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3476 lexicographically greater than or equal to @var{str_i+1}.
3479 @rnindex string-ci=?
3480 @deffn {Scheme Procedure} string-ci=? s1 s2 s3 @dots{}
3481 Case-insensitive string equality predicate; return @code{#t} if
3482 all strings are the same length and their component
3483 characters match (ignoring case) at each position; otherwise
3487 @rnindex string-ci<?
3488 @deffn {Scheme Procedure} string-ci<? s1 s2 s3 @dots{}
3489 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3490 for every pair of consecutive string arguments @var{str_i} and
3491 @var{str_i+1}, @var{str_i} is lexicographically less than @var{str_i+1}
3496 @deffn {Scheme Procedure} string-ci<=? s1 s2 s3 @dots{}
3497 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3498 for every pair of consecutive string arguments @var{str_i} and
3499 @var{str_i+1}, @var{str_i} is lexicographically less than or equal to
3500 @var{str_i+1} regardless of case.
3503 @rnindex string-ci>?
3504 @deffn {Scheme Procedure} string-ci>? s1 s2 s3 @dots{}
3505 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3506 for every pair of consecutive string arguments @var{str_i} and
3507 @var{str_i+1}, @var{str_i} is lexicographically greater than
3508 @var{str_i+1} regardless of case.
3511 @rnindex string-ci>=?
3512 @deffn {Scheme Procedure} string-ci>=? s1 s2 s3 @dots{}
3513 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3514 for every pair of consecutive string arguments @var{str_i} and
3515 @var{str_i+1}, @var{str_i} is lexicographically greater than or equal to
3516 @var{str_i+1} regardless of case.
3519 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3520 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3521 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3522 mismatch index, depending upon whether @var{s1} is less than,
3523 equal to, or greater than @var{s2}. The mismatch index is the
3524 largest index @var{i} such that for every 0 <= @var{j} <
3525 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3526 @var{i} is the first position that does not match.
3529 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3530 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3531 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3532 mismatch index, depending upon whether @var{s1} is less than,
3533 equal to, or greater than @var{s2}. The mismatch index is the
3534 largest index @var{i} such that for every 0 <= @var{j} <
3535 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3536 @var{i} is the first position where the lowercased letters
3541 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3542 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3543 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3547 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3548 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3549 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3553 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3554 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3555 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3556 true value otherwise.
3559 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3560 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3561 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3562 true value otherwise.
3565 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3566 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3567 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3571 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3572 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3573 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3577 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3578 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3579 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3580 value otherwise. The character comparison is done
3584 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3585 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3586 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3587 value otherwise. The character comparison is done
3591 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3592 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3593 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3594 true value otherwise. The character comparison is done
3598 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3599 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3600 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3601 true value otherwise. The character comparison is done
3605 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3606 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3607 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3608 value otherwise. The character comparison is done
3612 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3613 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3614 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3615 otherwise. The character comparison is done
3619 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3620 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3621 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).
3624 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3625 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3626 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).
3629 Because the same visual appearance of an abstract Unicode character can
3630 be obtained via multiple sequences of Unicode characters, even the
3631 case-insensitive string comparison functions described above may return
3632 @code{#f} when presented with strings containing different
3633 representations of the same character. For example, the Unicode
3634 character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be
3635 represented with a single character (U+1E69) or by the character ``LATIN
3636 SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING
3637 DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307).
3639 For this reason, it is often desirable to ensure that the strings
3640 to be compared are using a mutually consistent representation for every
3641 character. The Unicode standard defines two methods of normalizing the
3642 contents of strings: Decomposition, which breaks composite characters
3643 into a set of constituent characters with an ordering defined by the
3644 Unicode Standard; and composition, which performs the converse.
3646 There are two decomposition operations. ``Canonical decomposition''
3647 produces character sequences that share the same visual appearance as
3648 the original characters, while ``compatibility decomposition'' produces
3649 ones whose visual appearances may differ from the originals but which
3650 represent the same abstract character.
3652 These operations are encapsulated in the following set of normalization
3657 Characters are decomposed to their canonical forms.
3660 Characters are decomposed to their compatibility forms.
3663 Characters are decomposed to their canonical forms, then composed.
3666 Characters are decomposed to their compatibility forms, then composed.
3670 The functions below put their arguments into one of the forms described
3673 @deffn {Scheme Procedure} string-normalize-nfd s
3674 @deffnx {C Function} scm_string_normalize_nfd (s)
3675 Return the @code{NFD} normalized form of @var{s}.
3678 @deffn {Scheme Procedure} string-normalize-nfkd s
3679 @deffnx {C Function} scm_string_normalize_nfkd (s)
3680 Return the @code{NFKD} normalized form of @var{s}.
3683 @deffn {Scheme Procedure} string-normalize-nfc s
3684 @deffnx {C Function} scm_string_normalize_nfc (s)
3685 Return the @code{NFC} normalized form of @var{s}.
3688 @deffn {Scheme Procedure} string-normalize-nfkc s
3689 @deffnx {C Function} scm_string_normalize_nfkc (s)
3690 Return the @code{NFKC} normalized form of @var{s}.
3693 @node String Searching
3694 @subsubsection String Searching
3696 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3697 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3698 Search through the string @var{s} from left to right, returning
3699 the index of the first occurrence of a character which
3703 equals @var{char_pred}, if it is character,
3706 satisfies the predicate @var{char_pred}, if it is a procedure,
3709 is in the set @var{char_pred}, if it is a character set.
3712 Return @code{#f} if no match is found.
3715 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3716 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3717 Search through the string @var{s} from right to left, returning
3718 the index of the last occurrence of a character which
3722 equals @var{char_pred}, if it is character,
3725 satisfies the predicate @var{char_pred}, if it is a procedure,
3728 is in the set if @var{char_pred} is a character set.
3731 Return @code{#f} if no match is found.
3734 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3735 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3736 Return the length of the longest common prefix of the two
3740 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3741 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3742 Return the length of the longest common prefix of the two
3743 strings, ignoring character case.
3746 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3747 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3748 Return the length of the longest common suffix of the two
3752 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3753 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3754 Return the length of the longest common suffix of the two
3755 strings, ignoring character case.
3758 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3759 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3760 Is @var{s1} a prefix of @var{s2}?
3763 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3764 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3765 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3768 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3769 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3770 Is @var{s1} a suffix of @var{s2}?
3773 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3774 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3775 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3778 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3779 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3780 Search through the string @var{s} from right to left, returning
3781 the index of the last occurrence of a character which
3785 equals @var{char_pred}, if it is character,
3788 satisfies the predicate @var{char_pred}, if it is a procedure,
3791 is in the set if @var{char_pred} is a character set.
3794 Return @code{#f} if no match is found.
3797 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3798 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3799 Search through the string @var{s} from left to right, returning
3800 the index of the first occurrence of a character which
3804 does not equal @var{char_pred}, if it is character,
3807 does not satisfy the predicate @var{char_pred}, if it is a
3811 is not in the set if @var{char_pred} is a character set.
3815 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3816 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3817 Search through the string @var{s} from right to left, returning
3818 the index of the last occurrence of a character which
3822 does not equal @var{char_pred}, if it is character,
3825 does not satisfy the predicate @var{char_pred}, if it is a
3829 is not in the set if @var{char_pred} is a character set.
3833 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3834 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3835 Return the count of the number of characters in the string
3840 equals @var{char_pred}, if it is character,
3843 satisfies the predicate @var{char_pred}, if it is a procedure.
3846 is in the set @var{char_pred}, if it is a character set.
3850 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3851 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3852 Does string @var{s1} contain string @var{s2}? Return the index
3853 in @var{s1} where @var{s2} occurs as a substring, or false.
3854 The optional start/end indices restrict the operation to the
3855 indicated substrings.
3858 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3859 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3860 Does string @var{s1} contain string @var{s2}? Return the index
3861 in @var{s1} where @var{s2} occurs as a substring, or false.
3862 The optional start/end indices restrict the operation to the
3863 indicated substrings. Character comparison is done
3867 @node Alphabetic Case Mapping
3868 @subsubsection Alphabetic Case Mapping
3870 These are procedures for mapping strings to their upper- or lower-case
3871 equivalents, respectively, or for capitalizing strings.
3873 They use the basic case mapping rules for Unicode characters. No
3874 special language or context rules are considered. The resulting strings
3875 are guaranteed to be the same length as the input strings.
3877 @xref{Character Case Mapping, the @code{(ice-9
3878 i18n)} module}, for locale-dependent case conversions.
3880 @deffn {Scheme Procedure} string-upcase str [start [end]]
3881 @deffnx {C Function} scm_substring_upcase (str, start, end)
3882 @deffnx {C Function} scm_string_upcase (str)
3883 Upcase every character in @code{str}.
3886 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3887 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3888 @deffnx {C Function} scm_string_upcase_x (str)
3889 Destructively upcase every character in @code{str}.
3899 @deffn {Scheme Procedure} string-downcase str [start [end]]
3900 @deffnx {C Function} scm_substring_downcase (str, start, end)
3901 @deffnx {C Function} scm_string_downcase (str)
3902 Downcase every character in @var{str}.
3905 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3906 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3907 @deffnx {C Function} scm_string_downcase_x (str)
3908 Destructively downcase every character in @var{str}.
3913 (string-downcase! y)
3920 @deffn {Scheme Procedure} string-capitalize str
3921 @deffnx {C Function} scm_string_capitalize (str)
3922 Return a freshly allocated string with the characters in
3923 @var{str}, where the first character of every word is
3927 @deffn {Scheme Procedure} string-capitalize! str
3928 @deffnx {C Function} scm_string_capitalize_x (str)
3929 Upcase the first character of every word in @var{str}
3930 destructively and return @var{str}.
3933 y @result{} "hello world"
3934 (string-capitalize! y) @result{} "Hello World"
3935 y @result{} "Hello World"
3939 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3940 @deffnx {C Function} scm_string_titlecase (str, start, end)
3941 Titlecase every first character in a word in @var{str}.
3944 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3945 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3946 Destructively titlecase every first character in a word in
3950 @node Reversing and Appending Strings
3951 @subsubsection Reversing and Appending Strings
3953 @deffn {Scheme Procedure} string-reverse str [start [end]]
3954 @deffnx {C Function} scm_string_reverse (str, start, end)
3955 Reverse the string @var{str}. The optional arguments
3956 @var{start} and @var{end} delimit the region of @var{str} to
3960 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3961 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3962 Reverse the string @var{str} in-place. The optional arguments
3963 @var{start} and @var{end} delimit the region of @var{str} to
3964 operate on. The return value is unspecified.
3967 @rnindex string-append
3968 @deffn {Scheme Procedure} string-append arg @dots{}
3969 @deffnx {C Function} scm_string_append (args)
3970 Return a newly allocated string whose characters form the
3971 concatenation of the given strings, @var{arg} @enddots{}.
3975 (string-append h "world"))
3976 @result{} "hello world"
3980 @deffn {Scheme Procedure} string-append/shared arg @dots{}
3981 @deffnx {C Function} scm_string_append_shared (args)
3982 Like @code{string-append}, but the result may share memory
3983 with the argument strings.
3986 @deffn {Scheme Procedure} string-concatenate ls
3987 @deffnx {C Function} scm_string_concatenate (ls)
3988 Append the elements (which must be strings) of @var{ls} together into a
3989 single string. Guaranteed to return a freshly allocated string.
3992 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3993 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3994 Without optional arguments, this procedure is equivalent to
3997 (string-concatenate (reverse ls))
4000 If the optional argument @var{final_string} is specified, it is
4001 consed onto the beginning to @var{ls} before performing the
4002 list-reverse and string-concatenate operations. If @var{end}
4003 is given, only the characters of @var{final_string} up to index
4006 Guaranteed to return a freshly allocated string.
4009 @deffn {Scheme Procedure} string-concatenate/shared ls
4010 @deffnx {C Function} scm_string_concatenate_shared (ls)
4011 Like @code{string-concatenate}, but the result may share memory
4012 with the strings in the list @var{ls}.
4015 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
4016 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
4017 Like @code{string-concatenate-reverse}, but the result may
4018 share memory with the strings in the @var{ls} arguments.
4021 @node Mapping Folding and Unfolding
4022 @subsubsection Mapping, Folding, and Unfolding
4024 @deffn {Scheme Procedure} string-map proc s [start [end]]
4025 @deffnx {C Function} scm_string_map (proc, s, start, end)
4026 @var{proc} is a char->char procedure, it is mapped over
4027 @var{s}. The order in which the procedure is applied to the
4028 string elements is not specified.
4031 @deffn {Scheme Procedure} string-map! proc s [start [end]]
4032 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
4033 @var{proc} is a char->char procedure, it is mapped over
4034 @var{s}. The order in which the procedure is applied to the
4035 string elements is not specified. The string @var{s} is
4036 modified in-place, the return value is not specified.
4039 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
4040 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
4041 @var{proc} is mapped over @var{s} in left-to-right order. The
4042 return value is not specified.
4045 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
4046 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
4047 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
4050 For example, to change characters to alternately upper and lower case,
4053 (define str (string-copy "studly"))
4054 (string-for-each-index
4057 ((if (even? i) char-upcase char-downcase)
4058 (string-ref str i))))
4060 str @result{} "StUdLy"
4064 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
4065 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
4066 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4067 as the terminating element, from left to right. @var{kons}
4068 must expect two arguments: The actual character and the last
4069 result of @var{kons}' application.
4072 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
4073 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
4074 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4075 as the terminating element, from right to left. @var{kons}
4076 must expect two arguments: The actual character and the last
4077 result of @var{kons}' application.
4080 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
4081 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
4083 @item @var{g} is used to generate a series of @emph{seed}
4084 values from the initial @var{seed}: @var{seed}, (@var{g}
4085 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4087 @item @var{p} tells us when to stop -- when it returns true
4088 when applied to one of these seed values.
4089 @item @var{f} maps each seed value to the corresponding
4090 character in the result string. These chars are assembled
4091 into the string in a left-to-right order.
4092 @item @var{base} is the optional initial/leftmost portion
4093 of the constructed string; it default to the empty
4095 @item @var{make_final} is applied to the terminal seed
4096 value (on which @var{p} returns true) to produce
4097 the final/rightmost portion of the constructed string.
4098 The default is nothing extra.
4102 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
4103 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
4105 @item @var{g} is used to generate a series of @emph{seed}
4106 values from the initial @var{seed}: @var{seed}, (@var{g}
4107 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4109 @item @var{p} tells us when to stop -- when it returns true
4110 when applied to one of these seed values.
4111 @item @var{f} maps each seed value to the corresponding
4112 character in the result string. These chars are assembled
4113 into the string in a right-to-left order.
4114 @item @var{base} is the optional initial/rightmost portion
4115 of the constructed string; it default to the empty
4117 @item @var{make_final} is applied to the terminal seed
4118 value (on which @var{p} returns true) to produce
4119 the final/leftmost portion of the constructed string.
4120 It defaults to @code{(lambda (x) )}.
4124 @node Miscellaneous String Operations
4125 @subsubsection Miscellaneous String Operations
4127 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
4128 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
4129 This is the @emph{extended substring} procedure that implements
4130 replicated copying of a substring of some string.
4132 @var{s} is a string, @var{start} and @var{end} are optional
4133 arguments that demarcate a substring of @var{s}, defaulting to
4134 0 and the length of @var{s}. Replicate this substring up and
4135 down index space, in both the positive and negative directions.
4136 @code{xsubstring} returns the substring of this string
4137 beginning at index @var{from}, and ending at @var{to}, which
4138 defaults to @var{from} + (@var{end} - @var{start}).
4141 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
4142 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
4143 Exactly the same as @code{xsubstring}, but the extracted text
4144 is written into the string @var{target} starting at index
4145 @var{tstart}. The operation is not defined if @code{(eq?
4146 @var{target} @var{s})} or these arguments share storage -- you
4147 cannot copy a string on top of itself.
4150 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
4151 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
4152 Return the string @var{s1}, but with the characters
4153 @var{start1} @dots{} @var{end1} replaced by the characters
4154 @var{start2} @dots{} @var{end2} from @var{s2}.
4157 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
4158 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
4159 Split the string @var{s} into a list of substrings, where each
4160 substring is a maximal non-empty contiguous sequence of
4161 characters from the character set @var{token_set}, which
4162 defaults to @code{char-set:graphic}.
4163 If @var{start} or @var{end} indices are provided, they restrict
4164 @code{string-tokenize} to operating on the indicated substring
4168 @deffn {Scheme Procedure} string-filter char_pred s [start [end]]
4169 @deffnx {C Function} scm_string_filter (char_pred, s, start, end)
4170 Filter the string @var{s}, retaining only those characters which
4171 satisfy @var{char_pred}.
4173 If @var{char_pred} is a procedure, it is applied to each character as
4174 a predicate, if it is a character, it is tested for equality and if it
4175 is a character set, it is tested for membership.
4178 @deffn {Scheme Procedure} string-delete char_pred s [start [end]]
4179 @deffnx {C Function} scm_string_delete (char_pred, s, start, end)
4180 Delete characters satisfying @var{char_pred} from @var{s}.
4182 If @var{char_pred} is a procedure, it is applied to each character as
4183 a predicate, if it is a character, it is tested for equality and if it
4184 is a character set, it is tested for membership.
4187 @node Representing Strings as Bytes
4188 @subsubsection Representing Strings as Bytes
4190 Out in the cold world outside of Guile, not all strings are treated in
4191 the same way. Out there there are only bytes, and there are many ways
4192 of representing a strings (sequences of characters) as binary data
4193 (sequences of bytes).
4195 As a user, usually you don't have to think about this very much. When
4196 you type on your keyboard, your system encodes your keystrokes as bytes
4197 according to the locale that you have configured on your computer.
4198 Guile uses the locale to decode those bytes back into characters --
4199 hopefully the same characters that you typed in.
4201 All is not so clear when dealing with a system with multiple users, such
4202 as a web server. Your web server might get a request from one user for
4203 data encoded in the ISO-8859-1 character set, and then another request
4204 from a different user for UTF-8 data.
4207 @cindex character encoding
4208 Guile provides an @dfn{iconv} module for converting between strings and
4209 sequences of bytes. @xref{Bytevectors}, for more on how Guile
4210 represents raw byte sequences. This module gets its name from the
4211 common @sc{unix} command of the same name.
4213 Note that often it is sufficient to just read and write strings from
4214 ports instead of using these functions. To do this, specify the port
4215 encoding using @code{set-port-encoding!}. @xref{Ports}, for more on
4216 ports and character encodings.
4218 Unlike the rest of the procedures in this section, you have to load the
4219 @code{iconv} module before having access to these procedures:
4222 (use-modules (ice-9 iconv))
4225 @deffn {Scheme Procedure} string->bytevector string encoding [conversion-strategy]
4226 Encode @var{string} as a sequence of bytes.
4228 The string will be encoded in the character set specified by the
4229 @var{encoding} string. If the string has characters that cannot be
4230 represented in the encoding, by default this procedure raises an
4231 @code{encoding-error}. Pass a @var{conversion-strategy} argument to
4232 specify other behaviors.
4234 The return value is a bytevector. @xref{Bytevectors}, for more on
4235 bytevectors. @xref{Ports}, for more on character encodings and
4236 conversion strategies.
4239 @deffn {Scheme Procedure} bytevector->string bytevector encoding [conversion-strategy]
4240 Decode @var{bytevector} into a string.
4242 The bytes will be decoded from the character set by the @var{encoding}
4243 string. If the bytes do not form a valid encoding, by default this
4244 procedure raises an @code{decoding-error}. As with
4245 @code{string->bytevector}, pass the optional @var{conversion-strategy}
4246 argument to modify this behavior. @xref{Ports}, for more on character
4247 encodings and conversion strategies.
4250 @deffn {Scheme Procedure} call-with-output-encoded-string encoding proc [conversion-strategy]
4251 Like @code{call-with-output-string}, but instead of returning a string,
4252 returns a encoding of the string according to @var{encoding}, as a
4253 bytevector. This procedure can be more efficient than collecting a
4254 string and then converting it via @code{string->bytevector}.
4257 @node Conversion to/from C
4258 @subsubsection Conversion to/from C
4260 When creating a Scheme string from a C string or when converting a
4261 Scheme string to a C string, the concept of character encoding becomes
4264 In C, a string is just a sequence of bytes, and the character encoding
4265 describes the relation between these bytes and the actual characters
4266 that make up the string. For Scheme strings, character encoding is not
4267 an issue (most of the time), since in Scheme you usually treat strings
4268 as character sequences, not byte sequences.
4270 Converting to C and converting from C each have their own challenges.
4272 When converting from C to Scheme, it is important that the sequence of
4273 bytes in the C string be valid with respect to its encoding. ASCII
4274 strings, for example, can't have any bytes greater than 127. An ASCII
4275 byte greater than 127 is considered @emph{ill-formed} and cannot be
4276 converted into a Scheme character.
4278 Problems can occur in the reverse operation as well. Not all character
4279 encodings can hold all possible Scheme characters. Some encodings, like
4280 ASCII for example, can only describe a small subset of all possible
4281 characters. So, when converting to C, one must first decide what to do
4282 with Scheme characters that can't be represented in the C string.
4284 Converting a Scheme string to a C string will often allocate fresh
4285 memory to hold the result. You must take care that this memory is
4286 properly freed eventually. In many cases, this can be achieved by
4287 using @code{scm_dynwind_free} inside an appropriate dynwind context,
4288 @xref{Dynamic Wind}.
4290 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
4291 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
4292 Creates a new Scheme string that has the same contents as @var{str} when
4293 interpreted in the character encoding of the current locale.
4295 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
4297 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
4298 @var{str} in bytes, and @var{str} does not need to be null-terminated.
4299 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
4300 null-terminated and the real length will be found with @code{strlen}.
4302 If the C string is ill-formed, an error will be raised.
4304 Note that these functions should @emph{not} be used to convert C string
4305 constants, because there is no guarantee that the current locale will
4306 match that of the execution character set, used for string and character
4307 constants. Most modern C compilers use UTF-8 by default, so to convert
4308 C string constants we recommend @code{scm_from_utf8_string}.
4311 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
4312 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
4313 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
4314 respectively, but also frees @var{str} with @code{free} eventually.
4315 Thus, you can use this function when you would free @var{str} anyway
4316 immediately after creating the Scheme string. In certain cases, Guile
4317 can then use @var{str} directly as its internal representation.
4320 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
4321 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
4322 Returns a C string with the same contents as @var{str} in the character
4323 encoding of the current locale. The C string must be freed with
4324 @code{free} eventually, maybe by using @code{scm_dynwind_free},
4325 @xref{Dynamic Wind}.
4327 For @code{scm_to_locale_string}, the returned string is
4328 null-terminated and an error is signalled when @var{str} contains
4329 @code{#\nul} characters.
4331 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
4332 @var{str} might contain @code{#\nul} characters and the length of the
4333 returned string in bytes is stored in @code{*@var{lenp}}. The
4334 returned string will not be null-terminated in this case. If
4335 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
4336 @code{scm_to_locale_string}.
4338 If a character in @var{str} cannot be represented in the character
4339 encoding of the current locale, the default port conversion strategy is
4340 used. @xref{Ports}, for more on conversion strategies.
4342 If the conversion strategy is @code{error}, an error will be raised. If
4343 it is @code{substitute}, a replacement character, such as a question
4344 mark, will be inserted in its place. If it is @code{escape}, a hex
4345 escape will be inserted in its place.
4348 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
4349 Puts @var{str} as a C string in the current locale encoding into the
4350 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
4351 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
4352 more than that. No terminating @code{'\0'} will be stored.
4354 The return value of @code{scm_to_locale_stringbuf} is the number of
4355 bytes that are needed for all of @var{str}, regardless of whether
4356 @var{buf} was large enough to hold them. Thus, when the return value
4357 is larger than @var{max_len}, only @var{max_len} bytes have been
4358 stored and you probably need to try again with a larger buffer.
4361 For most situations, string conversion should occur using the current
4362 locale, such as with the functions above. But there may be cases where
4363 one wants to convert strings from a character encoding other than the
4364 locale's character encoding. For these cases, the lower-level functions
4365 @code{scm_to_stringn} and @code{scm_from_stringn} are provided. These
4366 functions should seldom be necessary if one is properly using locales.
4368 @deftp {C Type} scm_t_string_failed_conversion_handler
4369 This is an enumerated type that can take one of three values:
4370 @code{SCM_FAILED_CONVERSION_ERROR},
4371 @code{SCM_FAILED_CONVERSION_QUESTION_MARK}, and
4372 @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}. They are used to indicate
4373 a strategy for handling characters that cannot be converted to or from a
4374 given character encoding. @code{SCM_FAILED_CONVERSION_ERROR} indicates
4375 that a conversion should throw an error if some characters cannot be
4376 converted. @code{SCM_FAILED_CONVERSION_QUESTION_MARK} indicates that a
4377 conversion should replace unconvertable characters with the question
4378 mark character. And, @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}
4379 requests that a conversion should replace an unconvertable character
4380 with an escape sequence.
4382 While all three strategies apply when converting Scheme strings to C,
4383 only @code{SCM_FAILED_CONVERSION_ERROR} and
4384 @code{SCM_FAILED_CONVERSION_QUESTION_MARK} can be used when converting C
4388 @deftypefn {C Function} char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding, scm_t_string_failed_conversion_handler handler)
4389 This function returns a newly allocated C string from the Guile string
4390 @var{str}. The length of the returned string in bytes will be returned in
4391 @var{lenp}. The character encoding of the C string is passed as the ASCII,
4392 null-terminated C string @var{encoding}. The @var{handler} parameter
4393 gives a strategy for dealing with characters that cannot be converted
4394 into @var{encoding}.
4396 If @var{lenp} is @code{NULL}, this function will return a null-terminated C
4397 string. It will throw an error if the string contains a null
4400 The Scheme interface to this function is @code{string->bytevector}, from the
4401 @code{ice-9 iconv} module. @xref{Representing Strings as Bytes}.
4404 @deftypefn {C Function} SCM scm_from_stringn (const char *str, size_t len, const char *encoding, scm_t_string_failed_conversion_handler handler)
4405 This function returns a scheme string from the C string @var{str}. The
4406 length in bytes of the C string is input as @var{len}. The encoding of the C
4407 string is passed as the ASCII, null-terminated C string @code{encoding}.
4408 The @var{handler} parameters suggests a strategy for dealing with
4409 unconvertable characters.
4411 The Scheme interface to this function is @code{bytevector->string}.
4412 @xref{Representing Strings as Bytes}.
4415 The following conversion functions are provided as a convenience for the
4416 most commonly used encodings.
4418 @deftypefn {C Function} SCM scm_from_latin1_string (const char *str)
4419 @deftypefnx {C Function} SCM scm_from_utf8_string (const char *str)
4420 @deftypefnx {C Function} SCM scm_from_utf32_string (const scm_t_wchar *str)
4421 Return a scheme string from the null-terminated C string @var{str},
4422 which is ISO-8859-1-, UTF-8-, or UTF-32-encoded. These functions should
4423 be used to convert hard-coded C string constants into Scheme strings.
4426 @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len)
4427 @deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len)
4428 @deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
4429 Return a scheme string from C string @var{str}, which is ISO-8859-1-,
4430 UTF-8-, or UTF-32-encoded, of length @var{len}. @var{len} is the number
4431 of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and
4432 @code{scm_from_utf8_stringn}; it is the number of elements (code points)
4433 in @var{str} in the case of @code{scm_from_utf32_stringn}.
4436 @deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp)
4437 @deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp)
4438 @deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp)
4439 Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string
4440 from Scheme string @var{str}. An error is thrown when @var{str}
4441 cannot be converted to the specified encoding. If @var{lenp} is
4442 @code{NULL}, the returned C string will be null terminated, and an error
4443 will be thrown if the C string would otherwise contain null
4444 characters. If @var{lenp} is not @code{NULL}, the string is not null terminated,
4445 and the length of the returned string is returned in @var{lenp}. The length
4446 returned is the number of bytes for @code{scm_to_latin1_stringn} and
4447 @code{scm_to_utf8_stringn}; it is the number of elements (code points)
4448 for @code{scm_to_utf32_stringn}.
4451 It is not often the case, but sometimes when you are dealing with the
4452 implementation details of a port, you need to encode and decode strings
4453 according to the encoding and conversion strategy of the port. There
4454 are some convenience functions for that purpose as well.
4456 @deftypefn {C Function} SCM scm_from_port_string (const char *str, SCM port)
4457 @deftypefnx {C Function} SCM scm_from_port_stringn (const char *str, size_t len, SCM port)
4458 @deftypefnx {C Function} char* scm_to_port_string (SCM str, SCM port)
4459 @deftypefnx {C Function} char* scm_to_port_stringn (SCM str, size_t *lenp, SCM port)
4460 Like @code{scm_from_stringn} and friends, except they take their
4461 encoding and conversion strategy from a given port object.
4464 @node String Internals
4465 @subsubsection String Internals
4467 Guile stores each string in memory as a contiguous array of Unicode code
4468 points along with an associated set of attributes. If all of the code
4469 points of a string have an integer range between 0 and 255 inclusive,
4470 the code point array is stored as one byte per code point: it is stored
4471 as an ISO-8859-1 (aka Latin-1) string. If any of the code points of the
4472 string has an integer value greater that 255, the code point array is
4473 stored as four bytes per code point: it is stored as a UTF-32 string.
4475 Conversion between the one-byte-per-code-point and
4476 four-bytes-per-code-point representations happens automatically as
4479 No API is provided to set the internal representation of strings;
4480 however, there are pair of procedures available to query it. These are
4481 debugging procedures. Using them in production code is discouraged,
4482 since the details of Guile's internal representation of strings may
4483 change from release to release.
4485 @deffn {Scheme Procedure} string-bytes-per-char str
4486 @deffnx {C Function} scm_string_bytes_per_char (str)
4487 Return the number of bytes used to encode a Unicode code point in string
4488 @var{str}. The result is one or four.
4491 @deffn {Scheme Procedure} %string-dump str
4492 @deffnx {C Function} scm_sys_string_dump (str)
4493 Returns an association list containing debugging information for
4494 @var{str}. The association list has the following entries.
4501 The start index of the string into its stringbuf
4504 The length of the string
4507 If this string is a substring, it returns its
4508 parent string. Otherwise, it returns @code{#f}
4511 @code{#t} if the string is read-only
4513 @item stringbuf-chars
4514 A new string containing this string's stringbuf's characters
4516 @item stringbuf-length
4517 The number of characters in this stringbuf
4519 @item stringbuf-shared
4520 @code{#t} if this stringbuf is shared
4522 @item stringbuf-wide
4523 @code{#t} if this stringbuf's characters are stored in a 32-bit buffer,
4524 or @code{#f} if they are stored in an 8-bit buffer
4530 @subsection Bytevectors
4535 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevectors)}
4536 module provides the programming interface specified by the
4537 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
4538 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
4539 interpret their contents in a number of ways: bytevector contents can be
4540 accessed as signed or unsigned integer of various sizes and endianness,
4541 as IEEE-754 floating point numbers, or as strings. It is a useful tool
4542 to encode and decode binary data.
4544 The R6RS (Section 4.3.4) specifies an external representation for
4545 bytevectors, whereby the octets (integers in the range 0--255) contained
4546 in the bytevector are represented as a list prefixed by @code{#vu8}:
4552 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
4553 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
4554 they do not need to be quoted:
4558 @result{} #vu8(1 53 204)
4561 Bytevectors can be used with the binary input/output primitives of the
4562 R6RS (@pxref{R6RS I/O Ports}).
4565 * Bytevector Endianness:: Dealing with byte order.
4566 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
4567 * Bytevectors as Integers:: Interpreting bytes as integers.
4568 * Bytevectors and Integer Lists:: Converting to/from an integer list.
4569 * Bytevectors as Floats:: Interpreting bytes as real numbers.
4570 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
4571 * Bytevectors as Arrays:: Guile extension to the bytevector API.
4572 * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4.
4575 @node Bytevector Endianness
4576 @subsubsection Endianness
4582 Some of the following procedures take an @var{endianness} parameter.
4583 The @dfn{endianness} is defined as the order of bytes in multi-byte
4584 numbers: numbers encoded in @dfn{big endian} have their most
4585 significant bytes written first, whereas numbers encoded in
4586 @dfn{little endian} have their least significant bytes
4587 first@footnote{Big-endian and little-endian are the most common
4588 ``endiannesses'', but others do exist. For instance, the GNU MP
4589 library allows @dfn{word order} to be specified independently of
4590 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
4591 Multiple Precision Arithmetic Library Manual}).}.
4593 Little-endian is the native endianness of the IA32 architecture and
4594 its derivatives, while big-endian is native to SPARC and PowerPC,
4595 among others. The @code{native-endianness} procedure returns the
4596 native endianness of the machine it runs on.
4598 @deffn {Scheme Procedure} native-endianness
4599 @deffnx {C Function} scm_native_endianness ()
4600 Return a value denoting the native endianness of the host machine.
4603 @deffn {Scheme Macro} endianness symbol
4604 Return an object denoting the endianness specified by @var{symbol}. If
4605 @var{symbol} is neither @code{big} nor @code{little} then an error is
4606 raised at expand-time.
4609 @defvr {C Variable} scm_endianness_big
4610 @defvrx {C Variable} scm_endianness_little
4611 The objects denoting big- and little-endianness, respectively.
4615 @node Bytevector Manipulation
4616 @subsubsection Manipulating Bytevectors
4618 Bytevectors can be created, copied, and analyzed with the following
4619 procedures and C functions.
4621 @deffn {Scheme Procedure} make-bytevector len [fill]
4622 @deffnx {C Function} scm_make_bytevector (len, fill)
4623 @deffnx {C Function} scm_c_make_bytevector (size_t len)
4624 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
4625 is given, fill it with @var{fill}; @var{fill} must be in the range
4629 @deffn {Scheme Procedure} bytevector? obj
4630 @deffnx {C Function} scm_bytevector_p (obj)
4631 Return true if @var{obj} is a bytevector.
4634 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
4635 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
4638 @deffn {Scheme Procedure} bytevector-length bv
4639 @deffnx {C Function} scm_bytevector_length (bv)
4640 Return the length in bytes of bytevector @var{bv}.
4643 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
4644 Likewise, return the length in bytes of bytevector @var{bv}.
4647 @deffn {Scheme Procedure} bytevector=? bv1 bv2
4648 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
4649 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
4650 length and contents.
4653 @deffn {Scheme Procedure} bytevector-fill! bv fill
4654 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
4655 Fill bytevector @var{bv} with @var{fill}, a byte.
4658 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
4659 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
4660 Copy @var{len} bytes from @var{source} into @var{target}, starting
4661 reading from @var{source-start} (a positive index within @var{source})
4662 and start writing at @var{target-start}. It is permitted for the
4663 @var{source} and @var{target} regions to overlap.
4666 @deffn {Scheme Procedure} bytevector-copy bv
4667 @deffnx {C Function} scm_bytevector_copy (bv)
4668 Return a newly allocated copy of @var{bv}.
4671 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
4672 Return the byte at @var{index} in bytevector @var{bv}.
4675 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
4676 Set the byte at @var{index} in @var{bv} to @var{value}.
4679 Low-level C macros are available. They do not perform any
4680 type-checking; as such they should be used with care.
4682 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
4683 Return the length in bytes of bytevector @var{bv}.
4686 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
4687 Return a pointer to the contents of bytevector @var{bv}.
4691 @node Bytevectors as Integers
4692 @subsubsection Interpreting Bytevector Contents as Integers
4694 The contents of a bytevector can be interpreted as a sequence of
4695 integers of any given size, sign, and endianness.
4698 (let ((bv (make-bytevector 4)))
4699 (bytevector-u8-set! bv 0 #x12)
4700 (bytevector-u8-set! bv 1 #x34)
4701 (bytevector-u8-set! bv 2 #x56)
4702 (bytevector-u8-set! bv 3 #x78)
4704 (map (lambda (number)
4705 (number->string number 16))
4706 (list (bytevector-u8-ref bv 0)
4707 (bytevector-u16-ref bv 0 (endianness big))
4708 (bytevector-u32-ref bv 0 (endianness little)))))
4710 @result{} ("12" "1234" "78563412")
4713 The most generic procedures to interpret bytevector contents as integers
4714 are described below.
4716 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
4717 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
4718 Return the @var{size}-byte long unsigned integer at index @var{index} in
4719 @var{bv}, decoded according to @var{endianness}.
4722 @deffn {Scheme Procedure} bytevector-sint-ref bv index endianness size
4723 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
4724 Return the @var{size}-byte long signed integer at index @var{index} in
4725 @var{bv}, decoded according to @var{endianness}.
4728 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
4729 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
4730 Set the @var{size}-byte long unsigned integer at @var{index} to
4731 @var{value}, encoded according to @var{endianness}.
4734 @deffn {Scheme Procedure} bytevector-sint-set! bv index value endianness size
4735 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
4736 Set the @var{size}-byte long signed integer at @var{index} to
4737 @var{value}, encoded according to @var{endianness}.
4740 The following procedures are similar to the ones above, but specialized
4741 to a given integer size:
4743 @deffn {Scheme Procedure} bytevector-u8-ref bv index
4744 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
4745 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
4746 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
4747 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
4748 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
4749 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
4750 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
4751 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
4752 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
4753 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
4754 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
4755 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
4756 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
4757 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
4758 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
4759 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4760 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
4764 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
4765 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
4766 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
4767 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
4768 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
4769 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
4770 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
4771 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
4772 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
4773 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
4774 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
4775 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
4776 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
4777 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
4778 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
4779 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
4780 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4781 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
4785 Finally, a variant specialized for the host's endianness is available
4786 for each of these functions (with the exception of the @code{u8}
4787 accessors, for obvious reasons):
4789 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4790 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4791 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4792 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4793 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4794 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4795 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4796 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4797 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4798 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4799 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4800 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4801 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4802 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4803 host's native endianness.
4806 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4807 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4808 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4809 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4810 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4811 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4812 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4813 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4814 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4815 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4816 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4817 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4818 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4819 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4820 host's native endianness.
4824 @node Bytevectors and Integer Lists
4825 @subsubsection Converting Bytevectors to/from Integer Lists
4827 Bytevector contents can readily be converted to/from lists of signed or
4831 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4832 (endianness little) 2)
4836 @deffn {Scheme Procedure} bytevector->u8-list bv
4837 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4838 Return a newly allocated list of unsigned 8-bit integers from the
4839 contents of @var{bv}.
4842 @deffn {Scheme Procedure} u8-list->bytevector lst
4843 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4844 Return a newly allocated bytevector consisting of the unsigned 8-bit
4845 integers listed in @var{lst}.
4848 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4849 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4850 Return a list of unsigned integers of @var{size} bytes representing the
4851 contents of @var{bv}, decoded according to @var{endianness}.
4854 @deffn {Scheme Procedure} bytevector->sint-list bv endianness size
4855 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4856 Return a list of signed integers of @var{size} bytes representing the
4857 contents of @var{bv}, decoded according to @var{endianness}.
4860 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4861 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4862 Return a new bytevector containing the unsigned integers listed in
4863 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4866 @deffn {Scheme Procedure} sint-list->bytevector lst endianness size
4867 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4868 Return a new bytevector containing the signed integers listed in
4869 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4872 @node Bytevectors as Floats
4873 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4875 @cindex IEEE-754 floating point numbers
4877 Bytevector contents can also be accessed as IEEE-754 single- or
4878 double-precision floating point numbers (respectively 32 and 64-bit
4879 long) using the procedures described here.
4881 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4882 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4883 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4884 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4885 Return the IEEE-754 single-precision floating point number from @var{bv}
4886 at @var{index} according to @var{endianness}.
4889 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4890 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4891 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4892 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4893 Store real number @var{value} in @var{bv} at @var{index} according to
4897 Specialized procedures are also available:
4899 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4900 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4901 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4902 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4903 Return the IEEE-754 single-precision floating point number from @var{bv}
4904 at @var{index} according to the host's native endianness.
4907 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4908 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4909 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4910 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4911 Store real number @var{value} in @var{bv} at @var{index} according to
4912 the host's native endianness.
4916 @node Bytevectors as Strings
4917 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4919 @cindex Unicode string encoding
4921 Bytevector contents can also be interpreted as Unicode strings encoded
4922 in one of the most commonly available encoding formats.
4923 @xref{Representing Strings as Bytes}, for a more generic interface.
4926 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4929 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4930 @result{} #vu8(99 97 102 195 169)
4933 @deffn {Scheme Procedure} string->utf8 str
4934 @deffnx {Scheme Procedure} string->utf16 str [endianness]
4935 @deffnx {Scheme Procedure} string->utf32 str [endianness]
4936 @deffnx {C Function} scm_string_to_utf8 (str)
4937 @deffnx {C Function} scm_string_to_utf16 (str, endianness)
4938 @deffnx {C Function} scm_string_to_utf32 (str, endianness)
4939 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4940 UTF-32 (aka. UCS-4) encoding of @var{str}. For UTF-16 and UTF-32,
4941 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4942 it defaults to big endian.
4945 @deffn {Scheme Procedure} utf8->string utf
4946 @deffnx {Scheme Procedure} utf16->string utf [endianness]
4947 @deffnx {Scheme Procedure} utf32->string utf [endianness]
4948 @deffnx {C Function} scm_utf8_to_string (utf)
4949 @deffnx {C Function} scm_utf16_to_string (utf, endianness)
4950 @deffnx {C Function} scm_utf32_to_string (utf, endianness)
4951 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4952 or UTF-32-decoded contents of bytevector @var{utf}. For UTF-16 and UTF-32,
4953 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4954 it defaults to big endian.
4957 @node Bytevectors as Arrays
4958 @subsubsection Accessing Bytevectors with the Array API
4960 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4961 with the @dfn{array} procedures (@pxref{Arrays}). When using these
4962 APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4965 (define bv #vu8(0 1 2 3))
4976 ;; Note the different argument order on array-set!.
4977 (array-set! bv 77 2)
4986 @node Bytevectors as Uniform Vectors
4987 @subsubsection Accessing Bytevectors with the SRFI-4 API
4989 Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and
4990 Bytevectors}, for more information.
4997 Symbols in Scheme are widely used in three ways: as items of discrete
4998 data, as lookup keys for alists and hash tables, and to denote variable
5001 A @dfn{symbol} is similar to a string in that it is defined by a
5002 sequence of characters. The sequence of characters is known as the
5003 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
5004 name doesn't include any characters that could be confused with other
5005 elements of Scheme syntax --- a symbol is written in a Scheme program by
5006 writing the sequence of characters that make up the name, @emph{without}
5007 any quotation marks or other special syntax. For example, the symbol
5008 whose name is ``multiply-by-2'' is written, simply:
5014 Notice how this differs from a @emph{string} with contents
5015 ``multiply-by-2'', which is written with double quotation marks, like
5022 Looking beyond how they are written, symbols are different from strings
5023 in two important respects.
5025 The first important difference is uniqueness. If the same-looking
5026 string is read twice from two different places in a program, the result
5027 is two @emph{different} string objects whose contents just happen to be
5028 the same. If, on the other hand, the same-looking symbol is read twice
5029 from two different places in a program, the result is the @emph{same}
5030 symbol object both times.
5032 Given two read symbols, you can use @code{eq?} to test whether they are
5033 the same (that is, have the same name). @code{eq?} is the most
5034 efficient comparison operator in Scheme, and comparing two symbols like
5035 this is as fast as comparing, for example, two numbers. Given two
5036 strings, on the other hand, you must use @code{equal?} or
5037 @code{string=?}, which are much slower comparison operators, to
5038 determine whether the strings have the same contents.
5041 (define sym1 (quote hello))
5042 (define sym2 (quote hello))
5043 (eq? sym1 sym2) @result{} #t
5045 (define str1 "hello")
5046 (define str2 "hello")
5047 (eq? str1 str2) @result{} #f
5048 (equal? str1 str2) @result{} #t
5051 The second important difference is that symbols, unlike strings, are not
5052 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
5053 example above: @code{(quote hello)} evaluates to the symbol named
5054 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
5055 symbol named "hello" and evaluated as a variable reference @dots{} about
5056 which more below (@pxref{Symbol Variables}).
5059 * Symbol Data:: Symbols as discrete data.
5060 * Symbol Keys:: Symbols as lookup keys.
5061 * Symbol Variables:: Symbols as denoting variables.
5062 * Symbol Primitives:: Operations related to symbols.
5063 * Symbol Props:: Function slots and property lists.
5064 * Symbol Read Syntax:: Extended read syntax for symbols.
5065 * Symbol Uninterned:: Uninterned symbols.
5070 @subsubsection Symbols as Discrete Data
5072 Numbers and symbols are similar to the extent that they both lend
5073 themselves to @code{eq?} comparison. But symbols are more descriptive
5074 than numbers, because a symbol's name can be used directly to describe
5075 the concept for which that symbol stands.
5077 For example, imagine that you need to represent some colours in a
5078 computer program. Using numbers, you would have to choose arbitrarily
5079 some mapping between numbers and colours, and then take care to use that
5080 mapping consistently:
5083 ;; 1=red, 2=green, 3=purple
5085 (if (eq? (colour-of car) 1)
5090 You can make the mapping more explicit and the code more readable by
5098 (if (eq? (colour-of car) red)
5103 But the simplest and clearest approach is not to use numbers at all, but
5104 symbols whose names specify the colours that they refer to:
5107 (if (eq? (colour-of car) 'red)
5111 The descriptive advantages of symbols over numbers increase as the set
5112 of concepts that you want to describe grows. Suppose that a car object
5113 can have other properties as well, such as whether it has or uses:
5117 automatic or manual transmission
5119 leaded or unleaded fuel
5121 power steering (or not).
5125 Then a car's combined property set could be naturally represented and
5126 manipulated as a list of symbols:
5129 (properties-of car1)
5131 (red manual unleaded power-steering)
5133 (if (memq 'power-steering (properties-of car1))
5134 (display "Unfit people can drive this car.\n")
5135 (display "You'll need strong arms to drive this car!\n"))
5137 Unfit people can drive this car.
5140 Remember, the fundamental property of symbols that we are relying on
5141 here is that an occurrence of @code{'red} in one part of a program is an
5142 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
5143 another part of a program; this means that symbols can usefully be
5144 compared using @code{eq?}. At the same time, symbols have naturally
5145 descriptive names. This combination of efficiency and descriptive power
5146 makes them ideal for use as discrete data.
5150 @subsubsection Symbols as Lookup Keys
5152 Given their efficiency and descriptive power, it is natural to use
5153 symbols as the keys in an association list or hash table.
5155 To illustrate this, consider a more structured representation of the car
5156 properties example from the preceding subsection. Rather than
5157 mixing all the properties up together in a flat list, we could use an
5158 association list like this:
5161 (define car1-properties '((colour . red)
5162 (transmission . manual)
5164 (steering . power-assisted)))
5167 Notice how this structure is more explicit and extensible than the flat
5168 list. For example it makes clear that @code{manual} refers to the
5169 transmission rather than, say, the windows or the locking of the car.
5170 It also allows further properties to use the same symbols among their
5171 possible values without becoming ambiguous:
5174 (define car1-properties '((colour . red)
5175 (transmission . manual)
5177 (steering . power-assisted)
5179 (locking . manual)))
5182 With a representation like this, it is easy to use the efficient
5183 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
5184 extract or change individual pieces of information:
5187 (assq-ref car1-properties 'fuel) @result{} unleaded
5188 (assq-ref car1-properties 'transmission) @result{} manual
5190 (assq-set! car1-properties 'seat-colour 'black)
5193 (transmission . manual)
5195 (steering . power-assisted)
5196 (seat-colour . black)
5197 (locking . manual)))
5200 Hash tables also have keys, and exactly the same arguments apply to the
5201 use of symbols in hash tables as in association lists. The hash value
5202 that Guile uses to decide where to add a symbol-keyed entry to a hash
5203 table can be obtained by calling the @code{symbol-hash} procedure:
5205 @deffn {Scheme Procedure} symbol-hash symbol
5206 @deffnx {C Function} scm_symbol_hash (symbol)
5207 Return a hash value for @var{symbol}.
5210 See @ref{Hash Tables} for information about hash tables in general, and
5211 for why you might choose to use a hash table rather than an association
5215 @node Symbol Variables
5216 @subsubsection Symbols as Denoting Variables
5218 When an unquoted symbol in a Scheme program is evaluated, it is
5219 interpreted as a variable reference, and the result of the evaluation is
5220 the appropriate variable's value.
5222 For example, when the expression @code{(string-length "abcd")} is read
5223 and evaluated, the sequence of characters @code{string-length} is read
5224 as the symbol whose name is "string-length". This symbol is associated
5225 with a variable whose value is the procedure that implements string
5226 length calculation. Therefore evaluation of the @code{string-length}
5227 symbol results in that procedure.
5229 The details of the connection between an unquoted symbol and the
5230 variable to which it refers are explained elsewhere. See @ref{Binding
5231 Constructs}, for how associations between symbols and variables are
5232 created, and @ref{Modules}, for how those associations are affected by
5233 Guile's module system.
5236 @node Symbol Primitives
5237 @subsubsection Operations Related to Symbols
5239 Given any Scheme value, you can determine whether it is a symbol using
5240 the @code{symbol?} primitive:
5243 @deffn {Scheme Procedure} symbol? obj
5244 @deffnx {C Function} scm_symbol_p (obj)
5245 Return @code{#t} if @var{obj} is a symbol, otherwise return
5249 @deftypefn {C Function} int scm_is_symbol (SCM val)
5250 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
5253 Once you know that you have a symbol, you can obtain its name as a
5254 string by calling @code{symbol->string}. Note that Guile differs by
5255 default from R5RS on the details of @code{symbol->string} as regards
5258 @rnindex symbol->string
5259 @deffn {Scheme Procedure} symbol->string s
5260 @deffnx {C Function} scm_symbol_to_string (s)
5261 Return the name of symbol @var{s} as a string. By default, Guile reads
5262 symbols case-sensitively, so the string returned will have the same case
5263 variation as the sequence of characters that caused @var{s} to be
5266 If Guile is set to read symbols case-insensitively (as specified by
5267 R5RS), and @var{s} comes into being as part of a literal expression
5268 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
5269 by a call to the @code{read} or @code{string-ci->symbol} procedures,
5270 Guile converts any alphabetic characters in the symbol's name to
5271 lower case before creating the symbol object, so the string returned
5272 here will be in lower case.
5274 If @var{s} was created by @code{string->symbol}, the case of characters
5275 in the string returned will be the same as that in the string that was
5276 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5277 setting at the time @var{s} was created.
5279 It is an error to apply mutation procedures like @code{string-set!} to
5280 strings returned by this procedure.
5283 Most symbols are created by writing them literally in code. However it
5284 is also possible to create symbols programmatically using the following
5287 @deffn {Scheme Procedure} symbol char@dots{}
5289 Return a newly allocated symbol made from the given character arguments.
5292 (symbol #\x #\y #\z) @result{} xyz
5296 @deffn {Scheme Procedure} list->symbol lst
5297 @rnindex list->symbol
5298 Return a newly allocated symbol made from a list of characters.
5301 (list->symbol '(#\a #\b #\c)) @result{} abc
5305 @rnindex symbol-append
5306 @deffn {Scheme Procedure} symbol-append arg @dots{}
5307 Return a newly allocated symbol whose characters form the
5308 concatenation of the given symbols, @var{arg} @enddots{}.
5312 (symbol-append h 'world))
5313 @result{} helloworld
5317 @rnindex string->symbol
5318 @deffn {Scheme Procedure} string->symbol string
5319 @deffnx {C Function} scm_string_to_symbol (string)
5320 Return the symbol whose name is @var{string}. This procedure can create
5321 symbols with names containing special characters or letters in the
5322 non-standard case, but it is usually a bad idea to create such symbols
5323 because in some implementations of Scheme they cannot be read as
5327 @deffn {Scheme Procedure} string-ci->symbol str
5328 @deffnx {C Function} scm_string_ci_to_symbol (str)
5329 Return the symbol whose name is @var{str}. If Guile is currently
5330 reading symbols case-insensitively, @var{str} is converted to lowercase
5331 before the returned symbol is looked up or created.
5334 The following examples illustrate Guile's detailed behaviour as regards
5335 the case-sensitivity of symbols:
5338 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5340 (symbol->string 'flying-fish) @result{} "flying-fish"
5341 (symbol->string 'Martin) @result{} "martin"
5343 (string->symbol "Malvina")) @result{} "Malvina"
5345 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5346 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5347 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5349 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5350 (string=? "K. Harper, M.D."
5352 (string->symbol "K. Harper, M.D."))) @result{} #t
5354 (read-disable 'case-insensitive) ; Guile default behaviour
5356 (symbol->string 'flying-fish) @result{} "flying-fish"
5357 (symbol->string 'Martin) @result{} "Martin"
5359 (string->symbol "Malvina")) @result{} "Malvina"
5361 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5362 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5363 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5365 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5366 (string=? "K. Harper, M.D."
5368 (string->symbol "K. Harper, M.D."))) @result{} #t
5371 From C, there are lower level functions that construct a Scheme symbol
5372 from a C string in the current locale encoding.
5374 When you want to do more from C, you should convert between symbols
5375 and strings using @code{scm_symbol_to_string} and
5376 @code{scm_string_to_symbol} and work with the strings.
5378 @deftypefn {C Function} SCM scm_from_latin1_symbol (const char *name)
5379 @deftypefnx {C Function} SCM scm_from_utf8_symbol (const char *name)
5380 Construct and return a Scheme symbol whose name is specified by the
5381 null-terminated C string @var{name}. These are appropriate when
5382 the C string is hard-coded in the source code.
5385 @deftypefn {C Function} SCM scm_from_locale_symbol (const char *name)
5386 @deftypefnx {C Function} SCM scm_from_locale_symboln (const char *name, size_t len)
5387 Construct and return a Scheme symbol whose name is specified by
5388 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5389 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5390 specified explicitly by @var{len}.
5392 Note that these functions should @emph{not} be used when @var{name} is a
5393 C string constant, because there is no guarantee that the current locale
5394 will match that of the execution character set, used for string and
5395 character constants. Most modern C compilers use UTF-8 by default, so
5396 in such cases we recommend @code{scm_from_utf8_symbol}.
5399 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5400 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5401 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5402 respectively, but also frees @var{str} with @code{free} eventually.
5403 Thus, you can use this function when you would free @var{str} anyway
5404 immediately after creating the Scheme string. In certain cases, Guile
5405 can then use @var{str} directly as its internal representation.
5408 The size of a symbol can also be obtained from C:
5410 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5411 Return the number of characters in @var{sym}.
5414 Finally, some applications, especially those that generate new Scheme
5415 code dynamically, need to generate symbols for use in the generated
5416 code. The @code{gensym} primitive meets this need:
5418 @deffn {Scheme Procedure} gensym [prefix]
5419 @deffnx {C Function} scm_gensym (prefix)
5420 Create a new symbol with a name constructed from a prefix and a counter
5421 value. The string @var{prefix} can be specified as an optional
5422 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5423 at each call. There is no provision for resetting the counter.
5426 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5427 since their names begin with a space and it is only otherwise possible
5428 to generate such symbols if a programmer goes out of their way to do
5429 so. Uniqueness can be guaranteed by instead using uninterned symbols
5430 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5435 @subsubsection Function Slots and Property Lists
5437 In traditional Lisp dialects, symbols are often understood as having
5438 three kinds of value at once:
5442 a @dfn{variable} value, which is used when the symbol appears in
5443 code in a variable reference context
5446 a @dfn{function} value, which is used when the symbol appears in
5447 code in a function name position (i.e.@: as the first element in an
5451 a @dfn{property list} value, which is used when the symbol is given as
5452 the first argument to Lisp's @code{put} or @code{get} functions.
5455 Although Scheme (as one of its simplifications with respect to Lisp)
5456 does away with the distinction between variable and function namespaces,
5457 Guile currently retains some elements of the traditional structure in
5458 case they turn out to be useful when implementing translators for other
5459 languages, in particular Emacs Lisp.
5461 Specifically, Guile symbols have two extra slots, one for a symbol's
5462 property list, and one for its ``function value.'' The following procedures
5463 are provided to access these slots.
5465 @deffn {Scheme Procedure} symbol-fref symbol
5466 @deffnx {C Function} scm_symbol_fref (symbol)
5467 Return the contents of @var{symbol}'s @dfn{function slot}.
5470 @deffn {Scheme Procedure} symbol-fset! symbol value
5471 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5472 Set the contents of @var{symbol}'s function slot to @var{value}.
5475 @deffn {Scheme Procedure} symbol-pref symbol
5476 @deffnx {C Function} scm_symbol_pref (symbol)
5477 Return the @dfn{property list} currently associated with @var{symbol}.
5480 @deffn {Scheme Procedure} symbol-pset! symbol value
5481 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5482 Set @var{symbol}'s property list to @var{value}.
5485 @deffn {Scheme Procedure} symbol-property sym prop
5486 From @var{sym}'s property list, return the value for property
5487 @var{prop}. The assumption is that @var{sym}'s property list is an
5488 association list whose keys are distinguished from each other using
5489 @code{equal?}; @var{prop} should be one of the keys in that list. If
5490 the property list has no entry for @var{prop}, @code{symbol-property}
5494 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5495 In @var{sym}'s property list, set the value for property @var{prop} to
5496 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5497 none already exists. For the structure of the property list, see
5498 @code{symbol-property}.
5501 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5502 From @var{sym}'s property list, remove the entry for property
5503 @var{prop}, if there is one. For the structure of the property list,
5504 see @code{symbol-property}.
5507 Support for these extra slots may be removed in a future release, and it
5508 is probably better to avoid using them. For a more modern and Schemely
5509 approach to properties, see @ref{Object Properties}.
5512 @node Symbol Read Syntax
5513 @subsubsection Extended Read Syntax for Symbols
5515 The read syntax for a symbol is a sequence of letters, digits, and
5516 @dfn{extended alphabetic characters}, beginning with a character that
5517 cannot begin a number. In addition, the special cases of @code{+},
5518 @code{-}, and @code{...} are read as symbols even though numbers can
5519 begin with @code{+}, @code{-} or @code{.}.
5521 Extended alphabetic characters may be used within identifiers as if
5522 they were letters. The set of extended alphabetic characters is:
5525 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5528 In addition to the standard read syntax defined above (which is taken
5529 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5530 Scheme})), Guile provides an extended symbol read syntax that allows the
5531 inclusion of unusual characters such as space characters, newlines and
5532 parentheses. If (for whatever reason) you need to write a symbol
5533 containing characters not mentioned above, you can do so as follows.
5537 Begin the symbol with the characters @code{#@{},
5540 write the characters of the symbol and
5543 finish the symbol with the characters @code{@}#}.
5546 Here are a few examples of this form of read syntax. The first symbol
5547 needs to use extended syntax because it contains a space character, the
5548 second because it contains a line break, and the last because it looks
5560 Although Guile provides this extended read syntax for symbols,
5561 widespread usage of it is discouraged because it is not portable and not
5565 @node Symbol Uninterned
5566 @subsubsection Uninterned Symbols
5568 What makes symbols useful is that they are automatically kept unique.
5569 There are no two symbols that are distinct objects but have the same
5570 name. But of course, there is no rule without exception. In addition
5571 to the normal symbols that have been discussed up to now, you can also
5572 create special @dfn{uninterned} symbols that behave slightly
5575 To understand what is different about them and why they might be useful,
5576 we look at how normal symbols are actually kept unique.
5578 Whenever Guile wants to find the symbol with a specific name, for
5579 example during @code{read} or when executing @code{string->symbol}, it
5580 first looks into a table of all existing symbols to find out whether a
5581 symbol with the given name already exists. When this is the case, Guile
5582 just returns that symbol. When not, a new symbol with the name is
5583 created and entered into the table so that it can be found later.
5585 Sometimes you might want to create a symbol that is guaranteed `fresh',
5586 i.e.@: a symbol that did not exist previously. You might also want to
5587 somehow guarantee that no one else will ever unintentionally stumble
5588 across your symbol in the future. These properties of a symbol are
5589 often needed when generating code during macro expansion. When
5590 introducing new temporary variables, you want to guarantee that they
5591 don't conflict with variables in other people's code.
5593 The simplest way to arrange for this is to create a new symbol but
5594 not enter it into the global table of all symbols. That way, no one
5595 will ever get access to your symbol by chance. Symbols that are not in
5596 the table are called @dfn{uninterned}. Of course, symbols that
5597 @emph{are} in the table are called @dfn{interned}.
5599 You create new uninterned symbols with the function @code{make-symbol}.
5600 You can test whether a symbol is interned or not with
5601 @code{symbol-interned?}.
5603 Uninterned symbols break the rule that the name of a symbol uniquely
5604 identifies the symbol object. Because of this, they can not be written
5605 out and read back in like interned symbols. Currently, Guile has no
5606 support for reading uninterned symbols. Note that the function
5607 @code{gensym} does not return uninterned symbols for this reason.
5609 @deffn {Scheme Procedure} make-symbol name
5610 @deffnx {C Function} scm_make_symbol (name)
5611 Return a new uninterned symbol with the name @var{name}. The returned
5612 symbol is guaranteed to be unique and future calls to
5613 @code{string->symbol} will not return it.
5616 @deffn {Scheme Procedure} symbol-interned? symbol
5617 @deffnx {C Function} scm_symbol_interned_p (symbol)
5618 Return @code{#t} if @var{symbol} is interned, otherwise return
5625 (define foo-1 (string->symbol "foo"))
5626 (define foo-2 (string->symbol "foo"))
5627 (define foo-3 (make-symbol "foo"))
5628 (define foo-4 (make-symbol "foo"))
5632 ; Two interned symbols with the same name are the same object,
5636 ; but a call to make-symbol with the same name returns a
5641 ; A call to make-symbol always returns a new object, even for
5645 @result{} #<uninterned-symbol foo 8085290>
5646 ; Uninterned symbols print differently from interned symbols,
5650 ; but they are still symbols,
5652 (symbol-interned? foo-3)
5654 ; just not interned.
5659 @subsection Keywords
5662 Keywords are self-evaluating objects with a convenient read syntax that
5663 makes them easy to type.
5665 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5666 syntax extension to permit keywords to begin with @code{:} as well as
5667 @code{#:}, or to end with @code{:}.
5670 * Why Use Keywords?:: Motivation for keyword usage.
5671 * Coding With Keywords:: How to use keywords.
5672 * Keyword Read Syntax:: Read syntax for keywords.
5673 * Keyword Procedures:: Procedures for dealing with keywords.
5676 @node Why Use Keywords?
5677 @subsubsection Why Use Keywords?
5679 Keywords are useful in contexts where a program or procedure wants to be
5680 able to accept a large number of optional arguments without making its
5681 interface unmanageable.
5683 To illustrate this, consider a hypothetical @code{make-window}
5684 procedure, which creates a new window on the screen for drawing into
5685 using some graphical toolkit. There are many parameters that the caller
5686 might like to specify, but which could also be sensibly defaulted, for
5691 color depth -- Default: the color depth for the screen
5694 background color -- Default: white
5697 width -- Default: 600
5700 height -- Default: 400
5703 If @code{make-window} did not use keywords, the caller would have to
5704 pass in a value for each possible argument, remembering the correct
5705 argument order and using a special value to indicate the default value
5709 (make-window 'default ;; Color depth
5710 'default ;; Background color
5713 @dots{}) ;; More make-window arguments
5716 With keywords, on the other hand, defaulted arguments are omitted, and
5717 non-default arguments are clearly tagged by the appropriate keyword. As
5718 a result, the invocation becomes much clearer:
5721 (make-window #:width 800 #:height 100)
5724 On the other hand, for a simpler procedure with few arguments, the use
5725 of keywords would be a hindrance rather than a help. The primitive
5726 procedure @code{cons}, for example, would not be improved if it had to
5730 (cons #:car x #:cdr y)
5733 So the decision whether to use keywords or not is purely pragmatic: use
5734 them if they will clarify the procedure invocation at point of call.
5736 @node Coding With Keywords
5737 @subsubsection Coding With Keywords
5739 If a procedure wants to support keywords, it should take a rest argument
5740 and then use whatever means is convenient to extract keywords and their
5741 corresponding arguments from the contents of that rest argument.
5743 The following example illustrates the principle: the code for
5744 @code{make-window} uses a helper procedure called
5745 @code{get-keyword-value} to extract individual keyword arguments from
5749 (define (get-keyword-value args keyword default)
5750 (let ((kv (memq keyword args)))
5751 (if (and kv (>= (length kv) 2))
5755 (define (make-window . args)
5756 (let ((depth (get-keyword-value args #:depth screen-depth))
5757 (bg (get-keyword-value args #:bg "white"))
5758 (width (get-keyword-value args #:width 800))
5759 (height (get-keyword-value args #:height 100))
5764 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5765 optargs)} module provides a set of powerful macros that you can use to
5766 implement keyword-supporting procedures like this:
5769 (use-modules (ice-9 optargs))
5771 (define (make-window . args)
5772 (let-keywords args #f ((depth screen-depth)
5780 Or, even more economically, like this:
5783 (use-modules (ice-9 optargs))
5785 (define* (make-window #:key (depth screen-depth)
5792 For further details on @code{let-keywords}, @code{define*} and other
5793 facilities provided by the @code{(ice-9 optargs)} module, see
5794 @ref{Optional Arguments}.
5796 To handle keyword arguments from procedures implemented in C,
5797 use @code{scm_c_bind_keyword_arguments} (@pxref{Keyword Procedures}).
5799 @node Keyword Read Syntax
5800 @subsubsection Keyword Read Syntax
5802 Guile, by default, only recognizes a keyword syntax that is compatible
5803 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5804 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5805 external representation of the keyword named @code{NAME}. Keyword
5806 objects print using this syntax as well, so values containing keyword
5807 objects can be read back into Guile. When used in an expression,
5808 keywords are self-quoting objects.
5810 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5811 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5812 of the form @code{:NAME} are read as symbols, as required by R5RS.
5814 @cindex SRFI-88 keyword syntax
5816 If the @code{keyword} read option is set to @code{'postfix}, Guile
5817 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5818 Otherwise, tokens of this form are read as symbols.
5820 To enable and disable the alternative non-R5RS keyword syntax, you use
5821 the @code{read-set!} procedure documented @ref{Scheme Read}. Note that
5822 the @code{prefix} and @code{postfix} syntax are mutually exclusive.
5825 (read-set! keywords 'prefix)
5835 (read-set! keywords 'postfix)
5845 (read-set! keywords #f)
5853 ERROR: In expression :type:
5854 ERROR: Unbound variable: :type
5855 ABORT: (unbound-variable)
5858 @node Keyword Procedures
5859 @subsubsection Keyword Procedures
5861 @deffn {Scheme Procedure} keyword? obj
5862 @deffnx {C Function} scm_keyword_p (obj)
5863 Return @code{#t} if the argument @var{obj} is a keyword, else
5867 @deffn {Scheme Procedure} keyword->symbol keyword
5868 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5869 Return the symbol with the same name as @var{keyword}.
5872 @deffn {Scheme Procedure} symbol->keyword symbol
5873 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5874 Return the keyword with the same name as @var{symbol}.
5877 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5878 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5881 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *name)
5882 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *name, size_t len)
5883 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5884 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5885 (@var{name}, @var{len}))}, respectively.
5887 Note that these functions should @emph{not} be used when @var{name} is a
5888 C string constant, because there is no guarantee that the current locale
5889 will match that of the execution character set, used for string and
5890 character constants. Most modern C compilers use UTF-8 by default, so
5891 in such cases we recommend @code{scm_from_utf8_keyword}.
5894 @deftypefn {C Function} SCM scm_from_latin1_keyword (const char *name)
5895 @deftypefnx {C Function} SCM scm_from_utf8_keyword (const char *name)
5896 Equivalent to @code{scm_symbol_to_keyword (scm_from_latin1_symbol
5897 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_utf8_symbol
5898 (@var{name}))}, respectively.
5901 @deftypefn {C Function} void scm_c_bind_keyword_arguments (const char *subr, @
5902 SCM rest, scm_t_keyword_arguments_flags flags, @
5903 SCM keyword1, SCM *argp1, @
5905 SCM keywordN, SCM *argpN, @
5906 @nicode{SCM_UNDEFINED})
5908 Extract the specified keyword arguments from @var{rest}, which is not
5909 modified. If the keyword argument @var{keyword1} is present in
5910 @var{rest} with an associated value, that value is stored in the
5911 variable pointed to by @var{argp1}, otherwise the variable is left
5912 unchanged. Similarly for the other keywords and argument pointers up to
5913 @var{keywordN} and @var{argpN}. The argument list to
5914 @code{scm_c_bind_keyword_arguments} must be terminated by
5915 @code{SCM_UNDEFINED}.
5917 Note that since the variables pointed to by @var{argp1} through
5918 @var{argpN} are left unchanged if the associated keyword argument is not
5919 present, they should be initialized to their default values before
5920 calling @code{scm_c_bind_keyword_arguments}. Alternatively, you can
5921 initialize them to @code{SCM_UNDEFINED} before the call, and then use
5922 @code{SCM_UNBNDP} after the call to see which ones were provided.
5924 If an unrecognized keyword argument is present in @var{rest} and
5925 @var{flags} does not contain @code{SCM_ALLOW_OTHER_KEYS}, or if
5926 non-keyword arguments are present and @var{flags} does not contain
5927 @code{SCM_ALLOW_NON_KEYWORD_ARGUMENTS}, an exception is raised.
5928 @var{subr} should be the name of the procedure receiving the keyword
5929 arguments, for purposes of error reporting.
5938 SCM my_string_join (SCM strings, SCM rest)
5940 SCM delimiter = SCM_UNDEFINED;
5941 SCM grammar = sym_infix;
5943 scm_c_bind_keyword_arguments ("my-string-join", rest, 0,
5944 k_delimiter, &delimiter,
5945 k_grammar, &grammar,
5948 if (SCM_UNBNDP (delimiter))
5949 delimiter = scm_from_utf8_string (" ");
5951 return scm_string_join (strings, delimiter, grammar);
5956 k_delimiter = scm_from_utf8_keyword ("delimiter");
5957 k_grammar = scm_from_utf8_keyword ("grammar");
5958 sym_infix = scm_from_utf8_symbol ("infix");
5959 scm_c_define_gsubr ("my-string-join", 1, 0, 1, my_string_join);
5966 @subsection ``Functionality-Centric'' Data Types
5968 Procedures and macros are documented in their own sections: see
5969 @ref{Procedures} and @ref{Macros}.
5971 Variable objects are documented as part of the description of Guile's
5972 module system: see @ref{Variables}.
5974 Asyncs, dynamic roots and fluids are described in the section on
5975 scheduling: see @ref{Scheduling}.
5977 Hooks are documented in the section on general utility functions: see
5980 Ports are described in the section on I/O: see @ref{Input and Output}.
5982 Regular expressions are described in their own section: see @ref{Regular
5986 @c TeX-master: "guile.texi"