3 @chapter Data Types for Generic Use
5 This chapter describes all the data types that Guile provides for
8 One of the great strengths of Scheme is that there is no straightforward
9 distinction between ``data'' and ``functionality''. For example,
10 Guile's support for dynamic linking could be described
14 either in a ``data-centric'' way, as the behaviour and properties of the
15 ``dynamically linked object'' data type, and the operations that may be
16 applied to instances of this type
19 or in a ``functionality-centric'' way, as the set of procedures that
20 constitute Guile's support for dynamic linking, in the context of the
24 The contents of this chapter are, therefore, a matter of judgement. By
25 ``generic use'', we mean to select those data types whose typical use as
26 @emph{data} in a wide variety of programming contexts is more important
27 than their use in the implementation of a particular piece of
34 The table of contents for this chapter
37 The following table of contents
39 shows the data types that are documented in this chapter. The final
40 section of this chapter lists all the core Guile data types that are not
41 documented here, and provides links to the ``functionality-centric''
42 sections of this manual that cover them.
45 * Booleans:: True/false values.
46 * Numbers:: Numerical data types.
47 * Characters:: New character names.
48 * Strings:: Special things about strings.
49 * Regular Expressions:: Pattern matching and substitution.
50 * Symbols and Variables:: Manipulating the Scheme symbol table.
51 * Keywords:: Self-quoting, customizable display keywords.
52 * Pairs:: Scheme's basic building block.
53 * Lists:: Special list functions supported by Guile.
54 * Vectors:: One-dimensional arrays of Scheme objects.
57 * Arrays:: Arrays of values.
58 * Association Lists and Hash Tables:: Dictionary data types.
59 * Hooks:: User-customizable event lists.
60 * Other Data Types:: Data types that are documented elsewhere.
67 The two boolean values are @code{#t} for true and @code{#f} for false.
69 Boolean values are returned by predicate procedures, such as the general
70 equality predicates @code{eq?}, @code{eqv?} and @code{equal?}
71 (@pxref{Equality}) and numerical and string comparison operators like
72 @code{string=?} (@pxref{String Comparison}) and @code{<=}
84 (equal? "house" "houses")
93 In test condition contexts like @code{if} and @code{cond} (@pxref{if
94 cond case}), where a group of subexpressions will be evaluated only if a
95 @var{condition} expression evaluates to ``true'', ``true'' means any
96 value at all except @code{#f}.
112 A result of this asymmetry is that typical Scheme source code more often
113 uses @code{#f} explicitly than @code{#t}: @code{#f} is necessary to
114 represent an @code{if} or @code{cond} false value, whereas @code{#t} is
115 not necessary to represent an @code{if} or @code{cond} true value.
117 It is important to note that @code{#f} is @strong{not} equivalent to any
118 other Scheme value. In particular, @code{#f} is not the same as the
119 number 0 (like in C and C++), and not the same as the ``empty list''
120 (like in some Lisp dialects).
122 The @code{not} procedure returns the boolean inverse of its argument:
125 @deffn primitive not x
126 Return @code{#t} iff @var{x} is @code{#f}, else return @code{#f}.
129 The @code{boolean?} procedure is a predicate that returns @code{#t} if
130 its argument is one of the boolean values, otherwise @code{#f}.
133 @deffn primitive boolean? obj
134 Return @code{#t} iff @var{obj} is either @code{#t} or @code{#f}.
139 @section Numerical data types
141 Guile supports a rich ``tower'' of numerical types --- integer,
142 rational, real and complex --- and provides an extensive set of
143 mathematical and scientific functions for operating on numerical
144 data. This section of the manual documents those types and functions.
146 You may also find it illuminating to read R5RS's presentation of numbers
147 in Scheme, which is particularly clear and accessible: see
148 @xref{Numbers,,,r5rs}.
151 * Numerical Tower:: Scheme's numerical "tower".
152 * Integers:: Whole numbers.
153 * Reals and Rationals:: Real and rational numbers.
154 * Complex Numbers:: Complex numbers.
155 * Exactness:: Exactness and inexactness.
156 * Number Syntax:: Read syntax for numerical data.
157 * Integer Operations:: Operations on integer values.
158 * Comparison:: Comparison predicates.
159 * Conversion:: Converting numbers to and from strings.
160 * Complex:: Complex number operations.
161 * Arithmetic:: Arithmetic functions.
162 * Scientific:: Scientific functions.
163 * Primitive Numerics:: Primitive numeric functions.
164 * Bitwise Operations:: Logical AND, OR, NOT, and so on.
165 * Random:: Random number generation.
169 @node Numerical Tower
170 @subsection Scheme's Numerical ``Tower''
173 Scheme's numerical ``tower'' consists of the following categories of
178 integers (whole numbers)
181 rationals (the set of numbers that can be expressed as P/Q where P and Q
185 real numbers (the set of numbers that describes all possible positions
186 along a one dimensional line)
189 complex numbers (the set of numbers that describes all possible
190 positions in a two dimensional space)
193 It is called a tower because each category ``sits on'' the one that
194 follows it, in the sense that every integer is also a rational, every
195 rational is also real, and every real number is also a complex number
196 (but with zero imaginary part).
198 Of these, Guile implements integers, reals and complex numbers as
199 distinct types. Rationals are implemented as regards the read syntax
200 for rational numbers that is specified by R5RS, but are immediately
201 converted by Guile to the corresponding real number.
203 The @code{number?} predicate may be applied to any Scheme value to
204 discover whether the value is any of the supported numerical types.
206 @deffn primitive number? obj
207 Return @code{#t} if @var{obj} is any kind of number, @code{#f} else.
217 (number? "hello there!")
221 (define pi 3.141592654)
227 The next few subsections document each of Guile's numerical data types
235 Integers are whole numbers, that is numbers with no fractional part,
236 such as 2, 83 and -3789.
238 Integers in Guile can be arbitrarily big, as shown by the following
242 (define (factorial n)
243 (let loop ((n n) (product 1))
246 (loop (- n 1) (* product n)))))
258 -119622220865480194561963161495657715064383733760000000000
261 Readers whose background is in programming languages where integers are
262 limited by the need to fit into just 4 or 8 bytes of memory may find
263 this surprising, or suspect that Guile's representation of integers is
264 inefficient. In fact, Guile achieves a near optimal balance of
265 convenience and efficiency by using the host computer's native
266 representation of integers where possible, and a more general
267 representation where the required number does not fit in the native
268 form. Conversion between these two representations is automatic and
269 completely invisible to the Scheme level programmer.
271 @c REFFIXME Maybe point here to discussion of handling immediates/bignums
272 @c on the C level, where the conversion is not so automatic - NJ
274 @deffn primitive integer? x
275 Return @code{#t} if @var{x} is an integer number, @code{#f} else.
289 @node Reals and Rationals
290 @subsection Real and Rational Numbers
294 Mathematically, the real numbers are the set of numbers that describe
295 all possible points along a continuous, infinite, one-dimensional line.
296 The rational numbers are the set of all numbers that can be written as
297 fractions P/Q, where P and Q are integers. All rational numbers are
298 also real, but there are real numbers that are not rational, for example
299 the square root of 2, and pi.
301 Guile represents both real and rational numbers approximately using a
302 floating point encoding with limited precision. Even though the actual
303 encoding is in binary, it may be helpful to think of it as a decimal
304 number with a limited number of significant figures and a decimal point
305 somewhere, since this corresponds to the standard notation for non-whole
306 numbers. For example:
311 -5648394822220000000000.0
315 The limited precision of Guile's encoding means that any ``real'' number
316 in Guile can be written in a rational form, by multiplying and then dividing
317 by sufficient powers of 10 (or in fact, 2). For example,
318 @code{-0.00000142857931198} is the same as @code{142857931198} divided by
319 @code{100000000000000000}. In Guile's current incarnation, therefore,
320 the @code{rational?} and @code{real?} predicates are equivalent.
322 Another aspect of this equivalence is that Guile currently does not
323 preserve the exactness that is possible with rational arithmetic.
324 If such exactness is needed, it is of course possible to implement
325 exact rational arithmetic at the Scheme level using Guile's arbitrary
328 A planned future revision of Guile's numerical tower will make it
329 possible to implement exact representations and arithmetic for both
330 rational numbers and real irrational numbers such as square roots,
331 and in such a way that the new kinds of number integrate seamlessly
332 with those that are already implemented.
334 @deffn primitive real? obj
335 Return @code{#t} if @var{obj} is a real number, @code{#f} else.
336 Note that the sets of integer and rational values form subsets
337 of the set of real numbers, so the predicate will also be fulfilled
338 if @var{obj} is an integer number or a rational number.
341 @deffn primitive rational? x
342 Return @code{#t} if @var{x} is a rational number, @code{#f}
343 else. Note that the set of integer values forms a subset of
344 the set of rational numbers, i. e. the predicate will also be
345 fulfilled if @var{x} is an integer number. Real numbers
346 will also satisfy this predicate, because of their limited
351 @node Complex Numbers
352 @subsection Complex Numbers
355 Complex numbers are the set of numbers that describe all possible points
356 in a two-dimensional space. The two coordinates of a particular point
357 in this space are known as the @dfn{real} and @dfn{imaginary} parts of
358 the complex number that describes that point.
360 In Guile, complex numbers are written in rectangular form as the sum of
361 their real and imaginary parts, using the symbol @code{i} to indicate
374 Guile represents a complex number as a pair of numbers both of which are
375 real, so the real and imaginary parts of a complex number have the same
376 properties of inexactness and limited precision as single real numbers.
378 @deffn primitive complex? x
379 Return @code{#t} if @var{x} is a complex number, @code{#f}
380 else. Note that the sets of real, rational and integer
381 values form subsets of the set of complex numbers, i. e. the
382 predicate will also be fulfilled if @var{x} is a real,
383 rational or integer number.
388 @subsection Exact and Inexact Numbers
391 @rnindex exact->inexact
392 @rnindex inexact->exact
394 R5RS requires that a calculation involving inexact numbers always
395 produces an inexact result. To meet this requirement, Guile
396 distinguishes between an exact integer value such as @code{5} and the
397 corresponding inexact real value which, to the limited precision
398 available, has no fractional part, and is printed as @code{5.0}. Guile
399 will only convert the latter value to the former when forced to do so by
400 an invocation of the @code{inexact->exact} procedure.
402 @deffn primitive exact? x
403 Return @code{#t} if @var{x} is an exact number, @code{#f}
407 @deffn primitive inexact? x
408 Return @code{#t} if @var{x} is an inexact number, @code{#f}
412 @deffn primitive inexact->exact z
413 Return an exact number that is numerically closest to @var{z}.
416 @c begin (texi-doc-string "guile" "exact->inexact")
417 @deffn primitive exact->inexact z
418 Convert the number @var{z} to its inexact representation.
423 @subsection Read Syntax for Numerical Data
425 The read syntax for integers is a string of digits, optionally
426 preceded by a minus or plus character, a code indicating the
427 base in which the integer is encoded, and a code indicating whether
428 the number is exact or inexact. The supported base codes are:
432 @code{#b}, @code{#B} --- the integer is written in binary (base 2)
435 @code{#o}, @code{#O} --- the integer is written in octal (base 8)
438 @code{#d}, @code{#D} --- the integer is written in decimal (base 10)
441 @code{#x}, @code{#X} --- the integer is written in hexadecimal (base 16).
444 If the base code is omitted, the integer is assumed to be decimal. The
445 following examples show how these base codes are used.
469 The codes for indicating exactness (which can, incidentally, be applied
470 to all numerical values) are:
474 @code{#e}, @code{#E} --- the number is exact
477 @code{#i}, @code{#I} --- the number is inexact.
480 If the exactness indicator is omitted, the integer is assumed to be exact,
481 since Guile's internal representation for integers is always exact.
482 Real numbers have limited precision similar to the precision of the
483 @code{double} type in C. A consequence of the limited precision is that
484 all real numbers in Guile are also rational, since any number R with a
485 limited number of decimal places, say N, can be made into an integer by
489 @node Integer Operations
490 @subsection Operations on Integer Values
499 @deffn primitive odd? n
500 Return @code{#t} if @var{n} is an odd number, @code{#f}
504 @deffn primitive even? n
505 Return @code{#t} if @var{n} is an even number, @code{#f}
509 @c begin (texi-doc-string "guile" "quotient")
510 @deffn primitive quotient
511 Return the quotient of the numbers @var{x} and @var{y}.
514 @c begin (texi-doc-string "guile" "remainder")
515 @deffn primitive remainder
516 Return the remainder of the numbers @var{x} and @var{y}.
518 (remainder 13 4) @result{} 1
519 (remainder -13 4) @result{} -1
523 @c begin (texi-doc-string "guile" "modulo")
524 @deffn primitive modulo
525 Return the modulo of the numbers @var{x} and @var{y}.
527 (modulo 13 4) @result{} 1
528 (modulo -13 4) @result{} 3
532 @c begin (texi-doc-string "guile" "gcd")
534 Return the greatest common divisor of all arguments.
535 If called without arguments, 0 is returned.
538 @c begin (texi-doc-string "guile" "lcm")
540 Return the least common multiple of the arguments.
541 If called without arguments, 1 is returned.
546 @subsection Comparison Predicates
551 @c begin (texi-doc-string "guile" "=")
553 Return @code{#t} if all parameters are numerically equal.
556 @c begin (texi-doc-string "guile" "<")
558 Return @code{#t} if the list of parameters is monotonically
562 @c begin (texi-doc-string "guile" ">")
564 Return @code{#t} if the list of parameters is monotonically
568 @c begin (texi-doc-string "guile" "<=")
570 Return @code{#t} if the list of parameters is monotonically
574 @c begin (texi-doc-string "guile" ">=")
576 Return @code{#t} if the list of parameters is monotonically
580 @c begin (texi-doc-string "guile" "zero?")
581 @deffn primitive zero?
582 Return @code{#t} if @var{z} is an exact or inexact number equal to
586 @c begin (texi-doc-string "guile" "positive?")
587 @deffn primitive positive?
588 Return @code{#t} if @var{x} is an exact or inexact number greater than
592 @c begin (texi-doc-string "guile" "negative?")
593 @deffn primitive negative?
594 Return @code{#t} if @var{x} is an exact or inexact number less than
600 @subsection Converting Numbers To and From Strings
601 @rnindex number->string
602 @rnindex string->number
604 @deffn primitive number->string n [radix]
605 Return a string holding the external representation of the
606 number @var{n} in the given @var{radix}. If @var{n} is
607 inexact, a radix of 10 will be used.
610 @deffn primitive string->number string [radix]
611 Return a number of the maximally precise representation
612 expressed by the given @var{string}. @var{radix} must be an
613 exact integer, either 2, 8, 10, or 16. If supplied, @var{radix}
614 is a default radix that may be overridden by an explicit radix
615 prefix in @var{string} (e.g. "#o177"). If @var{radix} is not
616 supplied, then the default radix is 10. If string is not a
617 syntactically valid notation for a number, then
618 @code{string->number} returns @code{#f}.
623 @subsection Complex Number Operations
624 @rnindex make-rectangular
631 @deffn primitive make-rectangular real imaginary
632 Return a complex number constructed of the given @var{real} and
633 @var{imaginary} parts.
636 @deffn primitive make-polar x y
637 Return the complex number @var{x} * e^(i * @var{y}).
640 @c begin (texi-doc-string "guile" "real-part")
641 @deffn primitive real-part
642 Return the real part of the number @var{z}.
645 @c begin (texi-doc-string "guile" "imag-part")
646 @deffn primitive imag-part
647 Return the imaginary part of the number @var{z}.
650 @c begin (texi-doc-string "guile" "magnitude")
651 @deffn primitive magnitude
652 Return the magnitude of the number @var{z}. This is the same as
653 @code{abs} for real arguments, but also allows complex numbers.
656 @c begin (texi-doc-string "guile" "angle")
657 @deffn primitive angle
658 Return the angle of the complex number @var{z}.
663 @subsection Arithmetic Functions
676 @c begin (texi-doc-string "guile" "+")
677 @deffn primitive + z1 @dots{}
678 Return the sum of all parameter values. Return 0 if called without any
682 @c begin (texi-doc-string "guile" "-")
683 @deffn primitive - z1 z2 @dots{}
684 If called with one argument @var{z1}, -@var{z1} is returned. Otherwise
685 the sum of all but the first argument are subtracted from the first
689 @c begin (texi-doc-string "guile" "*")
690 @deffn primitive * z1 @dots{}
691 Return the product of all arguments. If called without arguments, 1 is
695 @c begin (texi-doc-string "guile" "/")
696 @deffn primitive / z1 z2 @dots{}
697 Divide the first argument by the product of the remaining arguments. If
698 called with one argument @var{z1}, 1/@var{z1} is returned.
701 @c begin (texi-doc-string "guile" "abs")
702 @deffn primitive abs x
703 Return the absolute value of @var{x}.
706 @c begin (texi-doc-string "guile" "max")
707 @deffn primitive max x1 x2 @dots{}
708 Return the maximum of all parameter values.
711 @c begin (texi-doc-string "guile" "min")
712 @deffn primitive min x1 x2 @dots{}
713 Return the minium of all parameter values.
716 @c begin (texi-doc-string "guile" "truncate")
717 @deffn primitive truncate
718 Round the inexact number @var{x} towards zero.
721 @c begin (texi-doc-string "guile" "round")
722 @deffn primitive round x
723 Round the inexact number @var{x} towards zero.
726 @c begin (texi-doc-string "guile" "floor")
727 @deffn primitive floor x
728 Round the number @var{x} towards minus infinity.
731 @c begin (texi-doc-string "guile" "ceiling")
732 @deffn primitive ceiling x
733 Round the number @var{x} towards infinity.
738 @subsection Scientific Functions
740 The following procedures accept any kind of number as arguments,
741 including complex numbers.
744 @c begin (texi-doc-string "guile" "sqrt")
745 @deffn procedure sqrt z
746 Return the square root of @var{z}.
750 @c begin (texi-doc-string "guile" "expt")
751 @deffn procedure expt z1 z2
752 Return @var{z1} raised to the power of @var{z2}.
756 @c begin (texi-doc-string "guile" "sin")
757 @deffn procedure sin z
758 Return the sine of @var{z}.
762 @c begin (texi-doc-string "guile" "cos")
763 @deffn procedure cos z
764 Return the cosine of @var{z}.
768 @c begin (texi-doc-string "guile" "tan")
769 @deffn procedure tan z
770 Return the tangent of @var{z}.
774 @c begin (texi-doc-string "guile" "asin")
775 @deffn procedure asin z
776 Return the arcsine of @var{z}.
780 @c begin (texi-doc-string "guile" "acos")
781 @deffn procedure acos z
782 Return the arccosine of @var{z}.
786 @c begin (texi-doc-string "guile" "atan")
787 @deffn procedure atan z
788 Return the arctangent of @var{z}.
792 @c begin (texi-doc-string "guile" "exp")
793 @deffn procedure exp z
794 Return e to the power of @var{z}, where e is the base of natural
795 logarithms (2.71828@dots{}).
799 @c begin (texi-doc-string "guile" "log")
800 @deffn procedure log z
801 Return the natural logarithm of @var{z}.
804 @c begin (texi-doc-string "guile" "log10")
805 @deffn procedure log10 z
806 Return the base 10 logarithm of @var{z}.
809 @c begin (texi-doc-string "guile" "sinh")
810 @deffn procedure sinh z
811 Return the hyperbolic sine of @var{z}.
814 @c begin (texi-doc-string "guile" "cosh")
815 @deffn procedure cosh z
816 Return the hyperbolic cosine of @var{z}.
819 @c begin (texi-doc-string "guile" "tanh")
820 @deffn procedure tanh z
821 Return the hyperbolic tangent of @var{z}.
824 @c begin (texi-doc-string "guile" "asinh")
825 @deffn procedure asinh z
826 Return the hyperbolic arcsine of @var{z}.
829 @c begin (texi-doc-string "guile" "acosh")
830 @deffn procedure acosh z
831 Return the hyperbolic arccosine of @var{z}.
834 @c begin (texi-doc-string "guile" "atanh")
835 @deffn procedure atanh z
836 Return the hyperbolic arctangent of @var{z}.
840 @node Primitive Numerics
841 @subsection Primitive Numeric Functions
843 Many of Guile's numeric procedures which accept any kind of numbers as
844 arguments, including complex numbers, are implemented as Scheme
845 procedures that use the following real number-based primitives. These
846 primitives signal an error if they are called with complex arguments.
848 @c begin (texi-doc-string "guile" "$abs")
849 @deffn primitive $abs x
850 Return the absolute value of @var{x}.
853 @c begin (texi-doc-string "guile" "$sqrt")
854 @deffn primitive $sqrt x
855 Return the square root of @var{x}.
858 @deffn primitive $expt x y
859 Return @var{x} raised to the power of @var{y}. This
860 procedure does not accept complex arguments.
863 @c begin (texi-doc-string "guile" "$sin")
864 @deffn primitive $sin x
865 Return the sine of @var{x}.
868 @c begin (texi-doc-string "guile" "$cos")
869 @deffn primitive $cos x
870 Return the cosine of @var{x}.
873 @c begin (texi-doc-string "guile" "$tan")
874 @deffn primitive $tan x
875 Return the tangent of @var{x}.
878 @c begin (texi-doc-string "guile" "$asin")
879 @deffn primitive $asin x
880 Return the arcsine of @var{x}.
883 @c begin (texi-doc-string "guile" "$acos")
884 @deffn primitive $acos x
885 Return the arccosine of @var{x}.
888 @c begin (texi-doc-string "guile" "$atan")
889 @deffn primitive $atan x
890 Return the arctangent of @var{x} in the range -PI/2 to PI/2.
893 @deffn primitive $atan2 x y
894 Return the arc tangent of the two arguments @var{x} and
895 @var{y}. This is similar to calculating the arc tangent of
896 @var{x} / @var{y}, except that the signs of both arguments
897 are used to determine the quadrant of the result. This
898 procedure does not accept complex arguments.
901 @c begin (texi-doc-string "guile" "$exp")
902 @deffn primitive $exp x
903 Return e to the power of @var{x}, where e is the base of natural
904 logarithms (2.71828@dots{}).
907 @c begin (texi-doc-string "guile" "$log")
908 @deffn primitive $log x
909 Return the natural logarithm of @var{x}.
912 @c begin (texi-doc-string "guile" "$sinh")
913 @deffn primitive $sinh x
914 Return the hyperbolic sine of @var{x}.
917 @c begin (texi-doc-string "guile" "$cosh")
918 @deffn primitive $cosh x
919 Return the hyperbolic cosine of @var{x}.
922 @c begin (texi-doc-string "guile" "$tanh")
923 @deffn primitive $tanh x
924 Return the hyperbolic tangent of @var{x}.
927 @c begin (texi-doc-string "guile" "$asinh")
928 @deffn primitive $asinh x
929 Return the hyperbolic arcsine of @var{x}.
932 @c begin (texi-doc-string "guile" "$acosh")
933 @deffn primitive $acosh x
934 Return the hyperbolic arccosine of @var{x}.
937 @c begin (texi-doc-string "guile" "$atanh")
938 @deffn primitive $atanh x
939 Return the hyperbolic arctangent of @var{x}.
943 @node Bitwise Operations
944 @subsection Bitwise Operations
946 @deffn primitive logand n1 n2
947 Return the integer which is the bit-wise AND of the two integer
951 (number->string (logand #b1100 #b1010) 2)
956 @deffn primitive logior n1 n2
957 Return the integer which is the bit-wise OR of the two integer
961 (number->string (logior #b1100 #b1010) 2)
966 @deffn primitive logxor n1 n2
967 Return the integer which is the bit-wise XOR of the two integer
971 (number->string (logxor #b1100 #b1010) 2)
976 @deffn primitive lognot n
977 Return the integer which is the 2s-complement of the integer
981 (number->string (lognot #b10000000) 2)
982 @result{} "-10000001"
983 (number->string (lognot #b0) 2)
988 @deffn primitive logtest j k
990 (logtest j k) @equiv{} (not (zero? (logand j k)))
992 (logtest #b0100 #b1011) @result{} #f
993 (logtest #b0100 #b0111) @result{} #t
997 @deffn primitive logbit? index j
999 (logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)
1001 (logbit? 0 #b1101) @result{} #t
1002 (logbit? 1 #b1101) @result{} #f
1003 (logbit? 2 #b1101) @result{} #t
1004 (logbit? 3 #b1101) @result{} #t
1005 (logbit? 4 #b1101) @result{} #f
1009 @deffn primitive ash n cnt
1010 The function ash performs an arithmetic shift left by @var{cnt}
1011 bits (or shift right, if @var{cnt} is negative). 'Arithmetic'
1012 means, that the function does not guarantee to keep the bit
1013 structure of @var{n}, but rather guarantees that the result
1014 will always be rounded towards minus infinity. Therefore, the
1015 results of ash and a corresponding bitwise shift will differ if
1016 @var{n} is negative.
1018 Formally, the function returns an integer equivalent to
1019 @code{(inexact->exact (floor (* @var{n} (expt 2 @var{cnt}))))}.
1022 (number->string (ash #b1 3) 2) @result{} "1000"
1023 (number->string (ash #b1010 -1) 2) @result{} "101"
1027 @deffn primitive logcount n
1028 Return the number of bits in integer @var{n}. If integer is
1029 positive, the 1-bits in its binary representation are counted.
1030 If negative, the 0-bits in its two's-complement binary
1031 representation are counted. If 0, 0 is returned.
1034 (logcount #b10101010)
1043 @deffn primitive integer-length n
1044 Return the number of bits neccessary to represent @var{n}.
1047 (integer-length #b10101010)
1051 (integer-length #b1111)
1056 @deffn primitive integer-expt n k
1057 Return @var{n} raised to the non-negative integer exponent
1068 @deffn primitive bit-extract n start end
1069 Return the integer composed of the @var{start} (inclusive)
1070 through @var{end} (exclusive) bits of @var{n}. The
1071 @var{start}th bit becomes the 0-th bit in the result.
1074 (number->string (bit-extract #b1101101010 0 4) 2)
1076 (number->string (bit-extract #b1101101010 4 9) 2)
1083 @subsection Random Number Generation
1085 @deffn primitive copy-random-state [state]
1086 Return a copy of the random state @var{state}.
1089 @deffn primitive random n [state]
1090 Return a number in [0,N).
1092 Accepts a positive integer or real n and returns a
1093 number of the same type between zero (inclusive) and
1094 N (exclusive). The values returned have a uniform
1097 The optional argument @var{state} must be of the type produced
1098 by @code{seed->random-state}. It defaults to the value of the
1099 variable @var{*random-state*}. This object is used to maintain
1100 the state of the pseudo-random-number generator and is altered
1101 as a side effect of the random operation.
1104 @deffn primitive random:exp [state]
1105 Return an inexact real in an exponential distribution with mean
1106 1. For an exponential distribution with mean u use (* u
1110 @deffn primitive random:hollow-sphere! v [state]
1111 Fills vect with inexact real random numbers
1112 the sum of whose squares is equal to 1.0.
1113 Thinking of vect as coordinates in space of
1114 dimension n = (vector-length vect), the coordinates
1115 are uniformly distributed over the surface of the
1119 @deffn primitive random:normal [state]
1120 Return an inexact real in a normal distribution. The
1121 distribution used has mean 0 and standard deviation 1. For a
1122 normal distribution with mean m and standard deviation d use
1123 @code{(+ m (* d (random:normal)))}.
1126 @deffn primitive random:normal-vector! v [state]
1127 Fills vect with inexact real random numbers that are
1128 independent and standard normally distributed
1129 (i.e., with mean 0 and variance 1).
1132 @deffn primitive random:solid-sphere! v [state]
1133 Fills vect with inexact real random numbers
1134 the sum of whose squares is less than 1.0.
1135 Thinking of vect as coordinates in space of
1136 dimension n = (vector-length vect), the coordinates
1137 are uniformly distributed within the unit n-shere.
1138 The sum of the squares of the numbers is returned.
1141 @deffn primitive random:uniform [state]
1142 Return a uniformly distributed inexact real random number in
1146 @deffn primitive seed->random-state seed
1147 Return a new random state using @var{seed}.
1155 Most of the characters in the ASCII character set may be referred to by
1156 name: for example, @code{#\tab}, @code{#\esc}, @code{#\stx}, and so on.
1157 The following table describes the ASCII names for each character.
1159 @multitable @columnfractions .25 .25 .25 .25
1160 @item 0 = @code{#\nul}
1161 @tab 1 = @code{#\soh}
1162 @tab 2 = @code{#\stx}
1163 @tab 3 = @code{#\etx}
1164 @item 4 = @code{#\eot}
1165 @tab 5 = @code{#\enq}
1166 @tab 6 = @code{#\ack}
1167 @tab 7 = @code{#\bel}
1168 @item 8 = @code{#\bs}
1169 @tab 9 = @code{#\ht}
1170 @tab 10 = @code{#\nl}
1171 @tab 11 = @code{#\vt}
1172 @item 12 = @code{#\np}
1173 @tab 13 = @code{#\cr}
1174 @tab 14 = @code{#\so}
1175 @tab 15 = @code{#\si}
1176 @item 16 = @code{#\dle}
1177 @tab 17 = @code{#\dc1}
1178 @tab 18 = @code{#\dc2}
1179 @tab 19 = @code{#\dc3}
1180 @item 20 = @code{#\dc4}
1181 @tab 21 = @code{#\nak}
1182 @tab 22 = @code{#\syn}
1183 @tab 23 = @code{#\etb}
1184 @item 24 = @code{#\can}
1185 @tab 25 = @code{#\em}
1186 @tab 26 = @code{#\sub}
1187 @tab 27 = @code{#\esc}
1188 @item 28 = @code{#\fs}
1189 @tab 29 = @code{#\gs}
1190 @tab 30 = @code{#\rs}
1191 @tab 31 = @code{#\us}
1192 @item 32 = @code{#\sp}
1195 The @code{delete} character (octal 177) may be referred to with the name
1198 Several characters have more than one name:
1202 @code{#\space}, @code{#\sp}
1204 @code{#\newline}, @code{#\nl}
1206 @code{#\tab}, @code{#\ht}
1208 @code{#\backspace}, @code{#\bs}
1210 @code{#\return}, @code{#\cr}
1212 @code{#\page}, @code{#\np}
1214 @code{#\null}, @code{#\nul}
1218 @deffn primitive char? x
1219 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1223 @deffn primitive char=? x y
1224 Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}.
1228 @deffn primitive char<? x y
1229 Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence,
1234 @deffn primitive char<=? x y
1235 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1236 ASCII sequence, else @code{#f}.
1240 @deffn primitive char>? x y
1241 Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
1242 sequence, else @code{#f}.
1246 @deffn primitive char>=? x y
1247 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1248 ASCII sequence, else @code{#f}.
1252 @deffn primitive char-ci=? x y
1253 Return @code{#t} iff @var{x} is the same character as @var{y} ignoring
1254 case, else @code{#f}.
1258 @deffn primitive char-ci<? x y
1259 Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence
1260 ignoring case, else @code{#f}.
1264 @deffn primitive char-ci<=? x y
1265 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1266 ASCII sequence ignoring case, else @code{#f}.
1270 @deffn primitive char-ci>? x y
1271 Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
1272 sequence ignoring case, else @code{#f}.
1276 @deffn primitive char-ci>=? x y
1277 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1278 ASCII sequence ignoring case, else @code{#f}.
1281 @rnindex char-alphabetic?
1282 @deffn primitive char-alphabetic? chr
1283 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1284 Alphabetic means the same thing as the isalpha C library function.
1287 @rnindex char-numeric?
1288 @deffn primitive char-numeric? chr
1289 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1290 Numeric means the same thing as the isdigit C library function.
1293 @rnindex char-whitespace?
1294 @deffn primitive char-whitespace? chr
1295 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1296 Whitespace means the same thing as the isspace C library function.
1299 @rnindex char-upper-case?
1300 @deffn primitive char-upper-case? chr
1301 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1302 Uppercase means the same thing as the isupper C library function.
1305 @rnindex char-lower-case?
1306 @deffn primitive char-lower-case? chr
1307 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1308 Lowercase means the same thing as the islower C library function.
1311 @deffn primitive char-is-both? chr
1312 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else @code{#f}.
1313 Uppercase and lowercase are as defined by the isupper and islower
1314 C library functions.
1317 @rnindex char->integer
1318 @deffn primitive char->integer chr
1319 Return the number corresponding to ordinal position of @var{chr} in the
1323 @rnindex integer->char
1324 @deffn primitive integer->char n
1325 Return the character at position @var{n} in the ASCII sequence.
1328 @rnindex char-upcase
1329 @deffn primitive char-upcase chr
1330 Return the uppercase character version of @var{chr}.
1333 @rnindex char-downcase
1334 @deffn primitive char-downcase chr
1335 Return the lowercase character version of @var{chr}.
1342 Strings are fixed-length sequences of characters. They can be created
1343 by calling constructor procedures, but they can also literally get
1344 entered at the REPL or in Scheme source files.
1346 Guile provides a rich set of string processing procedures, because text
1347 handling is very important when Guile is used as a scripting language.
1349 Strings always carry the information about how many characters they are
1350 composed of with them, so there is no special end-of-string character,
1351 like in C. That means that Scheme strings can contain any character,
1352 even the NUL character @code{'\0'}. But note: Since most operating
1353 system calls dealing with strings (such as for file operations) expect
1354 strings to be zero-terminated, they might do unexpected things when
1355 called with string containing unusal characters.
1358 * String Syntax:: Read syntax for strings.
1359 * String Predicates:: Testing strings for certain properties.
1360 * String Constructors:: Creating new string objects.
1361 * List/String Conversion:: Converting from/to lists of characters.
1362 * String Selection:: Select portions from strings.
1363 * String Modification:: Modify parts or whole strings.
1364 * String Comparison:: Lexicographic ordering predicates.
1365 * String Searching:: Searching in strings.
1366 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
1367 * Appending Strings:: Appending strings to form a new string.
1368 * String Miscellanea:: Miscellaneous string procedures.
1372 @subsection String Read Syntax
1374 The read syntax for strings is an arbitrarily long sequence of
1375 characters enclosed in double quotes (@code{"}). @footnote{Actually, the
1376 current implementation restricts strings to a length of 2^24
1377 characters.} If you want to insert a double quote character into a
1378 string literal, it must be prefixed with a backslash @code{\} character
1379 (called an @emph{escape character}).
1381 The following are examples of string literals:
1390 @c FIXME::martin: What about escape sequences like \r, \n etc.?
1392 @node String Predicates
1393 @subsection String Predicates
1395 The following procedures can be used to check whether a given string
1396 fulfills some specified property.
1399 @deffn primitive string? obj
1400 Return @code{#t} iff @var{obj} is a string, else returns
1404 @deffn primitive string-null? str
1405 Return @code{#t} if @var{str}'s length is nonzero, and
1406 @code{#f} otherwise.
1408 (string-null? "") @result{} #t
1410 (string-null? y) @result{} #f
1414 @node String Constructors
1415 @subsection String Constructors
1417 The string constructor procedures create new string objects, possibly
1418 initializing them with some specified character data.
1420 @c FIXME::martin: list->string belongs into `List/String Conversion'
1423 @rnindex list->string
1424 @deffn primitive string . chrs
1425 @deffnx primitive list->string chrs
1426 Return a newly allocated string composed of the arguments,
1430 @rnindex make-string
1431 @deffn primitive make-string k [chr]
1432 Return a newly allocated string of
1433 length @var{k}. If @var{chr} is given, then all elements of
1434 the string are initialized to @var{chr}, otherwise the contents
1435 of the @var{string} are unspecified.
1438 @node List/String Conversion
1439 @subsection List/String conversion
1441 When processing strings, it is often convenient to first convert them
1442 into a list representation by using the procedure @code{string->list},
1443 work with the resulting list, and then convert it back into a string.
1444 These procedures are useful for similar tasks.
1446 @rnindex string->list
1447 @deffn primitive string->list str
1448 Return a newly allocated list of the characters that make up
1449 the given string @var{str}. @code{string->list} and
1450 @code{list->string} are inverses as far as @samp{equal?} is
1454 @deffn primitive string-split str chr
1455 Split the string @var{str} into the a list of the substrings delimited
1456 by appearances of the character @var{chr}. Note that an empty substring
1457 between separator characters will result in an empty string in the
1460 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
1462 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
1464 (string-split "::" #\:)
1468 (string-split "" #\:)
1475 @node String Selection
1476 @subsection String Selection
1478 Portions of strings can be extracted by these procedures.
1479 @code{string-ref} delivers individual characters whereas
1480 @code{substring} can be used to extract substrings from longer strings.
1482 @rnindex string-length
1483 @deffn primitive string-length string
1484 Return the number of characters in @var{string}.
1488 @deffn primitive string-ref str k
1489 Return character @var{k} of @var{str} using zero-origin
1490 indexing. @var{k} must be a valid index of @var{str}.
1493 @rnindex string-copy
1494 @deffn primitive string-copy str
1495 Return a newly allocated copy of the given @var{string}.
1499 @deffn primitive substring str start [end]
1500 Return a newly allocated string formed from the characters
1501 of @var{str} beginning with index @var{start} (inclusive) and
1502 ending with index @var{end} (exclusive).
1503 @var{str} must be a string, @var{start} and @var{end} must be
1504 exact integers satisfying:
1506 0 <= @var{start} <= @var{end} <= (string-length @var{str}).
1509 @node String Modification
1510 @subsection String Modification
1512 These procedures are for modifying strings in-place. That means, that
1513 not a new string is the result of a string operation, but that the
1514 actual memory representation of a string is modified.
1516 @rnindex string-set!
1517 @deffn primitive string-set! str k chr
1518 Store @var{chr} in element @var{k} of @var{str} and return
1519 an unspecified value. @var{k} must be a valid index of
1523 @rnindex string-fill!
1524 @deffn primitive string-fill! str chr
1525 Store @var{char} in every element of the given @var{string} and
1526 return an unspecified value.
1529 @deffn primitive substring-fill! str start end fill
1530 Change every character in @var{str} between @var{start} and
1531 @var{end} to @var{fill}.
1534 (define y "abcdefg")
1535 (substring-fill! y 1 3 #\r)
1541 @deffn primitive substring-move! str1 start1 end1 str2 start2
1542 @deffnx primitive substring-move-left! str1 start1 end1 str2 start2
1543 @deffnx primitive substring-move-right! str1 start1 end1 str2 start2
1544 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
1545 into @var{str2} beginning at position @var{end2}.
1546 @code{substring-move-right!} begins copying from the rightmost character
1547 and moves left, and @code{substring-move-left!} copies from the leftmost
1548 character moving right.
1550 It is useful to have two functions that copy in different directions so
1551 that substrings can be copied back and forth within a single string. If
1552 you wish to copy text from the left-hand side of a string to the
1553 right-hand side of the same string, and the source and destination
1554 overlap, you must be careful to copy the rightmost characters of the
1555 text first, to avoid clobbering your data. Hence, when @var{str1} and
1556 @var{str2} are the same string, you should use
1557 @code{substring-move-right!} when moving text from left to right, and
1558 @code{substring-move-left!} otherwise. If @code{str1} and @samp{str2}
1559 are different strings, it does not matter which function you use.
1562 (define x (make-string 10 #\a))
1564 (substring-move-left! x 2 5 y 0)
1569 @result{} "aaaaaaaaaa"
1572 (substring-move-left! x 2 5 y 0)
1576 (define y "abcdefg")
1577 (substring-move-left! y 2 5 y 3)
1581 (define y "abcdefg")
1582 (substring-move-right! y 2 5 y 0)
1586 (define y "abcdefg")
1587 (substring-move-right! y 2 5 y 3)
1594 @node String Comparison
1595 @subsection String Comparison
1597 The procedures in this section are similar to the character ordering
1598 predicates (@pxref{Characters}), but are defined on character sequences.
1599 They all return @code{#t} on success and @code{#f} on failure. The
1600 predicates ending in @code{-ci} ignore the character case when comparing
1605 @deffn primitive string=? s1 s2
1606 Lexicographic equality predicate; return @code{#t} if the two
1607 strings are the same length and contain the same characters in
1608 the same positions, otherwise return @code{#f}.
1610 The procedure @code{string-ci=?} treats upper and lower case
1611 letters as though they were the same character, but
1612 @code{string=?} treats upper and lower case as distinct
1617 @deffn primitive string<? s1 s2
1618 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1619 is lexicographically less than @var{s2}.
1623 @deffn primitive string<=? s1 s2
1624 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1625 is lexicographically less than or equal to @var{s2}.
1629 @deffn primitive string>? s1 s2
1630 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1631 is lexicographically greater than @var{s2}.
1635 @deffn primitive string>=? s1 s2
1636 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1637 is lexicographically greater than or equal to @var{s2}.
1640 @rnindex string-ci=?
1641 @deffn primitive string-ci=? s1 s2
1642 Case-insensitive string equality predicate; return @code{#t} if
1643 the two strings are the same length and their component
1644 characters match (ignoring case) at each position; otherwise
1649 @deffn primitive string-ci<? s1 s2
1650 Case insensitive lexicographic ordering predicate; return
1651 @code{#t} if @var{s1} is lexicographically less than @var{s2}
1656 @deffn primitive string-ci<=? s1 s2
1657 Case insensitive lexicographic ordering predicate; return
1658 @code{#t} if @var{s1} is lexicographically less than or equal
1659 to @var{s2} regardless of case.
1662 @rnindex string-ci>?
1663 @deffn primitive string-ci>? s1 s2
1664 Case insensitive lexicographic ordering predicate; return
1665 @code{#t} if @var{s1} is lexicographically greater than
1666 @var{s2} regardless of case.
1669 @rnindex string-ci>=?
1670 @deffn primitive string-ci>=? s1 s2
1671 Case insensitive lexicographic ordering predicate; return
1672 @code{#t} if @var{s1} is lexicographically greater than or
1673 equal to @var{s2} regardless of case.
1677 @node String Searching
1678 @subsection String Searching
1680 When searching the index of a character in a string, these procedures
1683 @deffn primitive string-index str chr [frm [to]]
1684 Return the index of the first occurrence of @var{chr} in
1685 @var{str}. The optional integer arguments @var{frm} and
1686 @var{to} limit the search to a portion of the string. This
1687 procedure essentially implements the @code{index} or
1688 @code{strchr} functions from the C library.
1691 (string-index "weiner" #\e)
1694 (string-index "weiner" #\e 2)
1697 (string-index "weiner" #\e 2 4)
1702 @deffn primitive string-rindex str chr [frm [to]]
1703 Like @code{string-index}, but search from the right of the
1704 string rather than from the left. This procedure essentially
1705 implements the @code{rindex} or @code{strrchr} functions from
1709 (string-rindex "weiner" #\e)
1712 (string-rindex "weiner" #\e 2 4)
1715 (string-rindex "weiner" #\e 2 5)
1720 @node Alphabetic Case Mapping
1721 @subsection Alphabetic Case Mapping
1723 These are procedures for mapping strings to their upper- or lower-case
1724 equivalents, respectively, or for capitalizing strings.
1726 @deffn primitive string-upcase str
1727 Return a freshly allocated string containing the characters of
1728 @var{str} in upper case.
1731 @deffn primitive string-upcase! str
1732 Destructively upcase every character in @var{str} and return
1735 y @result{} "arrdefg"
1736 (string-upcase! y) @result{} "ARRDEFG"
1737 y @result{} "ARRDEFG"
1741 @deffn primitive string-downcase str
1742 Return a freshly allocation string containing the characters in
1743 @var{str} in lower case.
1746 @deffn primitive string-downcase! str
1747 Destructively downcase every character in @var{str} and return
1750 y @result{} "ARRDEFG"
1751 (string-downcase! y) @result{} "arrdefg"
1752 y @result{} "arrdefg"
1756 @deffn primitive string-capitalize str
1757 Return a freshly allocated string with the characters in
1758 @var{str}, where the first character of every word is
1762 @deffn primitive string-capitalize! str
1763 Upcase the first character of every word in @var{str}
1764 destructively and return @var{str}.
1767 y @result{} "hello world"
1768 (string-capitalize! y) @result{} "Hello World"
1769 y @result{} "Hello World"
1774 @node Appending Strings
1775 @subsection Appending Strings
1777 The procedure @code{string-append} appends several strings together to
1778 form a longer result string.
1780 @rnindex string-append
1781 @deffn primitive string-append string1 @dots{}
1782 Return a newly allocated string whose characters form the
1783 concatenation of the given strings.
1787 @node String Miscellanea
1788 @subsection String Miscellanea
1790 This section contains all remaining string procedures.
1792 @deffn primitive string-ci->symbol str
1793 Return the symbol whose name is @var{str}. @var{str} is
1794 converted to lowercase before the conversion is done, if Guile
1795 is currently reading symbols case-insensitively.
1799 @node Regular Expressions
1800 @section Regular Expressions
1802 @cindex regular expressions
1804 @cindex emacs regexp
1806 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
1807 describes a whole class of strings. A full description of regular
1808 expressions and their syntax is beyond the scope of this manual;
1809 an introduction can be found in the Emacs manual (@pxref{Regexps,
1810 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, or
1811 in many general Unix reference books.
1813 If your system does not include a POSIX regular expression library, and
1814 you have not linked Guile with a third-party regexp library such as Rx,
1815 these functions will not be available. You can tell whether your Guile
1816 installation includes regular expression support by checking whether the
1817 @code{*features*} list includes the @code{regex} symbol.
1820 * Regexp Functions:: Functions that create and match regexps.
1821 * Match Structures:: Finding what was matched by a regexp.
1822 * Backslash Escapes:: Removing the special meaning of regexp metacharacters.
1823 * Rx Interface:: Tom Lord's Rx library does things differently.
1826 [FIXME: it may be useful to include an Examples section. Parts of this
1827 interface are bewildering on first glance.]
1829 @node Regexp Functions
1830 @subsection Regexp Functions
1832 By default, Guile supports POSIX extended regular expressions.
1833 That means that the characters @samp{(}, @samp{)}, @samp{+} and
1834 @samp{?} are special, and must be escaped if you wish to match the
1837 This regular expression interface was modeled after that
1838 implemented by SCSH, the Scheme Shell. It is intended to be
1839 upwardly compatible with SCSH regular expressions.
1841 @c begin (scm-doc-string "regex.scm" "string-match")
1842 @deffn procedure string-match pattern str [start]
1843 Compile the string @var{pattern} into a regular expression and compare
1844 it with @var{str}. The optional numeric argument @var{start} specifies
1845 the position of @var{str} at which to begin matching.
1847 @code{string-match} returns a @dfn{match structure} which
1848 describes what, if anything, was matched by the regular
1849 expression. @xref{Match Structures}. If @var{str} does not match
1850 @var{pattern} at all, @code{string-match} returns @code{#f}.
1853 Each time @code{string-match} is called, it must compile its
1854 @var{pattern} argument into a regular expression structure. This
1855 operation is expensive, which makes @code{string-match} inefficient if
1856 the same regular expression is used several times (for example, in a
1857 loop). For better performance, you can compile a regular expression in
1858 advance and then match strings against the compiled regexp.
1860 @deffn primitive make-regexp pat . flags
1861 Compile the regular expression described by @var{pat}, and
1862 return the compiled regexp structure. If @var{pat} does not
1863 describe a legal regular expression, @code{make-regexp} throws
1864 a @code{regular-expression-syntax} error.
1866 The @var{flags} arguments change the behavior of the compiled
1867 regular expression. The following flags may be supplied:
1871 Consider uppercase and lowercase letters to be the same when
1873 @item regexp/newline
1874 If a newline appears in the target string, then permit the
1875 @samp{^} and @samp{$} operators to match immediately after or
1876 immediately before the newline, respectively. Also, the
1877 @samp{.} and @samp{[^...]} operators will never match a newline
1878 character. The intent of this flag is to treat the target
1879 string as a buffer containing many lines of text, and the
1880 regular expression as a pattern that may match a single one of
1883 Compile a basic (``obsolete'') regexp instead of the extended
1884 (``modern'') regexps that are the default. Basic regexps do
1885 not consider @samp{|}, @samp{+} or @samp{?} to be special
1886 characters, and require the @samp{@{...@}} and @samp{(...)}
1887 metacharacters to be backslash-escaped (@pxref{Backslash
1888 Escapes}). There are several other differences between basic
1889 and extended regular expressions, but these are the most
1891 @item regexp/extended
1892 Compile an extended regular expression rather than a basic
1893 regexp. This is the default behavior; this flag will not
1894 usually be needed. If a call to @code{make-regexp} includes
1895 both @code{regexp/basic} and @code{regexp/extended} flags, the
1896 one which comes last will override the earlier one.
1900 @deffn primitive regexp-exec rx str [start [flags]]
1901 Match the compiled regular expression @var{rx} against
1902 @code{str}. If the optional integer @var{start} argument is
1903 provided, begin matching from that position in the string.
1904 Return a match structure describing the results of the match,
1905 or @code{#f} if no match could be found.
1908 @deffn primitive regexp? obj
1909 Return @code{#t} if @var{obj} is a compiled regular expression,
1910 or @code{#f} otherwise.
1913 Regular expressions are commonly used to find patterns in one string and
1914 replace them with the contents of another string.
1916 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
1917 @deffn procedure regexp-substitute port match [item@dots{}]
1918 Write to the output port @var{port} selected contents of the match
1919 structure @var{match}. Each @var{item} specifies what should be
1920 written, and may be one of the following arguments:
1924 A string. String arguments are written out verbatim.
1927 An integer. The submatch with that number is written.
1930 The symbol @samp{pre}. The portion of the matched string preceding
1931 the regexp match is written.
1934 The symbol @samp{post}. The portion of the matched string following
1935 the regexp match is written.
1938 @var{port} may be @code{#f}, in which case nothing is written; instead,
1939 @code{regexp-substitute} constructs a string from the specified
1940 @var{item}s and returns that.
1943 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
1944 @deffn procedure regexp-substitute/global port regexp target [item@dots{}]
1945 Similar to @code{regexp-substitute}, but can be used to perform global
1946 substitutions on @var{str}. Instead of taking a match structure as an
1947 argument, @code{regexp-substitute/global} takes two string arguments: a
1948 @var{regexp} string describing a regular expression, and a @var{target}
1949 string which should be matched against this regular expression.
1951 Each @var{item} behaves as in @var{regexp-substitute}, with the
1952 following exceptions:
1956 A function may be supplied. When this function is called, it will be
1957 passed one argument: a match structure for a given regular expression
1958 match. It should return a string to be written out to @var{port}.
1961 The @samp{post} symbol causes @code{regexp-substitute/global} to recurse
1962 on the unmatched portion of @var{str}. This @emph{must} be supplied in
1963 order to perform global search-and-replace on @var{str}; if it is not
1964 present among the @var{item}s, then @code{regexp-substitute/global} will
1965 return after processing a single match.
1969 @node Match Structures
1970 @subsection Match Structures
1972 @cindex match structures
1974 A @dfn{match structure} is the object returned by @code{string-match} and
1975 @code{regexp-exec}. It describes which portion of a string, if any,
1976 matched the given regular expression. Match structures include: a
1977 reference to the string that was checked for matches; the starting and
1978 ending positions of the regexp match; and, if the regexp included any
1979 parenthesized subexpressions, the starting and ending positions of each
1982 In each of the regexp match functions described below, the @code{match}
1983 argument must be a match structure returned by a previous call to
1984 @code{string-match} or @code{regexp-exec}. Most of these functions
1985 return some information about the original target string that was
1986 matched against a regular expression; we will call that string
1987 @var{target} for easy reference.
1989 @c begin (scm-doc-string "regex.scm" "regexp-match?")
1990 @deffn procedure regexp-match? obj
1991 Return @code{#t} if @var{obj} is a match structure returned by a
1992 previous call to @code{regexp-exec}, or @code{#f} otherwise.
1995 @c begin (scm-doc-string "regex.scm" "match:substring")
1996 @deffn procedure match:substring match [n]
1997 Return the portion of @var{target} matched by subexpression number
1998 @var{n}. Submatch 0 (the default) represents the entire regexp match.
1999 If the regular expression as a whole matched, but the subexpression
2000 number @var{n} did not match, return @code{#f}.
2003 @c begin (scm-doc-string "regex.scm" "match:start")
2004 @deffn procedure match:start match [n]
2005 Return the starting position of submatch number @var{n}.
2008 @c begin (scm-doc-string "regex.scm" "match:end")
2009 @deffn procedure match:end match [n]
2010 Return the ending position of submatch number @var{n}.
2013 @c begin (scm-doc-string "regex.scm" "match:prefix")
2014 @deffn procedure match:prefix match
2015 Return the unmatched portion of @var{target} preceding the regexp match.
2018 @c begin (scm-doc-string "regex.scm" "match:suffix")
2019 @deffn procedure match:suffix match
2020 Return the unmatched portion of @var{target} following the regexp match.
2023 @c begin (scm-doc-string "regex.scm" "match:count")
2024 @deffn procedure match:count match
2025 Return the number of parenthesized subexpressions from @var{match}.
2026 Note that the entire regular expression match itself counts as a
2027 subexpression, and failed submatches are included in the count.
2030 @c begin (scm-doc-string "regex.scm" "match:string")
2031 @deffn procedure match:string match
2032 Return the original @var{target} string.
2035 @node Backslash Escapes
2036 @subsection Backslash Escapes
2038 Sometimes you will want a regexp to match characters like @samp{*} or
2039 @samp{$} exactly. For example, to check whether a particular string
2040 represents a menu entry from an Info node, it would be useful to match
2041 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
2042 because the asterisk is a metacharacter, it won't match the @samp{*} at
2043 the beginning of the string. In this case, we want to make the first
2046 You can do this by preceding the metacharacter with a backslash
2047 character @samp{\}. (This is also called @dfn{quoting} the
2048 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
2049 sees a backslash in a regular expression, it considers the following
2050 glyph to be an ordinary character, no matter what special meaning it
2051 would ordinarily have. Therefore, we can make the above example work by
2052 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
2053 the regular expression engine to match only a single asterisk in the
2056 Since the backslash is itself a metacharacter, you may force a regexp to
2057 match a backslash in the target string by preceding the backslash with
2058 itself. For example, to find variable references in a @TeX{} program,
2059 you might want to find occurrences of the string @samp{\let\} followed
2060 by any number of alphabetic characters. The regular expression
2061 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
2062 regexp each match a single backslash in the target string.
2064 @c begin (scm-doc-string "regex.scm" "regexp-quote")
2065 @deffn procedure regexp-quote str
2066 Quote each special character found in @var{str} with a backslash, and
2067 return the resulting string.
2070 @strong{Very important:} Using backslash escapes in Guile source code
2071 (as in Emacs Lisp or C) can be tricky, because the backslash character
2072 has special meaning for the Guile reader. For example, if Guile
2073 encounters the character sequence @samp{\n} in the middle of a string
2074 while processing Scheme code, it replaces those characters with a
2075 newline character. Similarly, the character sequence @samp{\t} is
2076 replaced by a horizontal tab. Several of these @dfn{escape sequences}
2077 are processed by the Guile reader before your code is executed.
2078 Unrecognized escape sequences are ignored: if the characters @samp{\*}
2079 appear in a string, they will be translated to the single character
2082 This translation is obviously undesirable for regular expressions, since
2083 we want to be able to include backslashes in a string in order to
2084 escape regexp metacharacters. Therefore, to make sure that a backslash
2085 is preserved in a string in your Guile program, you must use @emph{two}
2086 consecutive backslashes:
2089 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
2092 The string in this example is preprocessed by the Guile reader before
2093 any code is executed. The resulting argument to @code{make-regexp} is
2094 the string @samp{^\* [^:]*}, which is what we really want.
2096 This also means that in order to write a regular expression that matches
2097 a single backslash character, the regular expression string in the
2098 source code must include @emph{four} backslashes. Each consecutive pair
2099 of backslashes gets translated by the Guile reader to a single
2100 backslash, and the resulting double-backslash is interpreted by the
2101 regexp engine as matching a single backslash character. Hence:
2104 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
2107 The reason for the unwieldiness of this syntax is historical. Both
2108 regular expression pattern matchers and Unix string processing systems
2109 have traditionally used backslashes with the special meanings
2110 described above. The POSIX regular expression specification and ANSI C
2111 standard both require these semantics. Attempting to abandon either
2112 convention would cause other kinds of compatibility problems, possibly
2113 more severe ones. Therefore, without extending the Scheme reader to
2114 support strings with different quoting conventions (an ungainly and
2115 confusing extension when implemented in other languages), we must adhere
2116 to this cumbersome escape syntax.
2119 @subsection Rx Interface
2121 @c FIXME::martin: Shouldn't this be removed or moved to the
2122 @c ``Guile Modules'' chapter? The functions are not available in
2125 [FIXME: this is taken from Gary and Mark's quick summaries and should be
2126 reviewed and expanded. Rx is pretty stable, so could already be done!]
2129 @cindex finite automaton
2131 Guile includes an interface to Tom Lord's Rx library (currently only to
2132 POSIX regular expressions). Use of the library requires a two step
2133 process: compile a regular expression into an efficient structure, then
2134 use the structure in any number of string comparisons.
2136 For example, given the
2137 regular expression @samp{abc.} (which matches any string containing
2138 @samp{abc} followed by any single character):
2141 guile> @kbd{(define r (regcomp "abc."))}
2144 guile> @kbd{(regexec r "abc")}
2146 guile> @kbd{(regexec r "abcd")}
2151 The definitions of @code{regcomp} and @code{regexec} are as follows:
2153 @c NJFIXME not in libguile!
2154 @deffn primitive regcomp pattern [flags]
2155 Compile the regular expression pattern using POSIX rules. Flags is
2156 optional and should be specified using symbolic names:
2157 @defvar REG_EXTENDED
2158 use extended POSIX syntax
2161 use case-insensitive matching
2164 allow anchors to match after newline characters in the
2165 string and prevents @code{.} or @code{[^...]} from matching newlines.
2168 The @code{logior} procedure can be used to combine multiple flags.
2169 The default is to use
2170 POSIX basic syntax, which makes @code{+} and @code{?} literals and @code{\+}
2172 operators. Backslashes in @var{pattern} must be escaped if specified in a
2173 literal string e.g., @code{"\\(a\\)\\?"}.
2176 @c NJFIXME not in libguile!
2177 @deffn primitive regexec regex string [match-pick] [flags]
2179 Match @var{string} against the compiled POSIX regular expression
2181 @var{match-pick} and @var{flags} are optional. Possible flags (which can be
2182 combined using the logior procedure) are:
2185 The beginning of line operator won't match the beginning of
2186 @var{string} (presumably because it's not the beginning of a line)
2190 Similar to REG_NOTBOL, but prevents the end of line operator
2191 from matching the end of @var{string}.
2194 If no match is possible, regexec returns #f. Otherwise @var{match-pick}
2195 determines the return value:
2197 @code{#t} or unspecified: a newly-allocated vector is returned,
2198 containing pairs with the indices of the matched part of @var{string} and any
2201 @code{""}: a list is returned: the first element contains a nested list
2202 with the matched part of @var{string} surrounded by the the unmatched parts.
2203 Remaining elements are matched substrings (if any). All returned
2204 substrings share memory with @var{string}.
2206 @code{#f}: regexec returns #t if a match is made, otherwise #f.
2208 vector: the supplied vector is returned, with the first element replaced
2209 by a pair containing the indices of the matched portion of @var{string} and
2210 further elements replaced by pairs containing the indices of matched
2211 substrings (if any).
2213 list: a list will be returned, with each member of the list
2214 specified by a code in the corresponding position of the supplied list:
2216 a number: the numbered matching substring (0 for the entire match).
2218 @code{#\<}: the beginning of @var{string} to the beginning of the part matched
2221 @code{#\>}: the end of the matched part of @var{string} to the end of
2224 @code{#\c}: the "final tag", which seems to be associated with the "cut
2225 operator", which doesn't seem to be available through the posix
2228 e.g., @code{(list #\< 0 1 #\>)}. The returned substrings share memory with
2232 Here are some other procedures that might be used when using regular
2235 @c NJFIXME not in libguile!
2236 @deffn primitive compiled-regexp? obj
2237 Test whether obj is a compiled regular expression.
2240 @c NJFIXME not in libguile!
2241 @deffn primitive regexp->dfa regex [flags]
2244 @c NJFIXME not in libguile!
2245 @deffn primitive dfa-fork dfa
2248 @c NJFIXME not in libguile!
2249 @deffn primitive reset-dfa! dfa
2252 @c NJFIXME not in libguile!
2253 @deffn primitive dfa-final-tag dfa
2256 @c NJFIXME not in libguile!
2257 @deffn primitive dfa-continuable? dfa
2260 @c NJFIXME not in libguile!
2261 @deffn primitive advance-dfa! dfa string
2265 @node Symbols and Variables
2266 @section Symbols and Variables
2268 @c FIXME::martin: Review me!
2270 Symbols are a data type with a special property. On the one hand,
2271 symbols are used for denoting variables in a Scheme program, on the
2272 other they can be used as literal data as well.
2274 The association between symbols and values is maintained in special data
2275 structures, the symbol tables.
2277 In addition, Guile offers variables as first-class objects. They can
2278 be used for interacting with the module system.
2281 * Symbols:: All about symbols as a data type.
2282 * Symbol Tables:: Tables for mapping symbols to values.
2283 * Variables:: First-class variables.
2289 @c FIXME::martin: Review me!
2291 Symbols are especially useful because two symbols which are spelled the
2292 same way are equivalent in the sense of @code{eq?}. That means that
2293 they are actually the same Scheme object. The advantage is that symbols
2294 can be compared extremely efficiently, although they carry more
2295 information for the human reader than, say, numbers.
2297 It is very common in Scheme programs to use symbols as keys in
2298 association lists (@pxref{Association Lists}) or hash tables
2299 (@pxref{Hash Tables}), because this usage improves the readability a
2300 lot, and does not cause any performance loss.
2302 The read syntax for symbols is a sequence of letters, digits, and
2303 @emph{extended alphabetic characters} that begins with a character that
2304 cannot begin a number is an identifier. In addition, @code{+},
2305 @code{-}, and @code{...} are identifiers.
2307 Extended alphabetic characters may be used within identifiers as if
2308 they were letters. The following are extended alphabetic characters:
2311 ! $ % & * + - . / : < = > ? @@ ^ _ ~
2314 In addition to the read syntax defined above (which is taken from R5RS
2315 (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on Scheme})), Guile
2316 provides a method for writing symbols with unusual characters, such as
2317 space characters. If you (for whatever reason) need to write a symbol
2318 containing characters not mentioned above, you write symbols as follows:
2322 Begin the symbol with the two character @code{#@{},
2325 write the characters of the symbol and
2328 finish the symbol with the characters @code{@}#}.
2331 Here are a few examples of this form of read syntax; the first
2332 containing a space character, the second containing a line break and the
2333 last one looks like a number.
2342 Usage of this form of read syntax is discouraged, because it is not
2343 portable at all, and is not very readable.
2346 @deffn primitive symbol? obj
2347 Return @code{#t} if @var{obj} is a symbol, otherwise return
2351 @rnindex string->symbol
2352 @deffn primitive string->symbol string
2353 Return the symbol whose name is @var{string}. This procedure
2354 can create symbols with names containing special characters or
2355 letters in the non-standard case, but it is usually a bad idea
2356 to create such symbols because in some implementations of
2357 Scheme they cannot be read as themselves. See
2358 @code{symbol->string}.
2360 The following examples assume that the implementation's
2361 standard case is lower case:
2364 (eq? 'mISSISSIppi 'mississippi) @result{} #t
2365 (string->symbol "mISSISSIppi") @result{} @r{the symbol with name "mISSISSIppi"}
2366 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
2368 (string->symbol (symbol->string 'JollyWog))) @result{} #t
2369 (string=? "K. Harper, M.D."
2371 (string->symbol "K. Harper, M.D."))) @result{}#t
2375 @rnindex symbol->string
2376 @deffn primitive symbol->string s
2377 Return the name of @var{symbol} as a string. If the symbol was
2378 part of an object returned as the value of a literal expression
2379 (section @pxref{Literal expressions,,,r5rs, The Revised^5
2380 Report on Scheme}) or by a call to the @code{read} procedure,
2381 and its name contains alphabetic characters, then the string
2382 returned will contain characters in the implementation's
2383 preferred standard case--some implementations will prefer
2384 upper case, others lower case. If the symbol was returned by
2385 @code{string->symbol}, the case of characters in the string
2386 returned will be the same as the case in the string that was
2387 passed to @code{string->symbol}. It is an error to apply
2388 mutation procedures like @code{string-set!} to strings returned
2391 The following examples assume that the implementation's
2392 standard case is lower case:
2395 (symbol->string 'flying-fish) @result{} "flying-fish"
2396 (symbol->string 'Martin) @result{} "martin"
2398 (string->symbol "Malvina")) @result{} "Malvina"
2403 @subsection Symbol Tables
2405 @c FIXME::martin: Review me!
2407 @c FIXME::martin: Are all these procedures still relevant?
2409 Guile symbol tables are hash tables. Each hash table, also called an
2410 @dfn{obarray} (for `object array'), is a vector of association lists.
2411 Each entry in the alists is a pair (@var{SYMBOL} . @var{VALUE}). To
2412 @dfn{intern} a symbol in a symbol table means to return its
2413 (@var{SYMBOL} . @var{VALUE}) pair, adding a new entry to the symbol
2414 table (with an undefined value) if none is yet present.
2416 @c FIXME::martin: According to NEWS, removed. Remove here too, or
2417 @c leave for compatibility?
2418 @c @c docstring begin (texi-doc-string "guile" "builtin-bindings")
2419 @c @deffn primitive builtin-bindings
2420 @c Create and return a copy of the global symbol table, removing all
2424 @deffn primitive gensym [prefix]
2425 Create a new symbol with a name constructed from a prefix and
2426 a counter value. The string @var{prefix} can be specified as
2427 an optional argument. Default prefix is @code{g}. The counter
2428 is increased by 1 at each call. There is no provision for
2429 resetting the counter.
2432 @deffn primitive gentemp [prefix [obarray]]
2433 Create a new symbol with a name unique in an obarray.
2434 The name is constructed from an optional string @var{prefix}
2435 and a counter value. The default prefix is @code{t}. The
2436 @var{obarray} is specified as a second optional argument.
2437 Default is the system obarray where all normal symbols are
2438 interned. The counter is increased by 1 at each
2439 call. There is no provision for resetting the counter.
2442 @deffn primitive intern-symbol obarray string
2443 Add a new symbol to @var{obarray} with name @var{string}, bound to an
2444 unspecified initial value. The symbol table is not modified if a symbol
2445 with this name is already present.
2448 @deffn primitive string->obarray-symbol obarray string [soft?]
2449 Intern a new symbol in @var{obarray}, a symbol table, with name
2453 @deffn primitive symbol-binding obarray string
2454 Look up in @var{obarray} the symbol whose name is @var{string}, and
2455 return the value to which it is bound. If @var{obarray} is @code{#f},
2456 use the global symbol table. If @var{string} is not interned in
2457 @var{obarray}, an error is signalled.
2460 @deffn primitive symbol-bound? obarray string
2461 Return @code{#t} if @var{obarray} contains a symbol with name
2462 @var{string} bound to a defined value. This differs from
2463 @var{symbol-interned?} in that the mere mention of a symbol
2464 usually causes it to be interned; @code{symbol-bound?}
2465 determines whether a symbol has been given any meaningful
2469 @deffn primitive symbol-fref symbol
2470 Return the contents of @var{symbol}'s @dfn{function slot}.
2473 @deffn primitive symbol-fset! symbol value
2474 Change the binding of @var{symbol}'s function slot.
2477 @deffn primitive symbol-hash symbol
2478 Return a hash value for @var{symbol}.
2481 @deffn primitive symbol-interned? obarray string
2482 Return @code{#t} if @var{obarray} contains a symbol with name
2483 @var{string}, and @code{#f} otherwise.
2486 @deffn primitive symbol-pref symbol
2487 Return the @dfn{property list} currently associated with @var{symbol}.
2490 @deffn primitive symbol-pset! symbol value
2491 Change the binding of @var{symbol}'s property slot.
2494 @deffn primitive symbol-set! obarray string value
2495 Find the symbol in @var{obarray} whose name is @var{string}, and rebind
2496 it to @var{value}. An error is signalled if @var{string} is not present
2500 @deffn primitive unintern-symbol obarray string
2501 Remove the symbol with name @var{string} from @var{obarray}. This
2502 function returns @code{#t} if the symbol was present and @code{#f}
2507 @subsection Variables
2509 @c FIXME::martin: Review me!
2511 Variables are objects with two fields. They contain a value and they
2512 can contain a symbol, which is the name of the variable. A variable is
2513 said to be bound if it does not contain the object denoting unbound
2514 variables in the value slot.
2516 Variables do not have a read syntax, they have to be created by calling
2517 one of the constructor procedures @code{make-variable} or
2518 @code{make-undefined-variable} or retrieved by @code{builtin-variable}.
2520 First-class variables are especially useful for interacting with the
2521 current module system (@pxref{The Guile module system}).
2523 @deffn primitive builtin-variable name
2524 Return the built-in variable with the name @var{name}.
2525 @var{name} must be a symbol (not a string).
2526 Then use @code{variable-ref} to access its value.
2529 @deffn primitive make-undefined-variable [name-hint]
2530 Return a variable object initialized to an undefined value.
2531 If given, uses @var{name-hint} as its internal (debugging)
2532 name, otherwise just treat it as an anonymous variable.
2533 Remember, of course, that multiple bindings to the same
2534 variable may exist, so @var{name-hint} is just that---a hint.
2537 @deffn primitive make-variable init [name-hint]
2538 Return a variable object initialized to value @var{init}.
2539 If given, uses @var{name-hint} as its internal (debugging)
2540 name, otherwise just treat it as an anonymous variable.
2541 Remember, of course, that multiple bindings to the same
2542 variable may exist, so @var{name-hint} is just that---a hint.
2545 @deffn primitive variable-bound? var
2546 Return @code{#t} iff @var{var} is bound to a value.
2547 Throws an error if @var{var} is not a variable object.
2550 @deffn primitive variable-ref var
2551 Dereference @var{var} and return its value.
2552 @var{var} must be a variable object; see @code{make-variable}
2553 and @code{make-undefined-variable}.
2556 @deffn primitive variable-set! var val
2557 Set the value of the variable @var{var} to @var{val}.
2558 @var{var} must be a variable object, @var{val} can be any
2559 value. Return an unspecified value.
2562 @deffn primitive variable? obj
2563 Return @code{#t} iff @var{obj} is a variable object, else
2571 Keywords are self-evaluating objects with a convenient read syntax that
2572 makes them easy to type.
2574 Guile's keyword support conforms to R5RS, and adds a (switchable) read
2575 syntax extension to permit keywords to begin with @code{:} as well as
2579 * Why Use Keywords?:: Motivation for keyword usage.
2580 * Coding With Keywords:: How to use keywords.
2581 * Keyword Read Syntax:: Read syntax for keywords.
2582 * Keyword Procedures:: Procedures for dealing with keywords.
2583 * Keyword Primitives:: The underlying primitive procedures.
2586 @node Why Use Keywords?
2587 @subsection Why Use Keywords?
2589 Keywords are useful in contexts where a program or procedure wants to be
2590 able to accept a large number of optional arguments without making its
2591 interface unmanageable.
2593 To illustrate this, consider a hypothetical @code{make-window}
2594 procedure, which creates a new window on the screen for drawing into
2595 using some graphical toolkit. There are many parameters that the caller
2596 might like to specify, but which could also be sensibly defaulted, for
2601 colour depth -- Default: the colour depth for the screen
2604 background colour -- Default: white
2607 width -- Default: 600
2610 height -- Default: 400
2613 If @code{make-window} did not use keywords, the caller would have to
2614 pass in a value for each possible argument, remembering the correct
2615 argument order and using a special value to indicate the default value
2619 (make-window 'default ;; Colour depth
2620 'default ;; Background colour
2623 @dots{}) ;; More make-window arguments
2626 With keywords, on the other hand, defaulted arguments are omitted, and
2627 non-default arguments are clearly tagged by the appropriate keyword. As
2628 a result, the invocation becomes much clearer:
2631 (make-window #:width 800 #:height 100)
2634 On the other hand, for a simpler procedure with few arguments, the use
2635 of keywords would be a hindrance rather than a help. The primitive
2636 procedure @code{cons}, for example, would not be improved if it had to
2640 (cons #:car x #:cdr y)
2643 So the decision whether to use keywords or not is purely pragmatic: use
2644 them if they will clarify the procedure invocation at point of call.
2646 @node Coding With Keywords
2647 @subsection Coding With Keywords
2649 If a procedure wants to support keywords, it should take a rest argument
2650 and then use whatever means is convenient to extract keywords and their
2651 corresponding arguments from the contents of that rest argument.
2653 The following example illustrates the principle: the code for
2654 @code{make-window} uses a helper procedure called
2655 @code{get-keyword-value} to extract individual keyword arguments from
2659 (define (get-keyword-value args keyword default)
2660 (let ((kv (memq keyword args)))
2661 (if (and kv (>= (length kv) 2))
2665 (define (make-window . args)
2666 (let ((depth (get-keyword-value args #:depth screen-depth))
2667 (bg (get-keyword-value args #:bg "white"))
2668 (width (get-keyword-value args #:width 800))
2669 (height (get-keyword-value args #:height 100))
2674 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
2675 optargs)} module provides a set of powerful macros that you can use to
2676 implement keyword-supporting procedures like this:
2679 (use-modules (ice-9 optargs))
2681 (define (make-window . args)
2682 (let-keywords args #f ((depth screen-depth)
2690 Or, even more economically, like this:
2693 (use-modules (ice-9 optargs))
2695 (define* (make-window #:key (depth screen-depth)
2702 For further details on @code{let-keywords}, @code{define*} and other
2703 facilities provided by the @code{(ice-9 optargs)} module, @ref{Optional
2707 @node Keyword Read Syntax
2708 @subsection Keyword Read Syntax
2710 Guile, by default, only recognizes the keyword syntax specified by R5RS.
2711 A token of the form @code{#:NAME}, where @code{NAME} has the same syntax
2712 as a Scheme symbol, is the external representation of the keyword named
2713 @code{NAME}. Keyword objects print using this syntax as well, so values
2714 containing keyword objects can be read back into Guile. When used in an
2715 expression, keywords are self-quoting objects.
2717 If the @code{keyword} read option is set to @code{'prefix}, Guile also
2718 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
2719 of the form @code{:NAME} are read as symbols, as required by R5RS.
2721 To enable and disable the alternative non-R5RS keyword syntax, you use
2722 the @code{read-options} procedure documented in @ref{General option
2723 interface} and @ref{Reader options}.
2726 (read-set! keywords 'prefix)
2736 (read-set! keywords #f)
2744 ERROR: In expression :type:
2745 ERROR: Unbound variable: :type
2746 ABORT: (unbound-variable)
2749 @node Keyword Procedures
2750 @subsection Keyword Procedures
2752 @c FIXME::martin: Review me!
2754 The following procedures can be used for converting symbols to keywords
2757 @deffn procedure symbol->keyword sym
2758 Return a keyword with the same characters as in @var{sym}.
2761 @deffn procedure keyword->symbol kw
2762 Return a symbol with the same characters as in @var{kw}.
2766 @node Keyword Primitives
2767 @subsection Keyword Primitives
2769 Internally, a keyword is implemented as something like a tagged symbol,
2770 where the tag identifies the keyword as being self-evaluating, and the
2771 symbol, known as the keyword's @dfn{dash symbol} has the same name as
2772 the keyword name but prefixed by a single dash. For example, the
2773 keyword @code{#:name} has the corresponding dash symbol @code{-name}.
2775 Most keyword objects are constructed automatically by the reader when it
2776 reads a token beginning with @code{#:}. However, if you need to
2777 construct a keyword object programmatically, you can do so by calling
2778 @code{make-keyword-from-dash-symbol} with the corresponding dash symbol
2779 (as the reader does). The dash symbol for a keyword object can be
2780 retrieved using the @code{keyword-dash-symbol} procedure.
2782 @deffn primitive make-keyword-from-dash-symbol symbol
2783 Make a keyword object from a @var{symbol} that starts with a dash.
2786 @deffn primitive keyword? obj
2787 Return @code{#t} if the argument @var{obj} is a keyword, else
2791 @deffn primitive keyword-dash-symbol keyword
2792 Return the dash symbol for @var{keyword}.
2793 This is the inverse of @code{make-keyword-from-dash-symbol}.
2799 @c FIXME::martin: Review me!
2801 Pairs are used to combine two Scheme objects into one compound object.
2802 Hence the name: A pair stores a pair of objects.
2804 The data type @emph{pair} is extremely important in Scheme, just like in
2805 any other Lisp dialect. The reason is that pairs are not only used to
2806 make two values available as one object, but that pairs are used for
2807 constructing lists of values. Because lists are so important in Scheme,
2808 they are described in a section of their own (@pxref{Lists}).
2810 Pairs can literally get entered in source code or at the REPL, in the
2811 so-called @dfn{dotted list} syntax. This syntax consists of an opening
2812 parentheses, the first element of the pair, a dot, the second element
2813 and a closing parentheses. The following example shows how a pair
2814 consisting of the two numbers 1 and 2, and a pair containing the symbols
2815 @code{foo} and @code{bar} can be entered. It is very important to write
2816 the whitespace before and after the dot, because otherwise the Scheme
2817 parser whould not be able to figure out where to split the tokens.
2824 But beware, if you want to try out these examples, you have to
2825 @dfn{quote} the expressions. More information about quotation is
2826 available in the section (REFFIXME). The correct way to try these
2827 examples is as follows.
2838 A new pair is made by calling the procedure @code{cons} with two
2839 arguments. Then the argument values are stored into a newly allocated
2840 pair, and the pair is returned. The name @code{cons} stands for
2841 @emph{construct}. Use the procedure @code{pair?} to test whether a
2842 given Scheme object is a pair or not.
2845 @deffn primitive cons x y
2846 Return a newly allocated pair whose car is @var{x} and whose
2847 cdr is @var{y}. The pair is guaranteed to be different (in the
2848 sense of @code{eq?}) from every previously existing object.
2852 @deffn primitive pair? x
2853 Return @code{#t} if @var{x} is a pair; otherwise return
2857 The two parts of a pair are traditionally called @emph{car} and
2858 @emph{cdr}. They can be retrieved with procedures of the same name
2859 (@code{car} and @code{cdr}), and can be modified with the procedures
2860 @code{set-car!} and @code{set-cdr!}. Since a very common operation in
2861 Scheme programs is to access the car of a pair, or the car of the cdr of
2862 a pair, etc., the procedures called @code{caar}, @code{cadr} and so on
2863 are also predefined.
2867 @deffn primitive car pair
2868 @deffnx primitive cdr pair
2869 Return the car or the cdr of @var{pair}, respectively.
2872 @deffn primitive caar pair
2873 @deffnx primitive cadr pair @dots{}
2874 @deffnx primitive cdddar pair
2875 @deffnx primitive cddddr pair
2876 These procedures are compositions of @code{car} and @code{cdr}, where
2877 for example @code{caddr} could be defined by
2880 (define caddr (lambda (x) (car (cdr (cdr x)))))
2885 @deffn primitive set-car! pair value
2886 Stores @var{value} in the car field of @var{pair}. The value returned
2887 by @code{set-car!} is unspecified.
2891 @deffn primitive set-cdr! pair value
2892 Stores @var{value} in the cdr field of @var{pair}. The value returned
2893 by @code{set-cdr!} is unspecified.
2900 @c FIXME::martin: Review me!
2902 A very important data type in Scheme---as well as in all other Lisp
2903 dialects---is the data type @dfn{list}.@footnote{Strictly speaking,
2904 Scheme does not have a real datatype @emph{list}. Lists are made up of
2905 chained @emph{pairs}, and only exist by definition---a list is a chain
2906 of pairs which looks like a list.}
2908 This is the short definition of what a list is:
2912 Either the empty list @code{()},
2915 or a pair which has a list in its cdr.
2918 @c FIXME::martin: Describe the pair chaining in more detail.
2920 @c FIXME::martin: What is a proper, what an improper list?
2921 @c What is a circular list?
2923 @c FIXME::martin: Maybe steal some graphics from the Elisp reference
2927 * List Syntax:: Writing literal lists.
2928 * List Predicates:: Testing lists.
2929 * List Constructors:: Creating new lists.
2930 * List Selection:: Selecting from lists, getting their length.
2931 * Append/Reverse:: Appending and reversing lists.
2932 * List Modifification:: Modifying list structure.
2933 * List Searching:: Searching for list elements
2934 * List Mapping:: Applying procedures to lists.
2938 @subsection List Read Syntax
2940 @c FIXME::martin: Review me!
2942 The syntax for lists is an opening parentheses, then all the elements of
2943 the list (separated by whitespace) and finally a closing
2944 parentheses.@footnote{Note that there is no separation character between
2945 the list elements, like a comma or a semicolon.}.
2948 (1 2 3) ; @r{a list of the numbers 1, 2 and 3}
2949 ("foo" bar 3.1415) ; @r{a string, a symbol and a real number}
2950 () ; @r{the empty list}
2953 The last example needs a bit more explanation. A list with no elements,
2954 called the @dfn{empty list}, is special in some ways. It is used for
2955 terminating lists by storing it into the cdr of the last pair that makes
2956 up a list. An example will clear that up:
2967 This example also shows that lists have to be quoted (REFFIXME) when
2968 written, because they would otherwise be mistakingly taken as procedure
2969 applications (@pxref{Simple Invocation}).
2972 @node List Predicates
2973 @subsection List Predicates
2975 @c FIXME::martin: Review me!
2977 Often it is useful to test whether a given Scheme object is a list or
2978 not. List-processing procedures could use this information to test
2979 whether their input is valid, or they could do different things
2980 depending on the datatype of their arguments.
2983 @deffn primitive list? x
2984 Return @code{#t} iff @var{x} is a proper list, else @code{#f}.
2987 The predicate @code{null?} is often used in list-processing code to
2988 tell whether a given list has run out of elements. That is, a loop
2989 somehow deals with the elements of a list until the list satisfies
2990 @code{null?}. Then, teh algorithm terminates.
2993 @deffn primitive null? x
2994 Return @code{#t} iff @var{x} is the empty list, else @code{#f}.
2997 @node List Constructors
2998 @subsection List Constructors
3000 This section describes the procedures for constructing new lists.
3001 @code{list} simply returns a list where the elements are the arguments,
3002 @code{cons*} is similar, but the last argument is stored in the cdr of
3003 the last pair of the list.
3006 @deffn primitive list arg1 @dots{}
3007 Return a list containing @var{objs}, the arguments to
3011 @deffn primitive cons* arg1 arg2 @dots{}
3012 Like @code{list}, but the last arg provides the tail of the
3013 constructed list, returning @code{(cons @var{arg1} (cons
3014 @var{arg2} (cons @dots{} @var{argn})))}. Requires at least one
3015 argument. If given one argument, that argument is returned as
3016 result. This function is called @code{list*} in some other
3017 Schemes and in Common LISP.
3020 @deffn primitive list-copy lst
3021 Return a (newly-created) copy of @var{lst}.
3024 Note that @code{list-copy} only makes a copy of the pairs which make up
3025 the spine of the lists. The list elements are not copied, which means
3026 that modifying the elements of the new list also modyfies the elements
3027 of the old list. On the other hand, applying procedures like
3028 @code{set-cdr!} or @code{delv!} to the new list will not alter the old
3029 list. If you also need to copy the list elements (making a deep copy),
3030 use the procedure @code{copy-tree} (@pxref{Copying}).
3032 @node List Selection
3033 @subsection List Selection
3035 @c FIXME::martin: Review me!
3037 These procedures are used to get some information about a list, or to
3038 retrieve one or more elements of a list.
3041 @deffn primitive length lst
3042 Return the number of elements in list @var{lst}.
3045 @deffn primitive last-pair lst
3046 Return a pointer to the last pair in @var{lst}, signalling an error if
3047 @var{lst} is circular.
3051 @deffn primitive list-ref list k
3052 Return the @var{k}th element from @var{list}.
3056 @deffn primitive list-tail lst k
3057 @deffnx primitive list-cdr-ref lst k
3058 Return the "tail" of @var{lst} beginning with its @var{k}th element.
3059 The first element of the list is considered to be element 0.
3061 @code{list-tail} and @code{list-cdr-ref} are identical. It may help to
3062 think of @code{list-cdr-ref} as accessing the @var{k}th cdr of the list,
3063 or returning the results of cdring @var{k} times down @var{lst}.
3066 @deffn primitive list-head lst k
3067 Copy the first @var{k} elements from @var{lst} into a new list, and
3071 @node Append/Reverse
3072 @subsection Append and Reverse
3074 @c FIXME::martin: Review me!
3076 @code{append} and @code{append!} are used to concatenate two or more
3077 lists in order to form a new list. @code{reverse} and @code{reverse!}
3078 return lists with the same elements as their arguments, but in reverse
3079 order. The procedure variants with an @code{!} directly modify the
3080 pairs which form the list, whereas the other procedures create new
3081 pairs. This is why you should be careful when using the side-effecting
3085 @deffn primitive append . args
3086 Return a list consisting of the elements the lists passed as
3089 (append '(x) '(y)) @result{} (x y)
3090 (append '(a) '(b c d)) @result{} (a b c d)
3091 (append '(a (b)) '((c))) @result{} (a (b) (c))
3093 The resulting list is always newly allocated, except that it
3094 shares structure with the last list argument. The last
3095 argument may actually be any object; an improper list results
3096 if the last argument is not a proper list.
3098 (append '(a b) '(c . d)) @result{} (a b c . d)
3099 (append '() 'a) @result{} a
3103 @deffn primitive append! . lists
3104 A destructive version of @code{append} (@pxref{Pairs and
3105 lists,,,r5rs, The Revised^5 Report on Scheme}). The cdr field
3106 of each list's final pair is changed to point to the head of
3107 the next list, so no consing is performed. Return a pointer to
3112 @deffn primitive reverse lst
3113 Return a new list that contains the elements of @var{lst} but
3117 @c NJFIXME explain new_tail
3118 @deffn primitive reverse! lst [new_tail]
3119 A destructive version of @code{reverse} (@pxref{Pairs and lists,,,r5rs,
3120 The Revised^5 Report on Scheme}). The cdr of each cell in @var{lst} is
3121 modified to point to the previous list element. Return a pointer to the
3122 head of the reversed list.
3124 Caveat: because the list is modified in place, the tail of the original
3125 list now becomes its head, and the head of the original list now becomes
3126 the tail. Therefore, the @var{lst} symbol to which the head of the
3127 original list was bound now points to the tail. To ensure that the head
3128 of the modified list is not lost, it is wise to save the return value of
3132 @node List Modifification
3133 @subsection List Modification
3135 @c FIXME::martin: Review me!
3137 The following procedures modify existing list. @code{list-set!} and
3138 @code{list-cdr-set!} change which elements a list contains, the various
3139 deletion procedures @code{delq}, @code{delv} etc.
3141 @deffn primitive list-set! list k val
3142 Set the @var{k}th element of @var{list} to @var{val}.
3145 @deffn primitive list-cdr-set! list k val
3146 Set the @var{k}th cdr of @var{list} to @var{val}.
3149 @deffn primitive delq item lst
3150 Return a newly-created copy of @var{lst} with elements
3151 @code{eq?} to @var{item} removed. This procedure mirrors
3152 @code{memq}: @code{delq} compares elements of @var{lst} against
3153 @var{item} with @code{eq?}.
3156 @deffn primitive delv item lst
3157 Return a newly-created copy of @var{lst} with elements
3158 @code{eqv?} to @var{item} removed. This procedure mirrors
3159 @code{memv}: @code{delv} compares elements of @var{lst} against
3160 @var{item} with @code{eqv?}.
3163 @deffn primitive delete item lst
3164 Return a newly-created copy of @var{lst} with elements
3165 @code{equal?} to @var{item} removed. This procedure mirrors
3166 @code{member}: @code{delete} compares elements of @var{lst}
3167 against @var{item} with @code{equal?}.
3170 @deffn primitive delq! item lst
3171 @deffnx primitive delv! item lst
3172 @deffnx primitive delete! item lst
3173 These procedures are destructive versions of @code{delq}, @code{delv}
3174 and @code{delete}: they modify the pointers in the existing @var{lst}
3175 rather than creating a new list. Caveat evaluator: Like other
3176 destructive list functions, these functions cannot modify the binding of
3177 @var{lst}, and so cannot be used to delete the first element of
3178 @var{lst} destructively.
3181 @deffn primitive delq1! item lst
3182 Like @code{delq!}, but only deletes the first occurrence of
3183 @var{item} from @var{lst}. Tests for equality using
3184 @code{eq?}. See also @code{delv1!} and @code{delete1!}.
3187 @deffn primitive delv1! item lst
3188 Like @code{delv!}, but only deletes the first occurrence of
3189 @var{item} from @var{lst}. Tests for equality using
3190 @code{eqv?}. See also @code{delq1!} and @code{delete1!}.
3193 @deffn primitive delete1! item lst
3194 Like @code{delete!}, but only deletes the first occurrence of
3195 @var{item} from @var{lst}. Tests for equality using
3196 @code{equal?}. See also @code{delq1!} and @code{delv1!}.
3199 @node List Searching
3200 @subsection List Searching
3202 @c FIXME::martin: Review me!
3204 The following procedures search lists for particular elements. They use
3205 different comparison predicates for comparing list elements with the
3206 object to be seached. When they fail, they return @code{#f}, otherwise
3207 they return the sublist whose car is equal to the search object, where
3208 equality depends on the equality predicate used.
3211 @deffn primitive memq x lst
3212 Return the first sublist of @var{lst} whose car is @code{eq?}
3213 to @var{x} where the sublists of @var{lst} are the non-empty
3214 lists returned by @code{(list-tail @var{lst} @var{k})} for
3215 @var{k} less than the length of @var{lst}. If @var{x} does not
3216 occur in @var{lst}, then @code{#f} (not the empty list) is
3221 @deffn primitive memv x lst
3222 Return the first sublist of @var{lst} whose car is @code{eqv?}
3223 to @var{x} where the sublists of @var{lst} are the non-empty
3224 lists returned by @code{(list-tail @var{lst} @var{k})} for
3225 @var{k} less than the length of @var{lst}. If @var{x} does not
3226 occur in @var{lst}, then @code{#f} (not the empty list) is
3231 @deffn primitive member x lst
3232 Return the first sublist of @var{lst} whose car is
3233 @code{equal?} to @var{x} where the sublists of @var{lst} are
3234 the non-empty lists returned by @code{(list-tail @var{lst}
3235 @var{k})} for @var{k} less than the length of @var{lst}. If
3236 @var{x} does not occur in @var{lst}, then @code{#f} (not the
3237 empty list) is returned.
3240 [FIXME: is there any reason to have the `sloppy' functions available at
3241 high level at all? Maybe these docs should be relegated to a "Guile
3242 Internals" node or something. -twp]
3244 @deffn primitive sloppy-memq x lst
3245 This procedure behaves like @code{memq}, but does no type or error checking.
3246 Its use is recommended only in writing Guile internals,
3247 not for high-level Scheme programs.
3250 @deffn primitive sloppy-memv x lst
3251 This procedure behaves like @code{memv}, but does no type or error checking.
3252 Its use is recommended only in writing Guile internals,
3253 not for high-level Scheme programs.
3256 @deffn primitive sloppy-member x lst
3257 This procedure behaves like @code{member}, but does no type or error checking.
3258 Its use is recommended only in writing Guile internals,
3259 not for high-level Scheme programs.
3263 @subsection List Mapping
3265 @c FIXME::martin: Review me!
3267 List processing is very convenient in Scheme because the process of
3268 iterating over the elements of a list can be highly abstracted. The
3269 procedures in this section are the most basic iterating procedures for
3270 lists. They take a procedure and one or more lists as arguments, and
3271 apply the procedure to each element of the list. They differ in what
3272 the result of the invocation is.
3275 @c begin (texi-doc-string "guile" "map")
3276 @deffn primitive map proc arg1 arg2 @dots{}
3277 @deffnx primitive map-in-order proc arg1 arg2 @dots{}
3278 Apply @var{proc} to each element of the list @var{arg1} (if only two
3279 arguments are given), or to the corresponding elements of the argument
3280 lists (if more than two arguments are given). The result(s) of the
3281 procedure applications are saved and returned in a list. For
3282 @code{map}, the order of procedure applications is not specified,
3283 @code{map-in-order} applies the procedure from left to right to the list
3288 @c begin (texi-doc-string "guile" "for-each")
3289 @deffn primitive for-each proc arg1 arg2 @dots{}
3290 Like @code{map}, but the procedure is always applied from left to right,
3291 and the result(s) of the procedure applications are thrown away. The
3292 return value is not specified.
3299 @c FIXME::martin: Review me!
3301 @c FIXME::martin: Should the subsections of this section be nodes
3302 @c of their own, or are the resulting nodes too short, then?
3304 Vectors are sequences of Scheme objects. Unlike lists, the length of a
3305 vector, once the vector is created, cannot be changed. The advantage of
3306 vectors over lists is that the time required to access one element of a
3307 vector is constant, whereas lists have an access time linear to the
3308 index of the accessed element in the list.
3310 Note that the vectors documented in this section can contain any kind of
3311 Scheme object, it is even possible to have different types of objects in
3314 @subsection Vector Read Syntax
3316 Vectors can literally be entered in source code, just like strings,
3317 characters or some of the other data types. The read syntax for vectors
3318 is as follows: A sharp sign (@code{#}), followed by an opening
3319 parentheses, all elements of the vector in their respective read syntax,
3320 and finally a closing parentheses. The following are examples of the
3321 read syntax for vectors; where the first vector only contains numbers
3322 and the second three different object types: a string, a symbol and a
3323 number in hexidecimal notation.
3327 #("Hello" foo #xdeadbeef)
3330 @subsection Vector Predicates
3333 @deffn primitive vector? obj
3334 Return @code{#t} if @var{obj} is a vector, otherwise return
3338 @subsection Vector Constructors
3340 @rnindex make-vector
3341 @deffn primitive make-vector k [fill]
3342 Return a newly allocated vector of @var{k} elements. If a
3343 second argument is given, then each element is initialized to
3344 @var{fill}. Otherwise the initial contents of each element is
3349 @rnindex list->vector
3350 @deffn primitive vector . l
3351 @deffnx primitive list->vector l
3352 Return a newly allocated vector whose elements contain the
3353 given arguments. Analogous to @code{list}.
3356 (vector 'a 'b 'c) @result{} #(a b c)
3360 @rnindex vector->list
3361 @deffn primitive vector->list v
3362 Return a newly allocated list of the objects contained in the
3363 elements of @var{vector}.
3366 (vector->list '#(dah dah didah)) @result{} (dah dah didah)
3367 (list->vector '(dididit dah)) @result{} #(dididit dah)
3371 @subsection Vector Modification
3373 A vector created by any of the vector constructor procedures
3374 (@pxref{Vectors}) documented above can be modified using the
3375 following procedures.
3377 According to R5RS, using any of these procedures on literally entered
3378 vectors is an error, because these vectors are considered to be
3379 constant, although Guile currently does not detect this error.
3381 @rnindex vector-set!
3382 @deffn primitive vector-set! vector k obj
3383 @var{k} must be a valid index of @var{vector}.
3384 @code{Vector-set!} stores @var{obj} in element @var{k} of @var{vector}.
3385 The value returned by @samp{vector-set!} is unspecified.
3387 (let ((vec (vector 0 '(2 2 2 2) "Anna")))
3388 (vector-set! vec 1 '("Sue" "Sue"))
3389 vec) @result{} #(0 ("Sue" "Sue") "Anna")
3390 (vector-set! '#(0 1 2) 1 "doe") @result{} @emph{error} ; constant vector
3394 @rnindex vector-fill!
3395 @deffn primitive vector-fill! v fill
3396 Store @var{fill} in every element of @var{vector}. The value
3397 returned by @code{vector-fill!} is unspecified.
3400 @deffn primitive vector-move-left! vec1 start1 end1 vec2 start2
3401 Vector version of @code{substring-move-left!}.
3404 @deffn primitive vector-move-right! vec1 start1 end1 vec2 start2
3405 Vector version of @code{substring-move-right!}.
3408 @subsection Vector Selection
3410 These procedures return information about a given vector, such as the
3411 size or what elements are contained in the vector.
3413 @rnindex vector-length
3414 @deffn primitive vector-length vector
3415 Returns the number of elements in @var{vector} as an exact integer.
3419 @deffn primitive vector-ref vector k
3420 @var{k} must be a valid index of @var{vector}.
3421 @samp{Vector-ref} returns the contents of element @var{k} of
3424 (vector-ref '#(1 1 2 3 5 8 13 21) 5) @result{} 8
3425 (vector-ref '#(1 1 2 3 5 8 13 21)
3426 (let ((i (round (* 2 (acos -1)))))
3437 [FIXME: this is pasted in from Tom Lord's original guile.texi and should
3440 A @dfn{record type} is a first class object representing a user-defined
3441 data type. A @dfn{record} is an instance of a record type.
3443 @deffn procedure record? obj
3444 Returns @code{#t} if @var{obj} is a record of any type and @code{#f}
3447 Note that @code{record?} may be true of any Scheme value; there is no
3448 promise that records are disjoint with other Scheme types.
3451 @deffn procedure make-record-type type-name field-names
3452 Returns a @dfn{record-type descriptor}, a value representing a new data
3453 type disjoint from all others. The @var{type-name} argument must be a
3454 string, but is only used for debugging purposes (such as the printed
3455 representation of a record of the new type). The @var{field-names}
3456 argument is a list of symbols naming the @dfn{fields} of a record of the
3457 new type. It is an error if the list contains any duplicates. It is
3458 unspecified how record-type descriptors are represented.@refill
3461 @deffn procedure record-constructor rtd [field-names]
3462 Returns a procedure for constructing new members of the type represented
3463 by @var{rtd}. The returned procedure accepts exactly as many arguments
3464 as there are symbols in the given list, @var{field-names}; these are
3465 used, in order, as the initial values of those fields in a new record,
3466 which is returned by the constructor procedure. The values of any
3467 fields not named in that list are unspecified. The @var{field-names}
3468 argument defaults to the list of field names in the call to
3469 @code{make-record-type} that created the type represented by @var{rtd};
3470 if the @var{field-names} argument is provided, it is an error if it
3471 contains any duplicates or any symbols not in the default list.@refill
3474 @deffn procedure record-predicate rtd
3475 Returns a procedure for testing membership in the type represented by
3476 @var{rtd}. The returned procedure accepts exactly one argument and
3477 returns a true value if the argument is a member of the indicated record
3478 type; it returns a false value otherwise.@refill
3481 @deffn procedure record-accessor rtd field-name
3482 Returns a procedure for reading the value of a particular field of a
3483 member of the type represented by @var{rtd}. The returned procedure
3484 accepts exactly one argument which must be a record of the appropriate
3485 type; it returns the current value of the field named by the symbol
3486 @var{field-name} in that record. The symbol @var{field-name} must be a
3487 member of the list of field-names in the call to @code{make-record-type}
3488 that created the type represented by @var{rtd}.@refill
3491 @deffn procedure record-modifier rtd field-name
3492 Returns a procedure for writing the value of a particular field of a
3493 member of the type represented by @var{rtd}. The returned procedure
3494 accepts exactly two arguments: first, a record of the appropriate type,
3495 and second, an arbitrary Scheme value; it modifies the field named by
3496 the symbol @var{field-name} in that record to contain the given value.
3497 The returned value of the modifier procedure is unspecified. The symbol
3498 @var{field-name} must be a member of the list of field-names in the call
3499 to @code{make-record-type} that created the type represented by
3503 @deffn procedure record-type-descriptor record
3504 Returns a record-type descriptor representing the type of the given
3505 record. That is, for example, if the returned descriptor were passed to
3506 @code{record-predicate}, the resulting predicate would return a true
3507 value when passed the given record. Note that it is not necessarily the
3508 case that the returned descriptor is the one that was passed to
3509 @code{record-constructor} in the call that created the constructor
3510 procedure that created the given record.@refill
3513 @deffn procedure record-type-name rtd
3514 Returns the type-name associated with the type represented by rtd. The
3515 returned value is @code{eqv?} to the @var{type-name} argument given in
3516 the call to @code{make-record-type} that created the type represented by
3520 @deffn procedure record-type-fields rtd
3521 Returns a list of the symbols naming the fields in members of the type
3522 represented by @var{rtd}. The returned value is @code{equal?} to the
3523 field-names argument given in the call to @code{make-record-type} that
3524 created the type represented by @var{rtd}.@refill
3531 [FIXME: this is pasted in from Tom Lord's original guile.texi and should
3534 A @dfn{structure type} is a first class user-defined data type. A
3535 @dfn{structure} is an instance of a structure type. A structure type is
3538 Structures are less abstract and more general than traditional records.
3539 In fact, in Guile Scheme, records are implemented using structures.
3542 * Structure Concepts:: The structure of Structures
3543 * Structure Layout:: Defining the layout of structure types
3544 * Structure Basics:: make-, -ref and -set! procedures for structs
3545 * Vtables:: Accessing type-specific data
3548 @node Structure Concepts
3549 @subsection Structure Concepts
3551 A structure object consists of a handle, structure data, and a vtable.
3552 The handle is a Scheme value which points to both the vtable and the
3553 structure's data. Structure data is a dynamically allocated region of
3554 memory, private to the structure, divided up into typed fields. A
3555 vtable is another structure used to hold type-specific data. Multiple
3556 structures can share a common vtable.
3558 Three concepts are key to understanding structures.
3561 @item @dfn{layout specifications}
3563 Layout specifications determine how memory allocated to structures is
3564 divided up into fields. Programmers must write a layout specification
3565 whenever a new type of structure is defined.
3567 @item @dfn{structural accessors}
3569 Structure access is by field number. There is only one set of
3570 accessors common to all structure objects.
3574 Vtables, themselves structures, are first class representations of
3575 disjoint sub-types of structures in general. In most cases, when a
3576 new structure is created, programmers must specifiy a vtable for the
3577 new structure. Each vtable has a field describing the layout of its
3578 instances. Vtables can have additional, user-defined fields as well.
3583 @node Structure Layout
3584 @subsection Structure Layout
3586 When a structure is created, a region of memory is allocated to hold its
3587 state. The @dfn{layout} of the structure's type determines how that
3588 memory is divided into fields.
3590 Each field has a specified type. There are only three types allowed, each
3591 corresponding to a one letter code. The allowed types are:
3594 @item 'u' -- unprotected
3596 The field holds binary data that is not GC protected.
3598 @item 'p' -- protected
3600 The field holds a Scheme value and is GC protected.
3604 The field holds a Scheme value and is GC protected. When a structure is
3605 created with this type of field, the field is initialized to refer to
3606 the structure's own handle. This kind of field is mainly useful when
3607 mixing Scheme and C code in which the C code may need to compute a
3608 structure's handle given only the address of its malloced data.
3612 Each field also has an associated access protection. There are only
3613 three kinds of protection, each corresponding to a one letter code.
3614 The allowed protections are:
3617 @item 'w' -- writable
3619 The field can be read and written.
3621 @item 'r' -- readable
3623 The field can be read, but not written.
3627 The field can be neither read nor written. This kind
3628 of protection is for fields useful only to built-in routines.
3631 A layout specification is described by stringing together pairs
3632 of letters: one to specify a field type and one to specify a field
3633 protection. For example, a traditional cons pair type object could
3637 ; cons pairs have two writable fields of Scheme data
3641 A pair object in which the first field is held constant could be:
3647 Binary fields, (fields of type "u"), hold one @emph{word} each. The
3648 size of a word is a machine dependent value defined to be equal to the
3649 value of the C expression: @code{sizeof (long)}.
3651 The last field of a structure layout may specify a tail array.
3652 A tail array is indicated by capitalizing the field's protection
3653 code ('W', 'R' or 'O'). A tail-array field is replaced by
3654 a read-only binary data field containing an array size. The array
3655 size is determined at the time the structure is created. It is followed
3656 by a corresponding number of fields of the type specified for the
3657 tail array. For example, a conventional Scheme vector can be
3661 ; A vector is an arbitrary number of writable fields holding Scheme
3666 In the above example, field 0 contains the size of the vector and
3667 fields beginning at 1 contain the vector elements.
3669 A kind of tagged vector (a constant tag followed by conventioal
3670 vector elements) might be:
3677 Structure layouts are represented by specially interned symbols whose
3678 name is a string of type and protection codes. To create a new
3679 structure layout, use this procedure:
3681 @deffn primitive make-struct-layout fields
3682 Return a new structure layout object.
3684 @var{fields} must be a string made up of pairs of characters
3685 strung together. The first character of each pair describes a field
3686 type, the second a field protection. Allowed types are 'p' for
3687 GC-protected Scheme data, 'u' for unprotected binary data, and 's' for
3688 a field that points to the structure itself. Allowed protections
3689 are 'w' for mutable fields, 'r' for read-only fields, and 'o' for opaque
3690 fields. The last field protection specification may be capitalized to
3691 indicate that the field is a tail-array.
3696 @node Structure Basics
3697 @subsection Structure Basics
3699 This section describes the basic procedures for creating and accessing
3702 @deffn primitive make-struct vtable tail_array_size . init
3703 Create a new structure.
3705 @var{type} must be a vtable structure (@pxref{Vtables}).
3707 @var{tail-elts} must be a non-negative integer. If the layout
3708 specification indicated by @var{type} includes a tail-array,
3709 this is the number of elements allocated to that array.
3711 The @var{init1}, @dots{} are optional arguments describing how
3712 successive fields of the structure should be initialized. Only fields
3713 with protection 'r' or 'w' can be initialized, except for fields of
3714 type 's', which are automatically initialized to point to the new
3715 structure itself; fields with protection 'o' can not be initialized by
3718 If fewer optional arguments than initializable fields are supplied,
3719 fields of type 'p' get default value #f while fields of type 'u' are
3722 Structs are currently the basic representation for record-like data
3723 structures in Guile. The plan is to eventually replace them with a
3724 new representation which will at the same time be easier to use and
3727 For more information, see the documentation for @code{make-vtable-vtable}.
3730 @deffn primitive struct? x
3731 Return @code{#t} iff @var{obj} is a structure object, else
3736 @deffn primitive struct-ref handle pos
3737 @deffnx primitive struct-set! struct n value
3738 Access (or modify) the @var{n}th field of @var{struct}.
3740 If the field is of type 'p', then it can be set to an arbitrary value.
3742 If the field is of type 'u', then it can only be set to a non-negative
3743 integer value small enough to fit in one machine word.
3751 Vtables are structures that are used to represent structure types. Each
3752 vtable contains a layout specification in field
3753 @code{vtable-index-layout} -- instances of the type are laid out
3754 according to that specification. Vtables contain additional fields
3755 which are used only internally to libguile. The variable
3756 @code{vtable-offset-user} is bound to a field number. Vtable fields
3757 at that position or greater are user definable.
3759 @deffn primitive struct-vtable handle
3760 Return the vtable structure that describes the type of @var{struct}.
3763 @deffn primitive struct-vtable? x
3764 Return @code{#t} iff obj is a vtable structure.
3767 If you have a vtable structure, @code{V}, you can create an instance of
3768 the type it describes by using @code{(make-struct V ...)}. But where
3769 does @code{V} itself come from? One possibility is that @code{V} is an
3770 instance of a user-defined vtable type, @code{V'}, so that @code{V} is
3771 created by using @code{(make-struct V' ...)}. Another possibility is
3772 that @code{V} is an instance of the type it itself describes. Vtable
3773 structures of the second sort are created by this procedure:
3775 @deffn primitive make-vtable-vtable user_fields tail_array_size . init
3776 Return a new, self-describing vtable structure.
3778 @var{user-fields} is a string describing user defined fields of the
3779 vtable beginning at index @code{vtable-offset-user}
3780 (see @code{make-struct-layout}).
3782 @var{tail-size} specifies the size of the tail-array (if any) of
3785 @var{init1}, @dots{} are the optional initializers for the fields of
3788 Vtables have one initializable system field---the struct printer.
3789 This field comes before the user fields in the initializers passed
3790 to @code{make-vtable-vtable} and @code{make-struct}, and thus works as
3791 a third optional argument to @code{make-vtable-vtable} and a fourth to
3792 @code{make-struct} when creating vtables:
3794 If the value is a procedure, it will be called instead of the standard
3795 printer whenever a struct described by this vtable is printed.
3796 The procedure will be called with arguments STRUCT and PORT.
3798 The structure of a struct is described by a vtable, so the vtable is
3799 in essence the type of the struct. The vtable is itself a struct with
3800 a vtable. This could go on forever if it weren't for the
3801 vtable-vtables which are self-describing vtables, and thus terminate
3804 There are several potential ways of using structs, but the standard
3805 one is to use three kinds of structs, together building up a type
3806 sub-system: one vtable-vtable working as the root and one or several
3807 "types", each with a set of "instances". (The vtable-vtable should be
3808 compared to the class <class> which is the class of itself.)
3811 (define ball-root (make-vtable-vtable "pr" 0))
3813 (define (make-ball-type ball-color)
3814 (make-struct ball-root 0
3815 (make-struct-layout "pw")
3817 (format port "#<a ~A ball owned by ~A>"
3821 (define (color ball) (struct-ref (struct-vtable ball) vtable-offset-user))
3822 (define (owner ball) (struct-ref ball 0))
3824 (define red (make-ball-type 'red))
3825 (define green (make-ball-type 'green))
3827 (define (make-ball type owner) (make-struct type 0 owner))
3829 (define ball (make-ball green 'Nisse))
3830 ball @result{} #<a green ball owned by Nisse>
3834 @deffn primitive struct-vtable-name vtable
3835 Return the name of the vtable @var{vtable}.
3838 @deffn primitive set-struct-vtable-name! vtable name
3839 Set the name of the vtable @var{vtable} to @var{name}.
3842 @deffn primitive struct-vtable-tag handle
3843 Return the vtable tag of the structure @var{handle}.
3851 * Conventional Arrays:: Arrays with arbitrary data.
3852 * Array Mapping:: Applying a procedure to the contents of an array.
3853 * Uniform Arrays:: Arrays with data of a single type.
3854 * Bit Vectors:: Vectors of bits.
3857 @node Conventional Arrays
3858 @subsection Conventional Arrays
3860 @dfn{Conventional arrays} are a collection of cells organised into an
3861 arbitrary number of dimensions. Each cell can hold any kind of Scheme
3862 value and can be accessed in constant time by supplying an index for
3863 each dimension. This contrasts with uniform arrays, which use memory
3864 more efficiently but can hold data of only a single type, and lists
3865 where inserting and deleting cells is more efficient, but more time
3866 is usually required to access a particular cell.
3868 A conventional array is displayed as @code{#} followed by the @dfn{rank}
3869 (number of dimensions) followed by the cells, organised into dimensions
3870 using parentheses. The nesting depth of the parentheses is equal to
3873 When an array is created, the number of dimensions and range of each
3874 dimension must be specified, e.g., to create a 2x3 array with a
3878 (make-array 'ho 2 3) @result{}
3879 #2((ho ho ho) (ho ho ho))
3882 The range of each dimension can also be given explicitly, e.g., another
3883 way to create the same array:
3886 (make-array 'ho '(0 1) '(0 2)) @result{}
3887 #2((ho ho ho) (ho ho ho))
3890 A conventional array with one dimension based at zero is identical to
3894 (make-array 'ho 3) @result{}
3898 The following procedures can be used with conventional arrays (or vectors).
3900 @deffn primitive array? v [prot]
3901 Return @code{#t} if the @var{obj} is an array, and @code{#f} if
3902 not. The @var{prototype} argument is used with uniform arrays
3903 and is described elsewhere.
3906 @deffn procedure make-array initial-value bound1 bound2 @dots{}
3907 Creates and returns an array that has as many dimensions as there are
3908 @var{bound}s and fills it with @var{initial-value}.
3911 @c array-ref's type is `compiled-closure'. There's some weird stuff
3912 @c going on in array.c, too. Let's call it a primitive. -twp
3914 @deffn primitive uniform-vector-ref v args
3915 @deffnx primitive array-ref v . args
3916 Return the element at the @code{(index1, index2)} element in
3920 @deffn primitive array-in-bounds? v . args
3921 Return @code{#t} if its arguments would be acceptable to
3925 @deffn primitive array-set! v obj . args
3926 @deffnx primitive uniform-array-set1! v obj args
3927 Sets the element at the @code{(index1, index2)} element in @var{array} to
3928 @var{new-value}. The value returned by array-set! is unspecified.
3931 @deffn primitive make-shared-array oldra mapfunc . dims
3932 @code{make-shared-array} can be used to create shared subarrays of other
3933 arrays. The @var{mapper} is a function that translates coordinates in
3934 the new array into coordinates in the old array. A @var{mapper} must be
3935 linear, and its range must stay within the bounds of the old array, but
3936 it can be otherwise arbitrary. A simple example:
3938 (define fred (make-array #f 8 8))
3939 (define freds-diagonal
3940 (make-shared-array fred (lambda (i) (list i i)) 8))
3941 (array-set! freds-diagonal 'foo 3)
3942 (array-ref fred 3 3) @result{} foo
3943 (define freds-center
3944 (make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j))) 2 2))
3945 (array-ref freds-center 0 0) @result{} foo
3949 @deffn primitive shared-array-increments ra
3950 For each dimension, return the distance between elements in the root vector.
3953 @deffn primitive shared-array-offset ra
3954 Return the root vector index of the first element in the array.
3957 @deffn primitive shared-array-root ra
3958 Return the root vector of a shared array.
3961 @deffn primitive transpose-array ra . args
3962 Return an array sharing contents with @var{array}, but with
3963 dimensions arranged in a different order. There must be one
3964 @var{dim} argument for each dimension of @var{array}.
3965 @var{dim0}, @var{dim1}, @dots{} should be integers between 0
3966 and the rank of the array to be returned. Each integer in that
3967 range must appear at least once in the argument list.
3969 The values of @var{dim0}, @var{dim1}, @dots{} correspond to
3970 dimensions in the array to be returned, their positions in the
3971 argument list to dimensions of @var{array}. Several @var{dim}s
3972 may have the same value, in which case the returned array will
3973 have smaller rank than @var{array}.
3976 (transpose-array '#2((a b) (c d)) 1 0) @result{} #2((a c) (b d))
3977 (transpose-array '#2((a b) (c d)) 0 0) @result{} #1(a d)
3978 (transpose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 1 0) @result{}
3979 #2((a 4) (b 5) (c 6))
3983 @deffn primitive enclose-array ra . axes
3984 @var{dim0}, @var{dim1} @dots{} should be nonnegative integers less than
3985 the rank of @var{array}. @var{enclose-array} returns an array
3986 resembling an array of shared arrays. The dimensions of each shared
3987 array are the same as the @var{dim}th dimensions of the original array,
3988 the dimensions of the outer array are the same as those of the original
3989 array that did not match a @var{dim}.
3991 An enclosed array is not a general Scheme array. Its elements may not
3992 be set using @code{array-set!}. Two references to the same element of
3993 an enclosed array will be @code{equal?} but will not in general be
3994 @code{eq?}. The value returned by @var{array-prototype} when given an
3995 enclosed array is unspecified.
3999 (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1) @result{}
4000 #<enclosed-array (#1(a d) #1(b e) #1(c f)) (#1(1 4) #1(2 5) #1(3 6))>
4002 (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 0) @result{}
4003 #<enclosed-array #2((a 1) (d 4)) #2((b 2) (e 5)) #2((c 3) (f 6))>
4007 @deffn procedure array-shape array
4008 Returns a list of inclusive bounds of integers.
4010 (array-shape (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) (0 4))
4014 @deffn primitive array-dimensions ra
4015 @code{Array-dimensions} is similar to @code{array-shape} but replaces
4016 elements with a @code{0} minimum with one greater than the maximum. So:
4018 (array-dimensions (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) 5)
4022 @deffn primitive array-rank ra
4023 Return the number of dimensions of @var{obj}. If @var{obj} is
4024 not an array, @code{0} is returned.
4027 @deffn primitive array->list v
4028 Return a list consisting of all the elements, in order, of
4032 @deffn primitive array-copy! src dst
4033 @deffnx primitive array-copy-in-order! src dst
4034 Copies every element from vector or array @var{source} to the
4035 corresponding element of @var{destination}. @var{destination} must have
4036 the same rank as @var{source}, and be at least as large in each
4037 dimension. The order is unspecified.
4040 @deffn primitive array-fill! ra fill
4041 Stores @var{fill} in every element of @var{array}. The value returned
4045 @c begin (texi-doc-string "guile" "array-equal?")
4046 @deffn primitive array-equal? ra0 ra1
4047 Returns @code{#t} iff all arguments are arrays with the same shape, the
4048 same type, and have corresponding elements which are either
4049 @code{equal?} or @code{array-equal?}. This function differs from
4050 @code{equal?} in that a one dimensional shared array may be
4051 @var{array-equal?} but not @var{equal?} to a vector or uniform vector.
4054 @deffn primitive array-contents ra [strict]
4055 @deffnx primitive array-contents array strict
4056 If @var{array} may be @dfn{unrolled} into a one dimensional shared array
4057 without changing their order (last subscript changing fastest), then
4058 @code{array-contents} returns that shared array, otherwise it returns
4059 @code{#f}. All arrays made by @var{make-array} and
4060 @var{make-uniform-array} may be unrolled, some arrays made by
4061 @var{make-shared-array} may not be.
4063 If the optional argument @var{strict} is provided, a shared array will
4064 be returned only if its elements are stored internally contiguous in
4069 @subsection Array Mapping
4071 @deffn primitive array-map! ra0 proc . lra
4072 @deffnx primitive array-map-in-order! ra0 proc . lra
4073 @var{array1}, @dots{} must have the same number of dimensions as
4074 @var{array0} and have a range for each index which includes the range
4075 for the corresponding index in @var{array0}. @var{proc} is applied to
4076 each tuple of elements of @var{array1} @dots{} and the result is stored
4077 as the corresponding element in @var{array0}. The value returned is
4078 unspecified. The order of application is unspecified.
4081 @deffn primitive array-for-each proc ra0 . lra
4082 @var{proc} is applied to each tuple of elements of @var{array0} @dots{}
4083 in row-major order. The value returned is unspecified.
4086 @deffn primitive array-index-map! ra proc
4087 applies @var{proc} to the indices of each element of @var{array} in
4088 turn, storing the result in the corresponding element. The value
4089 returned and the order of application are unspecified.
4091 One can implement @var{array-indexes} as
4093 (define (array-indexes array)
4094 (let ((ra (apply make-array #f (array-shape array))))
4095 (array-index-map! ra (lambda x x))
4100 (define (apl:index-generator n)
4101 (let ((v (make-uniform-vector n 1)))
4102 (array-index-map! v (lambda (i) i))
4107 @node Uniform Arrays
4108 @subsection Uniform Arrays
4111 @dfn{Uniform arrays} have elements all of the
4112 same type and occupy less storage than conventional
4113 arrays. Uniform arrays with a single zero-based dimension
4114 are also known as @dfn{uniform vectors}. The procedures in
4115 this section can also be used on conventional arrays, vectors,
4116 bit-vectors and strings.
4119 When creating a uniform array, the type of data to be stored
4120 is indicated with a @var{prototype} argument. The following table
4121 lists the types available and example prototypes:
4124 prototype type printing character
4126 #t boolean (bit-vector) b
4128 #\nul byte (integer) y
4129 's short (integer) h
4130 1 unsigned long (integer) u
4131 -1 signed long (integer) e
4132 'l signed long long (integer) l
4133 1.0 float (single precision) s
4134 1/3 double (double precision float) i
4135 0+i complex (double precision) c
4136 () conventional vector
4140 Unshared uniform arrays of characters with a single zero-based dimension
4141 are identical to strings:
4144 (make-uniform-array #\a 3) @result{}
4149 Unshared uniform arrays of booleans with a single zero-based dimension
4150 are identical to @ref{Bit Vectors, bit-vectors}.
4153 (make-uniform-array #t 3) @result{}
4158 Other uniform vectors are written in a form similar to that of vectors,
4159 except that a single character from the above table is put between
4160 @code{#} and @code{(}. For example, a uniform vector of signed
4161 long integers is displayed in the form @code{'#e(3 5 9)}.
4163 @deffn primitive array? v [prot]
4164 Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not.
4166 The @var{prototype} argument is used with uniform arrays and is described
4170 @deffn procedure make-uniform-array prototype bound1 bound2 @dots{}
4171 Creates and returns a uniform array of type corresponding to
4172 @var{prototype} that has as many dimensions as there are @var{bound}s
4173 and fills it with @var{prototype}.
4176 @deffn primitive array-prototype ra
4177 Return an object that would produce an array of the same type
4178 as @var{array}, if used as the @var{prototype} for
4179 @code{make-uniform-array}.
4182 @deffn primitive list->uniform-array ndim prot lst
4183 @deffnx procedure list->uniform-vector prot lst
4184 Return a uniform array of the type indicated by prototype
4185 @var{prot} with elements the same as those of @var{lst}.
4186 Elements must be of the appropriate type, no coercions are
4190 @deffn primitive uniform-vector-fill! uve fill
4191 Stores @var{fill} in every element of @var{uve}. The value returned is
4195 @deffn primitive uniform-vector-length v
4196 Return the number of elements in @var{uve}.
4199 @deffn primitive dimensions->uniform-array dims prot [fill]
4200 @deffnx primitive make-uniform-vector length prototype [fill]
4201 Create and return a uniform array or vector of type
4202 corresponding to @var{prototype} with dimensions @var{dims} or
4203 length @var{length}. If @var{fill} is supplied, it's used to
4204 fill the array, otherwise @var{prototype} is used.
4207 @c Another compiled-closure. -twp
4209 @deffn primitive uniform-array-read! ra [port_or_fd [start [end]]]
4210 @deffnx primitive uniform-vector-read! uve [port-or-fdes] [start] [end]
4211 Attempts to read all elements of @var{ura}, in lexicographic order, as
4212 binary objects from @var{port-or-fdes}.
4213 If an end of file is encountered during
4214 uniform-array-read! the objects up to that point only are put into @var{ura}
4215 (starting at the beginning) and the remainder of the array is
4218 The optional arguments @var{start} and @var{end} allow
4219 a specified region of a vector (or linearized array) to be read,
4220 leaving the remainder of the vector unchanged.
4222 @code{uniform-array-read!} returns the number of objects read.
4223 @var{port-or-fdes} may be omitted, in which case it defaults to the value
4224 returned by @code{(current-input-port)}.
4227 @deffn primitive uniform-array-write v [port_or_fd [start [end]]]
4228 @deffnx primitive uniform-vector-write uve [port-or-fdes] [start] [end]
4229 Writes all elements of @var{ura} as binary objects to
4232 The optional arguments @var{start}
4234 a specified region of a vector (or linearized array) to be written.
4236 The number of objects actually written is returned.
4237 @var{port-or-fdes} may be
4238 omitted, in which case it defaults to the value returned by
4239 @code{(current-output-port)}.
4243 @subsection Bit Vectors
4246 Bit vectors are a specific type of uniform array: an array of booleans
4247 with a single zero-based index.
4250 They are displayed as a sequence of @code{0}s and
4251 @code{1}s prefixed by @code{#*}, e.g.,
4254 (make-uniform-vector 8 #t #f) @result{}
4257 #b(#t #f #t) @result{}
4261 @deffn primitive bit-count b bitvector
4262 Return the number of occurrences of the boolean @var{b} in
4266 @deffn primitive bit-position item v k
4267 Return the minimum index of an occurrence of @var{bool} in
4268 @var{bv} which is at least @var{k}. If no @var{bool} occurs
4269 within the specified range @code{#f} is returned.
4272 @deffn primitive bit-invert! v
4273 Modifies @var{bv} by replacing each element with its negation.
4276 @deffn primitive bit-set*! v kv obj
4277 If uve is a bit-vector @var{bv} and uve must be of the same
4278 length. If @var{bool} is @code{#t}, uve is OR'ed into
4279 @var{bv}; If @var{bool} is @code{#f}, the inversion of uve is
4280 AND'ed into @var{bv}.
4282 If uve is a unsigned long integer vector all the elements of uve
4283 must be between 0 and the @code{length} of @var{bv}. The bits
4284 of @var{bv} corresponding to the indexes in uve are set to
4285 @var{bool}. The return value is unspecified.
4288 @deffn primitive bit-count* v kv obj
4291 (bit-count (bit-set*! (if bool bv (bit-invert! bv)) uve #t) #t).
4293 @var{bv} is not modified.
4297 @node Association Lists and Hash Tables
4298 @section Association Lists and Hash Tables
4300 This chapter discusses dictionary objects: data structures that are
4301 useful for organizing and indexing large bodies of information.
4304 * Dictionary Types:: About dictionary types; what they're good for.
4305 * Association Lists::
4309 @node Dictionary Types
4310 @subsection Dictionary Types
4312 A @dfn{dictionary} object is a data structure used to index
4313 information in a user-defined way. In standard Scheme, the main
4314 aggregate data types are lists and vectors. Lists are not really
4315 indexed at all, and vectors are indexed only by number
4316 (e.g. @code{(vector-ref foo 5)}). Often you will find it useful
4317 to index your data on some other type; for example, in a library
4318 catalog you might want to look up a book by the name of its
4319 author. Dictionaries are used to help you organize information in
4322 An @dfn{association list} (or @dfn{alist} for short) is a list of
4323 key-value pairs. Each pair represents a single quantity or
4324 object; the @code{car} of the pair is a key which is used to
4325 identify the object, and the @code{cdr} is the object's value.
4327 A @dfn{hash table} also permits you to index objects with
4328 arbitrary keys, but in a way that makes looking up any one object
4329 extremely fast. A well-designed hash system makes hash table
4330 lookups almost as fast as conventional array or vector references.
4332 Alists are popular among Lisp programmers because they use only
4333 the language's primitive operations (lists, @dfn{car}, @dfn{cdr}
4334 and the equality primitives). No changes to the language core are
4335 necessary. Therefore, with Scheme's built-in list manipulation
4336 facilities, it is very convenient to handle data stored in an
4337 association list. Also, alists are highly portable and can be
4338 easily implemented on even the most minimal Lisp systems.
4340 However, alists are inefficient, especially for storing large
4341 quantities of data. Because we want Guile to be useful for large
4342 software systems as well as small ones, Guile provides a rich set
4343 of tools for using either association lists or hash tables.
4345 @node Association Lists
4346 @subsection Association Lists
4347 @cindex Association List
4351 An association list is a conventional data structure that is often used
4352 to implement simple key-value databases. It consists of a list of
4353 entries in which each entry is a pair. The @dfn{key} of each entry is
4354 the @code{car} of the pair and the @dfn{value} of each entry is the
4358 ASSOCIATION LIST ::= '( (KEY1 . VALUE1)
4366 Association lists are also known, for short, as @dfn{alists}.
4368 The structure of an association list is just one example of the infinite
4369 number of possible structures that can be built using pairs and lists.
4370 As such, the keys and values in an association list can be manipulated
4371 using the general list structure procedures @code{cons}, @code{car},
4372 @code{cdr}, @code{set-car!}, @code{set-cdr!} and so on. However,
4373 because association lists are so useful, Guile also provides specific
4374 procedures for manipulating them.
4377 * Alist Key Equality::
4378 * Adding or Setting Alist Entries::
4379 * Retrieving Alist Entries::
4380 * Removing Alist Entries::
4381 * Sloppy Alist Functions::
4385 @node Alist Key Equality
4386 @subsubsection Alist Key Equality
4388 All of Guile's dedicated association list procedures, apart from
4389 @code{acons}, come in three flavours, depending on the level of equality
4390 that is required to decide whether an existing key in the association
4391 list is the same as the key that the procedure call uses to identify the
4396 Procedures with @dfn{assq} in their name use @code{eq?} to determine key
4400 Procedures with @dfn{assv} in their name use @code{eqv?} to determine
4404 Procedures with @dfn{assoc} in their name use @code{equal?} to
4405 determine key equality.
4408 @code{acons} is an exception because it is used to build association
4409 lists which do not require their entries' keys to be unique.
4411 @node Adding or Setting Alist Entries
4412 @subsubsection Adding or Setting Alist Entries
4414 @code{acons} adds a new entry to an association list and returns the
4415 combined association list. The combined alist is formed by consing the
4416 new entry onto the head of the alist specified in the @code{acons}
4417 procedure call. So the specified alist is not modified, but its
4418 contents become shared with the tail of the combined alist that
4419 @code{acons} returns.
4421 In the most common usage of @code{acons}, a variable holding the
4422 original association list is updated with the combined alist:
4425 (set! address-list (acons name address address-list))
4428 In such cases, it doesn't matter that the old and new values of
4429 @code{address-list} share some of their contents, since the old value is
4430 usually no longer independently accessible.
4432 Note that @code{acons} adds the specified new entry regardless of
4433 whether the alist may already contain entries with keys that are, in
4434 some sense, the same as that of the new entry. Thus @code{acons} is
4435 ideal for building alists where there is no concept of key uniqueness.
4438 (set! task-list (acons 3 "pay gas bill" '()))
4441 ((3 . "pay gas bill"))
4443 (set! task-list (acons 3 "tidy bedroom" task-list))
4446 ((3 . "tidy bedroom") (3 . "pay gas bill"))
4449 @code{assq-set!}, @code{assv-set!} and @code{assoc-set!} are used to add
4450 or replace an entry in an association list where there @emph{is} a
4451 concept of key uniqueness. If the specified association list already
4452 contains an entry whose key is the same as that specified in the
4453 procedure call, the existing entry is replaced by the new one.
4454 Otherwise, the new entry is consed onto the head of the old association
4455 list to create the combined alist. In all cases, these procedures
4456 return the combined alist.
4458 @code{assq-set!} and friends @emph{may} destructively modify the
4459 structure of the old association list in such a way that an existing
4460 variable is correctly updated without having to @code{set!} it to the
4466 (("mary" . "34 Elm Road") ("james" . "16 Bow Street"))
4468 (assoc-set! address-list "james" "1a London Road")
4470 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4474 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4480 (assoc-set! address-list "bob" "11 Newington Avenue")
4482 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4483 ("james" . "1a London Road"))
4487 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4490 The only safe way to update an association list variable when adding or
4491 replacing an entry like this is to @code{set!} the variable to the
4496 (assoc-set! address-list "bob" "11 Newington Avenue"))
4499 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4500 ("james" . "1a London Road"))
4503 Because of this slight inconvenience, you may find it more convenient to
4504 use hash tables to store dictionary data. If your application will not
4505 be modifying the contents of an alist very often, this may not make much
4508 If you need to keep the old value of an association list in a form
4509 independent from the list that results from modification by
4510 @code{acons}, @code{assq-set!}, @code{assv-set!} or @code{assoc-set!},
4511 use @code{list-copy} to copy the old association list before modifying
4514 @deffn primitive acons key value alist
4515 Adds a new key-value pair to @var{alist}. A new pair is
4516 created whose car is @var{key} and whose cdr is @var{value}, and the
4517 pair is consed onto @var{alist}, and the new list is returned. This
4518 function is @emph{not} destructive; @var{alist} is not modified.
4521 @deffn primitive assq-set! alist key val
4522 @deffnx primitive assv-set! alist key value
4523 @deffnx primitive assoc-set! alist key value
4524 Reassociate @var{key} in @var{alist} with @var{value}: find any existing
4525 @var{alist} entry for @var{key} and associate it with the new
4526 @var{value}. If @var{alist} does not contain an entry for @var{key},
4527 add a new one. Return the (possibly new) alist.
4529 These functions do not attempt to verify the structure of @var{alist},
4530 and so may cause unusual results if passed an object that is not an
4534 @node Retrieving Alist Entries
4535 @subsubsection Retrieving Alist Entries
4540 @code{assq}, @code{assv} and @code{assoc} take an alist and a key as
4541 arguments and return the entry for that key if an entry exists, or
4542 @code{#f} if there is no entry for that key. Note that, in the cases
4543 where an entry exists, these procedures return the complete entry, that
4544 is @code{(KEY . VALUE)}, not just the value.
4546 @deffn primitive assq key alist
4547 @deffnx primitive assv key alist
4548 @deffnx primitive assoc key alist
4549 Fetches the entry in @var{alist} that is associated with @var{key}. To
4550 decide whether the argument @var{key} matches a particular entry in
4551 @var{alist}, @code{assq} compares keys with @code{eq?}, @code{assv}
4552 uses @code{eqv?} and @code{assoc} uses @code{equal?}. If @var{key}
4553 cannot be found in @var{alist} (according to whichever equality
4554 predicate is in use), then @code{#f} is returned. These functions
4555 return the entire alist entry found (i.e. both the key and the value).
4558 @code{assq-ref}, @code{assv-ref} and @code{assoc-ref}, on the other
4559 hand, take an alist and a key and return @emph{just the value} for that
4560 key, if an entry exists. If there is no entry for the specified key,
4561 these procedures return @code{#f}.
4563 This creates an ambiguity: if the return value is @code{#f}, it means
4564 either that there is no entry with the specified key, or that there
4565 @emph{is} an entry for the specified key, with value @code{#f}.
4566 Consequently, @code{assq-ref} and friends should only be used where it
4567 is known that an entry exists, or where the ambiguity doesn't matter
4568 for some other reason.
4570 @deffn primitive assq-ref alist key
4571 @deffnx primitive assv-ref alist key
4572 @deffnx primitive assoc-ref alist key
4573 Like @code{assq}, @code{assv} and @code{assoc}, except that only the
4574 value associated with @var{key} in @var{alist} is returned. These
4575 functions are equivalent to
4578 (let ((ent (@var{associator} @var{key} @var{alist})))
4579 (and ent (cdr ent)))
4582 where @var{associator} is one of @code{assq}, @code{assv} or @code{assoc}.
4585 @node Removing Alist Entries
4586 @subsubsection Removing Alist Entries
4588 To remove the element from an association list whose key matches a
4589 specified key, use @code{assq-remove!}, @code{assv-remove!} or
4590 @code{assoc-remove!} (depending, as usual, on the level of equality
4591 required between the key that you specify and the keys in the
4594 As with @code{assq-set!} and friends, the specified alist may or may not
4595 be modified destructively, and the only safe way to update a variable
4596 containing the alist is to @code{set!} it to the value that
4597 @code{assq-remove!} and friends return.
4602 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4603 ("james" . "1a London Road"))
4605 (set! address-list (assoc-remove! address-list "mary"))
4608 (("bob" . "11 Newington Avenue") ("james" . "1a London Road"))
4611 Note that, when @code{assq/v/oc-remove!} is used to modify an
4612 association list that has been constructed only using the corresponding
4613 @code{assq/v/oc-set!}, there can be at most one matching entry in the
4614 alist, so the question of multiple entries being removed in one go does
4615 not arise. If @code{assq/v/oc-remove!} is applied to an association
4616 list that has been constructed using @code{acons}, or an
4617 @code{assq/v/oc-set!} with a different level of equality, or any mixture
4618 of these, it removes only the first matching entry from the alist, even
4619 if the alist might contain further matching entries. For example:
4622 (define address-list '())
4623 (set! address-list (assq-set! address-list "mary" "11 Elm Street"))
4624 (set! address-list (assq-set! address-list "mary" "57 Pine Drive"))
4627 (("mary" . "57 Pine Drive") ("mary" . "11 Elm Street"))
4629 (set! address-list (assoc-remove! address-list "mary"))
4632 (("mary" . "11 Elm Street"))
4635 In this example, the two instances of the string "mary" are not the same
4636 when compared using @code{eq?}, so the two @code{assq-set!} calls add
4637 two distinct entries to @code{address-list}. When compared using
4638 @code{equal?}, both "mary"s in @code{address-list} are the same as the
4639 "mary" in the @code{assoc-remove!} call, but @code{assoc-remove!} stops
4640 after removing the first matching entry that it finds, and so one of the
4641 "mary" entries is left in place.
4643 @deffn primitive assq-remove! alist key
4644 @deffnx primitive assv-remove! alist key
4645 @deffnx primitive assoc-remove! alist key
4646 Delete the first entry in @var{alist} associated with @var{key}, and return
4647 the resulting alist.
4650 @node Sloppy Alist Functions
4651 @subsubsection Sloppy Alist Functions
4653 @code{sloppy-assq}, @code{sloppy-assv} and @code{sloppy-assoc} behave
4654 like the corresponding non-@code{sloppy-} procedures, except that they
4655 return @code{#f} when the specified association list is not well-formed,
4656 where the non-@code{sloppy-} versions would signal an error.
4658 Specifically, there are two conditions for which the non-@code{sloppy-}
4659 procedures signal an error, which the @code{sloppy-} procedures handle
4660 instead by returning @code{#f}. Firstly, if the specified alist as a
4661 whole is not a proper list:
4664 (assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
4666 ERROR: In procedure assoc in expression (assoc "mary" (quote #)):
4667 ERROR: Wrong type argument in position 2 (expecting NULLP): "open sesame"
4668 ABORT: (wrong-type-arg)
4670 (sloppy-assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
4676 Secondly, if one of the entries in the specified alist is not a pair:
4679 (assoc 2 '((1 . 1) 2 (3 . 9)))
4681 ERROR: In procedure assoc in expression (assoc 2 (quote #)):
4682 ERROR: Wrong type argument in position 2 (expecting CONSP): 2
4683 ABORT: (wrong-type-arg)
4685 (sloppy-assoc 2 '((1 . 1) 2 (3 . 9)))
4690 Unless you are explicitly working with badly formed association lists,
4691 it is much safer to use the non-@code{sloppy-} procedures, because they
4692 help to highlight coding and data errors that the @code{sloppy-}
4693 versions would silently cover up.
4695 @deffn primitive sloppy-assq key alist
4696 Behaves like @code{assq} but does not do any error checking.
4697 Recommended only for use in Guile internals.
4700 @deffn primitive sloppy-assv key alist
4701 Behaves like @code{assv} but does not do any error checking.
4702 Recommended only for use in Guile internals.
4705 @deffn primitive sloppy-assoc key alist
4706 Behaves like @code{assoc} but does not do any error checking.
4707 Recommended only for use in Guile internals.
4711 @subsubsection Alist Example
4713 Here is a longer example of how alists may be used in practice.
4716 (define capitals '(("New York" . "Albany")
4717 ("Oregon" . "Salem")
4718 ("Florida" . "Miami")))
4720 ;; What's the capital of Oregon?
4721 (assoc "Oregon" capitals) @result{} ("Oregon" . "Salem")
4722 (assoc-ref capitals "Oregon") @result{} "Salem"
4724 ;; We left out South Dakota.
4726 (assoc-set! capitals "South Dakota" "Bismarck"))
4728 @result{} (("South Dakota" . "Bismarck")
4729 ("New York" . "Albany")
4730 ("Oregon" . "Salem")
4731 ("Florida" . "Miami"))
4733 ;; And we got Florida wrong.
4735 (assoc-set! capitals "Florida" "Tallahassee"))
4737 @result{} (("South Dakota" . "Bismarck")
4738 ("New York" . "Albany")
4739 ("Oregon" . "Salem")
4740 ("Florida" . "Tallahassee"))
4742 ;; After Oregon secedes, we can remove it.
4744 (assoc-remove! capitals "Oregon"))
4746 @result{} (("South Dakota" . "Bismarck")
4747 ("New York" . "Albany")
4748 ("Florida" . "Tallahassee"))
4752 @subsection Hash Tables
4754 Like the association list functions, the hash table functions come
4755 in several varieties: @code{hashq}, @code{hashv}, and @code{hash}.
4756 The @code{hashq} functions use @code{eq?} to determine whether two
4757 keys match. The @code{hashv} functions use @code{eqv?}, and the
4758 @code{hash} functions use @code{equal?}.
4760 In each of the functions that follow, the @var{table} argument
4761 must be a vector. The @var{key} and @var{value} arguments may be
4764 @deffn primitive hashq-ref table key [dflt]
4765 Look up @var{key} in the hash table @var{table}, and return the
4766 value (if any) associated with it. If @var{key} is not found,
4767 return @var{default} (or @code{#f} if no @var{default} argument
4768 is supplied). Uses @code{eq?} for equality testing.
4771 @deffn primitive hashv-ref table key [dflt]
4772 Look up @var{key} in the hash table @var{table}, and return the
4773 value (if any) associated with it. If @var{key} is not found,
4774 return @var{default} (or @code{#f} if no @var{default} argument
4775 is supplied). Uses @code{eqv?} for equality testing.
4778 @deffn primitive hash-ref table key [dflt]
4779 Look up @var{key} in the hash table @var{table}, and return the
4780 value (if any) associated with it. If @var{key} is not found,
4781 return @var{default} (or @code{#f} if no @var{default} argument
4782 is supplied). Uses @code{equal?} for equality testing.
4785 @deffn primitive hashq-set! table key val
4786 Find the entry in @var{table} associated with @var{key}, and
4787 store @var{value} there. Uses @code{eq?} for equality testing.
4790 @deffn primitive hashv-set! table key val
4791 Find the entry in @var{table} associated with @var{key}, and
4792 store @var{value} there. Uses @code{eqv?} for equality testing.
4795 @deffn primitive hash-set! table key val
4796 Find the entry in @var{table} associated with @var{key}, and
4797 store @var{value} there. Uses @code{equal?} for equality
4801 @deffn primitive hashq-remove! table key
4802 Remove @var{key} (and any value associated with it) from
4803 @var{table}. Uses @code{eq?} for equality tests.
4806 @deffn primitive hashv-remove! table key
4807 Remove @var{key} (and any value associated with it) from
4808 @var{table}. Uses @code{eqv?} for equality tests.
4811 @deffn primitive hash-remove! table key
4812 Remove @var{key} (and any value associated with it) from
4813 @var{table}. Uses @code{equal?} for equality tests.
4816 The standard hash table functions may be too limited for some
4817 applications. For example, you may want a hash table to store
4818 strings in a case-insensitive manner, so that references to keys
4819 named ``foobar'', ``FOOBAR'' and ``FooBaR'' will all yield the
4820 same item. Guile provides you with @dfn{extended} hash tables
4821 that permit you to specify a hash function and associator function
4822 of your choosing. The functions described in the rest of this section
4823 can be used to implement such custom hash table structures.
4825 If you are unfamiliar with the inner workings of hash tables, then
4826 this facility will probably be a little too abstract for you to
4827 use comfortably. If you are interested in learning more, see an
4828 introductory textbook on data structures or algorithms for an
4829 explanation of how hash tables are implemented.
4831 @deffn primitive hashq key size
4832 Determine a hash value for @var{key} that is suitable for
4833 lookups in a hashtable of size @var{size}, where @code{eq?} is
4834 used as the equality predicate. The function returns an
4835 integer in the range 0 to @var{size} - 1. Note that
4836 @code{hashq} may use internal addresses. Thus two calls to
4837 hashq where the keys are @code{eq?} are not guaranteed to
4838 deliver the same value if the key object gets garbage collected
4839 in between. This can happen, for example with symbols:
4840 @code{(hashq 'foo n) (gc) (hashq 'foo n)} may produce two
4841 different values, since @code{foo} will be garbage collected.
4844 @deffn primitive hashv key size
4845 Determine a hash value for @var{key} that is suitable for
4846 lookups in a hashtable of size @var{size}, where @code{eqv?} is
4847 used as the equality predicate. The function returns an
4848 integer in the range 0 to @var{size} - 1. Note that
4849 @code{(hashv key)} may use internal addresses. Thus two calls
4850 to hashv where the keys are @code{eqv?} are not guaranteed to
4851 deliver the same value if the key object gets garbage collected
4852 in between. This can happen, for example with symbols:
4853 @code{(hashv 'foo n) (gc) (hashv 'foo n)} may produce two
4854 different values, since @code{foo} will be garbage collected.
4857 @deffn primitive hash key size
4858 Determine a hash value for @var{key} that is suitable for
4859 lookups in a hashtable of size @var{size}, where @code{equal?}
4860 is used as the equality predicate. The function returns an
4861 integer in the range 0 to @var{size} - 1.
4864 @deffn primitive hashx-ref hash assoc table key [dflt]
4865 This behaves the same way as the corresponding @code{ref}
4866 function, but uses @var{hash} as a hash function and
4867 @var{assoc} to compare keys. @code{hash} must be a function
4868 that takes two arguments, a key to be hashed and a table size.
4869 @code{assoc} must be an associator function, like @code{assoc},
4870 @code{assq} or @code{assv}.
4872 By way of illustration, @code{hashq-ref table key} is
4873 equivalent to @code{hashx-ref hashq assq table key}.
4876 @deffn primitive hashx-set! hash assoc table key val
4877 This behaves the same way as the corresponding @code{set!}
4878 function, but uses @var{hash} as a hash function and
4879 @var{assoc} to compare keys. @code{hash} must be a function
4880 that takes two arguments, a key to be hashed and a table size.
4881 @code{assoc} must be an associator function, like @code{assoc},
4882 @code{assq} or @code{assv}.
4884 By way of illustration, @code{hashq-set! table key} is
4885 equivalent to @code{hashx-set! hashq assq table key}.
4888 @deffn primitive hashq-get-handle table key
4889 This procedure returns the @code{(key . value)} pair from the
4890 hash table @var{table}. If @var{table} does not hold an
4891 associated value for @var{key}, @code{#f} is returned.
4892 Uses @code{eq?} for equality testing.
4895 @deffn primitive hashv-get-handle table key
4896 This procedure returns the @code{(key . value)} pair from the
4897 hash table @var{table}. If @var{table} does not hold an
4898 associated value for @var{key}, @code{#f} is returned.
4899 Uses @code{eqv?} for equality testing.
4902 @deffn primitive hash-get-handle table key
4903 This procedure returns the @code{(key . value)} pair from the
4904 hash table @var{table}. If @var{table} does not hold an
4905 associated value for @var{key}, @code{#f} is returned.
4906 Uses @code{equal?} for equality testing.
4909 @deffn primitive hashx-get-handle hash assoc table key
4910 This behaves the same way as the corresponding
4911 @code{-get-handle} function, but uses @var{hash} as a hash
4912 function and @var{assoc} to compare keys. @code{hash} must be
4913 a function that takes two arguments, a key to be hashed and a
4914 table size. @code{assoc} must be an associator function, like
4915 @code{assoc}, @code{assq} or @code{assv}.
4918 @deffn primitive hashq-create-handle! table key init
4919 This function looks up @var{key} in @var{table} and returns its handle.
4920 If @var{key} is not already present, a new handle is created which
4921 associates @var{key} with @var{init}.
4924 @deffn primitive hashv-create-handle! table key init
4925 This function looks up @var{key} in @var{table} and returns its handle.
4926 If @var{key} is not already present, a new handle is created which
4927 associates @var{key} with @var{init}.
4930 @deffn primitive hash-create-handle! table key init
4931 This function looks up @var{key} in @var{table} and returns its handle.
4932 If @var{key} is not already present, a new handle is created which
4933 associates @var{key} with @var{init}.
4936 @deffn primitive hashx-create-handle! hash assoc table key init
4937 This behaves the same way as the corresponding
4938 @code{-create-handle} function, but uses @var{hash} as a hash
4939 function and @var{assoc} to compare keys. @code{hash} must be
4940 a function that takes two arguments, a key to be hashed and a
4941 table size. @code{assoc} must be an associator function, like
4942 @code{assoc}, @code{assq} or @code{assv}.
4945 @deffn primitive hash-fold proc init table
4946 An iterator over hash-table elements.
4947 Accumulates and returns a result by applying PROC successively.
4948 The arguments to PROC are "(key value prior-result)" where key
4949 and value are successive pairs from the hash table TABLE, and
4950 prior-result is either INIT (for the first application of PROC)
4951 or the return value of the previous application of PROC.
4952 For example, @code{(hash-fold acons () tab)} will convert a hash
4953 table into an a-list of key-value pairs.
4960 @c FIXME::martin: Review me!
4962 A hook is basically a list of procedures to be called at well defined
4963 points in time. Hooks are used internally for several debugging
4964 facilities, but they can be used in user code, too.
4966 Hooks are created with @code{make-hook}, then procedures can be added to
4967 a hook with @code{add-hook!} or removed with @code{remove-hook!} or
4968 @code{reset-hook!}. The procedures stored in a hook can be invoked with
4972 * Hook Examples:: Hook usage by example.
4973 * Hook Reference:: Reference of all hook procedures.
4977 @subsection Hook Examples
4979 Hook usage is shown by some examples in this section. First, we will
4980 define a hook of arity 2 --- that is, the procedures stored in the hook
4981 will have to accept two arguments.
4984 (define hook (make-hook 2))
4986 @result{} #<hook 2 40286c90>
4989 Now we are ready to add some procedures to the newly created hook with
4990 @code{add-hook!}. In the following example, two procedures are added,
4991 which print different messages and do different things with their
4992 arguments. When the procedures have been added, we can invoke them
4993 using @code{run-hook}.
4996 (add-hook! hook (lambda (x y)
5000 (add-hook! hook (lambda (x y)
5009 Note that the procedures are called in reverse order than they were
5010 added. This can be changed by providing the optional third argument
5011 on the second call to @code{add-hook!}.
5014 (add-hook! hook (lambda (x y)
5018 (add-hook! hook (lambda (x y)
5022 #t) ; @r{<- Change here!}
5028 @node Hook Reference
5029 @subsection Hook Reference
5031 When a hook is created with @code{make-hook}, you can supply the arity
5032 of the procedures which can be added to the hook. The arity defaults to
5033 zero. All procedures of a hook must have the same arity, and when the
5034 procedures are invoked using @code{run-hook}, the number of arguments
5035 must match the arity of the procedures.
5037 The order in which procedures are added to a hook matters. If the third
5038 parameter to @var{add-hook!} is omitted or is equal to @code{#f}, the
5039 procedure is added in front of the procedures which might already be on
5040 that hook, otherwise the procedure is added at the end. The procedures
5041 are always called from first to last when they are invoked via
5044 When calling @code{hook->list}, the procedures in the resulting list are
5045 in the same order as they would have been called by @code{run-hook}.
5047 @deffn primitive make-hook-with-name name [n_args]
5048 Create a named hook with the name @var{name} for storing
5049 procedures of arity @var{n_args}. @var{n_args} defaults to
5053 @deffn primitive make-hook [n_args]
5054 Create a hook for storing procedure of arity
5055 @var{n_args}. @var{n_args} defaults to zero.
5058 @deffn primitive hook? x
5059 Return @code{#t} if @var{x} is a hook, @code{#f} otherwise.
5062 @deffn primitive hook-empty? hook
5063 Return @code{#t} if @var{hook} is an empty hook, @code{#f}
5067 @deffn primitive add-hook! hook proc [append_p]
5068 Add the procedure @var{proc} to the hook @var{hook}. The
5069 procedure is added to the end if @var{append_p} is true,
5070 otherwise it is added to the front.
5073 @deffn primitive remove-hook! hook proc
5074 Remove the procedure @var{proc} from the hook @var{hook}.
5077 @deffn primitive reset-hook! hook
5078 Remove all procedures from the hook @var{hook}.
5081 @deffn primitive run-hook hook . args
5082 Apply all procedures from the hook @var{hook} to the arguments
5083 @var{args}. The order of the procedure application is first to
5087 @deffn primitive hook->list hook
5088 Convert the procedure list of @var{hook} to a list.
5092 @node Other Data Types
5093 @section Other Core Guile Data Types
5097 @c TeX-master: "guile.texi"