2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007,
4 @c 2008, 2009, 2010, 2011, 2012, 2013, 2014 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.
59 They can also be written as @code{#true} and @code{#false}, as per R7RS.
61 Boolean values are returned by predicate procedures, such as the general
62 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
63 (@pxref{Equality}) and numerical and string comparison operators like
64 @code{string=?} (@pxref{String Comparison}) and @code{<=}
74 (equal? "house" "houses")
82 In test condition contexts like @code{if} and @code{cond}
83 (@pxref{Conditionals}), where a group of subexpressions will be
84 evaluated only if a @var{condition} expression evaluates to ``true'',
85 ``true'' means any value at all except @code{#f}.
98 A result of this asymmetry is that typical Scheme source code more often
99 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
100 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
101 not necessary to represent an @code{if} or @code{cond} true value.
103 It is important to note that @code{#f} is @strong{not} equivalent to any
104 other Scheme value. In particular, @code{#f} is not the same as the
105 number 0 (like in C and C++), and not the same as the ``empty list''
106 (like in some Lisp dialects).
108 In C, the two Scheme boolean values are available as the two constants
109 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
110 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
111 false when used in C conditionals. In order to test for it, use
112 @code{scm_is_false} or @code{scm_is_true}.
115 @deffn {Scheme Procedure} not x
116 @deffnx {C Function} scm_not (x)
117 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
121 @deffn {Scheme Procedure} boolean? obj
122 @deffnx {C Function} scm_boolean_p (obj)
123 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
127 @deftypevr {C Macro} SCM SCM_BOOL_T
128 The @code{SCM} representation of the Scheme object @code{#t}.
131 @deftypevr {C Macro} SCM SCM_BOOL_F
132 The @code{SCM} representation of the Scheme object @code{#f}.
135 @deftypefn {C Function} int scm_is_true (SCM obj)
136 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
139 @deftypefn {C Function} int scm_is_false (SCM obj)
140 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
143 @deftypefn {C Function} int scm_is_bool (SCM obj)
144 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
148 @deftypefn {C Function} SCM scm_from_bool (int val)
149 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
152 @deftypefn {C Function} int scm_to_bool (SCM val)
153 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
154 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
156 You should probably use @code{scm_is_true} instead of this function
157 when you just want to test a @code{SCM} value for trueness.
161 @subsection Numerical data types
164 Guile supports a rich ``tower'' of numerical types --- integer,
165 rational, real and complex --- and provides an extensive set of
166 mathematical and scientific functions for operating on numerical
167 data. This section of the manual documents those types and functions.
169 You may also find it illuminating to read R5RS's presentation of numbers
170 in Scheme, which is particularly clear and accessible: see
171 @ref{Numbers,,,r5rs,R5RS}.
174 * Numerical Tower:: Scheme's numerical "tower".
175 * Integers:: Whole numbers.
176 * Reals and Rationals:: Real and rational numbers.
177 * Complex Numbers:: Complex numbers.
178 * Exactness:: Exactness and inexactness.
179 * Number Syntax:: Read syntax for numerical data.
180 * Integer Operations:: Operations on integer values.
181 * Comparison:: Comparison predicates.
182 * Conversion:: Converting numbers to and from strings.
183 * Complex:: Complex number operations.
184 * Arithmetic:: Arithmetic functions.
185 * Scientific:: Scientific functions.
186 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
187 * Random:: Random number generation.
191 @node Numerical Tower
192 @subsubsection Scheme's Numerical ``Tower''
195 Scheme's numerical ``tower'' consists of the following categories of
200 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
203 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
204 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
205 pi (an irrational number) doesn't. These include integers
209 The set of numbers that describes all possible positions along a
210 one-dimensional line. This includes rationals as well as irrational
213 @item complex numbers
214 The set of numbers that describes all possible positions in a two
215 dimensional space. This includes real as well as imaginary numbers
216 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
217 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
221 It is called a tower because each category ``sits on'' the one that
222 follows it, in the sense that every integer is also a rational, every
223 rational is also real, and every real number is also a complex number
224 (but with zero imaginary part).
226 In addition to the classification into integers, rationals, reals and
227 complex numbers, Scheme also distinguishes between whether a number is
228 represented exactly or not. For example, the result of
229 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
230 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
231 Instead, it stores an inexact approximation, using the C type
234 Guile can represent exact rationals of any magnitude, inexact
235 rationals that fit into a C @code{double}, and inexact complex numbers
236 with @code{double} real and imaginary parts.
238 The @code{number?} predicate may be applied to any Scheme value to
239 discover whether the value is any of the supported numerical types.
241 @deffn {Scheme Procedure} number? obj
242 @deffnx {C Function} scm_number_p (obj)
243 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
252 (number? "hello there!")
255 (define pi 3.141592654)
260 @deftypefn {C Function} int scm_is_number (SCM obj)
261 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
264 The next few subsections document each of Guile's numerical data types
268 @subsubsection Integers
270 @tpindex Integer numbers
274 Integers are whole numbers, that is numbers with no fractional part,
275 such as 2, 83, and @minus{}3789.
277 Integers in Guile can be arbitrarily big, as shown by the following
281 (define (factorial n)
282 (let loop ((n n) (product 1))
285 (loop (- n 1) (* product n)))))
291 @result{} 2432902008176640000
294 @result{} -119622220865480194561963161495657715064383733760000000000
297 Readers whose background is in programming languages where integers are
298 limited by the need to fit into just 4 or 8 bytes of memory may find
299 this surprising, or suspect that Guile's representation of integers is
300 inefficient. In fact, Guile achieves a near optimal balance of
301 convenience and efficiency by using the host computer's native
302 representation of integers where possible, and a more general
303 representation where the required number does not fit in the native
304 form. Conversion between these two representations is automatic and
305 completely invisible to the Scheme level programmer.
307 C has a host of different integer types, and Guile offers a host of
308 functions to convert between them and the @code{SCM} representation.
309 For example, a C @code{int} can be handled with @code{scm_to_int} and
310 @code{scm_from_int}. Guile also defines a few C integer types of its
311 own, to help with differences between systems.
313 C integer types that are not covered can be handled with the generic
314 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
315 signed types, or with @code{scm_to_unsigned_integer} and
316 @code{scm_from_unsigned_integer} for unsigned types.
318 Scheme integers can be exact and inexact. For example, a number
319 written as @code{3.0} with an explicit decimal-point is inexact, but
320 it is also an integer. The functions @code{integer?} and
321 @code{scm_is_integer} report true for such a number, but the functions
322 @code{exact-integer?}, @code{scm_is_exact_integer},
323 @code{scm_is_signed_integer}, and @code{scm_is_unsigned_integer} only
324 allow exact integers and thus report false. Likewise, the conversion
325 functions like @code{scm_to_signed_integer} only accept exact
328 The motivation for this behavior is that the inexactness of a number
329 should not be lost silently. If you want to allow inexact integers,
330 you can explicitly insert a call to @code{inexact->exact} or to its C
331 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
332 be converted by this call into exact integers; inexact non-integers
333 will become exact fractions.)
335 @deffn {Scheme Procedure} integer? x
336 @deffnx {C Function} scm_integer_p (x)
337 Return @code{#t} if @var{x} is an exact or inexact integer number, else
355 @deftypefn {C Function} int scm_is_integer (SCM x)
356 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
359 @deffn {Scheme Procedure} exact-integer? x
360 @deffnx {C Function} scm_exact_integer_p (x)
361 Return @code{#t} if @var{x} is an exact integer number, else
373 @deftypefn {C Function} int scm_is_exact_integer (SCM x)
374 This is equivalent to @code{scm_is_true (scm_exact_integer_p (x))}.
377 @defvr {C Type} scm_t_int8
378 @defvrx {C Type} scm_t_uint8
379 @defvrx {C Type} scm_t_int16
380 @defvrx {C Type} scm_t_uint16
381 @defvrx {C Type} scm_t_int32
382 @defvrx {C Type} scm_t_uint32
383 @defvrx {C Type} scm_t_int64
384 @defvrx {C Type} scm_t_uint64
385 @defvrx {C Type} scm_t_intmax
386 @defvrx {C Type} scm_t_uintmax
387 The C types are equivalent to the corresponding ISO C types but are
388 defined on all platforms, with the exception of @code{scm_t_int64} and
389 @code{scm_t_uint64}, which are only defined when a 64-bit type is
390 available. For example, @code{scm_t_int8} is equivalent to
393 You can regard these definitions as a stop-gap measure until all
394 platforms provide these types. If you know that all the platforms
395 that you are interested in already provide these types, it is better
396 to use them directly instead of the types provided by Guile.
399 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
400 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
401 Return @code{1} when @var{x} represents an exact integer that is
402 between @var{min} and @var{max}, inclusive.
404 These functions can be used to check whether a @code{SCM} value will
405 fit into a given range, such as the range of a given C integer type.
406 If you just want to convert a @code{SCM} value to a given C integer
407 type, use one of the conversion functions directly.
410 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
411 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
412 When @var{x} represents an exact integer that is between @var{min} and
413 @var{max} inclusive, return that integer. Else signal an error,
414 either a `wrong-type' error when @var{x} is not an exact integer, or
415 an `out-of-range' error when it doesn't fit the given range.
418 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
419 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
420 Return the @code{SCM} value that represents the integer @var{x}. This
421 function will always succeed and will always return an exact number.
424 @deftypefn {C Function} char scm_to_char (SCM x)
425 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
426 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
427 @deftypefnx {C Function} short scm_to_short (SCM x)
428 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
429 @deftypefnx {C Function} int scm_to_int (SCM x)
430 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
431 @deftypefnx {C Function} long scm_to_long (SCM x)
432 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
433 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
434 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
435 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
436 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
437 @deftypefnx {C Function} scm_t_ptrdiff scm_to_ptrdiff_t (SCM x)
438 @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x)
439 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
440 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
441 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
442 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
443 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
444 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
445 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
446 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
447 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
448 When @var{x} represents an exact integer that fits into the indicated
449 C type, return that integer. Else signal an error, either a
450 `wrong-type' error when @var{x} is not an exact integer, or an
451 `out-of-range' error when it doesn't fit the given range.
453 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
454 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
455 the corresponding types are.
458 @deftypefn {C Function} SCM scm_from_char (char x)
459 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
460 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
461 @deftypefnx {C Function} SCM scm_from_short (short x)
462 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
463 @deftypefnx {C Function} SCM scm_from_int (int x)
464 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
465 @deftypefnx {C Function} SCM scm_from_long (long x)
466 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
467 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
468 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
469 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
470 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
471 @deftypefnx {C Function} SCM scm_from_ptrdiff_t (scm_t_ptrdiff x)
472 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
473 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
474 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
475 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
476 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
477 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
478 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
479 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
480 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
481 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
482 Return the @code{SCM} value that represents the integer @var{x}.
483 These functions will always succeed and will always return an exact
487 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
488 Assign @var{val} to the multiple precision integer @var{rop}.
489 @var{val} must be an exact integer, otherwise an error will be
490 signalled. @var{rop} must have been initialized with @code{mpz_init}
491 before this function is called. When @var{rop} is no longer needed
492 the occupied space must be freed with @code{mpz_clear}.
493 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
496 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
497 Return the @code{SCM} value that represents @var{val}.
500 @node Reals and Rationals
501 @subsubsection Real and Rational Numbers
502 @tpindex Real numbers
503 @tpindex Rational numbers
508 Mathematically, the real numbers are the set of numbers that describe
509 all possible points along a continuous, infinite, one-dimensional line.
510 The rational numbers are the set of all numbers that can be written as
511 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
512 All rational numbers are also real, but there are real numbers that
513 are not rational, for example @m{\sqrt{2}, the square root of 2}, and
516 Guile can represent both exact and inexact rational numbers, but it
517 cannot represent precise finite irrational numbers. Exact rationals are
518 represented by storing the numerator and denominator as two exact
519 integers. Inexact rationals are stored as floating point numbers using
520 the C type @code{double}.
522 Exact rationals are written as a fraction of integers. There must be
523 no whitespace around the slash:
530 Even though the actual encoding of inexact rationals is in binary, it
531 may be helpful to think of it as a decimal number with a limited
532 number of significant figures and a decimal point somewhere, since
533 this corresponds to the standard notation for non-whole numbers. For
539 -5648394822220000000000.0
543 The limited precision of Guile's encoding means that any finite ``real''
544 number in Guile can be written in a rational form, by multiplying and
545 then dividing by sufficient powers of 10 (or in fact, 2). For example,
546 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided
547 by 100000000000000000. In Guile's current incarnation, therefore, the
548 @code{rational?} and @code{real?} predicates are equivalent for finite
552 Dividing by an exact zero leads to a error message, as one might expect.
553 However, dividing by an inexact zero does not produce an error.
554 Instead, the result of the division is either plus or minus infinity,
555 depending on the sign of the divided number and the sign of the zero
556 divisor (some platforms support signed zeroes @samp{-0.0} and
557 @samp{+0.0}; @samp{0.0} is the same as @samp{+0.0}).
559 Dividing zero by an inexact zero yields a @acronym{NaN} (`not a number')
560 value, although they are actually considered numbers by Scheme.
561 Attempts to compare a @acronym{NaN} value with any number (including
562 itself) using @code{=}, @code{<}, @code{>}, @code{<=} or @code{>=}
563 always returns @code{#f}. Although a @acronym{NaN} value is not
564 @code{=} to itself, it is both @code{eqv?} and @code{equal?} to itself
565 and other @acronym{NaN} values. However, the preferred way to test for
566 them is by using @code{nan?}.
568 The real @acronym{NaN} values and infinities are written @samp{+nan.0},
569 @samp{+inf.0} and @samp{-inf.0}. This syntax is also recognized by
570 @code{read} as an extension to the usual Scheme syntax. These special
571 values are considered by Scheme to be inexact real numbers but not
572 rational. Note that non-real complex numbers may also contain
573 infinities or @acronym{NaN} values in their real or imaginary parts. To
574 test a real number to see if it is infinite, a @acronym{NaN} value, or
575 neither, use @code{inf?}, @code{nan?}, or @code{finite?}, respectively.
576 Every real number in Scheme belongs to precisely one of those three
579 On platforms that follow @acronym{IEEE} 754 for their floating point
580 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
581 are implemented using the corresponding @acronym{IEEE} 754 values.
582 They behave in arithmetic operations like @acronym{IEEE} 754 describes
583 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
585 @deffn {Scheme Procedure} real? obj
586 @deffnx {C Function} scm_real_p (obj)
587 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
588 that the sets of integer and rational values form subsets of the set
589 of real numbers, so the predicate will also be fulfilled if @var{obj}
590 is an integer number or a rational number.
593 @deffn {Scheme Procedure} rational? x
594 @deffnx {C Function} scm_rational_p (x)
595 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
596 Note that the set of integer values forms a subset of the set of
597 rational numbers, i.e.@: the predicate will also be fulfilled if
598 @var{x} is an integer number.
601 @deffn {Scheme Procedure} rationalize x eps
602 @deffnx {C Function} scm_rationalize (x, eps)
603 Returns the @emph{simplest} rational number differing
604 from @var{x} by no more than @var{eps}.
606 As required by @acronym{R5RS}, @code{rationalize} only returns an
607 exact result when both its arguments are exact. Thus, you might need
608 to use @code{inexact->exact} on the arguments.
611 (rationalize (inexact->exact 1.2) 1/100)
617 @deffn {Scheme Procedure} inf? x
618 @deffnx {C Function} scm_inf_p (x)
619 Return @code{#t} if the real number @var{x} is @samp{+inf.0} or
620 @samp{-inf.0}. Otherwise return @code{#f}.
623 @deffn {Scheme Procedure} nan? x
624 @deffnx {C Function} scm_nan_p (x)
625 Return @code{#t} if the real number @var{x} is @samp{+nan.0}, or
629 @deffn {Scheme Procedure} finite? x
630 @deffnx {C Function} scm_finite_p (x)
631 Return @code{#t} if the real number @var{x} is neither infinite nor a
632 NaN, @code{#f} otherwise.
635 @deffn {Scheme Procedure} nan
636 @deffnx {C Function} scm_nan ()
637 Return @samp{+nan.0}, a @acronym{NaN} value.
640 @deffn {Scheme Procedure} inf
641 @deffnx {C Function} scm_inf ()
642 Return @samp{+inf.0}, positive infinity.
645 @deffn {Scheme Procedure} numerator x
646 @deffnx {C Function} scm_numerator (x)
647 Return the numerator of the rational number @var{x}.
650 @deffn {Scheme Procedure} denominator x
651 @deffnx {C Function} scm_denominator (x)
652 Return the denominator of the rational number @var{x}.
655 @deftypefn {C Function} int scm_is_real (SCM val)
656 @deftypefnx {C Function} int scm_is_rational (SCM val)
657 Equivalent to @code{scm_is_true (scm_real_p (val))} and
658 @code{scm_is_true (scm_rational_p (val))}, respectively.
661 @deftypefn {C Function} double scm_to_double (SCM val)
662 Returns the number closest to @var{val} that is representable as a
663 @code{double}. Returns infinity for a @var{val} that is too large in
664 magnitude. The argument @var{val} must be a real number.
667 @deftypefn {C Function} SCM scm_from_double (double val)
668 Return the @code{SCM} value that represents @var{val}. The returned
669 value is inexact according to the predicate @code{inexact?}, but it
670 will be exactly equal to @var{val}.
673 @node Complex Numbers
674 @subsubsection Complex Numbers
675 @tpindex Complex numbers
679 Complex numbers are the set of numbers that describe all possible points
680 in a two-dimensional space. The two coordinates of a particular point
681 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
682 the complex number that describes that point.
684 In Guile, complex numbers are written in rectangular form as the sum of
685 their real and imaginary parts, using the symbol @code{i} to indicate
700 Polar form can also be used, with an @samp{@@} between magnitude and
704 1@@3.141592 @result{} -1.0 (approx)
705 -1@@1.57079 @result{} 0.0-1.0i (approx)
708 Guile represents a complex number as a pair of inexact reals, so the
709 real and imaginary parts of a complex number have the same properties of
710 inexactness and limited precision as single inexact real numbers.
712 Note that each part of a complex number may contain any inexact real
713 value, including the special values @samp{+nan.0}, @samp{+inf.0} and
714 @samp{-inf.0}, as well as either of the signed zeroes @samp{0.0} or
718 @deffn {Scheme Procedure} complex? z
719 @deffnx {C Function} scm_complex_p (z)
720 Return @code{#t} if @var{z} is a complex number, @code{#f}
721 otherwise. Note that the sets of real, rational and integer
722 values form subsets of the set of complex numbers, i.e.@: the
723 predicate will also be fulfilled if @var{z} is a real,
724 rational or integer number.
727 @deftypefn {C Function} int scm_is_complex (SCM val)
728 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
732 @subsubsection Exact and Inexact Numbers
733 @tpindex Exact numbers
734 @tpindex Inexact numbers
738 @rnindex exact->inexact
739 @rnindex inexact->exact
741 R5RS requires that, with few exceptions, a calculation involving inexact
742 numbers always produces an inexact result. To meet this requirement,
743 Guile distinguishes between an exact integer value such as @samp{5} and
744 the corresponding inexact integer value which, to the limited precision
745 available, has no fractional part, and is printed as @samp{5.0}. Guile
746 will only convert the latter value to the former when forced to do so by
747 an invocation of the @code{inexact->exact} procedure.
749 The only exception to the above requirement is when the values of the
750 inexact numbers do not affect the result. For example @code{(expt n 0)}
751 is @samp{1} for any value of @code{n}, therefore @code{(expt 5.0 0)} is
752 permitted to return an exact @samp{1}.
754 @deffn {Scheme Procedure} exact? z
755 @deffnx {C Function} scm_exact_p (z)
756 Return @code{#t} if the number @var{z} is exact, @code{#f}
772 @deftypefn {C Function} int scm_is_exact (SCM z)
773 Return a @code{1} if the number @var{z} is exact, and @code{0}
774 otherwise. This is equivalent to @code{scm_is_true (scm_exact_p (z))}.
776 An alternate approch to testing the exactness of a number is to
777 use @code{scm_is_signed_integer} or @code{scm_is_unsigned_integer}.
780 @deffn {Scheme Procedure} inexact? z
781 @deffnx {C Function} scm_inexact_p (z)
782 Return @code{#t} if the number @var{z} is inexact, @code{#f}
786 @deftypefn {C Function} int scm_is_inexact (SCM z)
787 Return a @code{1} if the number @var{z} is inexact, and @code{0}
788 otherwise. This is equivalent to @code{scm_is_true (scm_inexact_p (z))}.
791 @deffn {Scheme Procedure} inexact->exact z
792 @deffnx {C Function} scm_inexact_to_exact (z)
793 Return an exact number that is numerically closest to @var{z}, when
794 there is one. For inexact rationals, Guile returns the exact rational
795 that is numerically equal to the inexact rational. Inexact complex
796 numbers with a non-zero imaginary part can not be made exact.
803 The following happens because 12/10 is not exactly representable as a
804 @code{double} (on most platforms). However, when reading a decimal
805 number that has been marked exact with the ``#e'' prefix, Guile is
806 able to represent it correctly.
810 @result{} 5404319552844595/4503599627370496
818 @c begin (texi-doc-string "guile" "exact->inexact")
819 @deffn {Scheme Procedure} exact->inexact z
820 @deffnx {C Function} scm_exact_to_inexact (z)
821 Convert the number @var{z} to its inexact representation.
826 @subsubsection Read Syntax for Numerical Data
828 The read syntax for integers is a string of digits, optionally
829 preceded by a minus or plus character, a code indicating the
830 base in which the integer is encoded, and a code indicating whether
831 the number is exact or inexact. The supported base codes are:
836 the integer is written in binary (base 2)
840 the integer is written in octal (base 8)
844 the integer is written in decimal (base 10)
848 the integer is written in hexadecimal (base 16)
851 If the base code is omitted, the integer is assumed to be decimal. The
852 following examples show how these base codes are used.
871 The codes for indicating exactness (which can, incidentally, be applied
872 to all numerical values) are:
881 the number is inexact.
884 If the exactness indicator is omitted, the number is exact unless it
885 contains a radix point. Since Guile can not represent exact complex
886 numbers, an error is signalled when asking for them.
896 ERROR: Wrong type argument
899 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
900 plus and minus infinity, respectively. The value must be written
901 exactly as shown, that is, they always must have a sign and exactly
902 one zero digit after the decimal point. It also understands
903 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
904 The sign is ignored for `not-a-number' and the value is always printed
907 @node Integer Operations
908 @subsubsection Operations on Integer Values
917 @deffn {Scheme Procedure} odd? n
918 @deffnx {C Function} scm_odd_p (n)
919 Return @code{#t} if @var{n} is an odd number, @code{#f}
923 @deffn {Scheme Procedure} even? n
924 @deffnx {C Function} scm_even_p (n)
925 Return @code{#t} if @var{n} is an even number, @code{#f}
929 @c begin (texi-doc-string "guile" "quotient")
930 @c begin (texi-doc-string "guile" "remainder")
931 @deffn {Scheme Procedure} quotient n d
932 @deffnx {Scheme Procedure} remainder n d
933 @deffnx {C Function} scm_quotient (n, d)
934 @deffnx {C Function} scm_remainder (n, d)
935 Return the quotient or remainder from @var{n} divided by @var{d}. The
936 quotient is rounded towards zero, and the remainder will have the same
937 sign as @var{n}. In all cases quotient and remainder satisfy
938 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
941 (remainder 13 4) @result{} 1
942 (remainder -13 4) @result{} -1
945 See also @code{truncate-quotient}, @code{truncate-remainder} and
946 related operations in @ref{Arithmetic}.
949 @c begin (texi-doc-string "guile" "modulo")
950 @deffn {Scheme Procedure} modulo n d
951 @deffnx {C Function} scm_modulo (n, d)
952 Return the remainder from @var{n} divided by @var{d}, with the same
956 (modulo 13 4) @result{} 1
957 (modulo -13 4) @result{} 3
958 (modulo 13 -4) @result{} -3
959 (modulo -13 -4) @result{} -1
962 See also @code{floor-quotient}, @code{floor-remainder} and
963 related operations in @ref{Arithmetic}.
966 @c begin (texi-doc-string "guile" "gcd")
967 @deffn {Scheme Procedure} gcd x@dots{}
968 @deffnx {C Function} scm_gcd (x, y)
969 Return the greatest common divisor of all arguments.
970 If called without arguments, 0 is returned.
972 The C function @code{scm_gcd} always takes two arguments, while the
973 Scheme function can take an arbitrary number.
976 @c begin (texi-doc-string "guile" "lcm")
977 @deffn {Scheme Procedure} lcm x@dots{}
978 @deffnx {C Function} scm_lcm (x, y)
979 Return the least common multiple of the arguments.
980 If called without arguments, 1 is returned.
982 The C function @code{scm_lcm} always takes two arguments, while the
983 Scheme function can take an arbitrary number.
986 @deffn {Scheme Procedure} modulo-expt n k m
987 @deffnx {C Function} scm_modulo_expt (n, k, m)
988 Return @var{n} raised to the integer exponent
989 @var{k}, modulo @var{m}.
997 @deftypefn {Scheme Procedure} {} exact-integer-sqrt @var{k}
998 @deftypefnx {C Function} void scm_exact_integer_sqrt (SCM @var{k}, SCM *@var{s}, SCM *@var{r})
999 Return two exact non-negative integers @var{s} and @var{r}
1000 such that @math{@var{k} = @var{s}^2 + @var{r}} and
1001 @math{@var{s}^2 <= @var{k} < (@var{s} + 1)^2}.
1002 An error is raised if @var{k} is not an exact non-negative integer.
1005 (exact-integer-sqrt 10) @result{} 3 and 1
1010 @subsubsection Comparison Predicates
1015 The C comparison functions below always takes two arguments, while the
1016 Scheme functions can take an arbitrary number. Also keep in mind that
1017 the C functions return one of the Scheme boolean values
1018 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
1019 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
1020 y))} when testing the two Scheme numbers @code{x} and @code{y} for
1021 equality, for example.
1023 @c begin (texi-doc-string "guile" "=")
1024 @deffn {Scheme Procedure} =
1025 @deffnx {C Function} scm_num_eq_p (x, y)
1026 Return @code{#t} if all parameters are numerically equal.
1029 @c begin (texi-doc-string "guile" "<")
1030 @deffn {Scheme Procedure} <
1031 @deffnx {C Function} scm_less_p (x, y)
1032 Return @code{#t} if the list of parameters is monotonically
1036 @c begin (texi-doc-string "guile" ">")
1037 @deffn {Scheme Procedure} >
1038 @deffnx {C Function} scm_gr_p (x, y)
1039 Return @code{#t} if the list of parameters is monotonically
1043 @c begin (texi-doc-string "guile" "<=")
1044 @deffn {Scheme Procedure} <=
1045 @deffnx {C Function} scm_leq_p (x, y)
1046 Return @code{#t} if the list of parameters is monotonically
1050 @c begin (texi-doc-string "guile" ">=")
1051 @deffn {Scheme Procedure} >=
1052 @deffnx {C Function} scm_geq_p (x, y)
1053 Return @code{#t} if the list of parameters is monotonically
1057 @c begin (texi-doc-string "guile" "zero?")
1058 @deffn {Scheme Procedure} zero? z
1059 @deffnx {C Function} scm_zero_p (z)
1060 Return @code{#t} if @var{z} is an exact or inexact number equal to
1064 @c begin (texi-doc-string "guile" "positive?")
1065 @deffn {Scheme Procedure} positive? x
1066 @deffnx {C Function} scm_positive_p (x)
1067 Return @code{#t} if @var{x} is an exact or inexact number greater than
1071 @c begin (texi-doc-string "guile" "negative?")
1072 @deffn {Scheme Procedure} negative? x
1073 @deffnx {C Function} scm_negative_p (x)
1074 Return @code{#t} if @var{x} is an exact or inexact number less than
1080 @subsubsection Converting Numbers To and From Strings
1081 @rnindex number->string
1082 @rnindex string->number
1084 The following procedures read and write numbers according to their
1085 external representation as defined by R5RS (@pxref{Lexical structure,
1086 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1087 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1088 i18n)} module}, for locale-dependent number parsing.
1090 @deffn {Scheme Procedure} number->string n [radix]
1091 @deffnx {C Function} scm_number_to_string (n, radix)
1092 Return a string holding the external representation of the
1093 number @var{n} in the given @var{radix}. If @var{n} is
1094 inexact, a radix of 10 will be used.
1097 @deffn {Scheme Procedure} string->number string [radix]
1098 @deffnx {C Function} scm_string_to_number (string, radix)
1099 Return a number of the maximally precise representation
1100 expressed by the given @var{string}. @var{radix} must be an
1101 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1102 is a default radix that may be overridden by an explicit radix
1103 prefix in @var{string} (e.g.@: "#o177"). If @var{radix} is not
1104 supplied, then the default radix is 10. If string is not a
1105 syntactically valid notation for a number, then
1106 @code{string->number} returns @code{#f}.
1109 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1110 As per @code{string->number} above, but taking a C string, as pointer
1111 and length. The string characters should be in the current locale
1112 encoding (@code{locale} in the name refers only to that, there's no
1113 locale-dependent parsing).
1118 @subsubsection Complex Number Operations
1119 @rnindex make-rectangular
1126 @deffn {Scheme Procedure} make-rectangular real_part imaginary_part
1127 @deffnx {C Function} scm_make_rectangular (real_part, imaginary_part)
1128 Return a complex number constructed of the given @var{real-part} and @var{imaginary-part} parts.
1131 @deffn {Scheme Procedure} make-polar mag ang
1132 @deffnx {C Function} scm_make_polar (mag, ang)
1134 Return the complex number @var{mag} * e^(i * @var{ang}).
1137 @c begin (texi-doc-string "guile" "real-part")
1138 @deffn {Scheme Procedure} real-part z
1139 @deffnx {C Function} scm_real_part (z)
1140 Return the real part of the number @var{z}.
1143 @c begin (texi-doc-string "guile" "imag-part")
1144 @deffn {Scheme Procedure} imag-part z
1145 @deffnx {C Function} scm_imag_part (z)
1146 Return the imaginary part of the number @var{z}.
1149 @c begin (texi-doc-string "guile" "magnitude")
1150 @deffn {Scheme Procedure} magnitude z
1151 @deffnx {C Function} scm_magnitude (z)
1152 Return the magnitude of the number @var{z}. This is the same as
1153 @code{abs} for real arguments, but also allows complex numbers.
1156 @c begin (texi-doc-string "guile" "angle")
1157 @deffn {Scheme Procedure} angle z
1158 @deffnx {C Function} scm_angle (z)
1159 Return the angle of the complex number @var{z}.
1162 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1163 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1164 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1165 respectively, but these functions take @code{double}s as their
1169 @deftypefn {C Function} double scm_c_real_part (z)
1170 @deftypefnx {C Function} double scm_c_imag_part (z)
1171 Returns the real or imaginary part of @var{z} as a @code{double}.
1174 @deftypefn {C Function} double scm_c_magnitude (z)
1175 @deftypefnx {C Function} double scm_c_angle (z)
1176 Returns the magnitude or angle of @var{z} as a @code{double}.
1181 @subsubsection Arithmetic Functions
1196 @rnindex euclidean-quotient
1197 @rnindex euclidean-remainder
1199 @rnindex floor-quotient
1200 @rnindex floor-remainder
1202 @rnindex ceiling-quotient
1203 @rnindex ceiling-remainder
1205 @rnindex truncate-quotient
1206 @rnindex truncate-remainder
1208 @rnindex centered-quotient
1209 @rnindex centered-remainder
1211 @rnindex round-quotient
1212 @rnindex round-remainder
1214 The C arithmetic functions below always takes two arguments, while the
1215 Scheme functions can take an arbitrary number. When you need to
1216 invoke them with just one argument, for example to compute the
1217 equivalent of @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1218 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1220 @c begin (texi-doc-string "guile" "+")
1221 @deffn {Scheme Procedure} + z1 @dots{}
1222 @deffnx {C Function} scm_sum (z1, z2)
1223 Return the sum of all parameter values. Return 0 if called without any
1227 @c begin (texi-doc-string "guile" "-")
1228 @deffn {Scheme Procedure} - z1 z2 @dots{}
1229 @deffnx {C Function} scm_difference (z1, z2)
1230 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1231 the sum of all but the first argument are subtracted from the first
1235 @c begin (texi-doc-string "guile" "*")
1236 @deffn {Scheme Procedure} * z1 @dots{}
1237 @deffnx {C Function} scm_product (z1, z2)
1238 Return the product of all arguments. If called without arguments, 1 is
1242 @c begin (texi-doc-string "guile" "/")
1243 @deffn {Scheme Procedure} / z1 z2 @dots{}
1244 @deffnx {C Function} scm_divide (z1, z2)
1245 Divide the first argument by the product of the remaining arguments. If
1246 called with one argument @var{z1}, 1/@var{z1} is returned.
1249 @deffn {Scheme Procedure} 1+ z
1250 @deffnx {C Function} scm_oneplus (z)
1251 Return @math{@var{z} + 1}.
1254 @deffn {Scheme Procedure} 1- z
1255 @deffnx {C function} scm_oneminus (z)
1256 Return @math{@var{z} - 1}.
1259 @c begin (texi-doc-string "guile" "abs")
1260 @deffn {Scheme Procedure} abs x
1261 @deffnx {C Function} scm_abs (x)
1262 Return the absolute value of @var{x}.
1264 @var{x} must be a number with zero imaginary part. To calculate the
1265 magnitude of a complex number, use @code{magnitude} instead.
1268 @c begin (texi-doc-string "guile" "max")
1269 @deffn {Scheme Procedure} max x1 x2 @dots{}
1270 @deffnx {C Function} scm_max (x1, x2)
1271 Return the maximum of all parameter values.
1274 @c begin (texi-doc-string "guile" "min")
1275 @deffn {Scheme Procedure} min x1 x2 @dots{}
1276 @deffnx {C Function} scm_min (x1, x2)
1277 Return the minimum of all parameter values.
1280 @c begin (texi-doc-string "guile" "truncate")
1281 @deffn {Scheme Procedure} truncate x
1282 @deffnx {C Function} scm_truncate_number (x)
1283 Round the inexact number @var{x} towards zero.
1286 @c begin (texi-doc-string "guile" "round")
1287 @deffn {Scheme Procedure} round x
1288 @deffnx {C Function} scm_round_number (x)
1289 Round the inexact number @var{x} to the nearest integer. When exactly
1290 halfway between two integers, round to the even one.
1293 @c begin (texi-doc-string "guile" "floor")
1294 @deffn {Scheme Procedure} floor x
1295 @deffnx {C Function} scm_floor (x)
1296 Round the number @var{x} towards minus infinity.
1299 @c begin (texi-doc-string "guile" "ceiling")
1300 @deffn {Scheme Procedure} ceiling x
1301 @deffnx {C Function} scm_ceiling (x)
1302 Round the number @var{x} towards infinity.
1305 @deftypefn {C Function} double scm_c_truncate (double x)
1306 @deftypefnx {C Function} double scm_c_round (double x)
1307 Like @code{scm_truncate_number} or @code{scm_round_number},
1308 respectively, but these functions take and return @code{double}
1312 @deftypefn {Scheme Procedure} {} euclidean/ @var{x} @var{y}
1313 @deftypefnx {Scheme Procedure} {} euclidean-quotient @var{x} @var{y}
1314 @deftypefnx {Scheme Procedure} {} euclidean-remainder @var{x} @var{y}
1315 @deftypefnx {C Function} void scm_euclidean_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1316 @deftypefnx {C Function} SCM scm_euclidean_quotient (SCM @var{x}, SCM @var{y})
1317 @deftypefnx {C Function} SCM scm_euclidean_remainder (SCM @var{x}, SCM @var{y})
1318 These procedures accept two real numbers @var{x} and @var{y}, where the
1319 divisor @var{y} must be non-zero. @code{euclidean-quotient} returns the
1320 integer @var{q} and @code{euclidean-remainder} returns the real number
1321 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1322 @math{0 <= @var{r} < |@var{y}|}. @code{euclidean/} returns both @var{q} and
1323 @var{r}, and is more efficient than computing each separately. Note
1324 that when @math{@var{y} > 0}, @code{euclidean-quotient} returns
1325 @math{floor(@var{x}/@var{y})}, otherwise it returns
1326 @math{ceiling(@var{x}/@var{y})}.
1328 Note that these operators are equivalent to the R6RS operators
1329 @code{div}, @code{mod}, and @code{div-and-mod}.
1332 (euclidean-quotient 123 10) @result{} 12
1333 (euclidean-remainder 123 10) @result{} 3
1334 (euclidean/ 123 10) @result{} 12 and 3
1335 (euclidean/ 123 -10) @result{} -12 and 3
1336 (euclidean/ -123 10) @result{} -13 and 7
1337 (euclidean/ -123 -10) @result{} 13 and 7
1338 (euclidean/ -123.2 -63.5) @result{} 2.0 and 3.8
1339 (euclidean/ 16/3 -10/7) @result{} -3 and 22/21
1343 @deftypefn {Scheme Procedure} {} floor/ @var{x} @var{y}
1344 @deftypefnx {Scheme Procedure} {} floor-quotient @var{x} @var{y}
1345 @deftypefnx {Scheme Procedure} {} floor-remainder @var{x} @var{y}
1346 @deftypefnx {C Function} void scm_floor_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1347 @deftypefnx {C Function} SCM scm_floor_quotient (@var{x}, @var{y})
1348 @deftypefnx {C Function} SCM scm_floor_remainder (@var{x}, @var{y})
1349 These procedures accept two real numbers @var{x} and @var{y}, where the
1350 divisor @var{y} must be non-zero. @code{floor-quotient} returns the
1351 integer @var{q} and @code{floor-remainder} returns the real number
1352 @var{r} such that @math{@var{q} = floor(@var{x}/@var{y})} and
1353 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{floor/} returns
1354 both @var{q} and @var{r}, and is more efficient than computing each
1355 separately. Note that @var{r}, if non-zero, will have the same sign
1358 When @var{x} and @var{y} are integers, @code{floor-remainder} is
1359 equivalent to the R5RS integer-only operator @code{modulo}.
1362 (floor-quotient 123 10) @result{} 12
1363 (floor-remainder 123 10) @result{} 3
1364 (floor/ 123 10) @result{} 12 and 3
1365 (floor/ 123 -10) @result{} -13 and -7
1366 (floor/ -123 10) @result{} -13 and 7
1367 (floor/ -123 -10) @result{} 12 and -3
1368 (floor/ -123.2 -63.5) @result{} 1.0 and -59.7
1369 (floor/ 16/3 -10/7) @result{} -4 and -8/21
1373 @deftypefn {Scheme Procedure} {} ceiling/ @var{x} @var{y}
1374 @deftypefnx {Scheme Procedure} {} ceiling-quotient @var{x} @var{y}
1375 @deftypefnx {Scheme Procedure} {} ceiling-remainder @var{x} @var{y}
1376 @deftypefnx {C Function} void scm_ceiling_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1377 @deftypefnx {C Function} SCM scm_ceiling_quotient (@var{x}, @var{y})
1378 @deftypefnx {C Function} SCM scm_ceiling_remainder (@var{x}, @var{y})
1379 These procedures accept two real numbers @var{x} and @var{y}, where the
1380 divisor @var{y} must be non-zero. @code{ceiling-quotient} returns the
1381 integer @var{q} and @code{ceiling-remainder} returns the real number
1382 @var{r} such that @math{@var{q} = ceiling(@var{x}/@var{y})} and
1383 @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{ceiling/} returns
1384 both @var{q} and @var{r}, and is more efficient than computing each
1385 separately. Note that @var{r}, if non-zero, will have the opposite sign
1389 (ceiling-quotient 123 10) @result{} 13
1390 (ceiling-remainder 123 10) @result{} -7
1391 (ceiling/ 123 10) @result{} 13 and -7
1392 (ceiling/ 123 -10) @result{} -12 and 3
1393 (ceiling/ -123 10) @result{} -12 and -3
1394 (ceiling/ -123 -10) @result{} 13 and 7
1395 (ceiling/ -123.2 -63.5) @result{} 2.0 and 3.8
1396 (ceiling/ 16/3 -10/7) @result{} -3 and 22/21
1400 @deftypefn {Scheme Procedure} {} truncate/ @var{x} @var{y}
1401 @deftypefnx {Scheme Procedure} {} truncate-quotient @var{x} @var{y}
1402 @deftypefnx {Scheme Procedure} {} truncate-remainder @var{x} @var{y}
1403 @deftypefnx {C Function} void scm_truncate_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1404 @deftypefnx {C Function} SCM scm_truncate_quotient (@var{x}, @var{y})
1405 @deftypefnx {C Function} SCM scm_truncate_remainder (@var{x}, @var{y})
1406 These procedures accept two real numbers @var{x} and @var{y}, where the
1407 divisor @var{y} must be non-zero. @code{truncate-quotient} returns the
1408 integer @var{q} and @code{truncate-remainder} returns the real number
1409 @var{r} such that @var{q} is @math{@var{x}/@var{y}} rounded toward zero,
1410 and @math{@var{x} = @var{q}*@var{y} + @var{r}}. @code{truncate/} returns
1411 both @var{q} and @var{r}, and is more efficient than computing each
1412 separately. Note that @var{r}, if non-zero, will have the same sign
1415 When @var{x} and @var{y} are integers, these operators are
1416 equivalent to the R5RS integer-only operators @code{quotient} and
1420 (truncate-quotient 123 10) @result{} 12
1421 (truncate-remainder 123 10) @result{} 3
1422 (truncate/ 123 10) @result{} 12 and 3
1423 (truncate/ 123 -10) @result{} -12 and 3
1424 (truncate/ -123 10) @result{} -12 and -3
1425 (truncate/ -123 -10) @result{} 12 and -3
1426 (truncate/ -123.2 -63.5) @result{} 1.0 and -59.7
1427 (truncate/ 16/3 -10/7) @result{} -3 and 22/21
1431 @deftypefn {Scheme Procedure} {} centered/ @var{x} @var{y}
1432 @deftypefnx {Scheme Procedure} {} centered-quotient @var{x} @var{y}
1433 @deftypefnx {Scheme Procedure} {} centered-remainder @var{x} @var{y}
1434 @deftypefnx {C Function} void scm_centered_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1435 @deftypefnx {C Function} SCM scm_centered_quotient (SCM @var{x}, SCM @var{y})
1436 @deftypefnx {C Function} SCM scm_centered_remainder (SCM @var{x}, SCM @var{y})
1437 These procedures accept two real numbers @var{x} and @var{y}, where the
1438 divisor @var{y} must be non-zero. @code{centered-quotient} returns the
1439 integer @var{q} and @code{centered-remainder} returns the real number
1440 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1441 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}. @code{centered/}
1442 returns both @var{q} and @var{r}, and is more efficient than computing
1445 Note that @code{centered-quotient} returns @math{@var{x}/@var{y}}
1446 rounded to the nearest integer. When @math{@var{x}/@var{y}} lies
1447 exactly half-way between two integers, the tie is broken according to
1448 the sign of @var{y}. If @math{@var{y} > 0}, ties are rounded toward
1449 positive infinity, otherwise they are rounded toward negative infinity.
1450 This is a consequence of the requirement that
1451 @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}.
1453 Note that these operators are equivalent to the R6RS operators
1454 @code{div0}, @code{mod0}, and @code{div0-and-mod0}.
1457 (centered-quotient 123 10) @result{} 12
1458 (centered-remainder 123 10) @result{} 3
1459 (centered/ 123 10) @result{} 12 and 3
1460 (centered/ 123 -10) @result{} -12 and 3
1461 (centered/ -123 10) @result{} -12 and -3
1462 (centered/ -123 -10) @result{} 12 and -3
1463 (centered/ 125 10) @result{} 13 and -5
1464 (centered/ 127 10) @result{} 13 and -3
1465 (centered/ 135 10) @result{} 14 and -5
1466 (centered/ -123.2 -63.5) @result{} 2.0 and 3.8
1467 (centered/ 16/3 -10/7) @result{} -4 and -8/21
1471 @deftypefn {Scheme Procedure} {} round/ @var{x} @var{y}
1472 @deftypefnx {Scheme Procedure} {} round-quotient @var{x} @var{y}
1473 @deftypefnx {Scheme Procedure} {} round-remainder @var{x} @var{y}
1474 @deftypefnx {C Function} void scm_round_divide (SCM @var{x}, SCM @var{y}, SCM *@var{q}, SCM *@var{r})
1475 @deftypefnx {C Function} SCM scm_round_quotient (@var{x}, @var{y})
1476 @deftypefnx {C Function} SCM scm_round_remainder (@var{x}, @var{y})
1477 These procedures accept two real numbers @var{x} and @var{y}, where the
1478 divisor @var{y} must be non-zero. @code{round-quotient} returns the
1479 integer @var{q} and @code{round-remainder} returns the real number
1480 @var{r} such that @math{@var{x} = @var{q}*@var{y} + @var{r}} and
1481 @var{q} is @math{@var{x}/@var{y}} rounded to the nearest integer,
1482 with ties going to the nearest even integer. @code{round/}
1483 returns both @var{q} and @var{r}, and is more efficient than computing
1486 Note that @code{round/} and @code{centered/} are almost equivalent, but
1487 their behavior differs when @math{@var{x}/@var{y}} lies exactly half-way
1488 between two integers. In this case, @code{round/} chooses the nearest
1489 even integer, whereas @code{centered/} chooses in such a way to satisfy
1490 the constraint @math{-|@var{y}/2| <= @var{r} < |@var{y}/2|}, which
1491 is stronger than the corresponding constraint for @code{round/},
1492 @math{-|@var{y}/2| <= @var{r} <= |@var{y}/2|}. In particular,
1493 when @var{x} and @var{y} are integers, the number of possible remainders
1494 returned by @code{centered/} is @math{|@var{y}|}, whereas the number of
1495 possible remainders returned by @code{round/} is @math{|@var{y}|+1} when
1499 (round-quotient 123 10) @result{} 12
1500 (round-remainder 123 10) @result{} 3
1501 (round/ 123 10) @result{} 12 and 3
1502 (round/ 123 -10) @result{} -12 and 3
1503 (round/ -123 10) @result{} -12 and -3
1504 (round/ -123 -10) @result{} 12 and -3
1505 (round/ 125 10) @result{} 12 and 5
1506 (round/ 127 10) @result{} 13 and -3
1507 (round/ 135 10) @result{} 14 and -5
1508 (round/ -123.2 -63.5) @result{} 2.0 and 3.8
1509 (round/ 16/3 -10/7) @result{} -4 and -8/21
1514 @subsubsection Scientific Functions
1516 The following procedures accept any kind of number as arguments,
1517 including complex numbers.
1520 @c begin (texi-doc-string "guile" "sqrt")
1521 @deffn {Scheme Procedure} sqrt z
1522 Return the square root of @var{z}. Of the two possible roots
1523 (positive and negative), the one with a positive real part is
1524 returned, or if that's zero then a positive imaginary part. Thus,
1527 (sqrt 9.0) @result{} 3.0
1528 (sqrt -9.0) @result{} 0.0+3.0i
1529 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1530 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1535 @c begin (texi-doc-string "guile" "expt")
1536 @deffn {Scheme Procedure} expt z1 z2
1537 Return @var{z1} raised to the power of @var{z2}.
1541 @c begin (texi-doc-string "guile" "sin")
1542 @deffn {Scheme Procedure} sin z
1543 Return the sine of @var{z}.
1547 @c begin (texi-doc-string "guile" "cos")
1548 @deffn {Scheme Procedure} cos z
1549 Return the cosine of @var{z}.
1553 @c begin (texi-doc-string "guile" "tan")
1554 @deffn {Scheme Procedure} tan z
1555 Return the tangent of @var{z}.
1559 @c begin (texi-doc-string "guile" "asin")
1560 @deffn {Scheme Procedure} asin z
1561 Return the arcsine of @var{z}.
1565 @c begin (texi-doc-string "guile" "acos")
1566 @deffn {Scheme Procedure} acos z
1567 Return the arccosine of @var{z}.
1571 @c begin (texi-doc-string "guile" "atan")
1572 @deffn {Scheme Procedure} atan z
1573 @deffnx {Scheme Procedure} atan y x
1574 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1578 @c begin (texi-doc-string "guile" "exp")
1579 @deffn {Scheme Procedure} exp z
1580 Return e to the power of @var{z}, where e is the base of natural
1581 logarithms (2.71828@dots{}).
1585 @c begin (texi-doc-string "guile" "log")
1586 @deffn {Scheme Procedure} log z
1587 Return the natural logarithm of @var{z}.
1590 @c begin (texi-doc-string "guile" "log10")
1591 @deffn {Scheme Procedure} log10 z
1592 Return the base 10 logarithm of @var{z}.
1595 @c begin (texi-doc-string "guile" "sinh")
1596 @deffn {Scheme Procedure} sinh z
1597 Return the hyperbolic sine of @var{z}.
1600 @c begin (texi-doc-string "guile" "cosh")
1601 @deffn {Scheme Procedure} cosh z
1602 Return the hyperbolic cosine of @var{z}.
1605 @c begin (texi-doc-string "guile" "tanh")
1606 @deffn {Scheme Procedure} tanh z
1607 Return the hyperbolic tangent of @var{z}.
1610 @c begin (texi-doc-string "guile" "asinh")
1611 @deffn {Scheme Procedure} asinh z
1612 Return the hyperbolic arcsine of @var{z}.
1615 @c begin (texi-doc-string "guile" "acosh")
1616 @deffn {Scheme Procedure} acosh z
1617 Return the hyperbolic arccosine of @var{z}.
1620 @c begin (texi-doc-string "guile" "atanh")
1621 @deffn {Scheme Procedure} atanh z
1622 Return the hyperbolic arctangent of @var{z}.
1626 @node Bitwise Operations
1627 @subsubsection Bitwise Operations
1629 For the following bitwise functions, negative numbers are treated as
1630 infinite precision twos-complements. For instance @math{-6} is bits
1631 @math{@dots{}111010}, with infinitely many ones on the left. It can
1632 be seen that adding 6 (binary 110) to such a bit pattern gives all
1635 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1636 @deffnx {C Function} scm_logand (n1, n2)
1637 Return the bitwise @sc{and} of the integer arguments.
1640 (logand) @result{} -1
1641 (logand 7) @result{} 7
1642 (logand #b111 #b011 #b001) @result{} 1
1646 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1647 @deffnx {C Function} scm_logior (n1, n2)
1648 Return the bitwise @sc{or} of the integer arguments.
1651 (logior) @result{} 0
1652 (logior 7) @result{} 7
1653 (logior #b000 #b001 #b011) @result{} 3
1657 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1658 @deffnx {C Function} scm_loxor (n1, n2)
1659 Return the bitwise @sc{xor} of the integer arguments. A bit is
1660 set in the result if it is set in an odd number of arguments.
1663 (logxor) @result{} 0
1664 (logxor 7) @result{} 7
1665 (logxor #b000 #b001 #b011) @result{} 2
1666 (logxor #b000 #b001 #b011 #b011) @result{} 1
1670 @deffn {Scheme Procedure} lognot n
1671 @deffnx {C Function} scm_lognot (n)
1672 Return the integer which is the ones-complement of the integer
1673 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1676 (number->string (lognot #b10000000) 2)
1677 @result{} "-10000001"
1678 (number->string (lognot #b0) 2)
1683 @deffn {Scheme Procedure} logtest j k
1684 @deffnx {C Function} scm_logtest (j, k)
1685 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1686 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1687 calculating the @code{logand}, just testing for non-zero.
1690 (logtest #b0100 #b1011) @result{} #f
1691 (logtest #b0100 #b0111) @result{} #t
1695 @deffn {Scheme Procedure} logbit? index j
1696 @deffnx {C Function} scm_logbit_p (index, j)
1697 Test whether bit number @var{index} in @var{j} is set. @var{index}
1698 starts from 0 for the least significant bit.
1701 (logbit? 0 #b1101) @result{} #t
1702 (logbit? 1 #b1101) @result{} #f
1703 (logbit? 2 #b1101) @result{} #t
1704 (logbit? 3 #b1101) @result{} #t
1705 (logbit? 4 #b1101) @result{} #f
1709 @deffn {Scheme Procedure} ash n count
1710 @deffnx {C Function} scm_ash (n, count)
1711 Return @math{floor(n * 2^count)}.
1712 @var{n} and @var{count} must be exact integers.
1714 With @var{n} viewed as an infinite-precision twos-complement
1715 integer, @code{ash} means a left shift introducing zero bits
1716 when @var{count} is positive, or a right shift dropping bits
1717 when @var{count} is negative. This is an ``arithmetic'' shift.
1720 (number->string (ash #b1 3) 2) @result{} "1000"
1721 (number->string (ash #b1010 -1) 2) @result{} "101"
1723 ;; -23 is bits ...11101001, -6 is bits ...111010
1724 (ash -23 -2) @result{} -6
1728 @deffn {Scheme Procedure} round-ash n count
1729 @deffnx {C Function} scm_round_ash (n, count)
1730 Return @math{round(n * 2^count)}.
1731 @var{n} and @var{count} must be exact integers.
1733 With @var{n} viewed as an infinite-precision twos-complement
1734 integer, @code{round-ash} means a left shift introducing zero
1735 bits when @var{count} is positive, or a right shift rounding
1736 to the nearest integer (with ties going to the nearest even
1737 integer) when @var{count} is negative. This is a rounded
1738 ``arithmetic'' shift.
1741 (number->string (round-ash #b1 3) 2) @result{} \"1000\"
1742 (number->string (round-ash #b1010 -1) 2) @result{} \"101\"
1743 (number->string (round-ash #b1010 -2) 2) @result{} \"10\"
1744 (number->string (round-ash #b1011 -2) 2) @result{} \"11\"
1745 (number->string (round-ash #b1101 -2) 2) @result{} \"11\"
1746 (number->string (round-ash #b1110 -2) 2) @result{} \"100\"
1750 @deffn {Scheme Procedure} logcount n
1751 @deffnx {C Function} scm_logcount (n)
1752 Return the number of bits in integer @var{n}. If @var{n} is
1753 positive, the 1-bits in its binary representation are counted.
1754 If negative, the 0-bits in its two's-complement binary
1755 representation are counted. If zero, 0 is returned.
1758 (logcount #b10101010)
1767 @deffn {Scheme Procedure} integer-length n
1768 @deffnx {C Function} scm_integer_length (n)
1769 Return the number of bits necessary to represent @var{n}.
1771 For positive @var{n} this is how many bits to the most significant one
1772 bit. For negative @var{n} it's how many bits to the most significant
1773 zero bit in twos complement form.
1776 (integer-length #b10101010) @result{} 8
1777 (integer-length #b1111) @result{} 4
1778 (integer-length 0) @result{} 0
1779 (integer-length -1) @result{} 0
1780 (integer-length -256) @result{} 8
1781 (integer-length -257) @result{} 9
1785 @deffn {Scheme Procedure} integer-expt n k
1786 @deffnx {C Function} scm_integer_expt (n, k)
1787 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1788 integer, @var{n} can be any number.
1790 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1791 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1795 (integer-expt 2 5) @result{} 32
1796 (integer-expt -3 3) @result{} -27
1797 (integer-expt 5 -3) @result{} 1/125
1798 (integer-expt 0 0) @result{} 1
1802 @deffn {Scheme Procedure} bit-extract n start end
1803 @deffnx {C Function} scm_bit_extract (n, start, end)
1804 Return the integer composed of the @var{start} (inclusive)
1805 through @var{end} (exclusive) bits of @var{n}. The
1806 @var{start}th bit becomes the 0-th bit in the result.
1809 (number->string (bit-extract #b1101101010 0 4) 2)
1811 (number->string (bit-extract #b1101101010 4 9) 2)
1818 @subsubsection Random Number Generation
1820 Pseudo-random numbers are generated from a random state object, which
1821 can be created with @code{seed->random-state} or
1822 @code{datum->random-state}. An external representation (i.e.@: one
1823 which can written with @code{write} and read with @code{read}) of a
1824 random state object can be obtained via
1825 @code{random-state->datum}. The @var{state} parameter to the
1826 various functions below is optional, it defaults to the state object
1827 in the @code{*random-state*} variable.
1829 @deffn {Scheme Procedure} copy-random-state [state]
1830 @deffnx {C Function} scm_copy_random_state (state)
1831 Return a copy of the random state @var{state}.
1834 @deffn {Scheme Procedure} random n [state]
1835 @deffnx {C Function} scm_random (n, state)
1836 Return a number in [0, @var{n}).
1838 Accepts a positive integer or real n and returns a
1839 number of the same type between zero (inclusive) and
1840 @var{n} (exclusive). The values returned have a uniform
1844 @deffn {Scheme Procedure} random:exp [state]
1845 @deffnx {C Function} scm_random_exp (state)
1846 Return an inexact real in an exponential distribution with mean
1847 1. For an exponential distribution with mean @var{u} use @code{(*
1848 @var{u} (random:exp))}.
1851 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1852 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1853 Fills @var{vect} with inexact real random numbers the sum of whose
1854 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1855 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1856 the coordinates are uniformly distributed over the surface of the unit
1860 @deffn {Scheme Procedure} random:normal [state]
1861 @deffnx {C Function} scm_random_normal (state)
1862 Return an inexact real in a normal distribution. The distribution
1863 used has mean 0 and standard deviation 1. For a normal distribution
1864 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1865 (* @var{d} (random:normal)))}.
1868 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1869 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1870 Fills @var{vect} with inexact real random numbers that are
1871 independent and standard normally distributed
1872 (i.e., with mean 0 and variance 1).
1875 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1876 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1877 Fills @var{vect} with inexact real random numbers the sum of whose
1878 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1879 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1880 the coordinates are uniformly distributed within the unit
1882 @c FIXME: What does this mean, particularly the n-sphere part?
1885 @deffn {Scheme Procedure} random:uniform [state]
1886 @deffnx {C Function} scm_random_uniform (state)
1887 Return a uniformly distributed inexact real random number in
1891 @deffn {Scheme Procedure} seed->random-state seed
1892 @deffnx {C Function} scm_seed_to_random_state (seed)
1893 Return a new random state using @var{seed}.
1896 @deffn {Scheme Procedure} datum->random-state datum
1897 @deffnx {C Function} scm_datum_to_random_state (datum)
1898 Return a new random state from @var{datum}, which should have been
1899 obtained by @code{random-state->datum}.
1902 @deffn {Scheme Procedure} random-state->datum state
1903 @deffnx {C Function} scm_random_state_to_datum (state)
1904 Return a datum representation of @var{state} that may be written out and
1905 read back with the Scheme reader.
1908 @deffn {Scheme Procedure} random-state-from-platform
1909 @deffnx {C Function} scm_random_state_from_platform ()
1910 Construct a new random state seeded from a platform-specific source of
1911 entropy, appropriate for use in non-security-critical applications.
1912 Currently @file{/dev/urandom} is tried first, or else the seed is based
1913 on the time, date, process ID, an address from a freshly allocated heap
1914 cell, an address from the local stack frame, and a high-resolution timer
1918 @defvar *random-state*
1919 The global random state used by the above functions when the
1920 @var{state} parameter is not given.
1923 Note that the initial value of @code{*random-state*} is the same every
1924 time Guile starts up. Therefore, if you don't pass a @var{state}
1925 parameter to the above procedures, and you don't set
1926 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1927 @code{your-seed} is something that @emph{isn't} the same every time,
1928 you'll get the same sequence of ``random'' numbers on every run.
1930 For example, unless the relevant source code has changed, @code{(map
1931 random (cdr (iota 30)))}, if the first use of random numbers since
1932 Guile started up, will always give:
1935 (map random (cdr (iota 19)))
1937 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1940 To seed the random state in a sensible way for non-security-critical
1941 applications, do this during initialization of your program:
1944 (set! *random-state* (random-state-from-platform))
1949 @subsection Characters
1952 In Scheme, there is a data type to describe a single character.
1954 Defining what exactly a character @emph{is} can be more complicated
1955 than it seems. Guile follows the advice of R6RS and uses The Unicode
1956 Standard to help define what a character is. So, for Guile, a
1957 character is anything in the Unicode Character Database.
1960 @cindex Unicode code point
1962 The Unicode Character Database is basically a table of characters
1963 indexed using integers called 'code points'. Valid code points are in
1964 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1965 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1967 @cindex designated code point
1968 @cindex code point, designated
1970 Any code point that has been assigned to a character or that has
1971 otherwise been given a meaning by Unicode is called a 'designated code
1972 point'. Most of the designated code points, about 200,000 of them,
1973 indicate characters, accents or other combining marks that modify
1974 other characters, symbols, whitespace, and control characters. Some
1975 are not characters but indicators that suggest how to format or
1976 display neighboring characters.
1978 @cindex reserved code point
1979 @cindex code point, reserved
1981 If a code point is not a designated code point -- if it has not been
1982 assigned to a character by The Unicode Standard -- it is a 'reserved
1983 code point', meaning that they are reserved for future use. Most of
1984 the code points, about 800,000, are 'reserved code points'.
1986 By convention, a Unicode code point is written as
1987 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1988 this convenient notation is not valid code. Guile does not interpret
1989 ``U+XXXX'' as a character.
1991 In Scheme, a character literal is written as @code{#\@var{name}} where
1992 @var{name} is the name of the character that you want. Printable
1993 characters have their usual single character name; for example,
1994 @code{#\a} is a lower case @code{a}.
1996 Some of the code points are 'combining characters' that are not meant
1997 to be printed by themselves but are instead meant to modify the
1998 appearance of the previous character. For combining characters, an
1999 alternate form of the character literal is @code{#\} followed by
2000 U+25CC (a small, dotted circle), followed by the combining character.
2001 This allows the combining character to be drawn on the circle, not on
2002 the backslash of @code{#\}.
2004 Many of the non-printing characters, such as whitespace characters and
2005 control characters, also have names.
2007 The most commonly used non-printing characters have long character
2008 names, described in the table below.
2010 @multitable {@code{#\backspace}} {Preferred}
2011 @item Character Name @tab Codepoint
2012 @item @code{#\nul} @tab U+0000
2013 @item @code{#\alarm} @tab u+0007
2014 @item @code{#\backspace} @tab U+0008
2015 @item @code{#\tab} @tab U+0009
2016 @item @code{#\linefeed} @tab U+000A
2017 @item @code{#\newline} @tab U+000A
2018 @item @code{#\vtab} @tab U+000B
2019 @item @code{#\page} @tab U+000C
2020 @item @code{#\return} @tab U+000D
2021 @item @code{#\esc} @tab U+001B
2022 @item @code{#\space} @tab U+0020
2023 @item @code{#\delete} @tab U+007F
2026 There are also short names for all of the ``C0 control characters''
2027 (those with code points below 32). The following table lists the short
2028 name for each character.
2030 @multitable @columnfractions .25 .25 .25 .25
2031 @item 0 = @code{#\nul}
2032 @tab 1 = @code{#\soh}
2033 @tab 2 = @code{#\stx}
2034 @tab 3 = @code{#\etx}
2035 @item 4 = @code{#\eot}
2036 @tab 5 = @code{#\enq}
2037 @tab 6 = @code{#\ack}
2038 @tab 7 = @code{#\bel}
2039 @item 8 = @code{#\bs}
2040 @tab 9 = @code{#\ht}
2041 @tab 10 = @code{#\lf}
2042 @tab 11 = @code{#\vt}
2043 @item 12 = @code{#\ff}
2044 @tab 13 = @code{#\cr}
2045 @tab 14 = @code{#\so}
2046 @tab 15 = @code{#\si}
2047 @item 16 = @code{#\dle}
2048 @tab 17 = @code{#\dc1}
2049 @tab 18 = @code{#\dc2}
2050 @tab 19 = @code{#\dc3}
2051 @item 20 = @code{#\dc4}
2052 @tab 21 = @code{#\nak}
2053 @tab 22 = @code{#\syn}
2054 @tab 23 = @code{#\etb}
2055 @item 24 = @code{#\can}
2056 @tab 25 = @code{#\em}
2057 @tab 26 = @code{#\sub}
2058 @tab 27 = @code{#\esc}
2059 @item 28 = @code{#\fs}
2060 @tab 29 = @code{#\gs}
2061 @tab 30 = @code{#\rs}
2062 @tab 31 = @code{#\us}
2063 @item 32 = @code{#\sp}
2066 The short name for the ``delete'' character (code point U+007F) is
2069 The R7RS name for the ``escape'' character (code point U+001B) is
2072 There are also a few alternative names left over for compatibility with
2073 previous versions of Guile.
2075 @multitable {@code{#\backspace}} {Preferred}
2076 @item Alternate @tab Standard
2077 @item @code{#\nl} @tab @code{#\newline}
2078 @item @code{#\np} @tab @code{#\page}
2079 @item @code{#\null} @tab @code{#\nul}
2082 Characters may also be written using their code point values. They can
2083 be written with as an octal number, such as @code{#\10} for
2084 @code{#\bs} or @code{#\177} for @code{#\del}.
2086 If one prefers hex to octal, there is an additional syntax for character
2087 escapes: @code{#\xHHHH} -- the letter 'x' followed by a hexadecimal
2088 number of one to eight digits.
2091 @deffn {Scheme Procedure} char? x
2092 @deffnx {C Function} scm_char_p (x)
2093 Return @code{#t} if @var{x} is a character, else @code{#f}.
2096 Fundamentally, the character comparison operations below are
2097 numeric comparisons of the character's code points.
2100 @deffn {Scheme Procedure} char=? x y
2101 Return @code{#t} if code point of @var{x} is equal to the code point
2102 of @var{y}, else @code{#f}.
2106 @deffn {Scheme Procedure} char<? x y
2107 Return @code{#t} if the code point of @var{x} is less than the code
2108 point of @var{y}, else @code{#f}.
2112 @deffn {Scheme Procedure} char<=? x y
2113 Return @code{#t} if the code point of @var{x} is less than or equal
2114 to the code point of @var{y}, else @code{#f}.
2118 @deffn {Scheme Procedure} char>? x y
2119 Return @code{#t} if the code point of @var{x} is greater than the
2120 code point of @var{y}, else @code{#f}.
2124 @deffn {Scheme Procedure} char>=? x y
2125 Return @code{#t} if the code point of @var{x} is greater than or
2126 equal to the code point of @var{y}, else @code{#f}.
2129 @cindex case folding
2131 Case-insensitive character comparisons use @emph{Unicode case
2132 folding}. In case folding comparisons, if a character is lowercase
2133 and has an uppercase form that can be expressed as a single character,
2134 it is converted to uppercase before comparison. All other characters
2135 undergo no conversion before the comparison occurs. This includes the
2136 German sharp S (Eszett) which is not uppercased before conversion
2137 because its uppercase form has two characters. Unicode case folding
2138 is language independent: it uses rules that are generally true, but,
2139 it cannot cover all cases for all languages.
2142 @deffn {Scheme Procedure} char-ci=? x y
2143 Return @code{#t} if the case-folded code point of @var{x} is the same
2144 as the case-folded code point of @var{y}, else @code{#f}.
2148 @deffn {Scheme Procedure} char-ci<? x y
2149 Return @code{#t} if the case-folded code point of @var{x} is less
2150 than the case-folded code point of @var{y}, else @code{#f}.
2154 @deffn {Scheme Procedure} char-ci<=? x y
2155 Return @code{#t} if the case-folded code point of @var{x} is less
2156 than or equal to the case-folded code point of @var{y}, else
2161 @deffn {Scheme Procedure} char-ci>? x y
2162 Return @code{#t} if the case-folded code point of @var{x} is greater
2163 than the case-folded code point of @var{y}, else @code{#f}.
2167 @deffn {Scheme Procedure} char-ci>=? x y
2168 Return @code{#t} if the case-folded code point of @var{x} is greater
2169 than or equal to the case-folded code point of @var{y}, else
2173 @rnindex char-alphabetic?
2174 @deffn {Scheme Procedure} char-alphabetic? chr
2175 @deffnx {C Function} scm_char_alphabetic_p (chr)
2176 Return @code{#t} if @var{chr} is alphabetic, else @code{#f}.
2179 @rnindex char-numeric?
2180 @deffn {Scheme Procedure} char-numeric? chr
2181 @deffnx {C Function} scm_char_numeric_p (chr)
2182 Return @code{#t} if @var{chr} is numeric, else @code{#f}.
2185 @rnindex char-whitespace?
2186 @deffn {Scheme Procedure} char-whitespace? chr
2187 @deffnx {C Function} scm_char_whitespace_p (chr)
2188 Return @code{#t} if @var{chr} is whitespace, else @code{#f}.
2191 @rnindex char-upper-case?
2192 @deffn {Scheme Procedure} char-upper-case? chr
2193 @deffnx {C Function} scm_char_upper_case_p (chr)
2194 Return @code{#t} if @var{chr} is uppercase, else @code{#f}.
2197 @rnindex char-lower-case?
2198 @deffn {Scheme Procedure} char-lower-case? chr
2199 @deffnx {C Function} scm_char_lower_case_p (chr)
2200 Return @code{#t} if @var{chr} is lowercase, else @code{#f}.
2203 @deffn {Scheme Procedure} char-is-both? chr
2204 @deffnx {C Function} scm_char_is_both_p (chr)
2205 Return @code{#t} if @var{chr} is either uppercase or lowercase, else
2209 @deffn {Scheme Procedure} char-general-category chr
2210 @deffnx {C Function} scm_char_general_category (chr)
2211 Return a symbol giving the two-letter name of the Unicode general
2212 category assigned to @var{chr} or @code{#f} if no named category is
2213 assigned. The following table provides a list of category names along
2214 with their meanings.
2216 @multitable @columnfractions .1 .4 .1 .4
2218 @tab Uppercase letter
2220 @tab Final quote punctuation
2222 @tab Lowercase letter
2224 @tab Other punctuation
2226 @tab Titlecase letter
2230 @tab Modifier letter
2232 @tab Currency symbol
2236 @tab Modifier symbol
2238 @tab Non-spacing mark
2242 @tab Combining spacing mark
2244 @tab Space separator
2250 @tab Decimal digit number
2252 @tab Paragraph separator
2262 @tab Connector punctuation
2266 @tab Dash punctuation
2270 @tab Open punctuation
2274 @tab Close punctuation
2278 @tab Initial quote punctuation
2284 @rnindex char->integer
2285 @deffn {Scheme Procedure} char->integer chr
2286 @deffnx {C Function} scm_char_to_integer (chr)
2287 Return the code point of @var{chr}.
2290 @rnindex integer->char
2291 @deffn {Scheme Procedure} integer->char n
2292 @deffnx {C Function} scm_integer_to_char (n)
2293 Return the character that has code point @var{n}. The integer @var{n}
2294 must be a valid code point. Valid code points are in the ranges 0 to
2295 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
2298 @rnindex char-upcase
2299 @deffn {Scheme Procedure} char-upcase chr
2300 @deffnx {C Function} scm_char_upcase (chr)
2301 Return the uppercase character version of @var{chr}.
2304 @rnindex char-downcase
2305 @deffn {Scheme Procedure} char-downcase chr
2306 @deffnx {C Function} scm_char_downcase (chr)
2307 Return the lowercase character version of @var{chr}.
2310 @rnindex char-titlecase
2311 @deffn {Scheme Procedure} char-titlecase chr
2312 @deffnx {C Function} scm_char_titlecase (chr)
2313 Return the titlecase character version of @var{chr} if one exists;
2314 otherwise return the uppercase version.
2316 For most characters these will be the same, but the Unicode Standard
2317 includes certain digraph compatibility characters, such as @code{U+01F3}
2318 ``dz'', for which the uppercase and titlecase characters are different
2319 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
2324 @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c})
2325 @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c})
2326 @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c})
2328 These C functions take an integer representation of a Unicode
2329 codepoint and return the codepoint corresponding to its uppercase,
2330 lowercase, and titlecase forms respectively. The type
2331 @code{scm_t_wchar} is a signed, 32-bit integer.
2334 @node Character Sets
2335 @subsection Character Sets
2337 The features described in this section correspond directly to SRFI-14.
2339 The data type @dfn{charset} implements sets of characters
2340 (@pxref{Characters}). Because the internal representation of
2341 character sets is not visible to the user, a lot of procedures for
2342 handling them are provided.
2344 Character sets can be created, extended, tested for the membership of a
2345 characters and be compared to other character sets.
2348 * Character Set Predicates/Comparison::
2349 * Iterating Over Character Sets:: Enumerate charset elements.
2350 * Creating Character Sets:: Making new charsets.
2351 * Querying Character Sets:: Test charsets for membership etc.
2352 * Character-Set Algebra:: Calculating new charsets.
2353 * Standard Character Sets:: Variables containing predefined charsets.
2356 @node Character Set Predicates/Comparison
2357 @subsubsection Character Set Predicates/Comparison
2359 Use these procedures for testing whether an object is a character set,
2360 or whether several character sets are equal or subsets of each other.
2361 @code{char-set-hash} can be used for calculating a hash value, maybe for
2362 usage in fast lookup procedures.
2364 @deffn {Scheme Procedure} char-set? obj
2365 @deffnx {C Function} scm_char_set_p (obj)
2366 Return @code{#t} if @var{obj} is a character set, @code{#f}
2370 @deffn {Scheme Procedure} char-set= char_set @dots{}
2371 @deffnx {C Function} scm_char_set_eq (char_sets)
2372 Return @code{#t} if all given character sets are equal.
2375 @deffn {Scheme Procedure} char-set<= char_set @dots{}
2376 @deffnx {C Function} scm_char_set_leq (char_sets)
2377 Return @code{#t} if every character set @var{char_set}i is a subset
2378 of character set @var{char_set}i+1.
2381 @deffn {Scheme Procedure} char-set-hash cs [bound]
2382 @deffnx {C Function} scm_char_set_hash (cs, bound)
2383 Compute a hash value for the character set @var{cs}. If
2384 @var{bound} is given and non-zero, it restricts the
2385 returned value to the range 0 @dots{} @var{bound} - 1.
2388 @c ===================================================================
2390 @node Iterating Over Character Sets
2391 @subsubsection Iterating Over Character Sets
2393 Character set cursors are a means for iterating over the members of a
2394 character sets. After creating a character set cursor with
2395 @code{char-set-cursor}, a cursor can be dereferenced with
2396 @code{char-set-ref}, advanced to the next member with
2397 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2398 element of the set can be checked with @code{end-of-char-set?}.
2400 Additionally, mapping and (un-)folding procedures for character sets are
2403 @deffn {Scheme Procedure} char-set-cursor cs
2404 @deffnx {C Function} scm_char_set_cursor (cs)
2405 Return a cursor into the character set @var{cs}.
2408 @deffn {Scheme Procedure} char-set-ref cs cursor
2409 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2410 Return the character at the current cursor position
2411 @var{cursor} in the character set @var{cs}. It is an error to
2412 pass a cursor for which @code{end-of-char-set?} returns true.
2415 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2416 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2417 Advance the character set cursor @var{cursor} to the next
2418 character in the character set @var{cs}. It is an error if the
2419 cursor given satisfies @code{end-of-char-set?}.
2422 @deffn {Scheme Procedure} end-of-char-set? cursor
2423 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2424 Return @code{#t} if @var{cursor} has reached the end of a
2425 character set, @code{#f} otherwise.
2428 @deffn {Scheme Procedure} char-set-fold kons knil cs
2429 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2430 Fold the procedure @var{kons} over the character set @var{cs},
2431 initializing it with @var{knil}.
2434 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2435 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2436 This is a fundamental constructor for character sets.
2438 @item @var{g} is used to generate a series of ``seed'' values
2439 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2440 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2441 @item @var{p} tells us when to stop -- when it returns true
2442 when applied to one of the seed values.
2443 @item @var{f} maps each seed value to a character. These
2444 characters are added to the base character set @var{base_cs} to
2445 form the result; @var{base_cs} defaults to the empty set.
2449 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2450 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2451 This is a fundamental constructor for character sets.
2453 @item @var{g} is used to generate a series of ``seed'' values
2454 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2455 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2456 @item @var{p} tells us when to stop -- when it returns true
2457 when applied to one of the seed values.
2458 @item @var{f} maps each seed value to a character. These
2459 characters are added to the base character set @var{base_cs} to
2460 form the result; @var{base_cs} defaults to the empty set.
2464 @deffn {Scheme Procedure} char-set-for-each proc cs
2465 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2466 Apply @var{proc} to every character in the character set
2467 @var{cs}. The return value is not specified.
2470 @deffn {Scheme Procedure} char-set-map proc cs
2471 @deffnx {C Function} scm_char_set_map (proc, cs)
2472 Map the procedure @var{proc} over every character in @var{cs}.
2473 @var{proc} must be a character -> character procedure.
2476 @c ===================================================================
2478 @node Creating Character Sets
2479 @subsubsection Creating Character Sets
2481 New character sets are produced with these procedures.
2483 @deffn {Scheme Procedure} char-set-copy cs
2484 @deffnx {C Function} scm_char_set_copy (cs)
2485 Return a newly allocated character set containing all
2486 characters in @var{cs}.
2489 @deffn {Scheme Procedure} char-set chr @dots{}
2490 @deffnx {C Function} scm_char_set (chrs)
2491 Return a character set containing all given characters.
2494 @deffn {Scheme Procedure} list->char-set list [base_cs]
2495 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2496 Convert the character list @var{list} to a character set. If
2497 the character set @var{base_cs} is given, the character in this
2498 set are also included in the result.
2501 @deffn {Scheme Procedure} list->char-set! list base_cs
2502 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2503 Convert the character list @var{list} to a character set. The
2504 characters are added to @var{base_cs} and @var{base_cs} is
2508 @deffn {Scheme Procedure} string->char-set str [base_cs]
2509 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2510 Convert the string @var{str} to a character set. If the
2511 character set @var{base_cs} is given, the characters in this
2512 set are also included in the result.
2515 @deffn {Scheme Procedure} string->char-set! str base_cs
2516 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2517 Convert the string @var{str} to a character set. The
2518 characters from the string are added to @var{base_cs}, and
2519 @var{base_cs} is returned.
2522 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2523 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2524 Return a character set containing every character from @var{cs}
2525 so that it satisfies @var{pred}. If provided, the characters
2526 from @var{base_cs} are added to the result.
2529 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2530 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2531 Return a character set containing every character from @var{cs}
2532 so that it satisfies @var{pred}. The characters are added to
2533 @var{base_cs} and @var{base_cs} is returned.
2536 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2537 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2538 Return a character set containing all characters whose
2539 character codes lie in the half-open range
2540 [@var{lower},@var{upper}).
2542 If @var{error} is a true value, an error is signalled if the
2543 specified range contains characters which are not contained in
2544 the implemented character range. If @var{error} is @code{#f},
2545 these characters are silently left out of the resulting
2548 The characters in @var{base_cs} are added to the result, if
2552 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2553 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2554 Return a character set containing all characters whose
2555 character codes lie in the half-open range
2556 [@var{lower},@var{upper}).
2558 If @var{error} is a true value, an error is signalled if the
2559 specified range contains characters which are not contained in
2560 the implemented character range. If @var{error} is @code{#f},
2561 these characters are silently left out of the resulting
2564 The characters are added to @var{base_cs} and @var{base_cs} is
2568 @deffn {Scheme Procedure} ->char-set x
2569 @deffnx {C Function} scm_to_char_set (x)
2570 Coerces x into a char-set. @var{x} may be a string, character or
2571 char-set. A string is converted to the set of its constituent
2572 characters; a character is converted to a singleton set; a char-set is
2576 @c ===================================================================
2578 @node Querying Character Sets
2579 @subsubsection Querying Character Sets
2581 Access the elements and other information of a character set with these
2584 @deffn {Scheme Procedure} %char-set-dump cs
2585 Returns an association list containing debugging information
2586 for @var{cs}. The association list has the following entries.
2591 The number of groups of contiguous code points the char-set
2594 A list of lists where each sublist is a range of code points
2595 and their associated characters
2597 The return value of this function cannot be relied upon to be
2598 consistent between versions of Guile and should not be used in code.
2601 @deffn {Scheme Procedure} char-set-size cs
2602 @deffnx {C Function} scm_char_set_size (cs)
2603 Return the number of elements in character set @var{cs}.
2606 @deffn {Scheme Procedure} char-set-count pred cs
2607 @deffnx {C Function} scm_char_set_count (pred, cs)
2608 Return the number of the elements int the character set
2609 @var{cs} which satisfy the predicate @var{pred}.
2612 @deffn {Scheme Procedure} char-set->list cs
2613 @deffnx {C Function} scm_char_set_to_list (cs)
2614 Return a list containing the elements of the character set
2618 @deffn {Scheme Procedure} char-set->string cs
2619 @deffnx {C Function} scm_char_set_to_string (cs)
2620 Return a string containing the elements of the character set
2621 @var{cs}. The order in which the characters are placed in the
2622 string is not defined.
2625 @deffn {Scheme Procedure} char-set-contains? cs ch
2626 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2627 Return @code{#t} if the character @var{ch} is contained in the
2628 character set @var{cs}, or @code{#f} otherwise.
2631 @deffn {Scheme Procedure} char-set-every pred cs
2632 @deffnx {C Function} scm_char_set_every (pred, cs)
2633 Return a true value if every character in the character set
2634 @var{cs} satisfies the predicate @var{pred}.
2637 @deffn {Scheme Procedure} char-set-any pred cs
2638 @deffnx {C Function} scm_char_set_any (pred, cs)
2639 Return a true value if any character in the character set
2640 @var{cs} satisfies the predicate @var{pred}.
2643 @c ===================================================================
2645 @node Character-Set Algebra
2646 @subsubsection Character-Set Algebra
2648 Character sets can be manipulated with the common set algebra operation,
2649 such as union, complement, intersection etc. All of these procedures
2650 provide side-effecting variants, which modify their character set
2653 @deffn {Scheme Procedure} char-set-adjoin cs chr @dots{}
2654 @deffnx {C Function} scm_char_set_adjoin (cs, chrs)
2655 Add all character arguments to the first argument, which must
2659 @deffn {Scheme Procedure} char-set-delete cs chr @dots{}
2660 @deffnx {C Function} scm_char_set_delete (cs, chrs)
2661 Delete all character arguments from the first argument, which
2662 must be a character set.
2665 @deffn {Scheme Procedure} char-set-adjoin! cs chr @dots{}
2666 @deffnx {C Function} scm_char_set_adjoin_x (cs, chrs)
2667 Add all character arguments to the first argument, which must
2671 @deffn {Scheme Procedure} char-set-delete! cs chr @dots{}
2672 @deffnx {C Function} scm_char_set_delete_x (cs, chrs)
2673 Delete all character arguments from the first argument, which
2674 must be a character set.
2677 @deffn {Scheme Procedure} char-set-complement cs
2678 @deffnx {C Function} scm_char_set_complement (cs)
2679 Return the complement of the character set @var{cs}.
2682 Note that the complement of a character set is likely to contain many
2683 reserved code points (code points that are not associated with
2684 characters). It may be helpful to modify the output of
2685 @code{char-set-complement} by computing its intersection with the set
2686 of designated code points, @code{char-set:designated}.
2688 @deffn {Scheme Procedure} char-set-union cs @dots{}
2689 @deffnx {C Function} scm_char_set_union (char_sets)
2690 Return the union of all argument character sets.
2693 @deffn {Scheme Procedure} char-set-intersection cs @dots{}
2694 @deffnx {C Function} scm_char_set_intersection (char_sets)
2695 Return the intersection of all argument character sets.
2698 @deffn {Scheme Procedure} char-set-difference cs1 cs @dots{}
2699 @deffnx {C Function} scm_char_set_difference (cs1, char_sets)
2700 Return the difference of all argument character sets.
2703 @deffn {Scheme Procedure} char-set-xor cs @dots{}
2704 @deffnx {C Function} scm_char_set_xor (char_sets)
2705 Return the exclusive-or of all argument character sets.
2708 @deffn {Scheme Procedure} char-set-diff+intersection cs1 cs @dots{}
2709 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, char_sets)
2710 Return the difference and the intersection of all argument
2714 @deffn {Scheme Procedure} char-set-complement! cs
2715 @deffnx {C Function} scm_char_set_complement_x (cs)
2716 Return the complement of the character set @var{cs}.
2719 @deffn {Scheme Procedure} char-set-union! cs1 cs @dots{}
2720 @deffnx {C Function} scm_char_set_union_x (cs1, char_sets)
2721 Return the union of all argument character sets.
2724 @deffn {Scheme Procedure} char-set-intersection! cs1 cs @dots{}
2725 @deffnx {C Function} scm_char_set_intersection_x (cs1, char_sets)
2726 Return the intersection of all argument character sets.
2729 @deffn {Scheme Procedure} char-set-difference! cs1 cs @dots{}
2730 @deffnx {C Function} scm_char_set_difference_x (cs1, char_sets)
2731 Return the difference of all argument character sets.
2734 @deffn {Scheme Procedure} char-set-xor! cs1 cs @dots{}
2735 @deffnx {C Function} scm_char_set_xor_x (cs1, char_sets)
2736 Return the exclusive-or of all argument character sets.
2739 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 cs @dots{}
2740 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, char_sets)
2741 Return the difference and the intersection of all argument
2745 @c ===================================================================
2747 @node Standard Character Sets
2748 @subsubsection Standard Character Sets
2750 In order to make the use of the character set data type and procedures
2751 useful, several predefined character set variables exist.
2757 These character sets are locale independent and are not recomputed
2758 upon a @code{setlocale} call. They contain characters from the whole
2759 range of Unicode code points. For instance, @code{char-set:letter}
2760 contains about 100,000 characters.
2762 @defvr {Scheme Variable} char-set:lower-case
2763 @defvrx {C Variable} scm_char_set_lower_case
2764 All lower-case characters.
2767 @defvr {Scheme Variable} char-set:upper-case
2768 @defvrx {C Variable} scm_char_set_upper_case
2769 All upper-case characters.
2772 @defvr {Scheme Variable} char-set:title-case
2773 @defvrx {C Variable} scm_char_set_title_case
2774 All single characters that function as if they were an upper-case
2775 letter followed by a lower-case letter.
2778 @defvr {Scheme Variable} char-set:letter
2779 @defvrx {C Variable} scm_char_set_letter
2780 All letters. This includes @code{char-set:lower-case},
2781 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2782 letters that have no case at all. For example, Chinese and Japanese
2783 characters typically have no concept of case.
2786 @defvr {Scheme Variable} char-set:digit
2787 @defvrx {C Variable} scm_char_set_digit
2791 @defvr {Scheme Variable} char-set:letter+digit
2792 @defvrx {C Variable} scm_char_set_letter_and_digit
2793 The union of @code{char-set:letter} and @code{char-set:digit}.
2796 @defvr {Scheme Variable} char-set:graphic
2797 @defvrx {C Variable} scm_char_set_graphic
2798 All characters which would put ink on the paper.
2801 @defvr {Scheme Variable} char-set:printing
2802 @defvrx {C Variable} scm_char_set_printing
2803 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2806 @defvr {Scheme Variable} char-set:whitespace
2807 @defvrx {C Variable} scm_char_set_whitespace
2808 All whitespace characters.
2811 @defvr {Scheme Variable} char-set:blank
2812 @defvrx {C Variable} scm_char_set_blank
2813 All horizontal whitespace characters, which notably includes
2814 @code{#\space} and @code{#\tab}.
2817 @defvr {Scheme Variable} char-set:iso-control
2818 @defvrx {C Variable} scm_char_set_iso_control
2819 The ISO control characters are the C0 control characters (U+0000 to
2820 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2824 @defvr {Scheme Variable} char-set:punctuation
2825 @defvrx {C Variable} scm_char_set_punctuation
2826 All punctuation characters, such as the characters
2827 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2830 @defvr {Scheme Variable} char-set:symbol
2831 @defvrx {C Variable} scm_char_set_symbol
2832 All symbol characters, such as the characters @code{$+<=>^`|~}.
2835 @defvr {Scheme Variable} char-set:hex-digit
2836 @defvrx {C Variable} scm_char_set_hex_digit
2837 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2840 @defvr {Scheme Variable} char-set:ascii
2841 @defvrx {C Variable} scm_char_set_ascii
2842 All ASCII characters.
2845 @defvr {Scheme Variable} char-set:empty
2846 @defvrx {C Variable} scm_char_set_empty
2847 The empty character set.
2850 @defvr {Scheme Variable} char-set:designated
2851 @defvrx {C Variable} scm_char_set_designated
2852 This character set contains all designated code points. This includes
2853 all the code points to which Unicode has assigned a character or other
2857 @defvr {Scheme Variable} char-set:full
2858 @defvrx {C Variable} scm_char_set_full
2859 This character set contains all possible code points. This includes
2860 both designated and reserved code points.
2867 Strings are fixed-length sequences of characters. They can be created
2868 by calling constructor procedures, but they can also literally get
2869 entered at the @acronym{REPL} or in Scheme source files.
2871 @c Guile provides a rich set of string processing procedures, because text
2872 @c handling is very important when Guile is used as a scripting language.
2874 Strings always carry the information about how many characters they are
2875 composed of with them, so there is no special end-of-string character,
2876 like in C. That means that Scheme strings can contain any character,
2877 even the @samp{#\nul} character @samp{\0}.
2879 To use strings efficiently, you need to know a bit about how Guile
2880 implements them. In Guile, a string consists of two parts, a head and
2881 the actual memory where the characters are stored. When a string (or
2882 a substring of it) is copied, only a new head gets created, the memory
2883 is usually not copied. The two heads start out pointing to the same
2886 When one of these two strings is modified, as with @code{string-set!},
2887 their common memory does get copied so that each string has its own
2888 memory and modifying one does not accidentally modify the other as well.
2889 Thus, Guile's strings are `copy on write'; the actual copying of their
2890 memory is delayed until one string is written to.
2892 This implementation makes functions like @code{substring} very
2893 efficient in the common case that no modifications are done to the
2896 If you do know that your strings are getting modified right away, you
2897 can use @code{substring/copy} instead of @code{substring}. This
2898 function performs the copy immediately at the time of creation. This
2899 is more efficient, especially in a multi-threaded program. Also,
2900 @code{substring/copy} can avoid the problem that a short substring
2901 holds on to the memory of a very large original string that could
2902 otherwise be recycled.
2904 If you want to avoid the copy altogether, so that modifications of one
2905 string show up in the other, you can use @code{substring/shared}. The
2906 strings created by this procedure are called @dfn{mutation sharing
2907 substrings} since the substring and the original string share
2908 modifications to each other.
2910 If you want to prevent modifications, use @code{substring/read-only}.
2912 Guile provides all procedures of SRFI-13 and a few more.
2915 * String Syntax:: Read syntax for strings.
2916 * String Predicates:: Testing strings for certain properties.
2917 * String Constructors:: Creating new string objects.
2918 * List/String Conversion:: Converting from/to lists of characters.
2919 * String Selection:: Select portions from strings.
2920 * String Modification:: Modify parts or whole strings.
2921 * String Comparison:: Lexicographic ordering predicates.
2922 * String Searching:: Searching in strings.
2923 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2924 * Reversing and Appending Strings:: Appending strings to form a new string.
2925 * Mapping Folding and Unfolding:: Iterating over strings.
2926 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2927 * Representing Strings as Bytes:: Encoding and decoding strings.
2928 * Conversion to/from C::
2929 * String Internals:: The storage strategy for strings.
2933 @subsubsection String Read Syntax
2935 @c In the following @code is used to get a good font in TeX etc, but
2936 @c is omitted for Info format, so as not to risk any confusion over
2937 @c whether surrounding ` ' quotes are part of the escape or are
2938 @c special in a string (they're not).
2940 The read syntax for strings is an arbitrarily long sequence of
2941 characters enclosed in double quotes (@nicode{"}).
2943 Backslash is an escape character and can be used to insert the following
2944 special characters. @nicode{\"} and @nicode{\\} are R5RS standard,
2945 @nicode{\|} is R7RS standard, the next seven are R6RS standard ---
2946 notice they follow C syntax --- and the remaining four are Guile
2951 Backslash character.
2954 Double quote character (an unescaped @nicode{"} is otherwise the end
2958 Vertical bar character.
2961 Bell character (ASCII 7).
2964 Formfeed character (ASCII 12).
2967 Newline character (ASCII 10).
2970 Carriage return character (ASCII 13).
2973 Tab character (ASCII 9).
2976 Vertical tab character (ASCII 11).
2979 Backspace character (ASCII 8).
2982 NUL character (ASCII 0).
2984 @item @nicode{\} followed by newline (ASCII 10)
2985 Nothing. This way if @nicode{\} is the last character in a line, the
2986 string will continue with the first character from the next line,
2987 without a line break.
2989 If the @code{hungry-eol-escapes} reader option is enabled, which is not
2990 the case by default, leading whitespace on the next line is discarded.
2996 (read-enable 'hungry-eol-escapes)
3002 Character code given by two hexadecimal digits. For example
3003 @nicode{\x7f} for an ASCII DEL (127).
3005 @item @nicode{\uHHHH}
3006 Character code given by four hexadecimal digits. For example
3007 @nicode{\u0100} for a capital A with macron (U+0100).
3009 @item @nicode{\UHHHHHH}
3010 Character code given by six hexadecimal digits. For example
3015 The following are examples of string literals:
3024 The three escape sequences @code{\xHH}, @code{\uHHHH} and @code{\UHHHHHH} were
3025 chosen to not break compatibility with code written for previous versions of
3026 Guile. The R6RS specification suggests a different, incompatible syntax for hex
3027 escapes: @code{\xHHHH;} -- a character code followed by one to eight hexadecimal
3028 digits terminated with a semicolon. If this escape format is desired instead,
3029 it can be enabled with the reader option @code{r6rs-hex-escapes}.
3032 (read-enable 'r6rs-hex-escapes)
3035 For more on reader options, @xref{Scheme Read}.
3037 @node String Predicates
3038 @subsubsection String Predicates
3040 The following procedures can be used to check whether a given string
3041 fulfills some specified property.
3044 @deffn {Scheme Procedure} string? obj
3045 @deffnx {C Function} scm_string_p (obj)
3046 Return @code{#t} if @var{obj} is a string, else @code{#f}.
3049 @deftypefn {C Function} int scm_is_string (SCM obj)
3050 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
3053 @deffn {Scheme Procedure} string-null? str
3054 @deffnx {C Function} scm_string_null_p (str)
3055 Return @code{#t} if @var{str}'s length is zero, and
3056 @code{#f} otherwise.
3058 (string-null? "") @result{} #t
3060 (string-null? y) @result{} #f
3064 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
3065 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
3066 Check if @var{char_pred} is true for any character in string @var{s}.
3068 @var{char_pred} can be a character to check for any equal to that, or
3069 a character set (@pxref{Character Sets}) to check for any in that set,
3070 or a predicate procedure to call.
3072 For a procedure, calls @code{(@var{char_pred} c)} are made
3073 successively on the characters from @var{start} to @var{end}. If
3074 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
3075 stops and that return value is the return from @code{string-any}. The
3076 call on the last character (ie.@: at @math{@var{end}-1}), if that
3077 point is reached, is a tail call.
3079 If there are no characters in @var{s} (ie.@: @var{start} equals
3080 @var{end}) then the return is @code{#f}.
3083 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
3084 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
3085 Check if @var{char_pred} is true for every character in string
3088 @var{char_pred} can be a character to check for every character equal
3089 to that, or a character set (@pxref{Character Sets}) to check for
3090 every character being in that set, or a predicate procedure to call.
3092 For a procedure, calls @code{(@var{char_pred} c)} are made
3093 successively on the characters from @var{start} to @var{end}. If
3094 @var{char_pred} returns @code{#f}, @code{string-every} stops and
3095 returns @code{#f}. The call on the last character (ie.@: at
3096 @math{@var{end}-1}), if that point is reached, is a tail call and the
3097 return from that call is the return from @code{string-every}.
3099 If there are no characters in @var{s} (ie.@: @var{start} equals
3100 @var{end}) then the return is @code{#t}.
3103 @node String Constructors
3104 @subsubsection String Constructors
3106 The string constructor procedures create new string objects, possibly
3107 initializing them with some specified character data. See also
3108 @xref{String Selection}, for ways to create strings from existing
3111 @c FIXME::martin: list->string belongs into `List/String Conversion'
3113 @deffn {Scheme Procedure} string char@dots{}
3115 Return a newly allocated string made from the given character
3119 (string #\x #\y #\z) @result{} "xyz"
3120 (string) @result{} ""
3124 @deffn {Scheme Procedure} list->string lst
3125 @deffnx {C Function} scm_string (lst)
3126 @rnindex list->string
3127 Return a newly allocated string made from a list of characters.
3130 (list->string '(#\a #\b #\c)) @result{} "abc"
3134 @deffn {Scheme Procedure} reverse-list->string lst
3135 @deffnx {C Function} scm_reverse_list_to_string (lst)
3136 Return a newly allocated string made from a list of characters, in
3140 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
3144 @rnindex make-string
3145 @deffn {Scheme Procedure} make-string k [chr]
3146 @deffnx {C Function} scm_make_string (k, chr)
3147 Return a newly allocated string of
3148 length @var{k}. If @var{chr} is given, then all elements of
3149 the string are initialized to @var{chr}, otherwise the contents
3150 of the string are unspecified.
3153 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
3154 Like @code{scm_make_string}, but expects the length as a
3158 @deffn {Scheme Procedure} string-tabulate proc len
3159 @deffnx {C Function} scm_string_tabulate (proc, len)
3160 @var{proc} is an integer->char procedure. Construct a string
3161 of size @var{len} by applying @var{proc} to each index to
3162 produce the corresponding string element. The order in which
3163 @var{proc} is applied to the indices is not specified.
3166 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
3167 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
3168 Append the string in the string list @var{ls}, using the string
3169 @var{delimiter} as a delimiter between the elements of @var{ls}.
3170 @var{grammar} is a symbol which specifies how the delimiter is
3171 placed between the strings, and defaults to the symbol
3176 Insert the separator between list elements. An empty string
3177 will produce an empty list.
3179 Like @code{infix}, but will raise an error if given the empty
3182 Insert the separator after every list element.
3184 Insert the separator before each list element.
3188 @node List/String Conversion
3189 @subsubsection List/String conversion
3191 When processing strings, it is often convenient to first convert them
3192 into a list representation by using the procedure @code{string->list},
3193 work with the resulting list, and then convert it back into a string.
3194 These procedures are useful for similar tasks.
3196 @rnindex string->list
3197 @deffn {Scheme Procedure} string->list str [start [end]]
3198 @deffnx {C Function} scm_substring_to_list (str, start, end)
3199 @deffnx {C Function} scm_string_to_list (str)
3200 Convert the string @var{str} into a list of characters.
3203 @deffn {Scheme Procedure} string-split str char_pred
3204 @deffnx {C Function} scm_string_split (str, char_pred)
3205 Split the string @var{str} into a list of substrings delimited
3206 by appearances of characters that
3210 equal @var{char_pred}, if it is a character,
3213 satisfy the predicate @var{char_pred}, if it is a procedure,
3216 are in the set @var{char_pred}, if it is a character set.
3219 Note that an empty substring between separator characters will result in
3220 an empty string in the result list.
3223 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
3225 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
3227 (string-split "::" #\:)
3231 (string-split "" #\:)
3238 @node String Selection
3239 @subsubsection String Selection
3241 Portions of strings can be extracted by these procedures.
3242 @code{string-ref} delivers individual characters whereas
3243 @code{substring} can be used to extract substrings from longer strings.
3245 @rnindex string-length
3246 @deffn {Scheme Procedure} string-length string
3247 @deffnx {C Function} scm_string_length (string)
3248 Return the number of characters in @var{string}.
3251 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
3252 Return the number of characters in @var{str} as a @code{size_t}.
3256 @deffn {Scheme Procedure} string-ref str k
3257 @deffnx {C Function} scm_string_ref (str, k)
3258 Return character @var{k} of @var{str} using zero-origin
3259 indexing. @var{k} must be a valid index of @var{str}.
3262 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
3263 Return character @var{k} of @var{str} using zero-origin
3264 indexing. @var{k} must be a valid index of @var{str}.
3267 @rnindex string-copy
3268 @deffn {Scheme Procedure} string-copy str [start [end]]
3269 @deffnx {C Function} scm_substring_copy (str, start, end)
3270 @deffnx {C Function} scm_string_copy (str)
3271 Return a copy of the given string @var{str}.
3273 The returned string shares storage with @var{str} initially, but it is
3274 copied as soon as one of the two strings is modified.
3278 @deffn {Scheme Procedure} substring str start [end]
3279 @deffnx {C Function} scm_substring (str, start, end)
3280 Return a new string formed from the characters
3281 of @var{str} beginning with index @var{start} (inclusive) and
3282 ending with index @var{end} (exclusive).
3283 @var{str} must be a string, @var{start} and @var{end} must be
3284 exact integers satisfying:
3286 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
3288 The returned string shares storage with @var{str} initially, but it is
3289 copied as soon as one of the two strings is modified.
3292 @deffn {Scheme Procedure} substring/shared str start [end]
3293 @deffnx {C Function} scm_substring_shared (str, start, end)
3294 Like @code{substring}, but the strings continue to share their storage
3295 even if they are modified. Thus, modifications to @var{str} show up
3296 in the new string, and vice versa.
3299 @deffn {Scheme Procedure} substring/copy str start [end]
3300 @deffnx {C Function} scm_substring_copy (str, start, end)
3301 Like @code{substring}, but the storage for the new string is copied
3305 @deffn {Scheme Procedure} substring/read-only str start [end]
3306 @deffnx {C Function} scm_substring_read_only (str, start, end)
3307 Like @code{substring}, but the resulting string can not be modified.
3310 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
3311 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
3312 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
3313 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
3314 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
3317 @deffn {Scheme Procedure} string-take s n
3318 @deffnx {C Function} scm_string_take (s, n)
3319 Return the @var{n} first characters of @var{s}.
3322 @deffn {Scheme Procedure} string-drop s n
3323 @deffnx {C Function} scm_string_drop (s, n)
3324 Return all but the first @var{n} characters of @var{s}.
3327 @deffn {Scheme Procedure} string-take-right s n
3328 @deffnx {C Function} scm_string_take_right (s, n)
3329 Return the @var{n} last characters of @var{s}.
3332 @deffn {Scheme Procedure} string-drop-right s n
3333 @deffnx {C Function} scm_string_drop_right (s, n)
3334 Return all but the last @var{n} characters of @var{s}.
3337 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
3338 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
3339 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
3340 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
3341 Take characters @var{start} to @var{end} from the string @var{s} and
3342 either pad with @var{chr} or truncate them to give @var{len}
3345 @code{string-pad} pads or truncates on the left, so for example
3348 (string-pad "x" 3) @result{} " x"
3349 (string-pad "abcde" 3) @result{} "cde"
3352 @code{string-pad-right} pads or truncates on the right, so for example
3355 (string-pad-right "x" 3) @result{} "x "
3356 (string-pad-right "abcde" 3) @result{} "abc"
3360 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
3361 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
3362 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
3363 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
3364 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
3365 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
3366 Trim occurrences of @var{char_pred} from the ends of @var{s}.
3368 @code{string-trim} trims @var{char_pred} characters from the left
3369 (start) of the string, @code{string-trim-right} trims them from the
3370 right (end) of the string, @code{string-trim-both} trims from both
3373 @var{char_pred} can be a character, a character set, or a predicate
3374 procedure to call on each character. If @var{char_pred} is not given
3375 the default is whitespace as per @code{char-set:whitespace}
3376 (@pxref{Standard Character Sets}).
3379 (string-trim " x ") @result{} "x "
3380 (string-trim-right "banana" #\a) @result{} "banan"
3381 (string-trim-both ".,xy:;" char-set:punctuation)
3383 (string-trim-both "xyzzy" (lambda (c)
3390 @node String Modification
3391 @subsubsection String Modification
3393 These procedures are for modifying strings in-place. This means that the
3394 result of the operation is not a new string; instead, the original string's
3395 memory representation is modified.
3397 @rnindex string-set!
3398 @deffn {Scheme Procedure} string-set! str k chr
3399 @deffnx {C Function} scm_string_set_x (str, k, chr)
3400 Store @var{chr} in element @var{k} of @var{str} and return
3401 an unspecified value. @var{k} must be a valid index of
3405 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
3406 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
3409 @rnindex string-fill!
3410 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
3411 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
3412 @deffnx {C Function} scm_string_fill_x (str, chr)
3413 Stores @var{chr} in every element of the given @var{str} and
3414 returns an unspecified value.
3417 @deffn {Scheme Procedure} substring-fill! str start end fill
3418 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
3419 Change every character in @var{str} between @var{start} and
3420 @var{end} to @var{fill}.
3423 (define y (string-copy "abcdefg"))
3424 (substring-fill! y 1 3 #\r)
3430 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
3431 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
3432 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
3433 into @var{str2} beginning at position @var{start2}.
3434 @var{str1} and @var{str2} can be the same string.
3437 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
3438 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
3439 Copy the sequence of characters from index range [@var{start},
3440 @var{end}) in string @var{s} to string @var{target}, beginning
3441 at index @var{tstart}. The characters are copied left-to-right
3442 or right-to-left as needed -- the copy is guaranteed to work,
3443 even if @var{target} and @var{s} are the same string. It is an
3444 error if the copy operation runs off the end of the target
3449 @node String Comparison
3450 @subsubsection String Comparison
3452 The procedures in this section are similar to the character ordering
3453 predicates (@pxref{Characters}), but are defined on character sequences.
3455 The first set is specified in R5RS and has names that end in @code{?}.
3456 The second set is specified in SRFI-13 and the names have not ending
3459 The predicates ending in @code{-ci} ignore the character case
3460 when comparing strings. For now, case-insensitive comparison is done
3461 using the R5RS rules, where every lower-case character that has a
3462 single character upper-case form is converted to uppercase before
3463 comparison. See @xref{Text Collation, the @code{(ice-9
3464 i18n)} module}, for locale-dependent string comparison.
3467 @deffn {Scheme Procedure} string=? s1 s2 s3 @dots{}
3468 Lexicographic equality predicate; return @code{#t} if all strings are
3469 the same length and contain the same characters in the same positions,
3470 otherwise return @code{#f}.
3472 The procedure @code{string-ci=?} treats upper and lower case
3473 letters as though they were the same character, but
3474 @code{string=?} treats upper and lower case as distinct
3479 @deffn {Scheme Procedure} string<? s1 s2 s3 @dots{}
3480 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3481 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3482 lexicographically less than @var{str_i+1}.
3486 @deffn {Scheme Procedure} string<=? s1 s2 s3 @dots{}
3487 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3488 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3489 lexicographically less than or equal to @var{str_i+1}.
3493 @deffn {Scheme Procedure} string>? s1 s2 s3 @dots{}
3494 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3495 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3496 lexicographically greater than @var{str_i+1}.
3500 @deffn {Scheme Procedure} string>=? s1 s2 s3 @dots{}
3501 Lexicographic ordering predicate; return @code{#t} if, for every pair of
3502 consecutive string arguments @var{str_i} and @var{str_i+1}, @var{str_i} is
3503 lexicographically greater than or equal to @var{str_i+1}.
3506 @rnindex string-ci=?
3507 @deffn {Scheme Procedure} string-ci=? s1 s2 s3 @dots{}
3508 Case-insensitive string equality predicate; return @code{#t} if
3509 all strings are the same length and their component
3510 characters match (ignoring case) at each position; otherwise
3514 @rnindex string-ci<?
3515 @deffn {Scheme Procedure} string-ci<? s1 s2 s3 @dots{}
3516 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3517 for every pair of consecutive string arguments @var{str_i} and
3518 @var{str_i+1}, @var{str_i} is lexicographically less than @var{str_i+1}
3523 @deffn {Scheme Procedure} string-ci<=? s1 s2 s3 @dots{}
3524 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3525 for every pair of consecutive string arguments @var{str_i} and
3526 @var{str_i+1}, @var{str_i} is lexicographically less than or equal to
3527 @var{str_i+1} regardless of case.
3530 @rnindex string-ci>?
3531 @deffn {Scheme Procedure} string-ci>? s1 s2 s3 @dots{}
3532 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3533 for every pair of consecutive string arguments @var{str_i} and
3534 @var{str_i+1}, @var{str_i} is lexicographically greater than
3535 @var{str_i+1} regardless of case.
3538 @rnindex string-ci>=?
3539 @deffn {Scheme Procedure} string-ci>=? s1 s2 s3 @dots{}
3540 Case insensitive lexicographic ordering predicate; return @code{#t} if,
3541 for every pair of consecutive string arguments @var{str_i} and
3542 @var{str_i+1}, @var{str_i} is lexicographically greater than or equal to
3543 @var{str_i+1} regardless of case.
3546 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3547 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3548 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3549 mismatch index, depending upon whether @var{s1} is less than,
3550 equal to, or greater than @var{s2}. The mismatch index is the
3551 largest index @var{i} such that for every 0 <= @var{j} <
3552 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3553 @var{i} is the first position that does not match.
3556 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3557 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3558 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3559 mismatch index, depending upon whether @var{s1} is less than,
3560 equal to, or greater than @var{s2}. The mismatch index is the
3561 largest index @var{i} such that for every 0 <= @var{j} <
3562 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3563 @var{i} is the first position where the lowercased letters
3568 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3569 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3570 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3574 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3575 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3576 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3580 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3581 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3582 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3583 true value otherwise.
3586 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3587 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3588 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3589 true value otherwise.
3592 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3593 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3594 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3598 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3599 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3600 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3604 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3605 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3606 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3607 value otherwise. The character comparison is done
3611 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3612 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3613 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3614 value otherwise. The character comparison is done
3618 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3619 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3620 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3621 true value otherwise. The character comparison is done
3625 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3626 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3627 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3628 true value otherwise. The character comparison is done
3632 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3633 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3634 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3635 value otherwise. The character comparison is done
3639 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3640 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3641 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3642 otherwise. The character comparison is done
3646 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3647 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3648 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).
3651 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3652 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3653 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).
3656 Because the same visual appearance of an abstract Unicode character can
3657 be obtained via multiple sequences of Unicode characters, even the
3658 case-insensitive string comparison functions described above may return
3659 @code{#f} when presented with strings containing different
3660 representations of the same character. For example, the Unicode
3661 character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be
3662 represented with a single character (U+1E69) or by the character ``LATIN
3663 SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING
3664 DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307).
3666 For this reason, it is often desirable to ensure that the strings
3667 to be compared are using a mutually consistent representation for every
3668 character. The Unicode standard defines two methods of normalizing the
3669 contents of strings: Decomposition, which breaks composite characters
3670 into a set of constituent characters with an ordering defined by the
3671 Unicode Standard; and composition, which performs the converse.
3673 There are two decomposition operations. ``Canonical decomposition''
3674 produces character sequences that share the same visual appearance as
3675 the original characters, while ``compatibility decomposition'' produces
3676 ones whose visual appearances may differ from the originals but which
3677 represent the same abstract character.
3679 These operations are encapsulated in the following set of normalization
3684 Characters are decomposed to their canonical forms.
3687 Characters are decomposed to their compatibility forms.
3690 Characters are decomposed to their canonical forms, then composed.
3693 Characters are decomposed to their compatibility forms, then composed.
3697 The functions below put their arguments into one of the forms described
3700 @deffn {Scheme Procedure} string-normalize-nfd s
3701 @deffnx {C Function} scm_string_normalize_nfd (s)
3702 Return the @code{NFD} normalized form of @var{s}.
3705 @deffn {Scheme Procedure} string-normalize-nfkd s
3706 @deffnx {C Function} scm_string_normalize_nfkd (s)
3707 Return the @code{NFKD} normalized form of @var{s}.
3710 @deffn {Scheme Procedure} string-normalize-nfc s
3711 @deffnx {C Function} scm_string_normalize_nfc (s)
3712 Return the @code{NFC} normalized form of @var{s}.
3715 @deffn {Scheme Procedure} string-normalize-nfkc s
3716 @deffnx {C Function} scm_string_normalize_nfkc (s)
3717 Return the @code{NFKC} normalized form of @var{s}.
3720 @node String Searching
3721 @subsubsection String Searching
3723 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3724 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3725 Search through the string @var{s} from left to right, returning
3726 the index of the first occurrence of a character which
3730 equals @var{char_pred}, if it is character,
3733 satisfies the predicate @var{char_pred}, if it is a procedure,
3736 is in the set @var{char_pred}, if it is a character set.
3739 Return @code{#f} if no match is found.
3742 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3743 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3744 Search through the string @var{s} from right to left, returning
3745 the index of the last occurrence of a character which
3749 equals @var{char_pred}, if it is character,
3752 satisfies the predicate @var{char_pred}, if it is a procedure,
3755 is in the set if @var{char_pred} is a character set.
3758 Return @code{#f} if no match is found.
3761 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3762 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3763 Return the length of the longest common prefix of the two
3767 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3768 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3769 Return the length of the longest common prefix of the two
3770 strings, ignoring character case.
3773 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3774 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3775 Return the length of the longest common suffix of the two
3779 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3780 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3781 Return the length of the longest common suffix of the two
3782 strings, ignoring character case.
3785 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3786 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3787 Is @var{s1} a prefix of @var{s2}?
3790 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3791 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3792 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3795 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3796 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3797 Is @var{s1} a suffix of @var{s2}?
3800 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3801 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3802 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3805 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3806 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3807 Search through the string @var{s} from right to left, returning
3808 the index of the last occurrence of a character which
3812 equals @var{char_pred}, if it is character,
3815 satisfies the predicate @var{char_pred}, if it is a procedure,
3818 is in the set if @var{char_pred} is a character set.
3821 Return @code{#f} if no match is found.
3824 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3825 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3826 Search through the string @var{s} from left to right, returning
3827 the index of the first occurrence of a character which
3831 does not equal @var{char_pred}, if it is character,
3834 does not satisfy the predicate @var{char_pred}, if it is a
3838 is not in the set if @var{char_pred} is a character set.
3842 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3843 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3844 Search through the string @var{s} from right to left, returning
3845 the index of the last occurrence of a character which
3849 does not equal @var{char_pred}, if it is character,
3852 does not satisfy the predicate @var{char_pred}, if it is a
3856 is not in the set if @var{char_pred} is a character set.
3860 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3861 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3862 Return the count of the number of characters in the string
3867 equals @var{char_pred}, if it is character,
3870 satisfies the predicate @var{char_pred}, if it is a procedure.
3873 is in the set @var{char_pred}, if it is a character set.
3877 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3878 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3879 Does string @var{s1} contain string @var{s2}? Return the index
3880 in @var{s1} where @var{s2} occurs as a substring, or false.
3881 The optional start/end indices restrict the operation to the
3882 indicated substrings.
3885 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3886 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3887 Does string @var{s1} contain string @var{s2}? Return the index
3888 in @var{s1} where @var{s2} occurs as a substring, or false.
3889 The optional start/end indices restrict the operation to the
3890 indicated substrings. Character comparison is done
3894 @node Alphabetic Case Mapping
3895 @subsubsection Alphabetic Case Mapping
3897 These are procedures for mapping strings to their upper- or lower-case
3898 equivalents, respectively, or for capitalizing strings.
3900 They use the basic case mapping rules for Unicode characters. No
3901 special language or context rules are considered. The resulting strings
3902 are guaranteed to be the same length as the input strings.
3904 @xref{Character Case Mapping, the @code{(ice-9
3905 i18n)} module}, for locale-dependent case conversions.
3907 @deffn {Scheme Procedure} string-upcase str [start [end]]
3908 @deffnx {C Function} scm_substring_upcase (str, start, end)
3909 @deffnx {C Function} scm_string_upcase (str)
3910 Upcase every character in @code{str}.
3913 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3914 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3915 @deffnx {C Function} scm_string_upcase_x (str)
3916 Destructively upcase every character in @code{str}.
3926 @deffn {Scheme Procedure} string-downcase str [start [end]]
3927 @deffnx {C Function} scm_substring_downcase (str, start, end)
3928 @deffnx {C Function} scm_string_downcase (str)
3929 Downcase every character in @var{str}.
3932 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3933 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3934 @deffnx {C Function} scm_string_downcase_x (str)
3935 Destructively downcase every character in @var{str}.
3940 (string-downcase! y)
3947 @deffn {Scheme Procedure} string-capitalize str
3948 @deffnx {C Function} scm_string_capitalize (str)
3949 Return a freshly allocated string with the characters in
3950 @var{str}, where the first character of every word is
3954 @deffn {Scheme Procedure} string-capitalize! str
3955 @deffnx {C Function} scm_string_capitalize_x (str)
3956 Upcase the first character of every word in @var{str}
3957 destructively and return @var{str}.
3960 y @result{} "hello world"
3961 (string-capitalize! y) @result{} "Hello World"
3962 y @result{} "Hello World"
3966 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3967 @deffnx {C Function} scm_string_titlecase (str, start, end)
3968 Titlecase every first character in a word in @var{str}.
3971 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3972 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3973 Destructively titlecase every first character in a word in
3977 @node Reversing and Appending Strings
3978 @subsubsection Reversing and Appending Strings
3980 @deffn {Scheme Procedure} string-reverse str [start [end]]
3981 @deffnx {C Function} scm_string_reverse (str, start, end)
3982 Reverse the string @var{str}. The optional arguments
3983 @var{start} and @var{end} delimit the region of @var{str} to
3987 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3988 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3989 Reverse the string @var{str} in-place. The optional arguments
3990 @var{start} and @var{end} delimit the region of @var{str} to
3991 operate on. The return value is unspecified.
3994 @rnindex string-append
3995 @deffn {Scheme Procedure} string-append arg @dots{}
3996 @deffnx {C Function} scm_string_append (args)
3997 Return a newly allocated string whose characters form the
3998 concatenation of the given strings, @var{arg} @enddots{}.
4002 (string-append h "world"))
4003 @result{} "hello world"
4007 @deffn {Scheme Procedure} string-append/shared arg @dots{}
4008 @deffnx {C Function} scm_string_append_shared (args)
4009 Like @code{string-append}, but the result may share memory
4010 with the argument strings.
4013 @deffn {Scheme Procedure} string-concatenate ls
4014 @deffnx {C Function} scm_string_concatenate (ls)
4015 Append the elements (which must be strings) of @var{ls} together into a
4016 single string. Guaranteed to return a freshly allocated string.
4019 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
4020 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
4021 Without optional arguments, this procedure is equivalent to
4024 (string-concatenate (reverse ls))
4027 If the optional argument @var{final_string} is specified, it is
4028 consed onto the beginning to @var{ls} before performing the
4029 list-reverse and string-concatenate operations. If @var{end}
4030 is given, only the characters of @var{final_string} up to index
4033 Guaranteed to return a freshly allocated string.
4036 @deffn {Scheme Procedure} string-concatenate/shared ls
4037 @deffnx {C Function} scm_string_concatenate_shared (ls)
4038 Like @code{string-concatenate}, but the result may share memory
4039 with the strings in the list @var{ls}.
4042 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
4043 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
4044 Like @code{string-concatenate-reverse}, but the result may
4045 share memory with the strings in the @var{ls} arguments.
4048 @node Mapping Folding and Unfolding
4049 @subsubsection Mapping, Folding, and Unfolding
4051 @deffn {Scheme Procedure} string-map proc s [start [end]]
4052 @deffnx {C Function} scm_string_map (proc, s, start, end)
4053 @var{proc} is a char->char procedure, it is mapped over
4054 @var{s}. The order in which the procedure is applied to the
4055 string elements is not specified.
4058 @deffn {Scheme Procedure} string-map! proc s [start [end]]
4059 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
4060 @var{proc} is a char->char procedure, it is mapped over
4061 @var{s}. The order in which the procedure is applied to the
4062 string elements is not specified. The string @var{s} is
4063 modified in-place, the return value is not specified.
4066 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
4067 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
4068 @var{proc} is mapped over @var{s} in left-to-right order. The
4069 return value is not specified.
4072 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
4073 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
4074 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
4077 For example, to change characters to alternately upper and lower case,
4080 (define str (string-copy "studly"))
4081 (string-for-each-index
4084 ((if (even? i) char-upcase char-downcase)
4085 (string-ref str i))))
4087 str @result{} "StUdLy"
4091 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
4092 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
4093 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4094 as the terminating element, from left to right. @var{kons}
4095 must expect two arguments: The actual character and the last
4096 result of @var{kons}' application.
4099 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
4100 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
4101 Fold @var{kons} over the characters of @var{s}, with @var{knil}
4102 as the terminating element, from right to left. @var{kons}
4103 must expect two arguments: The actual character and the last
4104 result of @var{kons}' application.
4107 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
4108 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
4110 @item @var{g} is used to generate a series of @emph{seed}
4111 values from the initial @var{seed}: @var{seed}, (@var{g}
4112 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4114 @item @var{p} tells us when to stop -- when it returns true
4115 when applied to one of these seed values.
4116 @item @var{f} maps each seed value to the corresponding
4117 character in the result string. These chars are assembled
4118 into the string in a left-to-right order.
4119 @item @var{base} is the optional initial/leftmost portion
4120 of the constructed string; it default to the empty
4122 @item @var{make_final} is applied to the terminal seed
4123 value (on which @var{p} returns true) to produce
4124 the final/rightmost portion of the constructed string.
4125 The default is nothing extra.
4129 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
4130 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
4132 @item @var{g} is used to generate a series of @emph{seed}
4133 values from the initial @var{seed}: @var{seed}, (@var{g}
4134 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
4136 @item @var{p} tells us when to stop -- when it returns true
4137 when applied to one of these seed values.
4138 @item @var{f} maps each seed value to the corresponding
4139 character in the result string. These chars are assembled
4140 into the string in a right-to-left order.
4141 @item @var{base} is the optional initial/rightmost portion
4142 of the constructed string; it default to the empty
4144 @item @var{make_final} is applied to the terminal seed
4145 value (on which @var{p} returns true) to produce
4146 the final/leftmost portion of the constructed string.
4147 It defaults to @code{(lambda (x) )}.
4151 @node Miscellaneous String Operations
4152 @subsubsection Miscellaneous String Operations
4154 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
4155 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
4156 This is the @emph{extended substring} procedure that implements
4157 replicated copying of a substring of some string.
4159 @var{s} is a string, @var{start} and @var{end} are optional
4160 arguments that demarcate a substring of @var{s}, defaulting to
4161 0 and the length of @var{s}. Replicate this substring up and
4162 down index space, in both the positive and negative directions.
4163 @code{xsubstring} returns the substring of this string
4164 beginning at index @var{from}, and ending at @var{to}, which
4165 defaults to @var{from} + (@var{end} - @var{start}).
4168 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
4169 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
4170 Exactly the same as @code{xsubstring}, but the extracted text
4171 is written into the string @var{target} starting at index
4172 @var{tstart}. The operation is not defined if @code{(eq?
4173 @var{target} @var{s})} or these arguments share storage -- you
4174 cannot copy a string on top of itself.
4177 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
4178 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
4179 Return the string @var{s1}, but with the characters
4180 @var{start1} @dots{} @var{end1} replaced by the characters
4181 @var{start2} @dots{} @var{end2} from @var{s2}.
4184 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
4185 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
4186 Split the string @var{s} into a list of substrings, where each
4187 substring is a maximal non-empty contiguous sequence of
4188 characters from the character set @var{token_set}, which
4189 defaults to @code{char-set:graphic}.
4190 If @var{start} or @var{end} indices are provided, they restrict
4191 @code{string-tokenize} to operating on the indicated substring
4195 @deffn {Scheme Procedure} string-filter char_pred s [start [end]]
4196 @deffnx {C Function} scm_string_filter (char_pred, s, start, end)
4197 Filter the string @var{s}, retaining only those characters which
4198 satisfy @var{char_pred}.
4200 If @var{char_pred} is a procedure, it is applied to each character as
4201 a predicate, if it is a character, it is tested for equality and if it
4202 is a character set, it is tested for membership.
4205 @deffn {Scheme Procedure} string-delete char_pred s [start [end]]
4206 @deffnx {C Function} scm_string_delete (char_pred, s, start, end)
4207 Delete characters satisfying @var{char_pred} from @var{s}.
4209 If @var{char_pred} is a procedure, it is applied to each character as
4210 a predicate, if it is a character, it is tested for equality and if it
4211 is a character set, it is tested for membership.
4214 @node Representing Strings as Bytes
4215 @subsubsection Representing Strings as Bytes
4217 Out in the cold world outside of Guile, not all strings are treated in
4218 the same way. Out there there are only bytes, and there are many ways
4219 of representing a strings (sequences of characters) as binary data
4220 (sequences of bytes).
4222 As a user, usually you don't have to think about this very much. When
4223 you type on your keyboard, your system encodes your keystrokes as bytes
4224 according to the locale that you have configured on your computer.
4225 Guile uses the locale to decode those bytes back into characters --
4226 hopefully the same characters that you typed in.
4228 All is not so clear when dealing with a system with multiple users, such
4229 as a web server. Your web server might get a request from one user for
4230 data encoded in the ISO-8859-1 character set, and then another request
4231 from a different user for UTF-8 data.
4234 @cindex character encoding
4235 Guile provides an @dfn{iconv} module for converting between strings and
4236 sequences of bytes. @xref{Bytevectors}, for more on how Guile
4237 represents raw byte sequences. This module gets its name from the
4238 common @sc{unix} command of the same name.
4240 Note that often it is sufficient to just read and write strings from
4241 ports instead of using these functions. To do this, specify the port
4242 encoding using @code{set-port-encoding!}. @xref{Ports}, for more on
4243 ports and character encodings.
4245 Unlike the rest of the procedures in this section, you have to load the
4246 @code{iconv} module before having access to these procedures:
4249 (use-modules (ice-9 iconv))
4252 @deffn {Scheme Procedure} string->bytevector string encoding [conversion-strategy]
4253 Encode @var{string} as a sequence of bytes.
4255 The string will be encoded in the character set specified by the
4256 @var{encoding} string. If the string has characters that cannot be
4257 represented in the encoding, by default this procedure raises an
4258 @code{encoding-error}. Pass a @var{conversion-strategy} argument to
4259 specify other behaviors.
4261 The return value is a bytevector. @xref{Bytevectors}, for more on
4262 bytevectors. @xref{Ports}, for more on character encodings and
4263 conversion strategies.
4266 @deffn {Scheme Procedure} bytevector->string bytevector encoding [conversion-strategy]
4267 Decode @var{bytevector} into a string.
4269 The bytes will be decoded from the character set by the @var{encoding}
4270 string. If the bytes do not form a valid encoding, by default this
4271 procedure raises an @code{decoding-error}. As with
4272 @code{string->bytevector}, pass the optional @var{conversion-strategy}
4273 argument to modify this behavior. @xref{Ports}, for more on character
4274 encodings and conversion strategies.
4277 @deffn {Scheme Procedure} call-with-output-encoded-string encoding proc [conversion-strategy]
4278 Like @code{call-with-output-string}, but instead of returning a string,
4279 returns a encoding of the string according to @var{encoding}, as a
4280 bytevector. This procedure can be more efficient than collecting a
4281 string and then converting it via @code{string->bytevector}.
4284 @node Conversion to/from C
4285 @subsubsection Conversion to/from C
4287 When creating a Scheme string from a C string or when converting a
4288 Scheme string to a C string, the concept of character encoding becomes
4291 In C, a string is just a sequence of bytes, and the character encoding
4292 describes the relation between these bytes and the actual characters
4293 that make up the string. For Scheme strings, character encoding is not
4294 an issue (most of the time), since in Scheme you usually treat strings
4295 as character sequences, not byte sequences.
4297 Converting to C and converting from C each have their own challenges.
4299 When converting from C to Scheme, it is important that the sequence of
4300 bytes in the C string be valid with respect to its encoding. ASCII
4301 strings, for example, can't have any bytes greater than 127. An ASCII
4302 byte greater than 127 is considered @emph{ill-formed} and cannot be
4303 converted into a Scheme character.
4305 Problems can occur in the reverse operation as well. Not all character
4306 encodings can hold all possible Scheme characters. Some encodings, like
4307 ASCII for example, can only describe a small subset of all possible
4308 characters. So, when converting to C, one must first decide what to do
4309 with Scheme characters that can't be represented in the C string.
4311 Converting a Scheme string to a C string will often allocate fresh
4312 memory to hold the result. You must take care that this memory is
4313 properly freed eventually. In many cases, this can be achieved by
4314 using @code{scm_dynwind_free} inside an appropriate dynwind context,
4315 @xref{Dynamic Wind}.
4317 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
4318 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
4319 Creates a new Scheme string that has the same contents as @var{str} when
4320 interpreted in the character encoding of the current locale.
4322 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
4324 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
4325 @var{str} in bytes, and @var{str} does not need to be null-terminated.
4326 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
4327 null-terminated and the real length will be found with @code{strlen}.
4329 If the C string is ill-formed, an error will be raised.
4331 Note that these functions should @emph{not} be used to convert C string
4332 constants, because there is no guarantee that the current locale will
4333 match that of the execution character set, used for string and character
4334 constants. Most modern C compilers use UTF-8 by default, so to convert
4335 C string constants we recommend @code{scm_from_utf8_string}.
4338 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
4339 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
4340 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
4341 respectively, but also frees @var{str} with @code{free} eventually.
4342 Thus, you can use this function when you would free @var{str} anyway
4343 immediately after creating the Scheme string. In certain cases, Guile
4344 can then use @var{str} directly as its internal representation.
4347 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
4348 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
4349 Returns a C string with the same contents as @var{str} in the character
4350 encoding of the current locale. The C string must be freed with
4351 @code{free} eventually, maybe by using @code{scm_dynwind_free},
4352 @xref{Dynamic Wind}.
4354 For @code{scm_to_locale_string}, the returned string is
4355 null-terminated and an error is signalled when @var{str} contains
4356 @code{#\nul} characters.
4358 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
4359 @var{str} might contain @code{#\nul} characters and the length of the
4360 returned string in bytes is stored in @code{*@var{lenp}}. The
4361 returned string will not be null-terminated in this case. If
4362 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
4363 @code{scm_to_locale_string}.
4365 If a character in @var{str} cannot be represented in the character
4366 encoding of the current locale, the default port conversion strategy is
4367 used. @xref{Ports}, for more on conversion strategies.
4369 If the conversion strategy is @code{error}, an error will be raised. If
4370 it is @code{substitute}, a replacement character, such as a question
4371 mark, will be inserted in its place. If it is @code{escape}, a hex
4372 escape will be inserted in its place.
4375 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
4376 Puts @var{str} as a C string in the current locale encoding into the
4377 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
4378 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
4379 more than that. No terminating @code{'\0'} will be stored.
4381 The return value of @code{scm_to_locale_stringbuf} is the number of
4382 bytes that are needed for all of @var{str}, regardless of whether
4383 @var{buf} was large enough to hold them. Thus, when the return value
4384 is larger than @var{max_len}, only @var{max_len} bytes have been
4385 stored and you probably need to try again with a larger buffer.
4388 For most situations, string conversion should occur using the current
4389 locale, such as with the functions above. But there may be cases where
4390 one wants to convert strings from a character encoding other than the
4391 locale's character encoding. For these cases, the lower-level functions
4392 @code{scm_to_stringn} and @code{scm_from_stringn} are provided. These
4393 functions should seldom be necessary if one is properly using locales.
4395 @deftp {C Type} scm_t_string_failed_conversion_handler
4396 This is an enumerated type that can take one of three values:
4397 @code{SCM_FAILED_CONVERSION_ERROR},
4398 @code{SCM_FAILED_CONVERSION_QUESTION_MARK}, and
4399 @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}. They are used to indicate
4400 a strategy for handling characters that cannot be converted to or from a
4401 given character encoding. @code{SCM_FAILED_CONVERSION_ERROR} indicates
4402 that a conversion should throw an error if some characters cannot be
4403 converted. @code{SCM_FAILED_CONVERSION_QUESTION_MARK} indicates that a
4404 conversion should replace unconvertable characters with the question
4405 mark character. And, @code{SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE}
4406 requests that a conversion should replace an unconvertable character
4407 with an escape sequence.
4409 While all three strategies apply when converting Scheme strings to C,
4410 only @code{SCM_FAILED_CONVERSION_ERROR} and
4411 @code{SCM_FAILED_CONVERSION_QUESTION_MARK} can be used when converting C
4415 @deftypefn {C Function} char *scm_to_stringn (SCM str, size_t *lenp, const char *encoding, scm_t_string_failed_conversion_handler handler)
4416 This function returns a newly allocated C string from the Guile string
4417 @var{str}. The length of the returned string in bytes will be returned in
4418 @var{lenp}. The character encoding of the C string is passed as the ASCII,
4419 null-terminated C string @var{encoding}. The @var{handler} parameter
4420 gives a strategy for dealing with characters that cannot be converted
4421 into @var{encoding}.
4423 If @var{lenp} is @code{NULL}, this function will return a null-terminated C
4424 string. It will throw an error if the string contains a null
4427 The Scheme interface to this function is @code{string->bytevector}, from the
4428 @code{ice-9 iconv} module. @xref{Representing Strings as Bytes}.
4431 @deftypefn {C Function} SCM scm_from_stringn (const char *str, size_t len, const char *encoding, scm_t_string_failed_conversion_handler handler)
4432 This function returns a scheme string from the C string @var{str}. The
4433 length in bytes of the C string is input as @var{len}. The encoding of the C
4434 string is passed as the ASCII, null-terminated C string @code{encoding}.
4435 The @var{handler} parameters suggests a strategy for dealing with
4436 unconvertable characters.
4438 The Scheme interface to this function is @code{bytevector->string}.
4439 @xref{Representing Strings as Bytes}.
4442 The following conversion functions are provided as a convenience for the
4443 most commonly used encodings.
4445 @deftypefn {C Function} SCM scm_from_latin1_string (const char *str)
4446 @deftypefnx {C Function} SCM scm_from_utf8_string (const char *str)
4447 @deftypefnx {C Function} SCM scm_from_utf32_string (const scm_t_wchar *str)
4448 Return a scheme string from the null-terminated C string @var{str},
4449 which is ISO-8859-1-, UTF-8-, or UTF-32-encoded. These functions should
4450 be used to convert hard-coded C string constants into Scheme strings.
4453 @deftypefn {C Function} SCM scm_from_latin1_stringn (const char *str, size_t len)
4454 @deftypefnx {C Function} SCM scm_from_utf8_stringn (const char *str, size_t len)
4455 @deftypefnx {C Function} SCM scm_from_utf32_stringn (const scm_t_wchar *str, size_t len)
4456 Return a scheme string from C string @var{str}, which is ISO-8859-1-,
4457 UTF-8-, or UTF-32-encoded, of length @var{len}. @var{len} is the number
4458 of bytes pointed to by @var{str} for @code{scm_from_latin1_stringn} and
4459 @code{scm_from_utf8_stringn}; it is the number of elements (code points)
4460 in @var{str} in the case of @code{scm_from_utf32_stringn}.
4463 @deftypefn {C function} char *scm_to_latin1_stringn (SCM str, size_t *lenp)
4464 @deftypefnx {C function} char *scm_to_utf8_stringn (SCM str, size_t *lenp)
4465 @deftypefnx {C function} scm_t_wchar *scm_to_utf32_stringn (SCM str, size_t *lenp)
4466 Return a newly allocated, ISO-8859-1-, UTF-8-, or UTF-32-encoded C string
4467 from Scheme string @var{str}. An error is thrown when @var{str}
4468 cannot be converted to the specified encoding. If @var{lenp} is
4469 @code{NULL}, the returned C string will be null terminated, and an error
4470 will be thrown if the C string would otherwise contain null
4471 characters. If @var{lenp} is not @code{NULL}, the string is not null terminated,
4472 and the length of the returned string is returned in @var{lenp}. The length
4473 returned is the number of bytes for @code{scm_to_latin1_stringn} and
4474 @code{scm_to_utf8_stringn}; it is the number of elements (code points)
4475 for @code{scm_to_utf32_stringn}.
4478 It is not often the case, but sometimes when you are dealing with the
4479 implementation details of a port, you need to encode and decode strings
4480 according to the encoding and conversion strategy of the port. There
4481 are some convenience functions for that purpose as well.
4483 @deftypefn {C Function} SCM scm_from_port_string (const char *str, SCM port)
4484 @deftypefnx {C Function} SCM scm_from_port_stringn (const char *str, size_t len, SCM port)
4485 @deftypefnx {C Function} char* scm_to_port_string (SCM str, SCM port)
4486 @deftypefnx {C Function} char* scm_to_port_stringn (SCM str, size_t *lenp, SCM port)
4487 Like @code{scm_from_stringn} and friends, except they take their
4488 encoding and conversion strategy from a given port object.
4491 @node String Internals
4492 @subsubsection String Internals
4494 Guile stores each string in memory as a contiguous array of Unicode code
4495 points along with an associated set of attributes. If all of the code
4496 points of a string have an integer range between 0 and 255 inclusive,
4497 the code point array is stored as one byte per code point: it is stored
4498 as an ISO-8859-1 (aka Latin-1) string. If any of the code points of the
4499 string has an integer value greater that 255, the code point array is
4500 stored as four bytes per code point: it is stored as a UTF-32 string.
4502 Conversion between the one-byte-per-code-point and
4503 four-bytes-per-code-point representations happens automatically as
4506 No API is provided to set the internal representation of strings;
4507 however, there are pair of procedures available to query it. These are
4508 debugging procedures. Using them in production code is discouraged,
4509 since the details of Guile's internal representation of strings may
4510 change from release to release.
4512 @deffn {Scheme Procedure} string-bytes-per-char str
4513 @deffnx {C Function} scm_string_bytes_per_char (str)
4514 Return the number of bytes used to encode a Unicode code point in string
4515 @var{str}. The result is one or four.
4518 @deffn {Scheme Procedure} %string-dump str
4519 @deffnx {C Function} scm_sys_string_dump (str)
4520 Returns an association list containing debugging information for
4521 @var{str}. The association list has the following entries.
4528 The start index of the string into its stringbuf
4531 The length of the string
4534 If this string is a substring, it returns its
4535 parent string. Otherwise, it returns @code{#f}
4538 @code{#t} if the string is read-only
4540 @item stringbuf-chars
4541 A new string containing this string's stringbuf's characters
4543 @item stringbuf-length
4544 The number of characters in this stringbuf
4546 @item stringbuf-shared
4547 @code{#t} if this stringbuf is shared
4549 @item stringbuf-wide
4550 @code{#t} if this stringbuf's characters are stored in a 32-bit buffer,
4551 or @code{#f} if they are stored in an 8-bit buffer
4557 @subsection Bytevectors
4562 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevectors)}
4563 module provides the programming interface specified by the
4564 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
4565 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
4566 interpret their contents in a number of ways: bytevector contents can be
4567 accessed as signed or unsigned integer of various sizes and endianness,
4568 as IEEE-754 floating point numbers, or as strings. It is a useful tool
4569 to encode and decode binary data.
4571 The R6RS (Section 4.3.4) specifies an external representation for
4572 bytevectors, whereby the octets (integers in the range 0--255) contained
4573 in the bytevector are represented as a list prefixed by @code{#vu8}:
4579 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
4580 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
4581 they do not need to be quoted:
4585 @result{} #vu8(1 53 204)
4588 Bytevectors can be used with the binary input/output primitives of the
4589 R6RS (@pxref{R6RS I/O Ports}).
4592 * Bytevector Endianness:: Dealing with byte order.
4593 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
4594 * Bytevectors as Integers:: Interpreting bytes as integers.
4595 * Bytevectors and Integer Lists:: Converting to/from an integer list.
4596 * Bytevectors as Floats:: Interpreting bytes as real numbers.
4597 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
4598 * Bytevectors as Arrays:: Guile extension to the bytevector API.
4599 * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4.
4602 @node Bytevector Endianness
4603 @subsubsection Endianness
4609 Some of the following procedures take an @var{endianness} parameter.
4610 The @dfn{endianness} is defined as the order of bytes in multi-byte
4611 numbers: numbers encoded in @dfn{big endian} have their most
4612 significant bytes written first, whereas numbers encoded in
4613 @dfn{little endian} have their least significant bytes
4614 first@footnote{Big-endian and little-endian are the most common
4615 ``endiannesses'', but others do exist. For instance, the GNU MP
4616 library allows @dfn{word order} to be specified independently of
4617 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
4618 Multiple Precision Arithmetic Library Manual}).}.
4620 Little-endian is the native endianness of the IA32 architecture and
4621 its derivatives, while big-endian is native to SPARC and PowerPC,
4622 among others. The @code{native-endianness} procedure returns the
4623 native endianness of the machine it runs on.
4625 @deffn {Scheme Procedure} native-endianness
4626 @deffnx {C Function} scm_native_endianness ()
4627 Return a value denoting the native endianness of the host machine.
4630 @deffn {Scheme Macro} endianness symbol
4631 Return an object denoting the endianness specified by @var{symbol}. If
4632 @var{symbol} is neither @code{big} nor @code{little} then an error is
4633 raised at expand-time.
4636 @defvr {C Variable} scm_endianness_big
4637 @defvrx {C Variable} scm_endianness_little
4638 The objects denoting big- and little-endianness, respectively.
4642 @node Bytevector Manipulation
4643 @subsubsection Manipulating Bytevectors
4645 Bytevectors can be created, copied, and analyzed with the following
4646 procedures and C functions.
4648 @deffn {Scheme Procedure} make-bytevector len [fill]
4649 @deffnx {C Function} scm_make_bytevector (len, fill)
4650 @deffnx {C Function} scm_c_make_bytevector (size_t len)
4651 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
4652 is given, fill it with @var{fill}; @var{fill} must be in the range
4656 @deffn {Scheme Procedure} bytevector? obj
4657 @deffnx {C Function} scm_bytevector_p (obj)
4658 Return true if @var{obj} is a bytevector.
4661 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
4662 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
4665 @deffn {Scheme Procedure} bytevector-length bv
4666 @deffnx {C Function} scm_bytevector_length (bv)
4667 Return the length in bytes of bytevector @var{bv}.
4670 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
4671 Likewise, return the length in bytes of bytevector @var{bv}.
4674 @deffn {Scheme Procedure} bytevector=? bv1 bv2
4675 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
4676 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
4677 length and contents.
4680 @deffn {Scheme Procedure} bytevector-fill! bv fill
4681 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
4682 Fill bytevector @var{bv} with @var{fill}, a byte.
4685 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
4686 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
4687 Copy @var{len} bytes from @var{source} into @var{target}, starting
4688 reading from @var{source-start} (a positive index within @var{source})
4689 and start writing at @var{target-start}. It is permitted for the
4690 @var{source} and @var{target} regions to overlap.
4693 @deffn {Scheme Procedure} bytevector-copy bv
4694 @deffnx {C Function} scm_bytevector_copy (bv)
4695 Return a newly allocated copy of @var{bv}.
4698 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
4699 Return the byte at @var{index} in bytevector @var{bv}.
4702 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
4703 Set the byte at @var{index} in @var{bv} to @var{value}.
4706 Low-level C macros are available. They do not perform any
4707 type-checking; as such they should be used with care.
4709 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
4710 Return the length in bytes of bytevector @var{bv}.
4713 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
4714 Return a pointer to the contents of bytevector @var{bv}.
4718 @node Bytevectors as Integers
4719 @subsubsection Interpreting Bytevector Contents as Integers
4721 The contents of a bytevector can be interpreted as a sequence of
4722 integers of any given size, sign, and endianness.
4725 (let ((bv (make-bytevector 4)))
4726 (bytevector-u8-set! bv 0 #x12)
4727 (bytevector-u8-set! bv 1 #x34)
4728 (bytevector-u8-set! bv 2 #x56)
4729 (bytevector-u8-set! bv 3 #x78)
4731 (map (lambda (number)
4732 (number->string number 16))
4733 (list (bytevector-u8-ref bv 0)
4734 (bytevector-u16-ref bv 0 (endianness big))
4735 (bytevector-u32-ref bv 0 (endianness little)))))
4737 @result{} ("12" "1234" "78563412")
4740 The most generic procedures to interpret bytevector contents as integers
4741 are described below.
4743 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
4744 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
4745 Return the @var{size}-byte long unsigned integer at index @var{index} in
4746 @var{bv}, decoded according to @var{endianness}.
4749 @deffn {Scheme Procedure} bytevector-sint-ref bv index endianness size
4750 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
4751 Return the @var{size}-byte long signed integer at index @var{index} in
4752 @var{bv}, decoded according to @var{endianness}.
4755 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
4756 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
4757 Set the @var{size}-byte long unsigned integer at @var{index} to
4758 @var{value}, encoded according to @var{endianness}.
4761 @deffn {Scheme Procedure} bytevector-sint-set! bv index value endianness size
4762 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
4763 Set the @var{size}-byte long signed integer at @var{index} to
4764 @var{value}, encoded according to @var{endianness}.
4767 The following procedures are similar to the ones above, but specialized
4768 to a given integer size:
4770 @deffn {Scheme Procedure} bytevector-u8-ref bv index
4771 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
4772 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
4773 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
4774 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
4775 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
4776 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
4777 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
4778 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
4779 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
4780 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
4781 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
4782 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
4783 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
4784 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
4785 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
4786 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4787 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
4791 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
4792 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
4793 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
4794 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
4795 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
4796 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
4797 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
4798 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
4799 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
4800 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
4801 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
4802 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
4803 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
4804 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
4805 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
4806 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
4807 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4808 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
4812 Finally, a variant specialized for the host's endianness is available
4813 for each of these functions (with the exception of the @code{u8}
4814 accessors, for obvious reasons):
4816 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4817 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4818 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4819 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4820 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4821 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4822 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4823 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4824 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4825 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4826 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4827 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4828 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4829 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4830 host's native endianness.
4833 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4834 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4835 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4836 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4837 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4838 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4839 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4840 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4841 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4842 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4843 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4844 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4845 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4846 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4847 host's native endianness.
4851 @node Bytevectors and Integer Lists
4852 @subsubsection Converting Bytevectors to/from Integer Lists
4854 Bytevector contents can readily be converted to/from lists of signed or
4858 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4859 (endianness little) 2)
4863 @deffn {Scheme Procedure} bytevector->u8-list bv
4864 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4865 Return a newly allocated list of unsigned 8-bit integers from the
4866 contents of @var{bv}.
4869 @deffn {Scheme Procedure} u8-list->bytevector lst
4870 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4871 Return a newly allocated bytevector consisting of the unsigned 8-bit
4872 integers listed in @var{lst}.
4875 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4876 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4877 Return a list of unsigned integers of @var{size} bytes representing the
4878 contents of @var{bv}, decoded according to @var{endianness}.
4881 @deffn {Scheme Procedure} bytevector->sint-list bv endianness size
4882 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4883 Return a list of signed integers of @var{size} bytes representing the
4884 contents of @var{bv}, decoded according to @var{endianness}.
4887 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4888 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4889 Return a new bytevector containing the unsigned integers listed in
4890 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4893 @deffn {Scheme Procedure} sint-list->bytevector lst endianness size
4894 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4895 Return a new bytevector containing the signed integers listed in
4896 @var{lst} and encoded on @var{size} bytes according to @var{endianness}.
4899 @node Bytevectors as Floats
4900 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4902 @cindex IEEE-754 floating point numbers
4904 Bytevector contents can also be accessed as IEEE-754 single- or
4905 double-precision floating point numbers (respectively 32 and 64-bit
4906 long) using the procedures described here.
4908 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4909 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4910 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4911 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4912 Return the IEEE-754 single-precision floating point number from @var{bv}
4913 at @var{index} according to @var{endianness}.
4916 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4917 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4918 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4919 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4920 Store real number @var{value} in @var{bv} at @var{index} according to
4924 Specialized procedures are also available:
4926 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4927 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4928 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4929 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4930 Return the IEEE-754 single-precision floating point number from @var{bv}
4931 at @var{index} according to the host's native endianness.
4934 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4935 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4936 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4937 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4938 Store real number @var{value} in @var{bv} at @var{index} according to
4939 the host's native endianness.
4943 @node Bytevectors as Strings
4944 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4946 @cindex Unicode string encoding
4948 Bytevector contents can also be interpreted as Unicode strings encoded
4949 in one of the most commonly available encoding formats.
4950 @xref{Representing Strings as Bytes}, for a more generic interface.
4953 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4956 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4957 @result{} #vu8(99 97 102 195 169)
4960 @deffn {Scheme Procedure} string->utf8 str
4961 @deffnx {Scheme Procedure} string->utf16 str [endianness]
4962 @deffnx {Scheme Procedure} string->utf32 str [endianness]
4963 @deffnx {C Function} scm_string_to_utf8 (str)
4964 @deffnx {C Function} scm_string_to_utf16 (str, endianness)
4965 @deffnx {C Function} scm_string_to_utf32 (str, endianness)
4966 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4967 UTF-32 (aka. UCS-4) encoding of @var{str}. For UTF-16 and UTF-32,
4968 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4969 it defaults to big endian.
4972 @deffn {Scheme Procedure} utf8->string utf
4973 @deffnx {Scheme Procedure} utf16->string utf [endianness]
4974 @deffnx {Scheme Procedure} utf32->string utf [endianness]
4975 @deffnx {C Function} scm_utf8_to_string (utf)
4976 @deffnx {C Function} scm_utf16_to_string (utf, endianness)
4977 @deffnx {C Function} scm_utf32_to_string (utf, endianness)
4978 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4979 or UTF-32-decoded contents of bytevector @var{utf}. For UTF-16 and UTF-32,
4980 @var{endianness} should be the symbol @code{big} or @code{little}; when omitted,
4981 it defaults to big endian.
4984 @node Bytevectors as Arrays
4985 @subsubsection Accessing Bytevectors with the Array API
4987 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4988 with the @dfn{array} procedures (@pxref{Arrays}). When using these
4989 APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4992 (define bv #vu8(0 1 2 3))
5003 ;; Note the different argument order on array-set!.
5004 (array-set! bv 77 2)
5013 @node Bytevectors as Uniform Vectors
5014 @subsubsection Accessing Bytevectors with the SRFI-4 API
5016 Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and
5017 Bytevectors}, for more information.
5024 Symbols in Scheme are widely used in three ways: as items of discrete
5025 data, as lookup keys for alists and hash tables, and to denote variable
5028 A @dfn{symbol} is similar to a string in that it is defined by a
5029 sequence of characters. The sequence of characters is known as the
5030 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
5031 name doesn't include any characters that could be confused with other
5032 elements of Scheme syntax --- a symbol is written in a Scheme program by
5033 writing the sequence of characters that make up the name, @emph{without}
5034 any quotation marks or other special syntax. For example, the symbol
5035 whose name is ``multiply-by-2'' is written, simply:
5041 Notice how this differs from a @emph{string} with contents
5042 ``multiply-by-2'', which is written with double quotation marks, like
5049 Looking beyond how they are written, symbols are different from strings
5050 in two important respects.
5052 The first important difference is uniqueness. If the same-looking
5053 string is read twice from two different places in a program, the result
5054 is two @emph{different} string objects whose contents just happen to be
5055 the same. If, on the other hand, the same-looking symbol is read twice
5056 from two different places in a program, the result is the @emph{same}
5057 symbol object both times.
5059 Given two read symbols, you can use @code{eq?} to test whether they are
5060 the same (that is, have the same name). @code{eq?} is the most
5061 efficient comparison operator in Scheme, and comparing two symbols like
5062 this is as fast as comparing, for example, two numbers. Given two
5063 strings, on the other hand, you must use @code{equal?} or
5064 @code{string=?}, which are much slower comparison operators, to
5065 determine whether the strings have the same contents.
5068 (define sym1 (quote hello))
5069 (define sym2 (quote hello))
5070 (eq? sym1 sym2) @result{} #t
5072 (define str1 "hello")
5073 (define str2 "hello")
5074 (eq? str1 str2) @result{} #f
5075 (equal? str1 str2) @result{} #t
5078 The second important difference is that symbols, unlike strings, are not
5079 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
5080 example above: @code{(quote hello)} evaluates to the symbol named
5081 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
5082 symbol named "hello" and evaluated as a variable reference @dots{} about
5083 which more below (@pxref{Symbol Variables}).
5086 * Symbol Data:: Symbols as discrete data.
5087 * Symbol Keys:: Symbols as lookup keys.
5088 * Symbol Variables:: Symbols as denoting variables.
5089 * Symbol Primitives:: Operations related to symbols.
5090 * Symbol Props:: Function slots and property lists.
5091 * Symbol Read Syntax:: Extended read syntax for symbols.
5092 * Symbol Uninterned:: Uninterned symbols.
5097 @subsubsection Symbols as Discrete Data
5099 Numbers and symbols are similar to the extent that they both lend
5100 themselves to @code{eq?} comparison. But symbols are more descriptive
5101 than numbers, because a symbol's name can be used directly to describe
5102 the concept for which that symbol stands.
5104 For example, imagine that you need to represent some colours in a
5105 computer program. Using numbers, you would have to choose arbitrarily
5106 some mapping between numbers and colours, and then take care to use that
5107 mapping consistently:
5110 ;; 1=red, 2=green, 3=purple
5112 (if (eq? (colour-of car) 1)
5117 You can make the mapping more explicit and the code more readable by
5125 (if (eq? (colour-of car) red)
5130 But the simplest and clearest approach is not to use numbers at all, but
5131 symbols whose names specify the colours that they refer to:
5134 (if (eq? (colour-of car) 'red)
5138 The descriptive advantages of symbols over numbers increase as the set
5139 of concepts that you want to describe grows. Suppose that a car object
5140 can have other properties as well, such as whether it has or uses:
5144 automatic or manual transmission
5146 leaded or unleaded fuel
5148 power steering (or not).
5152 Then a car's combined property set could be naturally represented and
5153 manipulated as a list of symbols:
5156 (properties-of car1)
5158 (red manual unleaded power-steering)
5160 (if (memq 'power-steering (properties-of car1))
5161 (display "Unfit people can drive this car.\n")
5162 (display "You'll need strong arms to drive this car!\n"))
5164 Unfit people can drive this car.
5167 Remember, the fundamental property of symbols that we are relying on
5168 here is that an occurrence of @code{'red} in one part of a program is an
5169 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
5170 another part of a program; this means that symbols can usefully be
5171 compared using @code{eq?}. At the same time, symbols have naturally
5172 descriptive names. This combination of efficiency and descriptive power
5173 makes them ideal for use as discrete data.
5177 @subsubsection Symbols as Lookup Keys
5179 Given their efficiency and descriptive power, it is natural to use
5180 symbols as the keys in an association list or hash table.
5182 To illustrate this, consider a more structured representation of the car
5183 properties example from the preceding subsection. Rather than
5184 mixing all the properties up together in a flat list, we could use an
5185 association list like this:
5188 (define car1-properties '((colour . red)
5189 (transmission . manual)
5191 (steering . power-assisted)))
5194 Notice how this structure is more explicit and extensible than the flat
5195 list. For example it makes clear that @code{manual} refers to the
5196 transmission rather than, say, the windows or the locking of the car.
5197 It also allows further properties to use the same symbols among their
5198 possible values without becoming ambiguous:
5201 (define car1-properties '((colour . red)
5202 (transmission . manual)
5204 (steering . power-assisted)
5206 (locking . manual)))
5209 With a representation like this, it is easy to use the efficient
5210 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
5211 extract or change individual pieces of information:
5214 (assq-ref car1-properties 'fuel) @result{} unleaded
5215 (assq-ref car1-properties 'transmission) @result{} manual
5217 (assq-set! car1-properties 'seat-colour 'black)
5220 (transmission . manual)
5222 (steering . power-assisted)
5223 (seat-colour . black)
5224 (locking . manual)))
5227 Hash tables also have keys, and exactly the same arguments apply to the
5228 use of symbols in hash tables as in association lists. The hash value
5229 that Guile uses to decide where to add a symbol-keyed entry to a hash
5230 table can be obtained by calling the @code{symbol-hash} procedure:
5232 @deffn {Scheme Procedure} symbol-hash symbol
5233 @deffnx {C Function} scm_symbol_hash (symbol)
5234 Return a hash value for @var{symbol}.
5237 See @ref{Hash Tables} for information about hash tables in general, and
5238 for why you might choose to use a hash table rather than an association
5242 @node Symbol Variables
5243 @subsubsection Symbols as Denoting Variables
5245 When an unquoted symbol in a Scheme program is evaluated, it is
5246 interpreted as a variable reference, and the result of the evaluation is
5247 the appropriate variable's value.
5249 For example, when the expression @code{(string-length "abcd")} is read
5250 and evaluated, the sequence of characters @code{string-length} is read
5251 as the symbol whose name is "string-length". This symbol is associated
5252 with a variable whose value is the procedure that implements string
5253 length calculation. Therefore evaluation of the @code{string-length}
5254 symbol results in that procedure.
5256 The details of the connection between an unquoted symbol and the
5257 variable to which it refers are explained elsewhere. See @ref{Binding
5258 Constructs}, for how associations between symbols and variables are
5259 created, and @ref{Modules}, for how those associations are affected by
5260 Guile's module system.
5263 @node Symbol Primitives
5264 @subsubsection Operations Related to Symbols
5266 Given any Scheme value, you can determine whether it is a symbol using
5267 the @code{symbol?} primitive:
5270 @deffn {Scheme Procedure} symbol? obj
5271 @deffnx {C Function} scm_symbol_p (obj)
5272 Return @code{#t} if @var{obj} is a symbol, otherwise return
5276 @deftypefn {C Function} int scm_is_symbol (SCM val)
5277 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
5280 Once you know that you have a symbol, you can obtain its name as a
5281 string by calling @code{symbol->string}. Note that Guile differs by
5282 default from R5RS on the details of @code{symbol->string} as regards
5285 @rnindex symbol->string
5286 @deffn {Scheme Procedure} symbol->string s
5287 @deffnx {C Function} scm_symbol_to_string (s)
5288 Return the name of symbol @var{s} as a string. By default, Guile reads
5289 symbols case-sensitively, so the string returned will have the same case
5290 variation as the sequence of characters that caused @var{s} to be
5293 If Guile is set to read symbols case-insensitively (as specified by
5294 R5RS), and @var{s} comes into being as part of a literal expression
5295 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
5296 by a call to the @code{read} or @code{string-ci->symbol} procedures,
5297 Guile converts any alphabetic characters in the symbol's name to
5298 lower case before creating the symbol object, so the string returned
5299 here will be in lower case.
5301 If @var{s} was created by @code{string->symbol}, the case of characters
5302 in the string returned will be the same as that in the string that was
5303 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5304 setting at the time @var{s} was created.
5306 It is an error to apply mutation procedures like @code{string-set!} to
5307 strings returned by this procedure.
5310 Most symbols are created by writing them literally in code. However it
5311 is also possible to create symbols programmatically using the following
5314 @deffn {Scheme Procedure} symbol char@dots{}
5316 Return a newly allocated symbol made from the given character arguments.
5319 (symbol #\x #\y #\z) @result{} xyz
5323 @deffn {Scheme Procedure} list->symbol lst
5324 @rnindex list->symbol
5325 Return a newly allocated symbol made from a list of characters.
5328 (list->symbol '(#\a #\b #\c)) @result{} abc
5332 @rnindex symbol-append
5333 @deffn {Scheme Procedure} symbol-append arg @dots{}
5334 Return a newly allocated symbol whose characters form the
5335 concatenation of the given symbols, @var{arg} @enddots{}.
5339 (symbol-append h 'world))
5340 @result{} helloworld
5344 @rnindex string->symbol
5345 @deffn {Scheme Procedure} string->symbol string
5346 @deffnx {C Function} scm_string_to_symbol (string)
5347 Return the symbol whose name is @var{string}. This procedure can create
5348 symbols with names containing special characters or letters in the
5349 non-standard case, but it is usually a bad idea to create such symbols
5350 because in some implementations of Scheme they cannot be read as
5354 @deffn {Scheme Procedure} string-ci->symbol str
5355 @deffnx {C Function} scm_string_ci_to_symbol (str)
5356 Return the symbol whose name is @var{str}. If Guile is currently
5357 reading symbols case-insensitively, @var{str} is converted to lowercase
5358 before the returned symbol is looked up or created.
5361 The following examples illustrate Guile's detailed behaviour as regards
5362 the case-sensitivity of symbols:
5365 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5367 (symbol->string 'flying-fish) @result{} "flying-fish"
5368 (symbol->string 'Martin) @result{} "martin"
5370 (string->symbol "Malvina")) @result{} "Malvina"
5372 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5373 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5374 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5376 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5377 (string=? "K. Harper, M.D."
5379 (string->symbol "K. Harper, M.D."))) @result{} #t
5381 (read-disable 'case-insensitive) ; Guile default behaviour
5383 (symbol->string 'flying-fish) @result{} "flying-fish"
5384 (symbol->string 'Martin) @result{} "Martin"
5386 (string->symbol "Malvina")) @result{} "Malvina"
5388 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5389 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5390 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5392 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5393 (string=? "K. Harper, M.D."
5395 (string->symbol "K. Harper, M.D."))) @result{} #t
5398 From C, there are lower level functions that construct a Scheme symbol
5399 from a C string in the current locale encoding.
5401 When you want to do more from C, you should convert between symbols
5402 and strings using @code{scm_symbol_to_string} and
5403 @code{scm_string_to_symbol} and work with the strings.
5405 @deftypefn {C Function} SCM scm_from_latin1_symbol (const char *name)
5406 @deftypefnx {C Function} SCM scm_from_utf8_symbol (const char *name)
5407 Construct and return a Scheme symbol whose name is specified by the
5408 null-terminated C string @var{name}. These are appropriate when
5409 the C string is hard-coded in the source code.
5412 @deftypefn {C Function} SCM scm_from_locale_symbol (const char *name)
5413 @deftypefnx {C Function} SCM scm_from_locale_symboln (const char *name, size_t len)
5414 Construct and return a Scheme symbol whose name is specified by
5415 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5416 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5417 specified explicitly by @var{len}.
5419 Note that these functions should @emph{not} be used when @var{name} is a
5420 C string constant, because there is no guarantee that the current locale
5421 will match that of the execution character set, used for string and
5422 character constants. Most modern C compilers use UTF-8 by default, so
5423 in such cases we recommend @code{scm_from_utf8_symbol}.
5426 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5427 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5428 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5429 respectively, but also frees @var{str} with @code{free} eventually.
5430 Thus, you can use this function when you would free @var{str} anyway
5431 immediately after creating the Scheme string. In certain cases, Guile
5432 can then use @var{str} directly as its internal representation.
5435 The size of a symbol can also be obtained from C:
5437 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5438 Return the number of characters in @var{sym}.
5441 Finally, some applications, especially those that generate new Scheme
5442 code dynamically, need to generate symbols for use in the generated
5443 code. The @code{gensym} primitive meets this need:
5445 @deffn {Scheme Procedure} gensym [prefix]
5446 @deffnx {C Function} scm_gensym (prefix)
5447 Create a new symbol with a name constructed from a prefix and a counter
5448 value. The string @var{prefix} can be specified as an optional
5449 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5450 at each call. There is no provision for resetting the counter.
5453 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5454 since their names begin with a space and it is only otherwise possible
5455 to generate such symbols if a programmer goes out of their way to do
5456 so. Uniqueness can be guaranteed by instead using uninterned symbols
5457 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5462 @subsubsection Function Slots and Property Lists
5464 In traditional Lisp dialects, symbols are often understood as having
5465 three kinds of value at once:
5469 a @dfn{variable} value, which is used when the symbol appears in
5470 code in a variable reference context
5473 a @dfn{function} value, which is used when the symbol appears in
5474 code in a function name position (i.e.@: as the first element in an
5478 a @dfn{property list} value, which is used when the symbol is given as
5479 the first argument to Lisp's @code{put} or @code{get} functions.
5482 Although Scheme (as one of its simplifications with respect to Lisp)
5483 does away with the distinction between variable and function namespaces,
5484 Guile currently retains some elements of the traditional structure in
5485 case they turn out to be useful when implementing translators for other
5486 languages, in particular Emacs Lisp.
5488 Specifically, Guile symbols have two extra slots, one for a symbol's
5489 property list, and one for its ``function value.'' The following procedures
5490 are provided to access these slots.
5492 @deffn {Scheme Procedure} symbol-fref symbol
5493 @deffnx {C Function} scm_symbol_fref (symbol)
5494 Return the contents of @var{symbol}'s @dfn{function slot}.
5497 @deffn {Scheme Procedure} symbol-fset! symbol value
5498 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5499 Set the contents of @var{symbol}'s function slot to @var{value}.
5502 @deffn {Scheme Procedure} symbol-pref symbol
5503 @deffnx {C Function} scm_symbol_pref (symbol)
5504 Return the @dfn{property list} currently associated with @var{symbol}.
5507 @deffn {Scheme Procedure} symbol-pset! symbol value
5508 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5509 Set @var{symbol}'s property list to @var{value}.
5512 @deffn {Scheme Procedure} symbol-property sym prop
5513 From @var{sym}'s property list, return the value for property
5514 @var{prop}. The assumption is that @var{sym}'s property list is an
5515 association list whose keys are distinguished from each other using
5516 @code{equal?}; @var{prop} should be one of the keys in that list. If
5517 the property list has no entry for @var{prop}, @code{symbol-property}
5521 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5522 In @var{sym}'s property list, set the value for property @var{prop} to
5523 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5524 none already exists. For the structure of the property list, see
5525 @code{symbol-property}.
5528 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5529 From @var{sym}'s property list, remove the entry for property
5530 @var{prop}, if there is one. For the structure of the property list,
5531 see @code{symbol-property}.
5534 Support for these extra slots may be removed in a future release, and it
5535 is probably better to avoid using them. For a more modern and Schemely
5536 approach to properties, see @ref{Object Properties}.
5539 @node Symbol Read Syntax
5540 @subsubsection Extended Read Syntax for Symbols
5542 The read syntax for a symbol is a sequence of letters, digits, and
5543 @dfn{extended alphabetic characters}, beginning with a character that
5544 cannot begin a number. In addition, the special cases of @code{+},
5545 @code{-}, and @code{...} are read as symbols even though numbers can
5546 begin with @code{+}, @code{-} or @code{.}.
5548 Extended alphabetic characters may be used within identifiers as if
5549 they were letters. The set of extended alphabetic characters is:
5552 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5555 In addition to the standard read syntax defined above (which is taken
5556 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5557 Scheme})), Guile provides an extended symbol read syntax that allows the
5558 inclusion of unusual characters such as space characters, newlines and
5559 parentheses. If (for whatever reason) you need to write a symbol
5560 containing characters not mentioned above, you can do so as follows.
5564 Begin the symbol with the characters @code{#@{},
5567 write the characters of the symbol and
5570 finish the symbol with the characters @code{@}#}.
5573 Here are a few examples of this form of read syntax. The first symbol
5574 needs to use extended syntax because it contains a space character, the
5575 second because it contains a line break, and the last because it looks
5587 Although Guile provides this extended read syntax for symbols,
5588 widespread usage of it is discouraged because it is not portable and not
5591 Alternatively, if you enable the @code{r7rs-symbols} read option (see
5592 @pxref{Scheme Read}), you can write arbitrary symbols using the same
5593 notation used for strings, except delimited by vertical bars instead of
5598 |\x3BB; is a greek lambda|
5599 |\| is a vertical bar|
5602 @node Symbol Uninterned
5603 @subsubsection Uninterned Symbols
5605 What makes symbols useful is that they are automatically kept unique.
5606 There are no two symbols that are distinct objects but have the same
5607 name. But of course, there is no rule without exception. In addition
5608 to the normal symbols that have been discussed up to now, you can also
5609 create special @dfn{uninterned} symbols that behave slightly
5612 To understand what is different about them and why they might be useful,
5613 we look at how normal symbols are actually kept unique.
5615 Whenever Guile wants to find the symbol with a specific name, for
5616 example during @code{read} or when executing @code{string->symbol}, it
5617 first looks into a table of all existing symbols to find out whether a
5618 symbol with the given name already exists. When this is the case, Guile
5619 just returns that symbol. When not, a new symbol with the name is
5620 created and entered into the table so that it can be found later.
5622 Sometimes you might want to create a symbol that is guaranteed `fresh',
5623 i.e.@: a symbol that did not exist previously. You might also want to
5624 somehow guarantee that no one else will ever unintentionally stumble
5625 across your symbol in the future. These properties of a symbol are
5626 often needed when generating code during macro expansion. When
5627 introducing new temporary variables, you want to guarantee that they
5628 don't conflict with variables in other people's code.
5630 The simplest way to arrange for this is to create a new symbol but
5631 not enter it into the global table of all symbols. That way, no one
5632 will ever get access to your symbol by chance. Symbols that are not in
5633 the table are called @dfn{uninterned}. Of course, symbols that
5634 @emph{are} in the table are called @dfn{interned}.
5636 You create new uninterned symbols with the function @code{make-symbol}.
5637 You can test whether a symbol is interned or not with
5638 @code{symbol-interned?}.
5640 Uninterned symbols break the rule that the name of a symbol uniquely
5641 identifies the symbol object. Because of this, they can not be written
5642 out and read back in like interned symbols. Currently, Guile has no
5643 support for reading uninterned symbols. Note that the function
5644 @code{gensym} does not return uninterned symbols for this reason.
5646 @deffn {Scheme Procedure} make-symbol name
5647 @deffnx {C Function} scm_make_symbol (name)
5648 Return a new uninterned symbol with the name @var{name}. The returned
5649 symbol is guaranteed to be unique and future calls to
5650 @code{string->symbol} will not return it.
5653 @deffn {Scheme Procedure} symbol-interned? symbol
5654 @deffnx {C Function} scm_symbol_interned_p (symbol)
5655 Return @code{#t} if @var{symbol} is interned, otherwise return
5662 (define foo-1 (string->symbol "foo"))
5663 (define foo-2 (string->symbol "foo"))
5664 (define foo-3 (make-symbol "foo"))
5665 (define foo-4 (make-symbol "foo"))
5669 ; Two interned symbols with the same name are the same object,
5673 ; but a call to make-symbol with the same name returns a
5678 ; A call to make-symbol always returns a new object, even for
5682 @result{} #<uninterned-symbol foo 8085290>
5683 ; Uninterned symbols print differently from interned symbols,
5687 ; but they are still symbols,
5689 (symbol-interned? foo-3)
5691 ; just not interned.
5696 @subsection Keywords
5699 Keywords are self-evaluating objects with a convenient read syntax that
5700 makes them easy to type.
5702 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5703 syntax extension to permit keywords to begin with @code{:} as well as
5704 @code{#:}, or to end with @code{:}.
5707 * Why Use Keywords?:: Motivation for keyword usage.
5708 * Coding With Keywords:: How to use keywords.
5709 * Keyword Read Syntax:: Read syntax for keywords.
5710 * Keyword Procedures:: Procedures for dealing with keywords.
5713 @node Why Use Keywords?
5714 @subsubsection Why Use Keywords?
5716 Keywords are useful in contexts where a program or procedure wants to be
5717 able to accept a large number of optional arguments without making its
5718 interface unmanageable.
5720 To illustrate this, consider a hypothetical @code{make-window}
5721 procedure, which creates a new window on the screen for drawing into
5722 using some graphical toolkit. There are many parameters that the caller
5723 might like to specify, but which could also be sensibly defaulted, for
5728 color depth -- Default: the color depth for the screen
5731 background color -- Default: white
5734 width -- Default: 600
5737 height -- Default: 400
5740 If @code{make-window} did not use keywords, the caller would have to
5741 pass in a value for each possible argument, remembering the correct
5742 argument order and using a special value to indicate the default value
5746 (make-window 'default ;; Color depth
5747 'default ;; Background color
5750 @dots{}) ;; More make-window arguments
5753 With keywords, on the other hand, defaulted arguments are omitted, and
5754 non-default arguments are clearly tagged by the appropriate keyword. As
5755 a result, the invocation becomes much clearer:
5758 (make-window #:width 800 #:height 100)
5761 On the other hand, for a simpler procedure with few arguments, the use
5762 of keywords would be a hindrance rather than a help. The primitive
5763 procedure @code{cons}, for example, would not be improved if it had to
5767 (cons #:car x #:cdr y)
5770 So the decision whether to use keywords or not is purely pragmatic: use
5771 them if they will clarify the procedure invocation at point of call.
5773 @node Coding With Keywords
5774 @subsubsection Coding With Keywords
5776 If a procedure wants to support keywords, it should take a rest argument
5777 and then use whatever means is convenient to extract keywords and their
5778 corresponding arguments from the contents of that rest argument.
5780 The following example illustrates the principle: the code for
5781 @code{make-window} uses a helper procedure called
5782 @code{get-keyword-value} to extract individual keyword arguments from
5786 (define (get-keyword-value args keyword default)
5787 (let ((kv (memq keyword args)))
5788 (if (and kv (>= (length kv) 2))
5792 (define (make-window . args)
5793 (let ((depth (get-keyword-value args #:depth screen-depth))
5794 (bg (get-keyword-value args #:bg "white"))
5795 (width (get-keyword-value args #:width 800))
5796 (height (get-keyword-value args #:height 100))
5801 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5802 optargs)} module provides a set of powerful macros that you can use to
5803 implement keyword-supporting procedures like this:
5806 (use-modules (ice-9 optargs))
5808 (define (make-window . args)
5809 (let-keywords args #f ((depth screen-depth)
5817 Or, even more economically, like this:
5820 (use-modules (ice-9 optargs))
5822 (define* (make-window #:key (depth screen-depth)
5829 For further details on @code{let-keywords}, @code{define*} and other
5830 facilities provided by the @code{(ice-9 optargs)} module, see
5831 @ref{Optional Arguments}.
5833 To handle keyword arguments from procedures implemented in C,
5834 use @code{scm_c_bind_keyword_arguments} (@pxref{Keyword Procedures}).
5836 @node Keyword Read Syntax
5837 @subsubsection Keyword Read Syntax
5839 Guile, by default, only recognizes a keyword syntax that is compatible
5840 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5841 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5842 external representation of the keyword named @code{NAME}. Keyword
5843 objects print using this syntax as well, so values containing keyword
5844 objects can be read back into Guile. When used in an expression,
5845 keywords are self-quoting objects.
5847 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5848 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5849 of the form @code{:NAME} are read as symbols, as required by R5RS.
5851 @cindex SRFI-88 keyword syntax
5853 If the @code{keyword} read option is set to @code{'postfix}, Guile
5854 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5855 Otherwise, tokens of this form are read as symbols.
5857 To enable and disable the alternative non-R5RS keyword syntax, you use
5858 the @code{read-set!} procedure documented @ref{Scheme Read}. Note that
5859 the @code{prefix} and @code{postfix} syntax are mutually exclusive.
5862 (read-set! keywords 'prefix)
5872 (read-set! keywords 'postfix)
5882 (read-set! keywords #f)
5890 ERROR: In expression :type:
5891 ERROR: Unbound variable: :type
5892 ABORT: (unbound-variable)
5895 @node Keyword Procedures
5896 @subsubsection Keyword Procedures
5898 @deffn {Scheme Procedure} keyword? obj
5899 @deffnx {C Function} scm_keyword_p (obj)
5900 Return @code{#t} if the argument @var{obj} is a keyword, else
5904 @deffn {Scheme Procedure} keyword->symbol keyword
5905 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5906 Return the symbol with the same name as @var{keyword}.
5909 @deffn {Scheme Procedure} symbol->keyword symbol
5910 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5911 Return the keyword with the same name as @var{symbol}.
5914 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5915 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5918 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *name)
5919 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *name, size_t len)
5920 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5921 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5922 (@var{name}, @var{len}))}, respectively.
5924 Note that these functions should @emph{not} be used when @var{name} is a
5925 C string constant, because there is no guarantee that the current locale
5926 will match that of the execution character set, used for string and
5927 character constants. Most modern C compilers use UTF-8 by default, so
5928 in such cases we recommend @code{scm_from_utf8_keyword}.
5931 @deftypefn {C Function} SCM scm_from_latin1_keyword (const char *name)
5932 @deftypefnx {C Function} SCM scm_from_utf8_keyword (const char *name)
5933 Equivalent to @code{scm_symbol_to_keyword (scm_from_latin1_symbol
5934 (@var{name}))} and @code{scm_symbol_to_keyword (scm_from_utf8_symbol
5935 (@var{name}))}, respectively.
5938 @deftypefn {C Function} void scm_c_bind_keyword_arguments (const char *subr, @
5939 SCM rest, scm_t_keyword_arguments_flags flags, @
5940 SCM keyword1, SCM *argp1, @
5942 SCM keywordN, SCM *argpN, @
5943 @nicode{SCM_UNDEFINED})
5945 Extract the specified keyword arguments from @var{rest}, which is not
5946 modified. If the keyword argument @var{keyword1} is present in
5947 @var{rest} with an associated value, that value is stored in the
5948 variable pointed to by @var{argp1}, otherwise the variable is left
5949 unchanged. Similarly for the other keywords and argument pointers up to
5950 @var{keywordN} and @var{argpN}. The argument list to
5951 @code{scm_c_bind_keyword_arguments} must be terminated by
5952 @code{SCM_UNDEFINED}.
5954 Note that since the variables pointed to by @var{argp1} through
5955 @var{argpN} are left unchanged if the associated keyword argument is not
5956 present, they should be initialized to their default values before
5957 calling @code{scm_c_bind_keyword_arguments}. Alternatively, you can
5958 initialize them to @code{SCM_UNDEFINED} before the call, and then use
5959 @code{SCM_UNBNDP} after the call to see which ones were provided.
5961 If an unrecognized keyword argument is present in @var{rest} and
5962 @var{flags} does not contain @code{SCM_ALLOW_OTHER_KEYS}, or if
5963 non-keyword arguments are present and @var{flags} does not contain
5964 @code{SCM_ALLOW_NON_KEYWORD_ARGUMENTS}, an exception is raised.
5965 @var{subr} should be the name of the procedure receiving the keyword
5966 arguments, for purposes of error reporting.
5975 SCM my_string_join (SCM strings, SCM rest)
5977 SCM delimiter = SCM_UNDEFINED;
5978 SCM grammar = sym_infix;
5980 scm_c_bind_keyword_arguments ("my-string-join", rest, 0,
5981 k_delimiter, &delimiter,
5982 k_grammar, &grammar,
5985 if (SCM_UNBNDP (delimiter))
5986 delimiter = scm_from_utf8_string (" ");
5988 return scm_string_join (strings, delimiter, grammar);
5993 k_delimiter = scm_from_utf8_keyword ("delimiter");
5994 k_grammar = scm_from_utf8_keyword ("grammar");
5995 sym_infix = scm_from_utf8_symbol ("infix");
5996 scm_c_define_gsubr ("my-string-join", 1, 0, 1, my_string_join);
6003 @subsection ``Functionality-Centric'' Data Types
6005 Procedures and macros are documented in their own sections: see
6006 @ref{Procedures} and @ref{Macros}.
6008 Variable objects are documented as part of the description of Guile's
6009 module system: see @ref{Variables}.
6011 Asyncs, dynamic roots and fluids are described in the section on
6012 scheduling: see @ref{Scheduling}.
6014 Hooks are documented in the section on general utility functions: see
6017 Ports are described in the section on I/O: see @ref{Input and Output}.
6019 Regular expressions are described in their own section: see @ref{Regular
6023 @c TeX-master: "guile.texi"