2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010
4 @c Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @node Simple Data Types
9 @section Simple Generic Data Types
11 This chapter describes those of Guile's simple data types which are
12 primarily used for their role as items of generic data. By
13 @dfn{simple} we mean data types that are not primarily used as
14 containers to hold other data --- i.e.@: pairs, lists, vectors and so on.
15 For the documentation of such @dfn{compound} data types, see
16 @ref{Compound Data Types}.
18 @c One of the great strengths of Scheme is that there is no straightforward
19 @c distinction between ``data'' and ``functionality''. For example,
20 @c Guile's support for dynamic linking could be described:
24 @c either in a ``data-centric'' way, as the behaviour and properties of the
25 @c ``dynamically linked object'' data type, and the operations that may be
26 @c applied to instances of this type
29 @c or in a ``functionality-centric'' way, as the set of procedures that
30 @c constitute Guile's support for dynamic linking, in the context of the
34 @c The contents of this chapter are, therefore, a matter of judgment. By
35 @c @dfn{generic}, we mean to select those data types whose typical use as
36 @c @emph{data} in a wide variety of programming contexts is more important
37 @c than their use in the implementation of a particular piece of
38 @c @emph{functionality}. The last section of this chapter provides
39 @c references for all the data types that are documented not here but in a
40 @c ``functionality-centric'' way elsewhere in the manual.
43 * Booleans:: True/false values.
44 * Numbers:: Numerical data types.
45 * Characters:: Single characters.
46 * Character Sets:: Sets of characters.
47 * Strings:: Sequences of characters.
48 * Bytevectors:: Sequences of bytes.
49 * Regular Expressions:: Pattern matching and substitution.
51 * Keywords:: Self-quoting, customizable display keywords.
52 * Other Types:: "Functionality-centric" data types.
60 The two boolean values are @code{#t} for true and @code{#f} for false.
62 Boolean values are returned by predicate procedures, such as the general
63 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
64 (@pxref{Equality}) and numerical and string comparison operators like
65 @code{string=?} (@pxref{String Comparison}) and @code{<=}
75 (equal? "house" "houses")
83 In test condition contexts like @code{if} and @code{cond} (@pxref{if
84 cond case}), where a group of subexpressions will be evaluated only if a
85 @var{condition} expression evaluates to ``true'', ``true'' means any
86 value at all except @code{#f}.
99 A result of this asymmetry is that typical Scheme source code more often
100 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
101 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
102 not necessary to represent an @code{if} or @code{cond} true value.
104 It is important to note that @code{#f} is @strong{not} equivalent to any
105 other Scheme value. In particular, @code{#f} is not the same as the
106 number 0 (like in C and C++), and not the same as the ``empty list''
107 (like in some Lisp dialects).
109 In C, the two Scheme boolean values are available as the two constants
110 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
111 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
112 false when used in C conditionals. In order to test for it, use
113 @code{scm_is_false} or @code{scm_is_true}.
116 @deffn {Scheme Procedure} not x
117 @deffnx {C Function} scm_not (x)
118 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
122 @deffn {Scheme Procedure} boolean? obj
123 @deffnx {C Function} scm_boolean_p (obj)
124 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
128 @deftypevr {C Macro} SCM SCM_BOOL_T
129 The @code{SCM} representation of the Scheme object @code{#t}.
132 @deftypevr {C Macro} SCM SCM_BOOL_F
133 The @code{SCM} representation of the Scheme object @code{#f}.
136 @deftypefn {C Function} int scm_is_true (SCM obj)
137 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
140 @deftypefn {C Function} int scm_is_false (SCM obj)
141 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
144 @deftypefn {C Function} int scm_is_bool (SCM obj)
145 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
149 @deftypefn {C Function} SCM scm_from_bool (int val)
150 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
153 @deftypefn {C Function} int scm_to_bool (SCM val)
154 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
155 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
157 You should probably use @code{scm_is_true} instead of this function
158 when you just want to test a @code{SCM} value for trueness.
162 @subsection Numerical data types
165 Guile supports a rich ``tower'' of numerical types --- integer,
166 rational, real and complex --- and provides an extensive set of
167 mathematical and scientific functions for operating on numerical
168 data. This section of the manual documents those types and functions.
170 You may also find it illuminating to read R5RS's presentation of numbers
171 in Scheme, which is particularly clear and accessible: see
172 @ref{Numbers,,,r5rs,R5RS}.
175 * Numerical Tower:: Scheme's numerical "tower".
176 * Integers:: Whole numbers.
177 * Reals and Rationals:: Real and rational numbers.
178 * Complex Numbers:: Complex numbers.
179 * Exactness:: Exactness and inexactness.
180 * Number Syntax:: Read syntax for numerical data.
181 * Integer Operations:: Operations on integer values.
182 * Comparison:: Comparison predicates.
183 * Conversion:: Converting numbers to and from strings.
184 * Complex:: Complex number operations.
185 * Arithmetic:: Arithmetic functions.
186 * Scientific:: Scientific functions.
187 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
188 * Random:: Random number generation.
192 @node Numerical Tower
193 @subsubsection Scheme's Numerical ``Tower''
196 Scheme's numerical ``tower'' consists of the following categories of
201 Whole numbers, positive or negative; e.g.@: --5, 0, 18.
204 The set of numbers that can be expressed as @math{@var{p}/@var{q}}
205 where @var{p} and @var{q} are integers; e.g.@: @math{9/16} works, but
206 pi (an irrational number) doesn't. These include integers
210 The set of numbers that describes all possible positions along a
211 one-dimensional line. This includes rationals as well as irrational
214 @item complex numbers
215 The set of numbers that describes all possible positions in a two
216 dimensional space. This includes real as well as imaginary numbers
217 (@math{@var{a}+@var{b}i}, where @var{a} is the @dfn{real part},
218 @var{b} is the @dfn{imaginary part}, and @math{i} is the square root of
222 It is called a tower because each category ``sits on'' the one that
223 follows it, in the sense that every integer is also a rational, every
224 rational is also real, and every real number is also a complex number
225 (but with zero imaginary part).
227 In addition to the classification into integers, rationals, reals and
228 complex numbers, Scheme also distinguishes between whether a number is
229 represented exactly or not. For example, the result of
230 @m{2\sin(\pi/4),2*sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)}, but Guile
231 can represent neither @m{\pi/4,pi/4} nor @m{\sqrt{2},2^(1/2)} exactly.
232 Instead, it stores an inexact approximation, using the C type
235 Guile can represent exact rationals of any magnitude, inexact
236 rationals that fit into a C @code{double}, and inexact complex numbers
237 with @code{double} real and imaginary parts.
239 The @code{number?} predicate may be applied to any Scheme value to
240 discover whether the value is any of the supported numerical types.
242 @deffn {Scheme Procedure} number? obj
243 @deffnx {C Function} scm_number_p (obj)
244 Return @code{#t} if @var{obj} is any kind of number, else @code{#f}.
253 (number? "hello there!")
256 (define pi 3.141592654)
261 @deftypefn {C Function} int scm_is_number (SCM obj)
262 This is equivalent to @code{scm_is_true (scm_number_p (obj))}.
265 The next few subsections document each of Guile's numerical data types
269 @subsubsection Integers
271 @tpindex Integer numbers
275 Integers are whole numbers, that is numbers with no fractional part,
276 such as 2, 83, and @minus{}3789.
278 Integers in Guile can be arbitrarily big, as shown by the following
282 (define (factorial n)
283 (let loop ((n n) (product 1))
286 (loop (- n 1) (* product n)))))
292 @result{} 2432902008176640000
295 @result{} -119622220865480194561963161495657715064383733760000000000
298 Readers whose background is in programming languages where integers are
299 limited by the need to fit into just 4 or 8 bytes of memory may find
300 this surprising, or suspect that Guile's representation of integers is
301 inefficient. In fact, Guile achieves a near optimal balance of
302 convenience and efficiency by using the host computer's native
303 representation of integers where possible, and a more general
304 representation where the required number does not fit in the native
305 form. Conversion between these two representations is automatic and
306 completely invisible to the Scheme level programmer.
308 The infinities @samp{+inf.0} and @samp{-inf.0} are considered to be
309 inexact integers. They are explained in detail in the next section,
310 together with reals and rationals.
312 C has a host of different integer types, and Guile offers a host of
313 functions to convert between them and the @code{SCM} representation.
314 For example, a C @code{int} can be handled with @code{scm_to_int} and
315 @code{scm_from_int}. Guile also defines a few C integer types of its
316 own, to help with differences between systems.
318 C integer types that are not covered can be handled with the generic
319 @code{scm_to_signed_integer} and @code{scm_from_signed_integer} for
320 signed types, or with @code{scm_to_unsigned_integer} and
321 @code{scm_from_unsigned_integer} for unsigned types.
323 Scheme integers can be exact and inexact. For example, a number
324 written as @code{3.0} with an explicit decimal-point is inexact, but
325 it is also an integer. The functions @code{integer?} and
326 @code{scm_is_integer} report true for such a number, but the functions
327 @code{scm_is_signed_integer} and @code{scm_is_unsigned_integer} only
328 allow exact integers and thus report false. Likewise, the conversion
329 functions like @code{scm_to_signed_integer} only accept exact
332 The motivation for this behavior is that the inexactness of a number
333 should not be lost silently. If you want to allow inexact integers,
334 you can explicitly insert a call to @code{inexact->exact} or to its C
335 equivalent @code{scm_inexact_to_exact}. (Only inexact integers will
336 be converted by this call into exact integers; inexact non-integers
337 will become exact fractions.)
339 @deffn {Scheme Procedure} integer? x
340 @deffnx {C Function} scm_integer_p (x)
341 Return @code{#t} if @var{x} is an exact or inexact integer number, else
359 @deftypefn {C Function} int scm_is_integer (SCM x)
360 This is equivalent to @code{scm_is_true (scm_integer_p (x))}.
363 @defvr {C Type} scm_t_int8
364 @defvrx {C Type} scm_t_uint8
365 @defvrx {C Type} scm_t_int16
366 @defvrx {C Type} scm_t_uint16
367 @defvrx {C Type} scm_t_int32
368 @defvrx {C Type} scm_t_uint32
369 @defvrx {C Type} scm_t_int64
370 @defvrx {C Type} scm_t_uint64
371 @defvrx {C Type} scm_t_intmax
372 @defvrx {C Type} scm_t_uintmax
373 The C types are equivalent to the corresponding ISO C types but are
374 defined on all platforms, with the exception of @code{scm_t_int64} and
375 @code{scm_t_uint64}, which are only defined when a 64-bit type is
376 available. For example, @code{scm_t_int8} is equivalent to
379 You can regard these definitions as a stop-gap measure until all
380 platforms provide these types. If you know that all the platforms
381 that you are interested in already provide these types, it is better
382 to use them directly instead of the types provided by Guile.
385 @deftypefn {C Function} int scm_is_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
386 @deftypefnx {C Function} int scm_is_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
387 Return @code{1} when @var{x} represents an exact integer that is
388 between @var{min} and @var{max}, inclusive.
390 These functions can be used to check whether a @code{SCM} value will
391 fit into a given range, such as the range of a given C integer type.
392 If you just want to convert a @code{SCM} value to a given C integer
393 type, use one of the conversion functions directly.
396 @deftypefn {C Function} scm_t_intmax scm_to_signed_integer (SCM x, scm_t_intmax min, scm_t_intmax max)
397 @deftypefnx {C Function} scm_t_uintmax scm_to_unsigned_integer (SCM x, scm_t_uintmax min, scm_t_uintmax max)
398 When @var{x} represents an exact integer that is between @var{min} and
399 @var{max} inclusive, return that integer. Else signal an error,
400 either a `wrong-type' error when @var{x} is not an exact integer, or
401 an `out-of-range' error when it doesn't fit the given range.
404 @deftypefn {C Function} SCM scm_from_signed_integer (scm_t_intmax x)
405 @deftypefnx {C Function} SCM scm_from_unsigned_integer (scm_t_uintmax x)
406 Return the @code{SCM} value that represents the integer @var{x}. This
407 function will always succeed and will always return an exact number.
410 @deftypefn {C Function} char scm_to_char (SCM x)
411 @deftypefnx {C Function} {signed char} scm_to_schar (SCM x)
412 @deftypefnx {C Function} {unsigned char} scm_to_uchar (SCM x)
413 @deftypefnx {C Function} short scm_to_short (SCM x)
414 @deftypefnx {C Function} {unsigned short} scm_to_ushort (SCM x)
415 @deftypefnx {C Function} int scm_to_int (SCM x)
416 @deftypefnx {C Function} {unsigned int} scm_to_uint (SCM x)
417 @deftypefnx {C Function} long scm_to_long (SCM x)
418 @deftypefnx {C Function} {unsigned long} scm_to_ulong (SCM x)
419 @deftypefnx {C Function} {long long} scm_to_long_long (SCM x)
420 @deftypefnx {C Function} {unsigned long long} scm_to_ulong_long (SCM x)
421 @deftypefnx {C Function} size_t scm_to_size_t (SCM x)
422 @deftypefnx {C Function} ssize_t scm_to_ssize_t (SCM x)
423 @deftypefnx {C Function} scm_t_int8 scm_to_int8 (SCM x)
424 @deftypefnx {C Function} scm_t_uint8 scm_to_uint8 (SCM x)
425 @deftypefnx {C Function} scm_t_int16 scm_to_int16 (SCM x)
426 @deftypefnx {C Function} scm_t_uint16 scm_to_uint16 (SCM x)
427 @deftypefnx {C Function} scm_t_int32 scm_to_int32 (SCM x)
428 @deftypefnx {C Function} scm_t_uint32 scm_to_uint32 (SCM x)
429 @deftypefnx {C Function} scm_t_int64 scm_to_int64 (SCM x)
430 @deftypefnx {C Function} scm_t_uint64 scm_to_uint64 (SCM x)
431 @deftypefnx {C Function} scm_t_intmax scm_to_intmax (SCM x)
432 @deftypefnx {C Function} scm_t_uintmax scm_to_uintmax (SCM x)
433 When @var{x} represents an exact integer that fits into the indicated
434 C type, return that integer. Else signal an error, either a
435 `wrong-type' error when @var{x} is not an exact integer, or an
436 `out-of-range' error when it doesn't fit the given range.
438 The functions @code{scm_to_long_long}, @code{scm_to_ulong_long},
439 @code{scm_to_int64}, and @code{scm_to_uint64} are only available when
440 the corresponding types are.
443 @deftypefn {C Function} SCM scm_from_char (char x)
444 @deftypefnx {C Function} SCM scm_from_schar (signed char x)
445 @deftypefnx {C Function} SCM scm_from_uchar (unsigned char x)
446 @deftypefnx {C Function} SCM scm_from_short (short x)
447 @deftypefnx {C Function} SCM scm_from_ushort (unsigned short x)
448 @deftypefnx {C Function} SCM scm_from_int (int x)
449 @deftypefnx {C Function} SCM scm_from_uint (unsigned int x)
450 @deftypefnx {C Function} SCM scm_from_long (long x)
451 @deftypefnx {C Function} SCM scm_from_ulong (unsigned long x)
452 @deftypefnx {C Function} SCM scm_from_long_long (long long x)
453 @deftypefnx {C Function} SCM scm_from_ulong_long (unsigned long long x)
454 @deftypefnx {C Function} SCM scm_from_size_t (size_t x)
455 @deftypefnx {C Function} SCM scm_from_ssize_t (ssize_t x)
456 @deftypefnx {C Function} SCM scm_from_int8 (scm_t_int8 x)
457 @deftypefnx {C Function} SCM scm_from_uint8 (scm_t_uint8 x)
458 @deftypefnx {C Function} SCM scm_from_int16 (scm_t_int16 x)
459 @deftypefnx {C Function} SCM scm_from_uint16 (scm_t_uint16 x)
460 @deftypefnx {C Function} SCM scm_from_int32 (scm_t_int32 x)
461 @deftypefnx {C Function} SCM scm_from_uint32 (scm_t_uint32 x)
462 @deftypefnx {C Function} SCM scm_from_int64 (scm_t_int64 x)
463 @deftypefnx {C Function} SCM scm_from_uint64 (scm_t_uint64 x)
464 @deftypefnx {C Function} SCM scm_from_intmax (scm_t_intmax x)
465 @deftypefnx {C Function} SCM scm_from_uintmax (scm_t_uintmax x)
466 Return the @code{SCM} value that represents the integer @var{x}.
467 These functions will always succeed and will always return an exact
471 @deftypefn {C Function} void scm_to_mpz (SCM val, mpz_t rop)
472 Assign @var{val} to the multiple precision integer @var{rop}.
473 @var{val} must be an exact integer, otherwise an error will be
474 signalled. @var{rop} must have been initialized with @code{mpz_init}
475 before this function is called. When @var{rop} is no longer needed
476 the occupied space must be freed with @code{mpz_clear}.
477 @xref{Initializing Integers,,, gmp, GNU MP Manual}, for details.
480 @deftypefn {C Function} SCM scm_from_mpz (mpz_t val)
481 Return the @code{SCM} value that represents @var{val}.
484 @node Reals and Rationals
485 @subsubsection Real and Rational Numbers
486 @tpindex Real numbers
487 @tpindex Rational numbers
492 Mathematically, the real numbers are the set of numbers that describe
493 all possible points along a continuous, infinite, one-dimensional line.
494 The rational numbers are the set of all numbers that can be written as
495 fractions @var{p}/@var{q}, where @var{p} and @var{q} are integers.
496 All rational numbers are also real, but there are real numbers that
497 are not rational, for example @m{\sqrt2, the square root of 2}, and
500 Guile can represent both exact and inexact rational numbers, but it
501 can not represent irrational numbers. Exact rationals are represented
502 by storing the numerator and denominator as two exact integers.
503 Inexact rationals are stored as floating point numbers using the C
506 Exact rationals are written as a fraction of integers. There must be
507 no whitespace around the slash:
514 Even though the actual encoding of inexact rationals is in binary, it
515 may be helpful to think of it as a decimal number with a limited
516 number of significant figures and a decimal point somewhere, since
517 this corresponds to the standard notation for non-whole numbers. For
523 -5648394822220000000000.0
527 The limited precision of Guile's encoding means that any ``real'' number
528 in Guile can be written in a rational form, by multiplying and then dividing
529 by sufficient powers of 10 (or in fact, 2). For example,
530 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided by
531 100000000000000000. In Guile's current incarnation, therefore, the
532 @code{rational?} and @code{real?} predicates are equivalent.
535 Dividing by an exact zero leads to a error message, as one might
536 expect. However, dividing by an inexact zero does not produce an
537 error. Instead, the result of the division is either plus or minus
538 infinity, depending on the sign of the divided number.
540 The infinities are written @samp{+inf.0} and @samp{-inf.0},
541 respectively. This syntax is also recognized by @code{read} as an
542 extension to the usual Scheme syntax.
544 Dividing zero by zero yields something that is not a number at all:
545 @samp{+nan.0}. This is the special `not a number' value.
547 On platforms that follow @acronym{IEEE} 754 for their floating point
548 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
549 are implemented using the corresponding @acronym{IEEE} 754 values.
550 They behave in arithmetic operations like @acronym{IEEE} 754 describes
551 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
553 The infinities are inexact integers and are considered to be both even
554 and odd. While @samp{+nan.0} is not @code{=} to itself, it is
555 @code{eqv?} to itself.
557 To test for the special values, use the functions @code{inf?} and
560 @deffn {Scheme Procedure} real? obj
561 @deffnx {C Function} scm_real_p (obj)
562 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
563 that the sets of integer and rational values form subsets of the set
564 of real numbers, so the predicate will also be fulfilled if @var{obj}
565 is an integer number or a rational number.
568 @deffn {Scheme Procedure} rational? x
569 @deffnx {C Function} scm_rational_p (x)
570 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
571 Note that the set of integer values forms a subset of the set of
572 rational numbers, i. e. the predicate will also be fulfilled if
573 @var{x} is an integer number.
575 Since Guile can not represent irrational numbers, every number
576 satisfying @code{real?} also satisfies @code{rational?} in Guile.
579 @deffn {Scheme Procedure} rationalize x eps
580 @deffnx {C Function} scm_rationalize (x, eps)
581 Returns the @emph{simplest} rational number differing
582 from @var{x} by no more than @var{eps}.
584 As required by @acronym{R5RS}, @code{rationalize} only returns an
585 exact result when both its arguments are exact. Thus, you might need
586 to use @code{inexact->exact} on the arguments.
589 (rationalize (inexact->exact 1.2) 1/100)
595 @deffn {Scheme Procedure} inf? x
596 @deffnx {C Function} scm_inf_p (x)
597 Return @code{#t} if @var{x} is either @samp{+inf.0} or @samp{-inf.0},
601 @deffn {Scheme Procedure} nan? x
602 @deffnx {C Function} scm_nan_p (x)
603 Return @code{#t} if @var{x} is @samp{+nan.0}, @code{#f} otherwise.
606 @deffn {Scheme Procedure} nan
607 @deffnx {C Function} scm_nan ()
611 @deffn {Scheme Procedure} inf
612 @deffnx {C Function} scm_inf ()
616 @deffn {Scheme Procedure} numerator x
617 @deffnx {C Function} scm_numerator (x)
618 Return the numerator of the rational number @var{x}.
621 @deffn {Scheme Procedure} denominator x
622 @deffnx {C Function} scm_denominator (x)
623 Return the denominator of the rational number @var{x}.
626 @deftypefn {C Function} int scm_is_real (SCM val)
627 @deftypefnx {C Function} int scm_is_rational (SCM val)
628 Equivalent to @code{scm_is_true (scm_real_p (val))} and
629 @code{scm_is_true (scm_rational_p (val))}, respectively.
632 @deftypefn {C Function} double scm_to_double (SCM val)
633 Returns the number closest to @var{val} that is representable as a
634 @code{double}. Returns infinity for a @var{val} that is too large in
635 magnitude. The argument @var{val} must be a real number.
638 @deftypefn {C Function} SCM scm_from_double (double val)
639 Return the @code{SCM} value that represents @var{val}. The returned
640 value is inexact according to the predicate @code{inexact?}, but it
641 will be exactly equal to @var{val}.
644 @node Complex Numbers
645 @subsubsection Complex Numbers
646 @tpindex Complex numbers
650 Complex numbers are the set of numbers that describe all possible points
651 in a two-dimensional space. The two coordinates of a particular point
652 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
653 the complex number that describes that point.
655 In Guile, complex numbers are written in rectangular form as the sum of
656 their real and imaginary parts, using the symbol @code{i} to indicate
671 Polar form can also be used, with an @samp{@@} between magnitude and
675 1@@3.141592 @result{} -1.0 (approx)
676 -1@@1.57079 @result{} 0.0-1.0i (approx)
679 Guile represents a complex number with a non-zero imaginary part as a
680 pair of inexact rationals, so the real and imaginary parts of a
681 complex number have the same properties of inexactness and limited
682 precision as single inexact rational numbers. Guile can not represent
683 exact complex numbers with non-zero imaginary parts.
685 @deffn {Scheme Procedure} complex? z
686 @deffnx {C Function} scm_complex_p (z)
687 Return @code{#t} if @var{x} is a complex number, @code{#f}
688 otherwise. Note that the sets of real, rational and integer
689 values form subsets of the set of complex numbers, i. e. the
690 predicate will also be fulfilled if @var{x} is a real,
691 rational or integer number.
694 @deftypefn {C Function} int scm_is_complex (SCM val)
695 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
699 @subsubsection Exact and Inexact Numbers
700 @tpindex Exact numbers
701 @tpindex Inexact numbers
705 @rnindex exact->inexact
706 @rnindex inexact->exact
708 R5RS requires that a calculation involving inexact numbers always
709 produces an inexact result. To meet this requirement, Guile
710 distinguishes between an exact integer value such as @samp{5} and the
711 corresponding inexact real value which, to the limited precision
712 available, has no fractional part, and is printed as @samp{5.0}. Guile
713 will only convert the latter value to the former when forced to do so by
714 an invocation of the @code{inexact->exact} procedure.
716 @deffn {Scheme Procedure} exact? z
717 @deffnx {C Function} scm_exact_p (z)
718 Return @code{#t} if the number @var{z} is exact, @code{#f}
734 @deffn {Scheme Procedure} inexact? z
735 @deffnx {C Function} scm_inexact_p (z)
736 Return @code{#t} if the number @var{z} is inexact, @code{#f}
740 @deffn {Scheme Procedure} inexact->exact z
741 @deffnx {C Function} scm_inexact_to_exact (z)
742 Return an exact number that is numerically closest to @var{z}, when
743 there is one. For inexact rationals, Guile returns the exact rational
744 that is numerically equal to the inexact rational. Inexact complex
745 numbers with a non-zero imaginary part can not be made exact.
752 The following happens because 12/10 is not exactly representable as a
753 @code{double} (on most platforms). However, when reading a decimal
754 number that has been marked exact with the ``#e'' prefix, Guile is
755 able to represent it correctly.
759 @result{} 5404319552844595/4503599627370496
767 @c begin (texi-doc-string "guile" "exact->inexact")
768 @deffn {Scheme Procedure} exact->inexact z
769 @deffnx {C Function} scm_exact_to_inexact (z)
770 Convert the number @var{z} to its inexact representation.
775 @subsubsection Read Syntax for Numerical Data
777 The read syntax for integers is a string of digits, optionally
778 preceded by a minus or plus character, a code indicating the
779 base in which the integer is encoded, and a code indicating whether
780 the number is exact or inexact. The supported base codes are:
785 the integer is written in binary (base 2)
789 the integer is written in octal (base 8)
793 the integer is written in decimal (base 10)
797 the integer is written in hexadecimal (base 16)
800 If the base code is omitted, the integer is assumed to be decimal. The
801 following examples show how these base codes are used.
820 The codes for indicating exactness (which can, incidentally, be applied
821 to all numerical values) are:
830 the number is inexact.
833 If the exactness indicator is omitted, the number is exact unless it
834 contains a radix point. Since Guile can not represent exact complex
835 numbers, an error is signalled when asking for them.
845 ERROR: Wrong type argument
848 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
849 plus and minus infinity, respectively. The value must be written
850 exactly as shown, that is, they always must have a sign and exactly
851 one zero digit after the decimal point. It also understands
852 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
853 The sign is ignored for `not-a-number' and the value is always printed
856 @node Integer Operations
857 @subsubsection Operations on Integer Values
866 @deffn {Scheme Procedure} odd? n
867 @deffnx {C Function} scm_odd_p (n)
868 Return @code{#t} if @var{n} is an odd number, @code{#f}
872 @deffn {Scheme Procedure} even? n
873 @deffnx {C Function} scm_even_p (n)
874 Return @code{#t} if @var{n} is an even number, @code{#f}
878 @c begin (texi-doc-string "guile" "quotient")
879 @c begin (texi-doc-string "guile" "remainder")
880 @deffn {Scheme Procedure} quotient n d
881 @deffnx {Scheme Procedure} remainder n d
882 @deffnx {C Function} scm_quotient (n, d)
883 @deffnx {C Function} scm_remainder (n, d)
884 Return the quotient or remainder from @var{n} divided by @var{d}. The
885 quotient is rounded towards zero, and the remainder will have the same
886 sign as @var{n}. In all cases quotient and remainder satisfy
887 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
890 (remainder 13 4) @result{} 1
891 (remainder -13 4) @result{} -1
895 @c begin (texi-doc-string "guile" "modulo")
896 @deffn {Scheme Procedure} modulo n d
897 @deffnx {C Function} scm_modulo (n, d)
898 Return the remainder from @var{n} divided by @var{d}, with the same
902 (modulo 13 4) @result{} 1
903 (modulo -13 4) @result{} 3
904 (modulo 13 -4) @result{} -3
905 (modulo -13 -4) @result{} -1
909 @c begin (texi-doc-string "guile" "gcd")
910 @deffn {Scheme Procedure} gcd x@dots{}
911 @deffnx {C Function} scm_gcd (x, y)
912 Return the greatest common divisor of all arguments.
913 If called without arguments, 0 is returned.
915 The C function @code{scm_gcd} always takes two arguments, while the
916 Scheme function can take an arbitrary number.
919 @c begin (texi-doc-string "guile" "lcm")
920 @deffn {Scheme Procedure} lcm x@dots{}
921 @deffnx {C Function} scm_lcm (x, y)
922 Return the least common multiple of the arguments.
923 If called without arguments, 1 is returned.
925 The C function @code{scm_lcm} always takes two arguments, while the
926 Scheme function can take an arbitrary number.
929 @deffn {Scheme Procedure} modulo-expt n k m
930 @deffnx {C Function} scm_modulo_expt (n, k, m)
931 Return @var{n} raised to the integer exponent
932 @var{k}, modulo @var{m}.
941 @subsubsection Comparison Predicates
946 The C comparison functions below always takes two arguments, while the
947 Scheme functions can take an arbitrary number. Also keep in mind that
948 the C functions return one of the Scheme boolean values
949 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
950 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
951 y))} when testing the two Scheme numbers @code{x} and @code{y} for
952 equality, for example.
954 @c begin (texi-doc-string "guile" "=")
955 @deffn {Scheme Procedure} =
956 @deffnx {C Function} scm_num_eq_p (x, y)
957 Return @code{#t} if all parameters are numerically equal.
960 @c begin (texi-doc-string "guile" "<")
961 @deffn {Scheme Procedure} <
962 @deffnx {C Function} scm_less_p (x, y)
963 Return @code{#t} if the list of parameters is monotonically
967 @c begin (texi-doc-string "guile" ">")
968 @deffn {Scheme Procedure} >
969 @deffnx {C Function} scm_gr_p (x, y)
970 Return @code{#t} if the list of parameters is monotonically
974 @c begin (texi-doc-string "guile" "<=")
975 @deffn {Scheme Procedure} <=
976 @deffnx {C Function} scm_leq_p (x, y)
977 Return @code{#t} if the list of parameters is monotonically
981 @c begin (texi-doc-string "guile" ">=")
982 @deffn {Scheme Procedure} >=
983 @deffnx {C Function} scm_geq_p (x, y)
984 Return @code{#t} if the list of parameters is monotonically
988 @c begin (texi-doc-string "guile" "zero?")
989 @deffn {Scheme Procedure} zero? z
990 @deffnx {C Function} scm_zero_p (z)
991 Return @code{#t} if @var{z} is an exact or inexact number equal to
995 @c begin (texi-doc-string "guile" "positive?")
996 @deffn {Scheme Procedure} positive? x
997 @deffnx {C Function} scm_positive_p (x)
998 Return @code{#t} if @var{x} is an exact or inexact number greater than
1002 @c begin (texi-doc-string "guile" "negative?")
1003 @deffn {Scheme Procedure} negative? x
1004 @deffnx {C Function} scm_negative_p (x)
1005 Return @code{#t} if @var{x} is an exact or inexact number less than
1011 @subsubsection Converting Numbers To and From Strings
1012 @rnindex number->string
1013 @rnindex string->number
1015 The following procedures read and write numbers according to their
1016 external representation as defined by R5RS (@pxref{Lexical structure,
1017 R5RS Lexical Structure,, r5rs, The Revised^5 Report on the Algorithmic
1018 Language Scheme}). @xref{Number Input and Output, the @code{(ice-9
1019 i18n)} module}, for locale-dependent number parsing.
1021 @deffn {Scheme Procedure} number->string n [radix]
1022 @deffnx {C Function} scm_number_to_string (n, radix)
1023 Return a string holding the external representation of the
1024 number @var{n} in the given @var{radix}. If @var{n} is
1025 inexact, a radix of 10 will be used.
1028 @deffn {Scheme Procedure} string->number string [radix]
1029 @deffnx {C Function} scm_string_to_number (string, radix)
1030 Return a number of the maximally precise representation
1031 expressed by the given @var{string}. @var{radix} must be an
1032 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1033 is a default radix that may be overridden by an explicit radix
1034 prefix in @var{string} (e.g. "#o177"). If @var{radix} is not
1035 supplied, then the default radix is 10. If string is not a
1036 syntactically valid notation for a number, then
1037 @code{string->number} returns @code{#f}.
1040 @deftypefn {C Function} SCM scm_c_locale_stringn_to_number (const char *string, size_t len, unsigned radix)
1041 As per @code{string->number} above, but taking a C string, as pointer
1042 and length. The string characters should be in the current locale
1043 encoding (@code{locale} in the name refers only to that, there's no
1044 locale-dependent parsing).
1049 @subsubsection Complex Number Operations
1050 @rnindex make-rectangular
1057 @deffn {Scheme Procedure} make-rectangular real_part imaginary_part
1058 @deffnx {C Function} scm_make_rectangular (real_part, imaginary_part)
1059 Return a complex number constructed of the given @var{real-part} and @var{imaginary-part} parts.
1062 @deffn {Scheme Procedure} make-polar x y
1063 @deffnx {C Function} scm_make_polar (x, y)
1065 Return the complex number @var{x} * e^(i * @var{y}).
1068 @c begin (texi-doc-string "guile" "real-part")
1069 @deffn {Scheme Procedure} real-part z
1070 @deffnx {C Function} scm_real_part (z)
1071 Return the real part of the number @var{z}.
1074 @c begin (texi-doc-string "guile" "imag-part")
1075 @deffn {Scheme Procedure} imag-part z
1076 @deffnx {C Function} scm_imag_part (z)
1077 Return the imaginary part of the number @var{z}.
1080 @c begin (texi-doc-string "guile" "magnitude")
1081 @deffn {Scheme Procedure} magnitude z
1082 @deffnx {C Function} scm_magnitude (z)
1083 Return the magnitude of the number @var{z}. This is the same as
1084 @code{abs} for real arguments, but also allows complex numbers.
1087 @c begin (texi-doc-string "guile" "angle")
1088 @deffn {Scheme Procedure} angle z
1089 @deffnx {C Function} scm_angle (z)
1090 Return the angle of the complex number @var{z}.
1093 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1094 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1095 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1096 respectively, but these functions take @code{double}s as their
1100 @deftypefn {C Function} double scm_c_real_part (z)
1101 @deftypefnx {C Function} double scm_c_imag_part (z)
1102 Returns the real or imaginary part of @var{z} as a @code{double}.
1105 @deftypefn {C Function} double scm_c_magnitude (z)
1106 @deftypefnx {C Function} double scm_c_angle (z)
1107 Returns the magnitude or angle of @var{z} as a @code{double}.
1112 @subsubsection Arithmetic Functions
1127 The C arithmetic functions below always takes two arguments, while the
1128 Scheme functions can take an arbitrary number. When you need to
1129 invoke them with just one argument, for example to compute the
1130 equivalent od @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1131 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1133 @c begin (texi-doc-string "guile" "+")
1134 @deffn {Scheme Procedure} + z1 @dots{}
1135 @deffnx {C Function} scm_sum (z1, z2)
1136 Return the sum of all parameter values. Return 0 if called without any
1140 @c begin (texi-doc-string "guile" "-")
1141 @deffn {Scheme Procedure} - z1 z2 @dots{}
1142 @deffnx {C Function} scm_difference (z1, z2)
1143 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1144 the sum of all but the first argument are subtracted from the first
1148 @c begin (texi-doc-string "guile" "*")
1149 @deffn {Scheme Procedure} * z1 @dots{}
1150 @deffnx {C Function} scm_product (z1, z2)
1151 Return the product of all arguments. If called without arguments, 1 is
1155 @c begin (texi-doc-string "guile" "/")
1156 @deffn {Scheme Procedure} / z1 z2 @dots{}
1157 @deffnx {C Function} scm_divide (z1, z2)
1158 Divide the first argument by the product of the remaining arguments. If
1159 called with one argument @var{z1}, 1/@var{z1} is returned.
1162 @deffn {Scheme Procedure} 1+ z
1163 @deffnx {C Function} scm_oneplus (z)
1164 Return @math{@var{z} + 1}.
1167 @deffn {Scheme Procedure} 1- z
1168 @deffnx {C function} scm_oneminus (z)
1169 Return @math{@var{z} - 1}.
1172 @c begin (texi-doc-string "guile" "abs")
1173 @deffn {Scheme Procedure} abs x
1174 @deffnx {C Function} scm_abs (x)
1175 Return the absolute value of @var{x}.
1177 @var{x} must be a number with zero imaginary part. To calculate the
1178 magnitude of a complex number, use @code{magnitude} instead.
1181 @c begin (texi-doc-string "guile" "max")
1182 @deffn {Scheme Procedure} max x1 x2 @dots{}
1183 @deffnx {C Function} scm_max (x1, x2)
1184 Return the maximum of all parameter values.
1187 @c begin (texi-doc-string "guile" "min")
1188 @deffn {Scheme Procedure} min x1 x2 @dots{}
1189 @deffnx {C Function} scm_min (x1, x2)
1190 Return the minimum of all parameter values.
1193 @c begin (texi-doc-string "guile" "truncate")
1194 @deffn {Scheme Procedure} truncate x
1195 @deffnx {C Function} scm_truncate_number (x)
1196 Round the inexact number @var{x} towards zero.
1199 @c begin (texi-doc-string "guile" "round")
1200 @deffn {Scheme Procedure} round x
1201 @deffnx {C Function} scm_round_number (x)
1202 Round the inexact number @var{x} to the nearest integer. When exactly
1203 halfway between two integers, round to the even one.
1206 @c begin (texi-doc-string "guile" "floor")
1207 @deffn {Scheme Procedure} floor x
1208 @deffnx {C Function} scm_floor (x)
1209 Round the number @var{x} towards minus infinity.
1212 @c begin (texi-doc-string "guile" "ceiling")
1213 @deffn {Scheme Procedure} ceiling x
1214 @deffnx {C Function} scm_ceiling (x)
1215 Round the number @var{x} towards infinity.
1218 @deftypefn {C Function} double scm_c_truncate (double x)
1219 @deftypefnx {C Function} double scm_c_round (double x)
1220 Like @code{scm_truncate_number} or @code{scm_round_number},
1221 respectively, but these functions take and return @code{double}
1226 @subsubsection Scientific Functions
1228 The following procedures accept any kind of number as arguments,
1229 including complex numbers.
1232 @c begin (texi-doc-string "guile" "sqrt")
1233 @deffn {Scheme Procedure} sqrt z
1234 Return the square root of @var{z}. Of the two possible roots
1235 (positive and negative), the one with the a positive real part is
1236 returned, or if that's zero then a positive imaginary part. Thus,
1239 (sqrt 9.0) @result{} 3.0
1240 (sqrt -9.0) @result{} 0.0+3.0i
1241 (sqrt 1.0+1.0i) @result{} 1.09868411346781+0.455089860562227i
1242 (sqrt -1.0-1.0i) @result{} 0.455089860562227-1.09868411346781i
1247 @c begin (texi-doc-string "guile" "expt")
1248 @deffn {Scheme Procedure} expt z1 z2
1249 Return @var{z1} raised to the power of @var{z2}.
1253 @c begin (texi-doc-string "guile" "sin")
1254 @deffn {Scheme Procedure} sin z
1255 Return the sine of @var{z}.
1259 @c begin (texi-doc-string "guile" "cos")
1260 @deffn {Scheme Procedure} cos z
1261 Return the cosine of @var{z}.
1265 @c begin (texi-doc-string "guile" "tan")
1266 @deffn {Scheme Procedure} tan z
1267 Return the tangent of @var{z}.
1271 @c begin (texi-doc-string "guile" "asin")
1272 @deffn {Scheme Procedure} asin z
1273 Return the arcsine of @var{z}.
1277 @c begin (texi-doc-string "guile" "acos")
1278 @deffn {Scheme Procedure} acos z
1279 Return the arccosine of @var{z}.
1283 @c begin (texi-doc-string "guile" "atan")
1284 @deffn {Scheme Procedure} atan z
1285 @deffnx {Scheme Procedure} atan y x
1286 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1290 @c begin (texi-doc-string "guile" "exp")
1291 @deffn {Scheme Procedure} exp z
1292 Return e to the power of @var{z}, where e is the base of natural
1293 logarithms (2.71828@dots{}).
1297 @c begin (texi-doc-string "guile" "log")
1298 @deffn {Scheme Procedure} log z
1299 Return the natural logarithm of @var{z}.
1302 @c begin (texi-doc-string "guile" "log10")
1303 @deffn {Scheme Procedure} log10 z
1304 Return the base 10 logarithm of @var{z}.
1307 @c begin (texi-doc-string "guile" "sinh")
1308 @deffn {Scheme Procedure} sinh z
1309 Return the hyperbolic sine of @var{z}.
1312 @c begin (texi-doc-string "guile" "cosh")
1313 @deffn {Scheme Procedure} cosh z
1314 Return the hyperbolic cosine of @var{z}.
1317 @c begin (texi-doc-string "guile" "tanh")
1318 @deffn {Scheme Procedure} tanh z
1319 Return the hyperbolic tangent of @var{z}.
1322 @c begin (texi-doc-string "guile" "asinh")
1323 @deffn {Scheme Procedure} asinh z
1324 Return the hyperbolic arcsine of @var{z}.
1327 @c begin (texi-doc-string "guile" "acosh")
1328 @deffn {Scheme Procedure} acosh z
1329 Return the hyperbolic arccosine of @var{z}.
1332 @c begin (texi-doc-string "guile" "atanh")
1333 @deffn {Scheme Procedure} atanh z
1334 Return the hyperbolic arctangent of @var{z}.
1338 @node Bitwise Operations
1339 @subsubsection Bitwise Operations
1341 For the following bitwise functions, negative numbers are treated as
1342 infinite precision twos-complements. For instance @math{-6} is bits
1343 @math{@dots{}111010}, with infinitely many ones on the left. It can
1344 be seen that adding 6 (binary 110) to such a bit pattern gives all
1347 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1348 @deffnx {C Function} scm_logand (n1, n2)
1349 Return the bitwise @sc{and} of the integer arguments.
1352 (logand) @result{} -1
1353 (logand 7) @result{} 7
1354 (logand #b111 #b011 #b001) @result{} 1
1358 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1359 @deffnx {C Function} scm_logior (n1, n2)
1360 Return the bitwise @sc{or} of the integer arguments.
1363 (logior) @result{} 0
1364 (logior 7) @result{} 7
1365 (logior #b000 #b001 #b011) @result{} 3
1369 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1370 @deffnx {C Function} scm_loxor (n1, n2)
1371 Return the bitwise @sc{xor} of the integer arguments. A bit is
1372 set in the result if it is set in an odd number of arguments.
1375 (logxor) @result{} 0
1376 (logxor 7) @result{} 7
1377 (logxor #b000 #b001 #b011) @result{} 2
1378 (logxor #b000 #b001 #b011 #b011) @result{} 1
1382 @deffn {Scheme Procedure} lognot n
1383 @deffnx {C Function} scm_lognot (n)
1384 Return the integer which is the ones-complement of the integer
1385 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1388 (number->string (lognot #b10000000) 2)
1389 @result{} "-10000001"
1390 (number->string (lognot #b0) 2)
1395 @deffn {Scheme Procedure} logtest j k
1396 @deffnx {C Function} scm_logtest (j, k)
1397 Test whether @var{j} and @var{k} have any 1 bits in common. This is
1398 equivalent to @code{(not (zero? (logand j k)))}, but without actually
1399 calculating the @code{logand}, just testing for non-zero.
1402 (logtest #b0100 #b1011) @result{} #f
1403 (logtest #b0100 #b0111) @result{} #t
1407 @deffn {Scheme Procedure} logbit? index j
1408 @deffnx {C Function} scm_logbit_p (index, j)
1409 Test whether bit number @var{index} in @var{j} is set. @var{index}
1410 starts from 0 for the least significant bit.
1413 (logbit? 0 #b1101) @result{} #t
1414 (logbit? 1 #b1101) @result{} #f
1415 (logbit? 2 #b1101) @result{} #t
1416 (logbit? 3 #b1101) @result{} #t
1417 (logbit? 4 #b1101) @result{} #f
1421 @deffn {Scheme Procedure} ash n cnt
1422 @deffnx {C Function} scm_ash (n, cnt)
1423 Return @var{n} shifted left by @var{cnt} bits, or shifted right if
1424 @var{cnt} is negative. This is an ``arithmetic'' shift.
1426 This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and
1427 when @var{cnt} is negative it's a division, rounded towards negative
1428 infinity. (Note that this is not the same rounding as @code{quotient}
1431 With @var{n} viewed as an infinite precision twos complement,
1432 @code{ash} means a left shift introducing zero bits, or a right shift
1436 (number->string (ash #b1 3) 2) @result{} "1000"
1437 (number->string (ash #b1010 -1) 2) @result{} "101"
1439 ;; -23 is bits ...11101001, -6 is bits ...111010
1440 (ash -23 -2) @result{} -6
1444 @deffn {Scheme Procedure} logcount n
1445 @deffnx {C Function} scm_logcount (n)
1446 Return the number of bits in integer @var{n}. If @var{n} is
1447 positive, the 1-bits in its binary representation are counted.
1448 If negative, the 0-bits in its two's-complement binary
1449 representation are counted. If zero, 0 is returned.
1452 (logcount #b10101010)
1461 @deffn {Scheme Procedure} integer-length n
1462 @deffnx {C Function} scm_integer_length (n)
1463 Return the number of bits necessary to represent @var{n}.
1465 For positive @var{n} this is how many bits to the most significant one
1466 bit. For negative @var{n} it's how many bits to the most significant
1467 zero bit in twos complement form.
1470 (integer-length #b10101010) @result{} 8
1471 (integer-length #b1111) @result{} 4
1472 (integer-length 0) @result{} 0
1473 (integer-length -1) @result{} 0
1474 (integer-length -256) @result{} 8
1475 (integer-length -257) @result{} 9
1479 @deffn {Scheme Procedure} integer-expt n k
1480 @deffnx {C Function} scm_integer_expt (n, k)
1481 Return @var{n} raised to the power @var{k}. @var{k} must be an exact
1482 integer, @var{n} can be any number.
1484 Negative @var{k} is supported, and results in @m{1/n^|k|, 1/n^abs(k)}
1485 in the usual way. @math{@var{n}^0} is 1, as usual, and that includes
1489 (integer-expt 2 5) @result{} 32
1490 (integer-expt -3 3) @result{} -27
1491 (integer-expt 5 -3) @result{} 1/125
1492 (integer-expt 0 0) @result{} 1
1496 @deffn {Scheme Procedure} bit-extract n start end
1497 @deffnx {C Function} scm_bit_extract (n, start, end)
1498 Return the integer composed of the @var{start} (inclusive)
1499 through @var{end} (exclusive) bits of @var{n}. The
1500 @var{start}th bit becomes the 0-th bit in the result.
1503 (number->string (bit-extract #b1101101010 0 4) 2)
1505 (number->string (bit-extract #b1101101010 4 9) 2)
1512 @subsubsection Random Number Generation
1514 Pseudo-random numbers are generated from a random state object, which
1515 can be created with @code{seed->random-state}. The @var{state}
1516 parameter to the various functions below is optional, it defaults to
1517 the state object in the @code{*random-state*} variable.
1519 @deffn {Scheme Procedure} copy-random-state [state]
1520 @deffnx {C Function} scm_copy_random_state (state)
1521 Return a copy of the random state @var{state}.
1524 @deffn {Scheme Procedure} random n [state]
1525 @deffnx {C Function} scm_random (n, state)
1526 Return a number in [0, @var{n}).
1528 Accepts a positive integer or real n and returns a
1529 number of the same type between zero (inclusive) and
1530 @var{n} (exclusive). The values returned have a uniform
1534 @deffn {Scheme Procedure} random:exp [state]
1535 @deffnx {C Function} scm_random_exp (state)
1536 Return an inexact real in an exponential distribution with mean
1537 1. For an exponential distribution with mean @var{u} use @code{(*
1538 @var{u} (random:exp))}.
1541 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1542 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1543 Fills @var{vect} with inexact real random numbers the sum of whose
1544 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1545 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1546 the coordinates are uniformly distributed over the surface of the unit
1550 @deffn {Scheme Procedure} random:normal [state]
1551 @deffnx {C Function} scm_random_normal (state)
1552 Return an inexact real in a normal distribution. The distribution
1553 used has mean 0 and standard deviation 1. For a normal distribution
1554 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1555 (* @var{d} (random:normal)))}.
1558 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1559 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1560 Fills @var{vect} with inexact real random numbers that are
1561 independent and standard normally distributed
1562 (i.e., with mean 0 and variance 1).
1565 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1566 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1567 Fills @var{vect} with inexact real random numbers the sum of whose
1568 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1569 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1570 the coordinates are uniformly distributed within the unit
1572 @c FIXME: What does this mean, particularly the n-sphere part?
1575 @deffn {Scheme Procedure} random:uniform [state]
1576 @deffnx {C Function} scm_random_uniform (state)
1577 Return a uniformly distributed inexact real random number in
1581 @deffn {Scheme Procedure} seed->random-state seed
1582 @deffnx {C Function} scm_seed_to_random_state (seed)
1583 Return a new random state using @var{seed}.
1586 @defvar *random-state*
1587 The global random state used by the above functions when the
1588 @var{state} parameter is not given.
1591 Note that the initial value of @code{*random-state*} is the same every
1592 time Guile starts up. Therefore, if you don't pass a @var{state}
1593 parameter to the above procedures, and you don't set
1594 @code{*random-state*} to @code{(seed->random-state your-seed)}, where
1595 @code{your-seed} is something that @emph{isn't} the same every time,
1596 you'll get the same sequence of ``random'' numbers on every run.
1598 For example, unless the relevant source code has changed, @code{(map
1599 random (cdr (iota 30)))}, if the first use of random numbers since
1600 Guile started up, will always give:
1603 (map random (cdr (iota 19)))
1605 (0 1 1 2 2 2 1 2 6 7 10 0 5 3 12 5 5 12)
1608 To use the time of day as the random seed, you can use code like this:
1611 (let ((time (gettimeofday)))
1612 (set! *random-state*
1613 (seed->random-state (+ (car time)
1618 And then (depending on the time of day, of course):
1621 (map random (cdr (iota 19)))
1623 (0 0 1 0 2 4 5 4 5 5 9 3 10 1 8 3 14 17)
1626 For security applications, such as password generation, you should use
1627 more bits of seed. Otherwise an open source password generator could
1628 be attacked by guessing the seed@dots{} but that's a subject for
1633 @subsection Characters
1636 In Scheme, there is a data type to describe a single character.
1638 Defining what exactly a character @emph{is} can be more complicated
1639 than it seems. Guile follows the advice of R6RS and uses The Unicode
1640 Standard to help define what a character is. So, for Guile, a
1641 character is anything in the Unicode Character Database.
1644 @cindex Unicode code point
1646 The Unicode Character Database is basically a table of characters
1647 indexed using integers called 'code points'. Valid code points are in
1648 the ranges 0 to @code{#xD7FF} inclusive or @code{#xE000} to
1649 @code{#x10FFFF} inclusive, which is about 1.1 million code points.
1651 @cindex designated code point
1652 @cindex code point, designated
1654 Any code point that has been assigned to a character or that has
1655 otherwise been given a meaning by Unicode is called a 'designated code
1656 point'. Most of the designated code points, about 200,000 of them,
1657 indicate characters, accents or other combining marks that modify
1658 other characters, symbols, whitespace, and control characters. Some
1659 are not characters but indicators that suggest how to format or
1660 display neighboring characters.
1662 @cindex reserved code point
1663 @cindex code point, reserved
1665 If a code point is not a designated code point -- if it has not been
1666 assigned to a character by The Unicode Standard -- it is a 'reserved
1667 code point', meaning that they are reserved for future use. Most of
1668 the code points, about 800,000, are 'reserved code points'.
1670 By convention, a Unicode code point is written as
1671 ``U+XXXX'' where ``XXXX'' is a hexadecimal number. Please note that
1672 this convenient notation is not valid code. Guile does not interpret
1673 ``U+XXXX'' as a character.
1675 In Scheme, a character literal is written as @code{#\@var{name}} where
1676 @var{name} is the name of the character that you want. Printable
1677 characters have their usual single character name; for example,
1678 @code{#\a} is a lower case @code{a}.
1680 Some of the code points are 'combining characters' that are not meant
1681 to be printed by themselves but are instead meant to modify the
1682 appearance of the previous character. For combining characters, an
1683 alternate form of the character literal is @code{#\} followed by
1684 U+25CC (a small, dotted circle), followed by the combining character.
1685 This allows the combining character to be drawn on the circle, not on
1686 the backslash of @code{#\}.
1688 Many of the non-printing characters, such as whitespace characters and
1689 control characters, also have names.
1691 The most commonly used non-printing characters have long character
1692 names, described in the table below.
1694 @multitable {@code{#\backspace}} {Preferred}
1695 @item Character Name @tab Codepoint
1696 @item @code{#\nul} @tab U+0000
1697 @item @code{#\alarm} @tab u+0007
1698 @item @code{#\backspace} @tab U+0008
1699 @item @code{#\tab} @tab U+0009
1700 @item @code{#\linefeed} @tab U+000A
1701 @item @code{#\newline} @tab U+000A
1702 @item @code{#\vtab} @tab U+000B
1703 @item @code{#\page} @tab U+000C
1704 @item @code{#\return} @tab U+000D
1705 @item @code{#\esc} @tab U+001B
1706 @item @code{#\space} @tab U+0020
1707 @item @code{#\delete} @tab U+007F
1710 There are also short names for all of the ``C0 control characters''
1711 (those with code points below 32). The following table lists the short
1712 name for each character.
1714 @multitable @columnfractions .25 .25 .25 .25
1715 @item 0 = @code{#\nul}
1716 @tab 1 = @code{#\soh}
1717 @tab 2 = @code{#\stx}
1718 @tab 3 = @code{#\etx}
1719 @item 4 = @code{#\eot}
1720 @tab 5 = @code{#\enq}
1721 @tab 6 = @code{#\ack}
1722 @tab 7 = @code{#\bel}
1723 @item 8 = @code{#\bs}
1724 @tab 9 = @code{#\ht}
1725 @tab 10 = @code{#\lf}
1726 @tab 11 = @code{#\vt}
1727 @item 12 = @code{#\ff}
1728 @tab 13 = @code{#\cr}
1729 @tab 14 = @code{#\so}
1730 @tab 15 = @code{#\si}
1731 @item 16 = @code{#\dle}
1732 @tab 17 = @code{#\dc1}
1733 @tab 18 = @code{#\dc2}
1734 @tab 19 = @code{#\dc3}
1735 @item 20 = @code{#\dc4}
1736 @tab 21 = @code{#\nak}
1737 @tab 22 = @code{#\syn}
1738 @tab 23 = @code{#\etb}
1739 @item 24 = @code{#\can}
1740 @tab 25 = @code{#\em}
1741 @tab 26 = @code{#\sub}
1742 @tab 27 = @code{#\esc}
1743 @item 28 = @code{#\fs}
1744 @tab 29 = @code{#\gs}
1745 @tab 30 = @code{#\rs}
1746 @tab 31 = @code{#\us}
1747 @item 32 = @code{#\sp}
1750 The short name for the ``delete'' character (code point U+007F) is
1753 There are also a few alternative names left over for compatibility with
1754 previous versions of Guile.
1756 @multitable {@code{#\backspace}} {Preferred}
1757 @item Alternate @tab Standard
1758 @item @code{#\nl} @tab @code{#\newline}
1759 @item @code{#\np} @tab @code{#\page}
1760 @item @code{#\null} @tab @code{#\nul}
1763 Characters may also be written using their code point values. They can
1764 be written with as an octal number, such as @code{#\10} for
1765 @code{#\bs} or @code{#\177} for @code{#\del}.
1768 @deffn {Scheme Procedure} char? x
1769 @deffnx {C Function} scm_char_p (x)
1770 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1773 Fundamentally, the character comparison operations below are
1774 numeric comparisons of the character's code points.
1777 @deffn {Scheme Procedure} char=? x y
1778 Return @code{#t} iff code point of @var{x} is equal to the code point
1779 of @var{y}, else @code{#f}.
1783 @deffn {Scheme Procedure} char<? x y
1784 Return @code{#t} iff the code point of @var{x} is less than the code
1785 point of @var{y}, else @code{#f}.
1789 @deffn {Scheme Procedure} char<=? x y
1790 Return @code{#t} iff the code point of @var{x} is less than or equal
1791 to the code point of @var{y}, else @code{#f}.
1795 @deffn {Scheme Procedure} char>? x y
1796 Return @code{#t} iff the code point of @var{x} is greater than the
1797 code point of @var{y}, else @code{#f}.
1801 @deffn {Scheme Procedure} char>=? x y
1802 Return @code{#t} iff the code point of @var{x} is greater than or
1803 equal to the code point of @var{y}, else @code{#f}.
1806 @cindex case folding
1808 Case-insensitive character comparisons use @emph{Unicode case
1809 folding}. In case folding comparisons, if a character is lowercase
1810 and has an uppercase form that can be expressed as a single character,
1811 it is converted to uppercase before comparison. All other characters
1812 undergo no conversion before the comparison occurs. This includes the
1813 German sharp S (Eszett) which is not uppercased before conversion
1814 because its uppercase form has two characters. Unicode case folding
1815 is language independent: it uses rules that are generally true, but,
1816 it cannot cover all cases for all languages.
1819 @deffn {Scheme Procedure} char-ci=? x y
1820 Return @code{#t} iff the case-folded code point of @var{x} is the same
1821 as the case-folded code point of @var{y}, else @code{#f}.
1825 @deffn {Scheme Procedure} char-ci<? x y
1826 Return @code{#t} iff the case-folded code point of @var{x} is less
1827 than the case-folded code point of @var{y}, else @code{#f}.
1831 @deffn {Scheme Procedure} char-ci<=? x y
1832 Return @code{#t} iff the case-folded code point of @var{x} is less
1833 than or equal to the case-folded code point of @var{y}, else
1838 @deffn {Scheme Procedure} char-ci>? x y
1839 Return @code{#t} iff the case-folded code point of @var{x} is greater
1840 than the case-folded code point of @var{y}, else @code{#f}.
1844 @deffn {Scheme Procedure} char-ci>=? x y
1845 Return @code{#t} iff the case-folded code point of @var{x} is greater
1846 than or equal to the case-folded code point of @var{y}, else
1850 @rnindex char-alphabetic?
1851 @deffn {Scheme Procedure} char-alphabetic? chr
1852 @deffnx {C Function} scm_char_alphabetic_p (chr)
1853 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1856 @rnindex char-numeric?
1857 @deffn {Scheme Procedure} char-numeric? chr
1858 @deffnx {C Function} scm_char_numeric_p (chr)
1859 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1862 @rnindex char-whitespace?
1863 @deffn {Scheme Procedure} char-whitespace? chr
1864 @deffnx {C Function} scm_char_whitespace_p (chr)
1865 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1868 @rnindex char-upper-case?
1869 @deffn {Scheme Procedure} char-upper-case? chr
1870 @deffnx {C Function} scm_char_upper_case_p (chr)
1871 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1874 @rnindex char-lower-case?
1875 @deffn {Scheme Procedure} char-lower-case? chr
1876 @deffnx {C Function} scm_char_lower_case_p (chr)
1877 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1880 @deffn {Scheme Procedure} char-is-both? chr
1881 @deffnx {C Function} scm_char_is_both_p (chr)
1882 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
1886 @deffn {Scheme Procedure} char-general-category chr
1887 @deffnx {C Function} scm_char_general_category (chr)
1888 Return a symbol giving the two-letter name of the Unicode general
1889 category assigned to @var{chr} or @code{#f} if no named category is
1890 assigned. The following table provides a list of category names along
1891 with their meanings.
1893 @multitable @columnfractions .1 .4 .1 .4
1895 @tab Uppercase letter
1897 @tab Final quote punctuation
1899 @tab Lowercase letter
1901 @tab Other punctuation
1903 @tab Titlecase letter
1907 @tab Modifier letter
1909 @tab Currency symbol
1913 @tab Modifier symbol
1915 @tab Non-spacing mark
1919 @tab Combining spacing mark
1921 @tab Space separator
1927 @tab Decimal digit number
1929 @tab Paragraph separator
1939 @tab Connector punctuation
1943 @tab Dash punctuation
1947 @tab Open punctuation
1951 @tab Close punctuation
1955 @tab Initial quote punctuation
1961 @rnindex char->integer
1962 @deffn {Scheme Procedure} char->integer chr
1963 @deffnx {C Function} scm_char_to_integer (chr)
1964 Return the code point of @var{chr}.
1967 @rnindex integer->char
1968 @deffn {Scheme Procedure} integer->char n
1969 @deffnx {C Function} scm_integer_to_char (n)
1970 Return the character that has code point @var{n}. The integer @var{n}
1971 must be a valid code point. Valid code points are in the ranges 0 to
1972 @code{#xD7FF} inclusive or @code{#xE000} to @code{#x10FFFF} inclusive.
1975 @rnindex char-upcase
1976 @deffn {Scheme Procedure} char-upcase chr
1977 @deffnx {C Function} scm_char_upcase (chr)
1978 Return the uppercase character version of @var{chr}.
1981 @rnindex char-downcase
1982 @deffn {Scheme Procedure} char-downcase chr
1983 @deffnx {C Function} scm_char_downcase (chr)
1984 Return the lowercase character version of @var{chr}.
1987 @rnindex char-titlecase
1988 @deffn {Scheme Procedure} char-titlecase chr
1989 @deffnx {C Function} scm_char_titlecase (chr)
1990 Return the titlecase character version of @var{chr} if one exists;
1991 otherwise return the uppercase version.
1993 For most characters these will be the same, but the Unicode Standard
1994 includes certain digraph compatibility characters, such as @code{U+01F3}
1995 ``dz'', for which the uppercase and titlecase characters are different
1996 (@code{U+01F1} ``DZ'' and @code{U+01F2} ``Dz'' in this case,
2001 @deftypefn {C Function} scm_t_wchar scm_c_upcase (scm_t_wchar @var{c})
2002 @deftypefnx {C Function} scm_t_wchar scm_c_downcase (scm_t_wchar @var{c})
2003 @deftypefnx {C Function} scm_t_wchar scm_c_titlecase (scm_t_wchar @var{c})
2005 These C functions take an integer representation of a Unicode
2006 codepoint and return the codepoint corresponding to its uppercase,
2007 lowercase, and titlecase forms respectively. The type
2008 @code{scm_t_wchar} is a signed, 32-bit integer.
2011 @node Character Sets
2012 @subsection Character Sets
2014 The features described in this section correspond directly to SRFI-14.
2016 The data type @dfn{charset} implements sets of characters
2017 (@pxref{Characters}). Because the internal representation of
2018 character sets is not visible to the user, a lot of procedures for
2019 handling them are provided.
2021 Character sets can be created, extended, tested for the membership of a
2022 characters and be compared to other character sets.
2025 * Character Set Predicates/Comparison::
2026 * Iterating Over Character Sets:: Enumerate charset elements.
2027 * Creating Character Sets:: Making new charsets.
2028 * Querying Character Sets:: Test charsets for membership etc.
2029 * Character-Set Algebra:: Calculating new charsets.
2030 * Standard Character Sets:: Variables containing predefined charsets.
2033 @node Character Set Predicates/Comparison
2034 @subsubsection Character Set Predicates/Comparison
2036 Use these procedures for testing whether an object is a character set,
2037 or whether several character sets are equal or subsets of each other.
2038 @code{char-set-hash} can be used for calculating a hash value, maybe for
2039 usage in fast lookup procedures.
2041 @deffn {Scheme Procedure} char-set? obj
2042 @deffnx {C Function} scm_char_set_p (obj)
2043 Return @code{#t} if @var{obj} is a character set, @code{#f}
2047 @deffn {Scheme Procedure} char-set= . char_sets
2048 @deffnx {C Function} scm_char_set_eq (char_sets)
2049 Return @code{#t} if all given character sets are equal.
2052 @deffn {Scheme Procedure} char-set<= . char_sets
2053 @deffnx {C Function} scm_char_set_leq (char_sets)
2054 Return @code{#t} if every character set @var{cs}i is a subset
2055 of character set @var{cs}i+1.
2058 @deffn {Scheme Procedure} char-set-hash cs [bound]
2059 @deffnx {C Function} scm_char_set_hash (cs, bound)
2060 Compute a hash value for the character set @var{cs}. If
2061 @var{bound} is given and non-zero, it restricts the
2062 returned value to the range 0 @dots{} @var{bound - 1}.
2065 @c ===================================================================
2067 @node Iterating Over Character Sets
2068 @subsubsection Iterating Over Character Sets
2070 Character set cursors are a means for iterating over the members of a
2071 character sets. After creating a character set cursor with
2072 @code{char-set-cursor}, a cursor can be dereferenced with
2073 @code{char-set-ref}, advanced to the next member with
2074 @code{char-set-cursor-next}. Whether a cursor has passed past the last
2075 element of the set can be checked with @code{end-of-char-set?}.
2077 Additionally, mapping and (un-)folding procedures for character sets are
2080 @deffn {Scheme Procedure} char-set-cursor cs
2081 @deffnx {C Function} scm_char_set_cursor (cs)
2082 Return a cursor into the character set @var{cs}.
2085 @deffn {Scheme Procedure} char-set-ref cs cursor
2086 @deffnx {C Function} scm_char_set_ref (cs, cursor)
2087 Return the character at the current cursor position
2088 @var{cursor} in the character set @var{cs}. It is an error to
2089 pass a cursor for which @code{end-of-char-set?} returns true.
2092 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
2093 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
2094 Advance the character set cursor @var{cursor} to the next
2095 character in the character set @var{cs}. It is an error if the
2096 cursor given satisfies @code{end-of-char-set?}.
2099 @deffn {Scheme Procedure} end-of-char-set? cursor
2100 @deffnx {C Function} scm_end_of_char_set_p (cursor)
2101 Return @code{#t} if @var{cursor} has reached the end of a
2102 character set, @code{#f} otherwise.
2105 @deffn {Scheme Procedure} char-set-fold kons knil cs
2106 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
2107 Fold the procedure @var{kons} over the character set @var{cs},
2108 initializing it with @var{knil}.
2111 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
2112 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
2113 This is a fundamental constructor for character sets.
2115 @item @var{g} is used to generate a series of ``seed'' values
2116 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2117 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2118 @item @var{p} tells us when to stop -- when it returns true
2119 when applied to one of the seed values.
2120 @item @var{f} maps each seed value to a character. These
2121 characters are added to the base character set @var{base_cs} to
2122 form the result; @var{base_cs} defaults to the empty set.
2126 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
2127 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2128 This is a fundamental constructor for character sets.
2130 @item @var{g} is used to generate a series of ``seed'' values
2131 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2132 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2133 @item @var{p} tells us when to stop -- when it returns true
2134 when applied to one of the seed values.
2135 @item @var{f} maps each seed value to a character. These
2136 characters are added to the base character set @var{base_cs} to
2137 form the result; @var{base_cs} defaults to the empty set.
2141 @deffn {Scheme Procedure} char-set-for-each proc cs
2142 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2143 Apply @var{proc} to every character in the character set
2144 @var{cs}. The return value is not specified.
2147 @deffn {Scheme Procedure} char-set-map proc cs
2148 @deffnx {C Function} scm_char_set_map (proc, cs)
2149 Map the procedure @var{proc} over every character in @var{cs}.
2150 @var{proc} must be a character -> character procedure.
2153 @c ===================================================================
2155 @node Creating Character Sets
2156 @subsubsection Creating Character Sets
2158 New character sets are produced with these procedures.
2160 @deffn {Scheme Procedure} char-set-copy cs
2161 @deffnx {C Function} scm_char_set_copy (cs)
2162 Return a newly allocated character set containing all
2163 characters in @var{cs}.
2166 @deffn {Scheme Procedure} char-set . rest
2167 @deffnx {C Function} scm_char_set (rest)
2168 Return a character set containing all given characters.
2171 @deffn {Scheme Procedure} list->char-set list [base_cs]
2172 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2173 Convert the character list @var{list} to a character set. If
2174 the character set @var{base_cs} is given, the character in this
2175 set are also included in the result.
2178 @deffn {Scheme Procedure} list->char-set! list base_cs
2179 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2180 Convert the character list @var{list} to a character set. The
2181 characters are added to @var{base_cs} and @var{base_cs} is
2185 @deffn {Scheme Procedure} string->char-set str [base_cs]
2186 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2187 Convert the string @var{str} to a character set. If the
2188 character set @var{base_cs} is given, the characters in this
2189 set are also included in the result.
2192 @deffn {Scheme Procedure} string->char-set! str base_cs
2193 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2194 Convert the string @var{str} to a character set. The
2195 characters from the string are added to @var{base_cs}, and
2196 @var{base_cs} is returned.
2199 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2200 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2201 Return a character set containing every character from @var{cs}
2202 so that it satisfies @var{pred}. If provided, the characters
2203 from @var{base_cs} are added to the result.
2206 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2207 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2208 Return a character set containing every character from @var{cs}
2209 so that it satisfies @var{pred}. The characters are added to
2210 @var{base_cs} and @var{base_cs} is returned.
2213 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2214 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2215 Return a character set containing all characters whose
2216 character codes lie in the half-open range
2217 [@var{lower},@var{upper}).
2219 If @var{error} is a true value, an error is signalled if the
2220 specified range contains characters which are not contained in
2221 the implemented character range. If @var{error} is @code{#f},
2222 these characters are silently left out of the resulting
2225 The characters in @var{base_cs} are added to the result, if
2229 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2230 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2231 Return a character set containing all characters whose
2232 character codes lie in the half-open range
2233 [@var{lower},@var{upper}).
2235 If @var{error} is a true value, an error is signalled if the
2236 specified range contains characters which are not contained in
2237 the implemented character range. If @var{error} is @code{#f},
2238 these characters are silently left out of the resulting
2241 The characters are added to @var{base_cs} and @var{base_cs} is
2245 @deffn {Scheme Procedure} ->char-set x
2246 @deffnx {C Function} scm_to_char_set (x)
2247 Coerces x into a char-set. @var{x} may be a string, character or
2248 char-set. A string is converted to the set of its constituent
2249 characters; a character is converted to a singleton set; a char-set is
2253 @c ===================================================================
2255 @node Querying Character Sets
2256 @subsubsection Querying Character Sets
2258 Access the elements and other information of a character set with these
2261 @deffn {Scheme Procedure} %char-set-dump cs
2262 Returns an association list containing debugging information
2263 for @var{cs}. The association list has the following entries.
2268 The number of groups of contiguous code points the char-set
2271 A list of lists where each sublist is a range of code points
2272 and their associated characters
2274 The return value of this function cannot be relied upon to be
2275 consistent between versions of Guile and should not be used in code.
2278 @deffn {Scheme Procedure} char-set-size cs
2279 @deffnx {C Function} scm_char_set_size (cs)
2280 Return the number of elements in character set @var{cs}.
2283 @deffn {Scheme Procedure} char-set-count pred cs
2284 @deffnx {C Function} scm_char_set_count (pred, cs)
2285 Return the number of the elements int the character set
2286 @var{cs} which satisfy the predicate @var{pred}.
2289 @deffn {Scheme Procedure} char-set->list cs
2290 @deffnx {C Function} scm_char_set_to_list (cs)
2291 Return a list containing the elements of the character set
2295 @deffn {Scheme Procedure} char-set->string cs
2296 @deffnx {C Function} scm_char_set_to_string (cs)
2297 Return a string containing the elements of the character set
2298 @var{cs}. The order in which the characters are placed in the
2299 string is not defined.
2302 @deffn {Scheme Procedure} char-set-contains? cs ch
2303 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2304 Return @code{#t} iff the character @var{ch} is contained in the
2305 character set @var{cs}.
2308 @deffn {Scheme Procedure} char-set-every pred cs
2309 @deffnx {C Function} scm_char_set_every (pred, cs)
2310 Return a true value if every character in the character set
2311 @var{cs} satisfies the predicate @var{pred}.
2314 @deffn {Scheme Procedure} char-set-any pred cs
2315 @deffnx {C Function} scm_char_set_any (pred, cs)
2316 Return a true value if any character in the character set
2317 @var{cs} satisfies the predicate @var{pred}.
2320 @c ===================================================================
2322 @node Character-Set Algebra
2323 @subsubsection Character-Set Algebra
2325 Character sets can be manipulated with the common set algebra operation,
2326 such as union, complement, intersection etc. All of these procedures
2327 provide side-effecting variants, which modify their character set
2330 @deffn {Scheme Procedure} char-set-adjoin cs . rest
2331 @deffnx {C Function} scm_char_set_adjoin (cs, rest)
2332 Add all character arguments to the first argument, which must
2336 @deffn {Scheme Procedure} char-set-delete cs . rest
2337 @deffnx {C Function} scm_char_set_delete (cs, rest)
2338 Delete all character arguments from the first argument, which
2339 must be a character set.
2342 @deffn {Scheme Procedure} char-set-adjoin! cs . rest
2343 @deffnx {C Function} scm_char_set_adjoin_x (cs, rest)
2344 Add all character arguments to the first argument, which must
2348 @deffn {Scheme Procedure} char-set-delete! cs . rest
2349 @deffnx {C Function} scm_char_set_delete_x (cs, rest)
2350 Delete all character arguments from the first argument, which
2351 must be a character set.
2354 @deffn {Scheme Procedure} char-set-complement cs
2355 @deffnx {C Function} scm_char_set_complement (cs)
2356 Return the complement of the character set @var{cs}.
2359 Note that the complement of a character set is likely to contain many
2360 reserved code points (code points that are not associated with
2361 characters). It may be helpful to modify the output of
2362 @code{char-set-complement} by computing its intersection with the set
2363 of designated code points, @code{char-set:designated}.
2365 @deffn {Scheme Procedure} char-set-union . rest
2366 @deffnx {C Function} scm_char_set_union (rest)
2367 Return the union of all argument character sets.
2370 @deffn {Scheme Procedure} char-set-intersection . rest
2371 @deffnx {C Function} scm_char_set_intersection (rest)
2372 Return the intersection of all argument character sets.
2375 @deffn {Scheme Procedure} char-set-difference cs1 . rest
2376 @deffnx {C Function} scm_char_set_difference (cs1, rest)
2377 Return the difference of all argument character sets.
2380 @deffn {Scheme Procedure} char-set-xor . rest
2381 @deffnx {C Function} scm_char_set_xor (rest)
2382 Return the exclusive-or of all argument character sets.
2385 @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest
2386 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest)
2387 Return the difference and the intersection of all argument
2391 @deffn {Scheme Procedure} char-set-complement! cs
2392 @deffnx {C Function} scm_char_set_complement_x (cs)
2393 Return the complement of the character set @var{cs}.
2396 @deffn {Scheme Procedure} char-set-union! cs1 . rest
2397 @deffnx {C Function} scm_char_set_union_x (cs1, rest)
2398 Return the union of all argument character sets.
2401 @deffn {Scheme Procedure} char-set-intersection! cs1 . rest
2402 @deffnx {C Function} scm_char_set_intersection_x (cs1, rest)
2403 Return the intersection of all argument character sets.
2406 @deffn {Scheme Procedure} char-set-difference! cs1 . rest
2407 @deffnx {C Function} scm_char_set_difference_x (cs1, rest)
2408 Return the difference of all argument character sets.
2411 @deffn {Scheme Procedure} char-set-xor! cs1 . rest
2412 @deffnx {C Function} scm_char_set_xor_x (cs1, rest)
2413 Return the exclusive-or of all argument character sets.
2416 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest
2417 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest)
2418 Return the difference and the intersection of all argument
2422 @c ===================================================================
2424 @node Standard Character Sets
2425 @subsubsection Standard Character Sets
2427 In order to make the use of the character set data type and procedures
2428 useful, several predefined character set variables exist.
2434 These character sets are locale independent and are not recomputed
2435 upon a @code{setlocale} call. They contain characters from the whole
2436 range of Unicode code points. For instance, @code{char-set:letter}
2437 contains about 94,000 characters.
2439 @defvr {Scheme Variable} char-set:lower-case
2440 @defvrx {C Variable} scm_char_set_lower_case
2441 All lower-case characters.
2444 @defvr {Scheme Variable} char-set:upper-case
2445 @defvrx {C Variable} scm_char_set_upper_case
2446 All upper-case characters.
2449 @defvr {Scheme Variable} char-set:title-case
2450 @defvrx {C Variable} scm_char_set_title_case
2451 All single characters that function as if they were an upper-case
2452 letter followed by a lower-case letter.
2455 @defvr {Scheme Variable} char-set:letter
2456 @defvrx {C Variable} scm_char_set_letter
2457 All letters. This includes @code{char-set:lower-case},
2458 @code{char-set:upper-case}, @code{char-set:title-case}, and many
2459 letters that have no case at all. For example, Chinese and Japanese
2460 characters typically have no concept of case.
2463 @defvr {Scheme Variable} char-set:digit
2464 @defvrx {C Variable} scm_char_set_digit
2468 @defvr {Scheme Variable} char-set:letter+digit
2469 @defvrx {C Variable} scm_char_set_letter_and_digit
2470 The union of @code{char-set:letter} and @code{char-set:digit}.
2473 @defvr {Scheme Variable} char-set:graphic
2474 @defvrx {C Variable} scm_char_set_graphic
2475 All characters which would put ink on the paper.
2478 @defvr {Scheme Variable} char-set:printing
2479 @defvrx {C Variable} scm_char_set_printing
2480 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2483 @defvr {Scheme Variable} char-set:whitespace
2484 @defvrx {C Variable} scm_char_set_whitespace
2485 All whitespace characters.
2488 @defvr {Scheme Variable} char-set:blank
2489 @defvrx {C Variable} scm_char_set_blank
2490 All horizontal whitespace characters, which notably includes
2491 @code{#\space} and @code{#\tab}.
2494 @defvr {Scheme Variable} char-set:iso-control
2495 @defvrx {C Variable} scm_char_set_iso_control
2496 The ISO control characters are the C0 control characters (U+0000 to
2497 U+001F), delete (U+007F), and the C1 control characters (U+0080 to
2501 @defvr {Scheme Variable} char-set:punctuation
2502 @defvrx {C Variable} scm_char_set_punctuation
2503 All punctuation characters, such as the characters
2504 @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2507 @defvr {Scheme Variable} char-set:symbol
2508 @defvrx {C Variable} scm_char_set_symbol
2509 All symbol characters, such as the characters @code{$+<=>^`|~}.
2512 @defvr {Scheme Variable} char-set:hex-digit
2513 @defvrx {C Variable} scm_char_set_hex_digit
2514 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2517 @defvr {Scheme Variable} char-set:ascii
2518 @defvrx {C Variable} scm_char_set_ascii
2519 All ASCII characters.
2522 @defvr {Scheme Variable} char-set:empty
2523 @defvrx {C Variable} scm_char_set_empty
2524 The empty character set.
2527 @defvr {Scheme Variable} char-set:designated
2528 @defvrx {C Variable} scm_char_set_designated
2529 This character set contains all designated code points. This includes
2530 all the code points to which Unicode has assigned a character or other
2534 @defvr {Scheme Variable} char-set:full
2535 @defvrx {C Variable} scm_char_set_full
2536 This character set contains all possible code points. This includes
2537 both designated and reserved code points.
2544 Strings are fixed-length sequences of characters. They can be created
2545 by calling constructor procedures, but they can also literally get
2546 entered at the @acronym{REPL} or in Scheme source files.
2548 @c Guile provides a rich set of string processing procedures, because text
2549 @c handling is very important when Guile is used as a scripting language.
2551 Strings always carry the information about how many characters they are
2552 composed of with them, so there is no special end-of-string character,
2553 like in C. That means that Scheme strings can contain any character,
2554 even the @samp{#\nul} character @samp{\0}.
2556 To use strings efficiently, you need to know a bit about how Guile
2557 implements them. In Guile, a string consists of two parts, a head and
2558 the actual memory where the characters are stored. When a string (or
2559 a substring of it) is copied, only a new head gets created, the memory
2560 is usually not copied. The two heads start out pointing to the same
2563 When one of these two strings is modified, as with @code{string-set!},
2564 their common memory does get copied so that each string has its own
2565 memory and modifying one does not accidentally modify the other as well.
2566 Thus, Guile's strings are `copy on write'; the actual copying of their
2567 memory is delayed until one string is written to.
2569 This implementation makes functions like @code{substring} very
2570 efficient in the common case that no modifications are done to the
2573 If you do know that your strings are getting modified right away, you
2574 can use @code{substring/copy} instead of @code{substring}. This
2575 function performs the copy immediately at the time of creation. This
2576 is more efficient, especially in a multi-threaded program. Also,
2577 @code{substring/copy} can avoid the problem that a short substring
2578 holds on to the memory of a very large original string that could
2579 otherwise be recycled.
2581 If you want to avoid the copy altogether, so that modifications of one
2582 string show up in the other, you can use @code{substring/shared}. The
2583 strings created by this procedure are called @dfn{mutation sharing
2584 substrings} since the substring and the original string share
2585 modifications to each other.
2587 If you want to prevent modifications, use @code{substring/read-only}.
2589 Guile provides all procedures of SRFI-13 and a few more.
2592 * String Syntax:: Read syntax for strings.
2593 * String Predicates:: Testing strings for certain properties.
2594 * String Constructors:: Creating new string objects.
2595 * List/String Conversion:: Converting from/to lists of characters.
2596 * String Selection:: Select portions from strings.
2597 * String Modification:: Modify parts or whole strings.
2598 * String Comparison:: Lexicographic ordering predicates.
2599 * String Searching:: Searching in strings.
2600 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2601 * Reversing and Appending Strings:: Appending strings to form a new string.
2602 * Mapping Folding and Unfolding:: Iterating over strings.
2603 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2604 * Conversion to/from C::
2608 @subsubsection String Read Syntax
2610 @c In the following @code is used to get a good font in TeX etc, but
2611 @c is omitted for Info format, so as not to risk any confusion over
2612 @c whether surrounding ` ' quotes are part of the escape or are
2613 @c special in a string (they're not).
2615 The read syntax for strings is an arbitrarily long sequence of
2616 characters enclosed in double quotes (@nicode{"}).
2618 Backslash is an escape character and can be used to insert the
2619 following special characters. @nicode{\"} and @nicode{\\} are R5RS
2620 standard, the rest are Guile extensions, notice they follow C string
2625 Backslash character.
2628 Double quote character (an unescaped @nicode{"} is otherwise the end
2632 NUL character (ASCII 0).
2635 Bell character (ASCII 7).
2638 Formfeed character (ASCII 12).
2641 Newline character (ASCII 10).
2644 Carriage return character (ASCII 13).
2647 Tab character (ASCII 9).
2650 Vertical tab character (ASCII 11).
2653 Character code given by two hexadecimal digits. For example
2654 @nicode{\x7f} for an ASCII DEL (127).
2656 @item @nicode{\uHHHH}
2657 Character code given by four hexadecimal digits. For example
2658 @nicode{\u0100} for a capital A with macron (U+0100).
2660 @item @nicode{\UHHHHHH}
2661 Character code given by six hexadecimal digits. For example
2666 The following are examples of string literals:
2676 @node String Predicates
2677 @subsubsection String Predicates
2679 The following procedures can be used to check whether a given string
2680 fulfills some specified property.
2683 @deffn {Scheme Procedure} string? obj
2684 @deffnx {C Function} scm_string_p (obj)
2685 Return @code{#t} if @var{obj} is a string, else @code{#f}.
2688 @deftypefn {C Function} int scm_is_string (SCM obj)
2689 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
2692 @deffn {Scheme Procedure} string-null? str
2693 @deffnx {C Function} scm_string_null_p (str)
2694 Return @code{#t} if @var{str}'s length is zero, and
2695 @code{#f} otherwise.
2697 (string-null? "") @result{} #t
2699 (string-null? y) @result{} #f
2703 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
2704 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
2705 Check if @var{char_pred} is true for any character in string @var{s}.
2707 @var{char_pred} can be a character to check for any equal to that, or
2708 a character set (@pxref{Character Sets}) to check for any in that set,
2709 or a predicate procedure to call.
2711 For a procedure, calls @code{(@var{char_pred} c)} are made
2712 successively on the characters from @var{start} to @var{end}. If
2713 @var{char_pred} returns true (ie.@: non-@code{#f}), @code{string-any}
2714 stops and that return value is the return from @code{string-any}. The
2715 call on the last character (ie.@: at @math{@var{end}-1}), if that
2716 point is reached, is a tail call.
2718 If there are no characters in @var{s} (ie.@: @var{start} equals
2719 @var{end}) then the return is @code{#f}.
2722 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
2723 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
2724 Check if @var{char_pred} is true for every character in string
2727 @var{char_pred} can be a character to check for every character equal
2728 to that, or a character set (@pxref{Character Sets}) to check for
2729 every character being in that set, or a predicate procedure to call.
2731 For a procedure, calls @code{(@var{char_pred} c)} are made
2732 successively on the characters from @var{start} to @var{end}. If
2733 @var{char_pred} returns @code{#f}, @code{string-every} stops and
2734 returns @code{#f}. The call on the last character (ie.@: at
2735 @math{@var{end}-1}), if that point is reached, is a tail call and the
2736 return from that call is the return from @code{string-every}.
2738 If there are no characters in @var{s} (ie.@: @var{start} equals
2739 @var{end}) then the return is @code{#t}.
2742 @node String Constructors
2743 @subsubsection String Constructors
2745 The string constructor procedures create new string objects, possibly
2746 initializing them with some specified character data. See also
2747 @xref{String Selection}, for ways to create strings from existing
2750 @c FIXME::martin: list->string belongs into `List/String Conversion'
2752 @deffn {Scheme Procedure} string char@dots{}
2754 Return a newly allocated string made from the given character
2758 (string #\x #\y #\z) @result{} "xyz"
2759 (string) @result{} ""
2763 @deffn {Scheme Procedure} list->string lst
2764 @deffnx {C Function} scm_string (lst)
2765 @rnindex list->string
2766 Return a newly allocated string made from a list of characters.
2769 (list->string '(#\a #\b #\c)) @result{} "abc"
2773 @deffn {Scheme Procedure} reverse-list->string lst
2774 @deffnx {C Function} scm_reverse_list_to_string (lst)
2775 Return a newly allocated string made from a list of characters, in
2779 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
2783 @rnindex make-string
2784 @deffn {Scheme Procedure} make-string k [chr]
2785 @deffnx {C Function} scm_make_string (k, chr)
2786 Return a newly allocated string of
2787 length @var{k}. If @var{chr} is given, then all elements of
2788 the string are initialized to @var{chr}, otherwise the contents
2789 of the @var{string} are unspecified.
2792 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
2793 Like @code{scm_make_string}, but expects the length as a
2797 @deffn {Scheme Procedure} string-tabulate proc len
2798 @deffnx {C Function} scm_string_tabulate (proc, len)
2799 @var{proc} is an integer->char procedure. Construct a string
2800 of size @var{len} by applying @var{proc} to each index to
2801 produce the corresponding string element. The order in which
2802 @var{proc} is applied to the indices is not specified.
2805 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
2806 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
2807 Append the string in the string list @var{ls}, using the string
2808 @var{delim} as a delimiter between the elements of @var{ls}.
2809 @var{grammar} is a symbol which specifies how the delimiter is
2810 placed between the strings, and defaults to the symbol
2815 Insert the separator between list elements. An empty string
2816 will produce an empty list.
2818 Like @code{infix}, but will raise an error if given the empty
2821 Insert the separator after every list element.
2823 Insert the separator before each list element.
2827 @node List/String Conversion
2828 @subsubsection List/String conversion
2830 When processing strings, it is often convenient to first convert them
2831 into a list representation by using the procedure @code{string->list},
2832 work with the resulting list, and then convert it back into a string.
2833 These procedures are useful for similar tasks.
2835 @rnindex string->list
2836 @deffn {Scheme Procedure} string->list str [start [end]]
2837 @deffnx {C Function} scm_substring_to_list (str, start, end)
2838 @deffnx {C Function} scm_string_to_list (str)
2839 Convert the string @var{str} into a list of characters.
2842 @deffn {Scheme Procedure} string-split str chr
2843 @deffnx {C Function} scm_string_split (str, chr)
2844 Split the string @var{str} into the a list of the substrings delimited
2845 by appearances of the character @var{chr}. Note that an empty substring
2846 between separator characters will result in an empty string in the
2850 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
2852 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
2854 (string-split "::" #\:)
2858 (string-split "" #\:)
2865 @node String Selection
2866 @subsubsection String Selection
2868 Portions of strings can be extracted by these procedures.
2869 @code{string-ref} delivers individual characters whereas
2870 @code{substring} can be used to extract substrings from longer strings.
2872 @rnindex string-length
2873 @deffn {Scheme Procedure} string-length string
2874 @deffnx {C Function} scm_string_length (string)
2875 Return the number of characters in @var{string}.
2878 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
2879 Return the number of characters in @var{str} as a @code{size_t}.
2883 @deffn {Scheme Procedure} string-ref str k
2884 @deffnx {C Function} scm_string_ref (str, k)
2885 Return character @var{k} of @var{str} using zero-origin
2886 indexing. @var{k} must be a valid index of @var{str}.
2889 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
2890 Return character @var{k} of @var{str} using zero-origin
2891 indexing. @var{k} must be a valid index of @var{str}.
2894 @rnindex string-copy
2895 @deffn {Scheme Procedure} string-copy str [start [end]]
2896 @deffnx {C Function} scm_substring_copy (str, start, end)
2897 @deffnx {C Function} scm_string_copy (str)
2898 Return a copy of the given string @var{str}.
2900 The returned string shares storage with @var{str} initially, but it is
2901 copied as soon as one of the two strings is modified.
2905 @deffn {Scheme Procedure} substring str start [end]
2906 @deffnx {C Function} scm_substring (str, start, end)
2907 Return a new string formed from the characters
2908 of @var{str} beginning with index @var{start} (inclusive) and
2909 ending with index @var{end} (exclusive).
2910 @var{str} must be a string, @var{start} and @var{end} must be
2911 exact integers satisfying:
2913 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
2915 The returned string shares storage with @var{str} initially, but it is
2916 copied as soon as one of the two strings is modified.
2919 @deffn {Scheme Procedure} substring/shared str start [end]
2920 @deffnx {C Function} scm_substring_shared (str, start, end)
2921 Like @code{substring}, but the strings continue to share their storage
2922 even if they are modified. Thus, modifications to @var{str} show up
2923 in the new string, and vice versa.
2926 @deffn {Scheme Procedure} substring/copy str start [end]
2927 @deffnx {C Function} scm_substring_copy (str, start, end)
2928 Like @code{substring}, but the storage for the new string is copied
2932 @deffn {Scheme Procedure} substring/read-only str start [end]
2933 @deffnx {C Function} scm_substring_read_only (str, start, end)
2934 Like @code{substring}, but the resulting string can not be modified.
2937 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
2938 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
2939 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
2940 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
2941 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
2944 @deffn {Scheme Procedure} string-take s n
2945 @deffnx {C Function} scm_string_take (s, n)
2946 Return the @var{n} first characters of @var{s}.
2949 @deffn {Scheme Procedure} string-drop s n
2950 @deffnx {C Function} scm_string_drop (s, n)
2951 Return all but the first @var{n} characters of @var{s}.
2954 @deffn {Scheme Procedure} string-take-right s n
2955 @deffnx {C Function} scm_string_take_right (s, n)
2956 Return the @var{n} last characters of @var{s}.
2959 @deffn {Scheme Procedure} string-drop-right s n
2960 @deffnx {C Function} scm_string_drop_right (s, n)
2961 Return all but the last @var{n} characters of @var{s}.
2964 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
2965 @deffnx {Scheme Procedure} string-pad-right s len [chr [start [end]]]
2966 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
2967 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
2968 Take characters @var{start} to @var{end} from the string @var{s} and
2969 either pad with @var{char} or truncate them to give @var{len}
2972 @code{string-pad} pads or truncates on the left, so for example
2975 (string-pad "x" 3) @result{} " x"
2976 (string-pad "abcde" 3) @result{} "cde"
2979 @code{string-pad-right} pads or truncates on the right, so for example
2982 (string-pad-right "x" 3) @result{} "x "
2983 (string-pad-right "abcde" 3) @result{} "abc"
2987 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
2988 @deffnx {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
2989 @deffnx {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
2990 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
2991 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
2992 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
2993 Trim occurrences of @var{char_pred} from the ends of @var{s}.
2995 @code{string-trim} trims @var{char_pred} characters from the left
2996 (start) of the string, @code{string-trim-right} trims them from the
2997 right (end) of the string, @code{string-trim-both} trims from both
3000 @var{char_pred} can be a character, a character set, or a predicate
3001 procedure to call on each character. If @var{char_pred} is not given
3002 the default is whitespace as per @code{char-set:whitespace}
3003 (@pxref{Standard Character Sets}).
3006 (string-trim " x ") @result{} "x "
3007 (string-trim-right "banana" #\a) @result{} "banan"
3008 (string-trim-both ".,xy:;" char-set:punctuation)
3010 (string-trim-both "xyzzy" (lambda (c)
3017 @node String Modification
3018 @subsubsection String Modification
3020 These procedures are for modifying strings in-place. This means that the
3021 result of the operation is not a new string; instead, the original string's
3022 memory representation is modified.
3024 @rnindex string-set!
3025 @deffn {Scheme Procedure} string-set! str k chr
3026 @deffnx {C Function} scm_string_set_x (str, k, chr)
3027 Store @var{chr} in element @var{k} of @var{str} and return
3028 an unspecified value. @var{k} must be a valid index of
3032 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
3033 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
3036 @rnindex string-fill!
3037 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
3038 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
3039 @deffnx {C Function} scm_string_fill_x (str, chr)
3040 Stores @var{chr} in every element of the given @var{str} and
3041 returns an unspecified value.
3044 @deffn {Scheme Procedure} substring-fill! str start end fill
3045 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
3046 Change every character in @var{str} between @var{start} and
3047 @var{end} to @var{fill}.
3050 (define y "abcdefg")
3051 (substring-fill! y 1 3 #\r)
3057 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
3058 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
3059 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
3060 into @var{str2} beginning at position @var{start2}.
3061 @var{str1} and @var{str2} can be the same string.
3064 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
3065 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
3066 Copy the sequence of characters from index range [@var{start},
3067 @var{end}) in string @var{s} to string @var{target}, beginning
3068 at index @var{tstart}. The characters are copied left-to-right
3069 or right-to-left as needed -- the copy is guaranteed to work,
3070 even if @var{target} and @var{s} are the same string. It is an
3071 error if the copy operation runs off the end of the target
3076 @node String Comparison
3077 @subsubsection String Comparison
3079 The procedures in this section are similar to the character ordering
3080 predicates (@pxref{Characters}), but are defined on character sequences.
3082 The first set is specified in R5RS and has names that end in @code{?}.
3083 The second set is specified in SRFI-13 and the names have not ending
3086 The predicates ending in @code{-ci} ignore the character case
3087 when comparing strings. For now, case-insensitive comparison is done
3088 using the R5RS rules, where every lower-case character that has a
3089 single character upper-case form is converted to uppercase before
3090 comparison. See @xref{Text Collation, the @code{(ice-9
3091 i18n)} module}, for locale-dependent string comparison.
3094 @deffn {Scheme Procedure} string=? [s1 [s2 . rest]]
3095 @deffnx {C Function} scm_i_string_equal_p (s1, s2, rest)
3096 Lexicographic equality predicate; return @code{#t} if the two
3097 strings are the same length and contain the same characters in
3098 the same positions, otherwise return @code{#f}.
3100 The procedure @code{string-ci=?} treats upper and lower case
3101 letters as though they were the same character, but
3102 @code{string=?} treats upper and lower case as distinct
3107 @deffn {Scheme Procedure} string<? [s1 [s2 . rest]]
3108 @deffnx {C Function} scm_i_string_less_p (s1, s2, rest)
3109 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3110 is lexicographically less than @var{s2}.
3114 @deffn {Scheme Procedure} string<=? [s1 [s2 . rest]]
3115 @deffnx {C Function} scm_i_string_leq_p (s1, s2, rest)
3116 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3117 is lexicographically less than or equal to @var{s2}.
3121 @deffn {Scheme Procedure} string>? [s1 [s2 . rest]]
3122 @deffnx {C Function} scm_i_string_gr_p (s1, s2, rest)
3123 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3124 is lexicographically greater than @var{s2}.
3128 @deffn {Scheme Procedure} string>=? [s1 [s2 . rest]]
3129 @deffnx {C Function} scm_i_string_geq_p (s1, s2, rest)
3130 Lexicographic ordering predicate; return @code{#t} if @var{s1}
3131 is lexicographically greater than or equal to @var{s2}.
3134 @rnindex string-ci=?
3135 @deffn {Scheme Procedure} string-ci=? [s1 [s2 . rest]]
3136 @deffnx {C Function} scm_i_string_ci_equal_p (s1, s2, rest)
3137 Case-insensitive string equality predicate; return @code{#t} if
3138 the two strings are the same length and their component
3139 characters match (ignoring case) at each position; otherwise
3143 @rnindex string-ci<?
3144 @deffn {Scheme Procedure} string-ci<? [s1 [s2 . rest]]
3145 @deffnx {C Function} scm_i_string_ci_less_p (s1, s2, rest)
3146 Case insensitive lexicographic ordering predicate; return
3147 @code{#t} if @var{s1} is lexicographically less than @var{s2}
3152 @deffn {Scheme Procedure} string-ci<=? [s1 [s2 . rest]]
3153 @deffnx {C Function} scm_i_string_ci_leq_p (s1, s2, rest)
3154 Case insensitive lexicographic ordering predicate; return
3155 @code{#t} if @var{s1} is lexicographically less than or equal
3156 to @var{s2} regardless of case.
3159 @rnindex string-ci>?
3160 @deffn {Scheme Procedure} string-ci>? [s1 [s2 . rest]]
3161 @deffnx {C Function} scm_i_string_ci_gr_p (s1, s2, rest)
3162 Case insensitive lexicographic ordering predicate; return
3163 @code{#t} if @var{s1} is lexicographically greater than
3164 @var{s2} regardless of case.
3167 @rnindex string-ci>=?
3168 @deffn {Scheme Procedure} string-ci>=? [s1 [s2 . rest]]
3169 @deffnx {C Function} scm_i_string_ci_geq_p (s1, s2, rest)
3170 Case insensitive lexicographic ordering predicate; return
3171 @code{#t} if @var{s1} is lexicographically greater than or
3172 equal to @var{s2} regardless of case.
3175 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3176 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3177 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3178 mismatch index, depending upon whether @var{s1} is less than,
3179 equal to, or greater than @var{s2}. The mismatch index is the
3180 largest index @var{i} such that for every 0 <= @var{j} <
3181 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3182 @var{i} is the first position that does not match.
3185 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
3186 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3187 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3188 mismatch index, depending upon whether @var{s1} is less than,
3189 equal to, or greater than @var{s2}. The mismatch index is the
3190 largest index @var{i} such that for every 0 <= @var{j} <
3191 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3192 @var{i} is the first position where the lowercased letters
3197 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3198 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3199 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3203 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3204 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3205 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3209 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3210 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3211 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3212 true value otherwise.
3215 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3216 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3217 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3218 true value otherwise.
3221 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3222 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3223 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3227 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3228 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3229 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3233 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3234 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3235 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3236 value otherwise. The character comparison is done
3240 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3241 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3242 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3243 value otherwise. The character comparison is done
3247 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3248 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3249 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3250 true value otherwise. The character comparison is done
3254 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3255 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3256 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3257 true value otherwise. The character comparison is done
3261 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3262 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3263 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3264 value otherwise. The character comparison is done
3268 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3269 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3270 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3271 otherwise. The character comparison is done
3275 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3276 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3277 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).
3280 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3281 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3282 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).
3285 Because the same visual appearance of an abstract Unicode character can
3286 be obtained via multiple sequences of Unicode characters, even the
3287 case-insensitive string comparison functions described above may return
3288 @code{#f} when presented with strings containing different
3289 representations of the same character. For example, the Unicode
3290 character ``LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE'' can be
3291 represented with a single character (U+1E69) or by the character ``LATIN
3292 SMALL LETTER S'' (U+0073) followed by the combining marks ``COMBINING
3293 DOT BELOW'' (U+0323) and ``COMBINING DOT ABOVE'' (U+0307).
3295 For this reason, it is often desirable to ensure that the strings
3296 to be compared are using a mutually consistent representation for every
3297 character. The Unicode standard defines two methods of normalizing the
3298 contents of strings: Decomposition, which breaks composite characters
3299 into a set of constituent characters with an ordering defined by the
3300 Unicode Standard; and composition, which performs the converse.
3302 There are two decomposition operations. ``Canonical decomposition''
3303 produces character sequences that share the same visual appearance as
3304 the original characters, while ``compatiblity decomposition'' produces
3305 ones whose visual appearances may differ from the originals but which
3306 represent the same abstract character.
3308 These operations are encapsulated in the following set of normalization
3313 Characters are decomposed to their canonical forms.
3316 Characters are decomposed to their compatibility forms.
3319 Characters are decomposed to their canonical forms, then composed.
3322 Characters are decomposed to their compatibility forms, then composed.
3326 The functions below put their arguments into one of the forms described
3329 @deffn {Scheme Procedure} string-normalize-nfd s
3330 @deffnx {C Function} scm_string_normalize_nfd (s)
3331 Return the @code{NFD} normalized form of @var{s}.
3334 @deffn {Scheme Procedure} string-normalize-nfkd s
3335 @deffnx {C Function} scm_string_normalize_nfkd (s)
3336 Return the @code{NFKD} normalized form of @var{s}.
3339 @deffn {Scheme Procedure} string-normalize-nfc s
3340 @deffnx {C Function} scm_string_normalize_nfc (s)
3341 Return the @code{NFC} normalized form of @var{s}.
3344 @deffn {Scheme Procedure} string-normalize-nfkc s
3345 @deffnx {C Function} scm_string_normalize_nfkc (s)
3346 Return the @code{NFKC} normalized form of @var{s}.
3349 @node String Searching
3350 @subsubsection String Searching
3352 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3353 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3354 Search through the string @var{s} from left to right, returning
3355 the index of the first occurrence of a character which
3359 equals @var{char_pred}, if it is character,
3362 satisfies the predicate @var{char_pred}, if it is a procedure,
3365 is in the set @var{char_pred}, if it is a character set.
3369 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3370 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3371 Search through the string @var{s} from right to left, returning
3372 the index of the last occurrence of a character which
3376 equals @var{char_pred}, if it is character,
3379 satisfies the predicate @var{char_pred}, if it is a procedure,
3382 is in the set if @var{char_pred} is a character set.
3386 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3387 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3388 Return the length of the longest common prefix of the two
3392 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3393 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3394 Return the length of the longest common prefix of the two
3395 strings, ignoring character case.
3398 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3399 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3400 Return the length of the longest common suffix of the two
3404 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3405 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3406 Return the length of the longest common suffix of the two
3407 strings, ignoring character case.
3410 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3411 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3412 Is @var{s1} a prefix of @var{s2}?
3415 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3416 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3417 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3420 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3421 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3422 Is @var{s1} a suffix of @var{s2}?
3425 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3426 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3427 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3430 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3431 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3432 Search through the string @var{s} from right to left, returning
3433 the index of the last occurrence of a character which
3437 equals @var{char_pred}, if it is character,
3440 satisfies the predicate @var{char_pred}, if it is a procedure,
3443 is in the set if @var{char_pred} is a character set.
3447 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3448 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3449 Search through the string @var{s} from left to right, returning
3450 the index of the first occurrence of a character which
3454 does not equal @var{char_pred}, if it is character,
3457 does not satisfy the predicate @var{char_pred}, if it is a
3461 is not in the set if @var{char_pred} is a character set.
3465 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3466 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3467 Search through the string @var{s} from right to left, returning
3468 the index of the last occurrence of a character which
3472 does not equal @var{char_pred}, if it is character,
3475 does not satisfy the predicate @var{char_pred}, if it is a
3479 is not in the set if @var{char_pred} is a character set.
3483 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3484 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3485 Return the count of the number of characters in the string
3490 equals @var{char_pred}, if it is character,
3493 satisfies the predicate @var{char_pred}, if it is a procedure.
3496 is in the set @var{char_pred}, if it is a character set.
3500 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3501 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3502 Does string @var{s1} contain string @var{s2}? Return the index
3503 in @var{s1} where @var{s2} occurs as a substring, or false.
3504 The optional start/end indices restrict the operation to the
3505 indicated substrings.
3508 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3509 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3510 Does string @var{s1} contain string @var{s2}? Return the index
3511 in @var{s1} where @var{s2} occurs as a substring, or false.
3512 The optional start/end indices restrict the operation to the
3513 indicated substrings. Character comparison is done
3517 @node Alphabetic Case Mapping
3518 @subsubsection Alphabetic Case Mapping
3520 These are procedures for mapping strings to their upper- or lower-case
3521 equivalents, respectively, or for capitalizing strings.
3523 @deffn {Scheme Procedure} string-upcase str [start [end]]
3524 @deffnx {C Function} scm_substring_upcase (str, start, end)
3525 @deffnx {C Function} scm_string_upcase (str)
3526 Upcase every character in @code{str}.
3529 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3530 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3531 @deffnx {C Function} scm_string_upcase_x (str)
3532 Destructively upcase every character in @code{str}.
3542 @deffn {Scheme Procedure} string-downcase str [start [end]]
3543 @deffnx {C Function} scm_substring_downcase (str, start, end)
3544 @deffnx {C Function} scm_string_downcase (str)
3545 Downcase every character in @var{str}.
3548 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3549 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3550 @deffnx {C Function} scm_string_downcase_x (str)
3551 Destructively downcase every character in @var{str}.
3556 (string-downcase! y)
3563 @deffn {Scheme Procedure} string-capitalize str
3564 @deffnx {C Function} scm_string_capitalize (str)
3565 Return a freshly allocated string with the characters in
3566 @var{str}, where the first character of every word is
3570 @deffn {Scheme Procedure} string-capitalize! str
3571 @deffnx {C Function} scm_string_capitalize_x (str)
3572 Upcase the first character of every word in @var{str}
3573 destructively and return @var{str}.
3576 y @result{} "hello world"
3577 (string-capitalize! y) @result{} "Hello World"
3578 y @result{} "Hello World"
3582 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3583 @deffnx {C Function} scm_string_titlecase (str, start, end)
3584 Titlecase every first character in a word in @var{str}.
3587 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3588 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3589 Destructively titlecase every first character in a word in
3593 @node Reversing and Appending Strings
3594 @subsubsection Reversing and Appending Strings
3596 @deffn {Scheme Procedure} string-reverse str [start [end]]
3597 @deffnx {C Function} scm_string_reverse (str, start, end)
3598 Reverse the string @var{str}. The optional arguments
3599 @var{start} and @var{end} delimit the region of @var{str} to
3603 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3604 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3605 Reverse the string @var{str} in-place. The optional arguments
3606 @var{start} and @var{end} delimit the region of @var{str} to
3607 operate on. The return value is unspecified.
3610 @rnindex string-append
3611 @deffn {Scheme Procedure} string-append . args
3612 @deffnx {C Function} scm_string_append (args)
3613 Return a newly allocated string whose characters form the
3614 concatenation of the given strings, @var{args}.
3618 (string-append h "world"))
3619 @result{} "hello world"
3623 @deffn {Scheme Procedure} string-append/shared . rest
3624 @deffnx {C Function} scm_string_append_shared (rest)
3625 Like @code{string-append}, but the result may share memory
3626 with the argument strings.
3629 @deffn {Scheme Procedure} string-concatenate ls
3630 @deffnx {C Function} scm_string_concatenate (ls)
3631 Append the elements of @var{ls} (which must be strings)
3632 together into a single string. Guaranteed to return a freshly
3636 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3637 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3638 Without optional arguments, this procedure is equivalent to
3641 (string-concatenate (reverse ls))
3644 If the optional argument @var{final_string} is specified, it is
3645 consed onto the beginning to @var{ls} before performing the
3646 list-reverse and string-concatenate operations. If @var{end}
3647 is given, only the characters of @var{final_string} up to index
3650 Guaranteed to return a freshly allocated string.
3653 @deffn {Scheme Procedure} string-concatenate/shared ls
3654 @deffnx {C Function} scm_string_concatenate_shared (ls)
3655 Like @code{string-concatenate}, but the result may share memory
3656 with the strings in the list @var{ls}.
3659 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3660 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3661 Like @code{string-concatenate-reverse}, but the result may
3662 share memory with the strings in the @var{ls} arguments.
3665 @node Mapping Folding and Unfolding
3666 @subsubsection Mapping, Folding, and Unfolding
3668 @deffn {Scheme Procedure} string-map proc s [start [end]]
3669 @deffnx {C Function} scm_string_map (proc, s, start, end)
3670 @var{proc} is a char->char procedure, it is mapped over
3671 @var{s}. The order in which the procedure is applied to the
3672 string elements is not specified.
3675 @deffn {Scheme Procedure} string-map! proc s [start [end]]
3676 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
3677 @var{proc} is a char->char procedure, it is mapped over
3678 @var{s}. The order in which the procedure is applied to the
3679 string elements is not specified. The string @var{s} is
3680 modified in-place, the return value is not specified.
3683 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
3684 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
3685 @var{proc} is mapped over @var{s} in left-to-right order. The
3686 return value is not specified.
3689 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
3690 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
3691 Call @code{(@var{proc} i)} for each index i in @var{s}, from left to
3694 For example, to change characters to alternately upper and lower case,
3697 (define str (string-copy "studly"))
3698 (string-for-each-index
3701 ((if (even? i) char-upcase char-downcase)
3702 (string-ref str i))))
3704 str @result{} "StUdLy"
3708 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
3709 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
3710 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3711 as the terminating element, from left to right. @var{kons}
3712 must expect two arguments: The actual character and the last
3713 result of @var{kons}' application.
3716 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
3717 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
3718 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3719 as the terminating element, from right to left. @var{kons}
3720 must expect two arguments: The actual character and the last
3721 result of @var{kons}' application.
3724 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
3725 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
3727 @item @var{g} is used to generate a series of @emph{seed}
3728 values from the initial @var{seed}: @var{seed}, (@var{g}
3729 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3731 @item @var{p} tells us when to stop -- when it returns true
3732 when applied to one of these seed values.
3733 @item @var{f} maps each seed value to the corresponding
3734 character in the result string. These chars are assembled
3735 into the string in a left-to-right order.
3736 @item @var{base} is the optional initial/leftmost portion
3737 of the constructed string; it default to the empty
3739 @item @var{make_final} is applied to the terminal seed
3740 value (on which @var{p} returns true) to produce
3741 the final/rightmost portion of the constructed string.
3742 The default is nothing extra.
3746 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
3747 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
3749 @item @var{g} is used to generate a series of @emph{seed}
3750 values from the initial @var{seed}: @var{seed}, (@var{g}
3751 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3753 @item @var{p} tells us when to stop -- when it returns true
3754 when applied to one of these seed values.
3755 @item @var{f} maps each seed value to the corresponding
3756 character in the result string. These chars are assembled
3757 into the string in a right-to-left order.
3758 @item @var{base} is the optional initial/rightmost portion
3759 of the constructed string; it default to the empty
3761 @item @var{make_final} is applied to the terminal seed
3762 value (on which @var{p} returns true) to produce
3763 the final/leftmost portion of the constructed string.
3764 It defaults to @code{(lambda (x) )}.
3768 @node Miscellaneous String Operations
3769 @subsubsection Miscellaneous String Operations
3771 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
3772 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
3773 This is the @emph{extended substring} procedure that implements
3774 replicated copying of a substring of some string.
3776 @var{s} is a string, @var{start} and @var{end} are optional
3777 arguments that demarcate a substring of @var{s}, defaulting to
3778 0 and the length of @var{s}. Replicate this substring up and
3779 down index space, in both the positive and negative directions.
3780 @code{xsubstring} returns the substring of this string
3781 beginning at index @var{from}, and ending at @var{to}, which
3782 defaults to @var{from} + (@var{end} - @var{start}).
3785 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
3786 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
3787 Exactly the same as @code{xsubstring}, but the extracted text
3788 is written into the string @var{target} starting at index
3789 @var{tstart}. The operation is not defined if @code{(eq?
3790 @var{target} @var{s})} or these arguments share storage -- you
3791 cannot copy a string on top of itself.
3794 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
3795 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
3796 Return the string @var{s1}, but with the characters
3797 @var{start1} @dots{} @var{end1} replaced by the characters
3798 @var{start2} @dots{} @var{end2} from @var{s2}.
3801 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
3802 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
3803 Split the string @var{s} into a list of substrings, where each
3804 substring is a maximal non-empty contiguous sequence of
3805 characters from the character set @var{token_set}, which
3806 defaults to @code{char-set:graphic}.
3807 If @var{start} or @var{end} indices are provided, they restrict
3808 @code{string-tokenize} to operating on the indicated substring
3812 @deffn {Scheme Procedure} string-filter s char_pred [start [end]]
3813 @deffnx {C Function} scm_string_filter (s, char_pred, start, end)
3814 Filter the string @var{s}, retaining only those characters which
3815 satisfy @var{char_pred}.
3817 If @var{char_pred} is a procedure, it is applied to each character as
3818 a predicate, if it is a character, it is tested for equality and if it
3819 is a character set, it is tested for membership.
3822 @deffn {Scheme Procedure} string-delete s char_pred [start [end]]
3823 @deffnx {C Function} scm_string_delete (s, char_pred, start, end)
3824 Delete characters satisfying @var{char_pred} from @var{s}.
3826 If @var{char_pred} is a procedure, it is applied to each character as
3827 a predicate, if it is a character, it is tested for equality and if it
3828 is a character set, it is tested for membership.
3831 @node Conversion to/from C
3832 @subsubsection Conversion to/from C
3834 When creating a Scheme string from a C string or when converting a
3835 Scheme string to a C string, the concept of character encoding becomes
3838 In C, a string is just a sequence of bytes, and the character encoding
3839 describes the relation between these bytes and the actual characters
3840 that make up the string. For Scheme strings, character encoding is
3841 not an issue (most of the time), since in Scheme you never get to see
3842 the bytes, only the characters.
3844 Well, ideally, anyway. Right now, Guile simply equates Scheme
3845 characters and bytes, ignoring the possibility of multi-byte encodings
3846 completely. This will change in the future, where Guile will use
3847 Unicode codepoints as its characters and UTF-8 or some other encoding
3848 as its internal encoding. When you exclusively use the functions
3849 listed in this section, you are `future-proof'.
3851 Converting a Scheme string to a C string will often allocate fresh
3852 memory to hold the result. You must take care that this memory is
3853 properly freed eventually. In many cases, this can be achieved by
3854 using @code{scm_dynwind_free} inside an appropriate dynwind context,
3855 @xref{Dynamic Wind}.
3857 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
3858 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
3859 Creates a new Scheme string that has the same contents as @var{str}
3860 when interpreted in the current locale character encoding.
3862 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
3864 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
3865 @var{str} in bytes, and @var{str} does not need to be null-terminated.
3866 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
3867 null-terminated and the real length will be found with @code{strlen}.
3870 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
3871 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
3872 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
3873 respectively, but also frees @var{str} with @code{free} eventually.
3874 Thus, you can use this function when you would free @var{str} anyway
3875 immediately after creating the Scheme string. In certain cases, Guile
3876 can then use @var{str} directly as its internal representation.
3879 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
3880 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
3881 Returns a C string in the current locale encoding with the same
3882 contents as @var{str}. The C string must be freed with @code{free}
3883 eventually, maybe by using @code{scm_dynwind_free}, @xref{Dynamic
3886 For @code{scm_to_locale_string}, the returned string is
3887 null-terminated and an error is signalled when @var{str} contains
3888 @code{#\nul} characters.
3890 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
3891 @var{str} might contain @code{#\nul} characters and the length of the
3892 returned string in bytes is stored in @code{*@var{lenp}}. The
3893 returned string will not be null-terminated in this case. If
3894 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
3895 @code{scm_to_locale_string}.
3898 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
3899 Puts @var{str} as a C string in the current locale encoding into the
3900 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
3901 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
3902 more than that. No terminating @code{'\0'} will be stored.
3904 The return value of @code{scm_to_locale_stringbuf} is the number of
3905 bytes that are needed for all of @var{str}, regardless of whether
3906 @var{buf} was large enough to hold them. Thus, when the return value
3907 is larger than @var{max_len}, only @var{max_len} bytes have been
3908 stored and you probably need to try again with a larger buffer.
3912 @subsection Bytevectors
3917 A @dfn{bytevector} is a raw bit string. The @code{(rnrs bytevector)}
3918 module provides the programming interface specified by the
3919 @uref{http://www.r6rs.org/, Revised^6 Report on the Algorithmic Language
3920 Scheme (R6RS)}. It contains procedures to manipulate bytevectors and
3921 interpret their contents in a number of ways: bytevector contents can be
3922 accessed as signed or unsigned integer of various sizes and endianness,
3923 as IEEE-754 floating point numbers, or as strings. It is a useful tool
3924 to encode and decode binary data.
3926 The R6RS (Section 4.3.4) specifies an external representation for
3927 bytevectors, whereby the octets (integers in the range 0--255) contained
3928 in the bytevector are represented as a list prefixed by @code{#vu8}:
3934 denotes a 3-byte bytevector containing the octets 1, 53, and 204. Like
3935 string literals, booleans, etc., bytevectors are ``self-quoting'', i.e.,
3936 they do not need to be quoted:
3940 @result{} #vu8(1 53 204)
3943 Bytevectors can be used with the binary input/output primitives of the
3944 R6RS (@pxref{R6RS I/O Ports}).
3947 * Bytevector Endianness:: Dealing with byte order.
3948 * Bytevector Manipulation:: Creating, copying, manipulating bytevectors.
3949 * Bytevectors as Integers:: Interpreting bytes as integers.
3950 * Bytevectors and Integer Lists:: Converting to/from an integer list.
3951 * Bytevectors as Floats:: Interpreting bytes as real numbers.
3952 * Bytevectors as Strings:: Interpreting bytes as Unicode strings.
3953 * Bytevectors as Generalized Vectors:: Guile extension to the bytevector API.
3954 * Bytevectors as Uniform Vectors:: Bytevectors and SRFI-4.
3957 @node Bytevector Endianness
3958 @subsubsection Endianness
3964 Some of the following procedures take an @var{endianness} parameter.
3965 The @dfn{endianness} is defined as the order of bytes in multi-byte
3966 numbers: numbers encoded in @dfn{big endian} have their most
3967 significant bytes written first, whereas numbers encoded in
3968 @dfn{little endian} have their least significant bytes
3969 first@footnote{Big-endian and little-endian are the most common
3970 ``endiannesses'', but others do exist. For instance, the GNU MP
3971 library allows @dfn{word order} to be specified independently of
3972 @dfn{byte order} (@pxref{Integer Import and Export,,, gmp, The GNU
3973 Multiple Precision Arithmetic Library Manual}).}.
3975 Little-endian is the native endianness of the IA32 architecture and
3976 its derivatives, while big-endian is native to SPARC and PowerPC,
3977 among others. The @code{native-endianness} procedure returns the
3978 native endianness of the machine it runs on.
3980 @deffn {Scheme Procedure} native-endianness
3981 @deffnx {C Function} scm_native_endianness ()
3982 Return a value denoting the native endianness of the host machine.
3985 @deffn {Scheme Macro} endianness symbol
3986 Return an object denoting the endianness specified by @var{symbol}. If
3987 @var{symbol} is neither @code{big} nor @code{little} then an error is
3988 raised at expand-time.
3991 @defvr {C Variable} scm_endianness_big
3992 @defvrx {C Variable} scm_endianness_little
3993 The objects denoting big- and little-endianness, respectively.
3997 @node Bytevector Manipulation
3998 @subsubsection Manipulating Bytevectors
4000 Bytevectors can be created, copied, and analyzed with the following
4001 procedures and C functions.
4003 @deffn {Scheme Procedure} make-bytevector len [fill]
4004 @deffnx {C Function} scm_make_bytevector (len, fill)
4005 @deffnx {C Function} scm_c_make_bytevector (size_t len)
4006 Return a new bytevector of @var{len} bytes. Optionally, if @var{fill}
4007 is given, fill it with @var{fill}; @var{fill} must be in the range
4011 @deffn {Scheme Procedure} bytevector? obj
4012 @deffnx {C Function} scm_bytevector_p (obj)
4013 Return true if @var{obj} is a bytevector.
4016 @deftypefn {C Function} int scm_is_bytevector (SCM obj)
4017 Equivalent to @code{scm_is_true (scm_bytevector_p (obj))}.
4020 @deffn {Scheme Procedure} bytevector-length bv
4021 @deffnx {C Function} scm_bytevector_length (bv)
4022 Return the length in bytes of bytevector @var{bv}.
4025 @deftypefn {C Function} size_t scm_c_bytevector_length (SCM bv)
4026 Likewise, return the length in bytes of bytevector @var{bv}.
4029 @deffn {Scheme Procedure} bytevector=? bv1 bv2
4030 @deffnx {C Function} scm_bytevector_eq_p (bv1, bv2)
4031 Return is @var{bv1} equals to @var{bv2}---i.e., if they have the same
4032 length and contents.
4035 @deffn {Scheme Procedure} bytevector-fill! bv fill
4036 @deffnx {C Function} scm_bytevector_fill_x (bv, fill)
4037 Fill bytevector @var{bv} with @var{fill}, a byte.
4040 @deffn {Scheme Procedure} bytevector-copy! source source-start target target-start len
4041 @deffnx {C Function} scm_bytevector_copy_x (source, source_start, target, target_start, len)
4042 Copy @var{len} bytes from @var{source} into @var{target}, starting
4043 reading from @var{source-start} (a positive index within @var{source})
4044 and start writing at @var{target-start}.
4047 @deffn {Scheme Procedure} bytevector-copy bv
4048 @deffnx {C Function} scm_bytevector_copy (bv)
4049 Return a newly allocated copy of @var{bv}.
4052 @deftypefn {C Function} scm_t_uint8 scm_c_bytevector_ref (SCM bv, size_t index)
4053 Return the byte at @var{index} in bytevector @var{bv}.
4056 @deftypefn {C Function} void scm_c_bytevector_set_x (SCM bv, size_t index, scm_t_uint8 value)
4057 Set the byte at @var{index} in @var{bv} to @var{value}.
4060 Low-level C macros are available. They do not perform any
4061 type-checking; as such they should be used with care.
4063 @deftypefn {C Macro} size_t SCM_BYTEVECTOR_LENGTH (bv)
4064 Return the length in bytes of bytevector @var{bv}.
4067 @deftypefn {C Macro} {signed char *} SCM_BYTEVECTOR_CONTENTS (bv)
4068 Return a pointer to the contents of bytevector @var{bv}.
4072 @node Bytevectors as Integers
4073 @subsubsection Interpreting Bytevector Contents as Integers
4075 The contents of a bytevector can be interpreted as a sequence of
4076 integers of any given size, sign, and endianness.
4079 (let ((bv (make-bytevector 4)))
4080 (bytevector-u8-set! bv 0 #x12)
4081 (bytevector-u8-set! bv 1 #x34)
4082 (bytevector-u8-set! bv 2 #x56)
4083 (bytevector-u8-set! bv 3 #x78)
4085 (map (lambda (number)
4086 (number->string number 16))
4087 (list (bytevector-u8-ref bv 0)
4088 (bytevector-u16-ref bv 0 (endianness big))
4089 (bytevector-u32-ref bv 0 (endianness little)))))
4091 @result{} ("12" "1234" "78563412")
4094 The most generic procedures to interpret bytevector contents as integers
4095 are described below.
4097 @deffn {Scheme Procedure} bytevector-uint-ref bv index endianness size
4098 @deffnx {Scheme Procedure} bytevector-sint-ref bv index endianness size
4099 @deffnx {C Function} scm_bytevector_uint_ref (bv, index, endianness, size)
4100 @deffnx {C Function} scm_bytevector_sint_ref (bv, index, endianness, size)
4101 Return the @var{size}-byte long unsigned (resp. signed) integer at
4102 index @var{index} in @var{bv}, decoded according to @var{endianness}.
4105 @deffn {Scheme Procedure} bytevector-uint-set! bv index value endianness size
4106 @deffnx {Scheme Procedure} bytevector-sint-set! bv index value endianness size
4107 @deffnx {C Function} scm_bytevector_uint_set_x (bv, index, value, endianness, size)
4108 @deffnx {C Function} scm_bytevector_sint_set_x (bv, index, value, endianness, size)
4109 Set the @var{size}-byte long unsigned (resp. signed) integer at
4110 @var{index} to @var{value}, encoded according to @var{endianness}.
4113 The following procedures are similar to the ones above, but specialized
4114 to a given integer size:
4116 @deffn {Scheme Procedure} bytevector-u8-ref bv index
4117 @deffnx {Scheme Procedure} bytevector-s8-ref bv index
4118 @deffnx {Scheme Procedure} bytevector-u16-ref bv index endianness
4119 @deffnx {Scheme Procedure} bytevector-s16-ref bv index endianness
4120 @deffnx {Scheme Procedure} bytevector-u32-ref bv index endianness
4121 @deffnx {Scheme Procedure} bytevector-s32-ref bv index endianness
4122 @deffnx {Scheme Procedure} bytevector-u64-ref bv index endianness
4123 @deffnx {Scheme Procedure} bytevector-s64-ref bv index endianness
4124 @deffnx {C Function} scm_bytevector_u8_ref (bv, index)
4125 @deffnx {C Function} scm_bytevector_s8_ref (bv, index)
4126 @deffnx {C Function} scm_bytevector_u16_ref (bv, index, endianness)
4127 @deffnx {C Function} scm_bytevector_s16_ref (bv, index, endianness)
4128 @deffnx {C Function} scm_bytevector_u32_ref (bv, index, endianness)
4129 @deffnx {C Function} scm_bytevector_s32_ref (bv, index, endianness)
4130 @deffnx {C Function} scm_bytevector_u64_ref (bv, index, endianness)
4131 @deffnx {C Function} scm_bytevector_s64_ref (bv, index, endianness)
4132 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4133 16, 32 or 64) from @var{bv} at @var{index}, decoded according to
4137 @deffn {Scheme Procedure} bytevector-u8-set! bv index value
4138 @deffnx {Scheme Procedure} bytevector-s8-set! bv index value
4139 @deffnx {Scheme Procedure} bytevector-u16-set! bv index value endianness
4140 @deffnx {Scheme Procedure} bytevector-s16-set! bv index value endianness
4141 @deffnx {Scheme Procedure} bytevector-u32-set! bv index value endianness
4142 @deffnx {Scheme Procedure} bytevector-s32-set! bv index value endianness
4143 @deffnx {Scheme Procedure} bytevector-u64-set! bv index value endianness
4144 @deffnx {Scheme Procedure} bytevector-s64-set! bv index value endianness
4145 @deffnx {C Function} scm_bytevector_u8_set_x (bv, index, value)
4146 @deffnx {C Function} scm_bytevector_s8_set_x (bv, index, value)
4147 @deffnx {C Function} scm_bytevector_u16_set_x (bv, index, value, endianness)
4148 @deffnx {C Function} scm_bytevector_s16_set_x (bv, index, value, endianness)
4149 @deffnx {C Function} scm_bytevector_u32_set_x (bv, index, value, endianness)
4150 @deffnx {C Function} scm_bytevector_s32_set_x (bv, index, value, endianness)
4151 @deffnx {C Function} scm_bytevector_u64_set_x (bv, index, value, endianness)
4152 @deffnx {C Function} scm_bytevector_s64_set_x (bv, index, value, endianness)
4153 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4154 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to
4158 Finally, a variant specialized for the host's endianness is available
4159 for each of these functions (with the exception of the @code{u8}
4160 accessors, for obvious reasons):
4162 @deffn {Scheme Procedure} bytevector-u16-native-ref bv index
4163 @deffnx {Scheme Procedure} bytevector-s16-native-ref bv index
4164 @deffnx {Scheme Procedure} bytevector-u32-native-ref bv index
4165 @deffnx {Scheme Procedure} bytevector-s32-native-ref bv index
4166 @deffnx {Scheme Procedure} bytevector-u64-native-ref bv index
4167 @deffnx {Scheme Procedure} bytevector-s64-native-ref bv index
4168 @deffnx {C Function} scm_bytevector_u16_native_ref (bv, index)
4169 @deffnx {C Function} scm_bytevector_s16_native_ref (bv, index)
4170 @deffnx {C Function} scm_bytevector_u32_native_ref (bv, index)
4171 @deffnx {C Function} scm_bytevector_s32_native_ref (bv, index)
4172 @deffnx {C Function} scm_bytevector_u64_native_ref (bv, index)
4173 @deffnx {C Function} scm_bytevector_s64_native_ref (bv, index)
4174 Return the unsigned @var{n}-bit (signed) integer (where @var{n} is 8,
4175 16, 32 or 64) from @var{bv} at @var{index}, decoded according to the
4176 host's native endianness.
4179 @deffn {Scheme Procedure} bytevector-u16-native-set! bv index value
4180 @deffnx {Scheme Procedure} bytevector-s16-native-set! bv index value
4181 @deffnx {Scheme Procedure} bytevector-u32-native-set! bv index value
4182 @deffnx {Scheme Procedure} bytevector-s32-native-set! bv index value
4183 @deffnx {Scheme Procedure} bytevector-u64-native-set! bv index value
4184 @deffnx {Scheme Procedure} bytevector-s64-native-set! bv index value
4185 @deffnx {C Function} scm_bytevector_u16_native_set_x (bv, index, value)
4186 @deffnx {C Function} scm_bytevector_s16_native_set_x (bv, index, value)
4187 @deffnx {C Function} scm_bytevector_u32_native_set_x (bv, index, value)
4188 @deffnx {C Function} scm_bytevector_s32_native_set_x (bv, index, value)
4189 @deffnx {C Function} scm_bytevector_u64_native_set_x (bv, index, value)
4190 @deffnx {C Function} scm_bytevector_s64_native_set_x (bv, index, value)
4191 Store @var{value} as an @var{n}-bit (signed) integer (where @var{n} is
4192 8, 16, 32 or 64) in @var{bv} at @var{index}, encoded according to the
4193 host's native endianness.
4197 @node Bytevectors and Integer Lists
4198 @subsubsection Converting Bytevectors to/from Integer Lists
4200 Bytevector contents can readily be converted to/from lists of signed or
4204 (bytevector->sint-list (u8-list->bytevector (make-list 4 255))
4205 (endianness little) 2)
4209 @deffn {Scheme Procedure} bytevector->u8-list bv
4210 @deffnx {C Function} scm_bytevector_to_u8_list (bv)
4211 Return a newly allocated list of unsigned 8-bit integers from the
4212 contents of @var{bv}.
4215 @deffn {Scheme Procedure} u8-list->bytevector lst
4216 @deffnx {C Function} scm_u8_list_to_bytevector (lst)
4217 Return a newly allocated bytevector consisting of the unsigned 8-bit
4218 integers listed in @var{lst}.
4221 @deffn {Scheme Procedure} bytevector->uint-list bv endianness size
4222 @deffnx {Scheme Procedure} bytevector->sint-list bv endianness size
4223 @deffnx {C Function} scm_bytevector_to_uint_list (bv, endianness, size)
4224 @deffnx {C Function} scm_bytevector_to_sint_list (bv, endianness, size)
4225 Return a list of unsigned (resp. signed) integers of @var{size} bytes
4226 representing the contents of @var{bv}, decoded according to
4230 @deffn {Scheme Procedure} uint-list->bytevector lst endianness size
4231 @deffnx {Scheme Procedure} sint-list->bytevector lst endianness size
4232 @deffnx {C Function} scm_uint_list_to_bytevector (lst, endianness, size)
4233 @deffnx {C Function} scm_sint_list_to_bytevector (lst, endianness, size)
4234 Return a new bytevector containing the unsigned (resp. signed) integers
4235 listed in @var{lst} and encoded on @var{size} bytes according to
4239 @node Bytevectors as Floats
4240 @subsubsection Interpreting Bytevector Contents as Floating Point Numbers
4242 @cindex IEEE-754 floating point numbers
4244 Bytevector contents can also be accessed as IEEE-754 single- or
4245 double-precision floating point numbers (respectively 32 and 64-bit
4246 long) using the procedures described here.
4248 @deffn {Scheme Procedure} bytevector-ieee-single-ref bv index endianness
4249 @deffnx {Scheme Procedure} bytevector-ieee-double-ref bv index endianness
4250 @deffnx {C Function} scm_bytevector_ieee_single_ref (bv, index, endianness)
4251 @deffnx {C Function} scm_bytevector_ieee_double_ref (bv, index, endianness)
4252 Return the IEEE-754 single-precision floating point number from @var{bv}
4253 at @var{index} according to @var{endianness}.
4256 @deffn {Scheme Procedure} bytevector-ieee-single-set! bv index value endianness
4257 @deffnx {Scheme Procedure} bytevector-ieee-double-set! bv index value endianness
4258 @deffnx {C Function} scm_bytevector_ieee_single_set_x (bv, index, value, endianness)
4259 @deffnx {C Function} scm_bytevector_ieee_double_set_x (bv, index, value, endianness)
4260 Store real number @var{value} in @var{bv} at @var{index} according to
4264 Specialized procedures are also available:
4266 @deffn {Scheme Procedure} bytevector-ieee-single-native-ref bv index
4267 @deffnx {Scheme Procedure} bytevector-ieee-double-native-ref bv index
4268 @deffnx {C Function} scm_bytevector_ieee_single_native_ref (bv, index)
4269 @deffnx {C Function} scm_bytevector_ieee_double_native_ref (bv, index)
4270 Return the IEEE-754 single-precision floating point number from @var{bv}
4271 at @var{index} according to the host's native endianness.
4274 @deffn {Scheme Procedure} bytevector-ieee-single-native-set! bv index value
4275 @deffnx {Scheme Procedure} bytevector-ieee-double-native-set! bv index value
4276 @deffnx {C Function} scm_bytevector_ieee_single_native_set_x (bv, index, value)
4277 @deffnx {C Function} scm_bytevector_ieee_double_native_set_x (bv, index, value)
4278 Store real number @var{value} in @var{bv} at @var{index} according to
4279 the host's native endianness.
4283 @node Bytevectors as Strings
4284 @subsubsection Interpreting Bytevector Contents as Unicode Strings
4286 @cindex Unicode string encoding
4288 Bytevector contents can also be interpreted as Unicode strings encoded
4289 in one of the most commonly available encoding formats@footnote{Guile
4290 1.8 does @emph{not} support Unicode strings. Therefore, the procedures
4291 described here assume that Guile strings are internally encoded
4292 according to the current locale. For instance, if @code{$LC_CTYPE} is
4293 @code{fr_FR.ISO-8859-1}, then @code{string->utf-8} @i{et al.} will
4294 assume that Guile strings are Latin-1-encoded.}.
4297 (utf8->string (u8-list->bytevector '(99 97 102 101)))
4300 (string->utf8 "caf@'e") ;; SMALL LATIN LETTER E WITH ACUTE ACCENT
4301 @result{} #vu8(99 97 102 195 169)
4304 @deffn {Scheme Procedure} string->utf8 str
4305 @deffnx {Scheme Procedure} string->utf16 str
4306 @deffnx {Scheme Procedure} string->utf32 str
4307 @deffnx {C Function} scm_string_to_utf8 (str)
4308 @deffnx {C Function} scm_string_to_utf16 (str)
4309 @deffnx {C Function} scm_string_to_utf32 (str)
4310 Return a newly allocated bytevector that contains the UTF-8, UTF-16, or
4311 UTF-32 (aka. UCS-4) encoding of @var{str}.
4314 @deffn {Scheme Procedure} utf8->string utf
4315 @deffnx {Scheme Procedure} utf16->string utf
4316 @deffnx {Scheme Procedure} utf32->string utf
4317 @deffnx {C Function} scm_utf8_to_string (utf)
4318 @deffnx {C Function} scm_utf16_to_string (utf)
4319 @deffnx {C Function} scm_utf32_to_string (utf)
4320 Return a newly allocated string that contains from the UTF-8-, UTF-16-,
4321 or UTF-32-decoded contents of bytevector @var{utf}.
4324 @node Bytevectors as Generalized Vectors
4325 @subsubsection Accessing Bytevectors with the Generalized Vector API
4327 As an extension to the R6RS, Guile allows bytevectors to be manipulated
4328 with the @dfn{generalized vector} procedures (@pxref{Generalized
4329 Vectors}). This also allows bytevectors to be accessed using the
4330 generic @dfn{array} procedures (@pxref{Array Procedures}). When using
4331 these APIs, bytes are accessed one at a time as 8-bit unsigned integers:
4334 (define bv #vu8(0 1 2 3))
4336 (generalized-vector? bv)
4339 (generalized-vector-ref bv 2)
4342 (generalized-vector-set! bv 2 77)
4351 @node Bytevectors as Uniform Vectors
4352 @subsubsection Accessing Bytevectors with the SRFI-4 API
4354 Bytevectors may also be accessed with the SRFI-4 API. @xref{SRFI-4 and
4355 Bytevectors}, for more information.
4358 @node Regular Expressions
4359 @subsection Regular Expressions
4360 @tpindex Regular expressions
4362 @cindex regular expressions
4364 @cindex emacs regexp
4366 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
4367 describes a whole class of strings. A full description of regular
4368 expressions and their syntax is beyond the scope of this manual;
4369 an introduction can be found in the Emacs manual (@pxref{Regexps,
4370 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}), or
4371 in many general Unix reference books.
4373 If your system does not include a POSIX regular expression library,
4374 and you have not linked Guile with a third-party regexp library such
4375 as Rx, these functions will not be available. You can tell whether
4376 your Guile installation includes regular expression support by
4377 checking whether @code{(provided? 'regex)} returns true.
4379 The following regexp and string matching features are provided by the
4380 @code{(ice-9 regex)} module. Before using the described functions,
4381 you should load this module by executing @code{(use-modules (ice-9
4385 * Regexp Functions:: Functions that create and match regexps.
4386 * Match Structures:: Finding what was matched by a regexp.
4387 * Backslash Escapes:: Removing the special meaning of regexp
4392 @node Regexp Functions
4393 @subsubsection Regexp Functions
4395 By default, Guile supports POSIX extended regular expressions.
4396 That means that the characters @samp{(}, @samp{)}, @samp{+} and
4397 @samp{?} are special, and must be escaped if you wish to match the
4400 This regular expression interface was modeled after that
4401 implemented by SCSH, the Scheme Shell. It is intended to be
4402 upwardly compatible with SCSH regular expressions.
4404 Zero bytes (@code{#\nul}) cannot be used in regex patterns or input
4405 strings, since the underlying C functions treat that as the end of
4406 string. If there's a zero byte an error is thrown.
4408 Patterns and input strings are treated as being in the locale
4409 character set if @code{setlocale} has been called (@pxref{Locales}),
4410 and in a multibyte locale this includes treating multi-byte sequences
4411 as a single character. (Guile strings are currently merely bytes,
4412 though this may change in the future, @xref{Conversion to/from C}.)
4414 @deffn {Scheme Procedure} string-match pattern str [start]
4415 Compile the string @var{pattern} into a regular expression and compare
4416 it with @var{str}. The optional numeric argument @var{start} specifies
4417 the position of @var{str} at which to begin matching.
4419 @code{string-match} returns a @dfn{match structure} which
4420 describes what, if anything, was matched by the regular
4421 expression. @xref{Match Structures}. If @var{str} does not match
4422 @var{pattern} at all, @code{string-match} returns @code{#f}.
4425 Two examples of a match follow. In the first example, the pattern
4426 matches the four digits in the match string. In the second, the pattern
4430 (string-match "[0-9][0-9][0-9][0-9]" "blah2002")
4431 @result{} #("blah2002" (4 . 8))
4433 (string-match "[A-Za-z]" "123456")
4437 Each time @code{string-match} is called, it must compile its
4438 @var{pattern} argument into a regular expression structure. This
4439 operation is expensive, which makes @code{string-match} inefficient if
4440 the same regular expression is used several times (for example, in a
4441 loop). For better performance, you can compile a regular expression in
4442 advance and then match strings against the compiled regexp.
4444 @deffn {Scheme Procedure} make-regexp pat flag@dots{}
4445 @deffnx {C Function} scm_make_regexp (pat, flaglst)
4446 Compile the regular expression described by @var{pat}, and
4447 return the compiled regexp structure. If @var{pat} does not
4448 describe a legal regular expression, @code{make-regexp} throws
4449 a @code{regular-expression-syntax} error.
4451 The @var{flag} arguments change the behavior of the compiled
4452 regular expression. The following values may be supplied:
4454 @defvar regexp/icase
4455 Consider uppercase and lowercase letters to be the same when
4459 @defvar regexp/newline
4460 If a newline appears in the target string, then permit the
4461 @samp{^} and @samp{$} operators to match immediately after or
4462 immediately before the newline, respectively. Also, the
4463 @samp{.} and @samp{[^...]} operators will never match a newline
4464 character. The intent of this flag is to treat the target
4465 string as a buffer containing many lines of text, and the
4466 regular expression as a pattern that may match a single one of
4470 @defvar regexp/basic
4471 Compile a basic (``obsolete'') regexp instead of the extended
4472 (``modern'') regexps that are the default. Basic regexps do
4473 not consider @samp{|}, @samp{+} or @samp{?} to be special
4474 characters, and require the @samp{@{...@}} and @samp{(...)}
4475 metacharacters to be backslash-escaped (@pxref{Backslash
4476 Escapes}). There are several other differences between basic
4477 and extended regular expressions, but these are the most
4481 @defvar regexp/extended
4482 Compile an extended regular expression rather than a basic
4483 regexp. This is the default behavior; this flag will not
4484 usually be needed. If a call to @code{make-regexp} includes
4485 both @code{regexp/basic} and @code{regexp/extended} flags, the
4486 one which comes last will override the earlier one.
4490 @deffn {Scheme Procedure} regexp-exec rx str [start [flags]]
4491 @deffnx {C Function} scm_regexp_exec (rx, str, start, flags)
4492 Match the compiled regular expression @var{rx} against
4493 @code{str}. If the optional integer @var{start} argument is
4494 provided, begin matching from that position in the string.
4495 Return a match structure describing the results of the match,
4496 or @code{#f} if no match could be found.
4498 The @var{flags} argument changes the matching behavior. The following
4499 flag values may be supplied, use @code{logior} (@pxref{Bitwise
4500 Operations}) to combine them,
4502 @defvar regexp/notbol
4503 Consider that the @var{start} offset into @var{str} is not the
4504 beginning of a line and should not match operator @samp{^}.
4506 If @var{rx} was created with the @code{regexp/newline} option above,
4507 @samp{^} will still match after a newline in @var{str}.
4510 @defvar regexp/noteol
4511 Consider that the end of @var{str} is not the end of a line and should
4512 not match operator @samp{$}.
4514 If @var{rx} was created with the @code{regexp/newline} option above,
4515 @samp{$} will still match before a newline in @var{str}.
4520 ;; Regexp to match uppercase letters
4521 (define r (make-regexp "[A-Z]*"))
4523 ;; Regexp to match letters, ignoring case
4524 (define ri (make-regexp "[A-Z]*" regexp/icase))
4526 ;; Search for bob using regexp r
4527 (match:substring (regexp-exec r "bob"))
4528 @result{} "" ; no match
4530 ;; Search for bob using regexp ri
4531 (match:substring (regexp-exec ri "Bob"))
4532 @result{} "Bob" ; matched case insensitive
4535 @deffn {Scheme Procedure} regexp? obj
4536 @deffnx {C Function} scm_regexp_p (obj)
4537 Return @code{#t} if @var{obj} is a compiled regular expression,
4538 or @code{#f} otherwise.
4542 @deffn {Scheme Procedure} list-matches regexp str [flags]
4543 Return a list of match structures which are the non-overlapping
4544 matches of @var{regexp} in @var{str}. @var{regexp} can be either a
4545 pattern string or a compiled regexp. The @var{flags} argument is as
4546 per @code{regexp-exec} above.
4549 (map match:substring (list-matches "[a-z]+" "abc 42 def 78"))
4550 @result{} ("abc" "def")
4554 @deffn {Scheme Procedure} fold-matches regexp str init proc [flags]
4555 Apply @var{proc} to the non-overlapping matches of @var{regexp} in
4556 @var{str}, to build a result. @var{regexp} can be either a pattern
4557 string or a compiled regexp. The @var{flags} argument is as per
4558 @code{regexp-exec} above.
4560 @var{proc} is called as @code{(@var{proc} match prev)} where
4561 @var{match} is a match structure and @var{prev} is the previous return
4562 from @var{proc}. For the first call @var{prev} is the given
4563 @var{init} parameter. @code{fold-matches} returns the final value
4566 For example to count matches,
4569 (fold-matches "[a-z][0-9]" "abc x1 def y2" 0
4570 (lambda (match count)
4577 Regular expressions are commonly used to find patterns in one string
4578 and replace them with the contents of another string. The following
4579 functions are convenient ways to do this.
4581 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4582 @deffn {Scheme Procedure} regexp-substitute port match [item@dots{}]
4583 Write to @var{port} selected parts of the match structure @var{match}.
4584 Or if @var{port} is @code{#f} then form a string from those parts and
4587 Each @var{item} specifies a part to be written, and may be one of the
4592 A string. String arguments are written out verbatim.
4595 An integer. The submatch with that number is written
4596 (@code{match:substring}). Zero is the entire match.
4599 The symbol @samp{pre}. The portion of the matched string preceding
4600 the regexp match is written (@code{match:prefix}).
4603 The symbol @samp{post}. The portion of the matched string following
4604 the regexp match is written (@code{match:suffix}).
4607 For example, changing a match and retaining the text before and after,
4610 (regexp-substitute #f (string-match "[0-9]+" "number 25 is good")
4612 @result{} "number 37 is good"
4615 Or matching a @sc{yyyymmdd} format date such as @samp{20020828} and
4616 re-ordering and hyphenating the fields.
4620 "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4621 (define s "Date 20020429 12am.")
4622 (regexp-substitute #f (string-match date-regex s)
4623 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4624 @result{} "Date 04-29-2002 12am. (20020429)"
4629 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
4630 @deffn {Scheme Procedure} regexp-substitute/global port regexp target [item@dots{}]
4631 @cindex search and replace
4632 Write to @var{port} selected parts of matches of @var{regexp} in
4633 @var{target}. If @var{port} is @code{#f} then form a string from
4634 those parts and return that. @var{regexp} can be a string or a
4637 This is similar to @code{regexp-substitute}, but allows global
4638 substitutions on @var{target}. Each @var{item} behaves as per
4639 @code{regexp-substitute}, with the following differences,
4643 A function. Called as @code{(@var{item} match)} with the match
4644 structure for the @var{regexp} match, it should return a string to be
4645 written to @var{port}.
4648 The symbol @samp{post}. This doesn't output anything, but instead
4649 causes @code{regexp-substitute/global} to recurse on the unmatched
4650 portion of @var{target}.
4652 This @emph{must} be supplied to perform a global search and replace on
4653 @var{target}; without it @code{regexp-substitute/global} returns after
4654 a single match and output.
4657 For example, to collapse runs of tabs and spaces to a single hyphen
4661 (regexp-substitute/global #f "[ \t]+" "this is the text"
4663 @result{} "this-is-the-text"
4666 Or using a function to reverse the letters in each word,
4669 (regexp-substitute/global #f "[a-z]+" "to do and not-do"
4670 'pre (lambda (m) (string-reverse (match:substring m))) 'post)
4671 @result{} "ot od dna ton-od"
4674 Without the @code{post} symbol, just one regexp match is made. For
4675 example the following is the date example from
4676 @code{regexp-substitute} above, without the need for the separate
4677 @code{string-match} call.
4681 "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
4682 (define s "Date 20020429 12am.")
4683 (regexp-substitute/global #f date-regex s
4684 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
4686 @result{} "Date 04-29-2002 12am. (20020429)"
4691 @node Match Structures
4692 @subsubsection Match Structures
4694 @cindex match structures
4696 A @dfn{match structure} is the object returned by @code{string-match} and
4697 @code{regexp-exec}. It describes which portion of a string, if any,
4698 matched the given regular expression. Match structures include: a
4699 reference to the string that was checked for matches; the starting and
4700 ending positions of the regexp match; and, if the regexp included any
4701 parenthesized subexpressions, the starting and ending positions of each
4704 In each of the regexp match functions described below, the @code{match}
4705 argument must be a match structure returned by a previous call to
4706 @code{string-match} or @code{regexp-exec}. Most of these functions
4707 return some information about the original target string that was
4708 matched against a regular expression; we will call that string
4709 @var{target} for easy reference.
4711 @c begin (scm-doc-string "regex.scm" "regexp-match?")
4712 @deffn {Scheme Procedure} regexp-match? obj
4713 Return @code{#t} if @var{obj} is a match structure returned by a
4714 previous call to @code{regexp-exec}, or @code{#f} otherwise.
4717 @c begin (scm-doc-string "regex.scm" "match:substring")
4718 @deffn {Scheme Procedure} match:substring match [n]
4719 Return the portion of @var{target} matched by subexpression number
4720 @var{n}. Submatch 0 (the default) represents the entire regexp match.
4721 If the regular expression as a whole matched, but the subexpression
4722 number @var{n} did not match, return @code{#f}.
4726 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4730 ;; match starting at offset 6 in the string
4732 (string-match "[0-9][0-9][0-9][0-9]" "blah987654" 6))
4736 @c begin (scm-doc-string "regex.scm" "match:start")
4737 @deffn {Scheme Procedure} match:start match [n]
4738 Return the starting position of submatch number @var{n}.
4741 In the following example, the result is 4, since the match starts at
4745 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4750 @c begin (scm-doc-string "regex.scm" "match:end")
4751 @deffn {Scheme Procedure} match:end match [n]
4752 Return the ending position of submatch number @var{n}.
4755 In the following example, the result is 8, since the match runs between
4756 characters 4 and 8 (i.e. the ``2002'').
4759 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4764 @c begin (scm-doc-string "regex.scm" "match:prefix")
4765 @deffn {Scheme Procedure} match:prefix match
4766 Return the unmatched portion of @var{target} preceding the regexp match.
4769 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4775 @c begin (scm-doc-string "regex.scm" "match:suffix")
4776 @deffn {Scheme Procedure} match:suffix match
4777 Return the unmatched portion of @var{target} following the regexp match.
4781 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4786 @c begin (scm-doc-string "regex.scm" "match:count")
4787 @deffn {Scheme Procedure} match:count match
4788 Return the number of parenthesized subexpressions from @var{match}.
4789 Note that the entire regular expression match itself counts as a
4790 subexpression, and failed submatches are included in the count.
4793 @c begin (scm-doc-string "regex.scm" "match:string")
4794 @deffn {Scheme Procedure} match:string match
4795 Return the original @var{target} string.
4799 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4801 @result{} "blah2002foo"
4805 @node Backslash Escapes
4806 @subsubsection Backslash Escapes
4808 Sometimes you will want a regexp to match characters like @samp{*} or
4809 @samp{$} exactly. For example, to check whether a particular string
4810 represents a menu entry from an Info node, it would be useful to match
4811 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
4812 because the asterisk is a metacharacter, it won't match the @samp{*} at
4813 the beginning of the string. In this case, we want to make the first
4816 You can do this by preceding the metacharacter with a backslash
4817 character @samp{\}. (This is also called @dfn{quoting} the
4818 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
4819 sees a backslash in a regular expression, it considers the following
4820 glyph to be an ordinary character, no matter what special meaning it
4821 would ordinarily have. Therefore, we can make the above example work by
4822 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
4823 the regular expression engine to match only a single asterisk in the
4826 Since the backslash is itself a metacharacter, you may force a regexp to
4827 match a backslash in the target string by preceding the backslash with
4828 itself. For example, to find variable references in a @TeX{} program,
4829 you might want to find occurrences of the string @samp{\let\} followed
4830 by any number of alphabetic characters. The regular expression
4831 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
4832 regexp each match a single backslash in the target string.
4834 @c begin (scm-doc-string "regex.scm" "regexp-quote")
4835 @deffn {Scheme Procedure} regexp-quote str
4836 Quote each special character found in @var{str} with a backslash, and
4837 return the resulting string.
4840 @strong{Very important:} Using backslash escapes in Guile source code
4841 (as in Emacs Lisp or C) can be tricky, because the backslash character
4842 has special meaning for the Guile reader. For example, if Guile
4843 encounters the character sequence @samp{\n} in the middle of a string
4844 while processing Scheme code, it replaces those characters with a
4845 newline character. Similarly, the character sequence @samp{\t} is
4846 replaced by a horizontal tab. Several of these @dfn{escape sequences}
4847 are processed by the Guile reader before your code is executed.
4848 Unrecognized escape sequences are ignored: if the characters @samp{\*}
4849 appear in a string, they will be translated to the single character
4852 This translation is obviously undesirable for regular expressions, since
4853 we want to be able to include backslashes in a string in order to
4854 escape regexp metacharacters. Therefore, to make sure that a backslash
4855 is preserved in a string in your Guile program, you must use @emph{two}
4856 consecutive backslashes:
4859 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
4862 The string in this example is preprocessed by the Guile reader before
4863 any code is executed. The resulting argument to @code{make-regexp} is
4864 the string @samp{^\* [^:]*}, which is what we really want.
4866 This also means that in order to write a regular expression that matches
4867 a single backslash character, the regular expression string in the
4868 source code must include @emph{four} backslashes. Each consecutive pair
4869 of backslashes gets translated by the Guile reader to a single
4870 backslash, and the resulting double-backslash is interpreted by the
4871 regexp engine as matching a single backslash character. Hence:
4874 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
4877 The reason for the unwieldiness of this syntax is historical. Both
4878 regular expression pattern matchers and Unix string processing systems
4879 have traditionally used backslashes with the special meanings
4880 described above. The POSIX regular expression specification and ANSI C
4881 standard both require these semantics. Attempting to abandon either
4882 convention would cause other kinds of compatibility problems, possibly
4883 more severe ones. Therefore, without extending the Scheme reader to
4884 support strings with different quoting conventions (an ungainly and
4885 confusing extension when implemented in other languages), we must adhere
4886 to this cumbersome escape syntax.
4893 Symbols in Scheme are widely used in three ways: as items of discrete
4894 data, as lookup keys for alists and hash tables, and to denote variable
4897 A @dfn{symbol} is similar to a string in that it is defined by a
4898 sequence of characters. The sequence of characters is known as the
4899 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4900 name doesn't include any characters that could be confused with other
4901 elements of Scheme syntax --- a symbol is written in a Scheme program by
4902 writing the sequence of characters that make up the name, @emph{without}
4903 any quotation marks or other special syntax. For example, the symbol
4904 whose name is ``multiply-by-2'' is written, simply:
4910 Notice how this differs from a @emph{string} with contents
4911 ``multiply-by-2'', which is written with double quotation marks, like
4918 Looking beyond how they are written, symbols are different from strings
4919 in two important respects.
4921 The first important difference is uniqueness. If the same-looking
4922 string is read twice from two different places in a program, the result
4923 is two @emph{different} string objects whose contents just happen to be
4924 the same. If, on the other hand, the same-looking symbol is read twice
4925 from two different places in a program, the result is the @emph{same}
4926 symbol object both times.
4928 Given two read symbols, you can use @code{eq?} to test whether they are
4929 the same (that is, have the same name). @code{eq?} is the most
4930 efficient comparison operator in Scheme, and comparing two symbols like
4931 this is as fast as comparing, for example, two numbers. Given two
4932 strings, on the other hand, you must use @code{equal?} or
4933 @code{string=?}, which are much slower comparison operators, to
4934 determine whether the strings have the same contents.
4937 (define sym1 (quote hello))
4938 (define sym2 (quote hello))
4939 (eq? sym1 sym2) @result{} #t
4941 (define str1 "hello")
4942 (define str2 "hello")
4943 (eq? str1 str2) @result{} #f
4944 (equal? str1 str2) @result{} #t
4947 The second important difference is that symbols, unlike strings, are not
4948 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
4949 example above: @code{(quote hello)} evaluates to the symbol named
4950 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
4951 symbol named "hello" and evaluated as a variable reference @dots{} about
4952 which more below (@pxref{Symbol Variables}).
4955 * Symbol Data:: Symbols as discrete data.
4956 * Symbol Keys:: Symbols as lookup keys.
4957 * Symbol Variables:: Symbols as denoting variables.
4958 * Symbol Primitives:: Operations related to symbols.
4959 * Symbol Props:: Function slots and property lists.
4960 * Symbol Read Syntax:: Extended read syntax for symbols.
4961 * Symbol Uninterned:: Uninterned symbols.
4966 @subsubsection Symbols as Discrete Data
4968 Numbers and symbols are similar to the extent that they both lend
4969 themselves to @code{eq?} comparison. But symbols are more descriptive
4970 than numbers, because a symbol's name can be used directly to describe
4971 the concept for which that symbol stands.
4973 For example, imagine that you need to represent some colours in a
4974 computer program. Using numbers, you would have to choose arbitrarily
4975 some mapping between numbers and colours, and then take care to use that
4976 mapping consistently:
4979 ;; 1=red, 2=green, 3=purple
4981 (if (eq? (colour-of car) 1)
4986 You can make the mapping more explicit and the code more readable by
4994 (if (eq? (colour-of car) red)
4999 But the simplest and clearest approach is not to use numbers at all, but
5000 symbols whose names specify the colours that they refer to:
5003 (if (eq? (colour-of car) 'red)
5007 The descriptive advantages of symbols over numbers increase as the set
5008 of concepts that you want to describe grows. Suppose that a car object
5009 can have other properties as well, such as whether it has or uses:
5013 automatic or manual transmission
5015 leaded or unleaded fuel
5017 power steering (or not).
5021 Then a car's combined property set could be naturally represented and
5022 manipulated as a list of symbols:
5025 (properties-of car1)
5027 (red manual unleaded power-steering)
5029 (if (memq 'power-steering (properties-of car1))
5030 (display "Unfit people can drive this car.\n")
5031 (display "You'll need strong arms to drive this car!\n"))
5033 Unfit people can drive this car.
5036 Remember, the fundamental property of symbols that we are relying on
5037 here is that an occurrence of @code{'red} in one part of a program is an
5038 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
5039 another part of a program; this means that symbols can usefully be
5040 compared using @code{eq?}. At the same time, symbols have naturally
5041 descriptive names. This combination of efficiency and descriptive power
5042 makes them ideal for use as discrete data.
5046 @subsubsection Symbols as Lookup Keys
5048 Given their efficiency and descriptive power, it is natural to use
5049 symbols as the keys in an association list or hash table.
5051 To illustrate this, consider a more structured representation of the car
5052 properties example from the preceding subsection. Rather than
5053 mixing all the properties up together in a flat list, we could use an
5054 association list like this:
5057 (define car1-properties '((colour . red)
5058 (transmission . manual)
5060 (steering . power-assisted)))
5063 Notice how this structure is more explicit and extensible than the flat
5064 list. For example it makes clear that @code{manual} refers to the
5065 transmission rather than, say, the windows or the locking of the car.
5066 It also allows further properties to use the same symbols among their
5067 possible values without becoming ambiguous:
5070 (define car1-properties '((colour . red)
5071 (transmission . manual)
5073 (steering . power-assisted)
5075 (locking . manual)))
5078 With a representation like this, it is easy to use the efficient
5079 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
5080 extract or change individual pieces of information:
5083 (assq-ref car1-properties 'fuel) @result{} unleaded
5084 (assq-ref car1-properties 'transmission) @result{} manual
5086 (assq-set! car1-properties 'seat-colour 'black)
5089 (transmission . manual)
5091 (steering . power-assisted)
5092 (seat-colour . black)
5093 (locking . manual)))
5096 Hash tables also have keys, and exactly the same arguments apply to the
5097 use of symbols in hash tables as in association lists. The hash value
5098 that Guile uses to decide where to add a symbol-keyed entry to a hash
5099 table can be obtained by calling the @code{symbol-hash} procedure:
5101 @deffn {Scheme Procedure} symbol-hash symbol
5102 @deffnx {C Function} scm_symbol_hash (symbol)
5103 Return a hash value for @var{symbol}.
5106 See @ref{Hash Tables} for information about hash tables in general, and
5107 for why you might choose to use a hash table rather than an association
5111 @node Symbol Variables
5112 @subsubsection Symbols as Denoting Variables
5114 When an unquoted symbol in a Scheme program is evaluated, it is
5115 interpreted as a variable reference, and the result of the evaluation is
5116 the appropriate variable's value.
5118 For example, when the expression @code{(string-length "abcd")} is read
5119 and evaluated, the sequence of characters @code{string-length} is read
5120 as the symbol whose name is "string-length". This symbol is associated
5121 with a variable whose value is the procedure that implements string
5122 length calculation. Therefore evaluation of the @code{string-length}
5123 symbol results in that procedure.
5125 The details of the connection between an unquoted symbol and the
5126 variable to which it refers are explained elsewhere. See @ref{Binding
5127 Constructs}, for how associations between symbols and variables are
5128 created, and @ref{Modules}, for how those associations are affected by
5129 Guile's module system.
5132 @node Symbol Primitives
5133 @subsubsection Operations Related to Symbols
5135 Given any Scheme value, you can determine whether it is a symbol using
5136 the @code{symbol?} primitive:
5139 @deffn {Scheme Procedure} symbol? obj
5140 @deffnx {C Function} scm_symbol_p (obj)
5141 Return @code{#t} if @var{obj} is a symbol, otherwise return
5145 @deftypefn {C Function} int scm_is_symbol (SCM val)
5146 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
5149 Once you know that you have a symbol, you can obtain its name as a
5150 string by calling @code{symbol->string}. Note that Guile differs by
5151 default from R5RS on the details of @code{symbol->string} as regards
5154 @rnindex symbol->string
5155 @deffn {Scheme Procedure} symbol->string s
5156 @deffnx {C Function} scm_symbol_to_string (s)
5157 Return the name of symbol @var{s} as a string. By default, Guile reads
5158 symbols case-sensitively, so the string returned will have the same case
5159 variation as the sequence of characters that caused @var{s} to be
5162 If Guile is set to read symbols case-insensitively (as specified by
5163 R5RS), and @var{s} comes into being as part of a literal expression
5164 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
5165 by a call to the @code{read} or @code{string-ci->symbol} procedures,
5166 Guile converts any alphabetic characters in the symbol's name to
5167 lower case before creating the symbol object, so the string returned
5168 here will be in lower case.
5170 If @var{s} was created by @code{string->symbol}, the case of characters
5171 in the string returned will be the same as that in the string that was
5172 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
5173 setting at the time @var{s} was created.
5175 It is an error to apply mutation procedures like @code{string-set!} to
5176 strings returned by this procedure.
5179 Most symbols are created by writing them literally in code. However it
5180 is also possible to create symbols programmatically using the following
5181 @code{string->symbol} and @code{string-ci->symbol} procedures:
5183 @rnindex string->symbol
5184 @deffn {Scheme Procedure} string->symbol string
5185 @deffnx {C Function} scm_string_to_symbol (string)
5186 Return the symbol whose name is @var{string}. This procedure can create
5187 symbols with names containing special characters or letters in the
5188 non-standard case, but it is usually a bad idea to create such symbols
5189 because in some implementations of Scheme they cannot be read as
5193 @deffn {Scheme Procedure} string-ci->symbol str
5194 @deffnx {C Function} scm_string_ci_to_symbol (str)
5195 Return the symbol whose name is @var{str}. If Guile is currently
5196 reading symbols case-insensitively, @var{str} is converted to lowercase
5197 before the returned symbol is looked up or created.
5200 The following examples illustrate Guile's detailed behaviour as regards
5201 the case-sensitivity of symbols:
5204 (read-enable 'case-insensitive) ; R5RS compliant behaviour
5206 (symbol->string 'flying-fish) @result{} "flying-fish"
5207 (symbol->string 'Martin) @result{} "martin"
5209 (string->symbol "Malvina")) @result{} "Malvina"
5211 (eq? 'mISSISSIppi 'mississippi) @result{} #t
5212 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5213 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
5215 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5216 (string=? "K. Harper, M.D."
5218 (string->symbol "K. Harper, M.D."))) @result{} #t
5220 (read-disable 'case-insensitive) ; Guile default behaviour
5222 (symbol->string 'flying-fish) @result{} "flying-fish"
5223 (symbol->string 'Martin) @result{} "Martin"
5225 (string->symbol "Malvina")) @result{} "Malvina"
5227 (eq? 'mISSISSIppi 'mississippi) @result{} #f
5228 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
5229 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
5231 (string->symbol (symbol->string 'LolliPop))) @result{} #t
5232 (string=? "K. Harper, M.D."
5234 (string->symbol "K. Harper, M.D."))) @result{} #t
5237 From C, there are lower level functions that construct a Scheme symbol
5238 from a C string in the current locale encoding.
5240 When you want to do more from C, you should convert between symbols
5241 and strings using @code{scm_symbol_to_string} and
5242 @code{scm_string_to_symbol} and work with the strings.
5244 @deffn {C Function} scm_from_locale_symbol (const char *name)
5245 @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
5246 Construct and return a Scheme symbol whose name is specified by
5247 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
5248 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
5249 specified explicitly by @var{len}.
5252 @deftypefn {C Function} SCM scm_take_locale_symbol (char *str)
5253 @deftypefnx {C Function} SCM scm_take_locale_symboln (char *str, size_t len)
5254 Like @code{scm_from_locale_symbol} and @code{scm_from_locale_symboln},
5255 respectively, but also frees @var{str} with @code{free} eventually.
5256 Thus, you can use this function when you would free @var{str} anyway
5257 immediately after creating the Scheme string. In certain cases, Guile
5258 can then use @var{str} directly as its internal representation.
5261 The size of a symbol can also be obtained from C:
5263 @deftypefn {C Function} size_t scm_c_symbol_length (SCM sym)
5264 Return the number of characters in @var{sym}.
5267 Finally, some applications, especially those that generate new Scheme
5268 code dynamically, need to generate symbols for use in the generated
5269 code. The @code{gensym} primitive meets this need:
5271 @deffn {Scheme Procedure} gensym [prefix]
5272 @deffnx {C Function} scm_gensym (prefix)
5273 Create a new symbol with a name constructed from a prefix and a counter
5274 value. The string @var{prefix} can be specified as an optional
5275 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
5276 at each call. There is no provision for resetting the counter.
5279 The symbols generated by @code{gensym} are @emph{likely} to be unique,
5280 since their names begin with a space and it is only otherwise possible
5281 to generate such symbols if a programmer goes out of their way to do
5282 so. Uniqueness can be guaranteed by instead using uninterned symbols
5283 (@pxref{Symbol Uninterned}), though they can't be usefully written out
5288 @subsubsection Function Slots and Property Lists
5290 In traditional Lisp dialects, symbols are often understood as having
5291 three kinds of value at once:
5295 a @dfn{variable} value, which is used when the symbol appears in
5296 code in a variable reference context
5299 a @dfn{function} value, which is used when the symbol appears in
5300 code in a function name position (i.e. as the first element in an
5304 a @dfn{property list} value, which is used when the symbol is given as
5305 the first argument to Lisp's @code{put} or @code{get} functions.
5308 Although Scheme (as one of its simplifications with respect to Lisp)
5309 does away with the distinction between variable and function namespaces,
5310 Guile currently retains some elements of the traditional structure in
5311 case they turn out to be useful when implementing translators for other
5312 languages, in particular Emacs Lisp.
5314 Specifically, Guile symbols have two extra slots. for a symbol's
5315 property list, and for its ``function value.'' The following procedures
5316 are provided to access these slots.
5318 @deffn {Scheme Procedure} symbol-fref symbol
5319 @deffnx {C Function} scm_symbol_fref (symbol)
5320 Return the contents of @var{symbol}'s @dfn{function slot}.
5323 @deffn {Scheme Procedure} symbol-fset! symbol value
5324 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
5325 Set the contents of @var{symbol}'s function slot to @var{value}.
5328 @deffn {Scheme Procedure} symbol-pref symbol
5329 @deffnx {C Function} scm_symbol_pref (symbol)
5330 Return the @dfn{property list} currently associated with @var{symbol}.
5333 @deffn {Scheme Procedure} symbol-pset! symbol value
5334 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
5335 Set @var{symbol}'s property list to @var{value}.
5338 @deffn {Scheme Procedure} symbol-property sym prop
5339 From @var{sym}'s property list, return the value for property
5340 @var{prop}. The assumption is that @var{sym}'s property list is an
5341 association list whose keys are distinguished from each other using
5342 @code{equal?}; @var{prop} should be one of the keys in that list. If
5343 the property list has no entry for @var{prop}, @code{symbol-property}
5347 @deffn {Scheme Procedure} set-symbol-property! sym prop val
5348 In @var{sym}'s property list, set the value for property @var{prop} to
5349 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
5350 none already exists. For the structure of the property list, see
5351 @code{symbol-property}.
5354 @deffn {Scheme Procedure} symbol-property-remove! sym prop
5355 From @var{sym}'s property list, remove the entry for property
5356 @var{prop}, if there is one. For the structure of the property list,
5357 see @code{symbol-property}.
5360 Support for these extra slots may be removed in a future release, and it
5361 is probably better to avoid using them. For a more modern and Schemely
5362 approach to properties, see @ref{Object Properties}.
5365 @node Symbol Read Syntax
5366 @subsubsection Extended Read Syntax for Symbols
5368 The read syntax for a symbol is a sequence of letters, digits, and
5369 @dfn{extended alphabetic characters}, beginning with a character that
5370 cannot begin a number. In addition, the special cases of @code{+},
5371 @code{-}, and @code{...} are read as symbols even though numbers can
5372 begin with @code{+}, @code{-} or @code{.}.
5374 Extended alphabetic characters may be used within identifiers as if
5375 they were letters. The set of extended alphabetic characters is:
5378 ! $ % & * + - . / : < = > ? @@ ^ _ ~
5381 In addition to the standard read syntax defined above (which is taken
5382 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
5383 Scheme})), Guile provides an extended symbol read syntax that allows the
5384 inclusion of unusual characters such as space characters, newlines and
5385 parentheses. If (for whatever reason) you need to write a symbol
5386 containing characters not mentioned above, you can do so as follows.
5390 Begin the symbol with the characters @code{#@{},
5393 write the characters of the symbol and
5396 finish the symbol with the characters @code{@}#}.
5399 Here are a few examples of this form of read syntax. The first symbol
5400 needs to use extended syntax because it contains a space character, the
5401 second because it contains a line break, and the last because it looks
5413 Although Guile provides this extended read syntax for symbols,
5414 widespread usage of it is discouraged because it is not portable and not
5418 @node Symbol Uninterned
5419 @subsubsection Uninterned Symbols
5421 What makes symbols useful is that they are automatically kept unique.
5422 There are no two symbols that are distinct objects but have the same
5423 name. But of course, there is no rule without exception. In addition
5424 to the normal symbols that have been discussed up to now, you can also
5425 create special @dfn{uninterned} symbols that behave slightly
5428 To understand what is different about them and why they might be useful,
5429 we look at how normal symbols are actually kept unique.
5431 Whenever Guile wants to find the symbol with a specific name, for
5432 example during @code{read} or when executing @code{string->symbol}, it
5433 first looks into a table of all existing symbols to find out whether a
5434 symbol with the given name already exists. When this is the case, Guile
5435 just returns that symbol. When not, a new symbol with the name is
5436 created and entered into the table so that it can be found later.
5438 Sometimes you might want to create a symbol that is guaranteed `fresh',
5439 i.e. a symbol that did not exist previously. You might also want to
5440 somehow guarantee that no one else will ever unintentionally stumble
5441 across your symbol in the future. These properties of a symbol are
5442 often needed when generating code during macro expansion. When
5443 introducing new temporary variables, you want to guarantee that they
5444 don't conflict with variables in other people's code.
5446 The simplest way to arrange for this is to create a new symbol but
5447 not enter it into the global table of all symbols. That way, no one
5448 will ever get access to your symbol by chance. Symbols that are not in
5449 the table are called @dfn{uninterned}. Of course, symbols that
5450 @emph{are} in the table are called @dfn{interned}.
5452 You create new uninterned symbols with the function @code{make-symbol}.
5453 You can test whether a symbol is interned or not with
5454 @code{symbol-interned?}.
5456 Uninterned symbols break the rule that the name of a symbol uniquely
5457 identifies the symbol object. Because of this, they can not be written
5458 out and read back in like interned symbols. Currently, Guile has no
5459 support for reading uninterned symbols. Note that the function
5460 @code{gensym} does not return uninterned symbols for this reason.
5462 @deffn {Scheme Procedure} make-symbol name
5463 @deffnx {C Function} scm_make_symbol (name)
5464 Return a new uninterned symbol with the name @var{name}. The returned
5465 symbol is guaranteed to be unique and future calls to
5466 @code{string->symbol} will not return it.
5469 @deffn {Scheme Procedure} symbol-interned? symbol
5470 @deffnx {C Function} scm_symbol_interned_p (symbol)
5471 Return @code{#t} if @var{symbol} is interned, otherwise return
5478 (define foo-1 (string->symbol "foo"))
5479 (define foo-2 (string->symbol "foo"))
5480 (define foo-3 (make-symbol "foo"))
5481 (define foo-4 (make-symbol "foo"))
5485 ; Two interned symbols with the same name are the same object,
5489 ; but a call to make-symbol with the same name returns a
5494 ; A call to make-symbol always returns a new object, even for
5498 @result{} #<uninterned-symbol foo 8085290>
5499 ; Uninterned symbols print differently from interned symbols,
5503 ; but they are still symbols,
5505 (symbol-interned? foo-3)
5507 ; just not interned.
5512 @subsection Keywords
5515 Keywords are self-evaluating objects with a convenient read syntax that
5516 makes them easy to type.
5518 Guile's keyword support conforms to R5RS, and adds a (switchable) read
5519 syntax extension to permit keywords to begin with @code{:} as well as
5520 @code{#:}, or to end with @code{:}.
5523 * Why Use Keywords?:: Motivation for keyword usage.
5524 * Coding With Keywords:: How to use keywords.
5525 * Keyword Read Syntax:: Read syntax for keywords.
5526 * Keyword Procedures:: Procedures for dealing with keywords.
5529 @node Why Use Keywords?
5530 @subsubsection Why Use Keywords?
5532 Keywords are useful in contexts where a program or procedure wants to be
5533 able to accept a large number of optional arguments without making its
5534 interface unmanageable.
5536 To illustrate this, consider a hypothetical @code{make-window}
5537 procedure, which creates a new window on the screen for drawing into
5538 using some graphical toolkit. There are many parameters that the caller
5539 might like to specify, but which could also be sensibly defaulted, for
5544 color depth -- Default: the color depth for the screen
5547 background color -- Default: white
5550 width -- Default: 600
5553 height -- Default: 400
5556 If @code{make-window} did not use keywords, the caller would have to
5557 pass in a value for each possible argument, remembering the correct
5558 argument order and using a special value to indicate the default value
5562 (make-window 'default ;; Color depth
5563 'default ;; Background color
5566 @dots{}) ;; More make-window arguments
5569 With keywords, on the other hand, defaulted arguments are omitted, and
5570 non-default arguments are clearly tagged by the appropriate keyword. As
5571 a result, the invocation becomes much clearer:
5574 (make-window #:width 800 #:height 100)
5577 On the other hand, for a simpler procedure with few arguments, the use
5578 of keywords would be a hindrance rather than a help. The primitive
5579 procedure @code{cons}, for example, would not be improved if it had to
5583 (cons #:car x #:cdr y)
5586 So the decision whether to use keywords or not is purely pragmatic: use
5587 them if they will clarify the procedure invocation at point of call.
5589 @node Coding With Keywords
5590 @subsubsection Coding With Keywords
5592 If a procedure wants to support keywords, it should take a rest argument
5593 and then use whatever means is convenient to extract keywords and their
5594 corresponding arguments from the contents of that rest argument.
5596 The following example illustrates the principle: the code for
5597 @code{make-window} uses a helper procedure called
5598 @code{get-keyword-value} to extract individual keyword arguments from
5602 (define (get-keyword-value args keyword default)
5603 (let ((kv (memq keyword args)))
5604 (if (and kv (>= (length kv) 2))
5608 (define (make-window . args)
5609 (let ((depth (get-keyword-value args #:depth screen-depth))
5610 (bg (get-keyword-value args #:bg "white"))
5611 (width (get-keyword-value args #:width 800))
5612 (height (get-keyword-value args #:height 100))
5617 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
5618 optargs)} module provides a set of powerful macros that you can use to
5619 implement keyword-supporting procedures like this:
5622 (use-modules (ice-9 optargs))
5624 (define (make-window . args)
5625 (let-keywords args #f ((depth screen-depth)
5633 Or, even more economically, like this:
5636 (use-modules (ice-9 optargs))
5638 (define* (make-window #:key (depth screen-depth)
5645 For further details on @code{let-keywords}, @code{define*} and other
5646 facilities provided by the @code{(ice-9 optargs)} module, see
5647 @ref{Optional Arguments}.
5650 @node Keyword Read Syntax
5651 @subsubsection Keyword Read Syntax
5653 Guile, by default, only recognizes a keyword syntax that is compatible
5654 with R5RS. A token of the form @code{#:NAME}, where @code{NAME} has the
5655 same syntax as a Scheme symbol (@pxref{Symbol Read Syntax}), is the
5656 external representation of the keyword named @code{NAME}. Keyword
5657 objects print using this syntax as well, so values containing keyword
5658 objects can be read back into Guile. When used in an expression,
5659 keywords are self-quoting objects.
5661 If the @code{keyword} read option is set to @code{'prefix}, Guile also
5662 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
5663 of the form @code{:NAME} are read as symbols, as required by R5RS.
5665 @cindex SRFI-88 keyword syntax
5667 If the @code{keyword} read option is set to @code{'postfix}, Guile
5668 recognizes the SRFI-88 read syntax @code{NAME:} (@pxref{SRFI-88}).
5669 Otherwise, tokens of this form are read as symbols.
5671 To enable and disable the alternative non-R5RS keyword syntax, you use
5672 the @code{read-set!} procedure documented in @ref{User level options
5673 interfaces} and @ref{Reader options}. Note that the @code{prefix} and
5674 @code{postfix} syntax are mutually exclusive.
5677 (read-set! keywords 'prefix)
5687 (read-set! keywords 'postfix)
5697 (read-set! keywords #f)
5705 ERROR: In expression :type:
5706 ERROR: Unbound variable: :type
5707 ABORT: (unbound-variable)
5710 @node Keyword Procedures
5711 @subsubsection Keyword Procedures
5713 @deffn {Scheme Procedure} keyword? obj
5714 @deffnx {C Function} scm_keyword_p (obj)
5715 Return @code{#t} if the argument @var{obj} is a keyword, else
5719 @deffn {Scheme Procedure} keyword->symbol keyword
5720 @deffnx {C Function} scm_keyword_to_symbol (keyword)
5721 Return the symbol with the same name as @var{keyword}.
5724 @deffn {Scheme Procedure} symbol->keyword symbol
5725 @deffnx {C Function} scm_symbol_to_keyword (symbol)
5726 Return the keyword with the same name as @var{symbol}.
5729 @deftypefn {C Function} int scm_is_keyword (SCM obj)
5730 Equivalent to @code{scm_is_true (scm_keyword_p (@var{obj}))}.
5733 @deftypefn {C Function} SCM scm_from_locale_keyword (const char *str)
5734 @deftypefnx {C Function} SCM scm_from_locale_keywordn (const char *str, size_t len)
5735 Equivalent to @code{scm_symbol_to_keyword (scm_from_locale_symbol
5736 (@var{str}))} and @code{scm_symbol_to_keyword (scm_from_locale_symboln
5737 (@var{str}, @var{len}))}, respectively.
5741 @subsection ``Functionality-Centric'' Data Types
5743 Procedures and macros are documented in their own chapter: see
5744 @ref{Procedures and Macros}.
5746 Variable objects are documented as part of the description of Guile's
5747 module system: see @ref{Variables}.
5749 Asyncs, dynamic roots and fluids are described in the chapter on
5750 scheduling: see @ref{Scheduling}.
5752 Hooks are documented in the chapter on general utility functions: see
5755 Ports are described in the chapter on I/O: see @ref{Input and Output}.
5759 @c TeX-master: "guile.texi"