2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004
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 * Regular Expressions:: Pattern matching and substitution.
50 * Keywords:: Self-quoting, customizable display keywords.
51 * Other Types:: "Functionality-centric" data types.
59 The two boolean values are @code{#t} for true and @code{#f} for false.
61 Boolean values are returned by predicate procedures, such as the general
62 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
63 (@pxref{Equality}) and numerical and string comparison operators like
64 @code{string=?} (@pxref{String Comparison}) and @code{<=}
74 (equal? "house" "houses")
82 In test condition contexts like @code{if} and @code{cond} (@pxref{if
83 cond case}), where a group of subexpressions will be evaluated only if a
84 @var{condition} expression evaluates to ``true'', ``true'' means any
85 value at all except @code{#f}.
98 A result of this asymmetry is that typical Scheme source code more often
99 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
100 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
101 not necessary to represent an @code{if} or @code{cond} true value.
103 It is important to note that @code{#f} is @strong{not} equivalent to any
104 other Scheme value. In particular, @code{#f} is not the same as the
105 number 0 (like in C and C++), and not the same as the ``empty list''
106 (like in some Lisp dialects).
108 In C, the two Scheme boolean values are available as the two constants
109 @code{SCM_BOOL_T} for @code{#t} and @code{SCM_BOOL_F} for @code{#f}.
110 Care must be taken with the false value @code{SCM_BOOL_F}: it is not
111 false when used in C conditionals. In order to test for it, use
112 @code{scm_is_false} or @code{scm_is_true}.
115 @deffn {Scheme Procedure} not x
116 @deffnx {C Function} scm_not (x)
117 Return @code{#t} if @var{x} is @code{#f}, else return @code{#f}.
121 @deffn {Scheme Procedure} boolean? obj
122 @deffnx {C Function} scm_boolean_p (obj)
123 Return @code{#t} if @var{obj} is either @code{#t} or @code{#f}, else
127 @deftypevr {C Macro} SCM SCM_BOOL_T
128 The @code{SCM} representation of the Scheme object @code{#t}.
131 @deftypevr {C Macro} SCM SCM_BOOL_F
132 The @code{SCM} representation of the Scheme object @code{#f}.
135 @deftypefn {C Function} int scm_is_true (SCM obj)
136 Return @code{0} if @var{obj} is @code{#f}, else return @code{1}.
139 @deftypefn {C Function} int scm_is_false (SCM obj)
140 Return @code{1} if @var{obj} is @code{#f}, else return @code{0}.
143 @deftypefn {C Function} int scm_is_bool (SCM obj)
144 Return @code{1} if @var{obj} is either @code{#t} or @code{#f}, else
148 @deftypefn {C Function} SCM scm_from_bool (int val)
149 Return @code{#f} if @var{val} is @code{0}, else return @code{#t}.
152 @deftypefn {C Function} int scm_to_bool (SCM val)
153 Return @code{1} if @var{val} is @code{SCM_BOOL_T}, return @code{0}
154 when @var{val} is @code{SCM_BOOL_F}, else signal a `wrong type' error.
156 You should probably use @code{scm_is_true} instead of this function
157 when you just want to test a @code{SCM} value for trueness.
161 @subsection Numerical data types
164 Guile supports a rich ``tower'' of numerical types --- integer,
165 rational, real and complex --- and provides an extensive set of
166 mathematical and scientific functions for operating on numerical
167 data. This section of the manual documents those types and functions.
169 You may also find it illuminating to read R5RS's presentation of numbers
170 in Scheme, which is particularly clear and accessible: see
171 @ref{Numbers,,,r5rs,R5RS}.
174 * Numerical Tower:: Scheme's numerical "tower".
175 * Integers:: Whole numbers.
176 * Reals and Rationals:: Real and rational numbers.
177 * Complex Numbers:: Complex numbers.
178 * Exactness:: Exactness and inexactness.
179 * Number Syntax:: Read syntax for numerical data.
180 * Integer Operations:: Operations on integer values.
181 * Comparison:: Comparison predicates.
182 * Conversion:: Converting numbers to and from strings.
183 * Complex:: Complex number operations.
184 * Arithmetic:: Arithmetic functions.
185 * Scientific:: Scientific functions.
186 * Primitive Numerics:: Primitive numeric 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),sin(pi/4)} is exactly @m{\sqrt{2},2^(1/2)} but Guile
231 can neither represent @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 explicitely 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 exactor 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_t (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 the square root of 2, and pi.
499 Guile can represent both exact and inexact rational numbers, but it
500 can not represent irrational numbers. Exact rationals are represented
501 by storing the numerator and denominator as two exact integers.
502 Inexact rationals are stored as floating point numbers using the C
505 Exact rationals are written as a fraction of integers. There must be
506 no whitespace around the slash:
513 Even though the actual encoding of inexact rationals is in binary, it
514 may be helpful to think of it as a decimal number with a limited
515 number of significant figures and a decimal point somewhere, since
516 this corresponds to the standard notation for non-whole numbers. For
522 -5648394822220000000000.0
526 The limited precision of Guile's encoding means that any ``real'' number
527 in Guile can be written in a rational form, by multiplying and then dividing
528 by sufficient powers of 10 (or in fact, 2). For example,
529 @samp{-0.00000142857931198} is the same as @minus{}142857931198 divided by
530 100000000000000000. In Guile's current incarnation, therefore, the
531 @code{rational?} and @code{real?} predicates are equivalent.
534 Dividing by an exact zero leads to a error message, as one might
535 expect. However, dividing by an inexact zero does not produce an
536 error. Instead, the result of the division is either plus or minus
537 infinity, depending on the sign of the divided number.
539 The infinities are written @samp{+inf.0} and @samp{-inf.0},
540 respectivly. This syntax is also recognized by @code{read} as an
541 extension to the usual Scheme syntax.
543 Dividing zero by zero yields something that is not a number at all:
544 @samp{+nan.0}. This is the special `not a number' value.
546 On platforms that follow @acronym{IEEE} 754 for their floating point
547 arithmetic, the @samp{+inf.0}, @samp{-inf.0}, and @samp{+nan.0} values
548 are implemented using the corresponding @acronym{IEEE} 754 values.
549 They behave in arithmetic operations like @acronym{IEEE} 754 describes
550 it, i.e., @code{(= +nan.0 +nan.0)} @result{} @code{#f}.
552 The infinities are inexact integers and are considered to be both even
553 and odd. While @samp{+nan.0} is not @code{=} to itself, it is
554 @code{eqv?} to itself.
556 To test for the special values, use the functions @code{inf?} and
559 @deffn {Scheme Procedure} real? obj
560 @deffnx {C Function} scm_real_p (obj)
561 Return @code{#t} if @var{obj} is a real number, else @code{#f}. Note
562 that the sets of integer and rational values form subsets of the set
563 of real numbers, so the predicate will also be fulfilled if @var{obj}
564 is an integer number or a rational number.
567 @deffn {Scheme Procedure} rational? x
568 @deffnx {C Function} scm_rational_p (x)
569 Return @code{#t} if @var{x} is a rational number, @code{#f} otherwise.
570 Note that the set of integer values forms a subset of the set of
571 rational numbers, i. e. the predicate will also be fulfilled if
572 @var{x} is an integer number.
574 Since Guile can not represent irrational numbers, every number
575 satisfying @code{real?} also satisfies @code{rational?} in Guile.
578 @deffn {Scheme Procedure} rationalize x eps
579 @deffnx {C Function} scm_rationalize (x, eps)
580 Returns the @emph{simplest} rational number differing
581 from @var{x} by no more than @var{eps}.
583 As required by @acronym{R5RS}, @code{rationalize} only returns an
584 exact result when both its arguments are exact. Thus, you might need
585 to use @code{inexact->exact} on the arguments.
588 (rationalize (inexact->exact 1.2) 1/100)
594 @deffn {Scheme Procedure} inf? x
595 @deffnx {C Function} scm_inf_p (x)
596 Return @code{#t} if @var{x} is either @samp{+inf.0} or @samp{-inf.0},
600 @deffn {Scheme Procedure} nan? x
601 @deffnx {C Function} scm_nan_p (x)
602 Return @code{#t} if @var{x} is @samp{+nan.0}, @code{#f} otherwise.
605 @deffn {Scheme Procedure} nan
606 @deffnx {C Function} scm_nan ()
610 @deffn {Scheme Procedure} inf
611 @deffnx {C Function} scm_inf ()
615 @deffn {Scheme Procedure} numerator x
616 @deffnx {C Function} scm_numerator (x)
617 Return the numerator of the rational number @var{x}.
620 @deffn {Scheme Procedure} denominator x
621 @deffnx {C Function} scm_denominator (x)
622 Return the denominator of the rational number @var{x}.
625 @deftypefn {C Function} int scm_is_real (SCM val)
626 @deftypefnx {C Function} int scm_is_rational (SCM val)
627 Equivalent to @code{scm_is_true (scm_real_p (val))} and
628 @code{scm_is_true (scm_rational_p (val))}, respectively.
631 @deftypefn {C Function} double scm_to_double (SCM val)
632 Returns the number closest to @var{val} that is representable as a
633 @code{double}. Returns infinity for a @var{val} that is too large in
634 magnitude. The argument @var{val} must be a real number.
637 @deftypefn {C Function} SCM scm_from_double (double val)
638 Return the @code{SCM} value that representats @var{val}. The returned
639 value is inexact according to the predicate @code{inexact?}, but it
640 will be exactly equal to @var{val}.
643 @node Complex Numbers
644 @subsubsection Complex Numbers
645 @tpindex Complex numbers
649 Complex numbers are the set of numbers that describe all possible points
650 in a two-dimensional space. The two coordinates of a particular point
651 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
652 the complex number that describes that point.
654 In Guile, complex numbers are written in rectangular form as the sum of
655 their real and imaginary parts, using the symbol @code{i} to indicate
668 Guile represents a complex number with a non-zero imaginary part as a
669 pair of inexact rationals, so the real and imaginary parts of a
670 complex number have the same properties of inexactness and limited
671 precision as single inexact rational numbers. Guile can not represent
672 exact complex numbers with non-zero imaginary parts.
674 @deffn {Scheme Procedure} complex? z
675 @deffnx {C Function} scm_complex_p (z)
676 Return @code{#t} if @var{x} is a complex number, @code{#f}
677 otherwise. Note that the sets of real, rational and integer
678 values form subsets of the set of complex numbers, i. e. the
679 predicate will also be fulfilled if @var{x} is a real,
680 rational or integer number.
683 @deftypefn {C Function} int scm_is_complex (SCM val)
684 Equivalent to @code{scm_is_true (scm_complex_p (val))}.
688 @subsubsection Exact and Inexact Numbers
689 @tpindex Exact numbers
690 @tpindex Inexact numbers
694 @rnindex exact->inexact
695 @rnindex inexact->exact
697 R5RS requires that a calculation involving inexact numbers always
698 produces an inexact result. To meet this requirement, Guile
699 distinguishes between an exact integer value such as @samp{5} and the
700 corresponding inexact real value which, to the limited precision
701 available, has no fractional part, and is printed as @samp{5.0}. Guile
702 will only convert the latter value to the former when forced to do so by
703 an invocation of the @code{inexact->exact} procedure.
705 @deffn {Scheme Procedure} exact? z
706 @deffnx {C Function} scm_exact_p (z)
707 Return @code{#t} if the number @var{z} is exact, @code{#f}
723 @deffn {Scheme Procedure} inexact? z
724 @deffnx {C Function} scm_inexact_p (z)
725 Return @code{#t} if the number @var{z} is inexact, @code{#f}
729 @deffn {Scheme Procedure} inexact->exact z
730 @deffnx {C Function} scm_inexact_to_exact (z)
731 Return an exact number that is numerically closest to @var{z}, when
732 there is one. For inexact rationals, Guile returns the exact rational
733 that is numerically equal to the inexact rational. Inexact complex
734 numbers with a non-zero imaginary part can not be made exact.
741 The following happens because 12/10 is not exactly representable as a
742 @code{double} (on most platforms). However, when reading a decimal
743 number that has been marked exact with the ``#e'' prefix, Guile is
744 able to represent it correctly.
748 @result{} 5404319552844595/4503599627370496
756 @c begin (texi-doc-string "guile" "exact->inexact")
757 @deffn {Scheme Procedure} exact->inexact z
758 @deffnx {C Function} scm_exact_to_inexact (z)
759 Convert the number @var{z} to its inexact representation.
764 @subsubsection Read Syntax for Numerical Data
766 The read syntax for integers is a string of digits, optionally
767 preceded by a minus or plus character, a code indicating the
768 base in which the integer is encoded, and a code indicating whether
769 the number is exact or inexact. The supported base codes are:
774 the integer is written in binary (base 2)
778 the integer is written in octal (base 8)
782 the integer is written in decimal (base 10)
786 the integer is written in hexadecimal (base 16)
789 If the base code is omitted, the integer is assumed to be decimal. The
790 following examples show how these base codes are used.
809 The codes for indicating exactness (which can, incidentally, be applied
810 to all numerical values) are:
819 the number is inexact.
822 If the exactness indicator is omitted, the number is exact unless it
823 contains a radix point. Since Guile can not represent exact complex
824 numbers, an error is signalled when asking for them.
834 ERROR: Wrong type argument
837 Guile also understands the syntax @samp{+inf.0} and @samp{-inf.0} for
838 plus and minus infinity, respectively. The value must be written
839 exactly as shown, that is, they always must have a sign and exactly
840 one zero digit after the decimal point. It also understands
841 @samp{+nan.0} and @samp{-nan.0} for the special `not-a-number' value.
842 The sign is ignored for `not-a-number' and the value is always printed
845 @node Integer Operations
846 @subsubsection Operations on Integer Values
855 @deffn {Scheme Procedure} odd? n
856 @deffnx {C Function} scm_odd_p (n)
857 Return @code{#t} if @var{n} is an odd number, @code{#f}
861 @deffn {Scheme Procedure} even? n
862 @deffnx {C Function} scm_even_p (n)
863 Return @code{#t} if @var{n} is an even number, @code{#f}
867 @c begin (texi-doc-string "guile" "quotient")
868 @c begin (texi-doc-string "guile" "remainder")
869 @deffn {Scheme Procedure} quotient n d
870 @deffnx {Scheme Procedure} remainder n d
871 @deffnx {C Function} scm_quotient (n, d)
872 @deffnx {C Function} scm_remainder (n, d)
873 Return the quotient or remainder from @var{n} divided by @var{d}. The
874 quotient is rounded towards zero, and the remainder will have the same
875 sign as @var{n}. In all cases quotient and remainder satisfy
876 @math{@var{n} = @var{q}*@var{d} + @var{r}}.
879 (remainder 13 4) @result{} 1
880 (remainder -13 4) @result{} -1
884 @c begin (texi-doc-string "guile" "modulo")
885 @deffn {Scheme Procedure} modulo n d
886 @deffnx {C Function} scm_modulo (n, d)
887 Return the remainder from @var{n} divided by @var{d}, with the same
891 (modulo 13 4) @result{} 1
892 (modulo -13 4) @result{} 3
893 (modulo 13 -4) @result{} -3
894 (modulo -13 -4) @result{} -1
898 @c begin (texi-doc-string "guile" "gcd")
899 @deffn {Scheme Procedure} gcd
900 @deffnx {C Function} scm_gcd (x, y)
901 Return the greatest common divisor of all arguments.
902 If called without arguments, 0 is returned.
904 The C function @code{scm_gcd} always takes two arguments, while the
905 Scheme function can take an arbitrary number.
908 @c begin (texi-doc-string "guile" "lcm")
909 @deffn {Scheme Procedure} lcm
910 @deffnx {C Function} scm_lcm (x, y)
911 Return the least common multiple of the arguments.
912 If called without arguments, 1 is returned.
914 The C function @code{scm_lcm} always takes two arguments, while the
915 Scheme function can take an arbitrary number.
918 @deffn {Scheme Procedure} modulo-expt n k m
919 @deffnx {C Function} scm_modulo_expt (n, k, m)
920 Return @var{n} raised to the integer exponent
921 @var{k}, modulo @var{m}.
930 @subsubsection Comparison Predicates
935 The C comparison functions below always takes two arguments, while the
936 Scheme functions can take an arbitrary number. Also keep in mind that
937 the C functions return one of the Scheme boolean values
938 @code{SCM_BOOL_T} or @code{SCM_BOOL_F} which are both true as far as C
939 is concerned. Thus, always write @code{scm_is_true (scm_num_eq_p (x,
940 y))} when testing the two Scheme numbers @code{x} and @code{y} for
941 equality, for example.
943 @c begin (texi-doc-string "guile" "=")
944 @deffn {Scheme Procedure} =
945 @deffnx {C Function} scm_num_eq_p (x, y)
946 Return @code{#t} if all parameters are numerically equal.
949 @c begin (texi-doc-string "guile" "<")
950 @deffn {Scheme Procedure} <
951 @deffnx {C Function} scm_less_p (x, y)
952 Return @code{#t} if the list of parameters is monotonically
956 @c begin (texi-doc-string "guile" ">")
957 @deffn {Scheme Procedure} >
958 @deffnx {C Function} scm_gr_p (x, y)
959 Return @code{#t} if the list of parameters is monotonically
963 @c begin (texi-doc-string "guile" "<=")
964 @deffn {Scheme Procedure} <=
965 @deffnx {C Function} scm_leq_p (x, y)
966 Return @code{#t} if the list of parameters is monotonically
970 @c begin (texi-doc-string "guile" ">=")
971 @deffn {Scheme Procedure} >=
972 @deffnx {C Function} scm_geq_p (x, y)
973 Return @code{#t} if the list of parameters is monotonically
977 @c begin (texi-doc-string "guile" "zero?")
978 @deffn {Scheme Procedure} zero? z
979 @deffnx {C Function} scm_zero_p (z)
980 Return @code{#t} if @var{z} is an exact or inexact number equal to
984 @c begin (texi-doc-string "guile" "positive?")
985 @deffn {Scheme Procedure} positive? x
986 @deffnx {C Function} scm_positive_p (x)
987 Return @code{#t} if @var{x} is an exact or inexact number greater than
991 @c begin (texi-doc-string "guile" "negative?")
992 @deffn {Scheme Procedure} negative? x
993 @deffnx {C Function} scm_negative_p (x)
994 Return @code{#t} if @var{x} is an exact or inexact number less than
1000 @subsubsection Converting Numbers To and From Strings
1001 @rnindex number->string
1002 @rnindex string->number
1004 @deffn {Scheme Procedure} number->string n [radix]
1005 @deffnx {C Function} scm_number_to_string (n, radix)
1006 Return a string holding the external representation of the
1007 number @var{n} in the given @var{radix}. If @var{n} is
1008 inexact, a radix of 10 will be used.
1011 @deffn {Scheme Procedure} string->number string [radix]
1012 @deffnx {C Function} scm_string_to_number (string, radix)
1013 Return a number of the maximally precise representation
1014 expressed by the given @var{string}. @var{radix} must be an
1015 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
1016 is a default radix that may be overridden by an explicit radix
1017 prefix in @var{string} (e.g. "#o177"). If @var{radix} is not
1018 supplied, then the default radix is 10. If string is not a
1019 syntactically valid notation for a number, then
1020 @code{string->number} returns @code{#f}.
1025 @subsubsection Complex Number Operations
1026 @rnindex make-rectangular
1033 @deffn {Scheme Procedure} make-rectangular real imaginary
1034 @deffnx {C Function} scm_make_rectangular (real, imaginary)
1035 Return a complex number constructed of the given @var{real} and
1036 @var{imaginary} parts.
1039 @deffn {Scheme Procedure} make-polar x y
1040 @deffnx {C Function} scm_make_polar (x, y)
1041 Return the complex number @var{x} * e^(i * @var{y}).
1044 @c begin (texi-doc-string "guile" "real-part")
1045 @deffn {Scheme Procedure} real-part z
1046 @deffnx {C Function} scm_real_part (z)
1047 Return the real part of the number @var{z}.
1050 @c begin (texi-doc-string "guile" "imag-part")
1051 @deffn {Scheme Procedure} imag-part z
1052 @deffnx {C Function} scm_imag_part (z)
1053 Return the imaginary part of the number @var{z}.
1056 @c begin (texi-doc-string "guile" "magnitude")
1057 @deffn {Scheme Procedure} magnitude z
1058 @deffnx {C Function} scm_magnitude (z)
1059 Return the magnitude of the number @var{z}. This is the same as
1060 @code{abs} for real arguments, but also allows complex numbers.
1063 @c begin (texi-doc-string "guile" "angle")
1064 @deffn {Scheme Procedure} angle z
1065 @deffnx {C Function} scm_angle (z)
1066 Return the angle of the complex number @var{z}.
1069 @deftypefn {C Function} SCM scm_c_make_rectangular (double re, double im)
1070 @deftypefnx {C Function} SCM scm_c_make_polar (double x, double y)
1071 Like @code{scm_make_rectangular} or @code{scm_make_polar},
1072 respectively, but these functions take @code{double}s as their
1076 @deftypefn {C Function} double scm_c_real_part (z)
1077 @deftypefnx {C Function} double scm_c_imag_part (z)
1078 Returns the real or imaginary part of @var{z} as a @code{double}.
1081 @deftypefn {C Function} double scm_c_magnitude (z)
1082 @deftypefnx {C Function} double scm_c_angle (z)
1083 Returns the magnitude or angle of @var{z} as a @code{double}.
1088 @subsubsection Arithmetic Functions
1101 The C arithmetic functions below always takes two arguments, while the
1102 Scheme functions can take an arbitrary number. When you need to
1103 invoke them with just one argument, for example to compute the
1104 equivalent od @code{(- x)}, pass @code{SCM_UNDEFINED} as the second
1105 one: @code{scm_difference (x, SCM_UNDEFINED)}.
1107 @c begin (texi-doc-string "guile" "+")
1108 @deffn {Scheme Procedure} + z1 @dots{}
1109 @deffnx {C Function} scm_sum (z1, z2)
1110 Return the sum of all parameter values. Return 0 if called without any
1114 @c begin (texi-doc-string "guile" "-")
1115 @deffn {Scheme Procedure} - z1 z2 @dots{}
1116 @deffnx {C Function} scm_difference (z1, z2)
1117 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
1118 the sum of all but the first argument are subtracted from the first
1122 @c begin (texi-doc-string "guile" "*")
1123 @deffn {Scheme Procedure} * z1 @dots{}
1124 @deffnx {C Function} scm_product (z1, z2)
1125 Return the product of all arguments. If called without arguments, 1 is
1129 @c begin (texi-doc-string "guile" "/")
1130 @deffn {Scheme Procedure} / z1 z2 @dots{}
1131 @deffnx {C Function} scm_divide (z1, z2)
1132 Divide the first argument by the product of the remaining arguments. If
1133 called with one argument @var{z1}, 1/@var{z1} is returned.
1136 @c begin (texi-doc-string "guile" "abs")
1137 @deffn {Scheme Procedure} abs x
1138 @deffnx {C Function} scm_abs (x)
1139 Return the absolute value of @var{x}.
1141 @var{x} must be a number with zero imaginary part. To calculate the
1142 magnitude of a complex number, use @code{magnitude} instead.
1145 @c begin (texi-doc-string "guile" "max")
1146 @deffn {Scheme Procedure} max x1 x2 @dots{}
1147 @deffnx {C Function} scm_max (x1, x2)
1148 Return the maximum of all parameter values.
1151 @c begin (texi-doc-string "guile" "min")
1152 @deffn {Scheme Procedure} min x1 x2 @dots{}
1153 @deffnx {C Function} scm_min (x1, x2)
1154 Return the minimum of all parameter values.
1157 @c begin (texi-doc-string "guile" "truncate")
1158 @deffn {Scheme Procedure} truncate
1159 @deffnx {C Function} scm_truncate_number (x)
1160 Round the inexact number @var{x} towards zero.
1163 @c begin (texi-doc-string "guile" "round")
1164 @deffn {Scheme Procedure} round x
1165 @deffnx {C Function} scm_round_number (x)
1166 Round the inexact number @var{x} to the nearest integer. When exactly
1167 halfway between two integers, round to the even one.
1170 @c begin (texi-doc-string "guile" "floor")
1171 @deffn {Scheme Procedure} floor x
1172 @deffnx {C Function} scm_floor (x)
1173 Round the number @var{x} towards minus infinity.
1176 @c begin (texi-doc-string "guile" "ceiling")
1177 @deffn {Scheme Procedure} ceiling x
1178 @deffnx {C Function} scm_ceiling (x)
1179 Round the number @var{x} towards infinity.
1182 @deftypefn {C Function} double scm_c_truncate (double x)
1183 @deftypefnx {C Function} double scm_c_round (double x)
1184 Like @code{scm_truncate_number} or @code{scm_round_number},
1185 respectively, but these functions take and return @code{double}
1190 @subsubsection Scientific Functions
1192 The following procedures accept any kind of number as arguments,
1193 including complex numbers.
1196 @c begin (texi-doc-string "guile" "sqrt")
1197 @deffn {Scheme Procedure} sqrt z
1198 Return the square root of @var{z}.
1202 @c begin (texi-doc-string "guile" "expt")
1203 @deffn {Scheme Procedure} expt z1 z2
1204 Return @var{z1} raised to the power of @var{z2}.
1208 @c begin (texi-doc-string "guile" "sin")
1209 @deffn {Scheme Procedure} sin z
1210 Return the sine of @var{z}.
1214 @c begin (texi-doc-string "guile" "cos")
1215 @deffn {Scheme Procedure} cos z
1216 Return the cosine of @var{z}.
1220 @c begin (texi-doc-string "guile" "tan")
1221 @deffn {Scheme Procedure} tan z
1222 Return the tangent of @var{z}.
1226 @c begin (texi-doc-string "guile" "asin")
1227 @deffn {Scheme Procedure} asin z
1228 Return the arcsine of @var{z}.
1232 @c begin (texi-doc-string "guile" "acos")
1233 @deffn {Scheme Procedure} acos z
1234 Return the arccosine of @var{z}.
1238 @c begin (texi-doc-string "guile" "atan")
1239 @deffn {Scheme Procedure} atan z
1240 @deffnx {Scheme Procedure} atan y x
1241 Return the arctangent of @var{z}, or of @math{@var{y}/@var{x}}.
1245 @c begin (texi-doc-string "guile" "exp")
1246 @deffn {Scheme Procedure} exp z
1247 Return e to the power of @var{z}, where e is the base of natural
1248 logarithms (2.71828@dots{}).
1252 @c begin (texi-doc-string "guile" "log")
1253 @deffn {Scheme Procedure} log z
1254 Return the natural logarithm of @var{z}.
1257 @c begin (texi-doc-string "guile" "log10")
1258 @deffn {Scheme Procedure} log10 z
1259 Return the base 10 logarithm of @var{z}.
1262 @c begin (texi-doc-string "guile" "sinh")
1263 @deffn {Scheme Procedure} sinh z
1264 Return the hyperbolic sine of @var{z}.
1267 @c begin (texi-doc-string "guile" "cosh")
1268 @deffn {Scheme Procedure} cosh z
1269 Return the hyperbolic cosine of @var{z}.
1272 @c begin (texi-doc-string "guile" "tanh")
1273 @deffn {Scheme Procedure} tanh z
1274 Return the hyperbolic tangent of @var{z}.
1277 @c begin (texi-doc-string "guile" "asinh")
1278 @deffn {Scheme Procedure} asinh z
1279 Return the hyperbolic arcsine of @var{z}.
1282 @c begin (texi-doc-string "guile" "acosh")
1283 @deffn {Scheme Procedure} acosh z
1284 Return the hyperbolic arccosine of @var{z}.
1287 @c begin (texi-doc-string "guile" "atanh")
1288 @deffn {Scheme Procedure} atanh z
1289 Return the hyperbolic arctangent of @var{z}.
1293 @node Primitive Numerics
1294 @subsubsection Primitive Numeric Functions
1296 Many of Guile's numeric procedures which accept any kind of numbers as
1297 arguments, including complex numbers, are implemented as Scheme
1298 procedures that use the following real number-based primitives. These
1299 primitives signal an error if they are called with complex arguments.
1301 @c begin (texi-doc-string "guile" "$abs")
1302 @deffn {Scheme Procedure} $abs x
1303 Return the absolute value of @var{x}.
1306 @c begin (texi-doc-string "guile" "$sqrt")
1307 @deffn {Scheme Procedure} $sqrt x
1308 Return the square root of @var{x}.
1311 @deffn {Scheme Procedure} $expt x y
1312 @deffnx {C Function} scm_sys_expt (x, y)
1313 Return @var{x} raised to the power of @var{y}. This
1314 procedure does not accept complex arguments.
1317 @c begin (texi-doc-string "guile" "$sin")
1318 @deffn {Scheme Procedure} $sin x
1319 Return the sine of @var{x}.
1322 @c begin (texi-doc-string "guile" "$cos")
1323 @deffn {Scheme Procedure} $cos x
1324 Return the cosine of @var{x}.
1327 @c begin (texi-doc-string "guile" "$tan")
1328 @deffn {Scheme Procedure} $tan x
1329 Return the tangent of @var{x}.
1332 @c begin (texi-doc-string "guile" "$asin")
1333 @deffn {Scheme Procedure} $asin x
1334 Return the arcsine of @var{x}.
1337 @c begin (texi-doc-string "guile" "$acos")
1338 @deffn {Scheme Procedure} $acos x
1339 Return the arccosine of @var{x}.
1342 @c begin (texi-doc-string "guile" "$atan")
1343 @deffn {Scheme Procedure} $atan x
1344 Return the arctangent of @var{x} in the range @minus{}@math{PI/2} to
1348 @deffn {Scheme Procedure} $atan2 x y
1349 @deffnx {C Function} scm_sys_atan2 (x, y)
1350 Return the arc tangent of the two arguments @var{x} and
1351 @var{y}. This is similar to calculating the arc tangent of
1352 @var{x} / @var{y}, except that the signs of both arguments
1353 are used to determine the quadrant of the result. This
1354 procedure does not accept complex arguments.
1357 @c begin (texi-doc-string "guile" "$exp")
1358 @deffn {Scheme Procedure} $exp x
1359 Return e to the power of @var{x}, where e is the base of natural
1360 logarithms (2.71828@dots{}).
1363 @c begin (texi-doc-string "guile" "$log")
1364 @deffn {Scheme Procedure} $log x
1365 Return the natural logarithm of @var{x}.
1368 @c begin (texi-doc-string "guile" "$sinh")
1369 @deffn {Scheme Procedure} $sinh x
1370 Return the hyperbolic sine of @var{x}.
1373 @c begin (texi-doc-string "guile" "$cosh")
1374 @deffn {Scheme Procedure} $cosh x
1375 Return the hyperbolic cosine of @var{x}.
1378 @c begin (texi-doc-string "guile" "$tanh")
1379 @deffn {Scheme Procedure} $tanh x
1380 Return the hyperbolic tangent of @var{x}.
1383 @c begin (texi-doc-string "guile" "$asinh")
1384 @deffn {Scheme Procedure} $asinh x
1385 Return the hyperbolic arcsine of @var{x}.
1388 @c begin (texi-doc-string "guile" "$acosh")
1389 @deffn {Scheme Procedure} $acosh x
1390 Return the hyperbolic arccosine of @var{x}.
1393 @c begin (texi-doc-string "guile" "$atanh")
1394 @deffn {Scheme Procedure} $atanh x
1395 Return the hyperbolic arctangent of @var{x}.
1398 C functions for the above are provided by the standard mathematics
1399 library. Naturally these expect and return @code{double} arguments
1400 (@pxref{Mathematics,,, libc, GNU C Library Reference Manual}).
1402 @multitable {xx} {Scheme Procedure} {C Function}
1403 @item @tab Scheme Procedure @tab C Function
1405 @item @tab @code{$abs} @tab @code{fabs}
1406 @item @tab @code{$sqrt} @tab @code{sqrt}
1407 @item @tab @code{$sin} @tab @code{sin}
1408 @item @tab @code{$cos} @tab @code{cos}
1409 @item @tab @code{$tan} @tab @code{tan}
1410 @item @tab @code{$asin} @tab @code{asin}
1411 @item @tab @code{$acos} @tab @code{acos}
1412 @item @tab @code{$atan} @tab @code{atan}
1413 @item @tab @code{$atan2} @tab @code{atan2}
1414 @item @tab @code{$exp} @tab @code{exp}
1415 @item @tab @code{$expt} @tab @code{pow}
1416 @item @tab @code{$log} @tab @code{log}
1417 @item @tab @code{$sinh} @tab @code{sinh}
1418 @item @tab @code{$cosh} @tab @code{cosh}
1419 @item @tab @code{$tanh} @tab @code{tanh}
1420 @item @tab @code{$asinh} @tab @code{asinh}
1421 @item @tab @code{$acosh} @tab @code{acosh}
1422 @item @tab @code{$atanh} @tab @code{atanh}
1425 @code{asinh}, @code{acosh} and @code{atanh} are C99 standard but might
1426 not be available on older systems. Guile provides the following
1427 equivalents (on all systems).
1429 @deftypefn {C Function} double scm_asinh (double x)
1430 @deftypefnx {C Function} double scm_acosh (double x)
1431 @deftypefnx {C Function} double scm_atanh (double x)
1432 Return the hyperbolic arcsine, arccosine or arctangent of @var{x}
1437 @node Bitwise Operations
1438 @subsubsection Bitwise Operations
1440 For the following bitwise functions, negative numbers are treated as
1441 infinite precision twos-complements. For instance @math{-6} is bits
1442 @math{@dots{}111010}, with infinitely many ones on the left. It can
1443 be seen that adding 6 (binary 110) to such a bit pattern gives all
1446 @deffn {Scheme Procedure} logand n1 n2 @dots{}
1447 @deffnx {C Function} scm_logand (n1, n2)
1448 Return the bitwise @sc{and} of the integer arguments.
1451 (logand) @result{} -1
1452 (logand 7) @result{} 7
1453 (logand #b111 #b011 #b001) @result{} 1
1457 @deffn {Scheme Procedure} logior n1 n2 @dots{}
1458 @deffnx {C Function} scm_logior (n1, n2)
1459 Return the bitwise @sc{or} of the integer arguments.
1462 (logior) @result{} 0
1463 (logior 7) @result{} 7
1464 (logior #b000 #b001 #b011) @result{} 3
1468 @deffn {Scheme Procedure} logxor n1 n2 @dots{}
1469 @deffnx {C Function} scm_loxor (n1, n2)
1470 Return the bitwise @sc{xor} of the integer arguments. A bit is
1471 set in the result if it is set in an odd number of arguments.
1474 (logxor) @result{} 0
1475 (logxor 7) @result{} 7
1476 (logxor #b000 #b001 #b011) @result{} 2
1477 (logxor #b000 #b001 #b011 #b011) @result{} 1
1481 @deffn {Scheme Procedure} lognot n
1482 @deffnx {C Function} scm_lognot (n)
1483 Return the integer which is the ones-complement of the integer
1484 argument, ie.@: each 0 bit is changed to 1 and each 1 bit to 0.
1487 (number->string (lognot #b10000000) 2)
1488 @result{} "-10000001"
1489 (number->string (lognot #b0) 2)
1494 @deffn {Scheme Procedure} logtest j k
1495 @deffnx {C Function} scm_logtest (j, k)
1497 (logtest j k) @equiv{} (not (zero? (logand j k)))
1499 (logtest #b0100 #b1011) @result{} #f
1500 (logtest #b0100 #b0111) @result{} #t
1504 @deffn {Scheme Procedure} logbit? index j
1505 @deffnx {C Function} scm_logbit_p (index, j)
1507 (logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)
1509 (logbit? 0 #b1101) @result{} #t
1510 (logbit? 1 #b1101) @result{} #f
1511 (logbit? 2 #b1101) @result{} #t
1512 (logbit? 3 #b1101) @result{} #t
1513 (logbit? 4 #b1101) @result{} #f
1517 @deffn {Scheme Procedure} ash n cnt
1518 @deffnx {C Function} scm_ash (n, cnt)
1519 Return @var{n} shifted left by @var{cnt} bits, or shifted right if
1520 @var{cnt} is negative. This is an ``arithmetic'' shift.
1522 This is effectively a multiplication by @m{2^{cnt}, 2^@var{cnt}}, and
1523 when @var{cnt} is negative it's a division, rounded towards negative
1524 infinity. (Note that this is not the same rounding as @code{quotient}
1527 With @var{n} viewed as an infinite precision twos complement,
1528 @code{ash} means a left shift introducing zero bits, or a right shift
1532 (number->string (ash #b1 3) 2) @result{} "1000"
1533 (number->string (ash #b1010 -1) 2) @result{} "101"
1535 ;; -23 is bits ...11101001, -6 is bits ...111010
1536 (ash -23 -2) @result{} -6
1540 @deffn {Scheme Procedure} logcount n
1541 @deffnx {C Function} scm_logcount (n)
1542 Return the number of bits in integer @var{n}. If integer is
1543 positive, the 1-bits in its binary representation are counted.
1544 If negative, the 0-bits in its two's-complement binary
1545 representation are counted. If 0, 0 is returned.
1548 (logcount #b10101010)
1557 @deffn {Scheme Procedure} integer-length n
1558 @deffnx {C Function} scm_integer_length (n)
1559 Return the number of bits necessary to represent @var{n}.
1561 For positive @var{n} this is how many bits to the most significant one
1562 bit. For negative @var{n} it's how many bits to the most significant
1563 zero bit in twos complement form.
1566 (integer-length #b10101010) @result{} 8
1567 (integer-length #b1111) @result{} 4
1568 (integer-length 0) @result{} 0
1569 (integer-length -1) @result{} 0
1570 (integer-length -256) @result{} 8
1571 (integer-length -257) @result{} 9
1575 @deffn {Scheme Procedure} integer-expt n k
1576 @deffnx {C Function} scm_integer_expt (n, k)
1577 Return @var{n} raised to the exact integer exponent
1588 @deffn {Scheme Procedure} bit-extract n start end
1589 @deffnx {C Function} scm_bit_extract (n, start, end)
1590 Return the integer composed of the @var{start} (inclusive)
1591 through @var{end} (exclusive) bits of @var{n}. The
1592 @var{start}th bit becomes the 0-th bit in the result.
1595 (number->string (bit-extract #b1101101010 0 4) 2)
1597 (number->string (bit-extract #b1101101010 4 9) 2)
1604 @subsubsection Random Number Generation
1606 Pseudo-random numbers are generated from a random state object, which
1607 can be created with @code{seed->random-state}. The @var{state}
1608 parameter to the various functions below is optional, it defaults to
1609 the state object in the @code{*random-state*} variable.
1611 @deffn {Scheme Procedure} copy-random-state [state]
1612 @deffnx {C Function} scm_copy_random_state (state)
1613 Return a copy of the random state @var{state}.
1616 @deffn {Scheme Procedure} random n [state]
1617 @deffnx {C Function} scm_random (n, state)
1618 Return a number in [0, @var{n}).
1620 Accepts a positive integer or real n and returns a
1621 number of the same type between zero (inclusive) and
1622 @var{n} (exclusive). The values returned have a uniform
1626 @deffn {Scheme Procedure} random:exp [state]
1627 @deffnx {C Function} scm_random_exp (state)
1628 Return an inexact real in an exponential distribution with mean
1629 1. For an exponential distribution with mean @var{u} use @code{(*
1630 @var{u} (random:exp))}.
1633 @deffn {Scheme Procedure} random:hollow-sphere! vect [state]
1634 @deffnx {C Function} scm_random_hollow_sphere_x (vect, state)
1635 Fills @var{vect} with inexact real random numbers the sum of whose
1636 squares is equal to 1.0. Thinking of @var{vect} as coordinates in
1637 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1638 the coordinates are uniformly distributed over the surface of the unit
1642 @deffn {Scheme Procedure} random:normal [state]
1643 @deffnx {C Function} scm_random_normal (state)
1644 Return an inexact real in a normal distribution. The distribution
1645 used has mean 0 and standard deviation 1. For a normal distribution
1646 with mean @var{m} and standard deviation @var{d} use @code{(+ @var{m}
1647 (* @var{d} (random:normal)))}.
1650 @deffn {Scheme Procedure} random:normal-vector! vect [state]
1651 @deffnx {C Function} scm_random_normal_vector_x (vect, state)
1652 Fills @var{vect} with inexact real random numbers that are
1653 independent and standard normally distributed
1654 (i.e., with mean 0 and variance 1).
1657 @deffn {Scheme Procedure} random:solid-sphere! vect [state]
1658 @deffnx {C Function} scm_random_solid_sphere_x (vect, state)
1659 Fills @var{vect} with inexact real random numbers the sum of whose
1660 squares is less than 1.0. Thinking of @var{vect} as coordinates in
1661 space of dimension @var{n} @math{=} @code{(vector-length @var{vect})},
1662 the coordinates are uniformly distributed within the unit
1663 @var{n}-sphere. The sum of the squares of the numbers is returned.
1664 @c FIXME: What does this mean, particularly the n-sphere part?
1667 @deffn {Scheme Procedure} random:uniform [state]
1668 @deffnx {C Function} scm_random_uniform (state)
1669 Return a uniformly distributed inexact real random number in
1673 @deffn {Scheme Procedure} seed->random-state seed
1674 @deffnx {C Function} scm_seed_to_random_state (seed)
1675 Return a new random state using @var{seed}.
1678 @defvar *random-state*
1679 The global random state used by the above functions when the
1680 @var{state} parameter is not given.
1685 @subsection Characters
1688 In Scheme, a character literal is written as @code{#\@var{name}} where
1689 @var{name} is the name of the character that you want. Printable
1690 characters have their usual single character name; for example,
1691 @code{#\a} is a lower case @code{a}.
1693 Most of the ``control characters'' (those below codepoint 32) in the
1694 @acronym{ASCII} character set, as well as the space, may be referred
1695 to by longer names: for example, @code{#\tab}, @code{#\esc},
1696 @code{#\stx}, and so on. The following table describes the
1697 @acronym{ASCII} names for each character.
1699 @multitable @columnfractions .25 .25 .25 .25
1700 @item 0 = @code{#\nul}
1701 @tab 1 = @code{#\soh}
1702 @tab 2 = @code{#\stx}
1703 @tab 3 = @code{#\etx}
1704 @item 4 = @code{#\eot}
1705 @tab 5 = @code{#\enq}
1706 @tab 6 = @code{#\ack}
1707 @tab 7 = @code{#\bel}
1708 @item 8 = @code{#\bs}
1709 @tab 9 = @code{#\ht}
1710 @tab 10 = @code{#\nl}
1711 @tab 11 = @code{#\vt}
1712 @item 12 = @code{#\np}
1713 @tab 13 = @code{#\cr}
1714 @tab 14 = @code{#\so}
1715 @tab 15 = @code{#\si}
1716 @item 16 = @code{#\dle}
1717 @tab 17 = @code{#\dc1}
1718 @tab 18 = @code{#\dc2}
1719 @tab 19 = @code{#\dc3}
1720 @item 20 = @code{#\dc4}
1721 @tab 21 = @code{#\nak}
1722 @tab 22 = @code{#\syn}
1723 @tab 23 = @code{#\etb}
1724 @item 24 = @code{#\can}
1725 @tab 25 = @code{#\em}
1726 @tab 26 = @code{#\sub}
1727 @tab 27 = @code{#\esc}
1728 @item 28 = @code{#\fs}
1729 @tab 29 = @code{#\gs}
1730 @tab 30 = @code{#\rs}
1731 @tab 31 = @code{#\us}
1732 @item 32 = @code{#\sp}
1735 The ``delete'' character (octal 177) may be referred to with the name
1738 Several characters have more than one name:
1740 @multitable {@code{#\backspace}} {Original}
1741 @item Alias @tab Original
1742 @item @code{#\space} @tab @code{#\sp}
1743 @item @code{#\newline} @tab @code{#\nl}
1744 @item @code{#\tab} @tab @code{#\ht}
1745 @item @code{#\backspace} @tab @code{#\bs}
1746 @item @code{#\return} @tab @code{#\cr}
1747 @item @code{#\page} @tab @code{#\np}
1748 @item @code{#\null} @tab @code{#\nul}
1752 @deffn {Scheme Procedure} char? x
1753 @deffnx {C Function} scm_char_p (x)
1754 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1758 @deffn {Scheme Procedure} char=? x y
1759 Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}.
1763 @deffn {Scheme Procedure} char<? x y
1764 Return @code{#t} iff @var{x} is less than @var{y} in the @acronym{ASCII} sequence,
1769 @deffn {Scheme Procedure} char<=? x y
1770 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1771 @acronym{ASCII} sequence, else @code{#f}.
1775 @deffn {Scheme Procedure} char>? x y
1776 Return @code{#t} iff @var{x} is greater than @var{y} in the @acronym{ASCII}
1777 sequence, else @code{#f}.
1781 @deffn {Scheme Procedure} char>=? x y
1782 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1783 @acronym{ASCII} sequence, else @code{#f}.
1787 @deffn {Scheme Procedure} char-ci=? x y
1788 Return @code{#t} iff @var{x} is the same character as @var{y} ignoring
1789 case, else @code{#f}.
1793 @deffn {Scheme Procedure} char-ci<? x y
1794 Return @code{#t} iff @var{x} is less than @var{y} in the @acronym{ASCII} sequence
1795 ignoring case, else @code{#f}.
1799 @deffn {Scheme Procedure} char-ci<=? x y
1800 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1801 @acronym{ASCII} sequence ignoring case, else @code{#f}.
1805 @deffn {Scheme Procedure} char-ci>? x y
1806 Return @code{#t} iff @var{x} is greater than @var{y} in the @acronym{ASCII}
1807 sequence ignoring case, else @code{#f}.
1811 @deffn {Scheme Procedure} char-ci>=? x y
1812 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1813 @acronym{ASCII} sequence ignoring case, else @code{#f}.
1816 @rnindex char-alphabetic?
1817 @deffn {Scheme Procedure} char-alphabetic? chr
1818 @deffnx {C Function} scm_char_alphabetic_p (chr)
1819 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1822 @rnindex char-numeric?
1823 @deffn {Scheme Procedure} char-numeric? chr
1824 @deffnx {C Function} scm_char_numeric_p (chr)
1825 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1828 @rnindex char-whitespace?
1829 @deffn {Scheme Procedure} char-whitespace? chr
1830 @deffnx {C Function} scm_char_whitespace_p (chr)
1831 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1834 @rnindex char-upper-case?
1835 @deffn {Scheme Procedure} char-upper-case? chr
1836 @deffnx {C Function} scm_char_upper_case_p (chr)
1837 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1840 @rnindex char-lower-case?
1841 @deffn {Scheme Procedure} char-lower-case? chr
1842 @deffnx {C Function} scm_char_lower_case_p (chr)
1843 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1846 @deffn {Scheme Procedure} char-is-both? chr
1847 @deffnx {C Function} scm_char_is_both_p (chr)
1848 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else
1852 @rnindex char->integer
1853 @deffn {Scheme Procedure} char->integer chr
1854 @deffnx {C Function} scm_char_to_integer (chr)
1855 Return the number corresponding to ordinal position of @var{chr} in the
1856 @acronym{ASCII} sequence.
1859 @rnindex integer->char
1860 @deffn {Scheme Procedure} integer->char n
1861 @deffnx {C Function} scm_integer_to_char (n)
1862 Return the character at position @var{n} in the @acronym{ASCII} sequence.
1865 @rnindex char-upcase
1866 @deffn {Scheme Procedure} char-upcase chr
1867 @deffnx {C Function} scm_char_upcase (chr)
1868 Return the uppercase character version of @var{chr}.
1871 @rnindex char-downcase
1872 @deffn {Scheme Procedure} char-downcase chr
1873 @deffnx {C Function} scm_char_downcase (chr)
1874 Return the lowercase character version of @var{chr}.
1877 @node Character Sets
1878 @subsection Character Sets
1880 The features described in this section correspond directly to SRFI-14.
1882 The data type @dfn{charset} implements sets of characters
1883 (@pxref{Characters}). Because the internal representation of
1884 character sets is not visible to the user, a lot of procedures for
1885 handling them are provided.
1887 Character sets can be created, extended, tested for the membership of a
1888 characters and be compared to other character sets.
1890 The Guile implementation of character sets currently deals only with
1891 8-bit characters. In the future, when Guile gets support for
1892 international character sets, this will change, but the functions
1893 provided here will always then be able to efficiently cope with very
1894 large character sets.
1897 * Character Set Predicates/Comparison::
1898 * Iterating Over Character Sets:: Enumerate charset elements.
1899 * Creating Character Sets:: Making new charsets.
1900 * Querying Character Sets:: Test charsets for membership etc.
1901 * Character-Set Algebra:: Calculating new charsets.
1902 * Standard Character Sets:: Variables containing predefined charsets.
1905 @node Character Set Predicates/Comparison
1906 @subsubsection Character Set Predicates/Comparison
1908 Use these procedures for testing whether an object is a character set,
1909 or whether several character sets are equal or subsets of each other.
1910 @code{char-set-hash} can be used for calculating a hash value, maybe for
1911 usage in fast lookup procedures.
1913 @deffn {Scheme Procedure} char-set? obj
1914 @deffnx {C Function} scm_char_set_p (obj)
1915 Return @code{#t} if @var{obj} is a character set, @code{#f}
1919 @deffn {Scheme Procedure} char-set= . char_sets
1920 @deffnx {C Function} scm_char_set_eq (char_sets)
1921 Return @code{#t} if all given character sets are equal.
1924 @deffn {Scheme Procedure} char-set<= . char_sets
1925 @deffnx {C Function} scm_char_set_leq (char_sets)
1926 Return @code{#t} if every character set @var{cs}i is a subset
1927 of character set @var{cs}i+1.
1930 @deffn {Scheme Procedure} char-set-hash cs [bound]
1931 @deffnx {C Function} scm_char_set_hash (cs, bound)
1932 Compute a hash value for the character set @var{cs}. If
1933 @var{bound} is given and non-zero, it restricts the
1934 returned value to the range 0 @dots{} @var{bound - 1}.
1937 @c ===================================================================
1939 @node Iterating Over Character Sets
1940 @subsubsection Iterating Over Character Sets
1942 Character set cursors are a means for iterating over the members of a
1943 character sets. After creating a character set cursor with
1944 @code{char-set-cursor}, a cursor can be dereferenced with
1945 @code{char-set-ref}, advanced to the next member with
1946 @code{char-set-cursor-next}. Whether a cursor has passed past the last
1947 element of the set can be checked with @code{end-of-char-set?}.
1949 Additionally, mapping and (un-)folding procedures for character sets are
1952 @deffn {Scheme Procedure} char-set-cursor cs
1953 @deffnx {C Function} scm_char_set_cursor (cs)
1954 Return a cursor into the character set @var{cs}.
1957 @deffn {Scheme Procedure} char-set-ref cs cursor
1958 @deffnx {C Function} scm_char_set_ref (cs, cursor)
1959 Return the character at the current cursor position
1960 @var{cursor} in the character set @var{cs}. It is an error to
1961 pass a cursor for which @code{end-of-char-set?} returns true.
1964 @deffn {Scheme Procedure} char-set-cursor-next cs cursor
1965 @deffnx {C Function} scm_char_set_cursor_next (cs, cursor)
1966 Advance the character set cursor @var{cursor} to the next
1967 character in the character set @var{cs}. It is an error if the
1968 cursor given satisfies @code{end-of-char-set?}.
1971 @deffn {Scheme Procedure} end-of-char-set? cursor
1972 @deffnx {C Function} scm_end_of_char_set_p (cursor)
1973 Return @code{#t} if @var{cursor} has reached the end of a
1974 character set, @code{#f} otherwise.
1977 @deffn {Scheme Procedure} char-set-fold kons knil cs
1978 @deffnx {C Function} scm_char_set_fold (kons, knil, cs)
1979 Fold the procedure @var{kons} over the character set @var{cs},
1980 initializing it with @var{knil}.
1983 @deffn {Scheme Procedure} char-set-unfold p f g seed [base_cs]
1984 @deffnx {C Function} scm_char_set_unfold (p, f, g, seed, base_cs)
1985 This is a fundamental constructor for character sets.
1987 @item @var{g} is used to generate a series of ``seed'' values
1988 from the initial seed: @var{seed}, (@var{g} @var{seed}),
1989 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
1990 @item @var{p} tells us when to stop -- when it returns true
1991 when applied to one of the seed values.
1992 @item @var{f} maps each seed value to a character. These
1993 characters are added to the base character set @var{base_cs} to
1994 form the result; @var{base_cs} defaults to the empty set.
1998 @deffn {Scheme Procedure} char-set-unfold! p f g seed base_cs
1999 @deffnx {C Function} scm_char_set_unfold_x (p, f, g, seed, base_cs)
2000 This is a fundamental constructor for character sets.
2002 @item @var{g} is used to generate a series of ``seed'' values
2003 from the initial seed: @var{seed}, (@var{g} @var{seed}),
2004 (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}), @dots{}
2005 @item @var{p} tells us when to stop -- when it returns true
2006 when applied to one of the seed values.
2007 @item @var{f} maps each seed value to a character. These
2008 characters are added to the base character set @var{base_cs} to
2009 form the result; @var{base_cs} defaults to the empty set.
2013 @deffn {Scheme Procedure} char-set-for-each proc cs
2014 @deffnx {C Function} scm_char_set_for_each (proc, cs)
2015 Apply @var{proc} to every character in the character set
2016 @var{cs}. The return value is not specified.
2019 @deffn {Scheme Procedure} char-set-map proc cs
2020 @deffnx {C Function} scm_char_set_map (proc, cs)
2021 Map the procedure @var{proc} over every character in @var{cs}.
2022 @var{proc} must be a character -> character procedure.
2025 @c ===================================================================
2027 @node Creating Character Sets
2028 @subsubsection Creating Character Sets
2030 New character sets are produced with these procedures.
2032 @deffn {Scheme Procedure} char-set-copy cs
2033 @deffnx {C Function} scm_char_set_copy (cs)
2034 Return a newly allocated character set containing all
2035 characters in @var{cs}.
2038 @deffn {Scheme Procedure} char-set . rest
2039 @deffnx {C Function} scm_char_set (rest)
2040 Return a character set containing all given characters.
2043 @deffn {Scheme Procedure} list->char-set list [base_cs]
2044 @deffnx {C Function} scm_list_to_char_set (list, base_cs)
2045 Convert the character list @var{list} to a character set. If
2046 the character set @var{base_cs} is given, the character in this
2047 set are also included in the result.
2050 @deffn {Scheme Procedure} list->char-set! list base_cs
2051 @deffnx {C Function} scm_list_to_char_set_x (list, base_cs)
2052 Convert the character list @var{list} to a character set. The
2053 characters are added to @var{base_cs} and @var{base_cs} is
2057 @deffn {Scheme Procedure} string->char-set str [base_cs]
2058 @deffnx {C Function} scm_string_to_char_set (str, base_cs)
2059 Convert the string @var{str} to a character set. If the
2060 character set @var{base_cs} is given, the characters in this
2061 set are also included in the result.
2064 @deffn {Scheme Procedure} string->char-set! str base_cs
2065 @deffnx {C Function} scm_string_to_char_set_x (str, base_cs)
2066 Convert the string @var{str} to a character set. The
2067 characters from the string are added to @var{base_cs}, and
2068 @var{base_cs} is returned.
2071 @deffn {Scheme Procedure} char-set-filter pred cs [base_cs]
2072 @deffnx {C Function} scm_char_set_filter (pred, cs, base_cs)
2073 Return a character set containing every character from @var{cs}
2074 so that it satisfies @var{pred}. If provided, the characters
2075 from @var{base_cs} are added to the result.
2078 @deffn {Scheme Procedure} char-set-filter! pred cs base_cs
2079 @deffnx {C Function} scm_char_set_filter_x (pred, cs, base_cs)
2080 Return a character set containing every character from @var{cs}
2081 so that it satisfies @var{pred}. The characters are added to
2082 @var{base_cs} and @var{base_cs} is returned.
2085 @deffn {Scheme Procedure} ucs-range->char-set lower upper [error [base_cs]]
2086 @deffnx {C Function} scm_ucs_range_to_char_set (lower, upper, error, base_cs)
2087 Return a character set containing all characters whose
2088 character codes lie in the half-open range
2089 [@var{lower},@var{upper}).
2091 If @var{error} is a true value, an error is signalled if the
2092 specified range contains characters which are not contained in
2093 the implemented character range. If @var{error} is @code{#f},
2094 these characters are silently left out of the resultung
2097 The characters in @var{base_cs} are added to the result, if
2101 @deffn {Scheme Procedure} ucs-range->char-set! lower upper error base_cs
2102 @deffnx {C Function} scm_ucs_range_to_char_set_x (lower, upper, error, base_cs)
2103 Return a character set containing all characters whose
2104 character codes lie in the half-open range
2105 [@var{lower},@var{upper}).
2107 If @var{error} is a true value, an error is signalled if the
2108 specified range contains characters which are not contained in
2109 the implemented character range. If @var{error} is @code{#f},
2110 these characters are silently left out of the resultung
2113 The characters are added to @var{base_cs} and @var{base_cs} is
2117 @deffn {Scheme Procedure} ->char-set x
2118 @deffnx {C Function} scm_to_char_set (x)
2119 Coerces x into a char-set. @var{x} may be a string, character or char-set. A string is converted to the set of its constituent characters; a character is converted to a singleton set; a char-set is returned as-is.
2122 @c ===================================================================
2124 @node Querying Character Sets
2125 @subsubsection Querying Character Sets
2127 Access the elements and other information of a character set with these
2130 @deffn {Scheme Procedure} char-set-size cs
2131 @deffnx {C Function} scm_char_set_size (cs)
2132 Return the number of elements in character set @var{cs}.
2135 @deffn {Scheme Procedure} char-set-count pred cs
2136 @deffnx {C Function} scm_char_set_count (pred, cs)
2137 Return the number of the elements int the character set
2138 @var{cs} which satisfy the predicate @var{pred}.
2141 @deffn {Scheme Procedure} char-set->list cs
2142 @deffnx {C Function} scm_char_set_to_list (cs)
2143 Return a list containing the elements of the character set
2147 @deffn {Scheme Procedure} char-set->string cs
2148 @deffnx {C Function} scm_char_set_to_string (cs)
2149 Return a string containing the elements of the character set
2150 @var{cs}. The order in which the characters are placed in the
2151 string is not defined.
2154 @deffn {Scheme Procedure} char-set-contains? cs ch
2155 @deffnx {C Function} scm_char_set_contains_p (cs, ch)
2156 Return @code{#t} iff the character @var{ch} is contained in the
2157 character set @var{cs}.
2160 @deffn {Scheme Procedure} char-set-every pred cs
2161 @deffnx {C Function} scm_char_set_every (pred, cs)
2162 Return a true value if every character in the character set
2163 @var{cs} satisfies the predicate @var{pred}.
2166 @deffn {Scheme Procedure} char-set-any pred cs
2167 @deffnx {C Function} scm_char_set_any (pred, cs)
2168 Return a true value if any character in the character set
2169 @var{cs} satisfies the predicate @var{pred}.
2172 @c ===================================================================
2174 @node Character-Set Algebra
2175 @subsubsection Character-Set Algebra
2177 Character sets can be manipulated with the common set algebra operation,
2178 such as union, complement, intersection etc. All of these procedures
2179 provide side-effecting variants, which modify their character set
2182 @deffn {Scheme Procedure} char-set-adjoin cs . rest
2183 @deffnx {C Function} scm_char_set_adjoin (cs, rest)
2184 Add all character arguments to the first argument, which must
2188 @deffn {Scheme Procedure} char-set-delete cs . rest
2189 @deffnx {C Function} scm_char_set_delete (cs, rest)
2190 Delete all character arguments from the first argument, which
2191 must be a character set.
2194 @deffn {Scheme Procedure} char-set-adjoin! cs . rest
2195 @deffnx {C Function} scm_char_set_adjoin_x (cs, rest)
2196 Add all character arguments to the first argument, which must
2200 @deffn {Scheme Procedure} char-set-delete! cs . rest
2201 @deffnx {C Function} scm_char_set_delete_x (cs, rest)
2202 Delete all character arguments from the first argument, which
2203 must be a character set.
2206 @deffn {Scheme Procedure} char-set-complement cs
2207 @deffnx {C Function} scm_char_set_complement (cs)
2208 Return the complement of the character set @var{cs}.
2211 @deffn {Scheme Procedure} char-set-union . rest
2212 @deffnx {C Function} scm_char_set_union (rest)
2213 Return the union of all argument character sets.
2216 @deffn {Scheme Procedure} char-set-intersection . rest
2217 @deffnx {C Function} scm_char_set_intersection (rest)
2218 Return the intersection of all argument character sets.
2221 @deffn {Scheme Procedure} char-set-difference cs1 . rest
2222 @deffnx {C Function} scm_char_set_difference (cs1, rest)
2223 Return the difference of all argument character sets.
2226 @deffn {Scheme Procedure} char-set-xor . rest
2227 @deffnx {C Function} scm_char_set_xor (rest)
2228 Return the exclusive-or of all argument character sets.
2231 @deffn {Scheme Procedure} char-set-diff+intersection cs1 . rest
2232 @deffnx {C Function} scm_char_set_diff_plus_intersection (cs1, rest)
2233 Return the difference and the intersection of all argument
2237 @deffn {Scheme Procedure} char-set-complement! cs
2238 @deffnx {C Function} scm_char_set_complement_x (cs)
2239 Return the complement of the character set @var{cs}.
2242 @deffn {Scheme Procedure} char-set-union! cs1 . rest
2243 @deffnx {C Function} scm_char_set_union_x (cs1, rest)
2244 Return the union of all argument character sets.
2247 @deffn {Scheme Procedure} char-set-intersection! cs1 . rest
2248 @deffnx {C Function} scm_char_set_intersection_x (cs1, rest)
2249 Return the intersection of all argument character sets.
2252 @deffn {Scheme Procedure} char-set-difference! cs1 . rest
2253 @deffnx {C Function} scm_char_set_difference_x (cs1, rest)
2254 Return the difference of all argument character sets.
2257 @deffn {Scheme Procedure} char-set-xor! cs1 . rest
2258 @deffnx {C Function} scm_char_set_xor_x (cs1, rest)
2259 Return the exclusive-or of all argument character sets.
2262 @deffn {Scheme Procedure} char-set-diff+intersection! cs1 cs2 . rest
2263 @deffnx {C Function} scm_char_set_diff_plus_intersection_x (cs1, cs2, rest)
2264 Return the difference and the intersection of all argument
2268 @c ===================================================================
2270 @node Standard Character Sets
2271 @subsubsection Standard Character Sets
2273 In order to make the use of the character set data type and procedures
2274 useful, several predefined character set variables exist.
2276 @defvr {Scheme Variable} char-set:lower-case
2277 @defvrx {C Variable} scm_char_set_lower_case
2278 All lower-case characters.
2281 @defvr {Scheme Variable} char-set:upper-case
2282 @defvrx {C Variable} scm_char_set_upper_case
2283 All upper-case characters.
2286 @defvr {Scheme Variable} char-set:title-case
2287 @defvrx {C Variable} scm_char_set_title_case
2288 This is empty, because ASCII has no titlecase characters.
2291 @defvr {Scheme Variable} char-set:letter
2292 @defvrx {C Variable} scm_char_set_letter
2293 All letters, e.g. the union of @code{char-set:lower-case} and
2294 @code{char-set:upper-case}.
2297 @defvr {Scheme Variable} char-set:digit
2298 @defvrx {C Variable} scm_char_set_digit
2302 @defvr {Scheme Variable} char-set:letter+digit
2303 @defvrx {C Variable} scm_char_set_letter_and_digit
2304 The union of @code{char-set:letter} and @code{char-set:digit}.
2307 @defvr {Scheme Variable} char-set:graphic
2308 @defvrx {C Variable} scm_char_set_graphic
2309 All characters which would put ink on the paper.
2312 @defvr {Scheme Variable} char-set:printing
2313 @defvrx {C Variable} scm_char_set_printing
2314 The union of @code{char-set:graphic} and @code{char-set:whitespace}.
2317 @defvr {Scheme Variable} char-set:whitespace
2318 @defvrx {C Variable} scm_char_set_whitespace
2319 All whitespace characters.
2322 @defvr {Scheme Variable} char-set:blank
2323 @defvrx {C Variable} scm_char_set_blank
2324 All horizontal whitespace characters, that is @code{#\space} and
2328 @defvr {Scheme Variable} char-set:iso-control
2329 @defvrx {C Variable} scm_char_set_iso_control
2330 The ISO control characters with the codes 0--31 and 127.
2333 @defvr {Scheme Variable} char-set:punctuation
2334 @defvrx {C Variable} scm_char_set_punctuation
2335 The characters @code{!"#%&'()*,-./:;?@@[\\]_@{@}}
2338 @defvr {Scheme Variable} char-set:symbol
2339 @defvrx {C Variable} scm_char_set_symbol
2340 The characters @code{$+<=>^`|~}.
2343 @defvr {Scheme Variable} char-set:hex-digit
2344 @defvrx {C Variable} scm_char_set_hex_digit
2345 The hexadecimal digits @code{0123456789abcdefABCDEF}.
2348 @defvr {Scheme Variable} char-set:ascii
2349 @defvrx {C Variable} scm_char_set_ascii
2350 All ASCII characters.
2353 @defvr {Scheme Variable} char-set:empty
2354 @defvrx {C Variable} scm_char_set_empty
2355 The empty character set.
2358 @defvr {Scheme Variable} char-set:full
2359 @defvrx {C Variable} scm_char_set_full
2360 This character set contains all possible characters.
2367 Strings are fixed-length sequences of characters. They can be created
2368 by calling constructor procedures, but they can also literally get
2369 entered at the @acronym{REPL} or in Scheme source files.
2371 @c Guile provides a rich set of string processing procedures, because text
2372 @c handling is very important when Guile is used as a scripting language.
2374 Strings always carry the information about how many characters they are
2375 composed of with them, so there is no special end-of-string character,
2376 like in C. That means that Scheme strings can contain any character,
2377 even the @samp{#\nul} character @samp{\0}.
2379 To use strings efficiently, you need to know a bit about how Guile
2380 implements them. In Guile, a string consists of two parts, a head and
2381 the actual memory where the characters are stored. When a string (or
2382 a substring of it) is copied, only a new head gets created, the memory
2383 is usually not copied. The two heads start out pointing to the same
2386 When one of these two strings is modified, as with @code{string-set!},
2387 their common memory does get copied so that each string has its own
2388 memory and modifying one does not accidently modify the other as well.
2389 Thus, Guile's strings are `copy on write'; the actual copying of their
2390 memory is delayed until one string is written to.
2392 This implementation makes functions like @code{substring} very
2393 efficient in the common case that no modifications are done to the
2396 If you do know that your strings are getting modified right away, you
2397 can use @code{substring/copy} instead of @code{substring}. This
2398 function performs the copy immediately at the time of creation. This
2399 is more efficient, especially in a multi-threaded program. Also,
2400 @code{substring/copy} can avoid the problem that a short substring
2401 holds on to the memory of a very large original string that could
2402 otherwise be recycled.
2404 If you want to avoid the copy altogether, so that modifications of one
2405 string show up in the other, you can use @code{substring/shared}. The
2406 strings created by this procedure are called @dfn{mutation sharing
2407 substrings} since the substring and the original string share
2408 modifications to each other.
2410 If you want to prevent modifications, use @code{substring/read-only}.
2412 Guile provides all procedures of SRFI-13 and a few more.
2415 * String Syntax:: Read syntax for strings.
2416 * String Predicates:: Testing strings for certain properties.
2417 * String Constructors:: Creating new string objects.
2418 * List/String Conversion:: Converting from/to lists of characters.
2419 * String Selection:: Select portions from strings.
2420 * String Modification:: Modify parts or whole strings.
2421 * String Comparison:: Lexicographic ordering predicates.
2422 * String Searching:: Searching in strings.
2423 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
2424 * Reversing and Appending Strings:: Appending strings to form a new string.
2425 * Mapping Folding and Unfolding:: Iterating over strings.
2426 * Miscellaneous String Operations:: Replicating, insertion, parsing, ...
2427 * Conversion to/from C::
2431 @subsubsection String Read Syntax
2433 @c In the following @code is used to get a good font in TeX etc, but
2434 @c is omitted for Info format, so as not to risk any confusion over
2435 @c whether surrounding ` ' quotes are part of the escape or are
2436 @c special in a string (they're not).
2438 The read syntax for strings is an arbitrarily long sequence of
2439 characters enclosed in double quotes (@nicode{"}).
2441 Backslash is an escape character and can be used to insert the
2442 following special characters. @nicode{\"} and @nicode{\\} are R5RS
2443 standard, the rest are Guile extensions, notice they follow C string
2448 Backslash character.
2451 Double quote character (an unescaped @nicode{"} is otherwise the end
2455 NUL character (ASCII 0).
2458 Bell character (ASCII 7).
2461 Formfeed character (ASCII 12).
2464 Newline character (ASCII 10).
2467 Carriage return character (ASCII 13).
2470 Tab character (ASCII 9).
2473 Vertical tab character (ASCII 11).
2476 Character code given by two hexadecimal digits. For example
2477 @nicode{\x7f} for an ASCII DEL (127).
2481 The following are examples of string literals:
2491 @node String Predicates
2492 @subsubsection String Predicates
2494 The following procedures can be used to check whether a given string
2495 fulfills some specified property.
2498 @deffn {Scheme Procedure} string? obj
2499 @deffnx {C Function} scm_string_p (obj)
2500 Return @code{#t} if @var{obj} is a string, else @code{#f}.
2503 @deftypefn {C Function} int scm_is_string (SCM obj)
2504 Returns @code{1} if @var{obj} is a string, @code{0} otherwise.
2507 @deffn {Scheme Procedure} string-null? str
2508 @deffnx {C Function} scm_string_null_p (str)
2509 Return @code{#t} if @var{str}'s length is zero, and
2510 @code{#f} otherwise.
2512 (string-null? "") @result{} #t
2514 (string-null? y) @result{} #f
2518 @deffn {Scheme Procedure} string-any char_pred s [start [end]]
2519 @deffnx {C Function} scm_string_any (char_pred, s, start, end)
2520 Check if the predicate @var{pred} is true for any character in
2523 Calls to @var{pred} are made from left to right across @var{s}.
2524 When it returns true (ie.@: non-@code{#f}), that return value
2525 is the return from @code{string-any}.
2527 The SRFI-13 specification requires that the call to @var{pred}
2528 on the last character of @var{s} (assuming that point is
2529 reached) be a tail call, but currently in Guile this is not the
2533 @deffn {Scheme Procedure} string-every char_pred s [start [end]]
2534 @deffnx {C Function} scm_string_every (char_pred, s, start, end)
2535 Check if the predicate @var{pred} is true for every character
2536 in the string @var{s}.
2538 Calls to @var{pred} are made from left to right across @var{s}.
2539 If the predicate is true for every character then the return
2540 value from the last @var{pred} call is the return from
2541 @code{string-every}.
2543 If there are no characters in @var{s} (ie.@: @var{start} equals
2544 @var{end}) then the return is @code{#t}.
2546 The SRFI-13 specification requires that the call to @var{pred}
2547 on the last character of @var{s} (assuming that point is
2548 reached) be a tail call, but currently in Guile this is not the
2552 @node String Constructors
2553 @subsubsection String Constructors
2555 The string constructor procedures create new string objects, possibly
2556 initializing them with some specified character data. See also
2557 @xref{String Selection}, for ways to create strings from existing
2560 @c FIXME::martin: list->string belongs into `List/String Conversion'
2563 @rnindex list->string
2564 @deffn {Scheme Procedure} string . chrs
2565 @deffnx {Scheme Procedure} list->string chrs
2566 @deffnx {C Function} scm_string (chrs)
2567 Return a newly allocated string composed of the arguments,
2571 @rnindex make-string
2572 @deffn {Scheme Procedure} make-string k [chr]
2573 @deffnx {C Function} scm_make_string (k, chr)
2574 Return a newly allocated string of
2575 length @var{k}. If @var{chr} is given, then all elements of
2576 the string are initialized to @var{chr}, otherwise the contents
2577 of the @var{string} are unspecified.
2580 @deftypefn {C Function} SCM scm_c_make_string (size_t len, SCM chr)
2581 Like @code{scm_make_string}, but expects the length as a
2585 @deffn {Scheme Procedure} string-tabulate proc len
2586 @deffnx {C Function} scm_string_tabulate (proc, len)
2587 @var{proc} is an integer->char procedure. Construct a string
2588 of size @var{len} by applying @var{proc} to each index to
2589 produce the corresponding string element. The order in which
2590 @var{proc} is applied to the indices is not specified.
2593 @deffn {Scheme Procedure} reverse-list->string chrs
2594 @deffnx {C Function} scm_reverse_list_to_string (chrs)
2595 An efficient implementation of @code{(compose string->list
2599 (reverse-list->string '(#\a #\B #\c)) @result{} "cBa"
2603 @deffn {Scheme Procedure} string-join ls [delimiter [grammar]]
2604 @deffnx {C Function} scm_string_join (ls, delimiter, grammar)
2605 Append the string in the string list @var{ls}, using the string
2606 @var{delim} as a delimiter between the elements of @var{ls}.
2607 @var{grammar} is a symbol which specifies how the delimiter is
2608 placed between the strings, and defaults to the symbol
2613 Insert the separator between list elements. An empty string
2614 will produce an empty list.
2616 Like @code{infix}, but will raise an error if given the empty
2619 Insert the separator after every list element.
2621 Insert the separator before each list element.
2625 @node List/String Conversion
2626 @subsubsection List/String conversion
2628 When processing strings, it is often convenient to first convert them
2629 into a list representation by using the procedure @code{string->list},
2630 work with the resulting list, and then convert it back into a string.
2631 These procedures are useful for similar tasks.
2633 @rnindex string->list
2634 @deffn {Scheme Procedure} string->list str [start [end]]
2635 @deffnx {C Function} scm_substring_to_list (str, start, end)
2636 @deffnx {C Function} scm_string_to_list (str)
2637 Convert the string @var{str} into a list of characters.
2640 @deffn {Scheme Procedure} string-split str chr
2641 @deffnx {C Function} scm_string_split (str, chr)
2642 Split the string @var{str} into the a list of the substrings delimited
2643 by appearances of the character @var{chr}. Note that an empty substring
2644 between separator characters will result in an empty string in the
2648 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
2650 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
2652 (string-split "::" #\:)
2656 (string-split "" #\:)
2663 @node String Selection
2664 @subsubsection String Selection
2666 Portions of strings can be extracted by these procedures.
2667 @code{string-ref} delivers individual characters whereas
2668 @code{substring} can be used to extract substrings from longer strings.
2670 @rnindex string-length
2671 @deffn {Scheme Procedure} string-length string
2672 @deffnx {C Function} scm_string_length (string)
2673 Return the number of characters in @var{string}.
2676 @deftypefn {C Function} size_t scm_c_string_length (SCM str)
2677 Return the number of characters in @var{str} as a @code{size_t}.
2681 @deffn {Scheme Procedure} string-ref str k
2682 @deffnx {C Function} scm_string_ref (str, k)
2683 Return character @var{k} of @var{str} using zero-origin
2684 indexing. @var{k} must be a valid index of @var{str}.
2687 @deftypefn {C Function} SCM scm_c_string_ref (SCM str, size_t k)
2688 Return character @var{k} of @var{str} using zero-origin
2689 indexing. @var{k} must be a valid index of @var{str}.
2692 @rnindex string-copy
2693 @deffn {Scheme Procedure} string-copy str [start [end]]
2694 @deffnx {C Function} scm_substring_copy (str, start, end)
2695 @deffnx {C Function} scm_string_copy (str)
2696 Return a copy of the given string @var{str}.
2698 The returned string shares storage with @var{str} initially, but it is
2699 copied as soon as one of the two strings is modified.
2703 @deffn {Scheme Procedure} substring str start [end]
2704 @deffnx {C Function} scm_substring (str, start, end)
2705 Return a new string formed from the characters
2706 of @var{str} beginning with index @var{start} (inclusive) and
2707 ending with index @var{end} (exclusive).
2708 @var{str} must be a string, @var{start} and @var{end} must be
2709 exact integers satisfying:
2711 0 <= @var{start} <= @var{end} <= @code{(string-length @var{str})}.
2713 The returned string shares storage with @var{str} initially, but it is
2714 copied as soon as one of the two strings is modified.
2717 @deffn {Scheme Procedure} substring/shared str start [end]
2718 @deffnx {C Function} scm_substring_shared (str, start, end)
2719 Like @code{substring}, but the strings continue to share their storage
2720 even if they are modified. Thus, modifications to @var{str} show up
2721 in the new string, and vice versa.
2724 @deffn {Scheme Procedure} substring/copy str start [end]
2725 @deffnx {C Function} scm_substring_copy (str, start, end)
2726 Like @code{substring}, but the storage for the new string is copied
2730 @deffn {Scheme Procedure} substring/read-only str start [end]
2731 @deffnx {C Function} scm_substring_read_only (str, start, end)
2732 Like @code{substring}, but the resulting string can not be modified.
2735 @deftypefn {C Function} SCM scm_c_substring (SCM str, size_t start, size_t end)
2736 @deftypefnx {C Function} SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
2737 @deftypefnx {C Function} SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
2738 @deftypefnx {C Function} SCM scm_c_substring_read_only (SCM str, size_t start, size_t end)
2739 Like @code{scm_substring}, etc. but the bounds are given as a @code{size_t}.
2742 @deffn {Scheme Procedure} string-take s n
2743 @deffnx {C Function} scm_string_take (s, n)
2744 Return the @var{n} first characters of @var{s}.
2747 @deffn {Scheme Procedure} string-drop s n
2748 @deffnx {C Function} scm_string_drop (s, n)
2749 Return all but the first @var{n} characters of @var{s}.
2752 @deffn {Scheme Procedure} string-take-right s n
2753 @deffnx {C Function} scm_string_take_right (s, n)
2754 Return the @var{n} last characters of @var{s}.
2757 @deffn {Scheme Procedure} string-drop-right s n
2758 @deffnx {C Function} scm_string_drop_right (s, n)
2759 Return all but the last @var{n} characters of @var{s}.
2762 @deffn {Scheme Procedure} string-pad s len [chr [start [end]]]
2763 @deffnx {C Function} scm_string_pad (s, len, chr, start, end)
2764 Take that characters from @var{start} to @var{end} from the
2765 string @var{s} and return a new string, right-padded by the
2766 character @var{chr} to length @var{len}. If the resulting
2767 string is longer than @var{len}, it is truncated on the right.
2770 @deffn {Scheme Procedure} string-pad-right s len [chr [start [end]]]
2771 @deffnx {C Function} scm_string_pad_right (s, len, chr, start, end)
2772 Take that characters from @var{start} to @var{end} from the
2773 string @var{s} and return a new string, left-padded by the
2774 character @var{chr} to length @var{len}. If the resulting
2775 string is longer than @var{len}, it is truncated on the left.
2778 @deffn {Scheme Procedure} string-trim s [char_pred [start [end]]]
2779 @deffnx {C Function} scm_string_trim (s, char_pred, start, end)
2780 Trim @var{s} by skipping over all characters on the left
2781 that satisfy the parameter @var{char_pred}:
2785 if it is the character @var{ch}, characters equal to
2786 @var{ch} are trimmed,
2789 if it is a procedure @var{pred} characters that
2790 satisfy @var{pred} are trimmed,
2793 if it is a character set, characters in that set are trimmed.
2796 If called without a @var{char_pred} argument, all whitespace is
2800 @deffn {Scheme Procedure} string-trim-right s [char_pred [start [end]]]
2801 @deffnx {C Function} scm_string_trim_right (s, char_pred, start, end)
2802 Trim @var{s} by skipping over all characters on the rightt
2803 that satisfy the parameter @var{char_pred}:
2807 if it is the character @var{ch}, characters equal to @var{ch}
2811 if it is a procedure @var{pred} characters that satisfy
2812 @var{pred} are trimmed,
2815 if it is a character sets, all characters in that set are
2819 If called without a @var{char_pred} argument, all whitespace is
2823 @deffn {Scheme Procedure} string-trim-both s [char_pred [start [end]]]
2824 @deffnx {C Function} scm_string_trim_both (s, char_pred, start, end)
2825 Trim @var{s} by skipping over all characters on both sides of
2826 the string that satisfy the parameter @var{char_pred}:
2830 if it is the character @var{ch}, characters equal to @var{ch}
2834 if it is a procedure @var{pred} characters that satisfy
2835 @var{pred} are trimmed,
2838 if it is a character set, the characters in the set are
2842 If called without a @var{char_pred} argument, all whitespace is
2846 @node String Modification
2847 @subsubsection String Modification
2849 These procedures are for modifying strings in-place. This means that the
2850 result of the operation is not a new string; instead, the original string's
2851 memory representation is modified.
2853 @rnindex string-set!
2854 @deffn {Scheme Procedure} string-set! str k chr
2855 @deffnx {C Function} scm_string_set_x (str, k, chr)
2856 Store @var{chr} in element @var{k} of @var{str} and return
2857 an unspecified value. @var{k} must be a valid index of
2861 @deftypefn {C Function} void scm_c_string_set_x (SCM str, size_t k, SCM chr)
2862 Like @code{scm_string_set_x}, but the index is given as a @code{size_t}.
2865 @rnindex string-fill!
2866 @deffn {Scheme Procedure} string-fill! str chr [start [end]]
2867 @deffnx {C Function} scm_substring_fill_x (str, chr, start, end)
2868 @deffnx {C Function} scm_string_fill_x (str, chr)
2869 Stores @var{chr} in every element of the given @var{str} and
2870 returns an unspecified value.
2873 @deffn {Scheme Procedure} substring-fill! str start end fill
2874 @deffnx {C Function} scm_substring_fill_x (str, start, end, fill)
2875 Change every character in @var{str} between @var{start} and
2876 @var{end} to @var{fill}.
2879 (define y "abcdefg")
2880 (substring-fill! y 1 3 #\r)
2886 @deffn {Scheme Procedure} substring-move! str1 start1 end1 str2 start2
2887 @deffnx {C Function} scm_substring_move_x (str1, start1, end1, str2, start2)
2888 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
2889 into @var{str2} beginning at position @var{start2}.
2890 @var{str1} and @var{str2} can be the same string.
2893 @deffn {Scheme Procedure} string-copy! target tstart s [start [end]]
2894 @deffnx {C Function} scm_string_copy_x (target, tstart, s, start, end)
2895 Copy the sequence of characters from index range [@var{start},
2896 @var{end}) in string @var{s} to string @var{target}, beginning
2897 at index @var{tstart}. The characters are copied left-to-right
2898 or right-to-left as needed -- the copy is guaranteed to work,
2899 even if @var{target} and @var{s} are the same string. It is an
2900 error if the copy operation runs off the end of the target
2905 @node String Comparison
2906 @subsubsection String Comparison
2908 The procedures in this section are similar to the character ordering
2909 predicates (@pxref{Characters}), but are defined on character sequences.
2911 The first set is specified in R5RS and has names that end in @code{?}.
2912 The second set is specified in SRFI-13 and the names have no ending
2913 @code{?}. The predicates ending in @code{-ci} ignore the character case
2914 when comparing strings.
2917 @deffn {Scheme Procedure} string=? s1 s2
2918 Lexicographic equality predicate; return @code{#t} if the two
2919 strings are the same length and contain the same characters in
2920 the same positions, otherwise return @code{#f}.
2922 The procedure @code{string-ci=?} treats upper and lower case
2923 letters as though they were the same character, but
2924 @code{string=?} treats upper and lower case as distinct
2929 @deffn {Scheme Procedure} string<? s1 s2
2930 Lexicographic ordering predicate; return @code{#t} if @var{s1}
2931 is lexicographically less than @var{s2}.
2935 @deffn {Scheme Procedure} string<=? s1 s2
2936 Lexicographic ordering predicate; return @code{#t} if @var{s1}
2937 is lexicographically less than or equal to @var{s2}.
2941 @deffn {Scheme Procedure} string>? s1 s2
2942 Lexicographic ordering predicate; return @code{#t} if @var{s1}
2943 is lexicographically greater than @var{s2}.
2947 @deffn {Scheme Procedure} string>=? s1 s2
2948 Lexicographic ordering predicate; return @code{#t} if @var{s1}
2949 is lexicographically greater than or equal to @var{s2}.
2952 @rnindex string-ci=?
2953 @deffn {Scheme Procedure} string-ci=? s1 s2
2954 Case-insensitive string equality predicate; return @code{#t} if
2955 the two strings are the same length and their component
2956 characters match (ignoring case) at each position; otherwise
2960 @rnindex string-ci<?
2961 @deffn {Scheme Procedure} string-ci<? s1 s2
2962 Case insensitive lexicographic ordering predicate; return
2963 @code{#t} if @var{s1} is lexicographically less than @var{s2}
2968 @deffn {Scheme Procedure} string-ci<=? s1 s2
2969 Case insensitive lexicographic ordering predicate; return
2970 @code{#t} if @var{s1} is lexicographically less than or equal
2971 to @var{s2} regardless of case.
2974 @rnindex string-ci>?
2975 @deffn {Scheme Procedure} string-ci>? s1 s2
2976 Case insensitive lexicographic ordering predicate; return
2977 @code{#t} if @var{s1} is lexicographically greater than
2978 @var{s2} regardless of case.
2981 @rnindex string-ci>=?
2982 @deffn {Scheme Procedure} string-ci>=? s1 s2
2983 Case insensitive lexicographic ordering predicate; return
2984 @code{#t} if @var{s1} is lexicographically greater than or
2985 equal to @var{s2} regardless of case.
2988 @deffn {Scheme Procedure} string-compare s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
2989 @deffnx {C Function} scm_string_compare (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
2990 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
2991 mismatch index, depending upon whether @var{s1} is less than,
2992 equal to, or greater than @var{s2}. The mismatch index is the
2993 largest index @var{i} such that for every 0 <= @var{j} <
2994 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
2995 @var{i} is the first position that does not match.
2998 @deffn {Scheme Procedure} string-compare-ci s1 s2 proc_lt proc_eq proc_gt [start1 [end1 [start2 [end2]]]]
2999 @deffnx {C Function} scm_string_compare_ci (s1, s2, proc_lt, proc_eq, proc_gt, start1, end1, start2, end2)
3000 Apply @var{proc_lt}, @var{proc_eq}, @var{proc_gt} to the
3001 mismatch index, depending upon whether @var{s1} is less than,
3002 equal to, or greater than @var{s2}. The mismatch index is the
3003 largest index @var{i} such that for every 0 <= @var{j} <
3004 @var{i}, @var{s1}[@var{j}] = @var{s2}[@var{j}] -- that is,
3005 @var{i} is the first position that does not match. The
3006 character comparison is done case-insensitively.
3009 @deffn {Scheme Procedure} string= s1 s2 [start1 [end1 [start2 [end2]]]]
3010 @deffnx {C Function} scm_string_eq (s1, s2, start1, end1, start2, end2)
3011 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3015 @deffn {Scheme Procedure} string<> s1 s2 [start1 [end1 [start2 [end2]]]]
3016 @deffnx {C Function} scm_string_neq (s1, s2, start1, end1, start2, end2)
3017 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3021 @deffn {Scheme Procedure} string< s1 s2 [start1 [end1 [start2 [end2]]]]
3022 @deffnx {C Function} scm_string_lt (s1, s2, start1, end1, start2, end2)
3023 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3024 true value otherwise.
3027 @deffn {Scheme Procedure} string> s1 s2 [start1 [end1 [start2 [end2]]]]
3028 @deffnx {C Function} scm_string_gt (s1, s2, start1, end1, start2, end2)
3029 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3030 true value otherwise.
3033 @deffn {Scheme Procedure} string<= s1 s2 [start1 [end1 [start2 [end2]]]]
3034 @deffnx {C Function} scm_string_le (s1, s2, start1, end1, start2, end2)
3035 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3039 @deffn {Scheme Procedure} string>= s1 s2 [start1 [end1 [start2 [end2]]]]
3040 @deffnx {C Function} scm_string_ge (s1, s2, start1, end1, start2, end2)
3041 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3045 @deffn {Scheme Procedure} string-ci= s1 s2 [start1 [end1 [start2 [end2]]]]
3046 @deffnx {C Function} scm_string_ci_eq (s1, s2, start1, end1, start2, end2)
3047 Return @code{#f} if @var{s1} and @var{s2} are not equal, a true
3048 value otherwise. The character comparison is done
3052 @deffn {Scheme Procedure} string-ci<> s1 s2 [start1 [end1 [start2 [end2]]]]
3053 @deffnx {C Function} scm_string_ci_neq (s1, s2, start1, end1, start2, end2)
3054 Return @code{#f} if @var{s1} and @var{s2} are equal, a true
3055 value otherwise. The character comparison is done
3059 @deffn {Scheme Procedure} string-ci< s1 s2 [start1 [end1 [start2 [end2]]]]
3060 @deffnx {C Function} scm_string_ci_lt (s1, s2, start1, end1, start2, end2)
3061 Return @code{#f} if @var{s1} is greater or equal to @var{s2}, a
3062 true value otherwise. The character comparison is done
3066 @deffn {Scheme Procedure} string-ci> s1 s2 [start1 [end1 [start2 [end2]]]]
3067 @deffnx {C Function} scm_string_ci_gt (s1, s2, start1, end1, start2, end2)
3068 Return @code{#f} if @var{s1} is less or equal to @var{s2}, a
3069 true value otherwise. The character comparison is done
3073 @deffn {Scheme Procedure} string-ci<= s1 s2 [start1 [end1 [start2 [end2]]]]
3074 @deffnx {C Function} scm_string_ci_le (s1, s2, start1, end1, start2, end2)
3075 Return @code{#f} if @var{s1} is greater to @var{s2}, a true
3076 value otherwise. The character comparison is done
3080 @deffn {Scheme Procedure} string-ci>= s1 s2 [start1 [end1 [start2 [end2]]]]
3081 @deffnx {C Function} scm_string_ci_ge (s1, s2, start1, end1, start2, end2)
3082 Return @code{#f} if @var{s1} is less to @var{s2}, a true value
3083 otherwise. The character comparison is done
3087 @deffn {Scheme Procedure} string-hash s [bound [start [end]]]
3088 @deffnx {C Function} scm_substring_hash (s, bound, start, end)
3089 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).
3092 @deffn {Scheme Procedure} string-hash-ci s [bound [start [end]]]
3093 @deffnx {C Function} scm_substring_hash_ci (s, bound, start, end)
3094 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).
3097 @node String Searching
3098 @subsubsection String Searching
3100 @deffn {Scheme Procedure} string-index s char_pred [start [end]]
3101 @deffnx {C Function} scm_string_index (s, char_pred, start, end)
3102 Search through the string @var{s} from left to right, returning
3103 the index of the first occurence of a character which
3107 equals @var{char_pred}, if it is character,
3110 satisifies the predicate @var{char_pred}, if it is a procedure,
3113 is in the set @var{char_pred}, if it is a character set.
3117 @deffn {Scheme Procedure} string-rindex s char_pred [start [end]]
3118 @deffnx {C Function} scm_string_rindex (s, char_pred, start, end)
3119 Search through the string @var{s} from right to left, returning
3120 the index of the last occurence of a character which
3124 equals @var{char_pred}, if it is character,
3127 satisifies the predicate @var{char_pred}, if it is a procedure,
3130 is in the set if @var{char_pred} is a character set.
3134 @deffn {Scheme Procedure} string-prefix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3135 @deffnx {C Function} scm_string_prefix_length (s1, s2, start1, end1, start2, end2)
3136 Return the length of the longest common prefix of the two
3140 @deffn {Scheme Procedure} string-prefix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3141 @deffnx {C Function} scm_string_prefix_length_ci (s1, s2, start1, end1, start2, end2)
3142 Return the length of the longest common prefix of the two
3143 strings, ignoring character case.
3146 @deffn {Scheme Procedure} string-suffix-length s1 s2 [start1 [end1 [start2 [end2]]]]
3147 @deffnx {C Function} scm_string_suffix_length (s1, s2, start1, end1, start2, end2)
3148 Return the length of the longest common suffix of the two
3152 @deffn {Scheme Procedure} string-suffix-length-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3153 @deffnx {C Function} scm_string_suffix_length_ci (s1, s2, start1, end1, start2, end2)
3154 Return the length of the longest common suffix of the two
3155 strings, ignoring character case.
3158 @deffn {Scheme Procedure} string-prefix? s1 s2 [start1 [end1 [start2 [end2]]]]
3159 @deffnx {C Function} scm_string_prefix_p (s1, s2, start1, end1, start2, end2)
3160 Is @var{s1} a prefix of @var{s2}?
3163 @deffn {Scheme Procedure} string-prefix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3164 @deffnx {C Function} scm_string_prefix_ci_p (s1, s2, start1, end1, start2, end2)
3165 Is @var{s1} a prefix of @var{s2}, ignoring character case?
3168 @deffn {Scheme Procedure} string-suffix? s1 s2 [start1 [end1 [start2 [end2]]]]
3169 @deffnx {C Function} scm_string_suffix_p (s1, s2, start1, end1, start2, end2)
3170 Is @var{s1} a suffix of @var{s2}?
3173 @deffn {Scheme Procedure} string-suffix-ci? s1 s2 [start1 [end1 [start2 [end2]]]]
3174 @deffnx {C Function} scm_string_suffix_ci_p (s1, s2, start1, end1, start2, end2)
3175 Is @var{s1} a suffix of @var{s2}, ignoring character case?
3178 @deffn {Scheme Procedure} string-index-right s char_pred [start [end]]
3179 @deffnx {C Function} scm_string_index_right (s, char_pred, start, end)
3180 Search through the string @var{s} from right to left, returning
3181 the index of the last occurence of a character which
3185 equals @var{char_pred}, if it is character,
3188 satisifies the predicate @var{char_pred}, if it is a procedure,
3191 is in the set if @var{char_pred} is a character set.
3195 @deffn {Scheme Procedure} string-skip s char_pred [start [end]]
3196 @deffnx {C Function} scm_string_skip (s, char_pred, start, end)
3197 Search through the string @var{s} from left to right, returning
3198 the index of the first occurence of a character which
3202 does not equal @var{char_pred}, if it is character,
3205 does not satisify the predicate @var{char_pred}, if it is a
3209 is not in the set if @var{char_pred} is a character set.
3213 @deffn {Scheme Procedure} string-skip-right s char_pred [start [end]]
3214 @deffnx {C Function} scm_string_skip_right (s, char_pred, start, end)
3215 Search through the string @var{s} from right to left, returning
3216 the index of the last occurence of a character which
3220 does not equal @var{char_pred}, if it is character,
3223 does not satisfy the predicate @var{char_pred}, if it is a
3227 is not in the set if @var{char_pred} is a character set.
3231 @deffn {Scheme Procedure} string-count s char_pred [start [end]]
3232 @deffnx {C Function} scm_string_count (s, char_pred, start, end)
3233 Return the count of the number of characters in the string
3238 equals @var{char_pred}, if it is character,
3241 satisifies the predicate @var{char_pred}, if it is a procedure.
3244 is in the set @var{char_pred}, if it is a character set.
3248 @deffn {Scheme Procedure} string-contains s1 s2 [start1 [end1 [start2 [end2]]]]
3249 @deffnx {C Function} scm_string_contains (s1, s2, start1, end1, start2, end2)
3250 Does string @var{s1} contain string @var{s2}? Return the index
3251 in @var{s1} where @var{s2} occurs as a substring, or false.
3252 The optional start/end indices restrict the operation to the
3253 indicated substrings.
3256 @deffn {Scheme Procedure} string-contains-ci s1 s2 [start1 [end1 [start2 [end2]]]]
3257 @deffnx {C Function} scm_string_contains_ci (s1, s2, start1, end1, start2, end2)
3258 Does string @var{s1} contain string @var{s2}? Return the index
3259 in @var{s1} where @var{s2} occurs as a substring, or false.
3260 The optional start/end indices restrict the operation to the
3261 indicated substrings. Character comparison is done
3265 @node Alphabetic Case Mapping
3266 @subsubsection Alphabetic Case Mapping
3268 These are procedures for mapping strings to their upper- or lower-case
3269 equivalents, respectively, or for capitalizing strings.
3271 @deffn {Scheme Procedure} string-upcase str [start [end]]
3272 @deffnx {C Function} scm_substring_upcase (str, start, end)
3273 @deffnx {C Function} scm_string_upcase (str)
3274 Upcase every character in @code{str}.
3277 @deffn {Scheme Procedure} string-upcase! str [start [end]]
3278 @deffnx {C Function} scm_substring_upcase_x (str, start, end)
3279 @deffnx {C Function} scm_string_upcase_x (str)
3280 Destructively upcase every character in @code{str}.
3290 @deffn {Scheme Procedure} string-downcase str [start [end]]
3291 @deffnx {C Function} scm_substring_downcase (str, start, end)
3292 @deffnx {C Function} scm_string_downcase (str)
3293 Downcase every character in @var{str}.
3296 @deffn {Scheme Procedure} string-downcase! str [start [end]]
3297 @deffnx {C Function} scm_substring_downcase_x (str, start, end)
3298 @deffnx {C Function} scm_string_downcase_x (str)
3299 Destructively downcase every character in @var{str}.
3304 (string-downcase! y)
3311 @deffn {Scheme Procedure} string-capitalize str
3312 @deffnx {C Function} scm_string_capitalize (str)
3313 Return a freshly allocated string with the characters in
3314 @var{str}, where the first character of every word is
3318 @deffn {Scheme Procedure} string-capitalize! str
3319 @deffnx {C Function} scm_string_capitalize_x (str)
3320 Upcase the first character of every word in @var{str}
3321 destructively and return @var{str}.
3324 y @result{} "hello world"
3325 (string-capitalize! y) @result{} "Hello World"
3326 y @result{} "Hello World"
3330 @deffn {Scheme Procedure} string-titlecase str [start [end]]
3331 @deffnx {C Function} scm_string_titlecase (str, start, end)
3332 Titlecase every first character in a word in @var{str}.
3335 @deffn {Scheme Procedure} string-titlecase! str [start [end]]
3336 @deffnx {C Function} scm_string_titlecase_x (str, start, end)
3337 Destructively titlecase every first character in a word in
3341 @node Reversing and Appending Strings
3342 @subsubsection Reversing and Appending Strings
3344 @deffn {Scheme Procedure} string-reverse str [start [end]]
3345 @deffnx {C Function} scm_string_reverse (str, start, end)
3346 Reverse the string @var{str}. The optional arguments
3347 @var{start} and @var{end} delimit the region of @var{str} to
3351 @deffn {Scheme Procedure} string-reverse! str [start [end]]
3352 @deffnx {C Function} scm_string_reverse_x (str, start, end)
3353 Reverse the string @var{str} in-place. The optional arguments
3354 @var{start} and @var{end} delimit the region of @var{str} to
3355 operate on. The return value is unspecified.
3358 @rnindex string-append
3359 @deffn {Scheme Procedure} string-append . args
3360 @deffnx {C Function} scm_string_append (args)
3361 Return a newly allocated string whose characters form the
3362 concatenation of the given strings, @var{args}.
3366 (string-append h "world"))
3367 @result{} "hello world"
3371 @deffn {Scheme Procedure} string-append/shared . ls
3372 @deffnx {C Function} scm_string_append_shared (ls)
3373 Like @code{string-append}, but the result may share memory
3374 with the argument strings.
3377 @deffn {Scheme Procedure} string-concatenate ls
3378 @deffnx {C Function} scm_string_concatenate (ls)
3379 Append the elements of @var{ls} (which must be strings)
3380 together into a single string. Guaranteed to return a freshly
3384 @deffn {Scheme Procedure} string-concatenate-reverse ls [final_string [end]]
3385 @deffnx {C Function} scm_string_concatenate_reverse (ls, final_string, end)
3386 Without optional arguments, this procedure is equivalent to
3389 (string-concatenate (reverse ls))
3392 If the optional argument @var{final_string} is specified, it is
3393 consed onto the beginning to @var{ls} before performing the
3394 list-reverse and string-concatenate operations. If @var{end}
3395 is given, only the characters of @var{final_string} up to index
3398 Guaranteed to return a freshly allocated string.
3401 @deffn {Scheme Procedure} string-concatenate/shared ls
3402 @deffnx {C Function} scm_string_concatenate_shared (ls)
3403 Like @code{string-concatenate}, but the result may share memory
3404 with the strings in the list @var{ls}.
3407 @deffn {Scheme Procedure} string-concatenate-reverse/shared ls [final_string [end]]
3408 @deffnx {C Function} scm_string_concatenate_reverse_shared (ls, final_string, end)
3409 Like @code{string-concatenate-reverse}, but the result may
3410 share memory with the the strings in the @var{ls} arguments.
3413 @node Mapping Folding and Unfolding
3414 @subsubsection Mapping, Folding, and Unfolding
3416 @deffn {Scheme Procedure} string-map proc s [start [end]]
3417 @deffnx {C Function} scm_string_map (proc, s, start, end)
3418 @var{proc} is a char->char procedure, it is mapped over
3419 @var{s}. The order in which the procedure is applied to the
3420 string elements is not specified.
3423 @deffn {Scheme Procedure} string-map! proc s [start [end]]
3424 @deffnx {C Function} scm_string_map_x (proc, s, start, end)
3425 @var{proc} is a char->char procedure, it is mapped over
3426 @var{s}. The order in which the procedure is applied to the
3427 string elements is not specified. The string @var{s} is
3428 modified in-place, the return value is not specified.
3431 @deffn {Scheme Procedure} string-for-each proc s [start [end]]
3432 @deffnx {C Function} scm_string_for_each (proc, s, start, end)
3433 @var{proc} is mapped over @var{s} in left-to-right order. The
3434 return value is not specified.
3437 @deffn {Scheme Procedure} string-for-each-index proc s [start [end]]
3438 @deffnx {C Function} scm_string_for_each_index (proc, s, start, end)
3439 @var{proc} is mapped over @var{s} in left-to-right order. The
3440 return value is not specified.
3443 @deffn {Scheme Procedure} string-fold kons knil s [start [end]]
3444 @deffnx {C Function} scm_string_fold (kons, knil, s, start, end)
3445 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3446 as the terminating element, from left to right. @var{kons}
3447 must expect two arguments: The actual character and the last
3448 result of @var{kons}' application.
3451 @deffn {Scheme Procedure} string-fold-right kons knil s [start [end]]
3452 @deffnx {C Function} scm_string_fold_right (kons, knil, s, start, end)
3453 Fold @var{kons} over the characters of @var{s}, with @var{knil}
3454 as the terminating element, from right to left. @var{kons}
3455 must expect two arguments: The actual character and the last
3456 result of @var{kons}' application.
3459 @deffn {Scheme Procedure} string-unfold p f g seed [base [make_final]]
3460 @deffnx {C Function} scm_string_unfold (p, f, g, seed, base, make_final)
3462 @item @var{g} is used to generate a series of @emph{seed}
3463 values from the initial @var{seed}: @var{seed}, (@var{g}
3464 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3466 @item @var{p} tells us when to stop -- when it returns true
3467 when applied to one of these seed values.
3468 @item @var{f} maps each seed value to the corresponding
3469 character in the result string. These chars are assembled
3470 into the string in a left-to-right order.
3471 @item @var{base} is the optional initial/leftmost portion
3472 of the constructed string; it default to the empty
3474 @item @var{make_final} is applied to the terminal seed
3475 value (on which @var{p} returns true) to produce
3476 the final/rightmost portion of the constructed string.
3477 It defaults to @code{(lambda (x) )}.
3481 @deffn {Scheme Procedure} string-unfold-right p f g seed [base [make_final]]
3482 @deffnx {C Function} scm_string_unfold_right (p, f, g, seed, base, make_final)
3484 @item @var{g} is used to generate a series of @emph{seed}
3485 values from the initial @var{seed}: @var{seed}, (@var{g}
3486 @var{seed}), (@var{g}^2 @var{seed}), (@var{g}^3 @var{seed}),
3488 @item @var{p} tells us when to stop -- when it returns true
3489 when applied to one of these seed values.
3490 @item @var{f} maps each seed value to the corresponding
3491 character in the result string. These chars are assembled
3492 into the string in a right-to-left order.
3493 @item @var{base} is the optional initial/rightmost portion
3494 of the constructed string; it default to the empty
3496 @item @var{make_final} is applied to the terminal seed
3497 value (on which @var{p} returns true) to produce
3498 the final/leftmost portion of the constructed string.
3499 It defaults to @code{(lambda (x) )}.
3503 @node Miscellaneous String Operations
3504 @subsubsection Miscellaneous String Operations
3506 @deffn {Scheme Procedure} xsubstring s from [to [start [end]]]
3507 @deffnx {C Function} scm_xsubstring (s, from, to, start, end)
3508 This is the @emph{extended substring} procedure that implements
3509 replicated copying of a substring of some string.
3511 @var{s} is a string, @var{start} and @var{end} are optional
3512 arguments that demarcate a substring of @var{s}, defaulting to
3513 0 and the length of @var{s}. Replicate this substring up and
3514 down index space, in both the positive and negative directions.
3515 @code{xsubstring} returns the substring of this string
3516 beginning at index @var{from}, and ending at @var{to}, which
3517 defaults to @var{from} + (@var{end} - @var{start}).
3520 @deffn {Scheme Procedure} string-xcopy! target tstart s sfrom [sto [start [end]]]
3521 @deffnx {C Function} scm_string_xcopy_x (target, tstart, s, sfrom, sto, start, end)
3522 Exactly the same as @code{xsubstring}, but the extracted text
3523 is written into the string @var{target} starting at index
3524 @var{tstart}. The operation is not defined if @code{(eq?
3525 @var{target} @var{s})} or these arguments share storage -- you
3526 cannot copy a string on top of itself.
3529 @deffn {Scheme Procedure} string-replace s1 s2 [start1 [end1 [start2 [end2]]]]
3530 @deffnx {C Function} scm_string_replace (s1, s2, start1, end1, start2, end2)
3531 Return the string @var{s1}, but with the characters
3532 @var{start1} @dots{} @var{end1} replaced by the characters
3533 @var{start2} @dots{} @var{end2} from @var{s2}.
3536 @deffn {Scheme Procedure} string-tokenize s [token_set [start [end]]]
3537 @deffnx {C Function} scm_string_tokenize (s, token_set, start, end)
3538 Split the string @var{s} into a list of substrings, where each
3539 substring is a maximal non-empty contiguous sequence of
3540 characters from the character set @var{token_set}, which
3541 defaults to @code{char-set:graphic}.
3542 If @var{start} or @var{end} indices are provided, they restrict
3543 @code{string-tokenize} to operating on the indicated substring
3547 @deffn {Scheme Procedure} string-filter s char_pred [start [end]]
3548 @deffnx {C Function} scm_string_filter (s, char_pred, start, end)
3549 Filter the string @var{s}, retaining only those characters that
3550 satisfy the @var{char_pred} argument. If the argument is a
3551 procedure, it is applied to each character as a predicate, if
3552 it is a character, it is tested for equality and if it is a
3553 character set, it is tested for membership.
3556 @deffn {Scheme Procedure} string-delete s char_pred [start [end]]
3557 @deffnx {C Function} scm_string_delete (s, char_pred, start, end)
3558 Filter the string @var{s}, retaining only those characters that
3559 do not satisfy the @var{char_pred} argument. If the argument
3560 is a procedure, it is applied to each character as a predicate,
3561 if it is a character, it is tested for equality and if it is a
3562 character set, it is tested for membership.
3565 @node Conversion to/from C
3566 @subsubsection Conversion to/from C
3568 When creating a Scheme string from a C string or when converting a
3569 Scheme string to a C string, the concept of character encoding becomes
3572 In C, a string is just a sequence of bytes, and the character encoding
3573 describes the relation between these bytes and the actual characters
3574 that make up the string. For Scheme strings, character encoding is
3575 not an issue (most of the time), since in Scheme you never get to see
3576 the bytes, only the characters.
3578 Well, ideally, anyway. Right now, Guile simply equates Scheme
3579 characters and bytes, ignoring the possibility of multi-byte encodings
3580 completely. This will change in the future, where Guile will use
3581 Unicode codepoints as its characters and UTF-8 or some other encoding
3582 as its internal encoding. When you exclusively use the functions
3583 listed in this section, you are `future-proof'.
3585 Converting a Scheme string to a C string will often allocate fresh
3586 memory to hold the result. You must take care that this memory is
3587 properly freed eventually. In many cases, this can be achieved by
3588 using @code{scm_frame_free} inside an appropriate frame,
3591 @deftypefn {C Function} SCM scm_from_locale_string (const char *str)
3592 @deftypefnx {C Function} SCM scm_from_locale_stringn (const char *str, size_t len)
3593 Creates a new Scheme string that has the same contents as @var{str}
3594 when interpreted in the current locale character encoding.
3596 For @code{scm_from_locale_string}, @var{str} must be null-terminated.
3598 For @code{scm_from_locale_stringn}, @var{len} specifies the length of
3599 @var{str} in bytes, and @var{str} does not need to be null-terminated.
3600 If @var{len} is @code{(size_t)-1}, then @var{str} does need to be
3601 null-terminated and the real length will be found with @code{strlen}.
3604 @deftypefn {C Function} SCM scm_take_locale_string (char *str)
3605 @deftypefnx {C Function} SCM scm_take_locale_stringn (char *str, size_t len)
3606 Like @code{scm_from_locale_string} and @code{scm_from_locale_stringn},
3607 respectively, but also frees @var{str} with @code{free} eventually.
3608 Thus, you can use this function when you would free @var{str} anyway
3609 immediately after creating the Scheme string. In certain cases, Guile
3610 can then use @var{str} directly as its internal representation.
3613 @deftypefn {C Function} {char *} scm_to_locale_string (SCM str)
3614 @deftypefnx {C Function} {char *} scm_to_locale_stringn (SCM str, size_t *lenp)
3615 Returns a C string in the current locale encoding with the same
3616 contents as @var{str}. The C string must be freed with @code{free}
3617 eventually, maybe by using @code{scm_frame_free}, @xref{Frames}.
3619 For @code{scm_to_locale_string}, the returned string is
3620 null-terminated and an error is signalled when @var{str} contains
3621 @code{#\nul} characters.
3623 For @code{scm_to_locale_stringn} and @var{lenp} not @code{NULL},
3624 @var{str} might contain @code{#\nul} characters and the length of the
3625 returned string in bytes is stored in @code{*@var{lenp}}. The
3626 returned string will not be null-terminated in this case. If
3627 @var{lenp} is @code{NULL}, @code{scm_to_locale_stringn} behaves like
3628 @code{scm_to_locale_string}.
3631 @deftypefn {C Function} size_t scm_to_locale_stringbuf (SCM str, char *buf, size_t max_len)
3632 Puts @var{str} as a C string in the current locale encoding into the
3633 memory pointed to by @var{buf}. The buffer at @var{buf} has room for
3634 @var{max_len} bytes and @code{scm_to_local_stringbuf} will never store
3635 more than that. No terminating @code{'\0'} will be stored.
3637 The return value of @code{scm_to_locale_stringbuf} is the number of
3638 bytes that are needed for all of @var{str}, regardless of whether
3639 @var{buf} was large enough to hold them. Thus, when the return value
3640 is larger than @var{max_len}, only @var{max_len} bytes have been
3641 stored and you probably need to try again with a larger buffer.
3644 @node Regular Expressions
3645 @subsection Regular Expressions
3646 @tpindex Regular expressions
3648 @cindex regular expressions
3650 @cindex emacs regexp
3652 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
3653 describes a whole class of strings. A full description of regular
3654 expressions and their syntax is beyond the scope of this manual;
3655 an introduction can be found in the Emacs manual (@pxref{Regexps,
3656 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}), or
3657 in many general Unix reference books.
3659 If your system does not include a POSIX regular expression library,
3660 and you have not linked Guile with a third-party regexp library such
3661 as Rx, these functions will not be available. You can tell whether
3662 your Guile installation includes regular expression support by
3663 checking whether @code{(provided? 'regex)} returns true.
3665 The following regexp and string matching features are provided by the
3666 @code{(ice-9 regex)} module. Before using the described functions,
3667 you should load this module by executing @code{(use-modules (ice-9
3671 * Regexp Functions:: Functions that create and match regexps.
3672 * Match Structures:: Finding what was matched by a regexp.
3673 * Backslash Escapes:: Removing the special meaning of regexp
3678 @node Regexp Functions
3679 @subsubsection Regexp Functions
3681 By default, Guile supports POSIX extended regular expressions.
3682 That means that the characters @samp{(}, @samp{)}, @samp{+} and
3683 @samp{?} are special, and must be escaped if you wish to match the
3686 This regular expression interface was modeled after that
3687 implemented by SCSH, the Scheme Shell. It is intended to be
3688 upwardly compatible with SCSH regular expressions.
3690 @deffn {Scheme Procedure} string-match pattern str [start]
3691 Compile the string @var{pattern} into a regular expression and compare
3692 it with @var{str}. The optional numeric argument @var{start} specifies
3693 the position of @var{str} at which to begin matching.
3695 @code{string-match} returns a @dfn{match structure} which
3696 describes what, if anything, was matched by the regular
3697 expression. @xref{Match Structures}. If @var{str} does not match
3698 @var{pattern} at all, @code{string-match} returns @code{#f}.
3701 Two examples of a match follow. In the first example, the pattern
3702 matches the four digits in the match string. In the second, the pattern
3706 (string-match "[0-9][0-9][0-9][0-9]" "blah2002")
3707 @result{} #("blah2002" (4 . 8))
3709 (string-match "[A-Za-z]" "123456")
3713 Each time @code{string-match} is called, it must compile its
3714 @var{pattern} argument into a regular expression structure. This
3715 operation is expensive, which makes @code{string-match} inefficient if
3716 the same regular expression is used several times (for example, in a
3717 loop). For better performance, you can compile a regular expression in
3718 advance and then match strings against the compiled regexp.
3720 @deffn {Scheme Procedure} make-regexp pat flag@dots{}
3721 @deffnx {C Function} scm_make_regexp (pat, flaglst)
3722 Compile the regular expression described by @var{pat}, and
3723 return the compiled regexp structure. If @var{pat} does not
3724 describe a legal regular expression, @code{make-regexp} throws
3725 a @code{regular-expression-syntax} error.
3727 The @var{flag} arguments change the behavior of the compiled
3728 regular expression. The following values may be supplied:
3730 @defvar regexp/icase
3731 Consider uppercase and lowercase letters to be the same when
3735 @defvar regexp/newline
3736 If a newline appears in the target string, then permit the
3737 @samp{^} and @samp{$} operators to match immediately after or
3738 immediately before the newline, respectively. Also, the
3739 @samp{.} and @samp{[^...]} operators will never match a newline
3740 character. The intent of this flag is to treat the target
3741 string as a buffer containing many lines of text, and the
3742 regular expression as a pattern that may match a single one of
3746 @defvar regexp/basic
3747 Compile a basic (``obsolete'') regexp instead of the extended
3748 (``modern'') regexps that are the default. Basic regexps do
3749 not consider @samp{|}, @samp{+} or @samp{?} to be special
3750 characters, and require the @samp{@{...@}} and @samp{(...)}
3751 metacharacters to be backslash-escaped (@pxref{Backslash
3752 Escapes}). There are several other differences between basic
3753 and extended regular expressions, but these are the most
3757 @defvar regexp/extended
3758 Compile an extended regular expression rather than a basic
3759 regexp. This is the default behavior; this flag will not
3760 usually be needed. If a call to @code{make-regexp} includes
3761 both @code{regexp/basic} and @code{regexp/extended} flags, the
3762 one which comes last will override the earlier one.
3766 @deffn {Scheme Procedure} regexp-exec rx str [start [flags]]
3767 @deffnx {C Function} scm_regexp_exec (rx, str, start, flags)
3768 Match the compiled regular expression @var{rx} against
3769 @code{str}. If the optional integer @var{start} argument is
3770 provided, begin matching from that position in the string.
3771 Return a match structure describing the results of the match,
3772 or @code{#f} if no match could be found.
3774 The @var{flags} arguments change the matching behavior.
3775 The following flags may be supplied:
3777 @defvar regexp/notbol
3778 Operator @samp{^} always fails (unless @code{regexp/newline}
3779 is used). Use this when the beginning of the string should
3780 not be considered the beginning of a line.
3783 @defvar regexp/noteol
3784 Operator @samp{$} always fails (unless @code{regexp/newline}
3785 is used). Use this when the end of the string should not be
3786 considered the end of a line.
3791 ;; Regexp to match uppercase letters
3792 (define r (make-regexp "[A-Z]*"))
3794 ;; Regexp to match letters, ignoring case
3795 (define ri (make-regexp "[A-Z]*" regexp/icase))
3797 ;; Search for bob using regexp r
3798 (match:substring (regexp-exec r "bob"))
3799 @result{} "" ; no match
3801 ;; Search for bob using regexp ri
3802 (match:substring (regexp-exec ri "Bob"))
3803 @result{} "Bob" ; matched case insensitive
3806 @deffn {Scheme Procedure} regexp? obj
3807 @deffnx {C Function} scm_regexp_p (obj)
3808 Return @code{#t} if @var{obj} is a compiled regular expression,
3809 or @code{#f} otherwise.
3812 Regular expressions are commonly used to find patterns in one string and
3813 replace them with the contents of another string.
3815 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
3816 @deffn {Scheme Procedure} regexp-substitute port match [item@dots{}]
3817 Write to the output port @var{port} selected contents of the match
3818 structure @var{match}. Each @var{item} specifies what should be
3819 written, and may be one of the following arguments:
3823 A string. String arguments are written out verbatim.
3826 An integer. The submatch with that number is written.
3829 The symbol @samp{pre}. The portion of the matched string preceding
3830 the regexp match is written.
3833 The symbol @samp{post}. The portion of the matched string following
3834 the regexp match is written.
3837 The @var{port} argument may be @code{#f}, in which case nothing is
3838 written; instead, @code{regexp-substitute} constructs a string from the
3839 specified @var{item}s and returns that.
3842 The following example takes a regular expression that matches a standard
3843 @sc{yyyymmdd}-format date such as @code{"20020828"}. The
3844 @code{regexp-substitute} call returns a string computed from the
3845 information in the match structure, consisting of the fields and text
3846 from the original string reordered and reformatted.
3849 (define date-regex "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
3850 (define s "Date 20020429 12am.")
3851 (define sm (string-match date-regex s))
3852 (regexp-substitute #f sm 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
3853 @result{} "Date 04-29-2002 12am. (20020429)"
3856 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
3857 @deffn {Scheme Procedure} regexp-substitute/global port regexp target [item@dots{}]
3858 Similar to @code{regexp-substitute}, but can be used to perform global
3859 substitutions on @var{str}. Instead of taking a match structure as an
3860 argument, @code{regexp-substitute/global} takes two string arguments: a
3861 @var{regexp} string describing a regular expression, and a @var{target}
3862 string which should be matched against this regular expression.
3864 Each @var{item} behaves as in @code{regexp-substitute}, with the
3865 following exceptions:
3869 A function may be supplied. When this function is called, it will be
3870 passed one argument: a match structure for a given regular expression
3871 match. It should return a string to be written out to @var{port}.
3874 The @samp{post} symbol causes @code{regexp-substitute/global} to recurse
3875 on the unmatched portion of @var{str}. This @emph{must} be supplied in
3876 order to perform global search-and-replace on @var{str}; if it is not
3877 present among the @var{item}s, then @code{regexp-substitute/global} will
3878 return after processing a single match.
3882 The example above for @code{regexp-substitute} could be rewritten as
3883 follows to remove the @code{string-match} stage:
3886 (define date-regex "([0-9][0-9][0-9][0-9])([0-9][0-9])([0-9][0-9])")
3887 (define s "Date 20020429 12am.")
3888 (regexp-substitute/global #f date-regex s
3889 'pre 2 "-" 3 "-" 1 'post " (" 0 ")")
3890 @result{} "Date 04-29-2002 12am. (20020429)"
3894 @node Match Structures
3895 @subsubsection Match Structures
3897 @cindex match structures
3899 A @dfn{match structure} is the object returned by @code{string-match} and
3900 @code{regexp-exec}. It describes which portion of a string, if any,
3901 matched the given regular expression. Match structures include: a
3902 reference to the string that was checked for matches; the starting and
3903 ending positions of the regexp match; and, if the regexp included any
3904 parenthesized subexpressions, the starting and ending positions of each
3907 In each of the regexp match functions described below, the @code{match}
3908 argument must be a match structure returned by a previous call to
3909 @code{string-match} or @code{regexp-exec}. Most of these functions
3910 return some information about the original target string that was
3911 matched against a regular expression; we will call that string
3912 @var{target} for easy reference.
3914 @c begin (scm-doc-string "regex.scm" "regexp-match?")
3915 @deffn {Scheme Procedure} regexp-match? obj
3916 Return @code{#t} if @var{obj} is a match structure returned by a
3917 previous call to @code{regexp-exec}, or @code{#f} otherwise.
3920 @c begin (scm-doc-string "regex.scm" "match:substring")
3921 @deffn {Scheme Procedure} match:substring match [n]
3922 Return the portion of @var{target} matched by subexpression number
3923 @var{n}. Submatch 0 (the default) represents the entire regexp match.
3924 If the regular expression as a whole matched, but the subexpression
3925 number @var{n} did not match, return @code{#f}.
3929 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
3933 ;; match starting at offset 6 in the string
3935 (string-match "[0-9][0-9][0-9][0-9]" "blah987654" 6))
3939 @c begin (scm-doc-string "regex.scm" "match:start")
3940 @deffn {Scheme Procedure} match:start match [n]
3941 Return the starting position of submatch number @var{n}.
3944 In the following example, the result is 4, since the match starts at
3948 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
3953 @c begin (scm-doc-string "regex.scm" "match:end")
3954 @deffn {Scheme Procedure} match:end match [n]
3955 Return the ending position of submatch number @var{n}.
3958 In the following example, the result is 8, since the match runs between
3959 characters 4 and 8 (i.e. the ``2002'').
3962 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
3967 @c begin (scm-doc-string "regex.scm" "match:prefix")
3968 @deffn {Scheme Procedure} match:prefix match
3969 Return the unmatched portion of @var{target} preceding the regexp match.
3972 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
3978 @c begin (scm-doc-string "regex.scm" "match:suffix")
3979 @deffn {Scheme Procedure} match:suffix match
3980 Return the unmatched portion of @var{target} following the regexp match.
3984 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
3989 @c begin (scm-doc-string "regex.scm" "match:count")
3990 @deffn {Scheme Procedure} match:count match
3991 Return the number of parenthesized subexpressions from @var{match}.
3992 Note that the entire regular expression match itself counts as a
3993 subexpression, and failed submatches are included in the count.
3996 @c begin (scm-doc-string "regex.scm" "match:string")
3997 @deffn {Scheme Procedure} match:string match
3998 Return the original @var{target} string.
4002 (define s (string-match "[0-9][0-9][0-9][0-9]" "blah2002foo"))
4004 @result{} "blah2002foo"
4008 @node Backslash Escapes
4009 @subsubsection Backslash Escapes
4011 Sometimes you will want a regexp to match characters like @samp{*} or
4012 @samp{$} exactly. For example, to check whether a particular string
4013 represents a menu entry from an Info node, it would be useful to match
4014 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
4015 because the asterisk is a metacharacter, it won't match the @samp{*} at
4016 the beginning of the string. In this case, we want to make the first
4019 You can do this by preceding the metacharacter with a backslash
4020 character @samp{\}. (This is also called @dfn{quoting} the
4021 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
4022 sees a backslash in a regular expression, it considers the following
4023 glyph to be an ordinary character, no matter what special meaning it
4024 would ordinarily have. Therefore, we can make the above example work by
4025 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
4026 the regular expression engine to match only a single asterisk in the
4029 Since the backslash is itself a metacharacter, you may force a regexp to
4030 match a backslash in the target string by preceding the backslash with
4031 itself. For example, to find variable references in a @TeX{} program,
4032 you might want to find occurrences of the string @samp{\let\} followed
4033 by any number of alphabetic characters. The regular expression
4034 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
4035 regexp each match a single backslash in the target string.
4037 @c begin (scm-doc-string "regex.scm" "regexp-quote")
4038 @deffn {Scheme Procedure} regexp-quote str
4039 Quote each special character found in @var{str} with a backslash, and
4040 return the resulting string.
4043 @strong{Very important:} Using backslash escapes in Guile source code
4044 (as in Emacs Lisp or C) can be tricky, because the backslash character
4045 has special meaning for the Guile reader. For example, if Guile
4046 encounters the character sequence @samp{\n} in the middle of a string
4047 while processing Scheme code, it replaces those characters with a
4048 newline character. Similarly, the character sequence @samp{\t} is
4049 replaced by a horizontal tab. Several of these @dfn{escape sequences}
4050 are processed by the Guile reader before your code is executed.
4051 Unrecognized escape sequences are ignored: if the characters @samp{\*}
4052 appear in a string, they will be translated to the single character
4055 This translation is obviously undesirable for regular expressions, since
4056 we want to be able to include backslashes in a string in order to
4057 escape regexp metacharacters. Therefore, to make sure that a backslash
4058 is preserved in a string in your Guile program, you must use @emph{two}
4059 consecutive backslashes:
4062 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
4065 The string in this example is preprocessed by the Guile reader before
4066 any code is executed. The resulting argument to @code{make-regexp} is
4067 the string @samp{^\* [^:]*}, which is what we really want.
4069 This also means that in order to write a regular expression that matches
4070 a single backslash character, the regular expression string in the
4071 source code must include @emph{four} backslashes. Each consecutive pair
4072 of backslashes gets translated by the Guile reader to a single
4073 backslash, and the resulting double-backslash is interpreted by the
4074 regexp engine as matching a single backslash character. Hence:
4077 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
4080 The reason for the unwieldiness of this syntax is historical. Both
4081 regular expression pattern matchers and Unix string processing systems
4082 have traditionally used backslashes with the special meanings
4083 described above. The POSIX regular expression specification and ANSI C
4084 standard both require these semantics. Attempting to abandon either
4085 convention would cause other kinds of compatibility problems, possibly
4086 more severe ones. Therefore, without extending the Scheme reader to
4087 support strings with different quoting conventions (an ungainly and
4088 confusing extension when implemented in other languages), we must adhere
4089 to this cumbersome escape syntax.
4096 Symbols in Scheme are widely used in three ways: as items of discrete
4097 data, as lookup keys for alists and hash tables, and to denote variable
4100 A @dfn{symbol} is similar to a string in that it is defined by a
4101 sequence of characters. The sequence of characters is known as the
4102 symbol's @dfn{name}. In the usual case --- that is, where the symbol's
4103 name doesn't include any characters that could be confused with other
4104 elements of Scheme syntax --- a symbol is written in a Scheme program by
4105 writing the sequence of characters that make up the name, @emph{without}
4106 any quotation marks or other special syntax. For example, the symbol
4107 whose name is ``multiply-by-2'' is written, simply:
4113 Notice how this differs from a @emph{string} with contents
4114 ``multiply-by-2'', which is written with double quotation marks, like
4121 Looking beyond how they are written, symbols are different from strings
4122 in two important respects.
4124 The first important difference is uniqueness. If the same-looking
4125 string is read twice from two different places in a program, the result
4126 is two @emph{different} string objects whose contents just happen to be
4127 the same. If, on the other hand, the same-looking symbol is read twice
4128 from two different places in a program, the result is the @emph{same}
4129 symbol object both times.
4131 Given two read symbols, you can use @code{eq?} to test whether they are
4132 the same (that is, have the same name). @code{eq?} is the most
4133 efficient comparison operator in Scheme, and comparing two symbols like
4134 this is as fast as comparing, for example, two numbers. Given two
4135 strings, on the other hand, you must use @code{equal?} or
4136 @code{string=?}, which are much slower comparison operators, to
4137 determine whether the strings have the same contents.
4140 (define sym1 (quote hello))
4141 (define sym2 (quote hello))
4142 (eq? sym1 sym2) @result{} #t
4144 (define str1 "hello")
4145 (define str2 "hello")
4146 (eq? str1 str2) @result{} #f
4147 (equal? str1 str2) @result{} #t
4150 The second important difference is that symbols, unlike strings, are not
4151 self-evaluating. This is why we need the @code{(quote @dots{})}s in the
4152 example above: @code{(quote hello)} evaluates to the symbol named
4153 "hello" itself, whereas an unquoted @code{hello} is @emph{read} as the
4154 symbol named "hello" and evaluated as a variable reference @dots{} about
4155 which more below (@pxref{Symbol Variables}).
4158 * Symbol Data:: Symbols as discrete data.
4159 * Symbol Keys:: Symbols as lookup keys.
4160 * Symbol Variables:: Symbols as denoting variables.
4161 * Symbol Primitives:: Operations related to symbols.
4162 * Symbol Props:: Function slots and property lists.
4163 * Symbol Read Syntax:: Extended read syntax for symbols.
4164 * Symbol Uninterned:: Uninterned symbols.
4169 @subsubsection Symbols as Discrete Data
4171 Numbers and symbols are similar to the extent that they both lend
4172 themselves to @code{eq?} comparison. But symbols are more descriptive
4173 than numbers, because a symbol's name can be used directly to describe
4174 the concept for which that symbol stands.
4176 For example, imagine that you need to represent some colours in a
4177 computer program. Using numbers, you would have to choose arbitrarily
4178 some mapping between numbers and colours, and then take care to use that
4179 mapping consistently:
4182 ;; 1=red, 2=green, 3=purple
4184 (if (eq? (colour-of car) 1)
4189 You can make the mapping more explicit and the code more readable by
4197 (if (eq? (colour-of car) red)
4202 But the simplest and clearest approach is not to use numbers at all, but
4203 symbols whose names specify the colours that they refer to:
4206 (if (eq? (colour-of car) 'red)
4210 The descriptive advantages of symbols over numbers increase as the set
4211 of concepts that you want to describe grows. Suppose that a car object
4212 can have other properties as well, such as whether it has or uses:
4216 automatic or manual transmission
4218 leaded or unleaded fuel
4220 power steering (or not).
4224 Then a car's combined property set could be naturally represented and
4225 manipulated as a list of symbols:
4228 (properties-of car1)
4230 (red manual unleaded power-steering)
4232 (if (memq 'power-steering (properties-of car1))
4233 (display "Unfit people can drive this car.\n")
4234 (display "You'll need strong arms to drive this car!\n"))
4236 Unfit people can drive this car.
4239 Remember, the fundamental property of symbols that we are relying on
4240 here is that an occurrence of @code{'red} in one part of a program is an
4241 @emph{indistinguishable} symbol from an occurrence of @code{'red} in
4242 another part of a program; this means that symbols can usefully be
4243 compared using @code{eq?}. At the same time, symbols have naturally
4244 descriptive names. This combination of efficiency and descriptive power
4245 makes them ideal for use as discrete data.
4249 @subsubsection Symbols as Lookup Keys
4251 Given their efficiency and descriptive power, it is natural to use
4252 symbols as the keys in an association list or hash table.
4254 To illustrate this, consider a more structured representation of the car
4255 properties example from the preceding subsection. Rather than
4256 mixing all the properties up together in a flat list, we could use an
4257 association list like this:
4260 (define car1-properties '((colour . red)
4261 (transmission . manual)
4263 (steering . power-assisted)))
4266 Notice how this structure is more explicit and extensible than the flat
4267 list. For example it makes clear that @code{manual} refers to the
4268 transmission rather than, say, the windows or the locking of the car.
4269 It also allows further properties to use the same symbols among their
4270 possible values without becoming ambiguous:
4273 (define car1-properties '((colour . red)
4274 (transmission . manual)
4276 (steering . power-assisted)
4278 (locking . manual)))
4281 With a representation like this, it is easy to use the efficient
4282 @code{assq-XXX} family of procedures (@pxref{Association Lists}) to
4283 extract or change individual pieces of information:
4286 (assq-ref car1-properties 'fuel) @result{} unleaded
4287 (assq-ref car1-properties 'transmission) @result{} manual
4289 (assq-set! car1-properties 'seat-colour 'black)
4292 (transmission . manual)
4294 (steering . power-assisted)
4295 (seat-colour . black)
4296 (locking . manual)))
4299 Hash tables also have keys, and exactly the same arguments apply to the
4300 use of symbols in hash tables as in association lists. The hash value
4301 that Guile uses to decide where to add a symbol-keyed entry to a hash
4302 table can be obtained by calling the @code{symbol-hash} procedure:
4304 @deffn {Scheme Procedure} symbol-hash symbol
4305 @deffnx {C Function} scm_symbol_hash (symbol)
4306 Return a hash value for @var{symbol}.
4309 See @ref{Hash Tables} for information about hash tables in general, and
4310 for why you might choose to use a hash table rather than an association
4314 @node Symbol Variables
4315 @subsubsection Symbols as Denoting Variables
4317 When an unquoted symbol in a Scheme program is evaluated, it is
4318 interpreted as a variable reference, and the result of the evaluation is
4319 the appropriate variable's value.
4321 For example, when the expression @code{(string-length "abcd")} is read
4322 and evaluated, the sequence of characters @code{string-length} is read
4323 as the symbol whose name is "string-length". This symbol is associated
4324 with a variable whose value is the procedure that implements string
4325 length calculation. Therefore evaluation of the @code{string-length}
4326 symbol results in that procedure.
4328 The details of the connection between an unquoted symbol and the
4329 variable to which it refers are explained elsewhere. See @ref{Binding
4330 Constructs}, for how associations between symbols and variables are
4331 created, and @ref{Modules}, for how those associations are affected by
4332 Guile's module system.
4335 @node Symbol Primitives
4336 @subsubsection Operations Related to Symbols
4338 Given any Scheme value, you can determine whether it is a symbol using
4339 the @code{symbol?} primitive:
4342 @deffn {Scheme Procedure} symbol? obj
4343 @deffnx {C Function} scm_symbol_p (obj)
4344 Return @code{#t} if @var{obj} is a symbol, otherwise return
4348 @deftypefn {C Function} int scm_is_symbol (SCM val)
4349 Equivalent to @code{scm_is_true (scm_symbol_p (val))}.
4352 Once you know that you have a symbol, you can obtain its name as a
4353 string by calling @code{symbol->string}. Note that Guile differs by
4354 default from R5RS on the details of @code{symbol->string} as regards
4357 @rnindex symbol->string
4358 @deffn {Scheme Procedure} symbol->string s
4359 @deffnx {C Function} scm_symbol_to_string (s)
4360 Return the name of symbol @var{s} as a string. By default, Guile reads
4361 symbols case-sensitively, so the string returned will have the same case
4362 variation as the sequence of characters that caused @var{s} to be
4365 If Guile is set to read symbols case-insensitively (as specified by
4366 R5RS), and @var{s} comes into being as part of a literal expression
4367 (@pxref{Literal expressions,,,r5rs, The Revised^5 Report on Scheme}) or
4368 by a call to the @code{read} or @code{string-ci->symbol} procedures,
4369 Guile converts any alphabetic characters in the symbol's name to
4370 lower case before creating the symbol object, so the string returned
4371 here will be in lower case.
4373 If @var{s} was created by @code{string->symbol}, the case of characters
4374 in the string returned will be the same as that in the string that was
4375 passed to @code{string->symbol}, regardless of Guile's case-sensitivity
4376 setting at the time @var{s} was created.
4378 It is an error to apply mutation procedures like @code{string-set!} to
4379 strings returned by this procedure.
4382 Most symbols are created by writing them literally in code. However it
4383 is also possible to create symbols programmatically using the following
4384 @code{string->symbol} and @code{string-ci->symbol} procedures:
4386 @rnindex string->symbol
4387 @deffn {Scheme Procedure} string->symbol string
4388 @deffnx {C Function} scm_string_to_symbol (string)
4389 Return the symbol whose name is @var{string}. This procedure can create
4390 symbols with names containing special characters or letters in the
4391 non-standard case, but it is usually a bad idea to create such symbols
4392 because in some implementations of Scheme they cannot be read as
4396 @deffn {Scheme Procedure} string-ci->symbol str
4397 @deffnx {C Function} scm_string_ci_to_symbol (str)
4398 Return the symbol whose name is @var{str}. If Guile is currently
4399 reading symbols case-insensitively, @var{str} is converted to lowercase
4400 before the returned symbol is looked up or created.
4403 The following examples illustrate Guile's detailed behaviour as regards
4404 the case-sensitivity of symbols:
4407 (read-enable 'case-insensitive) ; R5RS compliant behaviour
4409 (symbol->string 'flying-fish) @result{} "flying-fish"
4410 (symbol->string 'Martin) @result{} "martin"
4412 (string->symbol "Malvina")) @result{} "Malvina"
4414 (eq? 'mISSISSIppi 'mississippi) @result{} #t
4415 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
4416 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
4418 (string->symbol (symbol->string 'LolliPop))) @result{} #t
4419 (string=? "K. Harper, M.D."
4421 (string->symbol "K. Harper, M.D."))) @result{} #t
4423 (read-disable 'case-insensitive) ; Guile default behaviour
4425 (symbol->string 'flying-fish) @result{} "flying-fish"
4426 (symbol->string 'Martin) @result{} "Martin"
4428 (string->symbol "Malvina")) @result{} "Malvina"
4430 (eq? 'mISSISSIppi 'mississippi) @result{} #f
4431 (string->symbol "mISSISSIppi") @result{} mISSISSIppi
4432 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #t
4434 (string->symbol (symbol->string 'LolliPop))) @result{} #t
4435 (string=? "K. Harper, M.D."
4437 (string->symbol "K. Harper, M.D."))) @result{} #t
4440 From C, there are lower level functions that construct a Scheme symbol
4441 from a C string in the current locale encoding.
4443 When you want to do more from C, you should convert between symbols
4444 and strings using @code{scm_symbol_to_string} and
4445 @code{scm_string_to_symbol} and work with the strings.
4447 @deffn {C Function} scm_from_locale_symbol (const char *name)
4448 @deffnx {C Function} scm_from_locale_symboln (const char *name, size_t len)
4449 Construct and return a Scheme symbol whose name is specified by
4450 @var{name}. For @code{scm_from_locale_symbol}, @var{name} must be null
4451 terminated; for @code{scm_from_locale_symboln} the length of @var{name} is
4452 specified explicitly by @var{len}.
4455 Finally, some applications, especially those that generate new Scheme
4456 code dynamically, need to generate symbols for use in the generated
4457 code. The @code{gensym} primitive meets this need:
4459 @deffn {Scheme Procedure} gensym [prefix]
4460 @deffnx {C Function} scm_gensym (prefix)
4461 Create a new symbol with a name constructed from a prefix and a counter
4462 value. The string @var{prefix} can be specified as an optional
4463 argument. Default prefix is @samp{@w{ g}}. The counter is increased by 1
4464 at each call. There is no provision for resetting the counter.
4467 The symbols generated by @code{gensym} are @emph{likely} to be unique,
4468 since their names begin with a space and it is only otherwise possible
4469 to generate such symbols if a programmer goes out of their way to do
4470 so. Uniqueness can be guaranteed by instead using uninterned symbols
4471 (@pxref{Symbol Uninterned}), though they can't be usefully written out
4476 @subsubsection Function Slots and Property Lists
4478 In traditional Lisp dialects, symbols are often understood as having
4479 three kinds of value at once:
4483 a @dfn{variable} value, which is used when the symbol appears in
4484 code in a variable reference context
4487 a @dfn{function} value, which is used when the symbol appears in
4488 code in a function name position (i.e. as the first element in an
4492 a @dfn{property list} value, which is used when the symbol is given as
4493 the first argument to Lisp's @code{put} or @code{get} functions.
4496 Although Scheme (as one of its simplifications with respect to Lisp)
4497 does away with the distinction between variable and function namespaces,
4498 Guile currently retains some elements of the traditional structure in
4499 case they turn out to be useful when implementing translators for other
4500 languages, in particular Emacs Lisp.
4502 Specifically, Guile symbols have two extra slots. for a symbol's
4503 property list, and for its ``function value.'' The following procedures
4504 are provided to access these slots.
4506 @deffn {Scheme Procedure} symbol-fref symbol
4507 @deffnx {C Function} scm_symbol_fref (symbol)
4508 Return the contents of @var{symbol}'s @dfn{function slot}.
4511 @deffn {Scheme Procedure} symbol-fset! symbol value
4512 @deffnx {C Function} scm_symbol_fset_x (symbol, value)
4513 Set the contents of @var{symbol}'s function slot to @var{value}.
4516 @deffn {Scheme Procedure} symbol-pref symbol
4517 @deffnx {C Function} scm_symbol_pref (symbol)
4518 Return the @dfn{property list} currently associated with @var{symbol}.
4521 @deffn {Scheme Procedure} symbol-pset! symbol value
4522 @deffnx {C Function} scm_symbol_pset_x (symbol, value)
4523 Set @var{symbol}'s property list to @var{value}.
4526 @deffn {Scheme Procedure} symbol-property sym prop
4527 From @var{sym}'s property list, return the value for property
4528 @var{prop}. The assumption is that @var{sym}'s property list is an
4529 association list whose keys are distinguished from each other using
4530 @code{equal?}; @var{prop} should be one of the keys in that list. If
4531 the property list has no entry for @var{prop}, @code{symbol-property}
4535 @deffn {Scheme Procedure} set-symbol-property! sym prop val
4536 In @var{sym}'s property list, set the value for property @var{prop} to
4537 @var{val}, or add a new entry for @var{prop}, with value @var{val}, if
4538 none already exists. For the structure of the property list, see
4539 @code{symbol-property}.
4542 @deffn {Scheme Procedure} symbol-property-remove! sym prop
4543 From @var{sym}'s property list, remove the entry for property
4544 @var{prop}, if there is one. For the structure of the property list,
4545 see @code{symbol-property}.
4548 Support for these extra slots may be removed in a future release, and it
4549 is probably better to avoid using them. (In release 1.6, Guile itself
4550 uses the property list slot sparingly, and the function slot not at
4551 all.) For a more modern and Schemely approach to properties, see
4552 @ref{Object Properties}.
4555 @node Symbol Read Syntax
4556 @subsubsection Extended Read Syntax for Symbols
4558 The read syntax for a symbol is a sequence of letters, digits, and
4559 @dfn{extended alphabetic characters}, beginning with a character that
4560 cannot begin a number. In addition, the special cases of @code{+},
4561 @code{-}, and @code{...} are read as symbols even though numbers can
4562 begin with @code{+}, @code{-} or @code{.}.
4564 Extended alphabetic characters may be used within identifiers as if
4565 they were letters. The set of extended alphabetic characters is:
4568 ! $ % & * + - . / : < = > ? @@ ^ _ ~
4571 In addition to the standard read syntax defined above (which is taken
4572 from R5RS (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on
4573 Scheme})), Guile provides an extended symbol read syntax that allows the
4574 inclusion of unusual characters such as space characters, newlines and
4575 parentheses. If (for whatever reason) you need to write a symbol
4576 containing characters not mentioned above, you can do so as follows.
4580 Begin the symbol with the characters @code{#@{},
4583 write the characters of the symbol and
4586 finish the symbol with the characters @code{@}#}.
4589 Here are a few examples of this form of read syntax. The first symbol
4590 needs to use extended syntax because it contains a space character, the
4591 second because it contains a line break, and the last because it looks
4603 Although Guile provides this extended read syntax for symbols,
4604 widespread usage of it is discouraged because it is not portable and not
4608 @node Symbol Uninterned
4609 @subsubsection Uninterned Symbols
4611 What makes symbols useful is that they are automatically kept unique.
4612 There are no two symbols that are distinct objects but have the same
4613 name. But of course, there is no rule without exception. In addition
4614 to the normal symbols that have been discussed up to now, you can also
4615 create special @dfn{uninterned} symbols that behave slightly
4618 To understand what is different about them and why they might be useful,
4619 we look at how normal symbols are actually kept unique.
4621 Whenever Guile wants to find the symbol with a specific name, for
4622 example during @code{read} or when executing @code{string->symbol}, it
4623 first looks into a table of all existing symbols to find out whether a
4624 symbol with the given name already exists. When this is the case, Guile
4625 just returns that symbol. When not, a new symbol with the name is
4626 created and entered into the table so that it can be found later.
4628 Sometimes you might want to create a symbol that is guaranteed `fresh',
4629 i.e. a symbol that did not exist previously. You might also want to
4630 somehow guarantee that no one else will ever unintentionally stumble
4631 across your symbol in the future. These properties of a symbol are
4632 often needed when generating code during macro expansion. When
4633 introducing new temporary variables, you want to guarantee that they
4634 don't conflict with variables in other people's code.
4636 The simplest way to arrange for this is to create a new symbol but
4637 not enter it into the global table of all symbols. That way, no one
4638 will ever get access to your symbol by chance. Symbols that are not in
4639 the table are called @dfn{uninterned}. Of course, symbols that
4640 @emph{are} in the table are called @dfn{interned}.
4642 You create new uninterned symbols with the function @code{make-symbol}.
4643 You can test whether a symbol is interned or not with
4644 @code{symbol-interned?}.
4646 Uninterned symbols break the rule that the name of a symbol uniquely
4647 identifies the symbol object. Because of this, they can not be written
4648 out and read back in like interned symbols. Currently, Guile has no
4649 support for reading uninterned symbols. Note that the function
4650 @code{gensym} does not return uninterned symbols for this reason.
4652 @deffn {Scheme Procedure} make-symbol name
4653 @deffnx {C Function} scm_make_symbol (name)
4654 Return a new uninterned symbol with the name @var{name}. The returned
4655 symbol is guaranteed to be unique and future calls to
4656 @code{string->symbol} will not return it.
4659 @deffn {Scheme Procedure} symbol-interned? symbol
4660 @deffnx {C Function} scm_symbol_interned_p (symbol)
4661 Return @code{#t} if @var{symbol} is interned, otherwise return
4668 (define foo-1 (string->symbol "foo"))
4669 (define foo-2 (string->symbol "foo"))
4670 (define foo-3 (make-symbol "foo"))
4671 (define foo-4 (make-symbol "foo"))
4675 ; Two interned symbols with the same name are the same object,
4679 ; but a call to make-symbol with the same name returns a
4684 ; A call to make-symbol always returns a new object, even for
4688 @result{} #<uninterned-symbol foo 8085290>
4689 ; Uninterned symbols print differently from interned symbols,
4693 ; but they are still symbols,
4695 (symbol-interned? foo-3)
4697 ; just not interned.
4702 @subsection Keywords
4705 Keywords are self-evaluating objects with a convenient read syntax that
4706 makes them easy to type.
4708 Guile's keyword support conforms to R5RS, and adds a (switchable) read
4709 syntax extension to permit keywords to begin with @code{:} as well as
4713 * Why Use Keywords?:: Motivation for keyword usage.
4714 * Coding With Keywords:: How to use keywords.
4715 * Keyword Read Syntax:: Read syntax for keywords.
4716 * Keyword Procedures:: Procedures for dealing with keywords.
4717 * Keyword Primitives:: The underlying primitive procedures.
4720 @node Why Use Keywords?
4721 @subsubsection Why Use Keywords?
4723 Keywords are useful in contexts where a program or procedure wants to be
4724 able to accept a large number of optional arguments without making its
4725 interface unmanageable.
4727 To illustrate this, consider a hypothetical @code{make-window}
4728 procedure, which creates a new window on the screen for drawing into
4729 using some graphical toolkit. There are many parameters that the caller
4730 might like to specify, but which could also be sensibly defaulted, for
4735 color depth -- Default: the color depth for the screen
4738 background color -- Default: white
4741 width -- Default: 600
4744 height -- Default: 400
4747 If @code{make-window} did not use keywords, the caller would have to
4748 pass in a value for each possible argument, remembering the correct
4749 argument order and using a special value to indicate the default value
4753 (make-window 'default ;; Color depth
4754 'default ;; Background color
4757 @dots{}) ;; More make-window arguments
4760 With keywords, on the other hand, defaulted arguments are omitted, and
4761 non-default arguments are clearly tagged by the appropriate keyword. As
4762 a result, the invocation becomes much clearer:
4765 (make-window #:width 800 #:height 100)
4768 On the other hand, for a simpler procedure with few arguments, the use
4769 of keywords would be a hindrance rather than a help. The primitive
4770 procedure @code{cons}, for example, would not be improved if it had to
4774 (cons #:car x #:cdr y)
4777 So the decision whether to use keywords or not is purely pragmatic: use
4778 them if they will clarify the procedure invocation at point of call.
4780 @node Coding With Keywords
4781 @subsubsection Coding With Keywords
4783 If a procedure wants to support keywords, it should take a rest argument
4784 and then use whatever means is convenient to extract keywords and their
4785 corresponding arguments from the contents of that rest argument.
4787 The following example illustrates the principle: the code for
4788 @code{make-window} uses a helper procedure called
4789 @code{get-keyword-value} to extract individual keyword arguments from
4793 (define (get-keyword-value args keyword default)
4794 (let ((kv (memq keyword args)))
4795 (if (and kv (>= (length kv) 2))
4799 (define (make-window . args)
4800 (let ((depth (get-keyword-value args #:depth screen-depth))
4801 (bg (get-keyword-value args #:bg "white"))
4802 (width (get-keyword-value args #:width 800))
4803 (height (get-keyword-value args #:height 100))
4808 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
4809 optargs)} module provides a set of powerful macros that you can use to
4810 implement keyword-supporting procedures like this:
4813 (use-modules (ice-9 optargs))
4815 (define (make-window . args)
4816 (let-keywords args #f ((depth screen-depth)
4824 Or, even more economically, like this:
4827 (use-modules (ice-9 optargs))
4829 (define* (make-window #:key (depth screen-depth)
4836 For further details on @code{let-keywords}, @code{define*} and other
4837 facilities provided by the @code{(ice-9 optargs)} module, see
4838 @ref{Optional Arguments}.
4841 @node Keyword Read Syntax
4842 @subsubsection Keyword Read Syntax
4844 Guile, by default, only recognizes the keyword syntax specified by R5RS.
4845 A token of the form @code{#:NAME}, where @code{NAME} has the same syntax
4846 as a Scheme symbol (@pxref{Symbol Read Syntax}), is the external
4847 representation of the keyword named @code{NAME}. Keyword objects print
4848 using this syntax as well, so values containing keyword objects can be
4849 read back into Guile. When used in an expression, keywords are
4850 self-quoting objects.
4852 If the @code{keyword} read option is set to @code{'prefix}, Guile also
4853 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
4854 of the form @code{:NAME} are read as symbols, as required by R5RS.
4856 To enable and disable the alternative non-R5RS keyword syntax, you use
4857 the @code{read-set!} procedure documented in @ref{User level options
4858 interfaces} and @ref{Reader options}.
4861 (read-set! keywords 'prefix)
4871 (read-set! keywords #f)
4879 ERROR: In expression :type:
4880 ERROR: Unbound variable: :type
4881 ABORT: (unbound-variable)
4884 @node Keyword Procedures
4885 @subsubsection Keyword Procedures
4887 The following procedures can be used for converting symbols to keywords
4890 @deffn {Scheme Procedure} symbol->keyword sym
4891 Return a keyword with the same characters as in @var{sym}.
4894 @deffn {Scheme Procedure} keyword->symbol kw
4895 Return a symbol with the same characters as in @var{kw}.
4899 @node Keyword Primitives
4900 @subsubsection Keyword Primitives
4902 Internally, a keyword is implemented as something like a tagged symbol,
4903 where the tag identifies the keyword as being self-evaluating, and the
4904 symbol, known as the keyword's @dfn{dash symbol} has the same name as
4905 the keyword name but prefixed by a single dash. For example, the
4906 keyword @code{#:name} has the corresponding dash symbol @code{-name}.
4908 Most keyword objects are constructed automatically by the reader when it
4909 reads a token beginning with @code{#:}. However, if you need to
4910 construct a keyword object programmatically, you can do so by calling
4911 @code{make-keyword-from-dash-symbol} with the corresponding dash symbol
4912 (as the reader does). The dash symbol for a keyword object can be
4913 retrieved using the @code{keyword-dash-symbol} procedure.
4915 @deffn {Scheme Procedure} make-keyword-from-dash-symbol symbol
4916 @deffnx {C Function} scm_make_keyword_from_dash_symbol (symbol)
4917 Make a keyword object from a @var{symbol} that starts with a dash.
4921 (make-keyword-from-dash-symbol '-foo)
4926 @deffn {Scheme Procedure} keyword? obj
4927 @deffnx {C Function} scm_keyword_p (obj)
4928 Return @code{#t} if the argument @var{obj} is a keyword, else
4932 @deffn {Scheme Procedure} keyword-dash-symbol keyword
4933 @deffnx {C Function} scm_keyword_dash_symbol (keyword)
4934 Return the dash symbol for @var{keyword}.
4935 This is the inverse of @code{make-keyword-from-dash-symbol}.
4939 (keyword-dash-symbol #:foo)
4944 @deftypefn {C Function} SCM scm_c_make_keyword (char *@var{str})
4945 Make a keyword object from a string. For example,
4948 scm_c_make_keyword ("foo")
4952 @c FIXME: What can be said about the string argument? Currently it's
4953 @c not used after creation, but should that be documented?
4958 @subsection ``Functionality-Centric'' Data Types
4960 Procedures and macros are documented in their own chapter: see
4961 @ref{Procedures and Macros}.
4963 Variable objects are documented as part of the description of Guile's
4964 module system: see @ref{Variables}.
4966 Asyncs, dynamic roots and fluids are described in the chapter on
4967 scheduling: see @ref{Scheduling}.
4969 Hooks are documented in the chapter on general utility functions: see
4972 Ports are described in the chapter on I/O: see @ref{Input and Output}.
4976 @c TeX-master: "guile.texi"