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, 2012, 2013
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}
82 (@pxref{Conditionals}), where a group of subexpressions will be
83 evaluated only if a @var{condition} expression evaluates to ``true'',
84 ``true'' means any value at all except @code{#f}.
97 A result of this asymmetry is that typical Scheme source code more often
98 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
99 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
100 not necessary to represent an @code{if} or @code{cond} true value.
102 It is important to note that @code{#f} is @strong{not} equivalent to any
103 other Scheme value. In particular, @code{#f} is not the same as the
104 number 0 (like in C and C++), and not the same as the ``empty list''
105 (like in some Lisp dialects).
107 In C, the two Scheme boolean values are available as the two constants
108 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
109 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
110 false when used in C conditionals. In order to test for it, use
111 @code{scm_is_false} or @code{scm_is_true}.
114 @deffn {Scheme Procedure} not x
115 @deffnx {C Function} scm_not (x)
116 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
120 @deffn {Scheme Procedure} boolean? obj
121 @deffnx {C Function} scm_boolean_p (obj)
122 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
126 @deftypevr {C Macro} SCM SCM_BOOL_T
127 The @code{SCM} representation of the Scheme object @code{#t}.
130 @deftypevr {C Macro} SCM SCM_BOOL_F
131 The @code{SCM} representation of the Scheme object @code{#f}.
134 @deftypefn {C Function} int scm_is_true (SCM obj)
135 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
138 @deftypefn {C Function} int scm_is_false (SCM obj)
139 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
142 @deftypefn {C Function} int scm_is_bool (SCM obj)
143 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
147 @deftypefn {C Function} SCM scm_from_bool (int val)
148 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
151 @deftypefn {C Function} int scm_to_bool (SCM val)
152 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
153 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
155 You should probably use @code{scm_is_true} instead of this function
156 when you just want to test a @code{SCM} value for trueness.
160 @subsection Numerical data types
163 Guile supports a rich ``tower'' of numerical types --- integer,
164 rational, real and complex --- and provides an extensive set of
165 mathematical and scientific functions for operating on numerical
166 data. This section of the manual documents those types and functions.
168 You may also find it illuminating to read R5RS's presentation of numbers
169 in Scheme, which is particularly clear and accessible: see
170 @ref{Numbers,,,r5rs,R5RS}.
173 * Numerical Tower:: Scheme's numerical "tower".
174 * Integers:: Whole numbers.
175 * Reals and Rationals:: Real and rational numbers.
176 * Complex Numbers:: Complex numbers.
177 * Exactness:: Exactness and inexactness.
178 * Number Syntax:: Read syntax for numerical data.
179 * Integer Operations:: Operations on integer values.
180 * Comparison:: Comparison predicates.
181 * Conversion:: Converting numbers to and from strings.
182 * Complex:: Complex number operations.
183 * Arithmetic:: Arithmetic functions.
184 * Scientific:: Scientific functions.
185 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
186 * Random:: Random number generation.
190 @node Numerical Tower
191 @subsubsection Scheme's Numerical ``Tower''
194 Scheme's numerical ``tower'' consists of the following categories of
199 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
202 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
203 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
204 pi (an irrational number) doesn't. These include integers
208 The set of numbers that describes all possible positions along a
209 one-dimensional line. This includes rationals as well as irrational
212 @item complex numbers
213 The set of numbers that describes all possible positions in a two
214 dimensional space. This includes real as well as imaginary numbers
215 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
216 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
220 It is called a tower because each category ``sits on'' the one that
221 follows it, in the sense that every integer is also a rational, every
222 rational is also real, and every real number is also a complex number
223 (but with zero imaginary part).
225 In addition to the classification into integers, rationals, reals and
226 complex numbers, Scheme also distinguishes between whether a number is
227 represented exactly or not. For example, the result of
228 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
229 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
230 Instead, it stores an inexact approximation, using the C type
233 Guile can represent exact rationals of any magnitude, inexact
234 rationals that fit into a C @code{double}, and inexact complex numbers
235 with @code{double} real and imaginary parts.
237 The @code{number?} predicate may be applied to any Scheme value to
238 discover whether the value is any of the supported numerical types.
240 @deffn {Scheme Procedure} number? obj
241 @deffnx {C Function} scm_number_p (obj)
242 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
251 (number? "hello there!")
254 (define pi 3.141592654)
259 @deftypefn {C Function} int scm_is_number (SCM obj)
260 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
263 The next few subsections document each of Guile's numerical data types
267 @subsubsection Integers
269 @tpindex Integer numbers
273 Integers are whole numbers, that is numbers with no fractional part,
274 such as 2, 83, and @minus{}3789.
276 Integers in Guile can be arbitrarily big, as shown by the following
280 (define (factorial n)
281 (let loop ((n n) (product 1))
284 (loop (- n 1) (* product n)))))
290 @result{} 2432902008176640000
293 @result{} -119622220865480194561963161495657715064383733760000000000
296 Readers whose background is in programming languages where integers are
297 limited by the need to fit into just 4 or 8 bytes of memory may find
298 this surprising, or suspect that Guile's representation of integers is
299 inefficient. In fact, Guile achieves a near optimal balance of
300 convenience and efficiency by using the host computer's native
301 representation of integers where possible, and a more general
302 representation where the required number does not fit in the native
303 form. Conversion between these two representations is automatic and
304 completely invisible to the Scheme level programmer.
306 C has a host of different integer types, and Guile offers a host of
307 functions to convert between them and the @code{SCM} representation.
308 For example, a C @code{int} can be handled with @code{scm_to_int} and
309 @code{scm_from_int}. Guile also defines a few C integer types of its
310 own, to help with differences between systems.
312 C integer types that are not covered can be handled with the generic
313 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
314 signed types, or with @code{scm_to_unsigned_integer} and
315 @code{scm_from_unsigned_integer} for unsigned types.
317 Scheme integers can be exact and inexact. For example, a number
318 written as @code{3.0} with an explicit decimal-point is inexact, but
319 it is also an integer. The functions @code{integer?} and
320 @code{scm_is_integer} report true for such a number, but the functions
321 @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only
322 allow exact integers and thus report false. Likewise, the conversion
323 functions like @code{scm_to_signed_integer} only accept exact
326 The motivation for this behavior is that the inexactness of a number
327 should not be lost silently. If you want to allow inexact integers,
328 you can explicitly insert a call to @code{inexact->exact} or to its C
329 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
330 be converted by this call into exact integers; inexact non-integers
331 will become exact fractions.)
333 @deffn {Scheme Procedure} integer? x
334 @deffnx {C Function} scm_integer_p (x)
335 Return @code{#t} if @var{x} is an exact or inexact integer number, else
353 @deftypefn {C Function} int scm_is_integer (SCM x)
354 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
357 @defvr {C Type} scm_t_int8
358 @defvrx {C Type} scm_t_uint8
359 @defvrx {C Type} scm_t_int16
360 @defvrx {C Type} scm_t_uint16
361 @defvrx {C Type} scm_t_int32
362 @defvrx {C Type} scm_t_uint32
363 @defvrx {C Type} scm_t_int64
364 @defvrx {C Type} scm_t_uint64
365 @defvrx {C Type} scm_t_intmax
366 @defvrx {C Type} scm_t_uintmax
367 The C types are equivalent to the corresponding ISO C types but are
368 defined on all platforms, with the exception of @code{scm_t_int64} and
369 @code{scm_t_uint64}, which are only defined when a 64-bit type is
370 available. For example, @code{scm_t_int8} is equivalent to
373 You can regard these definitions as a stop-gap measure until all
374 platforms provide these types. If you know that all the platforms
375 that you are interested in already provide these types, it is better
376 to use them directly instead of the types provided by Guile.
379 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
380 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
381 Return @code{1} when @var{x} represents an exact integer that is
382 between @var{min} and @var{max}, inclusive.
384 These functions can be used to check whether a @code{SCM} value will
385 fit into a given range, such as the range of a given C integer type.
386 If you just want to convert a @code{SCM} value to a given C integer
387 type, use one of the conversion functions directly.
390 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
391 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
392 When @var{x} represents an exact integer that is between @var{min} and
393 @var{max} inclusive, return that integer. Else signal an error,
394 either a `wrong-type' error when @var{x} is not an exact integer, or
395 an `out-of-range' error when it doesn't fit the given range.
398 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
399 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
400 Return the @code{SCM} value that represents the integer @var{x}. This
401 function will always succeed and will always return an exact number.
404 @deftypefn {C Function} char scm_to_char (SCM x)
405 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
406 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
407 @deftypefnx {C Function} short scm_to_short (SCM x)
408 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
409 @deftypefnx {C Function} int scm_to_int (SCM x)
410 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
411 @deftypefnx {C Function} long scm_to_long (SCM x)
412 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
413 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
414 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
415 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
416 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
417 @deftypefnx {C Function} scm_t_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{z} 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{z} 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 @deffn {Scheme Procedure} random-state-from-platform
1869 @deffnx {C Function} scm_random_state_from_platform ()
1870 Construct a new random state seeded from a platform-specific source of
1871 entropy, appropriate for use in non-security-critical applications.
1872 Currently @file{/dev/urandom} is tried first, or else the seed is based
1873 on the time, date, process ID, an address from a freshly allocated heap
1874 cell, an address from the local stack frame, and a high-resolution timer
1878 @defvar *random-state*
1879 The global random state used by the above functions when the
1880 @var{state} parameter is not given.
1883 Note that the initial value of @code{*random-state*} is the same every
1884 time Guile starts up. Therefore, if you don't pass a @var{state}
1885 parameter to the above procedures, and you don't set
1886 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1887 @code{your-seed} is something that @emph{isn't} the same every time,
1888 you'll get the same sequence of ``random'' numbers on every run.
1890 For example, unless the relevant source code has changed, @code{(map
1891 random (cdr (iota 30)))}, if the first use of random numbers since
1892 Guile started up, will always give:
1895 (map random (cdr (iota 19)))
1897 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1900 To seed the random state in a sensible way for non-security-critical
1901 applications, do this during initialization of your program:
1904 (set! *random-state* (random-state-from-platform))
1909 @subsection Characters
1912 In Scheme, there is a data type to describe a single character.
1914 Defining what exactly a character @emph{is} can be more complicated
1915 than it seems. Guile follows the advice of R6RS and uses The Unicode
1916 Standard to help define what a character is. So, for Guile, a
1917 character is anything in the Unicode Character Database.
1920 @cindex Unicode code point
1922 The Unicode Character Database is basically a table of characters
1923 indexed using integers called 'code points'. Valid code points are in
1924 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1925 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1927 @cindex designated code point
1928 @cindex code point, designated
1930 Any code point that has been assigned to a character or that has
1931 otherwise been given a meaning by Unicode is called a 'designated code
1932 point'. Most of the designated code points, about 200,000 of them,
1933 indicate characters, accents or other combining marks that modify
1934 other characters, symbols, whitespace, and control characters. Some
1935 are not characters but indicators that suggest how to format or
1936 display neighboring characters.
1938 @cindex reserved code point
1939 @cindex code point, reserved
1941 If a code point is not a designated code point -- if it has not been
1942 assigned to a character by The Unicode Standard -- it is a 'reserved
1943 code point', meaning that they are reserved for future use. Most of
1944 the code points, about 800,000, are 'reserved code points'.
1946 By convention, a Unicode code point is written as
1947 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1948 this convenient notation is not valid code. Guile does not interpret
1949 ``U+XXXX'' as a character.
1951 In Scheme, a character literal is written as @code{#\@var{name}} where
1952 @var{name} is the name of the character that you want. Printable
1953 characters have their usual single character name; for example,
1954 @code{#\a} is a lower case @code{a}.
1956 Some of the code points are 'combining characters' that are not meant
1957 to be printed by themselves but are instead meant to modify the
1958 appearance of the previous character. For combining characters, an
1959 alternate form of the character literal is @code{#\} followed by
1960 U+25CC (a small, dotted circle), followed by the combining character.
1961 This allows the combining character to be drawn on the circle, not on
1962 the backslash of @code{#\}.
1964 Many of the non-printing characters, such as whitespace characters and
1965 control characters, also have names.
1967 The most commonly used non-printing characters have long character
1968 names, described in the table below.
1970 @multitable {@code{#\backspace}} {Preferred}
1971 @item Character Name @tab Codepoint
1972 @item @code{#\nul} @tab U+0000
1973 @item @code{#\alarm} @tab u+0007
1974 @item @code{#\backspace} @tab U+0008
1975 @item @code{#\tab} @tab U+0009
1976 @item @code{#\linefeed} @tab U+000A
1977 @item @code{#\newline} @tab U+000A
1978 @item @code{#\vtab} @tab U+000B
1979 @item @code{#\page} @tab U+000C
1980 @item @code{#\return} @tab U+000D
1981 @item @code{#\esc} @tab U+001B
1982 @item @code{#\space} @tab U+0020
1983 @item @code{#\delete} @tab U+007F
1986 There are also short names for all of the ``C0 control characters''
1987 (those with code points below 32). The following table lists the short
1988 name for each character.
1990 @multitable @columnfractions .25 .25 .25 .25
1991 @item 0 = @code{#\nul}
1992 @tab 1 = @code{#\soh}
1993 @tab 2 = @code{#\stx}
1994 @tab 3 = @code{#\etx}
1995 @item 4 = @code{#\eot}
1996 @tab 5 = @code{#\enq}
1997 @tab 6 = @code{#\ack}
1998 @tab 7 = @code{#\bel}
1999 @item 8 = @code{#\bs}
2000 @tab 9 = @code{#\ht}
2001 @tab 10 = @code{#\lf}
2002 @tab 11 = @code{#\vt}
2003 @item 12 = @code{#\ff}
2004 @tab 13 = @code{#\cr}
2005 @tab 14 = @code{#\so}
2006 @tab 15 = @code{#\si}
2007 @item 16 = @code{#\dle}
2008 @tab 17 = @code{#\dc1}
2009 @tab 18 = @code{#\dc2}
2010 @tab 19 = @code{#\dc3}
2011 @item 20 = @code{#\dc4}
2012 @tab 21 = @code{#\nak}
2013 @tab 22 = @code{#\syn}
2014 @tab 23 = @code{#\etb}
2015 @item 24 = @code{#\can}
2016 @tab 25 = @code{#\em}
2017 @tab 26 = @code{#\sub}
2018 @tab 27 = @code{#\esc}
2019 @item 28 = @code{#\fs}
2020 @tab 29 = @code{#\gs}
2021 @tab 30 = @code{#\rs}
2022 @tab 31 = @code{#\us}
2023 @item 32 = @code{#\sp}
2026 The short name for the ``delete'' character (code point U+007F) is
2029 There are also a few alternative names left over for compatibility with
2030 previous versions of Guile.
2032 @multitable {@code{#\backspace}} {Preferred}
2033 @item Alternate @tab Standard
2034 @item @code{#\nl} @tab @code{#\newline}
2035 @item @code{#\np} @tab @code{#\page}
2036 @item @code{#\null} @tab @code{#\nul}
2039 Characters may also be written using their code point values. They can
2040 be written with as an octal number, such as @code{#\10} for
2041 @code{#\bs} or @code{#\177} for @code{#\del}.
2043 If one prefers hex to octal, there is an additional syntax for character
2044 escapes: @code{#\xHHHH} -- the letter 'x' followed by a hexadecimal
2045 number of one to eight digits.
2048 @deffn {Scheme Procedure} char? x
2049 @deffnx {C Function} scm_char_p (x)
2050 Return @code{#t} iff @var{x} is a character, else @code{#f}.
2053 Fundamentally, the character comparison operations below are
2054 numeric comparisons of the character's code points.
2057 @deffn {Scheme Procedure} char=? x y
2058 Return @code{#t} iff code point of @var{x} is equal to the code point
2059 of @var{y}, else @code{#f}.
2063 @deffn {Scheme Procedure} char<? x y
2064 Return @code{#t} iff the code point of @var{x} is less than the code
2065 point 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 or equal
2071 to the code 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 greater than the
2077 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 or
2083 equal to the code point of @var{y}, else @code{#f}.
2086 @cindex case folding
2088 Case-insensitive character comparisons use @emph{Unicode case
2089 folding}. In case folding comparisons, if a character is lowercase
2090 and has an uppercase form that can be expressed as a single character,
2091 it is converted to uppercase before comparison. All other characters
2092 undergo no conversion before the comparison occurs. This includes the
2093 German sharp S (Eszett) which is not uppercased before conversion
2094 because its uppercase form has two characters. Unicode case folding
2095 is language independent: it uses rules that are generally true, but,
2096 it cannot cover all cases for all languages.
2099 @deffn {Scheme Procedure} char-ci=? x y
2100 Return @code{#t} iff the case-folded code point of @var{x} is the same
2101 as the case-folded code point of @var{y}, else @code{#f}.
2105 @deffn {Scheme Procedure} char-ci<? x y
2106 Return @code{#t} iff the case-folded code point of @var{x} is less
2107 than 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 or equal to the case-folded code point of @var{y}, else
2118 @deffn {Scheme Procedure} char-ci>? x y
2119 Return @code{#t} iff the case-folded code point of @var{x} is greater
2120 than the case-folded code point of @var{y}, else @code{#f}.
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 or equal to the case-folded code point of @var{y}, else
2130 @rnindex char-alphabetic?
2131 @deffn {Scheme Procedure} char-alphabetic? chr
2132 @deffnx {C Function} scm_char_alphabetic_p (chr)
2133 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
2136 @rnindex char-numeric?
2137 @deffn {Scheme Procedure} char-numeric? chr
2138 @deffnx {C Function} scm_char_numeric_p (chr)
2139 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
2142 @rnindex char-whitespace?
2143 @deffn {Scheme Procedure} char-whitespace? chr
2144 @deffnx {C Function} scm_char_whitespace_p (chr)
2145 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
2148 @rnindex char-upper-case?
2149 @deffn {Scheme Procedure} char-upper-case? chr
2150 @deffnx {C Function} scm_char_upper_case_p (chr)
2151 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
2154 @rnindex char-lower-case?
2155 @deffn {Scheme Procedure} char-lower-case? chr
2156 @deffnx {C Function} scm_char_lower_case_p (chr)
2157 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
2160 @deffn {Scheme Procedure} char-is-both? chr
2161 @deffnx {C Function} scm_char_is_both_p (chr)
2162 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
2166 @deffn {Scheme Procedure} char-general-category chr
2167 @deffnx {C Function} scm_char_general_category (chr)
2168 Return a symbol giving the two-letter name of the Unicode general
2169 category assigned to @var{chr} or @code{#f} if no named category is
2170 assigned. The following table provides a list of category names along
2171 with their meanings.
2173 @multitable @columnfractions .1 .4 .1 .4
2175 @tab Uppercase letter
2177 @tab Final quote punctuation
2179 @tab Lowercase letter
2181 @tab Other punctuation
2183 @tab Titlecase letter
2187 @tab Modifier letter
2189 @tab Currency symbol
2193 @tab Modifier symbol
2195 @tab Non-spacing mark
2199 @tab Combining spacing mark
2201 @tab Space separator
2207 @tab Decimal digit number
2209 @tab Paragraph separator
2219 @tab Connector punctuation
2223 @tab Dash punctuation
2227 @tab Open punctuation
2231 @tab Close punctuation
2235 @tab Initial quote punctuation
2241 @rnindex char->integer
2242 @deffn {Scheme Procedure} char->integer chr
2243 @deffnx {C Function} scm_char_to_integer (chr)
2244 Return the code point of @var{chr}.
2247 @rnindex integer->char
2248 @deffn {Scheme Procedure} integer->char n
2249 @deffnx {C Function} scm_integer_to_char (n)
2250 Return the character that has code point @var{n}. The integer @var{n}
2251 must be a valid code point. Valid code points are in the ranges 0 to
2252 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
2255 @rnindex char-upcase
2256 @deffn {Scheme Procedure} char-upcase chr
2257 @deffnx {C Function} scm_char_upcase (chr)
2258 Return the uppercase character version of @var{chr}.
2261 @rnindex char-downcase
2262 @deffn {Scheme Procedure} char-downcase chr
2263 @deffnx {C Function} scm_char_downcase (chr)
2264 Return the lowercase character version of @var{chr}.
2267 @rnindex char-titlecase
2268 @deffn {Scheme Procedure} char-titlecase chr
2269 @deffnx {C Function} scm_char_titlecase (chr)
2270 Return the titlecase character version of @var{chr} if one exists;
2271 otherwise return the uppercase version.
2273 For most characters these will be the same, but the Unicode Standard
2274 includes certain digraph compatibility characters, such as @code{U+01F3}
2275 ``dz'', for which the uppercase and titlecase characters are different
2276 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
2281 @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c})
2282 @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c})
2283 @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c})
2285 These C functions take an integer representation of a Unicode
2286 codepoint and return the codepoint corresponding to its uppercase,
2287 lowercase, and titlecase forms respectively. The type
2288 @code{scm_t_wchar} is a signed, 32-bit integer.
2291 @node Character Sets
2292 @subsection Character Sets
2294 The features described in this section correspond directly to SRFI-14.
2296 The data type @dfn{charset} implements sets of characters
2297 (@pxref{Characters}). Because the internal representation of
2298 character sets is not visible to the user, a lot of procedures for
2299 handling them are provided.
2301 Character sets can be created, extended, tested for the membership of a
2302 characters and be compared to other character sets.
2305 * Character Set Predicates/Comparison::
2306 * Iterating Over Character Sets:: Enumerate charset elements.
2307 * Creating Character Sets:: Making new charsets.
2308 * Querying Character Sets:: Test charsets for membership etc.
2309 * Character-Set Algebra:: Calculating new charsets.
2310 * Standard Character Sets:: Variables containing predefined charsets.
2313 @node Character Set Predicates/Comparison
2314 @subsubsection Character Set Predicates/Comparison
2316 Use these procedures for testing whether an object is a character set,
2317 or whether several character sets are equal or subsets of each other.
2318 @code{char-set-hash} can be used for calculating a hash value, maybe for
2319 usage in fast lookup procedures.
2321 @deffn {Scheme Procedure} char-set? obj
2322 @deffnx {C Function} scm_char_set_p (obj)
2323 Return @code{#t} if @var{obj} is a character set, @code{#f}
2327 @deffn {Scheme Procedure} char-set= char_set @dots{}
2328 @deffnx {C Function} scm_char_set_eq (char_sets)
2329 Return @code{#t} if all given character sets are equal.
2332 @deffn {Scheme Procedure} char-set<= char_set @dots{}
2333 @deffnx {C Function} scm_char_set_leq (char_sets)
2334 Return @code{#t} if every character set @var{char_set}i is a subset
2335 of character set @var{char_set}i+1.
2338 @deffn {Scheme Procedure} char-set-hash cs [bound]
2339 @deffnx {C Function} scm_char_set_hash (cs, bound)
2340 Compute a hash value for the character set @var{cs}. If
2341 @var{bound} is given and non-zero, it restricts the
2342 returned value to the range 0 @dots{} @var{bound} - 1.
2345 @c ===================================================================
2347 @node Iterating Over Character Sets
2348 @subsubsection Iterating Over Character Sets
2350 Character set cursors are a means for iterating over the members of a
2351 character sets. After creating a character set cursor with
2352 @code{char-set-cursor}, a cursor can be dereferenced with
2353 @code{char-set-ref}, advanced to the next member with
2354 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2355 element of the set can be checked with @code{end-of-char-set?}.
2357 Additionally, mapping and (un-)folding procedures for character sets are
2360 @deffn {Scheme Procedure} char-set-cursor cs
2361 @deffnx {C Function} scm_char_set_cursor (cs)
2362 Return a cursor into the character set @var{cs}.
2365 @deffn {Scheme Procedure} char-set-ref cs cursor
2366 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2367 Return the character at the current cursor position
2368 @var{cursor} in the character set @var{cs}. It is an error to
2369 pass a cursor for which @code{end-of-char-set?} returns true.
2372 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2373 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2374 Advance the character set cursor @var{cursor} to the next
2375 character in the character set @var{cs}. It is an error if the
2376 cursor given satisfies @code{end-of-char-set?}.
2379 @deffn {Scheme Procedure} end-of-char-set? cursor
2380 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2381 Return @code{#t} if @var{cursor} has reached the end of a
2382 character set, @code{#f} otherwise.
2385 @deffn {Scheme Procedure} char-set-fold kons knil cs
2386 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2387 Fold the procedure @var{kons} over the character set @var{cs},
2388 initializing it with @var{knil}.
2391 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2392 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2393 This is a fundamental constructor for character sets.
2395 @item @var{g} is used to generate a series of ``seed'' values
2396 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2397 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2398 @item @var{p} tells us when to stop -- when it returns true
2399 when applied to one of the seed values.
2400 @item @var{f} maps each seed value to a character. These
2401 characters are added to the base character set @var{base_cs} to
2402 form the result; @var{base_cs} defaults to the empty set.
2406 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2407 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2408 This is a fundamental constructor for character sets.
2410 @item @var{g} is used to generate a series of ``seed'' values
2411 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2412 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2413 @item @var{p} tells us when to stop -- when it returns true
2414 when applied to one of the seed values.
2415 @item @var{f} maps each seed value to a character. These
2416 characters are added to the base character set @var{base_cs} to
2417 form the result; @var{base_cs} defaults to the empty set.
2421 @deffn {Scheme Procedure} char-set-for-each proc cs
2422 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2423 Apply @var{proc} to every character in the character set
2424 @var{cs}. The return value is not specified.
2427 @deffn {Scheme Procedure} char-set-map proc cs
2428 @deffnx {C Function} scm_char_set_map (proc, cs)
2429 Map the procedure @var{proc} over every character in @var{cs}.
2430 @var{proc} must be a character -> character procedure.
2433 @c ===================================================================
2435 @node Creating Character Sets
2436 @subsubsection Creating Character Sets
2438 New character sets are produced with these procedures.
2440 @deffn {Scheme Procedure} char-set-copy cs
2441 @deffnx {C Function} scm_char_set_copy (cs)
2442 Return a newly allocated character set containing all
2443 characters in @var{cs}.
2446 @deffn {Scheme Procedure} char-set chr @dots{}
2447 @deffnx {C Function} scm_char_set (chrs)
2448 Return a character set containing all given characters.
2451 @deffn {Scheme Procedure} list->char-set list [base_cs]
2452 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2453 Convert the character list @var{list} to a character set. If
2454 the character set @var{base_cs} is given, the character in this
2455 set are also included in the result.
2458 @deffn {Scheme Procedure} list->char-set! list base_cs
2459 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2460 Convert the character list @var{list} to a character set. The
2461 characters are added to @var{base_cs} and @var{base_cs} is
2465 @deffn {Scheme Procedure} string->char-set str [base_cs]
2466 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2467 Convert the string @var{str} to a character set. If the
2468 character set @var{base_cs} is given, the characters in this
2469 set are also included in the result.
2472 @deffn {Scheme Procedure} string->char-set! str base_cs
2473 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2474 Convert the string @var{str} to a character set. The
2475 characters from the string are added to @var{base_cs}, and
2476 @var{base_cs} is returned.
2479 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2480 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2481 Return a character set containing every character from @var{cs}
2482 so that it satisfies @var{pred}. If provided, the characters
2483 from @var{base_cs} are added to the result.
2486 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2487 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2488 Return a character set containing every character from @var{cs}
2489 so that it satisfies @var{pred}. The characters are added to
2490 @var{base_cs} and @var{base_cs} is returned.
2493 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2494 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2495 Return a character set containing all characters whose
2496 character codes lie in the half-open range
2497 [@var{lower},@var{upper}).
2499 If @var{error} is a true value, an error is signalled if the
2500 specified range contains characters which are not contained in
2501 the implemented character range. If @var{error} is @code{#f},
2502 these characters are silently left out of the resulting
2505 The characters in @var{base_cs} are added to the result, if
2509 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2510 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2511 Return a character set containing all characters whose
2512 character codes lie in the half-open range
2513 [@var{lower},@var{upper}).
2515 If @var{error} is a true value, an error is signalled if the
2516 specified range contains characters which are not contained in
2517 the implemented character range. If @var{error} is @code{#f},
2518 these characters are silently left out of the resulting
2521 The characters are added to @var{base_cs} and @var{base_cs} is
2525 @deffn {Scheme Procedure} ->char-set x
2526 @deffnx {C Function} scm_to_char_set (x)
2527 Coerces x into a char-set. @var{x} may be a string, character or
2528 char-set. A string is converted to the set of its constituent
2529 characters; a character is converted to a singleton set; a char-set is
2533 @c ===================================================================
2535 @node Querying Character Sets
2536 @subsubsection Querying Character Sets
2538 Access the elements and other information of a character set with these
2541 @deffn {Scheme Procedure} %char-set-dump cs
2542 Returns an association list containing debugging information
2543 for @var{cs}. The association list has the following entries.
2548 The number of groups of contiguous code points the char-set
2551 A list of lists where each sublist is a range of code points
2552 and their associated characters
2554 The return value of this function cannot be relied upon to be
2555 consistent between versions of Guile and should not be used in code.
2558 @deffn {Scheme Procedure} char-set-size cs
2559 @deffnx {C Function} scm_char_set_size (cs)
2560 Return the number of elements in character set @var{cs}.
2563 @deffn {Scheme Procedure} char-set-count pred cs
2564 @deffnx {C Function} scm_char_set_count (pred, cs)
2565 Return the number of the elements int the character set
2566 @var{cs} which satisfy the predicate @var{pred}.
2569 @deffn {Scheme Procedure} char-set->list cs
2570 @deffnx {C Function} scm_char_set_to_list (cs)
2571 Return a list containing the elements of the character set
2575 @deffn {Scheme Procedure} char-set->string cs
2576 @deffnx {C Function} scm_char_set_to_string (cs)
2577 Return a string containing the elements of the character set
2578 @var{cs}. The order in which the characters are placed in the
2579 string is not defined.
2582 @deffn {Scheme Procedure} char-set-contains? cs ch
2583 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2584 Return @code{#t} iff the character @var{ch} is contained in the
2585 character set @var{cs}.
2588 @deffn {Scheme Procedure} char-set-every pred cs
2589 @deffnx {C Function} scm_char_set_every (pred, cs)
2590 Return a true value if every character in the character set
2591 @var{cs} satisfies the predicate @var{pred}.
2594 @deffn {Scheme Procedure} char-set-any pred cs
2595 @deffnx {C Function} scm_char_set_any (pred, cs)
2596 Return a true value if any character in the character set
2597 @var{cs} satisfies the predicate @var{pred}.
2600 @c ===================================================================
2602 @node Character-Set Algebra
2603 @subsubsection Character-Set Algebra
2605 Character sets can be manipulated with the common set algebra operation,
2606 such as union, complement, intersection etc. All of these procedures
2607 provide side-effecting variants, which modify their character set
2610 @deffn {Scheme Procedure} char-set-adjoin cs chr @dots{}
2611 @deffnx {C Function} scm_char_set_adjoin (cs, chrs)
2612 Add all character arguments to the first argument, which must
2616 @deffn {Scheme Procedure} char-set-delete cs chr @dots{}
2617 @deffnx {C Function} scm_char_set_delete (cs, chrs)
2618 Delete all character arguments from the first argument, which
2619 must be a character set.
2622 @deffn {Scheme Procedure} char-set-adjoin! cs chr @dots{}
2623 @deffnx {C Function} scm_char_set_adjoin_x (cs, chrs)
2624 Add all character arguments to the first argument, which must
2628 @deffn {Scheme Procedure} char-set-delete! cs chr @dots{}
2629 @deffnx {C Function} scm_char_set_delete_x (cs, chrs)
2630 Delete all character arguments from the first argument, which
2631 must be a character set.
2634 @deffn {Scheme Procedure} char-set-complement cs
2635 @deffnx {C Function} scm_char_set_complement (cs)
2636 Return the complement of the character set @var{cs}.
2639 Note that the complement of a character set is likely to contain many
2640 reserved code points (code points that are not associated with
2641 characters). It may be helpful to modify the output of
2642 @code{char-set-complement} by computing its intersection with the set
2643 of designated code points, @code{char-set:designated}.
2645 @deffn {Scheme Procedure} char-set-union cs @dots{}
2646 @deffnx {C Function} scm_char_set_union (char_sets)
2647 Return the union of all argument character sets.
2650 @deffn {Scheme Procedure} char-set-intersection cs @dots{}
2651 @deffnx {C Function} scm_char_set_intersection (char_sets)
2652 Return the intersection of all argument character sets.
2655 @deffn {Scheme Procedure} char-set-difference cs1 cs @dots{}
2656 @deffnx {C Function} scm_char_set_difference (cs1, char_sets)
2657 Return the difference of all argument character sets.
2660 @deffn {Scheme Procedure} char-set-xor cs @dots{}
2661 @deffnx {C Function} scm_char_set_xor (char_sets)
2662 Return the exclusive-or of all argument character sets.
2665 @deffn {Scheme Procedure} char-set-diff+intersection cs1 cs @dots{}
2666 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, char_sets)
2667 Return the difference and the intersection of all argument
2671 @deffn {Scheme Procedure} char-set-complement! cs
2672 @deffnx {C Function} scm_char_set_complement_x (cs)
2673 Return the complement of the character set @var{cs}.
2676 @deffn {Scheme Procedure} char-set-union! cs1 cs @dots{}
2677 @deffnx {C Function} scm_char_set_union_x (cs1, char_sets)
2678 Return the union of all argument character sets.
2681 @deffn {Scheme Procedure} char-set-intersection! cs1 cs @dots{}
2682 @deffnx {C Function} scm_char_set_intersection_x (cs1, char_sets)
2683 Return the intersection of all argument character sets.
2686 @deffn {Scheme Procedure} char-set-difference! cs1 cs @dots{}
2687 @deffnx {C Function} scm_char_set_difference_x (cs1, char_sets)
2688 Return the difference of all argument character sets.
2691 @deffn {Scheme Procedure} char-set-xor! cs1 cs @dots{}
2692 @deffnx {C Function} scm_char_set_xor_x (cs1, char_sets)
2693 Return the exclusive-or of all argument character sets.
2696 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 cs @dots{}
2697 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, char_sets)
2698 Return the difference and the intersection of all argument
2702 @c ===================================================================
2704 @node Standard Character Sets
2705 @subsubsection Standard Character Sets
2707 In order to make the use of the character set data type and procedures
2708 useful, several predefined character set variables exist.
2714 These character sets are locale independent and are not recomputed
2715 upon a @code{setlocale} call. They contain characters from the whole
2716 range of Unicode code points. For instance, @code{char-set:letter}
2717 contains about 100,000 characters.
2719 @defvr {Scheme Variable} char-set:lower-case
2720 @defvrx {C Variable} scm_char_set_lower_case
2721 All lower-case characters.
2724 @defvr {Scheme Variable} char-set:upper-case
2725 @defvrx {C Variable} scm_char_set_upper_case
2726 All upper-case characters.
2729 @defvr {Scheme Variable} char-set:title-case
2730 @defvrx {C Variable} scm_char_set_title_case
2731 All single characters that function as if they were an upper-case
2732 letter followed by a lower-case letter.
2735 @defvr {Scheme Variable} char-set:letter
2736 @defvrx {C Variable} scm_char_set_letter
2737 All letters. This includes @code{char-set:lower-case},
2738 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2739 letters that have no case at all. For example, Chinese and Japanese
2740 characters typically have no concept of case.
2743 @defvr {Scheme Variable} char-set:digit
2744 @defvrx {C Variable} scm_char_set_digit
2748 @defvr {Scheme Variable} char-set:letter+digit
2749 @defvrx {C Variable} scm_char_set_letter_and_digit
2750 The union of @code{char-set:letter} and @code{char-set:digit}.
2753 @defvr {Scheme Variable} char-set:graphic
2754 @defvrx {C Variable} scm_char_set_graphic
2755 All characters which would put ink on the paper.
2758 @defvr {Scheme Variable} char-set:printing
2759 @defvrx {C Variable} scm_char_set_printing
2760 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2763 @defvr {Scheme Variable} char-set:whitespace
2764 @defvrx {C Variable} scm_char_set_whitespace
2765 All whitespace characters.
2768 @defvr {Scheme Variable} char-set:blank
2769 @defvrx {C Variable} scm_char_set_blank
2770 All horizontal whitespace characters, which notably includes
2771 @code{#\space} and @code{#\tab}.
2774 @defvr {Scheme Variable} char-set:iso-control
2775 @defvrx {C Variable} scm_char_set_iso_control
2776 The ISO control characters are the C0 control characters (U+0000 to
2777 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2781 @defvr {Scheme Variable} char-set:punctuation
2782 @defvrx {C Variable} scm_char_set_punctuation
2783 All punctuation characters, such as the characters
2784 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2787 @defvr {Scheme Variable} char-set:symbol
2788 @defvrx {C Variable} scm_char_set_symbol
2789 All symbol characters, such as the characters @code{$+<=>^`|~}.
2792 @defvr {Scheme Variable} char-set:hex-digit
2793 @defvrx {C Variable} scm_char_set_hex_digit
2794 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2797 @defvr {Scheme Variable} char-set:ascii
2798 @defvrx {C Variable} scm_char_set_ascii
2799 All ASCII characters.
2802 @defvr {Scheme Variable} char-set:empty
2803 @defvrx {C Variable} scm_char_set_empty
2804 The empty character set.
2807 @defvr {Scheme Variable} char-set:designated
2808 @defvrx {C Variable} scm_char_set_designated
2809 This character set contains all designated code points. This includes
2810 all the code points to which Unicode has assigned a character or other
2814 @defvr {Scheme Variable} char-set:full
2815 @defvrx {C Variable} scm_char_set_full
2816 This character set contains all possible code points. This includes
2817 both designated and reserved code points.
2824 Strings are fixed-length sequences of characters. They can be created
2825 by calling constructor procedures, but they can also literally get
2826 entered at the @acronym{REPL} or in Scheme source files.
2828 @c Guile provides a rich set of string processing procedures, because text
2829 @c handling is very important when Guile is used as a scripting language.
2831 Strings always carry the information about how many characters they are
2832 composed of with them, so there is no special end-of-string character,
2833 like in C. That means that Scheme strings can contain any character,
2834 even the @samp{#\nul} character @samp{\0}.
2836 To use strings efficiently, you need to know a bit about how Guile
2837 implements them. In Guile, a string consists of two parts, a head and
2838 the actual memory where the characters are stored. When a string (or
2839 a substring of it) is copied, only a new head gets created, the memory
2840 is usually not copied. The two heads start out pointing to the same
2843 When one of these two strings is modified, as with @code{string-set!},
2844 their common memory does get copied so that each string has its own
2845 memory and modifying one does not accidentally modify the other as well.
2846 Thus, Guile's strings are `copy on write'; the actual copying of their
2847 memory is delayed until one string is written to.
2849 This implementation makes functions like @code{substring} very
2850 efficient in the common case that no modifications are done to the
2853 If you do know that your strings are getting modified right away, you
2854 can use @code{substring/copy} instead of @code{substring}. This
2855 function performs the copy immediately at the time of creation. This
2856 is more efficient, especially in a multi-threaded program. Also,
2857 @code{substring/copy} can avoid the problem that a short substring
2858 holds on to the memory of a very large original string that could
2859 otherwise be recycled.
2861 If you want to avoid the copy altogether, so that modifications of one
2862 string show up in the other, you can use @code{substring/shared}. The
2863 strings created by this procedure are called @dfn{mutation sharing
2864 substrings} since the substring and the original string share
2865 modifications to each other.
2867 If you want to prevent modifications, use @code{substring/read-only}.
2869 Guile provides all procedures of SRFI-13 and a few more.
2872 * String Syntax:: Read syntax for strings.
2873 * String Predicates:: Testing strings for certain properties.
2874 * String Constructors:: Creating new string objects.
2875 * List/String Conversion:: Converting from/to lists of characters.
2876 * String Selection:: Select portions from strings.
2877 * String Modification:: Modify parts or whole strings.
2878 * String Comparison:: Lexicographic ordering predicates.
2879 * String Searching:: Searching in strings.
2880 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2881 * Reversing and Appending Strings:: Appending strings to form a new string.
2882 * Mapping Folding and Unfolding:: Iterating over strings.
2883 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2884 * Representing Strings as Bytes:: Encoding and decoding strings.
2885 * Conversion to/from C::
2886 * String Internals:: The storage strategy for strings.
2890 @subsubsection String Read Syntax
2892 @c In the following @code is used to get a good font in TeX etc, but
2893 @c is omitted for Info format, so as not to risk any confusion over
2894 @c whether surrounding ` ' quotes are part of the escape or are
2895 @c special in a string (they're not).
2897 The read syntax for strings is an arbitrarily long sequence of
2898 characters enclosed in double quotes (@nicode{"}).
2900 Backslash is an escape character and can be used to insert the following
2901 special characters. @nicode{\"} and @nicode{\\} are R5RS standard, the
2902 next seven are R6RS standard --- notice they follow C syntax --- and the
2903 remaining four are Guile extensions.
2907 Backslash character.
2910 Double quote character (an unescaped @nicode{"} is otherwise the end
2914 Bell character (ASCII 7).
2917 Formfeed character (ASCII 12).
2920 Newline character (ASCII 10).
2923 Carriage return character (ASCII 13).
2926 Tab character (ASCII 9).
2929 Vertical tab character (ASCII 11).
2932 Backspace character (ASCII 8).
2935 NUL character (ASCII 0).
2937 @item @nicode{\} followed by newline (ASCII 10)
2938 Nothing. This way if @nicode{\} is the last character in a line, the
2939 string will continue with the first character from the next line,
2940 without a line break.
2942 If the @code{hungry-eol-escapes} reader option is enabled, which is not
2943 the case by default, leading whitespace on the next line is discarded.
2949 (read-enable 'hungry-eol-escapes)
2955 Character code given by two hexadecimal digits. For example
2956 @nicode{\x7f} for an ASCII DEL (127).
2958 @item @nicode{\uHHHH}
2959 Character code given by four hexadecimal digits. For example
2960 @nicode{\u0100} for a capital A with macron (U+0100).
2962 @item @nicode{\UHHHHHH}
2963 Character code given by six hexadecimal digits. For example
2968 The following are examples of string literals:
2977 The three escape sequences @code{\xHH}, @code{\uHHHH} and @code{\UHHHHHH} were
2978 chosen to not break compatibility with code written for previous versions of
2979 Guile. The R6RS specification suggests a different, incompatible syntax for hex
2980 escapes: @code{\xHHHH;} -- a character code followed by one to eight hexadecimal
2981 digits terminated with a semicolon. If this escape format is desired instead,
2982 it can be enabled with the reader option @code{r6rs-hex-escapes}.
2985 (read-enable 'r6rs-hex-escapes)
2988 For more on reader options, @xref{Scheme Read}.
2990 @node String Predicates
2991 @subsubsection String Predicates
2993 The following procedures can be used to check whether a given string
2994 fulfills some specified property.
2997 @deffn {Scheme Procedure} string? obj
2998 @deffnx {C Function} scm_string_p (obj)
2999 Return @code{#t} if @var{obj} is a string, else @code{#f}.
3002 @deftypefn {C Function} int scm_is_string (SCM obj)
3003 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
3006 @deffn {Scheme Procedure} string-null? str
3007 @deffnx {C Function} scm_string_null_p (str)
3008 Return @code{#t} if @var{str}'s length is zero, and
3009 @code{#f} otherwise.
3011 (string-null? "") @result{} #t
3013 (string-null? y) @result{} #f
3017 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
3018 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
3019 Check if @var{char_pred} is true for any character in string @var{s}.
3021 @var{char_pred} can be a character to check for any equal to that, or
3022 a character set (@pxref{Character Sets}) to check for any in that set,
3023 or a predicate procedure to call.
3025 For a procedure, calls @code{(@var{char_pred} c)} are made
3026 successively on the characters from @var{start} to @var{end}. If
3027 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
3028 stops and that return value is the return from @code{string-any}. The
3029 call on the last character (ie.@: at @math{@var{end}-1}), if that
3030 point is reached, is a tail call.
3032 If there are no characters in @var{s} (ie.@: @var{start} equals
3033 @var{end}) then the return is @code{#f}.
3036 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
3037 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
3038 Check if @var{char_pred} is true for every character in string
3041 @var{char_pred} can be a character to check for every character equal
3042 to that, or a character set (@pxref{Character Sets}) to check for
3043 every character being in that set, or a predicate procedure to call.
3045 For a procedure, calls @code{(@var{char_pred} c)} are made
3046 successively on the characters from @var{start} to @var{end}. If
3047 @var{char_pred} returns @code{#f}, @code{string-every} stops and
3048 returns @code{#f}. The call on the last character (ie.@: at
3049 @math{@var{end}-1}), if that point is reached, is a tail call and the
3050 return from that call is the return from @code{string-every}.
3052 If there are no characters in @var{s} (ie.@: @var{start} equals
3053 @var{end}) then the return is @code{#t}.
3056 @node String Constructors
3057 @subsubsection String Constructors
3059 The string constructor procedures create new string objects, possibly
3060 initializing them with some specified character data. See also
3061 @xref{String Selection}, for ways to create strings from existing
3064 @c FIXME::martin: list->string belongs into `List/String Conversion'
3066 @deffn {Scheme Procedure} string char@dots{}
3068 Return a newly allocated string made from the given character
3072 (string #\x #\y #\z) @result{} "xyz"
3073 (string) @result{} ""
3077 @deffn {Scheme Procedure} list->string lst
3078 @deffnx {C Function} scm_string (lst)
3079 @rnindex list->string
3080 Return a newly allocated string made from a list of characters.
3083 (list->string '(#\a #\b #\c)) @result{} "abc"
3087 @deffn {Scheme Procedure} reverse-list->string lst
3088 @deffnx {C Function} scm_reverse_list_to_string (lst)
3089 Return a newly allocated string made from a list of characters, in
3093 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
3097 @rnindex make-string
3098 @deffn {Scheme Procedure} make-string k [chr]
3099 @deffnx {C Function} scm_make_string (k, chr)
3100 Return a newly allocated string of
3101 length @var{k}. If @var{chr} is given, then all elements of
3102 the string are initialized to @var{chr}, otherwise the contents
3103 of the string are unspecified.
3106 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
3107 Like @code{scm_make_string}, but expects the length as a
3111 @deffn {Scheme Procedure} string-tabulate proc len
3112 @deffnx {C Function} scm_string_tabulate (proc, len)
3113 @var{proc} is an integer->char procedure. Construct a string
3114 of size @var{len} by applying @var{proc} to each index to
3115 produce the corresponding string element. The order in which
3116 @var{proc} is applied to the indices is not specified.
3119 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
3120 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
3121 Append the string in the string list @var{ls}, using the string
3122 @var{delimiter} as a delimiter between the elements of @var{ls}.
3123 @var{grammar} is a symbol which specifies how the delimiter is
3124 placed between the strings, and defaults to the symbol
3129 Insert the separator between list elements. An empty string
3130 will produce an empty list.
3132 Like @code{infix}, but will raise an error if given the empty
3135 Insert the separator after every list element.
3137 Insert the separator before each list element.
3141 @node List/String Conversion
3142 @subsubsection List/String conversion
3144 When processing strings, it is often convenient to first convert them
3145 into a list representation by using the procedure @code{string->list},
3146 work with the resulting list, and then convert it back into a string.
3147 These procedures are useful for similar tasks.
3149 @rnindex string->list
3150 @deffn {Scheme Procedure} string->list str [start [end]]
3151 @deffnx {C Function} scm_substring_to_list (str, start, end)
3152 @deffnx {C Function} scm_string_to_list (str)
3153 Convert the string @var{str} into a list of characters.
3156 @deffn {Scheme Procedure} string-split str char_pred
3157 @deffnx {C Function} scm_string_split (str, char_pred)
3158 Split the string @var{str} into a list of substrings delimited
3159 by appearances of characters that
3163 equal @var{char_pred}, if it is a character,
3166 satisfy the predicate @var{char_pred}, if it is a procedure,
3169 are in the set @var{char_pred}, if it is a character set.
3172 Note that an empty substring between separator characters will result in
3173 an empty string in the result list.
3176 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
3178 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
3180 (string-split "::" #\:)
3184 (string-split "" #\:)
3191 @node String Selection
3192 @subsubsection String Selection
3194 Portions of strings can be extracted by these procedures.
3195 @code{string-ref} delivers individual characters whereas
3196 @code{substring} can be used to extract substrings from longer strings.
3198 @rnindex string-length
3199 @deffn {Scheme Procedure} string-length string
3200 @deffnx {C Function} scm_string_length (string)
3201 Return the number of characters in @var{string}.
3204 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
3205 Return the number of characters in @var{str} as a @code{size_t}.
3209 @deffn {Scheme Procedure} string-ref str k
3210 @deffnx {C Function} scm_string_ref (str, k)
3211 Return character @var{k} of @var{str} using zero-origin
3212 indexing. @var{k} must be a valid index of @var{str}.
3215 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
3216 Return character @var{k} of @var{str} using zero-origin
3217 indexing. @var{k} must be a valid index of @var{str}.
3220 @rnindex string-copy
3221 @deffn {Scheme Procedure} string-copy str [start [end]]
3222 @deffnx {C Function} scm_substring_copy (str, start, end)
3223 @deffnx {C Function} scm_string_copy (str)
3224 Return a copy of the given string @var{str}.
3226 The returned string shares storage with @var{str} initially, but it is
3227 copied as soon as one of the two strings is modified.
3231 @deffn {Scheme Procedure} substring str start [end]
3232 @deffnx {C Function} scm_substring (str, start, end)
3233 Return a new string formed from the characters
3234 of @var{str} beginning with index @var{start} (inclusive) and
3235 ending with index @var{end} (exclusive).
3236 @var{str} must be a string, @var{start} and @var{end} must be
3237 exact integers satisfying:
3239 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
3241 The returned string shares storage with @var{str} initially, but it is
3242 copied as soon as one of the two strings is modified.
3245 @deffn {Scheme Procedure} substring/shared str start [end]
3246 @deffnx {C Function} scm_substring_shared (str, start, end)
3247 Like @code{substring}, but the strings continue to share their storage
3248 even if they are modified. Thus, modifications to @var{str} show up
3249 in the new string, and vice versa.
3252 @deffn {Scheme Procedure} substring/copy str start [end]
3253 @deffnx {C Function} scm_substring_copy (str, start, end)
3254 Like @code{substring}, but the storage for the new string is copied
3258 @deffn {Scheme Procedure} substring/read-only str start [end]
3259 @deffnx {C Function} scm_substring_read_only (str, start, end)
3260 Like @code{substring}, but the resulting string can not be modified.
3263 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
3264 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
3265 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
3266 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
3267 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
3270 @deffn {Scheme Procedure} string-take s n
3271 @deffnx {C Function} scm_string_take (s, n)
3272 Return the @var{n} first characters of @var{s}.
3275 @deffn {Scheme Procedure} string-drop s n
3276 @deffnx {C Function} scm_string_drop (s, n)
3277 Return all but the first @var{n} characters of @var{s}.
3280 @deffn {Scheme Procedure} string-take-right s n
3281 @deffnx {C Function} scm_string_take_right (s, n)
3282 Return the @var{n} last characters of @var{s}.
3285 @deffn {Scheme Procedure} string-drop-right s n
3286 @deffnx {C Function} scm_string_drop_right (s, n)
3287 Return all but the last @var{n} characters of @var{s}.
3290 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
3291 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
3292 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
3293 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
3294 Take characters @var{start} to @var{end} from the string @var{s} and
3295 either pad with @var{chr} or truncate them to give @var{len}
3298 @code{string-pad} pads or truncates on the left, so for example
3301 (string-pad "x" 3) @result{} " x"
3302 (string-pad "abcde" 3) @result{} "cde"
3305 @code{string-pad-right} pads or truncates on the right, so for example
3308 (string-pad-right "x" 3) @result{} "x "
3309 (string-pad-right "abcde" 3) @result{} "abc"
3313 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
3314 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
3315 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
3316 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
3317 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
3318 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
3319 Trim occurrences of @var{char_pred} from the ends of @var{s}.
3321 @code{string-trim} trims @var{char_pred} characters from the left
3322 (start) of the string, @code{string-trim-right} trims them from the
3323 right (end) of the string, @code{string-trim-both} trims from both
3326 @var{char_pred} can be a character, a character set, or a predicate
3327 procedure to call on each character. If @var{char_pred} is not given
3328 the default is whitespace as per @code{char-set:whitespace}
3329 (@pxref{Standard Character Sets}).
3332 (string-trim " x ") @result{} "x "
3333 (string-trim-right "banana" #\a) @result{} "banan"
3334 (string-trim-both ".,xy:;" char-set:punctuation)
3336 (string-trim-both "xyzzy" (lambda (c)
3343 @node String Modification
3344 @subsubsection String Modification
3346 These procedures are for modifying strings in-place. This means that the
3347 result of the operation is not a new string; instead, the original string's
3348 memory representation is modified.
3350 @rnindex string-set!
3351 @deffn {Scheme Procedure} string-set! str k chr
3352 @deffnx {C Function} scm_string_set_x (str, k, chr)
3353 Store @var{chr} in element @var{k} of @var{str} and return
3354 an unspecified value. @var{k} must be a valid index of
3358 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
3359 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
3362 @rnindex string-fill!
3363 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
3364 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
3365 @deffnx {C Function} scm_string_fill_x (str, chr)
3366 Stores @var{chr} in every element of the given @var{str} and
3367 returns an unspecified value.
3370 @deffn {Scheme Procedure} substring-fill! str start end fill
3371 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
3372 Change every character in @var{str} between @var{start} and
3373 @var{end} to @var{fill}.
3376 (define y (string-copy "abcdefg"))
3377 (substring-fill! y 1 3 #\r)
3383 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
3384 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
3385 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
3386 into @var{str2} beginning at position @var{start2}.
3387 @var{str1} and @var{str2} can be the same string.
3390 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
3391 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
3392 Copy the sequence of characters from index range [@var{start},
3393 @var{end}) in string @var{s} to string @var{target}, beginning
3394 at index @var{tstart}. The characters are copied left-to-right
3395 or right-to-left as needed -- the copy is guaranteed to work,
3396 even if @var{target} and @var{s} are the same string. It is an
3397 error if the copy operation runs off the end of the target
3402 @node String Comparison
3403 @subsubsection String Comparison
3405 The procedures in this section are similar to the character ordering
3406 predicates (@pxref{Characters}), but are defined on character sequences.
3408 The first set is specified in R5RS and has names that end in @code{?}.
3409 The second set is specified in SRFI-13 and the names have not ending
3412 The predicates ending in @code{-ci} ignore the character case
3413 when comparing strings. For now, case-insensitive comparison is done
3414 using the R5RS rules, where every lower-case character that has a
3415 single character upper-case form is converted to uppercase before
3416 comparison. See @xref{Text Collation, the @code{(ice-9
3417 i18n)} module}, for locale-dependent string comparison.
3420 @deffn {Scheme Procedure} string=? s1 s2 s3 @dots{}
3421 Lexicographic equality predicate; return @code{#t} if all strings are
3422 the same length and contain the same characters in the same positions,
3423 otherwise return @code{#f}.
3425 The procedure @code{string-ci=?} treats upper and lower case
3426 letters as though they were the same character, but
3427 @code{string=?} treats upper and lower case as distinct
3432 @deffn {Scheme Procedure} string<? s1 s2 s3 @dots{}
3433 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3434 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3435 lexicographically less than @var{str_i+1}.
3439 @deffn {Scheme Procedure} string<=? s1 s2 s3 @dots{}
3440 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3441 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3442 lexicographically less than or equal to @var{str_i+1}.
3446 @deffn {Scheme Procedure} string>? s1 s2 s3 @dots{}
3447 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3448 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3449 lexicographically greater than @var{str_i+1}.
3453 @deffn {Scheme Procedure} string>=? s1 s2 s3 @dots{}
3454 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3455 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3456 lexicographically greater than or equal to @var{str_i+1}.
3459 @rnindex string-ci=?
3460 @deffn {Scheme Procedure} string-ci=? s1 s2 s3 @dots{}
3461 Case-insensitive string equality predicate; return @code{#t} if
3462 all strings are the same length and their component
3463 characters match (ignoring case) at each position; otherwise
3467 @rnindex string-ci<?
3468 @deffn {Scheme Procedure} string-ci<? s1 s2 s3 @dots{}
3469 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3470 for every pair of consecutive string arguments @var{str_i} and
3471 @var{str_i+1}, @var{str_i} is lexicographically less than @var{str_i+1}
3476 @deffn {Scheme Procedure} string-ci<=? s1 s2 s3 @dots{}
3477 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3478 for every pair of consecutive string arguments @var{str_i} and
3479 @var{str_i+1}, @var{str_i} is lexicographically less than or equal to
3480 @var{str_i+1} regardless of case.
3483 @rnindex string-ci>?
3484 @deffn {Scheme Procedure} string-ci>? s1 s2 s3 @dots{}
3485 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3486 for every pair of consecutive string arguments @var{str_i} and
3487 @var{str_i+1}, @var{str_i} is lexicographically greater than
3488 @var{str_i+1} regardless of case.
3491 @rnindex string-ci>=?
3492 @deffn {Scheme Procedure} string-ci>=? s1 s2 s3 @dots{}
3493 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3494 for every pair of consecutive string arguments @var{str_i} and
3495 @var{str_i+1}, @var{str_i} is lexicographically greater than or equal to
3496 @var{str_i+1} regardless of case.
3499 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3500 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3501 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3502 mismatch index, depending upon whether @var{s1} is less than,
3503 equal to, or greater than @var{s2}. The mismatch index is the
3504 largest index @var{i} such that for every 0 <= @var{j} <
3505 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3506 @var{i} is the first position that does not match.
3509 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3510 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3511 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3512 mismatch index, depending upon whether @var{s1} is less than,
3513 equal to, or greater than @var{s2}. The mismatch index is the
3514 largest index @var{i} such that for every 0 <= @var{j} <
3515 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3516 @var{i} is the first position where the lowercased letters
3521 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3522 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3523 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3527 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3528 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3529 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3533 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3534 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3535 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3536 true value otherwise.
3539 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3540 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3541 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3542 true value otherwise.
3545 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3546 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3547 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3551 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3552 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3553 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3557 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3558 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3559 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3560 value otherwise. The character comparison is done
3564 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3565 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3566 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3567 value otherwise. The character comparison is done
3571 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3572 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3573 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3574 true value otherwise. The character comparison is done
3578 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3579 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3580 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3581 true value otherwise. The character comparison is done
3585 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3586 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3587 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3588 value otherwise. The character comparison is done
3592 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3593 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3594 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3595 otherwise. The character comparison is done
3599 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3600 @deffnx {C Function} scm_substring_hash (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 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3605 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3606 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).
3609 Because the same visual appearance of an abstract Unicode character can
3610 be obtained via multiple sequences of Unicode characters, even the
3611 case-insensitive string comparison functions described above may return
3612 @code{#f} when presented with strings containing different
3613 representations of the same character. For example, the Unicode
3614 character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be
3615 represented with a single character (U+1E69) or by the character ``LATIN
3616 SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING
3617 DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307).
3619 For this reason, it is often desirable to ensure that the strings
3620 to be compared are using a mutually consistent representation for every
3621 character. The Unicode standard defines two methods of normalizing the
3622 contents of strings: Decomposition, which breaks composite characters
3623 into a set of constituent characters with an ordering defined by the
3624 Unicode Standard; and composition, which performs the converse.
3626 There are two decomposition operations. ``Canonical decomposition''
3627 produces character sequences that share the same visual appearance as
3628 the original characters, while ``compatibility decomposition'' produces
3629 ones whose visual appearances may differ from the originals but which
3630 represent the same abstract character.
3632 These operations are encapsulated in the following set of normalization
3637 Characters are decomposed to their canonical forms.
3640 Characters are decomposed to their compatibility forms.
3643 Characters are decomposed to their canonical forms, then composed.
3646 Characters are decomposed to their compatibility forms, then composed.
3650 The functions below put their arguments into one of the forms described
3653 @deffn {Scheme Procedure} string-normalize-nfd s
3654 @deffnx {C Function} scm_string_normalize_nfd (s)
3655 Return the @code{NFD} normalized form of @var{s}.
3658 @deffn {Scheme Procedure} string-normalize-nfkd s
3659 @deffnx {C Function} scm_string_normalize_nfkd (s)
3660 Return the @code{NFKD} normalized form of @var{s}.
3663 @deffn {Scheme Procedure} string-normalize-nfc s
3664 @deffnx {C Function} scm_string_normalize_nfc (s)
3665 Return the @code{NFC} normalized form of @var{s}.
3668 @deffn {Scheme Procedure} string-normalize-nfkc s
3669 @deffnx {C Function} scm_string_normalize_nfkc (s)
3670 Return the @code{NFKC} normalized form of @var{s}.
3673 @node String Searching
3674 @subsubsection String Searching
3676 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3677 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3678 Search through the string @var{s} from left to right, returning
3679 the index of the first occurrence of a character which
3683 equals @var{char_pred}, if it is character,
3686 satisfies the predicate @var{char_pred}, if it is a procedure,
3689 is in the set @var{char_pred}, if it is a character set.
3692 Return @code{#f} if no match is found.
3695 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3696 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3697 Search through the string @var{s} from right to left, returning
3698 the index of the last occurrence of a character which
3702 equals @var{char_pred}, if it is character,
3705 satisfies the predicate @var{char_pred}, if it is a procedure,
3708 is in the set if @var{char_pred} is a character set.
3711 Return @code{#f} if no match is found.
3714 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3715 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3716 Return the length of the longest common prefix of the two
3720 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3721 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3722 Return the length of the longest common prefix of the two
3723 strings, ignoring character case.
3726 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3727 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3728 Return the length of the longest common suffix of the two
3732 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3733 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3734 Return the length of the longest common suffix of the two
3735 strings, ignoring character case.
3738 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3739 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3740 Is @var{s1} a prefix of @var{s2}?
3743 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3744 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3745 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3748 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3749 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3750 Is @var{s1} a suffix of @var{s2}?
3753 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3754 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3755 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3758 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3759 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3760 Search through the string @var{s} from right to left, returning
3761 the index of the last occurrence of a character which
3765 equals @var{char_pred}, if it is character,
3768 satisfies the predicate @var{char_pred}, if it is a procedure,
3771 is in the set if @var{char_pred} is a character set.
3774 Return @code{#f} if no match is found.
3777 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3778 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3779 Search through the string @var{s} from left to right, returning
3780 the index of the first occurrence of a character which
3784 does not equal @var{char_pred}, if it is character,
3787 does not satisfy the predicate @var{char_pred}, if it is a
3791 is not in the set if @var{char_pred} is a character set.
3795 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3796 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3797 Search through the string @var{s} from right to left, returning
3798 the index of the last occurrence of a character which
3802 does not equal @var{char_pred}, if it is character,
3805 does not satisfy the predicate @var{char_pred}, if it is a
3809 is not in the set if @var{char_pred} is a character set.
3813 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3814 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3815 Return the count of the number of characters in the string
3820 equals @var{char_pred}, if it is character,
3823 satisfies the predicate @var{char_pred}, if it is a procedure.
3826 is in the set @var{char_pred}, if it is a character set.
3830 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3831 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3832 Does string @var{s1} contain string @var{s2}? Return the index
3833 in @var{s1} where @var{s2} occurs as a substring, or false.
3834 The optional start/end indices restrict the operation to the
3835 indicated substrings.
3838 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3839 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3840 Does string @var{s1} contain string @var{s2}? Return the index
3841 in @var{s1} where @var{s2} occurs as a substring, or false.
3842 The optional start/end indices restrict the operation to the
3843 indicated substrings. Character comparison is done
3847 @node Alphabetic Case Mapping
3848 @subsubsection Alphabetic Case Mapping
3850 These are procedures for mapping strings to their upper- or lower-case
3851 equivalents, respectively, or for capitalizing strings.
3853 They use the basic case mapping rules for Unicode characters. No
3854 special language or context rules are considered. The resulting strings
3855 are guaranteed to be the same length as the input strings.
3857 @xref{Character Case Mapping, the @code{(ice-9
3858 i18n)} module}, for locale-dependent case conversions.
3860 @deffn {Scheme Procedure} string-upcase str [start [end]]
3861 @deffnx {C Function} scm_substring_upcase (str, start, end)
3862 @deffnx {C Function} scm_string_upcase (str)
3863 Upcase every character in @code{str}.
3866 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3867 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3868 @deffnx {C Function} scm_string_upcase_x (str)
3869 Destructively upcase every character in @code{str}.
3879 @deffn {Scheme Procedure} string-downcase str [start [end]]
3880 @deffnx {C Function} scm_substring_downcase (str, start, end)
3881 @deffnx {C Function} scm_string_downcase (str)
3882 Downcase every character in @var{str}.
3885 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3886 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3887 @deffnx {C Function} scm_string_downcase_x (str)
3888 Destructively downcase every character in @var{str}.
3893 (string-downcase! y)
3900 @deffn {Scheme Procedure} string-capitalize str
3901 @deffnx {C Function} scm_string_capitalize (str)
3902 Return a freshly allocated string with the characters in
3903 @var{str}, where the first character of every word is
3907 @deffn {Scheme Procedure} string-capitalize! str
3908 @deffnx {C Function} scm_string_capitalize_x (str)
3909 Upcase the first character of every word in @var{str}
3910 destructively and return @var{str}.
3913 y @result{} "hello world"
3914 (string-capitalize! y) @result{} "Hello World"
3915 y @result{} "Hello World"
3919 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3920 @deffnx {C Function} scm_string_titlecase (str, start, end)
3921 Titlecase every first character in a word in @var{str}.
3924 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3925 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3926 Destructively titlecase every first character in a word in
3930 @node Reversing and Appending Strings
3931 @subsubsection Reversing and Appending Strings
3933 @deffn {Scheme Procedure} string-reverse str [start [end]]
3934 @deffnx {C Function} scm_string_reverse (str, start, end)
3935 Reverse the string @var{str}. The optional arguments
3936 @var{start} and @var{end} delimit the region of @var{str} to
3940 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3941 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3942 Reverse the string @var{str} in-place. The optional arguments
3943 @var{start} and @var{end} delimit the region of @var{str} to
3944 operate on. The return value is unspecified.
3947 @rnindex string-append
3948 @deffn {Scheme Procedure} string-append arg @dots{}
3949 @deffnx {C Function} scm_string_append (args)
3950 Return a newly allocated string whose characters form the
3951 concatenation of the given strings, @var{arg} @enddots{}.
3955 (string-append h "world"))
3956 @result{} "hello world"
3960 @deffn {Scheme Procedure} string-append/shared arg @dots{}
3961 @deffnx {C Function} scm_string_append_shared (args)
3962 Like @code{string-append}, but the result may share memory
3963 with the argument strings.
3966 @deffn {Scheme Procedure} string-concatenate ls
3967 @deffnx {C Function} scm_string_concatenate (ls)
3968 Append the elements (which must be strings) of @var{ls} together into a
3969 single string. Guaranteed to return a freshly allocated string.
3972 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3973 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3974 Without optional arguments, this procedure is equivalent to
3977 (string-concatenate (reverse ls))
3980 If the optional argument @var{final_string} is specified, it is
3981 consed onto the beginning to @var{ls} before performing the
3982 list-reverse and string-concatenate operations. If @var{end}
3983 is given, only the characters of @var{final_string} up to index
3986 Guaranteed to return a freshly allocated string.
3989 @deffn {Scheme Procedure} string-concatenate/shared ls
3990 @deffnx {C Function} scm_string_concatenate_shared (ls)
3991 Like @code{string-concatenate}, but the result may share memory
3992 with the strings in the list @var{ls}.
3995 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3996 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3997 Like @code{string-concatenate-reverse}, but the result may
3998 share memory with the strings in the @var{ls} arguments.
4001 @node Mapping Folding and Unfolding
4002 @subsubsection Mapping, Folding, and Unfolding
4004 @deffn {Scheme Procedure} string-map proc s [start [end]]
4005 @deffnx {C Function} scm_string_map (proc, s, start, end)
4006 @var{proc} is a char->char procedure, it is mapped over
4007 @var{s}. The order in which the procedure is applied to the
4008 string elements is not specified.
4011 @deffn {Scheme Procedure} string-map! proc s [start [end]]
4012 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
4013 @var{proc} is a char->char procedure, it is mapped over
4014 @var{s}. The order in which the procedure is applied to the
4015 string elements is not specified. The string @var{s} is
4016 modified in-place, the return value is not specified.
4019 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
4020 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
4021 @var{proc} is mapped over @var{s} in left-to-right order. The
4022 return value is not specified.
4025 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
4026 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
4027 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
4030 For example, to change characters to alternately upper and lower case,
4033 (define str (string-copy "studly"))
4034 (string-for-each-index
4037 ((if (even? i) char-upcase char-downcase)
4038 (string-ref str i))))
4040 str @result{} "StUdLy"
4044 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
4045 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
4046 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4047 as the terminating element, from left to right. @var{kons}
4048 must expect two arguments: The actual character and the last
4049 result of @var{kons}' application.
4052 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
4053 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
4054 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4055 as the terminating element, from right to left. @var{kons}
4056 must expect two arguments: The actual character and the last
4057 result of @var{kons}' application.
4060 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
4061 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
4063 @item @var{g} is used to generate a series of @emph{seed}
4064 values from the initial @var{seed}: @var{seed}, (@var{g}
4065 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4067 @item @var{p} tells us when to stop -- when it returns true
4068 when applied to one of these seed values.
4069 @item @var{f} maps each seed value to the corresponding
4070 character in the result string. These chars are assembled
4071 into the string in a left-to-right order.
4072 @item @var{base} is the optional initial/leftmost portion
4073 of the constructed string; it default to the empty
4075 @item @var{make_final} is applied to the terminal seed
4076 value (on which @var{p} returns true) to produce
4077 the final/rightmost portion of the constructed string.
4078 The default is nothing extra.
4082 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
4083 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
4085 @item @var{g} is used to generate a series of @emph{seed}
4086 values from the initial @var{seed}: @var{seed}, (@var{g}
4087 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4089 @item @var{p} tells us when to stop -- when it returns true
4090 when applied to one of these seed values.
4091 @item @var{f} maps each seed value to the corresponding
4092 character in the result string. These chars are assembled
4093 into the string in a right-to-left order.
4094 @item @var{base} is the optional initial/rightmost portion
4095 of the constructed string; it default to the empty
4097 @item @var{make_final} is applied to the terminal seed
4098 value (on which @var{p} returns true) to produce
4099 the final/leftmost portion of the constructed string.
4100 It defaults to @code{(lambda (x) )}.
4104 @node Miscellaneous String Operations
4105 @subsubsection Miscellaneous String Operations
4107 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
4108 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
4109 This is the @emph{extended substring} procedure that implements
4110 replicated copying of a substring of some string.
4112 @var{s} is a string, @var{start} and @var{end} are optional
4113 arguments that demarcate a substring of @var{s}, defaulting to
4114 0 and the length of @var{s}. Replicate this substring up and
4115 down index space, in both the positive and negative directions.
4116 @code{xsubstring} returns the substring of this string
4117 beginning at index @var{from}, and ending at @var{to}, which
4118 defaults to @var{from} + (@var{end} - @var{start}).
4121 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
4122 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
4123 Exactly the same as @code{xsubstring}, but the extracted text
4124 is written into the string @var{target} starting at index
4125 @var{tstart}. The operation is not defined if @code{(eq?
4126 @var{target} @var{s})} or these arguments share storage -- you
4127 cannot copy a string on top of itself.
4130 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
4131 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
4132 Return the string @var{s1}, but with the characters
4133 @var{start1} @dots{} @var{end1} replaced by the characters
4134 @var{start2} @dots{} @var{end2} from @var{s2}.
4137 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
4138 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
4139 Split the string @var{s} into a list of substrings, where each
4140 substring is a maximal non-empty contiguous sequence of
4141 characters from the character set @var{token_set}, which
4142 defaults to @code{char-set:graphic}.
4143 If @var{start} or @var{end} indices are provided, they restrict
4144 @code{string-tokenize} to operating on the indicated substring
4148 @deffn {Scheme Procedure} string-filter char_pred s [start [end]]
4149 @deffnx {C Function} scm_string_filter (char_pred, s, start, end)
4150 Filter the string @var{s}, retaining only those characters which
4151 satisfy @var{char_pred}.
4153 If @var{char_pred} is a procedure, it is applied to each character as
4154 a predicate, if it is a character, it is tested for equality and if it
4155 is a character set, it is tested for membership.
4158 @deffn {Scheme Procedure} string-delete char_pred s [start [end]]
4159 @deffnx {C Function} scm_string_delete (char_pred, s, start, end)
4160 Delete characters satisfying @var{char_pred} from @var{s}.
4162 If @var{char_pred} is a procedure, it is applied to each character as
4163 a predicate, if it is a character, it is tested for equality and if it
4164 is a character set, it is tested for membership.
4167 @node Representing Strings as Bytes
4168 @subsubsection Representing Strings as Bytes
4170 Out in the cold world outside of Guile, not all strings are treated in
4171 the same way. Out there there are only bytes, and there are many ways
4172 of representing a strings (sequences of characters) as binary data
4173 (sequences of bytes).
4175 As a user, usually you don't have to think about this very much. When
4176 you type on your keyboard, your system encodes your keystrokes as bytes
4177 according to the locale that you have configured on your computer.
4178 Guile uses the locale to decode those bytes back into characters --
4179 hopefully the same characters that you typed in.
4181 All is not so clear when dealing with a system with multiple users, such
4182 as a web server. Your web server might get a request from one user for
4183 data encoded in the ISO-8859-1 character set, and then another request
4184 from a different user for UTF-8 data.
4187 @cindex character encoding
4188 Guile provides an @dfn{iconv} module for converting between strings and
4189 sequences of bytes. @xref{Bytevectors}, for more on how Guile
4190 represents raw byte sequences. This module gets its name from the
4191 common @sc{unix} command of the same name.
4193 Note that often it is sufficient to just read and write strings from
4194 ports instead of using these functions. To do this, specify the port
4195 encoding using @code{set-port-encoding!}. @xref{Ports}, for more on
4196 ports and character encodings.
4198 Unlike the rest of the procedures in this section, you have to load the
4199 @code{iconv} module before having access to these procedures:
4202 (use-modules (ice-9 iconv))
4205 @deffn string->bytevector string encoding [conversion-strategy]
4206 Encode @var{string} as a sequence of bytes.
4208 The string will be encoded in the character set specified by the
4209 @var{encoding} string. If the string has characters that cannot be
4210 represented in the encoding, by default this procedure raises an
4211 @code{encoding-error}. Pass a @var{conversion-strategy} argument to
4212 specify other behaviors.
4214 The return value is a bytevector. @xref{Bytevectors}, for more on
4215 bytevectors. @xref{Ports}, for more on character encodings and
4216 conversion strategies.
4219 @deffn bytevector->string bytevector encoding [conversion-strategy]
4220 Decode @var{bytevector} into a string.
4222 The bytes will be decoded from the character set by the @var{encoding}
4223 string. If the bytes do not form a valid encoding, by default this
4224 procedure raises an @code{decoding-error}. As with
4225 @code{string->bytevector}, pass the optional @var{conversion-strategy}
4226 argument to modify this behavior. @xref{Ports}, for more on character
4227 encodings and conversion strategies.
4230 @deffn call-with-output-encoded-string encoding proc [conversion-strategy]
4231 Like @code{call-with-output-string}, but instead of returning a string,
4232 returns a encoding of the string according to @var{encoding}, as a
4233 bytevector. This procedure can be more efficient than collecting a
4234 string and then converting it via @code{string->bytevector}.
4237 @node Conversion to/from C
4238 @subsubsection Conversion to/from C
4240 When creating a Scheme string from a C string or when converting a
4241 Scheme string to a C string, the concept of character encoding becomes
4244 In C, a string is just a sequence of bytes, and the character encoding
4245 describes the relation between these bytes and the actual characters
4246 that make up the string. For Scheme strings, character encoding is not
4247 an issue (most of the time), since in Scheme you usually treat strings
4248 as character sequences, not byte sequences.
4250 Converting to C and converting from C each have their own challenges.
4252 When converting from C to Scheme, it is important that the sequence of
4253 bytes in the C string be valid with respect to its encoding. ASCII
4254 strings, for example, can't have any bytes greater than 127. An ASCII
4255 byte greater than 127 is considered @emph{ill-formed} and cannot be
4256 converted into a Scheme character.
4258 Problems can occur in the reverse operation as well. Not all character
4259 encodings can hold all possible Scheme characters. Some encodings, like
4260 ASCII for example, can only describe a small subset of all possible
4261 characters. So, when converting to C, one must first decide what to do
4262 with Scheme characters that can't be represented in the C string.
4264 Converting a Scheme string to a C string will often allocate fresh
4265 memory to hold the result. You must take care that this memory is
4266 properly freed eventually. In many cases, this can be achieved by
4267 using @code{scm_dynwind_free} inside an appropriate dynwind context,
4268 @xref{Dynamic Wind}.
4270 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
4271 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
4272 Creates a new Scheme string that has the same contents as @var{str} when
4273 interpreted in the character encoding of the current locale.
4275 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
4277 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
4278 @var{str} in bytes, and @var{str} does not need to be null-terminated.
4279 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
4280 null-terminated and the real length will be found with @code{strlen}.
4282 If the C string is ill-formed, an error will be raised.
4284 Note that these functions should @emph{not} be used to convert C string
4285 constants, because there is no guarantee that the current locale will
4286 match that of the source code. To convert C string constants, use
4287 @code{scm_from_latin1_string}, @code{scm_from_utf8_string} or
4288 @code{scm_from_utf32_string}.
4291 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
4292 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
4293 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
4294 respectively, but also frees @var{str} with @code{free} eventually.
4295 Thus, you can use this function when you would free @var{str} anyway
4296 immediately after creating the Scheme string. In certain cases, Guile
4297 can then use @var{str} directly as its internal representation.
4300 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
4301 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
4302 Returns a C string with the same contents as @var{str} in the character
4303 encoding of the current locale. The C string must be freed with
4304 @code{free} eventually, maybe by using @code{scm_dynwind_free},
4305 @xref{Dynamic Wind}.
4307 For @code{scm_to_locale_string}, the returned string is
4308 null-terminated and an error is signalled when @var{str} contains
4309 @code{#\nul} characters.
4311 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
4312 @var{str} might contain @code{#\nul} characters and the length of the
4313 returned string in bytes is stored in @code{*@var{lenp}}. The
4314 returned string will not be null-terminated in this case. If
4315 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
4316 @code{scm_to_locale_string}.
4318 If a character in @var{str} cannot be represented in the character
4319 encoding of the current locale, the default port conversion strategy is
4320 used. @xref{Ports}, for more on conversion strategies.
4322 If the conversion strategy is @code{error}, an error will be raised. If
4323 it is @code{substitute}, a replacement character, such as a question
4324 mark, will be inserted in its place. If it is @code{escape}, a hex
4325 escape will be inserted in its place.
4328 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
4329 Puts @var{str} as a C string in the current locale encoding into the
4330 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
4331 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
4332 more than that. No terminating @code{'\0'} will be stored.
4334 The return value of @code{scm_to_locale_stringbuf} is the number of
4335 bytes that are needed for all of @var{str}, regardless of whether
4336 @var{buf} was large enough to hold them. Thus, when the return value
4337 is larger than @var{max_len}, only @var{max_len} bytes have been
4338 stored and you probably need to try again with a larger buffer.
4341 For most situations, string conversion should occur using the current
4342 locale, such as with the functions above. But there may be cases where
4343 one wants to convert strings from a character encoding other than the
4344 locale's character encoding. For these cases, the lower-level functions
4345 @code{scm_to_stringn} and @code{scm_from_stringn} are provided. These
4346 functions should seldom be necessary if one is properly using locales.
4348 @deftp {C Type} scm_t_string_failed_conversion_handler
4349 This is an enumerated type that can take one of three values:
4350 @code{SCM_FAILED_CONVERSION_ERROR},
4351 @code{SCM_FAILED_CONVERSION_QUESTION_MARK}, and
4352 @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}. They are used to indicate
4353 a strategy for handling characters that cannot be converted to or from a
4354 given character encoding. @code{SCM_FAILED_CONVERSION_ERROR} indicates
4355 that a conversion should throw an error if some characters cannot be
4356 converted. @code{SCM_FAILED_CONVERSION_QUESTION_MARK} indicates that a
4357 conversion should replace unconvertable characters with the question
4358 mark character. And, @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}
4359 requests that a conversion should replace an unconvertable character
4360 with an escape sequence.
4362 While all three strategies apply when converting Scheme strings to C,
4363 only @code{SCM_FAILED_CONVERSION_ERROR} and
4364 @code{SCM_FAILED_CONVERSION_QUESTION_MARK} can be used when converting C
4368 @deftypefn {C Function} char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding, scm_t_string_failed_conversion_handler handler)
4369 This function returns a newly allocated C string from the Guile string
4370 @var{str}. The length of the returned string in bytes will be returned in
4371 @var{lenp}. The character encoding of the C string is passed as the ASCII,
4372 null-terminated C string @var{encoding}. The @var{handler} parameter
4373 gives a strategy for dealing with characters that cannot be converted
4374 into @var{encoding}.
4376 If @var{lenp} is @code{NULL}, this function will return a null-terminated C
4377 string. It will throw an error if the string contains a null
4380 The Scheme interface to this function is @code{string->bytevector}, from the
4381 @code{ice-9 iconv} module. @xref{Representing Strings as Bytes}.
4384 @deftypefn {C Function} SCM scm_from_stringn (const char *str, size_t len, const char *encoding, scm_t_string_failed_conversion_handler handler)
4385 This function returns a scheme string from the C string @var{str}. The
4386 length in bytes of the C string is input as @var{len}. The encoding of the C
4387 string is passed as the ASCII, null-terminated C string @code{encoding}.
4388 The @var{handler} parameters suggests a strategy for dealing with
4389 unconvertable characters.
4391 The Scheme interface to this function is @code{bytevector->string}.
4392 @xref{Representing Strings as Bytes}.
4395 The following conversion functions are provided as a convenience for the
4396 most commonly used encodings.
4398 @deftypefn {C Function} SCM scm_from_latin1_string (const char *str)
4399 @deftypefnx {C Function} SCM scm_from_utf8_string (const char *str)
4400 @deftypefnx {C Function} SCM scm_from_utf32_string (const scm_t_wchar *str)
4401 Return a scheme string from the null-terminated C string @var{str},
4402 which is ISO-8859-1-, UTF-8-, or UTF-32-encoded. These functions should
4403 be used to convert hard-coded C string constants into Scheme strings.
4406 @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len)
4407 @deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len)
4408 @deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
4409 Return a scheme string from C string @var{str}, which is ISO-8859-1-,
4410 UTF-8-, or UTF-32-encoded, of length @var{len}. @var{len} is the number
4411 of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and
4412 @code{scm_from_utf8_stringn}; it is the number of elements (code points)
4413 in @var{str} in the case of @code{scm_from_utf32_stringn}.
4416 @deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp)
4417 @deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp)
4418 @deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp)
4419 Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string
4420 from Scheme string @var{str}. An error is thrown when @var{str}
4421 cannot be converted to the specified encoding. If @var{lenp} is
4422 @code{NULL}, the returned C string will be null terminated, and an error
4423 will be thrown if the C string would otherwise contain null
4424 characters. If @var{lenp} is not @code{NULL}, the string is not null terminated,
4425 and the length of the returned string is returned in @var{lenp}. The length
4426 returned is the number of bytes for @code{scm_to_latin1_stringn} and
4427 @code{scm_to_utf8_stringn}; it is the number of elements (code points)
4428 for @code{scm_to_utf32_stringn}.
4431 @node String Internals
4432 @subsubsection String Internals
4434 Guile stores each string in memory as a contiguous array of Unicode code
4435 points along with an associated set of attributes. If all of the code
4436 points of a string have an integer range between 0 and 255 inclusive,
4437 the code point array is stored as one byte per code point: it is stored
4438 as an ISO-8859-1 (aka Latin-1) string. If any of the code points of the
4439 string has an integer value greater that 255, the code point array is
4440 stored as four bytes per code point: it is stored as a UTF-32 string.
4442 Conversion between the one-byte-per-code-point and
4443 four-bytes-per-code-point representations happens automatically as
4446 No API is provided to set the internal representation of strings;
4447 however, there are pair of procedures available to query it. These are
4448 debugging procedures. Using them in production code is discouraged,
4449 since the details of Guile's internal representation of strings may
4450 change from release to release.
4452 @deffn {Scheme Procedure} string-bytes-per-char str
4453 @deffnx {C Function} scm_string_bytes_per_char (str)
4454 Return the number of bytes used to encode a Unicode code point in string
4455 @var{str}. The result is one or four.
4458 @deffn {Scheme Procedure} %string-dump str
4459 @deffnx {C Function} scm_sys_string_dump (str)
4460 Returns an association list containing debugging information for
4461 @var{str}. The association list has the following entries.
4468 The start index of the string into its stringbuf
4471 The length of the string
4474 If this string is a substring, it returns its
4475 parent string. Otherwise, it returns @code{#f}
4478 @code{#t} if the string is read-only
4480 @item stringbuf-chars
4481 A new string containing this string's stringbuf's characters
4483 @item stringbuf-length
4484 The number of characters in this stringbuf
4486 @item stringbuf-shared
4487 @code{#t} if this stringbuf is shared
4489 @item stringbuf-wide
4490 @code{#t} if this stringbuf's characters are stored in a 32-bit buffer,
4491 or @code{#f} if they are stored in an 8-bit buffer
4497 @subsection Bytevectors
4502 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevectors)}
4503 module provides the programming interface specified by the
4504 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
4505 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
4506 interpret their contents in a number of ways: bytevector contents can be
4507 accessed as signed or unsigned integer of various sizes and endianness,
4508 as IEEE-754 floating point numbers, or as strings. It is a useful tool
4509 to encode and decode binary data.
4511 The R6RS (Section 4.3.4) specifies an external representation for
4512 bytevectors, whereby the octets (integers in the range 0--255) contained
4513 in the bytevector are represented as a list prefixed by @code{#vu8}:
4519 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
4520 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
4521 they do not need to be quoted:
4525 @result{} #vu8(1 53 204)
4528 Bytevectors can be used with the binary input/output primitives of the
4529 R6RS (@pxref{R6RS I/O Ports}).
4532 * Bytevector Endianness:: Dealing with byte order.
4533 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
4534 * Bytevectors as Integers:: Interpreting bytes as integers.
4535 * Bytevectors and Integer Lists:: Converting to/from an integer list.
4536 * Bytevectors as Floats:: Interpreting bytes as real numbers.
4537 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
4538 * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API.
4539 * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4.
4542 @node Bytevector Endianness
4543 @subsubsection Endianness
4549 Some of the following procedures take an @var{endianness} parameter.
4550 The @dfn{endianness} is defined as the order of bytes in multi-byte
4551 numbers: numbers encoded in @dfn{big endian} have their most
4552 significant bytes written first, whereas numbers encoded in
4553 @dfn{little endian} have their least significant bytes
4554 first@footnote{Big-endian and little-endian are the most common
4555 ``endiannesses'', but others do exist. For instance, the GNU MP
4556 library allows @dfn{word order} to be specified independently of
4557 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
4558 Multiple Precision Arithmetic Library Manual}).}.
4560 Little-endian is the native endianness of the IA32 architecture and
4561 its derivatives, while big-endian is native to SPARC and PowerPC,
4562 among others. The @code{native-endianness} procedure returns the
4563 native endianness of the machine it runs on.
4565 @deffn {Scheme Procedure} native-endianness
4566 @deffnx {C Function} scm_native_endianness ()
4567 Return a value denoting the native endianness of the host machine.
4570 @deffn {Scheme Macro} endianness symbol
4571 Return an object denoting the endianness specified by @var{symbol}. If
4572 @var{symbol} is neither @code{big} nor @code{little} then an error is
4573 raised at expand-time.
4576 @defvr {C Variable} scm_endianness_big
4577 @defvrx {C Variable} scm_endianness_little
4578 The objects denoting big- and little-endianness, respectively.
4582 @node Bytevector Manipulation
4583 @subsubsection Manipulating Bytevectors
4585 Bytevectors can be created, copied, and analyzed with the following
4586 procedures and C functions.
4588 @deffn {Scheme Procedure} make-bytevector len [fill]
4589 @deffnx {C Function} scm_make_bytevector (len, fill)
4590 @deffnx {C Function} scm_c_make_bytevector (size_t len)
4591 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
4592 is given, fill it with @var{fill}; @var{fill} must be in the range
4596 @deffn {Scheme Procedure} bytevector? obj
4597 @deffnx {C Function} scm_bytevector_p (obj)
4598 Return true if @var{obj} is a bytevector.
4601 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
4602 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
4605 @deffn {Scheme Procedure} bytevector-length bv
4606 @deffnx {C Function} scm_bytevector_length (bv)
4607 Return the length in bytes of bytevector @var{bv}.
4610 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
4611 Likewise, return the length in bytes of bytevector @var{bv}.
4614 @deffn {Scheme Procedure} bytevector=? bv1 bv2
4615 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
4616 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
4617 length and contents.
4620 @deffn {Scheme Procedure} bytevector-fill! bv fill
4621 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
4622 Fill bytevector @var{bv} with @var{fill}, a byte.
4625 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
4626 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
4627 Copy @var{len} bytes from @var{source} into @var{target}, starting
4628 reading from @var{source-start} (a positive index within @var{source})
4629 and start writing at @var{target-start}. It is permitted for the
4630 @var{source} and @var{target} regions to overlap.
4633 @deffn {Scheme Procedure} bytevector-copy bv
4634 @deffnx {C Function} scm_bytevector_copy (bv)
4635 Return a newly allocated copy of @var{bv}.
4638 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
4639 Return the byte at @var{index} in bytevector @var{bv}.
4642 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
4643 Set the byte at @var{index} in @var{bv} to @var{value}.
4646 Low-level C macros are available. They do not perform any
4647 type-checking; as such they should be used with care.
4649 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
4650 Return the length in bytes of bytevector @var{bv}.
4653 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
4654 Return a pointer to the contents of bytevector @var{bv}.
4658 @node Bytevectors as Integers
4659 @subsubsection Interpreting Bytevector Contents as Integers
4661 The contents of a bytevector can be interpreted as a sequence of
4662 integers of any given size, sign, and endianness.
4665 (let ((bv (make-bytevector 4)))
4666 (bytevector-u8-set! bv 0 #x12)
4667 (bytevector-u8-set! bv 1 #x34)
4668 (bytevector-u8-set! bv 2 #x56)
4669 (bytevector-u8-set! bv 3 #x78)
4671 (map (lambda (number)
4672 (number->string number 16))
4673 (list (bytevector-u8-ref bv 0)
4674 (bytevector-u16-ref bv 0 (endianness big))
4675 (bytevector-u32-ref bv 0 (endianness little)))))
4677 @result{} ("12" "1234" "78563412")
4680 The most generic procedures to interpret bytevector contents as integers
4681 are described below.
4683 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
4684 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
4685 Return the @var{size}-byte long unsigned integer at index @var{index} in
4686 @var{bv}, decoded according to @var{endianness}.
4689 @deffn {Scheme Procedure} bytevector-sint-ref bv index endianness size
4690 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
4691 Return the @var{size}-byte long signed integer at index @var{index} in
4692 @var{bv}, decoded according to @var{endianness}.
4695 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
4696 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
4697 Set the @var{size}-byte long unsigned integer at @var{index} to
4698 @var{value}, encoded according to @var{endianness}.
4701 @deffn {Scheme Procedure} bytevector-sint-set! bv index value endianness size
4702 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
4703 Set the @var{size}-byte long signed integer at @var{index} to
4704 @var{value}, encoded according to @var{endianness}.
4707 The following procedures are similar to the ones above, but specialized
4708 to a given integer size:
4710 @deffn {Scheme Procedure} bytevector-u8-ref bv index
4711 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
4712 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
4713 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
4714 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
4715 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
4716 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
4717 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
4718 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
4719 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
4720 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
4721 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
4722 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
4723 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
4724 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
4725 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
4726 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4727 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
4731 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
4732 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
4733 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
4734 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
4735 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
4736 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
4737 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
4738 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
4739 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
4740 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
4741 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
4742 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
4743 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
4744 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
4745 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
4746 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
4747 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4748 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
4752 Finally, a variant specialized for the host's endianness is available
4753 for each of these functions (with the exception of the @code{u8}
4754 accessors, for obvious reasons):
4756 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4757 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4758 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4759 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4760 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4761 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4762 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4763 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4764 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4765 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4766 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4767 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4768 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4769 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4770 host's native endianness.
4773 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4774 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4775 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4776 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4777 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4778 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4779 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4780 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4781 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4782 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4783 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4784 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4785 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4786 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4787 host's native endianness.
4791 @node Bytevectors and Integer Lists
4792 @subsubsection Converting Bytevectors to/from Integer Lists
4794 Bytevector contents can readily be converted to/from lists of signed or
4798 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4799 (endianness little) 2)
4803 @deffn {Scheme Procedure} bytevector->u8-list bv
4804 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4805 Return a newly allocated list of unsigned 8-bit integers from the
4806 contents of @var{bv}.
4809 @deffn {Scheme Procedure} u8-list->bytevector lst
4810 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4811 Return a newly allocated bytevector consisting of the unsigned 8-bit
4812 integers listed in @var{lst}.
4815 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4816 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4817 Return a list of unsigned integers of @var{size} bytes representing the
4818 contents of @var{bv}, decoded according to @var{endianness}.
4821 @deffn {Scheme Procedure} bytevector->sint-list bv endianness size
4822 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4823 Return a list of signed integers of @var{size} bytes representing the
4824 contents of @var{bv}, decoded according to @var{endianness}.
4827 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4828 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4829 Return a new bytevector containing the unsigned integers listed in
4830 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4833 @deffn {Scheme Procedure} sint-list->bytevector lst endianness size
4834 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4835 Return a new bytevector containing the signed integers listed in
4836 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4839 @node Bytevectors as Floats
4840 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4842 @cindex IEEE-754 floating point numbers
4844 Bytevector contents can also be accessed as IEEE-754 single- or
4845 double-precision floating point numbers (respectively 32 and 64-bit
4846 long) using the procedures described here.
4848 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4849 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4850 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4851 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4852 Return the IEEE-754 single-precision floating point number from @var{bv}
4853 at @var{index} according to @var{endianness}.
4856 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4857 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4858 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4859 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4860 Store real number @var{value} in @var{bv} at @var{index} according to
4864 Specialized procedures are also available:
4866 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4867 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4868 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4869 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4870 Return the IEEE-754 single-precision floating point number from @var{bv}
4871 at @var{index} according to the host's native endianness.
4874 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4875 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4876 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4877 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4878 Store real number @var{value} in @var{bv} at @var{index} according to
4879 the host's native endianness.
4883 @node Bytevectors as Strings
4884 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4886 @cindex Unicode string encoding
4888 Bytevector contents can also be interpreted as Unicode strings encoded
4889 in one of the most commonly available encoding formats.
4890 @xref{Representing Strings as Bytes}, for a more generic interface.
4893 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4896 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4897 @result{} #vu8(99 97 102 195 169)
4900 @deffn {Scheme Procedure} string->utf8 str
4901 @deffnx {Scheme Procedure} string->utf16 str [endianness]
4902 @deffnx {Scheme Procedure} string->utf32 str [endianness]
4903 @deffnx {C Function} scm_string_to_utf8 (str)
4904 @deffnx {C Function} scm_string_to_utf16 (str, endianness)
4905 @deffnx {C Function} scm_string_to_utf32 (str, endianness)
4906 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4907 UTF-32 (aka. UCS-4) encoding of @var{str}. For UTF-16 and UTF-32,
4908 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4909 it defaults to big endian.
4912 @deffn {Scheme Procedure} utf8->string utf
4913 @deffnx {Scheme Procedure} utf16->string utf [endianness]
4914 @deffnx {Scheme Procedure} utf32->string utf [endianness]
4915 @deffnx {C Function} scm_utf8_to_string (utf)
4916 @deffnx {C Function} scm_utf16_to_string (utf, endianness)
4917 @deffnx {C Function} scm_utf32_to_string (utf, endianness)
4918 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4919 or UTF-32-decoded contents of bytevector @var{utf}. For UTF-16 and UTF-32,
4920 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4921 it defaults to big endian.
4924 @node Bytevectors as Generalized Vectors
4925 @subsubsection Accessing Bytevectors with the Generalized Vector API
4927 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4928 with the @dfn{generalized vector} procedures (@pxref{Generalized
4929 Vectors}). This also allows bytevectors to be accessed using the
4930 generic @dfn{array} procedures (@pxref{Array Procedures}). When using
4931 these APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4934 (define bv #vu8(0 1 2 3))
4936 (generalized-vector? bv)
4939 (generalized-vector-ref bv 2)
4942 (generalized-vector-set! bv 2 77)
4951 @node Bytevectors as Uniform Vectors
4952 @subsubsection Accessing Bytevectors with the SRFI-4 API
4954 Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and
4955 Bytevectors}, for more information.
4962 Symbols in Scheme are widely used in three ways: as items of discrete
4963 data, as lookup keys for alists and hash tables, and to denote variable
4966 A @dfn{symbol} is similar to a string in that it is defined by a
4967 sequence of characters. The sequence of characters is known as the
4968 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4969 name doesn't include any characters that could be confused with other
4970 elements of Scheme syntax --- a symbol is written in a Scheme program by
4971 writing the sequence of characters that make up the name, @emph{without}
4972 any quotation marks or other special syntax. For example, the symbol
4973 whose name is ``multiply-by-2'' is written, simply:
4979 Notice how this differs from a @emph{string} with contents
4980 ``multiply-by-2'', which is written with double quotation marks, like
4987 Looking beyond how they are written, symbols are different from strings
4988 in two important respects.
4990 The first important difference is uniqueness. If the same-looking
4991 string is read twice from two different places in a program, the result
4992 is two @emph{different} string objects whose contents just happen to be
4993 the same. If, on the other hand, the same-looking symbol is read twice
4994 from two different places in a program, the result is the @emph{same}
4995 symbol object both times.
4997 Given two read symbols, you can use @code{eq?} to test whether they are
4998 the same (that is, have the same name). @code{eq?} is the most
4999 efficient comparison operator in Scheme, and comparing two symbols like
5000 this is as fast as comparing, for example, two numbers. Given two
5001 strings, on the other hand, you must use @code{equal?} or
5002 @code{string=?}, which are much slower comparison operators, to
5003 determine whether the strings have the same contents.
5006 (define sym1 (quote hello))
5007 (define sym2 (quote hello))
5008 (eq? sym1 sym2) @result{} #t
5010 (define str1 "hello")
5011 (define str2 "hello")
5012 (eq? str1 str2) @result{} #f
5013 (equal? str1 str2) @result{} #t
5016 The second important difference is that symbols, unlike strings, are not
5017 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
5018 example above: @code{(quote hello)} evaluates to the symbol named
5019 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
5020 symbol named "hello" and evaluated as a variable reference @dots{} about
5021 which more below (@pxref{Symbol Variables}).
5024 * Symbol Data:: Symbols as discrete data.
5025 * Symbol Keys:: Symbols as lookup keys.
5026 * Symbol Variables:: Symbols as denoting variables.
5027 * Symbol Primitives:: Operations related to symbols.
5028 * Symbol Props:: Function slots and property lists.
5029 * Symbol Read Syntax:: Extended read syntax for symbols.
5030 * Symbol Uninterned:: Uninterned symbols.
5035 @subsubsection Symbols as Discrete Data
5037 Numbers and symbols are similar to the extent that they both lend
5038 themselves to @code{eq?} comparison. But symbols are more descriptive
5039 than numbers, because a symbol's name can be used directly to describe
5040 the concept for which that symbol stands.
5042 For example, imagine that you need to represent some colours in a
5043 computer program. Using numbers, you would have to choose arbitrarily
5044 some mapping between numbers and colours, and then take care to use that
5045 mapping consistently:
5048 ;; 1=red, 2=green, 3=purple
5050 (if (eq? (colour-of car) 1)
5055 You can make the mapping more explicit and the code more readable by
5063 (if (eq? (colour-of car) red)
5068 But the simplest and clearest approach is not to use numbers at all, but
5069 symbols whose names specify the colours that they refer to:
5072 (if (eq? (colour-of car) 'red)
5076 The descriptive advantages of symbols over numbers increase as the set
5077 of concepts that you want to describe grows. Suppose that a car object
5078 can have other properties as well, such as whether it has or uses:
5082 automatic or manual transmission
5084 leaded or unleaded fuel
5086 power steering (or not).
5090 Then a car's combined property set could be naturally represented and
5091 manipulated as a list of symbols:
5094 (properties-of car1)
5096 (red manual unleaded power-steering)
5098 (if (memq 'power-steering (properties-of car1))
5099 (display "Unfit people can drive this car.\n")
5100 (display "You'll need strong arms to drive this car!\n"))
5102 Unfit people can drive this car.
5105 Remember, the fundamental property of symbols that we are relying on
5106 here is that an occurrence of @code{'red} in one part of a program is an
5107 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
5108 another part of a program; this means that symbols can usefully be
5109 compared using @code{eq?}. At the same time, symbols have naturally
5110 descriptive names. This combination of efficiency and descriptive power
5111 makes them ideal for use as discrete data.
5115 @subsubsection Symbols as Lookup Keys
5117 Given their efficiency and descriptive power, it is natural to use
5118 symbols as the keys in an association list or hash table.
5120 To illustrate this, consider a more structured representation of the car
5121 properties example from the preceding subsection. Rather than
5122 mixing all the properties up together in a flat list, we could use an
5123 association list like this:
5126 (define car1-properties '((colour . red)
5127 (transmission . manual)
5129 (steering . power-assisted)))
5132 Notice how this structure is more explicit and extensible than the flat
5133 list. For example it makes clear that @code{manual} refers to the
5134 transmission rather than, say, the windows or the locking of the car.
5135 It also allows further properties to use the same symbols among their
5136 possible values without becoming ambiguous:
5139 (define car1-properties '((colour . red)
5140 (transmission . manual)
5142 (steering . power-assisted)
5144 (locking . manual)))
5147 With a representation like this, it is easy to use the efficient
5148 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
5149 extract or change individual pieces of information:
5152 (assq-ref car1-properties 'fuel) @result{} unleaded
5153 (assq-ref car1-properties 'transmission) @result{} manual
5155 (assq-set! car1-properties 'seat-colour 'black)
5158 (transmission . manual)
5160 (steering . power-assisted)
5161 (seat-colour . black)
5162 (locking . manual)))
5165 Hash tables also have keys, and exactly the same arguments apply to the
5166 use of symbols in hash tables as in association lists. The hash value
5167 that Guile uses to decide where to add a symbol-keyed entry to a hash
5168 table can be obtained by calling the @code{symbol-hash} procedure:
5170 @deffn {Scheme Procedure} symbol-hash symbol
5171 @deffnx {C Function} scm_symbol_hash (symbol)
5172 Return a hash value for @var{symbol}.
5175 See @ref{Hash Tables} for information about hash tables in general, and
5176 for why you might choose to use a hash table rather than an association
5180 @node Symbol Variables
5181 @subsubsection Symbols as Denoting Variables
5183 When an unquoted symbol in a Scheme program is evaluated, it is
5184 interpreted as a variable reference, and the result of the evaluation is
5185 the appropriate variable's value.
5187 For example, when the expression @code{(string-length "abcd")} is read
5188 and evaluated, the sequence of characters @code{string-length} is read
5189 as the symbol whose name is "string-length". This symbol is associated
5190 with a variable whose value is the procedure that implements string
5191 length calculation. Therefore evaluation of the @code{string-length}
5192 symbol results in that procedure.
5194 The details of the connection between an unquoted symbol and the
5195 variable to which it refers are explained elsewhere. See @ref{Binding
5196 Constructs}, for how associations between symbols and variables are
5197 created, and @ref{Modules}, for how those associations are affected by
5198 Guile's module system.
5201 @node Symbol Primitives
5202 @subsubsection Operations Related to Symbols
5204 Given any Scheme value, you can determine whether it is a symbol using
5205 the @code{symbol?} primitive:
5208 @deffn {Scheme Procedure} symbol? obj
5209 @deffnx {C Function} scm_symbol_p (obj)
5210 Return @code{#t} if @var{obj} is a symbol, otherwise return
5214 @deftypefn {C Function} int scm_is_symbol (SCM val)
5215 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
5218 Once you know that you have a symbol, you can obtain its name as a
5219 string by calling @code{symbol->string}. Note that Guile differs by
5220 default from R5RS on the details of @code{symbol->string} as regards
5223 @rnindex symbol->string
5224 @deffn {Scheme Procedure} symbol->string s
5225 @deffnx {C Function} scm_symbol_to_string (s)
5226 Return the name of symbol @var{s} as a string. By default, Guile reads
5227 symbols case-sensitively, so the string returned will have the same case
5228 variation as the sequence of characters that caused @var{s} to be
5231 If Guile is set to read symbols case-insensitively (as specified by
5232 R5RS), and @var{s} comes into being as part of a literal expression
5233 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
5234 by a call to the @code{read} or @code{string-ci->symbol} procedures,
5235 Guile converts any alphabetic characters in the symbol's name to
5236 lower case before creating the symbol object, so the string returned
5237 here will be in lower case.
5239 If @var{s} was created by @code{string->symbol}, the case of characters
5240 in the string returned will be the same as that in the string that was
5241 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5242 setting at the time @var{s} was created.
5244 It is an error to apply mutation procedures like @code{string-set!} to
5245 strings returned by this procedure.
5248 Most symbols are created by writing them literally in code. However it
5249 is also possible to create symbols programmatically using the following
5252 @deffn {Scheme Procedure} symbol char@dots{}
5254 Return a newly allocated symbol made from the given character arguments.
5257 (symbol #\x #\y #\z) @result{} xyz
5261 @deffn {Scheme Procedure} list->symbol lst
5262 @rnindex list->symbol
5263 Return a newly allocated symbol made from a list of characters.
5266 (list->symbol '(#\a #\b #\c)) @result{} abc
5270 @rnindex symbol-append
5271 @deffn {Scheme Procedure} symbol-append arg @dots{}
5272 Return a newly allocated symbol whose characters form the
5273 concatenation of the given symbols, @var{arg} @enddots{}.
5277 (symbol-append h 'world))
5278 @result{} helloworld
5282 @rnindex string->symbol
5283 @deffn {Scheme Procedure} string->symbol string
5284 @deffnx {C Function} scm_string_to_symbol (string)
5285 Return the symbol whose name is @var{string}. This procedure can create
5286 symbols with names containing special characters or letters in the
5287 non-standard case, but it is usually a bad idea to create such symbols
5288 because in some implementations of Scheme they cannot be read as
5292 @deffn {Scheme Procedure} string-ci->symbol str
5293 @deffnx {C Function} scm_string_ci_to_symbol (str)
5294 Return the symbol whose name is @var{str}. If Guile is currently
5295 reading symbols case-insensitively, @var{str} is converted to lowercase
5296 before the returned symbol is looked up or created.
5299 The following examples illustrate Guile's detailed behaviour as regards
5300 the case-sensitivity of symbols:
5303 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5305 (symbol->string 'flying-fish) @result{} "flying-fish"
5306 (symbol->string 'Martin) @result{} "martin"
5308 (string->symbol "Malvina")) @result{} "Malvina"
5310 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5311 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5312 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5314 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5315 (string=? "K. Harper, M.D."
5317 (string->symbol "K. Harper, M.D."))) @result{} #t
5319 (read-disable 'case-insensitive) ; Guile default behaviour
5321 (symbol->string 'flying-fish) @result{} "flying-fish"
5322 (symbol->string 'Martin) @result{} "Martin"
5324 (string->symbol "Malvina")) @result{} "Malvina"
5326 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5327 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5328 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5330 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5331 (string=? "K. Harper, M.D."
5333 (string->symbol "K. Harper, M.D."))) @result{} #t
5336 From C, there are lower level functions that construct a Scheme symbol
5337 from a C string in the current locale encoding.
5339 When you want to do more from C, you should convert between symbols
5340 and strings using @code{scm_symbol_to_string} and
5341 @code{scm_string_to_symbol} and work with the strings.
5343 @deftypefn {C Function} scm_from_latin1_symbol (const char *name)
5344 @deftypefnx {C Function} scm_from_utf8_symbol (const char *name)
5345 Construct and return a Scheme symbol whose name is specified by the
5346 null-terminated C string @var{name}. These are appropriate when
5347 the C string is hard-coded in the source code.
5350 @deftypefn {C Function} scm_from_locale_symbol (const char *name)
5351 @deftypefnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
5352 Construct and return a Scheme symbol whose name is specified by
5353 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5354 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5355 specified explicitly by @var{len}.
5357 Note that these functions should @emph{not} be used when @var{name} is a
5358 C string constant, because there is no guarantee that the current locale
5359 will match that of the source code. In such cases, use
5360 @code{scm_from_latin1_symbol} or @code{scm_from_utf8_symbol}.
5363 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5364 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5365 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5366 respectively, but also frees @var{str} with @code{free} eventually.
5367 Thus, you can use this function when you would free @var{str} anyway
5368 immediately after creating the Scheme string. In certain cases, Guile
5369 can then use @var{str} directly as its internal representation.
5372 The size of a symbol can also be obtained from C:
5374 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5375 Return the number of characters in @var{sym}.
5378 Finally, some applications, especially those that generate new Scheme
5379 code dynamically, need to generate symbols for use in the generated
5380 code. The @code{gensym} primitive meets this need:
5382 @deffn {Scheme Procedure} gensym [prefix]
5383 @deffnx {C Function} scm_gensym (prefix)
5384 Create a new symbol with a name constructed from a prefix and a counter
5385 value. The string @var{prefix} can be specified as an optional
5386 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5387 at each call. There is no provision for resetting the counter.
5390 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5391 since their names begin with a space and it is only otherwise possible
5392 to generate such symbols if a programmer goes out of their way to do
5393 so. Uniqueness can be guaranteed by instead using uninterned symbols
5394 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5399 @subsubsection Function Slots and Property Lists
5401 In traditional Lisp dialects, symbols are often understood as having
5402 three kinds of value at once:
5406 a @dfn{variable} value, which is used when the symbol appears in
5407 code in a variable reference context
5410 a @dfn{function} value, which is used when the symbol appears in
5411 code in a function name position (i.e.@: as the first element in an
5415 a @dfn{property list} value, which is used when the symbol is given as
5416 the first argument to Lisp's @code{put} or @code{get} functions.
5419 Although Scheme (as one of its simplifications with respect to Lisp)
5420 does away with the distinction between variable and function namespaces,
5421 Guile currently retains some elements of the traditional structure in
5422 case they turn out to be useful when implementing translators for other
5423 languages, in particular Emacs Lisp.
5425 Specifically, Guile symbols have two extra slots, one for a symbol's
5426 property list, and one for its ``function value.'' The following procedures
5427 are provided to access these slots.
5429 @deffn {Scheme Procedure} symbol-fref symbol
5430 @deffnx {C Function} scm_symbol_fref (symbol)
5431 Return the contents of @var{symbol}'s @dfn{function slot}.
5434 @deffn {Scheme Procedure} symbol-fset! symbol value
5435 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5436 Set the contents of @var{symbol}'s function slot to @var{value}.
5439 @deffn {Scheme Procedure} symbol-pref symbol
5440 @deffnx {C Function} scm_symbol_pref (symbol)
5441 Return the @dfn{property list} currently associated with @var{symbol}.
5444 @deffn {Scheme Procedure} symbol-pset! symbol value
5445 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5446 Set @var{symbol}'s property list to @var{value}.
5449 @deffn {Scheme Procedure} symbol-property sym prop
5450 From @var{sym}'s property list, return the value for property
5451 @var{prop}. The assumption is that @var{sym}'s property list is an
5452 association list whose keys are distinguished from each other using
5453 @code{equal?}; @var{prop} should be one of the keys in that list. If
5454 the property list has no entry for @var{prop}, @code{symbol-property}
5458 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5459 In @var{sym}'s property list, set the value for property @var{prop} to
5460 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5461 none already exists. For the structure of the property list, see
5462 @code{symbol-property}.
5465 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5466 From @var{sym}'s property list, remove the entry for property
5467 @var{prop}, if there is one. For the structure of the property list,
5468 see @code{symbol-property}.
5471 Support for these extra slots may be removed in a future release, and it
5472 is probably better to avoid using them. For a more modern and Schemely
5473 approach to properties, see @ref{Object Properties}.
5476 @node Symbol Read Syntax
5477 @subsubsection Extended Read Syntax for Symbols
5479 The read syntax for a symbol is a sequence of letters, digits, and
5480 @dfn{extended alphabetic characters}, beginning with a character that
5481 cannot begin a number. In addition, the special cases of @code{+},
5482 @code{-}, and @code{...} are read as symbols even though numbers can
5483 begin with @code{+}, @code{-} or @code{.}.
5485 Extended alphabetic characters may be used within identifiers as if
5486 they were letters. The set of extended alphabetic characters is:
5489 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5492 In addition to the standard read syntax defined above (which is taken
5493 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5494 Scheme})), Guile provides an extended symbol read syntax that allows the
5495 inclusion of unusual characters such as space characters, newlines and
5496 parentheses. If (for whatever reason) you need to write a symbol
5497 containing characters not mentioned above, you can do so as follows.
5501 Begin the symbol with the characters @code{#@{},
5504 write the characters of the symbol and
5507 finish the symbol with the characters @code{@}#}.
5510 Here are a few examples of this form of read syntax. The first symbol
5511 needs to use extended syntax because it contains a space character, the
5512 second because it contains a line break, and the last because it looks
5524 Although Guile provides this extended read syntax for symbols,
5525 widespread usage of it is discouraged because it is not portable and not
5529 @node Symbol Uninterned
5530 @subsubsection Uninterned Symbols
5532 What makes symbols useful is that they are automatically kept unique.
5533 There are no two symbols that are distinct objects but have the same
5534 name. But of course, there is no rule without exception. In addition
5535 to the normal symbols that have been discussed up to now, you can also
5536 create special @dfn{uninterned} symbols that behave slightly
5539 To understand what is different about them and why they might be useful,
5540 we look at how normal symbols are actually kept unique.
5542 Whenever Guile wants to find the symbol with a specific name, for
5543 example during @code{read} or when executing @code{string->symbol}, it
5544 first looks into a table of all existing symbols to find out whether a
5545 symbol with the given name already exists. When this is the case, Guile
5546 just returns that symbol. When not, a new symbol with the name is
5547 created and entered into the table so that it can be found later.
5549 Sometimes you might want to create a symbol that is guaranteed `fresh',
5550 i.e.@: a symbol that did not exist previously. You might also want to
5551 somehow guarantee that no one else will ever unintentionally stumble
5552 across your symbol in the future. These properties of a symbol are
5553 often needed when generating code during macro expansion. When
5554 introducing new temporary variables, you want to guarantee that they
5555 don't conflict with variables in other people's code.
5557 The simplest way to arrange for this is to create a new symbol but
5558 not enter it into the global table of all symbols. That way, no one
5559 will ever get access to your symbol by chance. Symbols that are not in
5560 the table are called @dfn{uninterned}. Of course, symbols that
5561 @emph{are} in the table are called @dfn{interned}.
5563 You create new uninterned symbols with the function @code{make-symbol}.
5564 You can test whether a symbol is interned or not with
5565 @code{symbol-interned?}.
5567 Uninterned symbols break the rule that the name of a symbol uniquely
5568 identifies the symbol object. Because of this, they can not be written
5569 out and read back in like interned symbols. Currently, Guile has no
5570 support for reading uninterned symbols. Note that the function
5571 @code{gensym} does not return uninterned symbols for this reason.
5573 @deffn {Scheme Procedure} make-symbol name
5574 @deffnx {C Function} scm_make_symbol (name)
5575 Return a new uninterned symbol with the name @var{name}. The returned
5576 symbol is guaranteed to be unique and future calls to
5577 @code{string->symbol} will not return it.
5580 @deffn {Scheme Procedure} symbol-interned? symbol
5581 @deffnx {C Function} scm_symbol_interned_p (symbol)
5582 Return @code{#t} if @var{symbol} is interned, otherwise return
5589 (define foo-1 (string->symbol "foo"))
5590 (define foo-2 (string->symbol "foo"))
5591 (define foo-3 (make-symbol "foo"))
5592 (define foo-4 (make-symbol "foo"))
5596 ; Two interned symbols with the same name are the same object,
5600 ; but a call to make-symbol with the same name returns a
5605 ; A call to make-symbol always returns a new object, even for
5609 @result{} #<uninterned-symbol foo 8085290>
5610 ; Uninterned symbols print differently from interned symbols,
5614 ; but they are still symbols,
5616 (symbol-interned? foo-3)
5618 ; just not interned.
5623 @subsection Keywords
5626 Keywords are self-evaluating objects with a convenient read syntax that
5627 makes them easy to type.
5629 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5630 syntax extension to permit keywords to begin with @code{:} as well as
5631 @code{#:}, or to end with @code{:}.
5634 * Why Use Keywords?:: Motivation for keyword usage.
5635 * Coding With Keywords:: How to use keywords.
5636 * Keyword Read Syntax:: Read syntax for keywords.
5637 * Keyword Procedures:: Procedures for dealing with keywords.
5640 @node Why Use Keywords?
5641 @subsubsection Why Use Keywords?
5643 Keywords are useful in contexts where a program or procedure wants to be
5644 able to accept a large number of optional arguments without making its
5645 interface unmanageable.
5647 To illustrate this, consider a hypothetical @code{make-window}
5648 procedure, which creates a new window on the screen for drawing into
5649 using some graphical toolkit. There are many parameters that the caller
5650 might like to specify, but which could also be sensibly defaulted, for
5655 color depth -- Default: the color depth for the screen
5658 background color -- Default: white
5661 width -- Default: 600
5664 height -- Default: 400
5667 If @code{make-window} did not use keywords, the caller would have to
5668 pass in a value for each possible argument, remembering the correct
5669 argument order and using a special value to indicate the default value
5673 (make-window 'default ;; Color depth
5674 'default ;; Background color
5677 @dots{}) ;; More make-window arguments
5680 With keywords, on the other hand, defaulted arguments are omitted, and
5681 non-default arguments are clearly tagged by the appropriate keyword. As
5682 a result, the invocation becomes much clearer:
5685 (make-window #:width 800 #:height 100)
5688 On the other hand, for a simpler procedure with few arguments, the use
5689 of keywords would be a hindrance rather than a help. The primitive
5690 procedure @code{cons}, for example, would not be improved if it had to
5694 (cons #:car x #:cdr y)
5697 So the decision whether to use keywords or not is purely pragmatic: use
5698 them if they will clarify the procedure invocation at point of call.
5700 @node Coding With Keywords
5701 @subsubsection Coding With Keywords
5703 If a procedure wants to support keywords, it should take a rest argument
5704 and then use whatever means is convenient to extract keywords and their
5705 corresponding arguments from the contents of that rest argument.
5707 The following example illustrates the principle: the code for
5708 @code{make-window} uses a helper procedure called
5709 @code{get-keyword-value} to extract individual keyword arguments from
5713 (define (get-keyword-value args keyword default)
5714 (let ((kv (memq keyword args)))
5715 (if (and kv (>= (length kv) 2))
5719 (define (make-window . args)
5720 (let ((depth (get-keyword-value args #:depth screen-depth))
5721 (bg (get-keyword-value args #:bg "white"))
5722 (width (get-keyword-value args #:width 800))
5723 (height (get-keyword-value args #:height 100))
5728 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5729 optargs)} module provides a set of powerful macros that you can use to
5730 implement keyword-supporting procedures like this:
5733 (use-modules (ice-9 optargs))
5735 (define (make-window . args)
5736 (let-keywords args #f ((depth screen-depth)
5744 Or, even more economically, like this:
5747 (use-modules (ice-9 optargs))
5749 (define* (make-window #:key (depth screen-depth)
5756 For further details on @code{let-keywords}, @code{define*} and other
5757 facilities provided by the @code{(ice-9 optargs)} module, see
5758 @ref{Optional Arguments}.
5761 @node Keyword Read Syntax
5762 @subsubsection Keyword Read Syntax
5764 Guile, by default, only recognizes a keyword syntax that is compatible
5765 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5766 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5767 external representation of the keyword named @code{NAME}. Keyword
5768 objects print using this syntax as well, so values containing keyword
5769 objects can be read back into Guile. When used in an expression,
5770 keywords are self-quoting objects.
5772 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5773 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5774 of the form @code{:NAME} are read as symbols, as required by R5RS.
5776 @cindex SRFI-88 keyword syntax
5778 If the @code{keyword} read option is set to @code{'postfix}, Guile
5779 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5780 Otherwise, tokens of this form are read as symbols.
5782 To enable and disable the alternative non-R5RS keyword syntax, you use
5783 the @code{read-set!} procedure documented @ref{Scheme Read}. Note that
5784 the @code{prefix} and @code{postfix} syntax are mutually exclusive.
5787 (read-set! keywords 'prefix)
5797 (read-set! keywords 'postfix)
5807 (read-set! keywords #f)
5815 ERROR: In expression :type:
5816 ERROR: Unbound variable: :type
5817 ABORT: (unbound-variable)
5820 @node Keyword Procedures
5821 @subsubsection Keyword Procedures
5823 @deffn {Scheme Procedure} keyword? obj
5824 @deffnx {C Function} scm_keyword_p (obj)
5825 Return @code{#t} if the argument @var{obj} is a keyword, else
5829 @deffn {Scheme Procedure} keyword->symbol keyword
5830 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5831 Return the symbol with the same name as @var{keyword}.
5834 @deffn {Scheme Procedure} symbol->keyword symbol
5835 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5836 Return the keyword with the same name as @var{symbol}.
5839 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5840 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5843 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *name)
5844 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *name, size_t len)
5845 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5846 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5847 (@var{name}, @var{len}))}, respectively.
5849 Note that these functions should @emph{not} be used when @var{name} is a
5850 C string constant, because there is no guarantee that the current locale
5851 will match that of the source code. In such cases, use
5852 @code{scm_from_latin1_keyword} or @code{scm_from_utf8_keyword}.
5855 @deftypefn {C Function} SCM scm_from_latin1_keyword (const char *name)
5856 @deftypefnx {C Function} SCM scm_from_utf8_keyword (const char *name)
5857 Equivalent to @code{scm_symbol_to_keyword (scm_from_latin1_symbol
5858 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_utf8_symbol
5859 (@var{name}))}, respectively.
5863 @subsection ``Functionality-Centric'' Data Types
5865 Procedures and macros are documented in their own sections: see
5866 @ref{Procedures} and @ref{Macros}.
5868 Variable objects are documented as part of the description of Guile's
5869 module system: see @ref{Variables}.
5871 Asyncs, dynamic roots and fluids are described in the section on
5872 scheduling: see @ref{Scheduling}.
5874 Hooks are documented in the section on general utility functions: see
5877 Ports are described in the section on I/O: see @ref{Input and Output}.
5879 Regular expressions are described in their own section: see @ref{Regular
5883 @c TeX-master: "guile.texi"