2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011
4 @c 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} (@pxref{if
82 cond case}), where a group of subexpressions will be evaluated only if a
83 @var{condition} expression evaluates to ``true'', ``true'' means any
84 value at all except @code{#f}.
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_int8 scm_to_int8 (SCM x)
418 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
419 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
420 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
421 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
422 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
423 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
424 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
425 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
426 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
427 When @var{x} represents an exact integer that fits into the indicated
428 C type, return that integer. Else signal an error, either a
429 `wrong-type' error when @var{x} is not an exact integer, or an
430 `out-of-range' error when it doesn't fit the given range.
432 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
433 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
434 the corresponding types are.
437 @deftypefn {C Function} SCM scm_from_char (char x)
438 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
439 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
440 @deftypefnx {C Function} SCM scm_from_short (short x)
441 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
442 @deftypefnx {C Function} SCM scm_from_int (int x)
443 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
444 @deftypefnx {C Function} SCM scm_from_long (long x)
445 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
446 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
447 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
448 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
449 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
450 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
451 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
452 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
453 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
454 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
455 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
456 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
457 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
458 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
459 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
460 Return the @code{SCM} value that represents the integer @var{x}.
461 These functions will always succeed and will always return an exact
465 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
466 Assign @var{val} to the multiple precision integer @var{rop}.
467 @var{val} must be an exact integer, otherwise an error will be
468 signalled. @var{rop} must have been initialized with @code{mpz_init}
469 before this function is called. When @var{rop} is no longer needed
470 the occupied space must be freed with @code{mpz_clear}.
471 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
474 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
475 Return the @code{SCM} value that represents @var{val}.
478 @node Reals and Rationals
479 @subsubsection Real and Rational Numbers
480 @tpindex Real numbers
481 @tpindex Rational numbers
486 Mathematically, the real numbers are the set of numbers that describe
487 all possible points along a continuous, infinite, one-dimensional line.
488 The rational numbers are the set of all numbers that can be written as
489 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
490 All rational numbers are also real, but there are real numbers that
491 are not rational, for example @m{\sqrt{2}, the square root of 2}, and
494 Guile can represent both exact and inexact rational numbers, but it
495 cannot represent precise finite irrational numbers. Exact rationals are
496 represented by storing the numerator and denominator as two exact
497 integers. Inexact rationals are stored as floating point numbers using
498 the C type @code{double}.
500 Exact rationals are written as a fraction of integers. There must be
501 no whitespace around the slash:
508 Even though the actual encoding of inexact rationals is in binary, it
509 may be helpful to think of it as a decimal number with a limited
510 number of significant figures and a decimal point somewhere, since
511 this corresponds to the standard notation for non-whole numbers. For
517 -5648394822220000000000.0
521 The limited precision of Guile's encoding means that any finite ``real''
522 number in Guile can be written in a rational form, by multiplying and
523 then dividing by sufficient powers of 10 (or in fact, 2). For example,
524 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided
525 by 100000000000000000. In Guile's current incarnation, therefore, the
526 @code{rational?} and @code{real?} predicates are equivalent for finite
530 Dividing by an exact zero leads to a error message, as one might expect.
531 However, dividing by an inexact zero does not produce an error.
532 Instead, the result of the division is either plus or minus infinity,
533 depending on the sign of the divided number and the sign of the zero
534 divisor (some platforms support signed zeroes @samp{-0.0} and
535 @samp{+0.0}; @samp{0.0} is the same as @samp{+0.0}).
537 Dividing zero by an inexact zero yields a @acronym{NaN} (`not a number')
538 value, although they are actually considered numbers by Scheme.
539 Attempts to compare a @acronym{NaN} value with any number (including
540 itself) using @code{=}, @code{<}, @code{>}, @code{<=} or @code{>=}
541 always returns @code{#f}. Although a @acronym{NaN} value is not
542 @code{=} to itself, it is both @code{eqv?} and @code{equal?} to itself
543 and other @acronym{NaN} values. However, the preferred way to test for
544 them is by using @code{nan?}.
546 The real @acronym{NaN} values and infinities are written @samp{+nan.0},
547 @samp{+inf.0} and @samp{-inf.0}. This syntax is also recognized by
548 @code{read} as an extension to the usual Scheme syntax. These special
549 values are considered by Scheme to be inexact real numbers but not
550 rational. Note that non-real complex numbers may also contain
551 infinities or @acronym{NaN} values in their real or imaginary parts. To
552 test a real number to see if it is infinite, a @acronym{NaN} value, or
553 neither, use @code{inf?}, @code{nan?}, or @code{finite?}, respectively.
554 Every real number in Scheme belongs to precisely one of those three
557 On platforms that follow @acronym{IEEE} 754 for their floating point
558 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
559 are implemented using the corresponding @acronym{IEEE} 754 values.
560 They behave in arithmetic operations like @acronym{IEEE} 754 describes
561 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
563 @deffn {Scheme Procedure} real? obj
564 @deffnx {C Function} scm_real_p (obj)
565 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
566 that the sets of integer and rational values form subsets of the set
567 of real numbers, so the predicate will also be fulfilled if @var{obj}
568 is an integer number or a rational number.
571 @deffn {Scheme Procedure} rational? x
572 @deffnx {C Function} scm_rational_p (x)
573 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
574 Note that the set of integer values forms a subset of the set of
575 rational numbers, i.e.@: the predicate will also be fulfilled if
576 @var{x} is an integer number.
579 @deffn {Scheme Procedure} rationalize x eps
580 @deffnx {C Function} scm_rationalize (x, eps)
581 Returns the @emph{simplest} rational number differing
582 from @var{x} by no more than @var{eps}.
584 As required by @acronym{R5RS}, @code{rationalize} only returns an
585 exact result when both its arguments are exact. Thus, you might need
586 to use @code{inexact->exact} on the arguments.
589 (rationalize (inexact->exact 1.2) 1/100)
595 @deffn {Scheme Procedure} inf? x
596 @deffnx {C Function} scm_inf_p (x)
597 Return @code{#t} if the real number @var{x} is @samp{+inf.0} or
598 @samp{-inf.0}. Otherwise return @code{#f}.
601 @deffn {Scheme Procedure} nan? x
602 @deffnx {C Function} scm_nan_p (x)
603 Return @code{#t} if the real number @var{x} is @samp{+nan.0}, or
607 @deffn {Scheme Procedure} finite? x
608 @deffnx {C Function} scm_finite_p (x)
609 Return @code{#t} if the real number @var{x} is neither infinite nor a
610 NaN, @code{#f} otherwise.
613 @deffn {Scheme Procedure} nan
614 @deffnx {C Function} scm_nan ()
615 Return @samp{+nan.0}, a @acronym{NaN} value.
618 @deffn {Scheme Procedure} inf
619 @deffnx {C Function} scm_inf ()
620 Return @samp{+inf.0}, positive infinity.
623 @deffn {Scheme Procedure} numerator x
624 @deffnx {C Function} scm_numerator (x)
625 Return the numerator of the rational number @var{x}.
628 @deffn {Scheme Procedure} denominator x
629 @deffnx {C Function} scm_denominator (x)
630 Return the denominator of the rational number @var{x}.
633 @deftypefn {C Function} int scm_is_real (SCM val)
634 @deftypefnx {C Function} int scm_is_rational (SCM val)
635 Equivalent to @code{scm_is_true (scm_real_p (val))} and
636 @code{scm_is_true (scm_rational_p (val))}, respectively.
639 @deftypefn {C Function} double scm_to_double (SCM val)
640 Returns the number closest to @var{val} that is representable as a
641 @code{double}. Returns infinity for a @var{val} that is too large in
642 magnitude. The argument @var{val} must be a real number.
645 @deftypefn {C Function} SCM scm_from_double (double val)
646 Return the @code{SCM} value that represents @var{val}. The returned
647 value is inexact according to the predicate @code{inexact?}, but it
648 will be exactly equal to @var{val}.
651 @node Complex Numbers
652 @subsubsection Complex Numbers
653 @tpindex Complex numbers
657 Complex numbers are the set of numbers that describe all possible points
658 in a two-dimensional space. The two coordinates of a particular point
659 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
660 the complex number that describes that point.
662 In Guile, complex numbers are written in rectangular form as the sum of
663 their real and imaginary parts, using the symbol @code{i} to indicate
678 Polar form can also be used, with an @samp{@@} between magnitude and
682 1@@3.141592 @result{} -1.0 (approx)
683 -1@@1.57079 @result{} 0.0-1.0i (approx)
686 Guile represents a complex number as a pair of inexact reals, so the
687 real and imaginary parts of a complex number have the same properties of
688 inexactness and limited precision as single inexact real numbers.
690 Note that each part of a complex number may contain any inexact real
691 value, including the special values @samp{+nan.0}, @samp{+inf.0} and
692 @samp{-inf.0}, as well as either of the signed zeroes @samp{0.0} or
696 @deffn {Scheme Procedure} complex? z
697 @deffnx {C Function} scm_complex_p (z)
698 Return @code{#t} if @var{x} is a complex number, @code{#f}
699 otherwise. Note that the sets of real, rational and integer
700 values form subsets of the set of complex numbers, i.e.@: the
701 predicate will also be fulfilled if @var{x} is a real,
702 rational or integer number.
705 @deftypefn {C Function} int scm_is_complex (SCM val)
706 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
710 @subsubsection Exact and Inexact Numbers
711 @tpindex Exact numbers
712 @tpindex Inexact numbers
716 @rnindex exact->inexact
717 @rnindex inexact->exact
719 R5RS requires that, with few exceptions, a calculation involving inexact
720 numbers always produces an inexact result. To meet this requirement,
721 Guile distinguishes between an exact integer value such as @samp{5} and
722 the corresponding inexact integer value which, to the limited precision
723 available, has no fractional part, and is printed as @samp{5.0}. Guile
724 will only convert the latter value to the former when forced to do so by
725 an invocation of the @code{inexact->exact} procedure.
727 The only exception to the above requirement is when the values of the
728 inexact numbers do not affect the result. For example @code{(expt n 0)}
729 is @samp{1} for any value of @code{n}, therefore @code{(expt 5.0 0)} is
730 permitted to return an exact @samp{1}.
732 @deffn {Scheme Procedure} exact? z
733 @deffnx {C Function} scm_exact_p (z)
734 Return @code{#t} if the number @var{z} is exact, @code{#f}
750 @deftypefn {C Function} int scm_is_exact (SCM z)
751 Return a @code{1} if the number @var{z} is exact, and @code{0}
752 otherwise. This is equivalent to @code{scm_is_true (scm_exact_p (z))}.
754 An alternate approch to testing the exactness of a number is to
755 use @code{scm_is_signed_integer} or @code{scm_is_unsigned_integer}.
758 @deffn {Scheme Procedure} inexact? z
759 @deffnx {C Function} scm_inexact_p (z)
760 Return @code{#t} if the number @var{z} is inexact, @code{#f}
764 @deftypefn {C Function} int scm_is_inexact (SCM z)
765 Return a @code{1} if the number @var{z} is inexact, and @code{0}
766 otherwise. This is equivalent to @code{scm_is_true (scm_inexact_p (z))}.
769 @deffn {Scheme Procedure} inexact->exact z
770 @deffnx {C Function} scm_inexact_to_exact (z)
771 Return an exact number that is numerically closest to @var{z}, when
772 there is one. For inexact rationals, Guile returns the exact rational
773 that is numerically equal to the inexact rational. Inexact complex
774 numbers with a non-zero imaginary part can not be made exact.
781 The following happens because 12/10 is not exactly representable as a
782 @code{double} (on most platforms). However, when reading a decimal
783 number that has been marked exact with the ``#e'' prefix, Guile is
784 able to represent it correctly.
788 @result{} 5404319552844595/4503599627370496
796 @c begin (texi-doc-string "guile" "exact->inexact")
797 @deffn {Scheme Procedure} exact->inexact z
798 @deffnx {C Function} scm_exact_to_inexact (z)
799 Convert the number @var{z} to its inexact representation.
804 @subsubsection Read Syntax for Numerical Data
806 The read syntax for integers is a string of digits, optionally
807 preceded by a minus or plus character, a code indicating the
808 base in which the integer is encoded, and a code indicating whether
809 the number is exact or inexact. The supported base codes are:
814 the integer is written in binary (base 2)
818 the integer is written in octal (base 8)
822 the integer is written in decimal (base 10)
826 the integer is written in hexadecimal (base 16)
829 If the base code is omitted, the integer is assumed to be decimal. The
830 following examples show how these base codes are used.
849 The codes for indicating exactness (which can, incidentally, be applied
850 to all numerical values) are:
859 the number is inexact.
862 If the exactness indicator is omitted, the number is exact unless it
863 contains a radix point. Since Guile can not represent exact complex
864 numbers, an error is signalled when asking for them.
874 ERROR: Wrong type argument
877 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
878 plus and minus infinity, respectively. The value must be written
879 exactly as shown, that is, they always must have a sign and exactly
880 one zero digit after the decimal point. It also understands
881 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
882 The sign is ignored for `not-a-number' and the value is always printed
885 @node Integer Operations
886 @subsubsection Operations on Integer Values
895 @deffn {Scheme Procedure} odd? n
896 @deffnx {C Function} scm_odd_p (n)
897 Return @code{#t} if @var{n} is an odd number, @code{#f}
901 @deffn {Scheme Procedure} even? n
902 @deffnx {C Function} scm_even_p (n)
903 Return @code{#t} if @var{n} is an even number, @code{#f}
907 @c begin (texi-doc-string "guile" "quotient")
908 @c begin (texi-doc-string "guile" "remainder")
909 @deffn {Scheme Procedure} quotient n d
910 @deffnx {Scheme Procedure} remainder n d
911 @deffnx {C Function} scm_quotient (n, d)
912 @deffnx {C Function} scm_remainder (n, d)
913 Return the quotient or remainder from @var{n} divided by @var{d}. The
914 quotient is rounded towards zero, and the remainder will have the same
915 sign as @var{n}. In all cases quotient and remainder satisfy
916 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
919 (remainder 13 4) @result{} 1
920 (remainder -13 4) @result{} -1
923 See also @code{truncate-quotient}, @code{truncate-remainder} and
924 related operations in @ref{Arithmetic}.
927 @c begin (texi-doc-string "guile" "modulo")
928 @deffn {Scheme Procedure} modulo n d
929 @deffnx {C Function} scm_modulo (n, d)
930 Return the remainder from @var{n} divided by @var{d}, with the same
934 (modulo 13 4) @result{} 1
935 (modulo -13 4) @result{} 3
936 (modulo 13 -4) @result{} -3
937 (modulo -13 -4) @result{} -1
940 See also @code{floor-quotient}, @code{floor-remainder} and
941 related operations in @ref{Arithmetic}.
944 @c begin (texi-doc-string "guile" "gcd")
945 @deffn {Scheme Procedure} gcd x@dots{}
946 @deffnx {C Function} scm_gcd (x, y)
947 Return the greatest common divisor of all arguments.
948 If called without arguments, 0 is returned.
950 The C function @code{scm_gcd} always takes two arguments, while the
951 Scheme function can take an arbitrary number.
954 @c begin (texi-doc-string "guile" "lcm")
955 @deffn {Scheme Procedure} lcm x@dots{}
956 @deffnx {C Function} scm_lcm (x, y)
957 Return the least common multiple of the arguments.
958 If called without arguments, 1 is returned.
960 The C function @code{scm_lcm} always takes two arguments, while the
961 Scheme function can take an arbitrary number.
964 @deffn {Scheme Procedure} modulo-expt n k m
965 @deffnx {C Function} scm_modulo_expt (n, k, m)
966 Return @var{n} raised to the integer exponent
967 @var{k}, modulo @var{m}.
975 @deftypefn {Scheme Procedure} {} exact-integer-sqrt @var{k}
976 @deftypefnx {C Function} void scm_exact_integer_sqrt (SCM @var{k}, SCM *@var{s}, SCM *@var{r})
977 Return two exact non-negative integers @var{s} and @var{r}
978 such that @math{@var{k} = @var{s}^2 + @var{r}} and
979 @math{@var{s}^2 <= @var{k} < (@var{s} + 1)^2}.
980 An error is raised if @var{k} is not an exact non-negative integer.
983 (exact-integer-sqrt 10) @result{} 3 and 1
988 @subsubsection Comparison Predicates
993 The C comparison functions below always takes two arguments, while the
994 Scheme functions can take an arbitrary number. Also keep in mind that
995 the C functions return one of the Scheme boolean values
996 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
997 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
998 y))} when testing the two Scheme numbers @code{x} and @code{y} for
999 equality, for example.
1001 @c begin (texi-doc-string "guile" "=")
1002 @deffn {Scheme Procedure} =
1003 @deffnx {C Function} scm_num_eq_p (x, y)
1004 Return @code{#t} if all parameters are numerically equal.
1007 @c begin (texi-doc-string "guile" "<")
1008 @deffn {Scheme Procedure} <
1009 @deffnx {C Function} scm_less_p (x, y)
1010 Return @code{#t} if the list of parameters is monotonically
1014 @c begin (texi-doc-string "guile" ">")
1015 @deffn {Scheme Procedure} >
1016 @deffnx {C Function} scm_gr_p (x, y)
1017 Return @code{#t} if the list of parameters is monotonically
1021 @c begin (texi-doc-string "guile" "<=")
1022 @deffn {Scheme Procedure} <=
1023 @deffnx {C Function} scm_leq_p (x, y)
1024 Return @code{#t} if the list of parameters is monotonically
1028 @c begin (texi-doc-string "guile" ">=")
1029 @deffn {Scheme Procedure} >=
1030 @deffnx {C Function} scm_geq_p (x, y)
1031 Return @code{#t} if the list of parameters is monotonically
1035 @c begin (texi-doc-string "guile" "zero?")
1036 @deffn {Scheme Procedure} zero? z
1037 @deffnx {C Function} scm_zero_p (z)
1038 Return @code{#t} if @var{z} is an exact or inexact number equal to
1042 @c begin (texi-doc-string "guile" "positive?")
1043 @deffn {Scheme Procedure} positive? x
1044 @deffnx {C Function} scm_positive_p (x)
1045 Return @code{#t} if @var{x} is an exact or inexact number greater than
1049 @c begin (texi-doc-string "guile" "negative?")
1050 @deffn {Scheme Procedure} negative? x
1051 @deffnx {C Function} scm_negative_p (x)
1052 Return @code{#t} if @var{x} is an exact or inexact number less than
1058 @subsubsection Converting Numbers To and From Strings
1059 @rnindex number->string
1060 @rnindex string->number
1062 The following procedures read and write numbers according to their
1063 external representation as defined by R5RS (@pxref{Lexical structure,
1064 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1065 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1066 i18n)} module}, for locale-dependent number parsing.
1068 @deffn {Scheme Procedure} number->string n [radix]
1069 @deffnx {C Function} scm_number_to_string (n, radix)
1070 Return a string holding the external representation of the
1071 number @var{n} in the given @var{radix}. If @var{n} is
1072 inexact, a radix of 10 will be used.
1075 @deffn {Scheme Procedure} string->number string [radix]
1076 @deffnx {C Function} scm_string_to_number (string, radix)
1077 Return a number of the maximally precise representation
1078 expressed by the given @var{string}. @var{radix} must be an
1079 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1080 is a default radix that may be overridden by an explicit radix
1081 prefix in @var{string} (e.g.@: "#o177"). If @var{radix} is not
1082 supplied, then the default radix is 10. If string is not a
1083 syntactically valid notation for a number, then
1084 @code{string->number} returns @code{#f}.
1087 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1088 As per @code{string->number} above, but taking a C string, as pointer
1089 and length. The string characters should be in the current locale
1090 encoding (@code{locale} in the name refers only to that, there's no
1091 locale-dependent parsing).
1096 @subsubsection Complex Number Operations
1097 @rnindex make-rectangular
1104 @deffn {Scheme Procedure} make-rectangular real_part imaginary_part
1105 @deffnx {C Function} scm_make_rectangular (real_part, imaginary_part)
1106 Return a complex number constructed of the given @var{real-part} and @var{imaginary-part} parts.
1109 @deffn {Scheme Procedure} make-polar mag ang
1110 @deffnx {C Function} scm_make_polar (mag, ang)
1112 Return the complex number @var{mag} * e^(i * @var{ang}).
1115 @c begin (texi-doc-string "guile" "real-part")
1116 @deffn {Scheme Procedure} real-part z
1117 @deffnx {C Function} scm_real_part (z)
1118 Return the real part of the number @var{z}.
1121 @c begin (texi-doc-string "guile" "imag-part")
1122 @deffn {Scheme Procedure} imag-part z
1123 @deffnx {C Function} scm_imag_part (z)
1124 Return the imaginary part of the number @var{z}.
1127 @c begin (texi-doc-string "guile" "magnitude")
1128 @deffn {Scheme Procedure} magnitude z
1129 @deffnx {C Function} scm_magnitude (z)
1130 Return the magnitude of the number @var{z}. This is the same as
1131 @code{abs} for real arguments, but also allows complex numbers.
1134 @c begin (texi-doc-string "guile" "angle")
1135 @deffn {Scheme Procedure} angle z
1136 @deffnx {C Function} scm_angle (z)
1137 Return the angle of the complex number @var{z}.
1140 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1141 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1142 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1143 respectively, but these functions take @code{double}s as their
1147 @deftypefn {C Function} double scm_c_real_part (z)
1148 @deftypefnx {C Function} double scm_c_imag_part (z)
1149 Returns the real or imaginary part of @var{z} as a @code{double}.
1152 @deftypefn {C Function} double scm_c_magnitude (z)
1153 @deftypefnx {C Function} double scm_c_angle (z)
1154 Returns the magnitude or angle of @var{z} as a @code{double}.
1159 @subsubsection Arithmetic Functions
1174 @rnindex euclidean-quotient
1175 @rnindex euclidean-remainder
1177 @rnindex floor-quotient
1178 @rnindex floor-remainder
1180 @rnindex ceiling-quotient
1181 @rnindex ceiling-remainder
1183 @rnindex truncate-quotient
1184 @rnindex truncate-remainder
1186 @rnindex centered-quotient
1187 @rnindex centered-remainder
1189 @rnindex round-quotient
1190 @rnindex round-remainder
1192 The C arithmetic functions below always takes two arguments, while the
1193 Scheme functions can take an arbitrary number. When you need to
1194 invoke them with just one argument, for example to compute the
1195 equivalent of @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1196 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1198 @c begin (texi-doc-string "guile" "+")
1199 @deffn {Scheme Procedure} + z1 @dots{}
1200 @deffnx {C Function} scm_sum (z1, z2)
1201 Return the sum of all parameter values. Return 0 if called without any
1205 @c begin (texi-doc-string "guile" "-")
1206 @deffn {Scheme Procedure} - z1 z2 @dots{}
1207 @deffnx {C Function} scm_difference (z1, z2)
1208 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1209 the sum of all but the first argument are subtracted from the first
1213 @c begin (texi-doc-string "guile" "*")
1214 @deffn {Scheme Procedure} * z1 @dots{}
1215 @deffnx {C Function} scm_product (z1, z2)
1216 Return the product of all arguments. If called without arguments, 1 is
1220 @c begin (texi-doc-string "guile" "/")
1221 @deffn {Scheme Procedure} / z1 z2 @dots{}
1222 @deffnx {C Function} scm_divide (z1, z2)
1223 Divide the first argument by the product of the remaining arguments. If
1224 called with one argument @var{z1}, 1/@var{z1} is returned.
1227 @deffn {Scheme Procedure} 1+ z
1228 @deffnx {C Function} scm_oneplus (z)
1229 Return @math{@var{z} + 1}.
1232 @deffn {Scheme Procedure} 1- z
1233 @deffnx {C function} scm_oneminus (z)
1234 Return @math{@var{z} - 1}.
1237 @c begin (texi-doc-string "guile" "abs")
1238 @deffn {Scheme Procedure} abs x
1239 @deffnx {C Function} scm_abs (x)
1240 Return the absolute value of @var{x}.
1242 @var{x} must be a number with zero imaginary part. To calculate the
1243 magnitude of a complex number, use @code{magnitude} instead.
1246 @c begin (texi-doc-string "guile" "max")
1247 @deffn {Scheme Procedure} max x1 x2 @dots{}
1248 @deffnx {C Function} scm_max (x1, x2)
1249 Return the maximum of all parameter values.
1252 @c begin (texi-doc-string "guile" "min")
1253 @deffn {Scheme Procedure} min x1 x2 @dots{}
1254 @deffnx {C Function} scm_min (x1, x2)
1255 Return the minimum of all parameter values.
1258 @c begin (texi-doc-string "guile" "truncate")
1259 @deffn {Scheme Procedure} truncate x
1260 @deffnx {C Function} scm_truncate_number (x)
1261 Round the inexact number @var{x} towards zero.
1264 @c begin (texi-doc-string "guile" "round")
1265 @deffn {Scheme Procedure} round x
1266 @deffnx {C Function} scm_round_number (x)
1267 Round the inexact number @var{x} to the nearest integer. When exactly
1268 halfway between two integers, round to the even one.
1271 @c begin (texi-doc-string "guile" "floor")
1272 @deffn {Scheme Procedure} floor x
1273 @deffnx {C Function} scm_floor (x)
1274 Round the number @var{x} towards minus infinity.
1277 @c begin (texi-doc-string "guile" "ceiling")
1278 @deffn {Scheme Procedure} ceiling x
1279 @deffnx {C Function} scm_ceiling (x)
1280 Round the number @var{x} towards infinity.
1283 @deftypefn {C Function} double scm_c_truncate (double x)
1284 @deftypefnx {C Function} double scm_c_round (double x)
1285 Like @code{scm_truncate_number} or @code{scm_round_number},
1286 respectively, but these functions take and return @code{double}
1290 @deftypefn {Scheme Procedure} {} euclidean/ @var{x} @var{y}
1291 @deftypefnx {Scheme Procedure} {} euclidean-quotient @var{x} @var{y}
1292 @deftypefnx {Scheme Procedure} {} euclidean-remainder @var{x} @var{y}
1293 @deftypefnx {C Function} void scm_euclidean_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1294 @deftypefnx {C Function} SCM scm_euclidean_quotient (SCM @var{x}, SCM @var{y})
1295 @deftypefnx {C Function} SCM scm_euclidean_remainder (SCM @var{x}, SCM @var{y})
1296 These procedures accept two real numbers @var{x} and @var{y}, where the
1297 divisor @var{y} must be non-zero. @code{euclidean-quotient} returns the
1298 integer @var{q} and @code{euclidean-remainder} returns the real number
1299 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1300 @math{0 <= @var{r} < |@var{y}|}. @code{euclidean/} returns both @var{q} and
1301 @var{r}, and is more efficient than computing each separately. Note
1302 that when @math{@var{y} > 0}, @code{euclidean-quotient} returns
1303 @math{floor(@var{x}/@var{y})}, otherwise it returns
1304 @math{ceiling(@var{x}/@var{y})}.
1306 Note that these operators are equivalent to the R6RS operators
1307 @code{div}, @code{mod}, and @code{div-and-mod}.
1310 (euclidean-quotient 123 10) @result{} 12
1311 (euclidean-remainder 123 10) @result{} 3
1312 (euclidean/ 123 10) @result{} 12 and 3
1313 (euclidean/ 123 -10) @result{} -12 and 3
1314 (euclidean/ -123 10) @result{} -13 and 7
1315 (euclidean/ -123 -10) @result{} 13 and 7
1316 (euclidean/ -123.2 -63.5) @result{} 2.0 and 3.8
1317 (euclidean/ 16/3 -10/7) @result{} -3 and 22/21
1321 @deftypefn {Scheme Procedure} {} floor/ @var{x} @var{y}
1322 @deftypefnx {Scheme Procedure} {} floor-quotient @var{x} @var{y}
1323 @deftypefnx {Scheme Procedure} {} floor-remainder @var{x} @var{y}
1324 @deftypefnx {C Function} void scm_floor_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1325 @deftypefnx {C Function} SCM scm_floor_quotient (@var{x}, @var{y})
1326 @deftypefnx {C Function} SCM scm_floor_remainder (@var{x}, @var{y})
1327 These procedures accept two real numbers @var{x} and @var{y}, where the
1328 divisor @var{y} must be non-zero. @code{floor-quotient} returns the
1329 integer @var{q} and @code{floor-remainder} returns the real number
1330 @var{r} such that @math{@var{q} = floor(@var{x}/@var{y})} and
1331 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{floor/} returns
1332 both @var{q} and @var{r}, and is more efficient than computing each
1333 separately. Note that @var{r}, if non-zero, will have the same sign
1336 When @var{x} and @var{y} are integers, @code{floor-remainder} is
1337 equivalent to the R5RS integer-only operator @code{modulo}.
1340 (floor-quotient 123 10) @result{} 12
1341 (floor-remainder 123 10) @result{} 3
1342 (floor/ 123 10) @result{} 12 and 3
1343 (floor/ 123 -10) @result{} -13 and -7
1344 (floor/ -123 10) @result{} -13 and 7
1345 (floor/ -123 -10) @result{} 12 and -3
1346 (floor/ -123.2 -63.5) @result{} 1.0 and -59.7
1347 (floor/ 16/3 -10/7) @result{} -4 and -8/21
1351 @deftypefn {Scheme Procedure} {} ceiling/ @var{x} @var{y}
1352 @deftypefnx {Scheme Procedure} {} ceiling-quotient @var{x} @var{y}
1353 @deftypefnx {Scheme Procedure} {} ceiling-remainder @var{x} @var{y}
1354 @deftypefnx {C Function} void scm_ceiling_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1355 @deftypefnx {C Function} SCM scm_ceiling_quotient (@var{x}, @var{y})
1356 @deftypefnx {C Function} SCM scm_ceiling_remainder (@var{x}, @var{y})
1357 These procedures accept two real numbers @var{x} and @var{y}, where the
1358 divisor @var{y} must be non-zero. @code{ceiling-quotient} returns the
1359 integer @var{q} and @code{ceiling-remainder} returns the real number
1360 @var{r} such that @math{@var{q} = ceiling(@var{x}/@var{y})} and
1361 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{ceiling/} returns
1362 both @var{q} and @var{r}, and is more efficient than computing each
1363 separately. Note that @var{r}, if non-zero, will have the opposite sign
1367 (ceiling-quotient 123 10) @result{} 13
1368 (ceiling-remainder 123 10) @result{} -7
1369 (ceiling/ 123 10) @result{} 13 and -7
1370 (ceiling/ 123 -10) @result{} -12 and 3
1371 (ceiling/ -123 10) @result{} -12 and -3
1372 (ceiling/ -123 -10) @result{} 13 and 7
1373 (ceiling/ -123.2 -63.5) @result{} 2.0 and 3.8
1374 (ceiling/ 16/3 -10/7) @result{} -3 and 22/21
1378 @deftypefn {Scheme Procedure} {} truncate/ @var{x} @var{y}
1379 @deftypefnx {Scheme Procedure} {} truncate-quotient @var{x} @var{y}
1380 @deftypefnx {Scheme Procedure} {} truncate-remainder @var{x} @var{y}
1381 @deftypefnx {C Function} void scm_truncate_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1382 @deftypefnx {C Function} SCM scm_truncate_quotient (@var{x}, @var{y})
1383 @deftypefnx {C Function} SCM scm_truncate_remainder (@var{x}, @var{y})
1384 These procedures accept two real numbers @var{x} and @var{y}, where the
1385 divisor @var{y} must be non-zero. @code{truncate-quotient} returns the
1386 integer @var{q} and @code{truncate-remainder} returns the real number
1387 @var{r} such that @var{q} is @math{@var{x}/@var{y}} rounded toward zero,
1388 and @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{truncate/} returns
1389 both @var{q} and @var{r}, and is more efficient than computing each
1390 separately. Note that @var{r}, if non-zero, will have the same sign
1393 When @var{x} and @var{y} are integers, these operators are
1394 equivalent to the R5RS integer-only operators @code{quotient} and
1398 (truncate-quotient 123 10) @result{} 12
1399 (truncate-remainder 123 10) @result{} 3
1400 (truncate/ 123 10) @result{} 12 and 3
1401 (truncate/ 123 -10) @result{} -12 and 3
1402 (truncate/ -123 10) @result{} -12 and -3
1403 (truncate/ -123 -10) @result{} 12 and -3
1404 (truncate/ -123.2 -63.5) @result{} 1.0 and -59.7
1405 (truncate/ 16/3 -10/7) @result{} -3 and 22/21
1409 @deftypefn {Scheme Procedure} {} centered/ @var{x} @var{y}
1410 @deftypefnx {Scheme Procedure} {} centered-quotient @var{x} @var{y}
1411 @deftypefnx {Scheme Procedure} {} centered-remainder @var{x} @var{y}
1412 @deftypefnx {C Function} void scm_centered_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1413 @deftypefnx {C Function} SCM scm_centered_quotient (SCM @var{x}, SCM @var{y})
1414 @deftypefnx {C Function} SCM scm_centered_remainder (SCM @var{x}, SCM @var{y})
1415 These procedures accept two real numbers @var{x} and @var{y}, where the
1416 divisor @var{y} must be non-zero. @code{centered-quotient} returns the
1417 integer @var{q} and @code{centered-remainder} returns the real number
1418 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1419 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}. @code{centered/}
1420 returns both @var{q} and @var{r}, and is more efficient than computing
1423 Note that @code{centered-quotient} returns @math{@var{x}/@var{y}}
1424 rounded to the nearest integer. When @math{@var{x}/@var{y}} lies
1425 exactly half-way between two integers, the tie is broken according to
1426 the sign of @var{y}. If @math{@var{y} > 0}, ties are rounded toward
1427 positive infinity, otherwise they are rounded toward negative infinity.
1428 This is a consequence of the requirement that
1429 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}.
1431 Note that these operators are equivalent to the R6RS operators
1432 @code{div0}, @code{mod0}, and @code{div0-and-mod0}.
1435 (centered-quotient 123 10) @result{} 12
1436 (centered-remainder 123 10) @result{} 3
1437 (centered/ 123 10) @result{} 12 and 3
1438 (centered/ 123 -10) @result{} -12 and 3
1439 (centered/ -123 10) @result{} -12 and -3
1440 (centered/ -123 -10) @result{} 12 and -3
1441 (centered/ 125 10) @result{} 13 and -5
1442 (centered/ 127 10) @result{} 13 and -3
1443 (centered/ 135 10) @result{} 14 and -5
1444 (centered/ -123.2 -63.5) @result{} 2.0 and 3.8
1445 (centered/ 16/3 -10/7) @result{} -4 and -8/21
1449 @deftypefn {Scheme Procedure} {} round/ @var{x} @var{y}
1450 @deftypefnx {Scheme Procedure} {} round-quotient @var{x} @var{y}
1451 @deftypefnx {Scheme Procedure} {} round-remainder @var{x} @var{y}
1452 @deftypefnx {C Function} void scm_round_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1453 @deftypefnx {C Function} SCM scm_round_quotient (@var{x}, @var{y})
1454 @deftypefnx {C Function} SCM scm_round_remainder (@var{x}, @var{y})
1455 These procedures accept two real numbers @var{x} and @var{y}, where the
1456 divisor @var{y} must be non-zero. @code{round-quotient} returns the
1457 integer @var{q} and @code{round-remainder} returns the real number
1458 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1459 @var{q} is @math{@var{x}/@var{y}} rounded to the nearest integer,
1460 with ties going to the nearest even integer. @code{round/}
1461 returns both @var{q} and @var{r}, and is more efficient than computing
1464 Note that @code{round/} and @code{centered/} are almost equivalent, but
1465 their behavior differs when @math{@var{x}/@var{y}} lies exactly half-way
1466 between two integers. In this case, @code{round/} chooses the nearest
1467 even integer, whereas @code{centered/} chooses in such a way to satisfy
1468 the constraint @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}, which
1469 is stronger than the corresponding constraint for @code{round/},
1470 @math{-|@var{y}/2| <= @var{r} <= |@var{y}/2|}. In particular,
1471 when @var{x} and @var{y} are integers, the number of possible remainders
1472 returned by @code{centered/} is @math{|@var{y}|}, whereas the number of
1473 possible remainders returned by @code{round/} is @math{|@var{y}|+1} when
1477 (round-quotient 123 10) @result{} 12
1478 (round-remainder 123 10) @result{} 3
1479 (round/ 123 10) @result{} 12 and 3
1480 (round/ 123 -10) @result{} -12 and 3
1481 (round/ -123 10) @result{} -12 and -3
1482 (round/ -123 -10) @result{} 12 and -3
1483 (round/ 125 10) @result{} 12 and 5
1484 (round/ 127 10) @result{} 13 and -3
1485 (round/ 135 10) @result{} 14 and -5
1486 (round/ -123.2 -63.5) @result{} 2.0 and 3.8
1487 (round/ 16/3 -10/7) @result{} -4 and -8/21
1492 @subsubsection Scientific Functions
1494 The following procedures accept any kind of number as arguments,
1495 including complex numbers.
1498 @c begin (texi-doc-string "guile" "sqrt")
1499 @deffn {Scheme Procedure} sqrt z
1500 Return the square root of @var{z}. Of the two possible roots
1501 (positive and negative), the one with a positive real part is
1502 returned, or if that's zero then a positive imaginary part. Thus,
1505 (sqrt 9.0) @result{} 3.0
1506 (sqrt -9.0) @result{} 0.0+3.0i
1507 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1508 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1513 @c begin (texi-doc-string "guile" "expt")
1514 @deffn {Scheme Procedure} expt z1 z2
1515 Return @var{z1} raised to the power of @var{z2}.
1519 @c begin (texi-doc-string "guile" "sin")
1520 @deffn {Scheme Procedure} sin z
1521 Return the sine of @var{z}.
1525 @c begin (texi-doc-string "guile" "cos")
1526 @deffn {Scheme Procedure} cos z
1527 Return the cosine of @var{z}.
1531 @c begin (texi-doc-string "guile" "tan")
1532 @deffn {Scheme Procedure} tan z
1533 Return the tangent of @var{z}.
1537 @c begin (texi-doc-string "guile" "asin")
1538 @deffn {Scheme Procedure} asin z
1539 Return the arcsine of @var{z}.
1543 @c begin (texi-doc-string "guile" "acos")
1544 @deffn {Scheme Procedure} acos z
1545 Return the arccosine of @var{z}.
1549 @c begin (texi-doc-string "guile" "atan")
1550 @deffn {Scheme Procedure} atan z
1551 @deffnx {Scheme Procedure} atan y x
1552 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1556 @c begin (texi-doc-string "guile" "exp")
1557 @deffn {Scheme Procedure} exp z
1558 Return e to the power of @var{z}, where e is the base of natural
1559 logarithms (2.71828@dots{}).
1563 @c begin (texi-doc-string "guile" "log")
1564 @deffn {Scheme Procedure} log z
1565 Return the natural logarithm of @var{z}.
1568 @c begin (texi-doc-string "guile" "log10")
1569 @deffn {Scheme Procedure} log10 z
1570 Return the base 10 logarithm of @var{z}.
1573 @c begin (texi-doc-string "guile" "sinh")
1574 @deffn {Scheme Procedure} sinh z
1575 Return the hyperbolic sine of @var{z}.
1578 @c begin (texi-doc-string "guile" "cosh")
1579 @deffn {Scheme Procedure} cosh z
1580 Return the hyperbolic cosine of @var{z}.
1583 @c begin (texi-doc-string "guile" "tanh")
1584 @deffn {Scheme Procedure} tanh z
1585 Return the hyperbolic tangent of @var{z}.
1588 @c begin (texi-doc-string "guile" "asinh")
1589 @deffn {Scheme Procedure} asinh z
1590 Return the hyperbolic arcsine of @var{z}.
1593 @c begin (texi-doc-string "guile" "acosh")
1594 @deffn {Scheme Procedure} acosh z
1595 Return the hyperbolic arccosine of @var{z}.
1598 @c begin (texi-doc-string "guile" "atanh")
1599 @deffn {Scheme Procedure} atanh z
1600 Return the hyperbolic arctangent of @var{z}.
1604 @node Bitwise Operations
1605 @subsubsection Bitwise Operations
1607 For the following bitwise functions, negative numbers are treated as
1608 infinite precision twos-complements. For instance @math{-6} is bits
1609 @math{@dots{}111010}, with infinitely many ones on the left. It can
1610 be seen that adding 6 (binary 110) to such a bit pattern gives all
1613 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1614 @deffnx {C Function} scm_logand (n1, n2)
1615 Return the bitwise @sc{and} of the integer arguments.
1618 (logand) @result{} -1
1619 (logand 7) @result{} 7
1620 (logand #b111 #b011 #b001) @result{} 1
1624 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1625 @deffnx {C Function} scm_logior (n1, n2)
1626 Return the bitwise @sc{or} of the integer arguments.
1629 (logior) @result{} 0
1630 (logior 7) @result{} 7
1631 (logior #b000 #b001 #b011) @result{} 3
1635 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1636 @deffnx {C Function} scm_loxor (n1, n2)
1637 Return the bitwise @sc{xor} of the integer arguments. A bit is
1638 set in the result if it is set in an odd number of arguments.
1641 (logxor) @result{} 0
1642 (logxor 7) @result{} 7
1643 (logxor #b000 #b001 #b011) @result{} 2
1644 (logxor #b000 #b001 #b011 #b011) @result{} 1
1648 @deffn {Scheme Procedure} lognot n
1649 @deffnx {C Function} scm_lognot (n)
1650 Return the integer which is the ones-complement of the integer
1651 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1654 (number->string (lognot #b10000000) 2)
1655 @result{} "-10000001"
1656 (number->string (lognot #b0) 2)
1661 @deffn {Scheme Procedure} logtest j k
1662 @deffnx {C Function} scm_logtest (j, k)
1663 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1664 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1665 calculating the @code{logand}, just testing for non-zero.
1668 (logtest #b0100 #b1011) @result{} #f
1669 (logtest #b0100 #b0111) @result{} #t
1673 @deffn {Scheme Procedure} logbit? index j
1674 @deffnx {C Function} scm_logbit_p (index, j)
1675 Test whether bit number @var{index} in @var{j} is set. @var{index}
1676 starts from 0 for the least significant bit.
1679 (logbit? 0 #b1101) @result{} #t
1680 (logbit? 1 #b1101) @result{} #f
1681 (logbit? 2 #b1101) @result{} #t
1682 (logbit? 3 #b1101) @result{} #t
1683 (logbit? 4 #b1101) @result{} #f
1687 @deffn {Scheme Procedure} ash n cnt
1688 @deffnx {C Function} scm_ash (n, cnt)
1689 Return @var{n} shifted left by @var{cnt} bits, or shifted right if
1690 @var{cnt} is negative. This is an ``arithmetic'' shift.
1692 This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and
1693 when @var{cnt} is negative it's a division, rounded towards negative
1694 infinity. (Note that this is not the same rounding as @code{quotient}
1697 With @var{n} viewed as an infinite precision twos complement,
1698 @code{ash} means a left shift introducing zero bits, or a right shift
1702 (number->string (ash #b1 3) 2) @result{} "1000"
1703 (number->string (ash #b1010 -1) 2) @result{} "101"
1705 ;; -23 is bits ...11101001, -6 is bits ...111010
1706 (ash -23 -2) @result{} -6
1710 @deffn {Scheme Procedure} logcount n
1711 @deffnx {C Function} scm_logcount (n)
1712 Return the number of bits in integer @var{n}. If @var{n} is
1713 positive, the 1-bits in its binary representation are counted.
1714 If negative, the 0-bits in its two's-complement binary
1715 representation are counted. If zero, 0 is returned.
1718 (logcount #b10101010)
1727 @deffn {Scheme Procedure} integer-length n
1728 @deffnx {C Function} scm_integer_length (n)
1729 Return the number of bits necessary to represent @var{n}.
1731 For positive @var{n} this is how many bits to the most significant one
1732 bit. For negative @var{n} it's how many bits to the most significant
1733 zero bit in twos complement form.
1736 (integer-length #b10101010) @result{} 8
1737 (integer-length #b1111) @result{} 4
1738 (integer-length 0) @result{} 0
1739 (integer-length -1) @result{} 0
1740 (integer-length -256) @result{} 8
1741 (integer-length -257) @result{} 9
1745 @deffn {Scheme Procedure} integer-expt n k
1746 @deffnx {C Function} scm_integer_expt (n, k)
1747 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1748 integer, @var{n} can be any number.
1750 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1751 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1755 (integer-expt 2 5) @result{} 32
1756 (integer-expt -3 3) @result{} -27
1757 (integer-expt 5 -3) @result{} 1/125
1758 (integer-expt 0 0) @result{} 1
1762 @deffn {Scheme Procedure} bit-extract n start end
1763 @deffnx {C Function} scm_bit_extract (n, start, end)
1764 Return the integer composed of the @var{start} (inclusive)
1765 through @var{end} (exclusive) bits of @var{n}. The
1766 @var{start}th bit becomes the 0-th bit in the result.
1769 (number->string (bit-extract #b1101101010 0 4) 2)
1771 (number->string (bit-extract #b1101101010 4 9) 2)
1778 @subsubsection Random Number Generation
1780 Pseudo-random numbers are generated from a random state object, which
1781 can be created with @code{seed->random-state} or
1782 @code{datum->random-state}. An external representation (i.e.@: one
1783 which can written with @code{write} and read with @code{read}) of a
1784 random state object can be obtained via
1785 @code{random-state->datum}. The @var{state} parameter to the
1786 various functions below is optional, it defaults to the state object
1787 in the @code{*random-state*} variable.
1789 @deffn {Scheme Procedure} copy-random-state [state]
1790 @deffnx {C Function} scm_copy_random_state (state)
1791 Return a copy of the random state @var{state}.
1794 @deffn {Scheme Procedure} random n [state]
1795 @deffnx {C Function} scm_random (n, state)
1796 Return a number in [0, @var{n}).
1798 Accepts a positive integer or real n and returns a
1799 number of the same type between zero (inclusive) and
1800 @var{n} (exclusive). The values returned have a uniform
1804 @deffn {Scheme Procedure} random:exp [state]
1805 @deffnx {C Function} scm_random_exp (state)
1806 Return an inexact real in an exponential distribution with mean
1807 1. For an exponential distribution with mean @var{u} use @code{(*
1808 @var{u} (random:exp))}.
1811 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1812 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1813 Fills @var{vect} with inexact real random numbers the sum of whose
1814 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1815 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1816 the coordinates are uniformly distributed over the surface of the unit
1820 @deffn {Scheme Procedure} random:normal [state]
1821 @deffnx {C Function} scm_random_normal (state)
1822 Return an inexact real in a normal distribution. The distribution
1823 used has mean 0 and standard deviation 1. For a normal distribution
1824 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1825 (* @var{d} (random:normal)))}.
1828 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1829 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1830 Fills @var{vect} with inexact real random numbers that are
1831 independent and standard normally distributed
1832 (i.e., with mean 0 and variance 1).
1835 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1836 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1837 Fills @var{vect} with inexact real random numbers the sum of whose
1838 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1839 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1840 the coordinates are uniformly distributed within the unit
1842 @c FIXME: What does this mean, particularly the n-sphere part?
1845 @deffn {Scheme Procedure} random:uniform [state]
1846 @deffnx {C Function} scm_random_uniform (state)
1847 Return a uniformly distributed inexact real random number in
1851 @deffn {Scheme Procedure} seed->random-state seed
1852 @deffnx {C Function} scm_seed_to_random_state (seed)
1853 Return a new random state using @var{seed}.
1856 @deffn {Scheme Procedure} datum->random-state datum
1857 @deffnx {C Function} scm_datum_to_random_state (datum)
1858 Return a new random state from @var{datum}, which should have been
1859 obtained by @code{random-state->datum}.
1862 @deffn {Scheme Procedure} random-state->datum state
1863 @deffnx {C Function} scm_random_state_to_datum (state)
1864 Return a datum representation of @var{state} that may be written out and
1865 read back with the Scheme reader.
1868 @defvar *random-state*
1869 The global random state used by the above functions when the
1870 @var{state} parameter is not given.
1873 Note that the initial value of @code{*random-state*} is the same every
1874 time Guile starts up. Therefore, if you don't pass a @var{state}
1875 parameter to the above procedures, and you don't set
1876 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1877 @code{your-seed} is something that @emph{isn't} the same every time,
1878 you'll get the same sequence of ``random'' numbers on every run.
1880 For example, unless the relevant source code has changed, @code{(map
1881 random (cdr (iota 30)))}, if the first use of random numbers since
1882 Guile started up, will always give:
1885 (map random (cdr (iota 19)))
1887 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1890 To use the time of day as the random seed, you can use code like this:
1893 (let ((time (gettimeofday)))
1894 (set! *random-state*
1895 (seed->random-state (+ (car time)
1900 And then (depending on the time of day, of course):
1903 (map random (cdr (iota 19)))
1905 (0 0 1 0 2 4 5 4 5 5 9 3 10 1 8 3 14 17)
1908 For security applications, such as password generation, you should use
1909 more bits of seed. Otherwise an open source password generator could
1910 be attacked by guessing the seed@dots{} but that's a subject for
1915 @subsection Characters
1918 In Scheme, there is a data type to describe a single character.
1920 Defining what exactly a character @emph{is} can be more complicated
1921 than it seems. Guile follows the advice of R6RS and uses The Unicode
1922 Standard to help define what a character is. So, for Guile, a
1923 character is anything in the Unicode Character Database.
1926 @cindex Unicode code point
1928 The Unicode Character Database is basically a table of characters
1929 indexed using integers called 'code points'. Valid code points are in
1930 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1931 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1933 @cindex designated code point
1934 @cindex code point, designated
1936 Any code point that has been assigned to a character or that has
1937 otherwise been given a meaning by Unicode is called a 'designated code
1938 point'. Most of the designated code points, about 200,000 of them,
1939 indicate characters, accents or other combining marks that modify
1940 other characters, symbols, whitespace, and control characters. Some
1941 are not characters but indicators that suggest how to format or
1942 display neighboring characters.
1944 @cindex reserved code point
1945 @cindex code point, reserved
1947 If a code point is not a designated code point -- if it has not been
1948 assigned to a character by The Unicode Standard -- it is a 'reserved
1949 code point', meaning that they are reserved for future use. Most of
1950 the code points, about 800,000, are 'reserved code points'.
1952 By convention, a Unicode code point is written as
1953 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1954 this convenient notation is not valid code. Guile does not interpret
1955 ``U+XXXX'' as a character.
1957 In Scheme, a character literal is written as @code{#\@var{name}} where
1958 @var{name} is the name of the character that you want. Printable
1959 characters have their usual single character name; for example,
1960 @code{#\a} is a lower case @code{a}.
1962 Some of the code points are 'combining characters' that are not meant
1963 to be printed by themselves but are instead meant to modify the
1964 appearance of the previous character. For combining characters, an
1965 alternate form of the character literal is @code{#\} followed by
1966 U+25CC (a small, dotted circle), followed by the combining character.
1967 This allows the combining character to be drawn on the circle, not on
1968 the backslash of @code{#\}.
1970 Many of the non-printing characters, such as whitespace characters and
1971 control characters, also have names.
1973 The most commonly used non-printing characters have long character
1974 names, described in the table below.
1976 @multitable {@code{#\backspace}} {Preferred}
1977 @item Character Name @tab Codepoint
1978 @item @code{#\nul} @tab U+0000
1979 @item @code{#\alarm} @tab u+0007
1980 @item @code{#\backspace} @tab U+0008
1981 @item @code{#\tab} @tab U+0009
1982 @item @code{#\linefeed} @tab U+000A
1983 @item @code{#\newline} @tab U+000A
1984 @item @code{#\vtab} @tab U+000B
1985 @item @code{#\page} @tab U+000C
1986 @item @code{#\return} @tab U+000D
1987 @item @code{#\esc} @tab U+001B
1988 @item @code{#\space} @tab U+0020
1989 @item @code{#\delete} @tab U+007F
1992 There are also short names for all of the ``C0 control characters''
1993 (those with code points below 32). The following table lists the short
1994 name for each character.
1996 @multitable @columnfractions .25 .25 .25 .25
1997 @item 0 = @code{#\nul}
1998 @tab 1 = @code{#\soh}
1999 @tab 2 = @code{#\stx}
2000 @tab 3 = @code{#\etx}
2001 @item 4 = @code{#\eot}
2002 @tab 5 = @code{#\enq}
2003 @tab 6 = @code{#\ack}
2004 @tab 7 = @code{#\bel}
2005 @item 8 = @code{#\bs}
2006 @tab 9 = @code{#\ht}
2007 @tab 10 = @code{#\lf}
2008 @tab 11 = @code{#\vt}
2009 @item 12 = @code{#\ff}
2010 @tab 13 = @code{#\cr}
2011 @tab 14 = @code{#\so}
2012 @tab 15 = @code{#\si}
2013 @item 16 = @code{#\dle}
2014 @tab 17 = @code{#\dc1}
2015 @tab 18 = @code{#\dc2}
2016 @tab 19 = @code{#\dc3}
2017 @item 20 = @code{#\dc4}
2018 @tab 21 = @code{#\nak}
2019 @tab 22 = @code{#\syn}
2020 @tab 23 = @code{#\etb}
2021 @item 24 = @code{#\can}
2022 @tab 25 = @code{#\em}
2023 @tab 26 = @code{#\sub}
2024 @tab 27 = @code{#\esc}
2025 @item 28 = @code{#\fs}
2026 @tab 29 = @code{#\gs}
2027 @tab 30 = @code{#\rs}
2028 @tab 31 = @code{#\us}
2029 @item 32 = @code{#\sp}
2032 The short name for the ``delete'' character (code point U+007F) is
2035 There are also a few alternative names left over for compatibility with
2036 previous versions of Guile.
2038 @multitable {@code{#\backspace}} {Preferred}
2039 @item Alternate @tab Standard
2040 @item @code{#\nl} @tab @code{#\newline}
2041 @item @code{#\np} @tab @code{#\page}
2042 @item @code{#\null} @tab @code{#\nul}
2045 Characters may also be written using their code point values. They can
2046 be written with as an octal number, such as @code{#\10} for
2047 @code{#\bs} or @code{#\177} for @code{#\del}.
2049 If one prefers hex to octal, there is an additional syntax for character
2050 escapes: @code{#\xHHHH} -- the letter 'x' followed by a hexadecimal
2051 number of one to eight digits.
2054 @deffn {Scheme Procedure} char? x
2055 @deffnx {C Function} scm_char_p (x)
2056 Return @code{#t} iff @var{x} is a character, else @code{#f}.
2059 Fundamentally, the character comparison operations below are
2060 numeric comparisons of the character's code points.
2063 @deffn {Scheme Procedure} char=? x y
2064 Return @code{#t} iff code point of @var{x} is equal to the code point
2065 of @var{y}, else @code{#f}.
2069 @deffn {Scheme Procedure} char<? x y
2070 Return @code{#t} iff the code point of @var{x} is less than the code
2071 point of @var{y}, else @code{#f}.
2075 @deffn {Scheme Procedure} char<=? x y
2076 Return @code{#t} iff the code point of @var{x} is less than or equal
2077 to the code point of @var{y}, else @code{#f}.
2081 @deffn {Scheme Procedure} char>? x y
2082 Return @code{#t} iff the code point of @var{x} is greater than the
2083 code point of @var{y}, else @code{#f}.
2087 @deffn {Scheme Procedure} char>=? x y
2088 Return @code{#t} iff the code point of @var{x} is greater than or
2089 equal to the code point of @var{y}, else @code{#f}.
2092 @cindex case folding
2094 Case-insensitive character comparisons use @emph{Unicode case
2095 folding}. In case folding comparisons, if a character is lowercase
2096 and has an uppercase form that can be expressed as a single character,
2097 it is converted to uppercase before comparison. All other characters
2098 undergo no conversion before the comparison occurs. This includes the
2099 German sharp S (Eszett) which is not uppercased before conversion
2100 because its uppercase form has two characters. Unicode case folding
2101 is language independent: it uses rules that are generally true, but,
2102 it cannot cover all cases for all languages.
2105 @deffn {Scheme Procedure} char-ci=? x y
2106 Return @code{#t} iff the case-folded code point of @var{x} is the same
2107 as the case-folded code point of @var{y}, else @code{#f}.
2111 @deffn {Scheme Procedure} char-ci<? x y
2112 Return @code{#t} iff the case-folded code point of @var{x} is less
2113 than the case-folded code point of @var{y}, else @code{#f}.
2117 @deffn {Scheme Procedure} char-ci<=? x y
2118 Return @code{#t} iff the case-folded code point of @var{x} is less
2119 than or equal to the case-folded code point of @var{y}, else
2124 @deffn {Scheme Procedure} char-ci>? x y
2125 Return @code{#t} iff the case-folded code point of @var{x} is greater
2126 than the case-folded code point of @var{y}, else @code{#f}.
2130 @deffn {Scheme Procedure} char-ci>=? x y
2131 Return @code{#t} iff the case-folded code point of @var{x} is greater
2132 than or equal to the case-folded code point of @var{y}, else
2136 @rnindex char-alphabetic?
2137 @deffn {Scheme Procedure} char-alphabetic? chr
2138 @deffnx {C Function} scm_char_alphabetic_p (chr)
2139 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
2142 @rnindex char-numeric?
2143 @deffn {Scheme Procedure} char-numeric? chr
2144 @deffnx {C Function} scm_char_numeric_p (chr)
2145 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
2148 @rnindex char-whitespace?
2149 @deffn {Scheme Procedure} char-whitespace? chr
2150 @deffnx {C Function} scm_char_whitespace_p (chr)
2151 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
2154 @rnindex char-upper-case?
2155 @deffn {Scheme Procedure} char-upper-case? chr
2156 @deffnx {C Function} scm_char_upper_case_p (chr)
2157 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
2160 @rnindex char-lower-case?
2161 @deffn {Scheme Procedure} char-lower-case? chr
2162 @deffnx {C Function} scm_char_lower_case_p (chr)
2163 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
2166 @deffn {Scheme Procedure} char-is-both? chr
2167 @deffnx {C Function} scm_char_is_both_p (chr)
2168 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
2172 @deffn {Scheme Procedure} char-general-category chr
2173 @deffnx {C Function} scm_char_general_category (chr)
2174 Return a symbol giving the two-letter name of the Unicode general
2175 category assigned to @var{chr} or @code{#f} if no named category is
2176 assigned. The following table provides a list of category names along
2177 with their meanings.
2179 @multitable @columnfractions .1 .4 .1 .4
2181 @tab Uppercase letter
2183 @tab Final quote punctuation
2185 @tab Lowercase letter
2187 @tab Other punctuation
2189 @tab Titlecase letter
2193 @tab Modifier letter
2195 @tab Currency symbol
2199 @tab Modifier symbol
2201 @tab Non-spacing mark
2205 @tab Combining spacing mark
2207 @tab Space separator
2213 @tab Decimal digit number
2215 @tab Paragraph separator
2225 @tab Connector punctuation
2229 @tab Dash punctuation
2233 @tab Open punctuation
2237 @tab Close punctuation
2241 @tab Initial quote punctuation
2247 @rnindex char->integer
2248 @deffn {Scheme Procedure} char->integer chr
2249 @deffnx {C Function} scm_char_to_integer (chr)
2250 Return the code point of @var{chr}.
2253 @rnindex integer->char
2254 @deffn {Scheme Procedure} integer->char n
2255 @deffnx {C Function} scm_integer_to_char (n)
2256 Return the character that has code point @var{n}. The integer @var{n}
2257 must be a valid code point. Valid code points are in the ranges 0 to
2258 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
2261 @rnindex char-upcase
2262 @deffn {Scheme Procedure} char-upcase chr
2263 @deffnx {C Function} scm_char_upcase (chr)
2264 Return the uppercase character version of @var{chr}.
2267 @rnindex char-downcase
2268 @deffn {Scheme Procedure} char-downcase chr
2269 @deffnx {C Function} scm_char_downcase (chr)
2270 Return the lowercase character version of @var{chr}.
2273 @rnindex char-titlecase
2274 @deffn {Scheme Procedure} char-titlecase chr
2275 @deffnx {C Function} scm_char_titlecase (chr)
2276 Return the titlecase character version of @var{chr} if one exists;
2277 otherwise return the uppercase version.
2279 For most characters these will be the same, but the Unicode Standard
2280 includes certain digraph compatibility characters, such as @code{U+01F3}
2281 ``dz'', for which the uppercase and titlecase characters are different
2282 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
2287 @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c})
2288 @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c})
2289 @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c})
2291 These C functions take an integer representation of a Unicode
2292 codepoint and return the codepoint corresponding to its uppercase,
2293 lowercase, and titlecase forms respectively. The type
2294 @code{scm_t_wchar} is a signed, 32-bit integer.
2297 @node Character Sets
2298 @subsection Character Sets
2300 The features described in this section correspond directly to SRFI-14.
2302 The data type @dfn{charset} implements sets of characters
2303 (@pxref{Characters}). Because the internal representation of
2304 character sets is not visible to the user, a lot of procedures for
2305 handling them are provided.
2307 Character sets can be created, extended, tested for the membership of a
2308 characters and be compared to other character sets.
2311 * Character Set Predicates/Comparison::
2312 * Iterating Over Character Sets:: Enumerate charset elements.
2313 * Creating Character Sets:: Making new charsets.
2314 * Querying Character Sets:: Test charsets for membership etc.
2315 * Character-Set Algebra:: Calculating new charsets.
2316 * Standard Character Sets:: Variables containing predefined charsets.
2319 @node Character Set Predicates/Comparison
2320 @subsubsection Character Set Predicates/Comparison
2322 Use these procedures for testing whether an object is a character set,
2323 or whether several character sets are equal or subsets of each other.
2324 @code{char-set-hash} can be used for calculating a hash value, maybe for
2325 usage in fast lookup procedures.
2327 @deffn {Scheme Procedure} char-set? obj
2328 @deffnx {C Function} scm_char_set_p (obj)
2329 Return @code{#t} if @var{obj} is a character set, @code{#f}
2333 @deffn {Scheme Procedure} char-set= . char_sets
2334 @deffnx {C Function} scm_char_set_eq (char_sets)
2335 Return @code{#t} if all given character sets are equal.
2338 @deffn {Scheme Procedure} char-set<= . char_sets
2339 @deffnx {C Function} scm_char_set_leq (char_sets)
2340 Return @code{#t} if every character set @var{cs}i is a subset
2341 of character set @var{cs}i+1.
2344 @deffn {Scheme Procedure} char-set-hash cs [bound]
2345 @deffnx {C Function} scm_char_set_hash (cs, bound)
2346 Compute a hash value for the character set @var{cs}. If
2347 @var{bound} is given and non-zero, it restricts the
2348 returned value to the range 0 @dots{} @var{bound - 1}.
2351 @c ===================================================================
2353 @node Iterating Over Character Sets
2354 @subsubsection Iterating Over Character Sets
2356 Character set cursors are a means for iterating over the members of a
2357 character sets. After creating a character set cursor with
2358 @code{char-set-cursor}, a cursor can be dereferenced with
2359 @code{char-set-ref}, advanced to the next member with
2360 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2361 element of the set can be checked with @code{end-of-char-set?}.
2363 Additionally, mapping and (un-)folding procedures for character sets are
2366 @deffn {Scheme Procedure} char-set-cursor cs
2367 @deffnx {C Function} scm_char_set_cursor (cs)
2368 Return a cursor into the character set @var{cs}.
2371 @deffn {Scheme Procedure} char-set-ref cs cursor
2372 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2373 Return the character at the current cursor position
2374 @var{cursor} in the character set @var{cs}. It is an error to
2375 pass a cursor for which @code{end-of-char-set?} returns true.
2378 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2379 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2380 Advance the character set cursor @var{cursor} to the next
2381 character in the character set @var{cs}. It is an error if the
2382 cursor given satisfies @code{end-of-char-set?}.
2385 @deffn {Scheme Procedure} end-of-char-set? cursor
2386 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2387 Return @code{#t} if @var{cursor} has reached the end of a
2388 character set, @code{#f} otherwise.
2391 @deffn {Scheme Procedure} char-set-fold kons knil cs
2392 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2393 Fold the procedure @var{kons} over the character set @var{cs},
2394 initializing it with @var{knil}.
2397 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2398 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2399 This is a fundamental constructor for character sets.
2401 @item @var{g} is used to generate a series of ``seed'' values
2402 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2403 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2404 @item @var{p} tells us when to stop -- when it returns true
2405 when applied to one of the seed values.
2406 @item @var{f} maps each seed value to a character. These
2407 characters are added to the base character set @var{base_cs} to
2408 form the result; @var{base_cs} defaults to the empty set.
2412 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2413 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2414 This is a fundamental constructor for character sets.
2416 @item @var{g} is used to generate a series of ``seed'' values
2417 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2418 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2419 @item @var{p} tells us when to stop -- when it returns true
2420 when applied to one of the seed values.
2421 @item @var{f} maps each seed value to a character. These
2422 characters are added to the base character set @var{base_cs} to
2423 form the result; @var{base_cs} defaults to the empty set.
2427 @deffn {Scheme Procedure} char-set-for-each proc cs
2428 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2429 Apply @var{proc} to every character in the character set
2430 @var{cs}. The return value is not specified.
2433 @deffn {Scheme Procedure} char-set-map proc cs
2434 @deffnx {C Function} scm_char_set_map (proc, cs)
2435 Map the procedure @var{proc} over every character in @var{cs}.
2436 @var{proc} must be a character -> character procedure.
2439 @c ===================================================================
2441 @node Creating Character Sets
2442 @subsubsection Creating Character Sets
2444 New character sets are produced with these procedures.
2446 @deffn {Scheme Procedure} char-set-copy cs
2447 @deffnx {C Function} scm_char_set_copy (cs)
2448 Return a newly allocated character set containing all
2449 characters in @var{cs}.
2452 @deffn {Scheme Procedure} char-set . rest
2453 @deffnx {C Function} scm_char_set (rest)
2454 Return a character set containing all given characters.
2457 @deffn {Scheme Procedure} list->char-set list [base_cs]
2458 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2459 Convert the character list @var{list} to a character set. If
2460 the character set @var{base_cs} is given, the character in this
2461 set are also included in the result.
2464 @deffn {Scheme Procedure} list->char-set! list base_cs
2465 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2466 Convert the character list @var{list} to a character set. The
2467 characters are added to @var{base_cs} and @var{base_cs} is
2471 @deffn {Scheme Procedure} string->char-set str [base_cs]
2472 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2473 Convert the string @var{str} to a character set. If the
2474 character set @var{base_cs} is given, the characters in this
2475 set are also included in the result.
2478 @deffn {Scheme Procedure} string->char-set! str base_cs
2479 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2480 Convert the string @var{str} to a character set. The
2481 characters from the string are added to @var{base_cs}, and
2482 @var{base_cs} is returned.
2485 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2486 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2487 Return a character set containing every character from @var{cs}
2488 so that it satisfies @var{pred}. If provided, the characters
2489 from @var{base_cs} are added to the result.
2492 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2493 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2494 Return a character set containing every character from @var{cs}
2495 so that it satisfies @var{pred}. The characters are added to
2496 @var{base_cs} and @var{base_cs} is returned.
2499 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2500 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2501 Return a character set containing all characters whose
2502 character codes lie in the half-open range
2503 [@var{lower},@var{upper}).
2505 If @var{error} is a true value, an error is signalled if the
2506 specified range contains characters which are not contained in
2507 the implemented character range. If @var{error} is @code{#f},
2508 these characters are silently left out of the resulting
2511 The characters in @var{base_cs} are added to the result, if
2515 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2516 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2517 Return a character set containing all characters whose
2518 character codes lie in the half-open range
2519 [@var{lower},@var{upper}).
2521 If @var{error} is a true value, an error is signalled if the
2522 specified range contains characters which are not contained in
2523 the implemented character range. If @var{error} is @code{#f},
2524 these characters are silently left out of the resulting
2527 The characters are added to @var{base_cs} and @var{base_cs} is
2531 @deffn {Scheme Procedure} ->char-set x
2532 @deffnx {C Function} scm_to_char_set (x)
2533 Coerces x into a char-set. @var{x} may be a string, character or
2534 char-set. A string is converted to the set of its constituent
2535 characters; a character is converted to a singleton set; a char-set is
2539 @c ===================================================================
2541 @node Querying Character Sets
2542 @subsubsection Querying Character Sets
2544 Access the elements and other information of a character set with these
2547 @deffn {Scheme Procedure} %char-set-dump cs
2548 Returns an association list containing debugging information
2549 for @var{cs}. The association list has the following entries.
2554 The number of groups of contiguous code points the char-set
2557 A list of lists where each sublist is a range of code points
2558 and their associated characters
2560 The return value of this function cannot be relied upon to be
2561 consistent between versions of Guile and should not be used in code.
2564 @deffn {Scheme Procedure} char-set-size cs
2565 @deffnx {C Function} scm_char_set_size (cs)
2566 Return the number of elements in character set @var{cs}.
2569 @deffn {Scheme Procedure} char-set-count pred cs
2570 @deffnx {C Function} scm_char_set_count (pred, cs)
2571 Return the number of the elements int the character set
2572 @var{cs} which satisfy the predicate @var{pred}.
2575 @deffn {Scheme Procedure} char-set->list cs
2576 @deffnx {C Function} scm_char_set_to_list (cs)
2577 Return a list containing the elements of the character set
2581 @deffn {Scheme Procedure} char-set->string cs
2582 @deffnx {C Function} scm_char_set_to_string (cs)
2583 Return a string containing the elements of the character set
2584 @var{cs}. The order in which the characters are placed in the
2585 string is not defined.
2588 @deffn {Scheme Procedure} char-set-contains? cs ch
2589 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2590 Return @code{#t} iff the character @var{ch} is contained in the
2591 character set @var{cs}.
2594 @deffn {Scheme Procedure} char-set-every pred cs
2595 @deffnx {C Function} scm_char_set_every (pred, cs)
2596 Return a true value if every character in the character set
2597 @var{cs} satisfies the predicate @var{pred}.
2600 @deffn {Scheme Procedure} char-set-any pred cs
2601 @deffnx {C Function} scm_char_set_any (pred, cs)
2602 Return a true value if any character in the character set
2603 @var{cs} satisfies the predicate @var{pred}.
2606 @c ===================================================================
2608 @node Character-Set Algebra
2609 @subsubsection Character-Set Algebra
2611 Character sets can be manipulated with the common set algebra operation,
2612 such as union, complement, intersection etc. All of these procedures
2613 provide side-effecting variants, which modify their character set
2616 @deffn {Scheme Procedure} char-set-adjoin cs . rest
2617 @deffnx {C Function} scm_char_set_adjoin (cs, rest)
2618 Add all character arguments to the first argument, which must
2622 @deffn {Scheme Procedure} char-set-delete cs . rest
2623 @deffnx {C Function} scm_char_set_delete (cs, rest)
2624 Delete all character arguments from the first argument, which
2625 must be a character set.
2628 @deffn {Scheme Procedure} char-set-adjoin! cs . rest
2629 @deffnx {C Function} scm_char_set_adjoin_x (cs, rest)
2630 Add all character arguments to the first argument, which must
2634 @deffn {Scheme Procedure} char-set-delete! cs . rest
2635 @deffnx {C Function} scm_char_set_delete_x (cs, rest)
2636 Delete all character arguments from the first argument, which
2637 must be a character set.
2640 @deffn {Scheme Procedure} char-set-complement cs
2641 @deffnx {C Function} scm_char_set_complement (cs)
2642 Return the complement of the character set @var{cs}.
2645 Note that the complement of a character set is likely to contain many
2646 reserved code points (code points that are not associated with
2647 characters). It may be helpful to modify the output of
2648 @code{char-set-complement} by computing its intersection with the set
2649 of designated code points, @code{char-set:designated}.
2651 @deffn {Scheme Procedure} char-set-union . rest
2652 @deffnx {C Function} scm_char_set_union (rest)
2653 Return the union of all argument character sets.
2656 @deffn {Scheme Procedure} char-set-intersection . rest
2657 @deffnx {C Function} scm_char_set_intersection (rest)
2658 Return the intersection of all argument character sets.
2661 @deffn {Scheme Procedure} char-set-difference cs1 . rest
2662 @deffnx {C Function} scm_char_set_difference (cs1, rest)
2663 Return the difference of all argument character sets.
2666 @deffn {Scheme Procedure} char-set-xor . rest
2667 @deffnx {C Function} scm_char_set_xor (rest)
2668 Return the exclusive-or of all argument character sets.
2671 @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest
2672 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest)
2673 Return the difference and the intersection of all argument
2677 @deffn {Scheme Procedure} char-set-complement! cs
2678 @deffnx {C Function} scm_char_set_complement_x (cs)
2679 Return the complement of the character set @var{cs}.
2682 @deffn {Scheme Procedure} char-set-union! cs1 . rest
2683 @deffnx {C Function} scm_char_set_union_x (cs1, rest)
2684 Return the union of all argument character sets.
2687 @deffn {Scheme Procedure} char-set-intersection! cs1 . rest
2688 @deffnx {C Function} scm_char_set_intersection_x (cs1, rest)
2689 Return the intersection of all argument character sets.
2692 @deffn {Scheme Procedure} char-set-difference! cs1 . rest
2693 @deffnx {C Function} scm_char_set_difference_x (cs1, rest)
2694 Return the difference of all argument character sets.
2697 @deffn {Scheme Procedure} char-set-xor! cs1 . rest
2698 @deffnx {C Function} scm_char_set_xor_x (cs1, rest)
2699 Return the exclusive-or of all argument character sets.
2702 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest
2703 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest)
2704 Return the difference and the intersection of all argument
2708 @c ===================================================================
2710 @node Standard Character Sets
2711 @subsubsection Standard Character Sets
2713 In order to make the use of the character set data type and procedures
2714 useful, several predefined character set variables exist.
2720 These character sets are locale independent and are not recomputed
2721 upon a @code{setlocale} call. They contain characters from the whole
2722 range of Unicode code points. For instance, @code{char-set:letter}
2723 contains about 94,000 characters.
2725 @defvr {Scheme Variable} char-set:lower-case
2726 @defvrx {C Variable} scm_char_set_lower_case
2727 All lower-case characters.
2730 @defvr {Scheme Variable} char-set:upper-case
2731 @defvrx {C Variable} scm_char_set_upper_case
2732 All upper-case characters.
2735 @defvr {Scheme Variable} char-set:title-case
2736 @defvrx {C Variable} scm_char_set_title_case
2737 All single characters that function as if they were an upper-case
2738 letter followed by a lower-case letter.
2741 @defvr {Scheme Variable} char-set:letter
2742 @defvrx {C Variable} scm_char_set_letter
2743 All letters. This includes @code{char-set:lower-case},
2744 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2745 letters that have no case at all. For example, Chinese and Japanese
2746 characters typically have no concept of case.
2749 @defvr {Scheme Variable} char-set:digit
2750 @defvrx {C Variable} scm_char_set_digit
2754 @defvr {Scheme Variable} char-set:letter+digit
2755 @defvrx {C Variable} scm_char_set_letter_and_digit
2756 The union of @code{char-set:letter} and @code{char-set:digit}.
2759 @defvr {Scheme Variable} char-set:graphic
2760 @defvrx {C Variable} scm_char_set_graphic
2761 All characters which would put ink on the paper.
2764 @defvr {Scheme Variable} char-set:printing
2765 @defvrx {C Variable} scm_char_set_printing
2766 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2769 @defvr {Scheme Variable} char-set:whitespace
2770 @defvrx {C Variable} scm_char_set_whitespace
2771 All whitespace characters.
2774 @defvr {Scheme Variable} char-set:blank
2775 @defvrx {C Variable} scm_char_set_blank
2776 All horizontal whitespace characters, which notably includes
2777 @code{#\space} and @code{#\tab}.
2780 @defvr {Scheme Variable} char-set:iso-control
2781 @defvrx {C Variable} scm_char_set_iso_control
2782 The ISO control characters are the C0 control characters (U+0000 to
2783 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2787 @defvr {Scheme Variable} char-set:punctuation
2788 @defvrx {C Variable} scm_char_set_punctuation
2789 All punctuation characters, such as the characters
2790 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2793 @defvr {Scheme Variable} char-set:symbol
2794 @defvrx {C Variable} scm_char_set_symbol
2795 All symbol characters, such as the characters @code{$+<=>^`|~}.
2798 @defvr {Scheme Variable} char-set:hex-digit
2799 @defvrx {C Variable} scm_char_set_hex_digit
2800 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2803 @defvr {Scheme Variable} char-set:ascii
2804 @defvrx {C Variable} scm_char_set_ascii
2805 All ASCII characters.
2808 @defvr {Scheme Variable} char-set:empty
2809 @defvrx {C Variable} scm_char_set_empty
2810 The empty character set.
2813 @defvr {Scheme Variable} char-set:designated
2814 @defvrx {C Variable} scm_char_set_designated
2815 This character set contains all designated code points. This includes
2816 all the code points to which Unicode has assigned a character or other
2820 @defvr {Scheme Variable} char-set:full
2821 @defvrx {C Variable} scm_char_set_full
2822 This character set contains all possible code points. This includes
2823 both designated and reserved code points.
2830 Strings are fixed-length sequences of characters. They can be created
2831 by calling constructor procedures, but they can also literally get
2832 entered at the @acronym{REPL} or in Scheme source files.
2834 @c Guile provides a rich set of string processing procedures, because text
2835 @c handling is very important when Guile is used as a scripting language.
2837 Strings always carry the information about how many characters they are
2838 composed of with them, so there is no special end-of-string character,
2839 like in C. That means that Scheme strings can contain any character,
2840 even the @samp{#\nul} character @samp{\0}.
2842 To use strings efficiently, you need to know a bit about how Guile
2843 implements them. In Guile, a string consists of two parts, a head and
2844 the actual memory where the characters are stored. When a string (or
2845 a substring of it) is copied, only a new head gets created, the memory
2846 is usually not copied. The two heads start out pointing to the same
2849 When one of these two strings is modified, as with @code{string-set!},
2850 their common memory does get copied so that each string has its own
2851 memory and modifying one does not accidentally modify the other as well.
2852 Thus, Guile's strings are `copy on write'; the actual copying of their
2853 memory is delayed until one string is written to.
2855 This implementation makes functions like @code{substring} very
2856 efficient in the common case that no modifications are done to the
2859 If you do know that your strings are getting modified right away, you
2860 can use @code{substring/copy} instead of @code{substring}. This
2861 function performs the copy immediately at the time of creation. This
2862 is more efficient, especially in a multi-threaded program. Also,
2863 @code{substring/copy} can avoid the problem that a short substring
2864 holds on to the memory of a very large original string that could
2865 otherwise be recycled.
2867 If you want to avoid the copy altogether, so that modifications of one
2868 string show up in the other, you can use @code{substring/shared}. The
2869 strings created by this procedure are called @dfn{mutation sharing
2870 substrings} since the substring and the original string share
2871 modifications to each other.
2873 If you want to prevent modifications, use @code{substring/read-only}.
2875 Guile provides all procedures of SRFI-13 and a few more.
2878 * String Syntax:: Read syntax for strings.
2879 * String Predicates:: Testing strings for certain properties.
2880 * String Constructors:: Creating new string objects.
2881 * List/String Conversion:: Converting from/to lists of characters.
2882 * String Selection:: Select portions from strings.
2883 * String Modification:: Modify parts or whole strings.
2884 * String Comparison:: Lexicographic ordering predicates.
2885 * String Searching:: Searching in strings.
2886 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2887 * Reversing and Appending Strings:: Appending strings to form a new string.
2888 * Mapping Folding and Unfolding:: Iterating over strings.
2889 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2890 * Conversion to/from C::
2891 * String Internals:: The storage strategy for strings.
2895 @subsubsection String Read Syntax
2897 @c In the following @code is used to get a good font in TeX etc, but
2898 @c is omitted for Info format, so as not to risk any confusion over
2899 @c whether surrounding ` ' quotes are part of the escape or are
2900 @c special in a string (they're not).
2902 The read syntax for strings is an arbitrarily long sequence of
2903 characters enclosed in double quotes (@nicode{"}).
2905 Backslash is an escape character and can be used to insert the following
2906 special characters. @nicode{\"} and @nicode{\\} are R5RS standard, the
2907 next seven are R6RS standard --- notice they follow C syntax --- and the
2908 remaining four are Guile extensions.
2912 Backslash character.
2915 Double quote character (an unescaped @nicode{"} is otherwise the end
2919 Bell character (ASCII 7).
2922 Formfeed character (ASCII 12).
2925 Newline character (ASCII 10).
2928 Carriage return character (ASCII 13).
2931 Tab character (ASCII 9).
2934 Vertical tab character (ASCII 11).
2937 Backspace character (ASCII 8).
2940 NUL character (ASCII 0).
2942 @item @nicode{\} followed by newline (ASCII 10)
2943 Nothing. This way if @nicode{\} is the last character in a line, the
2944 string will continue with the first character from the next line,
2945 without a line break.
2947 If the @code{hungry-eol-escapes} reader option is enabled, which is not
2948 the case by default, leading whitespace on the next line is discarded.
2954 (read-enable 'hungry-eol-escapes)
2960 Character code given by two hexadecimal digits. For example
2961 @nicode{\x7f} for an ASCII DEL (127).
2963 @item @nicode{\uHHHH}
2964 Character code given by four hexadecimal digits. For example
2965 @nicode{\u0100} for a capital A with macron (U+0100).
2967 @item @nicode{\UHHHHHH}
2968 Character code given by six hexadecimal digits. For example
2973 The following are examples of string literals:
2982 The three escape sequences @code{\xHH}, @code{\uHHHH} and @code{\UHHHHHH} were
2983 chosen to not break compatibility with code written for previous versions of
2984 Guile. The R6RS specification suggests a different, incompatible syntax for hex
2985 escapes: @code{\xHHHH;} -- a character code followed by one to eight hexadecimal
2986 digits terminated with a semicolon. If this escape format is desired instead,
2987 it can be enabled with the reader option @code{r6rs-hex-escapes}.
2990 (read-enable 'r6rs-hex-escapes)
2993 For more on reader options, @xref{Scheme Read}.
2995 @node String Predicates
2996 @subsubsection String Predicates
2998 The following procedures can be used to check whether a given string
2999 fulfills some specified property.
3002 @deffn {Scheme Procedure} string? obj
3003 @deffnx {C Function} scm_string_p (obj)
3004 Return @code{#t} if @var{obj} is a string, else @code{#f}.
3007 @deftypefn {C Function} int scm_is_string (SCM obj)
3008 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
3011 @deffn {Scheme Procedure} string-null? str
3012 @deffnx {C Function} scm_string_null_p (str)
3013 Return @code{#t} if @var{str}'s length is zero, and
3014 @code{#f} otherwise.
3016 (string-null? "") @result{} #t
3018 (string-null? y) @result{} #f
3022 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
3023 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
3024 Check if @var{char_pred} is true for any character in string @var{s}.
3026 @var{char_pred} can be a character to check for any equal to that, or
3027 a character set (@pxref{Character Sets}) to check for any in that set,
3028 or a predicate procedure to call.
3030 For a procedure, calls @code{(@var{char_pred} c)} are made
3031 successively on the characters from @var{start} to @var{end}. If
3032 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
3033 stops and that return value is the return from @code{string-any}. The
3034 call on the last character (ie.@: at @math{@var{end}-1}), if that
3035 point is reached, is a tail call.
3037 If there are no characters in @var{s} (ie.@: @var{start} equals
3038 @var{end}) then the return is @code{#f}.
3041 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
3042 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
3043 Check if @var{char_pred} is true for every character in string
3046 @var{char_pred} can be a character to check for every character equal
3047 to that, or a character set (@pxref{Character Sets}) to check for
3048 every character being in that set, or a predicate procedure to call.
3050 For a procedure, calls @code{(@var{char_pred} c)} are made
3051 successively on the characters from @var{start} to @var{end}. If
3052 @var{char_pred} returns @code{#f}, @code{string-every} stops and
3053 returns @code{#f}. The call on the last character (ie.@: at
3054 @math{@var{end}-1}), if that point is reached, is a tail call and the
3055 return from that call is the return from @code{string-every}.
3057 If there are no characters in @var{s} (ie.@: @var{start} equals
3058 @var{end}) then the return is @code{#t}.
3061 @node String Constructors
3062 @subsubsection String Constructors
3064 The string constructor procedures create new string objects, possibly
3065 initializing them with some specified character data. See also
3066 @xref{String Selection}, for ways to create strings from existing
3069 @c FIXME::martin: list->string belongs into `List/String Conversion'
3071 @deffn {Scheme Procedure} string char@dots{}
3073 Return a newly allocated string made from the given character
3077 (string #\x #\y #\z) @result{} "xyz"
3078 (string) @result{} ""
3082 @deffn {Scheme Procedure} list->string lst
3083 @deffnx {C Function} scm_string (lst)
3084 @rnindex list->string
3085 Return a newly allocated string made from a list of characters.
3088 (list->string '(#\a #\b #\c)) @result{} "abc"
3092 @deffn {Scheme Procedure} reverse-list->string lst
3093 @deffnx {C Function} scm_reverse_list_to_string (lst)
3094 Return a newly allocated string made from a list of characters, in
3098 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
3102 @rnindex make-string
3103 @deffn {Scheme Procedure} make-string k [chr]
3104 @deffnx {C Function} scm_make_string (k, chr)
3105 Return a newly allocated string of
3106 length @var{k}. If @var{chr} is given, then all elements of
3107 the string are initialized to @var{chr}, otherwise the contents
3108 of the @var{string} are unspecified.
3111 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
3112 Like @code{scm_make_string}, but expects the length as a
3116 @deffn {Scheme Procedure} string-tabulate proc len
3117 @deffnx {C Function} scm_string_tabulate (proc, len)
3118 @var{proc} is an integer->char procedure. Construct a string
3119 of size @var{len} by applying @var{proc} to each index to
3120 produce the corresponding string element. The order in which
3121 @var{proc} is applied to the indices is not specified.
3124 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
3125 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
3126 Append the string in the string list @var{ls}, using the string
3127 @var{delim} as a delimiter between the elements of @var{ls}.
3128 @var{grammar} is a symbol which specifies how the delimiter is
3129 placed between the strings, and defaults to the symbol
3134 Insert the separator between list elements. An empty string
3135 will produce an empty list.
3137 Like @code{infix}, but will raise an error if given the empty
3140 Insert the separator after every list element.
3142 Insert the separator before each list element.
3146 @node List/String Conversion
3147 @subsubsection List/String conversion
3149 When processing strings, it is often convenient to first convert them
3150 into a list representation by using the procedure @code{string->list},
3151 work with the resulting list, and then convert it back into a string.
3152 These procedures are useful for similar tasks.
3154 @rnindex string->list
3155 @deffn {Scheme Procedure} string->list str [start [end]]
3156 @deffnx {C Function} scm_substring_to_list (str, start, end)
3157 @deffnx {C Function} scm_string_to_list (str)
3158 Convert the string @var{str} into a list of characters.
3161 @deffn {Scheme Procedure} string-split str chr
3162 @deffnx {C Function} scm_string_split (str, chr)
3163 Split the string @var{str} into a list of substrings delimited
3164 by appearances of the character @var{chr}. Note that an empty substring
3165 between separator characters will result in an empty string in the
3169 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
3171 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
3173 (string-split "::" #\:)
3177 (string-split "" #\:)
3184 @node String Selection
3185 @subsubsection String Selection
3187 Portions of strings can be extracted by these procedures.
3188 @code{string-ref} delivers individual characters whereas
3189 @code{substring} can be used to extract substrings from longer strings.
3191 @rnindex string-length
3192 @deffn {Scheme Procedure} string-length string
3193 @deffnx {C Function} scm_string_length (string)
3194 Return the number of characters in @var{string}.
3197 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
3198 Return the number of characters in @var{str} as a @code{size_t}.
3202 @deffn {Scheme Procedure} string-ref str k
3203 @deffnx {C Function} scm_string_ref (str, k)
3204 Return character @var{k} of @var{str} using zero-origin
3205 indexing. @var{k} must be a valid index of @var{str}.
3208 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
3209 Return character @var{k} of @var{str} using zero-origin
3210 indexing. @var{k} must be a valid index of @var{str}.
3213 @rnindex string-copy
3214 @deffn {Scheme Procedure} string-copy str [start [end]]
3215 @deffnx {C Function} scm_substring_copy (str, start, end)
3216 @deffnx {C Function} scm_string_copy (str)
3217 Return a copy of the given string @var{str}.
3219 The returned string shares storage with @var{str} initially, but it is
3220 copied as soon as one of the two strings is modified.
3224 @deffn {Scheme Procedure} substring str start [end]
3225 @deffnx {C Function} scm_substring (str, start, end)
3226 Return a new string formed from the characters
3227 of @var{str} beginning with index @var{start} (inclusive) and
3228 ending with index @var{end} (exclusive).
3229 @var{str} must be a string, @var{start} and @var{end} must be
3230 exact integers satisfying:
3232 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
3234 The returned string shares storage with @var{str} initially, but it is
3235 copied as soon as one of the two strings is modified.
3238 @deffn {Scheme Procedure} substring/shared str start [end]
3239 @deffnx {C Function} scm_substring_shared (str, start, end)
3240 Like @code{substring}, but the strings continue to share their storage
3241 even if they are modified. Thus, modifications to @var{str} show up
3242 in the new string, and vice versa.
3245 @deffn {Scheme Procedure} substring/copy str start [end]
3246 @deffnx {C Function} scm_substring_copy (str, start, end)
3247 Like @code{substring}, but the storage for the new string is copied
3251 @deffn {Scheme Procedure} substring/read-only str start [end]
3252 @deffnx {C Function} scm_substring_read_only (str, start, end)
3253 Like @code{substring}, but the resulting string can not be modified.
3256 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
3257 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
3258 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
3259 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
3260 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
3263 @deffn {Scheme Procedure} string-take s n
3264 @deffnx {C Function} scm_string_take (s, n)
3265 Return the @var{n} first characters of @var{s}.
3268 @deffn {Scheme Procedure} string-drop s n
3269 @deffnx {C Function} scm_string_drop (s, n)
3270 Return all but the first @var{n} characters of @var{s}.
3273 @deffn {Scheme Procedure} string-take-right s n
3274 @deffnx {C Function} scm_string_take_right (s, n)
3275 Return the @var{n} last characters of @var{s}.
3278 @deffn {Scheme Procedure} string-drop-right s n
3279 @deffnx {C Function} scm_string_drop_right (s, n)
3280 Return all but the last @var{n} characters of @var{s}.
3283 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
3284 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
3285 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
3286 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
3287 Take characters @var{start} to @var{end} from the string @var{s} and
3288 either pad with @var{char} or truncate them to give @var{len}
3291 @code{string-pad} pads or truncates on the left, so for example
3294 (string-pad "x" 3) @result{} " x"
3295 (string-pad "abcde" 3) @result{} "cde"
3298 @code{string-pad-right} pads or truncates on the right, so for example
3301 (string-pad-right "x" 3) @result{} "x "
3302 (string-pad-right "abcde" 3) @result{} "abc"
3306 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
3307 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
3308 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
3309 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
3310 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
3311 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
3312 Trim occurrences of @var{char_pred} from the ends of @var{s}.
3314 @code{string-trim} trims @var{char_pred} characters from the left
3315 (start) of the string, @code{string-trim-right} trims them from the
3316 right (end) of the string, @code{string-trim-both} trims from both
3319 @var{char_pred} can be a character, a character set, or a predicate
3320 procedure to call on each character. If @var{char_pred} is not given
3321 the default is whitespace as per @code{char-set:whitespace}
3322 (@pxref{Standard Character Sets}).
3325 (string-trim " x ") @result{} "x "
3326 (string-trim-right "banana" #\a) @result{} "banan"
3327 (string-trim-both ".,xy:;" char-set:punctuation)
3329 (string-trim-both "xyzzy" (lambda (c)
3336 @node String Modification
3337 @subsubsection String Modification
3339 These procedures are for modifying strings in-place. This means that the
3340 result of the operation is not a new string; instead, the original string's
3341 memory representation is modified.
3343 @rnindex string-set!
3344 @deffn {Scheme Procedure} string-set! str k chr
3345 @deffnx {C Function} scm_string_set_x (str, k, chr)
3346 Store @var{chr} in element @var{k} of @var{str} and return
3347 an unspecified value. @var{k} must be a valid index of
3351 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
3352 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
3355 @rnindex string-fill!
3356 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
3357 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
3358 @deffnx {C Function} scm_string_fill_x (str, chr)
3359 Stores @var{chr} in every element of the given @var{str} and
3360 returns an unspecified value.
3363 @deffn {Scheme Procedure} substring-fill! str start end fill
3364 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
3365 Change every character in @var{str} between @var{start} and
3366 @var{end} to @var{fill}.
3369 (define y "abcdefg")
3370 (substring-fill! y 1 3 #\r)
3376 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
3377 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
3378 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
3379 into @var{str2} beginning at position @var{start2}.
3380 @var{str1} and @var{str2} can be the same string.
3383 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
3384 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
3385 Copy the sequence of characters from index range [@var{start},
3386 @var{end}) in string @var{s} to string @var{target}, beginning
3387 at index @var{tstart}. The characters are copied left-to-right
3388 or right-to-left as needed -- the copy is guaranteed to work,
3389 even if @var{target} and @var{s} are the same string. It is an
3390 error if the copy operation runs off the end of the target
3395 @node String Comparison
3396 @subsubsection String Comparison
3398 The procedures in this section are similar to the character ordering
3399 predicates (@pxref{Characters}), but are defined on character sequences.
3401 The first set is specified in R5RS and has names that end in @code{?}.
3402 The second set is specified in SRFI-13 and the names have not ending
3405 The predicates ending in @code{-ci} ignore the character case
3406 when comparing strings. For now, case-insensitive comparison is done
3407 using the R5RS rules, where every lower-case character that has a
3408 single character upper-case form is converted to uppercase before
3409 comparison. See @xref{Text Collation, the @code{(ice-9
3410 i18n)} module}, for locale-dependent string comparison.
3413 @deffn {Scheme Procedure} string=? [s1 [s2 . rest]]
3414 @deffnx {C Function} scm_i_string_equal_p (s1, s2, rest)
3415 Lexicographic equality predicate; return @code{#t} if the two
3416 strings are the same length and contain the same characters in
3417 the same positions, otherwise return @code{#f}.
3419 The procedure @code{string-ci=?} treats upper and lower case
3420 letters as though they were the same character, but
3421 @code{string=?} treats upper and lower case as distinct
3426 @deffn {Scheme Procedure} string<? [s1 [s2 . rest]]
3427 @deffnx {C Function} scm_i_string_less_p (s1, s2, rest)
3428 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3429 is lexicographically less than @var{s2}.
3433 @deffn {Scheme Procedure} string<=? [s1 [s2 . rest]]
3434 @deffnx {C Function} scm_i_string_leq_p (s1, s2, rest)
3435 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3436 is lexicographically less than or equal to @var{s2}.
3440 @deffn {Scheme Procedure} string>? [s1 [s2 . rest]]
3441 @deffnx {C Function} scm_i_string_gr_p (s1, s2, rest)
3442 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3443 is lexicographically greater than @var{s2}.
3447 @deffn {Scheme Procedure} string>=? [s1 [s2 . rest]]
3448 @deffnx {C Function} scm_i_string_geq_p (s1, s2, rest)
3449 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3450 is lexicographically greater than or equal to @var{s2}.
3453 @rnindex string-ci=?
3454 @deffn {Scheme Procedure} string-ci=? [s1 [s2 . rest]]
3455 @deffnx {C Function} scm_i_string_ci_equal_p (s1, s2, rest)
3456 Case-insensitive string equality predicate; return @code{#t} if
3457 the two strings are the same length and their component
3458 characters match (ignoring case) at each position; otherwise
3462 @rnindex string-ci<?
3463 @deffn {Scheme Procedure} string-ci<? [s1 [s2 . rest]]
3464 @deffnx {C Function} scm_i_string_ci_less_p (s1, s2, rest)
3465 Case insensitive lexicographic ordering predicate; return
3466 @code{#t} if @var{s1} is lexicographically less than @var{s2}
3471 @deffn {Scheme Procedure} string-ci<=? [s1 [s2 . rest]]
3472 @deffnx {C Function} scm_i_string_ci_leq_p (s1, s2, rest)
3473 Case insensitive lexicographic ordering predicate; return
3474 @code{#t} if @var{s1} is lexicographically less than or equal
3475 to @var{s2} regardless of case.
3478 @rnindex string-ci>?
3479 @deffn {Scheme Procedure} string-ci>? [s1 [s2 . rest]]
3480 @deffnx {C Function} scm_i_string_ci_gr_p (s1, s2, rest)
3481 Case insensitive lexicographic ordering predicate; return
3482 @code{#t} if @var{s1} is lexicographically greater than
3483 @var{s2} regardless of case.
3486 @rnindex string-ci>=?
3487 @deffn {Scheme Procedure} string-ci>=? [s1 [s2 . rest]]
3488 @deffnx {C Function} scm_i_string_ci_geq_p (s1, s2, rest)
3489 Case insensitive lexicographic ordering predicate; return
3490 @code{#t} if @var{s1} is lexicographically greater than or
3491 equal to @var{s2} regardless of case.
3494 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3495 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3496 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3497 mismatch index, depending upon whether @var{s1} is less than,
3498 equal to, or greater than @var{s2}. The mismatch index is the
3499 largest index @var{i} such that for every 0 <= @var{j} <
3500 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3501 @var{i} is the first position that does not match.
3504 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3505 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3506 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3507 mismatch index, depending upon whether @var{s1} is less than,
3508 equal to, or greater than @var{s2}. The mismatch index is the
3509 largest index @var{i} such that for every 0 <= @var{j} <
3510 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3511 @var{i} is the first position where the lowercased letters
3516 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3517 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3518 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3522 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3523 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3524 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3528 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3529 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3530 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3531 true value otherwise.
3534 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3535 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3536 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3537 true value otherwise.
3540 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3541 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3542 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3546 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3547 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3548 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3552 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3553 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3554 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3555 value otherwise. The character comparison is done
3559 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3560 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3561 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3562 value otherwise. The character comparison is done
3566 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3567 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3568 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3569 true value otherwise. The character comparison is done
3573 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3574 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3575 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3576 true value otherwise. The character comparison is done
3580 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3581 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3582 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3583 value otherwise. The character comparison is done
3587 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3588 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3589 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3590 otherwise. The character comparison is done
3594 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3595 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3596 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).
3599 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3600 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3601 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).
3604 Because the same visual appearance of an abstract Unicode character can
3605 be obtained via multiple sequences of Unicode characters, even the
3606 case-insensitive string comparison functions described above may return
3607 @code{#f} when presented with strings containing different
3608 representations of the same character. For example, the Unicode
3609 character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be
3610 represented with a single character (U+1E69) or by the character ``LATIN
3611 SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING
3612 DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307).
3614 For this reason, it is often desirable to ensure that the strings
3615 to be compared are using a mutually consistent representation for every
3616 character. The Unicode standard defines two methods of normalizing the
3617 contents of strings: Decomposition, which breaks composite characters
3618 into a set of constituent characters with an ordering defined by the
3619 Unicode Standard; and composition, which performs the converse.
3621 There are two decomposition operations. ``Canonical decomposition''
3622 produces character sequences that share the same visual appearance as
3623 the original characters, while ``compatibility decomposition'' produces
3624 ones whose visual appearances may differ from the originals but which
3625 represent the same abstract character.
3627 These operations are encapsulated in the following set of normalization
3632 Characters are decomposed to their canonical forms.
3635 Characters are decomposed to their compatibility forms.
3638 Characters are decomposed to their canonical forms, then composed.
3641 Characters are decomposed to their compatibility forms, then composed.
3645 The functions below put their arguments into one of the forms described
3648 @deffn {Scheme Procedure} string-normalize-nfd s
3649 @deffnx {C Function} scm_string_normalize_nfd (s)
3650 Return the @code{NFD} normalized form of @var{s}.
3653 @deffn {Scheme Procedure} string-normalize-nfkd s
3654 @deffnx {C Function} scm_string_normalize_nfkd (s)
3655 Return the @code{NFKD} normalized form of @var{s}.
3658 @deffn {Scheme Procedure} string-normalize-nfc s
3659 @deffnx {C Function} scm_string_normalize_nfc (s)
3660 Return the @code{NFC} normalized form of @var{s}.
3663 @deffn {Scheme Procedure} string-normalize-nfkc s
3664 @deffnx {C Function} scm_string_normalize_nfkc (s)
3665 Return the @code{NFKC} normalized form of @var{s}.
3668 @node String Searching
3669 @subsubsection String Searching
3671 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3672 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3673 Search through the string @var{s} from left to right, returning
3674 the index of the first occurrence of a character which
3678 equals @var{char_pred}, if it is character,
3681 satisfies the predicate @var{char_pred}, if it is a procedure,
3684 is in the set @var{char_pred}, if it is a character set.
3687 Return @code{#f} if no match is found.
3690 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3691 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3692 Search through the string @var{s} from right to left, returning
3693 the index of the last occurrence of a character which
3697 equals @var{char_pred}, if it is character,
3700 satisfies the predicate @var{char_pred}, if it is a procedure,
3703 is in the set if @var{char_pred} is a character set.
3706 Return @code{#f} if no match is found.
3709 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3710 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3711 Return the length of the longest common prefix of the two
3715 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3716 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3717 Return the length of the longest common prefix of the two
3718 strings, ignoring character case.
3721 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3722 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3723 Return the length of the longest common suffix of the two
3727 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3728 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3729 Return the length of the longest common suffix of the two
3730 strings, ignoring character case.
3733 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3734 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3735 Is @var{s1} a prefix of @var{s2}?
3738 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3739 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3740 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3743 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3744 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3745 Is @var{s1} a suffix of @var{s2}?
3748 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3749 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3750 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3753 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3754 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3755 Search through the string @var{s} from right to left, returning
3756 the index of the last occurrence of a character which
3760 equals @var{char_pred}, if it is character,
3763 satisfies the predicate @var{char_pred}, if it is a procedure,
3766 is in the set if @var{char_pred} is a character set.
3769 Return @code{#f} if no match is found.
3772 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3773 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3774 Search through the string @var{s} from left to right, returning
3775 the index of the first occurrence of a character which
3779 does not equal @var{char_pred}, if it is character,
3782 does not satisfy the predicate @var{char_pred}, if it is a
3786 is not in the set if @var{char_pred} is a character set.
3790 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3791 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3792 Search through the string @var{s} from right to left, returning
3793 the index of the last occurrence of a character which
3797 does not equal @var{char_pred}, if it is character,
3800 does not satisfy the predicate @var{char_pred}, if it is a
3804 is not in the set if @var{char_pred} is a character set.
3808 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3809 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3810 Return the count of the number of characters in the string
3815 equals @var{char_pred}, if it is character,
3818 satisfies the predicate @var{char_pred}, if it is a procedure.
3821 is in the set @var{char_pred}, if it is a character set.
3825 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3826 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3827 Does string @var{s1} contain string @var{s2}? Return the index
3828 in @var{s1} where @var{s2} occurs as a substring, or false.
3829 The optional start/end indices restrict the operation to the
3830 indicated substrings.
3833 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3834 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3835 Does string @var{s1} contain string @var{s2}? Return the index
3836 in @var{s1} where @var{s2} occurs as a substring, or false.
3837 The optional start/end indices restrict the operation to the
3838 indicated substrings. Character comparison is done
3842 @node Alphabetic Case Mapping
3843 @subsubsection Alphabetic Case Mapping
3845 These are procedures for mapping strings to their upper- or lower-case
3846 equivalents, respectively, or for capitalizing strings.
3848 They use the basic case mapping rules for Unicode characters. No
3849 special language or context rules are considered. The resulting strings
3850 are guaranteed to be the same length as the input strings.
3852 @xref{Character Case Mapping, the @code{(ice-9
3853 i18n)} module}, for locale-dependent case conversions.
3855 @deffn {Scheme Procedure} string-upcase str [start [end]]
3856 @deffnx {C Function} scm_substring_upcase (str, start, end)
3857 @deffnx {C Function} scm_string_upcase (str)
3858 Upcase every character in @code{str}.
3861 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3862 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3863 @deffnx {C Function} scm_string_upcase_x (str)
3864 Destructively upcase every character in @code{str}.
3874 @deffn {Scheme Procedure} string-downcase str [start [end]]
3875 @deffnx {C Function} scm_substring_downcase (str, start, end)
3876 @deffnx {C Function} scm_string_downcase (str)
3877 Downcase every character in @var{str}.
3880 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3881 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3882 @deffnx {C Function} scm_string_downcase_x (str)
3883 Destructively downcase every character in @var{str}.
3888 (string-downcase! y)
3895 @deffn {Scheme Procedure} string-capitalize str
3896 @deffnx {C Function} scm_string_capitalize (str)
3897 Return a freshly allocated string with the characters in
3898 @var{str}, where the first character of every word is
3902 @deffn {Scheme Procedure} string-capitalize! str
3903 @deffnx {C Function} scm_string_capitalize_x (str)
3904 Upcase the first character of every word in @var{str}
3905 destructively and return @var{str}.
3908 y @result{} "hello world"
3909 (string-capitalize! y) @result{} "Hello World"
3910 y @result{} "Hello World"
3914 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3915 @deffnx {C Function} scm_string_titlecase (str, start, end)
3916 Titlecase every first character in a word in @var{str}.
3919 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3920 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3921 Destructively titlecase every first character in a word in
3925 @node Reversing and Appending Strings
3926 @subsubsection Reversing and Appending Strings
3928 @deffn {Scheme Procedure} string-reverse str [start [end]]
3929 @deffnx {C Function} scm_string_reverse (str, start, end)
3930 Reverse the string @var{str}. The optional arguments
3931 @var{start} and @var{end} delimit the region of @var{str} to
3935 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3936 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3937 Reverse the string @var{str} in-place. The optional arguments
3938 @var{start} and @var{end} delimit the region of @var{str} to
3939 operate on. The return value is unspecified.
3942 @rnindex string-append
3943 @deffn {Scheme Procedure} string-append . args
3944 @deffnx {C Function} scm_string_append (args)
3945 Return a newly allocated string whose characters form the
3946 concatenation of the given strings, @var{args}.
3950 (string-append h "world"))
3951 @result{} "hello world"
3955 @deffn {Scheme Procedure} string-append/shared . rest
3956 @deffnx {C Function} scm_string_append_shared (rest)
3957 Like @code{string-append}, but the result may share memory
3958 with the argument strings.
3961 @deffn {Scheme Procedure} string-concatenate ls
3962 @deffnx {C Function} scm_string_concatenate (ls)
3963 Append the elements of @var{ls} (which must be strings)
3964 together into a single string. Guaranteed to return a freshly
3968 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3969 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3970 Without optional arguments, this procedure is equivalent to
3973 (string-concatenate (reverse ls))
3976 If the optional argument @var{final_string} is specified, it is
3977 consed onto the beginning to @var{ls} before performing the
3978 list-reverse and string-concatenate operations. If @var{end}
3979 is given, only the characters of @var{final_string} up to index
3982 Guaranteed to return a freshly allocated string.
3985 @deffn {Scheme Procedure} string-concatenate/shared ls
3986 @deffnx {C Function} scm_string_concatenate_shared (ls)
3987 Like @code{string-concatenate}, but the result may share memory
3988 with the strings in the list @var{ls}.
3991 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3992 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3993 Like @code{string-concatenate-reverse}, but the result may
3994 share memory with the strings in the @var{ls} arguments.
3997 @node Mapping Folding and Unfolding
3998 @subsubsection Mapping, Folding, and Unfolding
4000 @deffn {Scheme Procedure} string-map proc s [start [end]]
4001 @deffnx {C Function} scm_string_map (proc, s, start, end)
4002 @var{proc} is a char->char procedure, it is mapped over
4003 @var{s}. The order in which the procedure is applied to the
4004 string elements is not specified.
4007 @deffn {Scheme Procedure} string-map! proc s [start [end]]
4008 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
4009 @var{proc} is a char->char procedure, it is mapped over
4010 @var{s}. The order in which the procedure is applied to the
4011 string elements is not specified. The string @var{s} is
4012 modified in-place, the return value is not specified.
4015 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
4016 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
4017 @var{proc} is mapped over @var{s} in left-to-right order. The
4018 return value is not specified.
4021 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
4022 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
4023 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
4026 For example, to change characters to alternately upper and lower case,
4029 (define str (string-copy "studly"))
4030 (string-for-each-index
4033 ((if (even? i) char-upcase char-downcase)
4034 (string-ref str i))))
4036 str @result{} "StUdLy"
4040 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
4041 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
4042 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4043 as the terminating element, from left to right. @var{kons}
4044 must expect two arguments: The actual character and the last
4045 result of @var{kons}' application.
4048 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
4049 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
4050 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4051 as the terminating element, from right to left. @var{kons}
4052 must expect two arguments: The actual character and the last
4053 result of @var{kons}' application.
4056 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
4057 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
4059 @item @var{g} is used to generate a series of @emph{seed}
4060 values from the initial @var{seed}: @var{seed}, (@var{g}
4061 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4063 @item @var{p} tells us when to stop -- when it returns true
4064 when applied to one of these seed values.
4065 @item @var{f} maps each seed value to the corresponding
4066 character in the result string. These chars are assembled
4067 into the string in a left-to-right order.
4068 @item @var{base} is the optional initial/leftmost portion
4069 of the constructed string; it default to the empty
4071 @item @var{make_final} is applied to the terminal seed
4072 value (on which @var{p} returns true) to produce
4073 the final/rightmost portion of the constructed string.
4074 The default is nothing extra.
4078 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
4079 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
4081 @item @var{g} is used to generate a series of @emph{seed}
4082 values from the initial @var{seed}: @var{seed}, (@var{g}
4083 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4085 @item @var{p} tells us when to stop -- when it returns true
4086 when applied to one of these seed values.
4087 @item @var{f} maps each seed value to the corresponding
4088 character in the result string. These chars are assembled
4089 into the string in a right-to-left order.
4090 @item @var{base} is the optional initial/rightmost portion
4091 of the constructed string; it default to the empty
4093 @item @var{make_final} is applied to the terminal seed
4094 value (on which @var{p} returns true) to produce
4095 the final/leftmost portion of the constructed string.
4096 It defaults to @code{(lambda (x) )}.
4100 @node Miscellaneous String Operations
4101 @subsubsection Miscellaneous String Operations
4103 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
4104 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
4105 This is the @emph{extended substring} procedure that implements
4106 replicated copying of a substring of some string.
4108 @var{s} is a string, @var{start} and @var{end} are optional
4109 arguments that demarcate a substring of @var{s}, defaulting to
4110 0 and the length of @var{s}. Replicate this substring up and
4111 down index space, in both the positive and negative directions.
4112 @code{xsubstring} returns the substring of this string
4113 beginning at index @var{from}, and ending at @var{to}, which
4114 defaults to @var{from} + (@var{end} - @var{start}).
4117 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
4118 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
4119 Exactly the same as @code{xsubstring}, but the extracted text
4120 is written into the string @var{target} starting at index
4121 @var{tstart}. The operation is not defined if @code{(eq?
4122 @var{target} @var{s})} or these arguments share storage -- you
4123 cannot copy a string on top of itself.
4126 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
4127 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
4128 Return the string @var{s1}, but with the characters
4129 @var{start1} @dots{} @var{end1} replaced by the characters
4130 @var{start2} @dots{} @var{end2} from @var{s2}.
4133 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
4134 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
4135 Split the string @var{s} into a list of substrings, where each
4136 substring is a maximal non-empty contiguous sequence of
4137 characters from the character set @var{token_set}, which
4138 defaults to @code{char-set:graphic}.
4139 If @var{start} or @var{end} indices are provided, they restrict
4140 @code{string-tokenize} to operating on the indicated substring
4144 @deffn {Scheme Procedure} string-filter char_pred s [start [end]]
4145 @deffnx {C Function} scm_string_filter (char_pred, s, start, end)
4146 Filter the string @var{s}, retaining only those characters which
4147 satisfy @var{char_pred}.
4149 If @var{char_pred} is a procedure, it is applied to each character as
4150 a predicate, if it is a character, it is tested for equality and if it
4151 is a character set, it is tested for membership.
4154 @deffn {Scheme Procedure} string-delete char_pred s [start [end]]
4155 @deffnx {C Function} scm_string_delete (char_pred, s, start, end)
4156 Delete characters satisfying @var{char_pred} from @var{s}.
4158 If @var{char_pred} is a procedure, it is applied to each character as
4159 a predicate, if it is a character, it is tested for equality and if it
4160 is a character set, it is tested for membership.
4163 @node Conversion to/from C
4164 @subsubsection Conversion to/from C
4166 When creating a Scheme string from a C string or when converting a
4167 Scheme string to a C string, the concept of character encoding becomes
4170 In C, a string is just a sequence of bytes, and the character encoding
4171 describes the relation between these bytes and the actual characters
4172 that make up the string. For Scheme strings, character encoding is
4173 not an issue (most of the time), since in Scheme you never get to see
4174 the bytes, only the characters.
4176 Converting to C and converting from C each have their own challenges.
4178 When converting from C to Scheme, it is important that the sequence of
4179 bytes in the C string be valid with respect to its encoding. ASCII
4180 strings, for example, can't have any bytes greater than 127. An ASCII
4181 byte greater than 127 is considered @emph{ill-formed} and cannot be
4182 converted into a Scheme character.
4184 Problems can occur in the reverse operation as well. Not all character
4185 encodings can hold all possible Scheme characters. Some encodings, like
4186 ASCII for example, can only describe a small subset of all possible
4187 characters. So, when converting to C, one must first decide what to do
4188 with Scheme characters that can't be represented in the C string.
4190 Converting a Scheme string to a C string will often allocate fresh
4191 memory to hold the result. You must take care that this memory is
4192 properly freed eventually. In many cases, this can be achieved by
4193 using @code{scm_dynwind_free} inside an appropriate dynwind context,
4194 @xref{Dynamic Wind}.
4196 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
4197 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
4198 Creates a new Scheme string that has the same contents as @var{str} when
4199 interpreted in the character encoding of the current locale.
4201 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
4203 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
4204 @var{str} in bytes, and @var{str} does not need to be null-terminated.
4205 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
4206 null-terminated and the real length will be found with @code{strlen}.
4208 If the C string is ill-formed, an error will be raised.
4210 Note that these functions should @emph{not} be used to convert C string
4211 constants, because there is no guarantee that the current locale will
4212 match that of the source code. To convert C string constants, use
4213 @code{scm_from_latin1_string}, @code{scm_from_utf8_string} or
4214 @code{scm_from_utf32_string}.
4217 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
4218 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
4219 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
4220 respectively, but also frees @var{str} with @code{free} eventually.
4221 Thus, you can use this function when you would free @var{str} anyway
4222 immediately after creating the Scheme string. In certain cases, Guile
4223 can then use @var{str} directly as its internal representation.
4226 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
4227 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
4228 Returns a C string with the same contents as @var{str} in the character
4229 encoding of the current locale. The C string must be freed with
4230 @code{free} eventually, maybe by using @code{scm_dynwind_free},
4231 @xref{Dynamic Wind}.
4233 For @code{scm_to_locale_string}, the returned string is
4234 null-terminated and an error is signalled when @var{str} contains
4235 @code{#\nul} characters.
4237 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
4238 @var{str} might contain @code{#\nul} characters and the length of the
4239 returned string in bytes is stored in @code{*@var{lenp}}. The
4240 returned string will not be null-terminated in this case. If
4241 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
4242 @code{scm_to_locale_string}.
4244 If a character in @var{str} cannot be represented in the character
4245 encoding of the current locale, the default port conversion strategy is
4246 used. @xref{Ports}, for more on conversion strategies.
4248 If the conversion strategy is @code{error}, an error will be raised. If
4249 it is @code{substitute}, a replacement character, such as a question
4250 mark, will be inserted in its place. If it is @code{escape}, a hex
4251 escape will be inserted in its place.
4254 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
4255 Puts @var{str} as a C string in the current locale encoding into the
4256 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
4257 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
4258 more than that. No terminating @code{'\0'} will be stored.
4260 The return value of @code{scm_to_locale_stringbuf} is the number of
4261 bytes that are needed for all of @var{str}, regardless of whether
4262 @var{buf} was large enough to hold them. Thus, when the return value
4263 is larger than @var{max_len}, only @var{max_len} bytes have been
4264 stored and you probably need to try again with a larger buffer.
4267 For most situations, string conversion should occur using the current
4268 locale, such as with the functions above. But there may be cases where
4269 one wants to convert strings from a character encoding other than the
4270 locale's character encoding. For these cases, the lower-level functions
4271 @code{scm_to_stringn} and @code{scm_from_stringn} are provided. These
4272 functions should seldom be necessary if one is properly using locales.
4274 @deftp {C Type} scm_t_string_failed_conversion_handler
4275 This is an enumerated type that can take one of three values:
4276 @code{SCM_FAILED_CONVERSION_ERROR},
4277 @code{SCM_FAILED_CONVERSION_QUESTION_MARK}, and
4278 @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}. They are used to indicate
4279 a strategy for handling characters that cannot be converted to or from a
4280 given character encoding. @code{SCM_FAILED_CONVERSION_ERROR} indicates
4281 that a conversion should throw an error if some characters cannot be
4282 converted. @code{SCM_FAILED_CONVERSION_QUESTION_MARK} indicates that a
4283 conversion should replace unconvertable characters with the question
4284 mark character. And, @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}
4285 requests that a conversion should replace an unconvertable character
4286 with an escape sequence.
4288 While all three strategies apply when converting Scheme strings to C,
4289 only @code{SCM_FAILED_CONVERSION_ERROR} and
4290 @code{SCM_FAILED_CONVERSION_QUESTION_MARK} can be used when converting C
4294 @deftypefn {C Function} char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding, scm_t_string_failed_conversion_handler handler)
4295 This function returns a newly allocated C string from the Guile string
4296 @var{str}. The length of the returned string in bytes will be returned in
4297 @var{lenp}. The character encoding of the C string is passed as the ASCII,
4298 null-terminated C string @var{encoding}. The @var{handler} parameter
4299 gives a strategy for dealing with characters that cannot be converted
4300 into @var{encoding}.
4302 If @var{lenp} is @code{NULL}, this function will return a null-terminated C
4303 string. It will throw an error if the string contains a null
4307 @deftypefn {C Function} SCM scm_from_stringn (const char *str, size_t len, const char *encoding, scm_t_string_failed_conversion_handler handler)
4308 This function returns a scheme string from the C string @var{str}. The
4309 length in bytes of the C string is input as @var{len}. The encoding of the C
4310 string is passed as the ASCII, null-terminated C string @code{encoding}.
4311 The @var{handler} parameters suggests a strategy for dealing with
4312 unconvertable characters.
4315 The following conversion functions are provided as a convenience for the
4316 most commonly used encodings.
4318 @deftypefn {C Function} SCM scm_from_latin1_string (const char *str)
4319 @deftypefnx {C Function} SCM scm_from_utf8_string (const char *str)
4320 @deftypefnx {C Function} SCM scm_from_utf32_string (const scm_t_wchar *str)
4321 Return a scheme string from the null-terminated C string @var{str},
4322 which is ISO-8859-1-, UTF-8-, or UTF-32-encoded. These functions should
4323 be used to convert hard-coded C string constants into Scheme strings.
4326 @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len)
4327 @deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len)
4328 @deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
4329 Return a scheme string from C string @var{str}, which is ISO-8859-1-,
4330 UTF-8-, or UTF-32-encoded, of length @var{len}. @var{len} is the number
4331 of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and
4332 @code{scm_from_utf8_stringn}; it is the number of elements (code points)
4333 in @var{str} in the case of @code{scm_from_utf32_stringn}.
4336 @deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp)
4337 @deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp)
4338 @deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp)
4339 Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string
4340 from Scheme string @var{str}. An error is thrown when @var{str}
4341 cannot be converted to the specified encoding. If @var{lenp} is
4342 @code{NULL}, the returned C string will be null terminated, and an error
4343 will be thrown if the C string would otherwise contain null
4344 characters. If @var{lenp} is not @code{NULL}, the string is not null terminated,
4345 and the length of the returned string is returned in @var{lenp}. The length
4346 returned is the number of bytes for @code{scm_to_latin1_stringn} and
4347 @code{scm_to_utf8_stringn}; it is the number of elements (code points)
4348 for @code{scm_to_utf32_stringn}.
4351 @node String Internals
4352 @subsubsection String Internals
4354 Guile stores each string in memory as a contiguous array of Unicode code
4355 points along with an associated set of attributes. If all of the code
4356 points of a string have an integer range between 0 and 255 inclusive,
4357 the code point array is stored as one byte per code point: it is stored
4358 as an ISO-8859-1 (aka Latin-1) string. If any of the code points of the
4359 string has an integer value greater that 255, the code point array is
4360 stored as four bytes per code point: it is stored as a UTF-32 string.
4362 Conversion between the one-byte-per-code-point and
4363 four-bytes-per-code-point representations happens automatically as
4366 No API is provided to set the internal representation of strings;
4367 however, there are pair of procedures available to query it. These are
4368 debugging procedures. Using them in production code is discouraged,
4369 since the details of Guile's internal representation of strings may
4370 change from release to release.
4372 @deffn {Scheme Procedure} string-bytes-per-char str
4373 @deffnx {C Function} scm_string_bytes_per_char (str)
4374 Return the number of bytes used to encode a Unicode code point in string
4375 @var{str}. The result is one or four.
4378 @deffn {Scheme Procedure} %string-dump str
4379 @deffnx {C Function} scm_sys_string_dump (str)
4380 Returns an association list containing debugging information for
4381 @var{str}. The association list has the following entries.
4388 The start index of the string into its stringbuf
4391 The length of the string
4394 If this string is a substring, it returns its
4395 parent string. Otherwise, it returns @code{#f}
4398 @code{#t} if the string is read-only
4400 @item stringbuf-chars
4401 A new string containing this string's stringbuf's characters
4403 @item stringbuf-length
4404 The number of characters in this stringbuf
4406 @item stringbuf-shared
4407 @code{#t} if this stringbuf is shared
4409 @item stringbuf-wide
4410 @code{#t} if this stringbuf's characters are stored in a 32-bit buffer,
4411 or @code{#f} if they are stored in an 8-bit buffer
4417 @subsection Bytevectors
4422 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevectors)}
4423 module provides the programming interface specified by the
4424 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
4425 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
4426 interpret their contents in a number of ways: bytevector contents can be
4427 accessed as signed or unsigned integer of various sizes and endianness,
4428 as IEEE-754 floating point numbers, or as strings. It is a useful tool
4429 to encode and decode binary data.
4431 The R6RS (Section 4.3.4) specifies an external representation for
4432 bytevectors, whereby the octets (integers in the range 0--255) contained
4433 in the bytevector are represented as a list prefixed by @code{#vu8}:
4439 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
4440 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
4441 they do not need to be quoted:
4445 @result{} #vu8(1 53 204)
4448 Bytevectors can be used with the binary input/output primitives of the
4449 R6RS (@pxref{R6RS I/O Ports}).
4452 * Bytevector Endianness:: Dealing with byte order.
4453 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
4454 * Bytevectors as Integers:: Interpreting bytes as integers.
4455 * Bytevectors and Integer Lists:: Converting to/from an integer list.
4456 * Bytevectors as Floats:: Interpreting bytes as real numbers.
4457 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
4458 * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API.
4459 * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4.
4462 @node Bytevector Endianness
4463 @subsubsection Endianness
4469 Some of the following procedures take an @var{endianness} parameter.
4470 The @dfn{endianness} is defined as the order of bytes in multi-byte
4471 numbers: numbers encoded in @dfn{big endian} have their most
4472 significant bytes written first, whereas numbers encoded in
4473 @dfn{little endian} have their least significant bytes
4474 first@footnote{Big-endian and little-endian are the most common
4475 ``endiannesses'', but others do exist. For instance, the GNU MP
4476 library allows @dfn{word order} to be specified independently of
4477 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
4478 Multiple Precision Arithmetic Library Manual}).}.
4480 Little-endian is the native endianness of the IA32 architecture and
4481 its derivatives, while big-endian is native to SPARC and PowerPC,
4482 among others. The @code{native-endianness} procedure returns the
4483 native endianness of the machine it runs on.
4485 @deffn {Scheme Procedure} native-endianness
4486 @deffnx {C Function} scm_native_endianness ()
4487 Return a value denoting the native endianness of the host machine.
4490 @deffn {Scheme Macro} endianness symbol
4491 Return an object denoting the endianness specified by @var{symbol}. If
4492 @var{symbol} is neither @code{big} nor @code{little} then an error is
4493 raised at expand-time.
4496 @defvr {C Variable} scm_endianness_big
4497 @defvrx {C Variable} scm_endianness_little
4498 The objects denoting big- and little-endianness, respectively.
4502 @node Bytevector Manipulation
4503 @subsubsection Manipulating Bytevectors
4505 Bytevectors can be created, copied, and analyzed with the following
4506 procedures and C functions.
4508 @deffn {Scheme Procedure} make-bytevector len [fill]
4509 @deffnx {C Function} scm_make_bytevector (len, fill)
4510 @deffnx {C Function} scm_c_make_bytevector (size_t len)
4511 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
4512 is given, fill it with @var{fill}; @var{fill} must be in the range
4516 @deffn {Scheme Procedure} bytevector? obj
4517 @deffnx {C Function} scm_bytevector_p (obj)
4518 Return true if @var{obj} is a bytevector.
4521 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
4522 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
4525 @deffn {Scheme Procedure} bytevector-length bv
4526 @deffnx {C Function} scm_bytevector_length (bv)
4527 Return the length in bytes of bytevector @var{bv}.
4530 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
4531 Likewise, return the length in bytes of bytevector @var{bv}.
4534 @deffn {Scheme Procedure} bytevector=? bv1 bv2
4535 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
4536 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
4537 length and contents.
4540 @deffn {Scheme Procedure} bytevector-fill! bv fill
4541 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
4542 Fill bytevector @var{bv} with @var{fill}, a byte.
4545 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
4546 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
4547 Copy @var{len} bytes from @var{source} into @var{target}, starting
4548 reading from @var{source-start} (a positive index within @var{source})
4549 and start writing at @var{target-start}.
4552 @deffn {Scheme Procedure} bytevector-copy bv
4553 @deffnx {C Function} scm_bytevector_copy (bv)
4554 Return a newly allocated copy of @var{bv}.
4557 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
4558 Return the byte at @var{index} in bytevector @var{bv}.
4561 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
4562 Set the byte at @var{index} in @var{bv} to @var{value}.
4565 Low-level C macros are available. They do not perform any
4566 type-checking; as such they should be used with care.
4568 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
4569 Return the length in bytes of bytevector @var{bv}.
4572 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
4573 Return a pointer to the contents of bytevector @var{bv}.
4577 @node Bytevectors as Integers
4578 @subsubsection Interpreting Bytevector Contents as Integers
4580 The contents of a bytevector can be interpreted as a sequence of
4581 integers of any given size, sign, and endianness.
4584 (let ((bv (make-bytevector 4)))
4585 (bytevector-u8-set! bv 0 #x12)
4586 (bytevector-u8-set! bv 1 #x34)
4587 (bytevector-u8-set! bv 2 #x56)
4588 (bytevector-u8-set! bv 3 #x78)
4590 (map (lambda (number)
4591 (number->string number 16))
4592 (list (bytevector-u8-ref bv 0)
4593 (bytevector-u16-ref bv 0 (endianness big))
4594 (bytevector-u32-ref bv 0 (endianness little)))))
4596 @result{} ("12" "1234" "78563412")
4599 The most generic procedures to interpret bytevector contents as integers
4600 are described below.
4602 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
4603 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
4604 Return the @var{size}-byte long unsigned integer at index @var{index} in
4605 @var{bv}, decoded according to @var{endianness}.
4608 @deffn {Scheme Procedure} bytevector-sint-ref bv index endianness size
4609 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
4610 Return the @var{size}-byte long signed integer at index @var{index} in
4611 @var{bv}, decoded according to @var{endianness}.
4614 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
4615 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
4616 Set the @var{size}-byte long unsigned integer at @var{index} to
4617 @var{value}, encoded according to @var{endianness}.
4620 @deffn {Scheme Procedure} bytevector-sint-set! bv index value endianness size
4621 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
4622 Set the @var{size}-byte long signed integer at @var{index} to
4623 @var{value}, encoded according to @var{endianness}.
4626 The following procedures are similar to the ones above, but specialized
4627 to a given integer size:
4629 @deffn {Scheme Procedure} bytevector-u8-ref bv index
4630 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
4631 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
4632 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
4633 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
4634 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
4635 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
4636 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
4637 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
4638 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
4639 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
4640 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
4641 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
4642 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
4643 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
4644 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
4645 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4646 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
4650 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
4651 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
4652 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
4653 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
4654 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
4655 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
4656 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
4657 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
4658 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
4659 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
4660 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
4661 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
4662 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
4663 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
4664 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
4665 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
4666 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4667 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
4671 Finally, a variant specialized for the host's endianness is available
4672 for each of these functions (with the exception of the @code{u8}
4673 accessors, for obvious reasons):
4675 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4676 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4677 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4678 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4679 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4680 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4681 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4682 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4683 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4684 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4685 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4686 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4687 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4688 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4689 host's native endianness.
4692 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4693 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4694 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4695 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4696 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4697 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4698 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4699 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4700 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4701 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4702 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4703 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4704 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4705 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4706 host's native endianness.
4710 @node Bytevectors and Integer Lists
4711 @subsubsection Converting Bytevectors to/from Integer Lists
4713 Bytevector contents can readily be converted to/from lists of signed or
4717 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4718 (endianness little) 2)
4722 @deffn {Scheme Procedure} bytevector->u8-list bv
4723 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4724 Return a newly allocated list of unsigned 8-bit integers from the
4725 contents of @var{bv}.
4728 @deffn {Scheme Procedure} u8-list->bytevector lst
4729 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4730 Return a newly allocated bytevector consisting of the unsigned 8-bit
4731 integers listed in @var{lst}.
4734 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4735 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4736 Return a list of unsigned integers of @var{size} bytes representing the
4737 contents of @var{bv}, decoded according to @var{endianness}.
4740 @deffn {Scheme Procedure} bytevector->sint-list bv endianness size
4741 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4742 Return a list of signed integers of @var{size} bytes representing the
4743 contents of @var{bv}, decoded according to @var{endianness}.
4746 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4747 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4748 Return a new bytevector containing the unsigned integers listed in
4749 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4752 @deffn {Scheme Procedure} sint-list->bytevector lst endianness size
4753 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4754 Return a new bytevector containing the signed integers listed in
4755 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4758 @node Bytevectors as Floats
4759 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4761 @cindex IEEE-754 floating point numbers
4763 Bytevector contents can also be accessed as IEEE-754 single- or
4764 double-precision floating point numbers (respectively 32 and 64-bit
4765 long) using the procedures described here.
4767 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4768 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4769 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4770 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4771 Return the IEEE-754 single-precision floating point number from @var{bv}
4772 at @var{index} according to @var{endianness}.
4775 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4776 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4777 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4778 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4779 Store real number @var{value} in @var{bv} at @var{index} according to
4783 Specialized procedures are also available:
4785 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4786 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4787 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4788 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4789 Return the IEEE-754 single-precision floating point number from @var{bv}
4790 at @var{index} according to the host's native endianness.
4793 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4794 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4795 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4796 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4797 Store real number @var{value} in @var{bv} at @var{index} according to
4798 the host's native endianness.
4802 @node Bytevectors as Strings
4803 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4805 @cindex Unicode string encoding
4807 Bytevector contents can also be interpreted as Unicode strings encoded
4808 in one of the most commonly available encoding formats.
4811 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4814 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4815 @result{} #vu8(99 97 102 195 169)
4818 @deffn {Scheme Procedure} string->utf8 str
4819 @deffnx {Scheme Procedure} string->utf16 str [endianness]
4820 @deffnx {Scheme Procedure} string->utf32 str [endianness]
4821 @deffnx {C Function} scm_string_to_utf8 (str)
4822 @deffnx {C Function} scm_string_to_utf16 (str, endianness)
4823 @deffnx {C Function} scm_string_to_utf32 (str, endianness)
4824 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4825 UTF-32 (aka. UCS-4) encoding of @var{str}. For UTF-16 and UTF-32,
4826 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4827 it defaults to big endian.
4830 @deffn {Scheme Procedure} utf8->string utf
4831 @deffnx {Scheme Procedure} utf16->string utf [endianness]
4832 @deffnx {Scheme Procedure} utf32->string utf [endianness]
4833 @deffnx {C Function} scm_utf8_to_string (utf)
4834 @deffnx {C Function} scm_utf16_to_string (utf, endianness)
4835 @deffnx {C Function} scm_utf32_to_string (utf, endianness)
4836 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4837 or UTF-32-decoded contents of bytevector @var{utf}. For UTF-16 and UTF-32,
4838 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4839 it defaults to big endian.
4842 @node Bytevectors as Generalized Vectors
4843 @subsubsection Accessing Bytevectors with the Generalized Vector API
4845 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4846 with the @dfn{generalized vector} procedures (@pxref{Generalized
4847 Vectors}). This also allows bytevectors to be accessed using the
4848 generic @dfn{array} procedures (@pxref{Array Procedures}). When using
4849 these APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4852 (define bv #vu8(0 1 2 3))
4854 (generalized-vector? bv)
4857 (generalized-vector-ref bv 2)
4860 (generalized-vector-set! bv 2 77)
4869 @node Bytevectors as Uniform Vectors
4870 @subsubsection Accessing Bytevectors with the SRFI-4 API
4872 Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and
4873 Bytevectors}, for more information.
4880 Symbols in Scheme are widely used in three ways: as items of discrete
4881 data, as lookup keys for alists and hash tables, and to denote variable
4884 A @dfn{symbol} is similar to a string in that it is defined by a
4885 sequence of characters. The sequence of characters is known as the
4886 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4887 name doesn't include any characters that could be confused with other
4888 elements of Scheme syntax --- a symbol is written in a Scheme program by
4889 writing the sequence of characters that make up the name, @emph{without}
4890 any quotation marks or other special syntax. For example, the symbol
4891 whose name is ``multiply-by-2'' is written, simply:
4897 Notice how this differs from a @emph{string} with contents
4898 ``multiply-by-2'', which is written with double quotation marks, like
4905 Looking beyond how they are written, symbols are different from strings
4906 in two important respects.
4908 The first important difference is uniqueness. If the same-looking
4909 string is read twice from two different places in a program, the result
4910 is two @emph{different} string objects whose contents just happen to be
4911 the same. If, on the other hand, the same-looking symbol is read twice
4912 from two different places in a program, the result is the @emph{same}
4913 symbol object both times.
4915 Given two read symbols, you can use @code{eq?} to test whether they are
4916 the same (that is, have the same name). @code{eq?} is the most
4917 efficient comparison operator in Scheme, and comparing two symbols like
4918 this is as fast as comparing, for example, two numbers. Given two
4919 strings, on the other hand, you must use @code{equal?} or
4920 @code{string=?}, which are much slower comparison operators, to
4921 determine whether the strings have the same contents.
4924 (define sym1 (quote hello))
4925 (define sym2 (quote hello))
4926 (eq? sym1 sym2) @result{} #t
4928 (define str1 "hello")
4929 (define str2 "hello")
4930 (eq? str1 str2) @result{} #f
4931 (equal? str1 str2) @result{} #t
4934 The second important difference is that symbols, unlike strings, are not
4935 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
4936 example above: @code{(quote hello)} evaluates to the symbol named
4937 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
4938 symbol named "hello" and evaluated as a variable reference @dots{} about
4939 which more below (@pxref{Symbol Variables}).
4942 * Symbol Data:: Symbols as discrete data.
4943 * Symbol Keys:: Symbols as lookup keys.
4944 * Symbol Variables:: Symbols as denoting variables.
4945 * Symbol Primitives:: Operations related to symbols.
4946 * Symbol Props:: Function slots and property lists.
4947 * Symbol Read Syntax:: Extended read syntax for symbols.
4948 * Symbol Uninterned:: Uninterned symbols.
4953 @subsubsection Symbols as Discrete Data
4955 Numbers and symbols are similar to the extent that they both lend
4956 themselves to @code{eq?} comparison. But symbols are more descriptive
4957 than numbers, because a symbol's name can be used directly to describe
4958 the concept for which that symbol stands.
4960 For example, imagine that you need to represent some colours in a
4961 computer program. Using numbers, you would have to choose arbitrarily
4962 some mapping between numbers and colours, and then take care to use that
4963 mapping consistently:
4966 ;; 1=red, 2=green, 3=purple
4968 (if (eq? (colour-of car) 1)
4973 You can make the mapping more explicit and the code more readable by
4981 (if (eq? (colour-of car) red)
4986 But the simplest and clearest approach is not to use numbers at all, but
4987 symbols whose names specify the colours that they refer to:
4990 (if (eq? (colour-of car) 'red)
4994 The descriptive advantages of symbols over numbers increase as the set
4995 of concepts that you want to describe grows. Suppose that a car object
4996 can have other properties as well, such as whether it has or uses:
5000 automatic or manual transmission
5002 leaded or unleaded fuel
5004 power steering (or not).
5008 Then a car's combined property set could be naturally represented and
5009 manipulated as a list of symbols:
5012 (properties-of car1)
5014 (red manual unleaded power-steering)
5016 (if (memq 'power-steering (properties-of car1))
5017 (display "Unfit people can drive this car.\n")
5018 (display "You'll need strong arms to drive this car!\n"))
5020 Unfit people can drive this car.
5023 Remember, the fundamental property of symbols that we are relying on
5024 here is that an occurrence of @code{'red} in one part of a program is an
5025 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
5026 another part of a program; this means that symbols can usefully be
5027 compared using @code{eq?}. At the same time, symbols have naturally
5028 descriptive names. This combination of efficiency and descriptive power
5029 makes them ideal for use as discrete data.
5033 @subsubsection Symbols as Lookup Keys
5035 Given their efficiency and descriptive power, it is natural to use
5036 symbols as the keys in an association list or hash table.
5038 To illustrate this, consider a more structured representation of the car
5039 properties example from the preceding subsection. Rather than
5040 mixing all the properties up together in a flat list, we could use an
5041 association list like this:
5044 (define car1-properties '((colour . red)
5045 (transmission . manual)
5047 (steering . power-assisted)))
5050 Notice how this structure is more explicit and extensible than the flat
5051 list. For example it makes clear that @code{manual} refers to the
5052 transmission rather than, say, the windows or the locking of the car.
5053 It also allows further properties to use the same symbols among their
5054 possible values without becoming ambiguous:
5057 (define car1-properties '((colour . red)
5058 (transmission . manual)
5060 (steering . power-assisted)
5062 (locking . manual)))
5065 With a representation like this, it is easy to use the efficient
5066 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
5067 extract or change individual pieces of information:
5070 (assq-ref car1-properties 'fuel) @result{} unleaded
5071 (assq-ref car1-properties 'transmission) @result{} manual
5073 (assq-set! car1-properties 'seat-colour 'black)
5076 (transmission . manual)
5078 (steering . power-assisted)
5079 (seat-colour . black)
5080 (locking . manual)))
5083 Hash tables also have keys, and exactly the same arguments apply to the
5084 use of symbols in hash tables as in association lists. The hash value
5085 that Guile uses to decide where to add a symbol-keyed entry to a hash
5086 table can be obtained by calling the @code{symbol-hash} procedure:
5088 @deffn {Scheme Procedure} symbol-hash symbol
5089 @deffnx {C Function} scm_symbol_hash (symbol)
5090 Return a hash value for @var{symbol}.
5093 See @ref{Hash Tables} for information about hash tables in general, and
5094 for why you might choose to use a hash table rather than an association
5098 @node Symbol Variables
5099 @subsubsection Symbols as Denoting Variables
5101 When an unquoted symbol in a Scheme program is evaluated, it is
5102 interpreted as a variable reference, and the result of the evaluation is
5103 the appropriate variable's value.
5105 For example, when the expression @code{(string-length "abcd")} is read
5106 and evaluated, the sequence of characters @code{string-length} is read
5107 as the symbol whose name is "string-length". This symbol is associated
5108 with a variable whose value is the procedure that implements string
5109 length calculation. Therefore evaluation of the @code{string-length}
5110 symbol results in that procedure.
5112 The details of the connection between an unquoted symbol and the
5113 variable to which it refers are explained elsewhere. See @ref{Binding
5114 Constructs}, for how associations between symbols and variables are
5115 created, and @ref{Modules}, for how those associations are affected by
5116 Guile's module system.
5119 @node Symbol Primitives
5120 @subsubsection Operations Related to Symbols
5122 Given any Scheme value, you can determine whether it is a symbol using
5123 the @code{symbol?} primitive:
5126 @deffn {Scheme Procedure} symbol? obj
5127 @deffnx {C Function} scm_symbol_p (obj)
5128 Return @code{#t} if @var{obj} is a symbol, otherwise return
5132 @deftypefn {C Function} int scm_is_symbol (SCM val)
5133 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
5136 Once you know that you have a symbol, you can obtain its name as a
5137 string by calling @code{symbol->string}. Note that Guile differs by
5138 default from R5RS on the details of @code{symbol->string} as regards
5141 @rnindex symbol->string
5142 @deffn {Scheme Procedure} symbol->string s
5143 @deffnx {C Function} scm_symbol_to_string (s)
5144 Return the name of symbol @var{s} as a string. By default, Guile reads
5145 symbols case-sensitively, so the string returned will have the same case
5146 variation as the sequence of characters that caused @var{s} to be
5149 If Guile is set to read symbols case-insensitively (as specified by
5150 R5RS), and @var{s} comes into being as part of a literal expression
5151 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
5152 by a call to the @code{read} or @code{string-ci->symbol} procedures,
5153 Guile converts any alphabetic characters in the symbol's name to
5154 lower case before creating the symbol object, so the string returned
5155 here will be in lower case.
5157 If @var{s} was created by @code{string->symbol}, the case of characters
5158 in the string returned will be the same as that in the string that was
5159 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5160 setting at the time @var{s} was created.
5162 It is an error to apply mutation procedures like @code{string-set!} to
5163 strings returned by this procedure.
5166 Most symbols are created by writing them literally in code. However it
5167 is also possible to create symbols programmatically using the following
5170 @deffn {Scheme Procedure} symbol char@dots{}
5172 Return a newly allocated symbol made from the given character arguments.
5175 (symbol #\x #\y #\z) @result{} xyz
5179 @deffn {Scheme Procedure} list->symbol lst
5180 @rnindex list->symbol
5181 Return a newly allocated symbol made from a list of characters.
5184 (list->symbol '(#\a #\b #\c)) @result{} abc
5188 @rnindex symbol-append
5189 @deffn {Scheme Procedure} symbol-append . args
5190 Return a newly allocated symbol whose characters form the
5191 concatenation of the given symbols, @var{args}.
5195 (symbol-append h 'world))
5196 @result{} helloworld
5200 @rnindex string->symbol
5201 @deffn {Scheme Procedure} string->symbol string
5202 @deffnx {C Function} scm_string_to_symbol (string)
5203 Return the symbol whose name is @var{string}. This procedure can create
5204 symbols with names containing special characters or letters in the
5205 non-standard case, but it is usually a bad idea to create such symbols
5206 because in some implementations of Scheme they cannot be read as
5210 @deffn {Scheme Procedure} string-ci->symbol str
5211 @deffnx {C Function} scm_string_ci_to_symbol (str)
5212 Return the symbol whose name is @var{str}. If Guile is currently
5213 reading symbols case-insensitively, @var{str} is converted to lowercase
5214 before the returned symbol is looked up or created.
5217 The following examples illustrate Guile's detailed behaviour as regards
5218 the case-sensitivity of symbols:
5221 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5223 (symbol->string 'flying-fish) @result{} "flying-fish"
5224 (symbol->string 'Martin) @result{} "martin"
5226 (string->symbol "Malvina")) @result{} "Malvina"
5228 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5229 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5230 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5232 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5233 (string=? "K. Harper, M.D."
5235 (string->symbol "K. Harper, M.D."))) @result{} #t
5237 (read-disable 'case-insensitive) ; Guile default behaviour
5239 (symbol->string 'flying-fish) @result{} "flying-fish"
5240 (symbol->string 'Martin) @result{} "Martin"
5242 (string->symbol "Malvina")) @result{} "Malvina"
5244 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5245 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5246 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5248 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5249 (string=? "K. Harper, M.D."
5251 (string->symbol "K. Harper, M.D."))) @result{} #t
5254 From C, there are lower level functions that construct a Scheme symbol
5255 from a C string in the current locale encoding.
5257 When you want to do more from C, you should convert between symbols
5258 and strings using @code{scm_symbol_to_string} and
5259 @code{scm_string_to_symbol} and work with the strings.
5261 @deffn {C Function} scm_from_latin1_symbol (const char *name)
5262 @deffnx {C Function} scm_from_utf8_symbol (const char *name)
5263 Construct and return a Scheme symbol whose name is specified by the
5264 null-terminated C string @var{name}. These are appropriate when
5265 the C string is hard-coded in the source code.
5268 @deffn {C Function} scm_from_locale_symbol (const char *name)
5269 @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
5270 Construct and return a Scheme symbol whose name is specified by
5271 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5272 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5273 specified explicitly by @var{len}.
5275 Note that these functions should @emph{not} be used when @var{name} is a
5276 C string constant, because there is no guarantee that the current locale
5277 will match that of the source code. In such cases, use
5278 @code{scm_from_latin1_symbol} or @code{scm_from_utf8_symbol}.
5281 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5282 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5283 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5284 respectively, but also frees @var{str} with @code{free} eventually.
5285 Thus, you can use this function when you would free @var{str} anyway
5286 immediately after creating the Scheme string. In certain cases, Guile
5287 can then use @var{str} directly as its internal representation.
5290 The size of a symbol can also be obtained from C:
5292 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5293 Return the number of characters in @var{sym}.
5296 Finally, some applications, especially those that generate new Scheme
5297 code dynamically, need to generate symbols for use in the generated
5298 code. The @code{gensym} primitive meets this need:
5300 @deffn {Scheme Procedure} gensym [prefix]
5301 @deffnx {C Function} scm_gensym (prefix)
5302 Create a new symbol with a name constructed from a prefix and a counter
5303 value. The string @var{prefix} can be specified as an optional
5304 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5305 at each call. There is no provision for resetting the counter.
5308 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5309 since their names begin with a space and it is only otherwise possible
5310 to generate such symbols if a programmer goes out of their way to do
5311 so. Uniqueness can be guaranteed by instead using uninterned symbols
5312 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5317 @subsubsection Function Slots and Property Lists
5319 In traditional Lisp dialects, symbols are often understood as having
5320 three kinds of value at once:
5324 a @dfn{variable} value, which is used when the symbol appears in
5325 code in a variable reference context
5328 a @dfn{function} value, which is used when the symbol appears in
5329 code in a function name position (i.e.@: as the first element in an
5333 a @dfn{property list} value, which is used when the symbol is given as
5334 the first argument to Lisp's @code{put} or @code{get} functions.
5337 Although Scheme (as one of its simplifications with respect to Lisp)
5338 does away with the distinction between variable and function namespaces,
5339 Guile currently retains some elements of the traditional structure in
5340 case they turn out to be useful when implementing translators for other
5341 languages, in particular Emacs Lisp.
5343 Specifically, Guile symbols have two extra slots, one for a symbol's
5344 property list, and one for its ``function value.'' The following procedures
5345 are provided to access these slots.
5347 @deffn {Scheme Procedure} symbol-fref symbol
5348 @deffnx {C Function} scm_symbol_fref (symbol)
5349 Return the contents of @var{symbol}'s @dfn{function slot}.
5352 @deffn {Scheme Procedure} symbol-fset! symbol value
5353 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5354 Set the contents of @var{symbol}'s function slot to @var{value}.
5357 @deffn {Scheme Procedure} symbol-pref symbol
5358 @deffnx {C Function} scm_symbol_pref (symbol)
5359 Return the @dfn{property list} currently associated with @var{symbol}.
5362 @deffn {Scheme Procedure} symbol-pset! symbol value
5363 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5364 Set @var{symbol}'s property list to @var{value}.
5367 @deffn {Scheme Procedure} symbol-property sym prop
5368 From @var{sym}'s property list, return the value for property
5369 @var{prop}. The assumption is that @var{sym}'s property list is an
5370 association list whose keys are distinguished from each other using
5371 @code{equal?}; @var{prop} should be one of the keys in that list. If
5372 the property list has no entry for @var{prop}, @code{symbol-property}
5376 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5377 In @var{sym}'s property list, set the value for property @var{prop} to
5378 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5379 none already exists. For the structure of the property list, see
5380 @code{symbol-property}.
5383 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5384 From @var{sym}'s property list, remove the entry for property
5385 @var{prop}, if there is one. For the structure of the property list,
5386 see @code{symbol-property}.
5389 Support for these extra slots may be removed in a future release, and it
5390 is probably better to avoid using them. For a more modern and Schemely
5391 approach to properties, see @ref{Object Properties}.
5394 @node Symbol Read Syntax
5395 @subsubsection Extended Read Syntax for Symbols
5397 The read syntax for a symbol is a sequence of letters, digits, and
5398 @dfn{extended alphabetic characters}, beginning with a character that
5399 cannot begin a number. In addition, the special cases of @code{+},
5400 @code{-}, and @code{...} are read as symbols even though numbers can
5401 begin with @code{+}, @code{-} or @code{.}.
5403 Extended alphabetic characters may be used within identifiers as if
5404 they were letters. The set of extended alphabetic characters is:
5407 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5410 In addition to the standard read syntax defined above (which is taken
5411 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5412 Scheme})), Guile provides an extended symbol read syntax that allows the
5413 inclusion of unusual characters such as space characters, newlines and
5414 parentheses. If (for whatever reason) you need to write a symbol
5415 containing characters not mentioned above, you can do so as follows.
5419 Begin the symbol with the characters @code{#@{},
5422 write the characters of the symbol and
5425 finish the symbol with the characters @code{@}#}.
5428 Here are a few examples of this form of read syntax. The first symbol
5429 needs to use extended syntax because it contains a space character, the
5430 second because it contains a line break, and the last because it looks
5442 Although Guile provides this extended read syntax for symbols,
5443 widespread usage of it is discouraged because it is not portable and not
5447 @node Symbol Uninterned
5448 @subsubsection Uninterned Symbols
5450 What makes symbols useful is that they are automatically kept unique.
5451 There are no two symbols that are distinct objects but have the same
5452 name. But of course, there is no rule without exception. In addition
5453 to the normal symbols that have been discussed up to now, you can also
5454 create special @dfn{uninterned} symbols that behave slightly
5457 To understand what is different about them and why they might be useful,
5458 we look at how normal symbols are actually kept unique.
5460 Whenever Guile wants to find the symbol with a specific name, for
5461 example during @code{read} or when executing @code{string->symbol}, it
5462 first looks into a table of all existing symbols to find out whether a
5463 symbol with the given name already exists. When this is the case, Guile
5464 just returns that symbol. When not, a new symbol with the name is
5465 created and entered into the table so that it can be found later.
5467 Sometimes you might want to create a symbol that is guaranteed `fresh',
5468 i.e.@: a symbol that did not exist previously. You might also want to
5469 somehow guarantee that no one else will ever unintentionally stumble
5470 across your symbol in the future. These properties of a symbol are
5471 often needed when generating code during macro expansion. When
5472 introducing new temporary variables, you want to guarantee that they
5473 don't conflict with variables in other people's code.
5475 The simplest way to arrange for this is to create a new symbol but
5476 not enter it into the global table of all symbols. That way, no one
5477 will ever get access to your symbol by chance. Symbols that are not in
5478 the table are called @dfn{uninterned}. Of course, symbols that
5479 @emph{are} in the table are called @dfn{interned}.
5481 You create new uninterned symbols with the function @code{make-symbol}.
5482 You can test whether a symbol is interned or not with
5483 @code{symbol-interned?}.
5485 Uninterned symbols break the rule that the name of a symbol uniquely
5486 identifies the symbol object. Because of this, they can not be written
5487 out and read back in like interned symbols. Currently, Guile has no
5488 support for reading uninterned symbols. Note that the function
5489 @code{gensym} does not return uninterned symbols for this reason.
5491 @deffn {Scheme Procedure} make-symbol name
5492 @deffnx {C Function} scm_make_symbol (name)
5493 Return a new uninterned symbol with the name @var{name}. The returned
5494 symbol is guaranteed to be unique and future calls to
5495 @code{string->symbol} will not return it.
5498 @deffn {Scheme Procedure} symbol-interned? symbol
5499 @deffnx {C Function} scm_symbol_interned_p (symbol)
5500 Return @code{#t} if @var{symbol} is interned, otherwise return
5507 (define foo-1 (string->symbol "foo"))
5508 (define foo-2 (string->symbol "foo"))
5509 (define foo-3 (make-symbol "foo"))
5510 (define foo-4 (make-symbol "foo"))
5514 ; Two interned symbols with the same name are the same object,
5518 ; but a call to make-symbol with the same name returns a
5523 ; A call to make-symbol always returns a new object, even for
5527 @result{} #<uninterned-symbol foo 8085290>
5528 ; Uninterned symbols print differently from interned symbols,
5532 ; but they are still symbols,
5534 (symbol-interned? foo-3)
5536 ; just not interned.
5541 @subsection Keywords
5544 Keywords are self-evaluating objects with a convenient read syntax that
5545 makes them easy to type.
5547 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5548 syntax extension to permit keywords to begin with @code{:} as well as
5549 @code{#:}, or to end with @code{:}.
5552 * Why Use Keywords?:: Motivation for keyword usage.
5553 * Coding With Keywords:: How to use keywords.
5554 * Keyword Read Syntax:: Read syntax for keywords.
5555 * Keyword Procedures:: Procedures for dealing with keywords.
5558 @node Why Use Keywords?
5559 @subsubsection Why Use Keywords?
5561 Keywords are useful in contexts where a program or procedure wants to be
5562 able to accept a large number of optional arguments without making its
5563 interface unmanageable.
5565 To illustrate this, consider a hypothetical @code{make-window}
5566 procedure, which creates a new window on the screen for drawing into
5567 using some graphical toolkit. There are many parameters that the caller
5568 might like to specify, but which could also be sensibly defaulted, for
5573 color depth -- Default: the color depth for the screen
5576 background color -- Default: white
5579 width -- Default: 600
5582 height -- Default: 400
5585 If @code{make-window} did not use keywords, the caller would have to
5586 pass in a value for each possible argument, remembering the correct
5587 argument order and using a special value to indicate the default value
5591 (make-window 'default ;; Color depth
5592 'default ;; Background color
5595 @dots{}) ;; More make-window arguments
5598 With keywords, on the other hand, defaulted arguments are omitted, and
5599 non-default arguments are clearly tagged by the appropriate keyword. As
5600 a result, the invocation becomes much clearer:
5603 (make-window #:width 800 #:height 100)
5606 On the other hand, for a simpler procedure with few arguments, the use
5607 of keywords would be a hindrance rather than a help. The primitive
5608 procedure @code{cons}, for example, would not be improved if it had to
5612 (cons #:car x #:cdr y)
5615 So the decision whether to use keywords or not is purely pragmatic: use
5616 them if they will clarify the procedure invocation at point of call.
5618 @node Coding With Keywords
5619 @subsubsection Coding With Keywords
5621 If a procedure wants to support keywords, it should take a rest argument
5622 and then use whatever means is convenient to extract keywords and their
5623 corresponding arguments from the contents of that rest argument.
5625 The following example illustrates the principle: the code for
5626 @code{make-window} uses a helper procedure called
5627 @code{get-keyword-value} to extract individual keyword arguments from
5631 (define (get-keyword-value args keyword default)
5632 (let ((kv (memq keyword args)))
5633 (if (and kv (>= (length kv) 2))
5637 (define (make-window . args)
5638 (let ((depth (get-keyword-value args #:depth screen-depth))
5639 (bg (get-keyword-value args #:bg "white"))
5640 (width (get-keyword-value args #:width 800))
5641 (height (get-keyword-value args #:height 100))
5646 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5647 optargs)} module provides a set of powerful macros that you can use to
5648 implement keyword-supporting procedures like this:
5651 (use-modules (ice-9 optargs))
5653 (define (make-window . args)
5654 (let-keywords args #f ((depth screen-depth)
5662 Or, even more economically, like this:
5665 (use-modules (ice-9 optargs))
5667 (define* (make-window #:key (depth screen-depth)
5674 For further details on @code{let-keywords}, @code{define*} and other
5675 facilities provided by the @code{(ice-9 optargs)} module, see
5676 @ref{Optional Arguments}.
5679 @node Keyword Read Syntax
5680 @subsubsection Keyword Read Syntax
5682 Guile, by default, only recognizes a keyword syntax that is compatible
5683 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5684 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5685 external representation of the keyword named @code{NAME}. Keyword
5686 objects print using this syntax as well, so values containing keyword
5687 objects can be read back into Guile. When used in an expression,
5688 keywords are self-quoting objects.
5690 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5691 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5692 of the form @code{:NAME} are read as symbols, as required by R5RS.
5694 @cindex SRFI-88 keyword syntax
5696 If the @code{keyword} read option is set to @code{'postfix}, Guile
5697 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5698 Otherwise, tokens of this form are read as symbols.
5700 To enable and disable the alternative non-R5RS keyword syntax, you use
5701 the @code{read-set!} procedure documented @ref{Scheme Read}. Note that
5702 the @code{prefix} and @code{postfix} syntax are mutually exclusive.
5705 (read-set! keywords 'prefix)
5715 (read-set! keywords 'postfix)
5725 (read-set! keywords #f)
5733 ERROR: In expression :type:
5734 ERROR: Unbound variable: :type
5735 ABORT: (unbound-variable)
5738 @node Keyword Procedures
5739 @subsubsection Keyword Procedures
5741 @deffn {Scheme Procedure} keyword? obj
5742 @deffnx {C Function} scm_keyword_p (obj)
5743 Return @code{#t} if the argument @var{obj} is a keyword, else
5747 @deffn {Scheme Procedure} keyword->symbol keyword
5748 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5749 Return the symbol with the same name as @var{keyword}.
5752 @deffn {Scheme Procedure} symbol->keyword symbol
5753 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5754 Return the keyword with the same name as @var{symbol}.
5757 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5758 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5761 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *name)
5762 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *name, size_t len)
5763 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5764 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5765 (@var{name}, @var{len}))}, respectively.
5767 Note that these functions should @emph{not} be used when @var{name} is a
5768 C string constant, because there is no guarantee that the current locale
5769 will match that of the source code. In such cases, use
5770 @code{scm_from_latin1_keyword} or @code{scm_from_utf8_keyword}.
5773 @deftypefn {C Function} SCM scm_from_latin1_keyword (const char *name)
5774 @deftypefnx {C Function} SCM scm_from_utf8_keyword (const char *name)
5775 Equivalent to @code{scm_symbol_to_keyword (scm_from_latin1_symbol
5776 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_utf8_symbol
5777 (@var{name}))}, respectively.
5781 @subsection ``Functionality-Centric'' Data Types
5783 Procedures and macros are documented in their own sections: see
5784 @ref{Procedures} and @ref{Macros}.
5786 Variable objects are documented as part of the description of Guile's
5787 module system: see @ref{Variables}.
5789 Asyncs, dynamic roots and fluids are described in the section on
5790 scheduling: see @ref{Scheduling}.
5792 Hooks are documented in the section on general utility functions: see
5795 Ports are described in the section on I/O: see @ref{Input and Output}.
5797 Regular expressions are described in their own section: see @ref{Regular
5801 @c TeX-master: "guile.texi"