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.
56 * Arrays:: Arrays of values.
57 * Association Lists and Hash Tables:: Dictionary data types.
58 * Vectors:: One-dimensional arrays of Scheme objects.
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 without arguments, 0 is returned. Otherwise the sum of all but
685 the first argument are subtracted from the first argument.
688 @c begin (texi-doc-string "guile" "*")
689 @deffn primitive * z1 @dots{}
690 Return the product of all arguments. If called without arguments, 1 is
694 @c begin (texi-doc-string "guile" "/")
695 @deffn primitive / z1 z2 @dots{}
696 Divide the first argument by the product of the remaining arguments.
699 @c begin (texi-doc-string "guile" "abs")
700 @deffn primitive abs x
701 Return the absolute value of @var{x}.
704 @c begin (texi-doc-string "guile" "max")
705 @deffn primitive max x1 x2 @dots{}
706 Return the maximum of all parameter values.
709 @c begin (texi-doc-string "guile" "min")
710 @deffn primitive min x1 x2 @dots{}
711 Return the minium of all parameter values.
714 @c begin (texi-doc-string "guile" "truncate")
715 @deffn primitive truncate
716 Round the inexact number @var{x} towards zero.
719 @c begin (texi-doc-string "guile" "round")
720 @deffn primitive round x
721 Round the inexact number @var{x} towards zero.
724 @c begin (texi-doc-string "guile" "floor")
725 @deffn primitive floor x
726 Round the number @var{x} towards minus infinity.
729 @c begin (texi-doc-string "guile" "ceiling")
730 @deffn primitive ceiling x
731 Round the number @var{x} towards infinity.
736 @subsection Scientific Functions
748 The following procedures accept any kind of number as arguments,
749 including complex numbers.
751 @c begin (texi-doc-string "guile" "sqrt")
752 @deffn procedure sqrt z
753 Return the square root of @var{z}.
756 @c begin (texi-doc-string "guile" "expt")
757 @deffn procedure expt z1 z2
758 Return @var{z1} raised to the power of @var{z2}.
761 @c begin (texi-doc-string "guile" "sin")
762 @deffn procedure sin z
763 Return the sine of @var{z}.
766 @c begin (texi-doc-string "guile" "cos")
767 @deffn procedure cos z
768 Return the cosine of @var{z}.
771 @c begin (texi-doc-string "guile" "tan")
772 @deffn procedure tan z
773 Return the tangent of @var{z}.
776 @c begin (texi-doc-string "guile" "asin")
777 @deffn procedure asin z
778 Return the arcsine of @var{z}.
781 @c begin (texi-doc-string "guile" "acos")
782 @deffn procedure acos z
783 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}.
791 @c begin (texi-doc-string "guile" "exp")
792 @deffn procedure exp z
793 Return e to the power of @var{z}, where e is the base of natural
794 logarithms (2.71828@dots{}).
797 @c begin (texi-doc-string "guile" "log")
798 @deffn procedure log z
799 Return the natural logarithm of @var{z}.
802 @c begin (texi-doc-string "guile" "log10")
803 @deffn procedure log10 z
804 Return the base 10 logarithm of @var{z}.
807 @c begin (texi-doc-string "guile" "sinh")
808 @deffn procedure sinh z
809 Return the hyperbolic sine of @var{z}.
812 @c begin (texi-doc-string "guile" "cosh")
813 @deffn procedure cosh z
814 Return the hyperbolic cosine of @var{z}.
817 @c begin (texi-doc-string "guile" "tanh")
818 @deffn procedure tanh z
819 Return the hyperbolic tangent of @var{z}.
822 @c begin (texi-doc-string "guile" "asinh")
823 @deffn procedure asinh z
824 Return the hyperbolic arcsine of @var{z}.
827 @c begin (texi-doc-string "guile" "acosh")
828 @deffn procedure acosh z
829 Return the hyperbolic arccosine of @var{z}.
832 @c begin (texi-doc-string "guile" "atanh")
833 @deffn procedure atanh z
834 Return the hyperbolic arctangent of @var{z}.
838 @node Primitive Numerics
839 @subsection Primitive Numeric Functions
841 Many of Guile's numeric procedures which accept any kind of numbers as
842 arguments, including complex numbers, are implemented as Scheme
843 procedures that use the following real number-based primitives. These
844 primitives signal an error if they are called with complex arguments.
846 @c begin (texi-doc-string "guile" "$abs")
847 @deffn primitive $abs x
848 Return the absolute value of @var{x}.
851 @c begin (texi-doc-string "guile" "$sqrt")
852 @deffn primitive $sqrt x
853 Return the square root of @var{x}.
856 @deffn primitive $expt x y
857 Return @var{x} raised to the power of @var{y}. This
858 procedure does not accept complex arguments.
861 @c begin (texi-doc-string "guile" "$sin")
862 @deffn primitive $sin x
863 Return the sine of @var{x}.
866 @c begin (texi-doc-string "guile" "$cos")
867 @deffn primitive $cos x
868 Return the cosine of @var{x}.
871 @c begin (texi-doc-string "guile" "$tan")
872 @deffn primitive $tan x
873 Return the tangent of @var{x}.
876 @c begin (texi-doc-string "guile" "$asin")
877 @deffn primitive $asin x
878 Return the arcsine of @var{x}.
881 @c begin (texi-doc-string "guile" "$acos")
882 @deffn primitive $acos x
883 Return the arccosine of @var{x}.
886 @c begin (texi-doc-string "guile" "$atan")
887 @deffn primitive $atan x
888 Return the arctangent of @var{x} in the range -PI/2 to PI/2.
891 @deffn primitive $atan2 x y
892 Return the arc tangent of the two arguments @var{x} and
893 @var{y}. This is similar to calculating the arc tangent of
894 @var{x} / @var{y}, except that the signs of both arguments
895 are used to determine the quadrant of the result. This
896 procedure does not accept complex arguments.
899 @c begin (texi-doc-string "guile" "$exp")
900 @deffn primitive $exp x
901 Return e to the power of @var{x}, where e is the base of natural
902 logarithms (2.71828@dots{}).
905 @c begin (texi-doc-string "guile" "$log")
906 @deffn primitive $log x
907 Return the natural logarithm of @var{x}.
910 @c begin (texi-doc-string "guile" "$sinh")
911 @deffn primitive $sinh x
912 Return the hyperbolic sine of @var{x}.
915 @c begin (texi-doc-string "guile" "$cosh")
916 @deffn primitive $cosh x
917 Return the hyperbolic cosine of @var{x}.
920 @c begin (texi-doc-string "guile" "$tanh")
921 @deffn primitive $tanh x
922 Return the hyperbolic tangent of @var{x}.
925 @c begin (texi-doc-string "guile" "$asinh")
926 @deffn primitive $asinh x
927 Return the hyperbolic arcsine of @var{x}.
930 @c begin (texi-doc-string "guile" "$acosh")
931 @deffn primitive $acosh x
932 Return the hyperbolic arccosine of @var{x}.
935 @c begin (texi-doc-string "guile" "$atanh")
936 @deffn primitive $atanh x
937 Return the hyperbolic arctangent of @var{x}.
941 @node Bitwise Operations
942 @subsection Bitwise Operations
944 @deffn primitive logand n1 n2
945 Return the integer which is the bit-wise AND of the two integer
949 (number->string (logand #b1100 #b1010) 2)
954 @deffn primitive logior n1 n2
955 Return the integer which is the bit-wise OR of the two integer
959 (number->string (logior #b1100 #b1010) 2)
964 @deffn primitive logxor n1 n2
965 Return the integer which is the bit-wise XOR of the two integer
969 (number->string (logxor #b1100 #b1010) 2)
974 @deffn primitive lognot n
975 Return the integer which is the 2s-complement of the integer
979 (number->string (lognot #b10000000) 2)
980 @result{} "-10000001"
981 (number->string (lognot #b0) 2)
986 @deffn primitive logtest j k
988 (logtest j k) @equiv{} (not (zero? (logand j k)))
990 (logtest #b0100 #b1011) @result{} #f
991 (logtest #b0100 #b0111) @result{} #t
995 @deffn primitive logbit? index j
997 (logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)
999 (logbit? 0 #b1101) @result{} #t
1000 (logbit? 1 #b1101) @result{} #f
1001 (logbit? 2 #b1101) @result{} #t
1002 (logbit? 3 #b1101) @result{} #t
1003 (logbit? 4 #b1101) @result{} #f
1007 @deffn primitive ash n cnt
1008 The function ash performs an arithmetic shift left by @var{cnt}
1009 bits (or shift right, if @var{cnt} is negative). 'Arithmetic'
1010 means, that the function does not guarantee to keep the bit
1011 structure of @var{n}, but rather guarantees that the result
1012 will always be rounded towards minus infinity. Therefore, the
1013 results of ash and a corresponding bitwise shift will differ if
1014 @var{n} is negative.
1016 Formally, the function returns an integer equivalent to
1017 @code{(inexact->exact (floor (* @var{n} (expt 2 @var{cnt}))))}.
1020 (number->string (ash #b1 3) 2) @result{} "1000"
1021 (number->string (ash #b1010 -1) 2) @result{} "101"
1025 @deffn primitive logcount n
1026 Return the number of bits in integer @var{n}. If integer is
1027 positive, the 1-bits in its binary representation are counted.
1028 If negative, the 0-bits in its two's-complement binary
1029 representation are counted. If 0, 0 is returned.
1032 (logcount #b10101010)
1041 @deffn primitive integer-length n
1042 Return the number of bits neccessary to represent @var{n}.
1045 (integer-length #b10101010)
1049 (integer-length #b1111)
1054 @deffn primitive integer-expt n k
1055 Return @var{n} raised to the non-negative integer exponent
1066 @deffn primitive bit-extract n start end
1067 Return the integer composed of the @var{start} (inclusive)
1068 through @var{end} (exclusive) bits of @var{n}. The
1069 @var{start}th bit becomes the 0-th bit in the result.
1072 (number->string (bit-extract #b1101101010 0 4) 2)
1074 (number->string (bit-extract #b1101101010 4 9) 2)
1081 @subsection Random Number Generation
1083 @deffn primitive copy-random-state [state]
1084 Return a copy of the random state @var{state}.
1087 @deffn primitive random n [state]
1088 Return a number in [0,N).
1090 Accepts a positive integer or real n and returns a
1091 number of the same type between zero (inclusive) and
1092 N (exclusive). The values returned have a uniform
1095 The optional argument @var{state} must be of the type produced
1096 by @code{seed->random-state}. It defaults to the value of the
1097 variable @var{*random-state*}. This object is used to maintain
1098 the state of the pseudo-random-number generator and is altered
1099 as a side effect of the random operation.
1102 @deffn primitive random:exp [state]
1103 Return an inexact real in an exponential distribution with mean
1104 1. For an exponential distribution with mean u use (* u
1108 @deffn primitive random:hollow-sphere! v [state]
1109 Fills vect with inexact real random numbers
1110 the sum of whose squares is equal to 1.0.
1111 Thinking of vect as coordinates in space of
1112 dimension n = (vector-length vect), the coordinates
1113 are uniformly distributed over the surface of the
1117 @deffn primitive random:normal [state]
1118 Return an inexact real in a normal distribution. The
1119 distribution used has mean 0 and standard deviation 1. For a
1120 normal distribution with mean m and standard deviation d use
1121 @code{(+ m (* d (random:normal)))}.
1124 @deffn primitive random:normal-vector! v [state]
1125 Fills vect with inexact real random numbers that are
1126 independent and standard normally distributed
1127 (i.e., with mean 0 and variance 1).
1130 @deffn primitive random:solid-sphere! v [state]
1131 Fills vect with inexact real random numbers
1132 the sum of whose squares is less than 1.0.
1133 Thinking of vect as coordinates in space of
1134 dimension n = (vector-length vect), the coordinates
1135 are uniformly distributed within the unit n-shere.
1136 The sum of the squares of the numbers is returned.
1139 @deffn primitive random:uniform [state]
1140 Return a uniformly distributed inexact real random number in
1144 @deffn primitive seed->random-state seed
1145 Return a new random state using @var{seed}.
1153 Most of the characters in the ASCII character set may be referred to by
1154 name: for example, @code{#\tab}, @code{#\esc}, @code{#\stx}, and so on.
1155 The following table describes the ASCII names for each character.
1157 @multitable @columnfractions .25 .25 .25 .25
1158 @item 0 = @code{#\nul}
1159 @tab 1 = @code{#\soh}
1160 @tab 2 = @code{#\stx}
1161 @tab 3 = @code{#\etx}
1162 @item 4 = @code{#\eot}
1163 @tab 5 = @code{#\enq}
1164 @tab 6 = @code{#\ack}
1165 @tab 7 = @code{#\bel}
1166 @item 8 = @code{#\bs}
1167 @tab 9 = @code{#\ht}
1168 @tab 10 = @code{#\nl}
1169 @tab 11 = @code{#\vt}
1170 @item 12 = @code{#\np}
1171 @tab 13 = @code{#\cr}
1172 @tab 14 = @code{#\so}
1173 @tab 15 = @code{#\si}
1174 @item 16 = @code{#\dle}
1175 @tab 17 = @code{#\dc1}
1176 @tab 18 = @code{#\dc2}
1177 @tab 19 = @code{#\dc3}
1178 @item 20 = @code{#\dc4}
1179 @tab 21 = @code{#\nak}
1180 @tab 22 = @code{#\syn}
1181 @tab 23 = @code{#\etb}
1182 @item 24 = @code{#\can}
1183 @tab 25 = @code{#\em}
1184 @tab 26 = @code{#\sub}
1185 @tab 27 = @code{#\esc}
1186 @item 28 = @code{#\fs}
1187 @tab 29 = @code{#\gs}
1188 @tab 30 = @code{#\rs}
1189 @tab 31 = @code{#\us}
1190 @item 32 = @code{#\sp}
1193 The @code{delete} character (octal 177) may be referred to with the name
1196 Several characters have more than one name:
1216 @deffn primitive char? x
1217 Return @code{#t} iff @var{x} is a character, else @code{#f}.
1221 @deffn primitive char=? x y
1222 Return @code{#t} iff @var{x} is the same character as @var{y}, else @code{#f}.
1226 @deffn primitive char<? x y
1227 Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence,
1232 @deffn primitive char<=? x y
1233 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1234 ASCII sequence, else @code{#f}.
1238 @deffn primitive char>? x y
1239 Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
1240 sequence, else @code{#f}.
1244 @deffn primitive char>=? x y
1245 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1246 ASCII sequence, else @code{#f}.
1250 @deffn primitive char-ci=? x y
1251 Return @code{#t} iff @var{x} is the same character as @var{y} ignoring
1252 case, else @code{#f}.
1256 @deffn primitive char-ci<? x y
1257 Return @code{#t} iff @var{x} is less than @var{y} in the ASCII sequence
1258 ignoring case, else @code{#f}.
1262 @deffn primitive char-ci<=? x y
1263 Return @code{#t} iff @var{x} is less than or equal to @var{y} in the
1264 ASCII sequence ignoring case, else @code{#f}.
1268 @deffn primitive char-ci>? x y
1269 Return @code{#t} iff @var{x} is greater than @var{y} in the ASCII
1270 sequence ignoring case, else @code{#f}.
1274 @deffn primitive char-ci>=? x y
1275 Return @code{#t} iff @var{x} is greater than or equal to @var{y} in the
1276 ASCII sequence ignoring case, else @code{#f}.
1279 @rnindex char-alphabetic?
1280 @deffn primitive char-alphabetic? chr
1281 Return @code{#t} iff @var{chr} is alphabetic, else @code{#f}.
1282 Alphabetic means the same thing as the isalpha C library function.
1285 @rnindex char-numeric?
1286 @deffn primitive char-numeric? chr
1287 Return @code{#t} iff @var{chr} is numeric, else @code{#f}.
1288 Numeric means the same thing as the isdigit C library function.
1291 @rnindex char-whitespace?
1292 @deffn primitive char-whitespace? chr
1293 Return @code{#t} iff @var{chr} is whitespace, else @code{#f}.
1294 Whitespace means the same thing as the isspace C library function.
1297 @rnindex char-upper-case?
1298 @deffn primitive char-upper-case? chr
1299 Return @code{#t} iff @var{chr} is uppercase, else @code{#f}.
1300 Uppercase means the same thing as the isupper C library function.
1303 @rnindex char-lower-case?
1304 @deffn primitive char-lower-case? chr
1305 Return @code{#t} iff @var{chr} is lowercase, else @code{#f}.
1306 Lowercase means the same thing as the islower C library function.
1309 @deffn primitive char-is-both? chr
1310 Return @code{#t} iff @var{chr} is either uppercase or lowercase, else @code{#f}.
1311 Uppercase and lowercase are as defined by the isupper and islower
1312 C library functions.
1315 @rnindex char->integer
1316 @deffn primitive char->integer chr
1317 Return the number corresponding to ordinal position of @var{chr} in the
1321 @rnindex integer->char
1322 @deffn primitive integer->char n
1323 Return the character at position @var{n} in the ASCII sequence.
1326 @rnindex char-upcase
1327 @deffn primitive char-upcase chr
1328 Return the uppercase character version of @var{chr}.
1331 @rnindex char-downcase
1332 @deffn primitive char-downcase chr
1333 Return the lowercase character version of @var{chr}.
1340 Strings are fixed-length sequences of characters. They can be created
1341 by calling constructor procedures, but they can also literally get
1342 entered at the REPL or in Scheme source files.
1344 Guile provides a rich set of string processing procedures, because text
1345 handling is very important when Guile is used as a scripting language.
1347 Strings always carry the information about how many characters they are
1348 composed of with them, so there is no special end-of-string character,
1349 like in C. That means that Scheme strings can contain any character,
1350 even the NUL character @code{'\0'}. But note: Since most operating
1351 system calls dealing with strings (such as for file operations) expect
1352 strings to be zero-terminated, they might do unexpected things when
1353 called with string containing unusal characters.
1356 * String Syntax:: Read syntax for strings.
1357 * String Predicates:: Testing strings for certain properties.
1358 * String Constructors:: Creating new string objects.
1359 * List/String Conversion:: Converting from/to lists of characters.
1360 * String Selection:: Select portions from strings.
1361 * String Modification:: Modify parts or whole strings.
1362 * String Comparison:: Lexicographic ordering predicates.
1363 * String Searching:: Searching in strings.
1364 * Alphabetic Case Mapping:: Convert the alphabetic case of strings.
1365 * Appending Strings:: Appending strings to form a new string.
1366 * String Miscellanea:: Miscellaneous string procedures.
1370 @subsection String Read Syntax
1372 The read syntax for strings is an arbitrarily long sequence of
1373 characters enclosed in double quotes (@code{"}). @footnote{Actually, the
1374 current implementation restricts strings to a length of 2^24
1375 characters.} If you want to insert a double quote character into a
1376 string literal, it must be prefixed with a backslash @code{\} character
1377 (called an @emph{escape character}).
1379 The following are examples of string literals:
1388 @c FIXME::martin: What about escape sequences like \r, \n etc.?
1390 @node String Predicates
1391 @subsection String Predicates
1393 The following procedures can be used to check whether a given string
1394 fulfills some specified property.
1397 @deffn primitive string? obj
1398 Return @code{#t} iff @var{obj} is a string, else returns
1402 @deffn primitive string-null? str
1403 Return @code{#t} if @var{str}'s length is nonzero, and
1404 @code{#f} otherwise.
1406 (string-null? "") @result{} #t
1408 (string-null? y) @result{} #f
1412 @node String Constructors
1413 @subsection String Constructors
1415 The string constructor procedures create new string objects, possibly
1416 initializing them with some specified character data.
1418 @c FIXME::martin: list->string belongs into `List/String Conversion'
1421 @rnindex list->string
1422 @deffn primitive string . chrs
1423 @deffnx primitive list->string chrs
1424 Return a newly allocated string composed of the arguments,
1428 @rnindex make-string
1429 @deffn primitive make-string k [chr]
1430 Return a newly allocated string of
1431 length @var{k}. If @var{chr} is given, then all elements of
1432 the string are initialized to @var{chr}, otherwise the contents
1433 of the @var{string} are unspecified.
1436 @node List/String Conversion
1437 @subsection List/String conversion
1439 When processing strings, it is often convenient to first convert them
1440 into a list representation by using the procedure @code{string->list},
1441 work with the resulting list, and then convert it back into a string.
1442 These procedures are useful for similar tasks.
1444 @rnindex string->list
1445 @deffn primitive string->list str
1446 Return a newly allocated list of the characters that make up
1447 the given string @var{str}. @code{string->list} and
1448 @code{list->string} are inverses as far as @samp{equal?} is
1452 @deffn primitive string-split str chr
1453 Split the string @var{str} into the a list of the substrings delimited
1454 by appearances of the character @var{chr}. Note that an empty substring
1455 between separator characters will result in an empty string in the
1458 (string-split "root:x:0:0:root:/root:/bin/bash" #\:)
1460 ("root" "x" "0" "0" "root" "/root" "/bin/bash")
1462 (string-split "::" #\:)
1466 (string-split "" #\:)
1473 @node String Selection
1474 @subsection String Selection
1476 Portions of strings can be extracted by these procedures.
1477 @code{string-ref} delivers individual characters whereas
1478 @code{substring} can be used to extract substrings from longer strings.
1480 @rnindex string-length
1481 @deffn primitive string-length string
1482 Return the number of characters in @var{string}.
1486 @deffn primitive string-ref str k
1487 Return character @var{k} of @var{str} using zero-origin
1488 indexing. @var{k} must be a valid index of @var{str}.
1491 @rnindex string-copy
1492 @deffn primitive string-copy str
1493 Return a newly allocated copy of the given @var{string}.
1497 @deffn primitive substring str start [end]
1498 Return a newly allocated string formed from the characters
1499 of @var{str} beginning with index @var{start} (inclusive) and
1500 ending with index @var{end} (exclusive).
1501 @var{str} must be a string, @var{start} and @var{end} must be
1502 exact integers satisfying:
1504 0 <= @var{start} <= @var{end} <= (string-length @var{str}).
1507 @node String Modification
1508 @subsection String Modification
1510 These procedures are for modifying strings in-place. That means, that
1511 not a new string is the result of a string operation, but that the
1512 actual memory representation of a string is modified.
1514 @rnindex string-set!
1515 @deffn primitive string-set! str k chr
1516 Store @var{chr} in element @var{k} of @var{str} and return
1517 an unspecified value. @var{k} must be a valid index of
1521 @rnindex string-fill!
1522 @deffn primitive string-fill! str chr
1523 Store @var{char} in every element of the given @var{string} and
1524 return an unspecified value.
1527 @deffn primitive substring-fill! str start end fill
1528 Change every character in @var{str} between @var{start} and
1529 @var{end} to @var{fill}.
1532 (define y "abcdefg")
1533 (substring-fill! y 1 3 #\r)
1539 @deffn primitive substring-move! str1 start1 end1 str2 start2
1540 @deffnx primitive substring-move-left! str1 start1 end1 str2 start2
1541 @deffnx primitive substring-move-right! str1 start1 end1 str2 start2
1542 Copy the substring of @var{str1} bounded by @var{start1} and @var{end1}
1543 into @var{str2} beginning at position @var{end2}.
1544 @code{substring-move-right!} begins copying from the rightmost character
1545 and moves left, and @code{substring-move-left!} copies from the leftmost
1546 character moving right.
1548 It is useful to have two functions that copy in different directions so
1549 that substrings can be copied back and forth within a single string. If
1550 you wish to copy text from the left-hand side of a string to the
1551 right-hand side of the same string, and the source and destination
1552 overlap, you must be careful to copy the rightmost characters of the
1553 text first, to avoid clobbering your data. Hence, when @var{str1} and
1554 @var{str2} are the same string, you should use
1555 @code{substring-move-right!} when moving text from left to right, and
1556 @code{substring-move-left!} otherwise. If @code{str1} and @samp{str2}
1557 are different strings, it does not matter which function you use.
1560 @deffn primitive substring-move-left! str1 start1 end1 str2 start2
1562 @deftypefn {C Function} SCM scm_substring_move_left_x (SCM @var{str1}, SCM @var{start1}, SCM @var{end1}, SCM @var{str2}, SCM @var{start2})
1563 [@strong{Note:} this is only valid if you've applied the strop patch].
1565 Moves a substring of @var{str1}, from @var{start1} to @var{end1}
1566 (@var{end1} is exclusive), into @var{str2}, starting at
1567 @var{start2}. Allows overlapping strings.
1570 (define x (make-string 10 #\a))
1572 (substring-move-left! x 2 5 y 0)
1577 @result{} "aaaaaaaaaa"
1580 (substring-move-left! x 2 5 y 0)
1584 (define y "abcdefg")
1585 (substring-move-left! y 2 5 y 3)
1591 @deffn substring-move-right! str1 start1 end1 str2 start2
1593 @deftypefn {C Function} SCM scm_substring_move_right_x (SCM @var{str1}, SCM @var{start1}, SCM @var{end1}, SCM @var{str2}, SCM @var{start2})
1594 [@strong{Note:} this is only valid if you've applied the strop patch, if
1595 it hasn't made it into the guile tree].
1597 Does much the same thing as @code{substring-move-left!}, except it
1598 starts moving at the end of the sequence, rather than the beginning.
1600 (define y "abcdefg")
1601 (substring-move-right! y 2 5 y 0)
1605 (define y "abcdefg")
1606 (substring-move-right! y 2 5 y 3)
1613 @node String Comparison
1614 @subsection String Comparison
1616 The procedures in this section are similar to the character ordering
1617 predicates (@pxref{Characters}), but are defined on character sequences.
1618 They all return @code{#t} on success and @code{#f} on failure. The
1619 predicates ending in @code{-ci} ignore the character case when comparing
1624 @deffn primitive string=? s1 s2
1625 Lexicographic equality predicate; return @code{#t} if the two
1626 strings are the same length and contain the same characters in
1627 the same positions, otherwise return @code{#f}.
1629 The procedure @code{string-ci=?} treats upper and lower case
1630 letters as though they were the same character, but
1631 @code{string=?} treats upper and lower case as distinct
1636 @deffn primitive string<? s1 s2
1637 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1638 is lexicographically less than @var{s2}.
1642 @deffn primitive string<=? s1 s2
1643 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1644 is lexicographically less than or equal to @var{s2}.
1648 @deffn primitive string>? s1 s2
1649 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1650 is lexicographically greater than @var{s2}.
1654 @deffn primitive string>=? s1 s2
1655 Lexicographic ordering predicate; return @code{#t} if @var{s1}
1656 is lexicographically greater than or equal to @var{s2}.
1659 @rnindex string-ci=?
1660 @deffn primitive string-ci=? s1 s2
1661 Case-insensitive string equality predicate; return @code{#t} if
1662 the two strings are the same length and their component
1663 characters match (ignoring case) at each position; otherwise
1668 @deffn primitive string-ci<? s1 s2
1669 Case insensitive lexicographic ordering predicate; return
1670 @code{#t} if @var{s1} is lexicographically less than @var{s2}
1675 @deffn primitive string-ci<=? s1 s2
1676 Case insensitive lexicographic ordering predicate; return
1677 @code{#t} if @var{s1} is lexicographically less than or equal
1678 to @var{s2} regardless of case.
1681 @rnindex string-ci>?
1682 @deffn primitive string-ci>? s1 s2
1683 Case insensitive lexicographic ordering predicate; return
1684 @code{#t} if @var{s1} is lexicographically greater than
1685 @var{s2} regardless of case.
1688 @rnindex string-ci>=?
1689 @deffn primitive string-ci>=? s1 s2
1690 Case insensitive lexicographic ordering predicate; return
1691 @code{#t} if @var{s1} is lexicographically greater than or
1692 equal to @var{s2} regardless of case.
1696 @node String Searching
1697 @subsection String Searching
1699 When searching the index of a character in a string, these procedures
1702 @deffn primitive string-index str chr [frm [to]]
1703 Return the index of the first occurrence of @var{chr} in
1704 @var{str}. The optional integer arguments @var{frm} and
1705 @var{to} limit the search to a portion of the string. This
1706 procedure essentially implements the @code{index} or
1707 @code{strchr} functions from the C library.
1710 (string-index "weiner" #\e)
1713 (string-index "weiner" #\e 2)
1716 (string-index "weiner" #\e 2 4)
1721 @deffn primitive string-rindex str chr [frm [to]]
1722 Like @code{string-index}, but search from the right of the
1723 string rather than from the left. This procedure essentially
1724 implements the @code{rindex} or @code{strrchr} functions from
1728 (string-rindex "weiner" #\e)
1731 (string-rindex "weiner" #\e 2 4)
1734 (string-rindex "weiner" #\e 2 5)
1739 @node Alphabetic Case Mapping
1740 @subsection Alphabetic Case Mapping
1742 These are procedures for mapping strings to their upper- or lower-case
1743 equivalents, respectively, or for capitalizing strings.
1745 @deffn primitive string-upcase str
1746 Return a freshly allocated string containing the characters of
1747 @var{str} in upper case.
1750 @deffn primitive string-upcase! str
1751 Destructively upcase every character in @var{str} and return
1754 y @result{} "arrdefg"
1755 (string-upcase! y) @result{} "ARRDEFG"
1756 y @result{} "ARRDEFG"
1760 @deffn primitive string-downcase str
1761 Return a freshly allocation string containing the characters in
1762 @var{str} in lower case.
1765 @deffn primitive string-downcase! str
1766 Destructively downcase every character in @var{str} and return
1769 y @result{} "ARRDEFG"
1770 (string-downcase! y) @result{} "arrdefg"
1771 y @result{} "arrdefg"
1775 @deffn primitive string-capitalize str
1776 Return a freshly allocated string with the characters in
1777 @var{str}, where the first character of every word is
1781 @deffn primitive string-capitalize! str
1782 Upcase the first character of every word in @var{str}
1783 destructively and return @var{str}.
1786 y @result{} "hello world"
1787 (string-capitalize! y) @result{} "Hello World"
1788 y @result{} "Hello World"
1793 @node Appending Strings
1794 @subsection Appending Strings
1796 The procedure @code{string-append} appends several strings together to
1797 form a longer result string.
1799 @rnindex string-append
1800 @deffn primitive string-append . args
1801 Return a newly allocated string whose characters form the
1802 concatenation of the given strings, @var{args}.
1806 @node String Miscellanea
1807 @subsection String Miscellanea
1809 This section contains several remaining string procedures.
1811 @deffn primitive string-ci->symbol str
1812 Return the symbol whose name is @var{str}. @var{str} is
1813 converted to lowercase before the conversion is done, if Guile
1814 is currently reading symbols case-insensitively.
1818 @node Regular Expressions
1819 @section Regular Expressions
1821 @cindex regular expressions
1823 @cindex emacs regexp
1825 A @dfn{regular expression} (or @dfn{regexp}) is a pattern that
1826 describes a whole class of strings. A full description of regular
1827 expressions and their syntax is beyond the scope of this manual;
1828 an introduction can be found in the Emacs manual (@pxref{Regexps,
1829 , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, or
1830 in many general Unix reference books.
1832 If your system does not include a POSIX regular expression library, and
1833 you have not linked Guile with a third-party regexp library such as Rx,
1834 these functions will not be available. You can tell whether your Guile
1835 installation includes regular expression support by checking whether the
1836 @code{*features*} list includes the @code{regex} symbol.
1839 * Regexp Functions:: Functions that create and match regexps.
1840 * Match Structures:: Finding what was matched by a regexp.
1841 * Backslash Escapes:: Removing the special meaning of regexp metacharacters.
1842 * Rx Interface:: Tom Lord's Rx library does things differently.
1845 [FIXME: it may be useful to include an Examples section. Parts of this
1846 interface are bewildering on first glance.]
1848 @node Regexp Functions
1849 @subsection Regexp Functions
1851 By default, Guile supports POSIX extended regular expressions.
1852 That means that the characters @samp{(}, @samp{)}, @samp{+} and
1853 @samp{?} are special, and must be escaped if you wish to match the
1856 This regular expression interface was modeled after that
1857 implemented by SCSH, the Scheme Shell. It is intended to be
1858 upwardly compatible with SCSH regular expressions.
1860 @c begin (scm-doc-string "regex.scm" "string-match")
1861 @deffn procedure string-match pattern str [start]
1862 Compile the string @var{pattern} into a regular expression and compare
1863 it with @var{str}. The optional numeric argument @var{start} specifies
1864 the position of @var{str} at which to begin matching.
1866 @code{string-match} returns a @dfn{match structure} which
1867 describes what, if anything, was matched by the regular
1868 expression. @xref{Match Structures}. If @var{str} does not match
1869 @var{pattern} at all, @code{string-match} returns @code{#f}.
1872 Each time @code{string-match} is called, it must compile its
1873 @var{pattern} argument into a regular expression structure. This
1874 operation is expensive, which makes @code{string-match} inefficient if
1875 the same regular expression is used several times (for example, in a
1876 loop). For better performance, you can compile a regular expression in
1877 advance and then match strings against the compiled regexp.
1879 @deffn primitive make-regexp pat . flags
1880 Compile the regular expression described by @var{pat}, and
1881 return the compiled regexp structure. If @var{pat} does not
1882 describe a legal regular expression, @code{make-regexp} throws
1883 a @code{regular-expression-syntax} error.
1885 The @var{flags} arguments change the behavior of the compiled
1886 regular expression. The following flags may be supplied:
1890 Consider uppercase and lowercase letters to be the same when
1892 @item regexp/newline
1893 If a newline appears in the target string, then permit the
1894 @samp{^} and @samp{$} operators to match immediately after or
1895 immediately before the newline, respectively. Also, the
1896 @samp{.} and @samp{[^...]} operators will never match a newline
1897 character. The intent of this flag is to treat the target
1898 string as a buffer containing many lines of text, and the
1899 regular expression as a pattern that may match a single one of
1902 Compile a basic (``obsolete'') regexp instead of the extended
1903 (``modern'') regexps that are the default. Basic regexps do
1904 not consider @samp{|}, @samp{+} or @samp{?} to be special
1905 characters, and require the @samp{@{...@}} and @samp{(...)}
1906 metacharacters to be backslash-escaped (@pxref{Backslash
1907 Escapes}). There are several other differences between basic
1908 and extended regular expressions, but these are the most
1910 @item regexp/extended
1911 Compile an extended regular expression rather than a basic
1912 regexp. This is the default behavior; this flag will not
1913 usually be needed. If a call to @code{make-regexp} includes
1914 both @code{regexp/basic} and @code{regexp/extended} flags, the
1915 one which comes last will override the earlier one.
1919 @deffn primitive regexp-exec rx str [start [flags]]
1920 Match the compiled regular expression @var{rx} against
1921 @code{str}. If the optional integer @var{start} argument is
1922 provided, begin matching from that position in the string.
1923 Return a match structure describing the results of the match,
1924 or @code{#f} if no match could be found.
1927 @deffn primitive regexp? obj
1928 Return @code{#t} if @var{obj} is a compiled regular expression,
1929 or @code{#f} otherwise.
1932 Regular expressions are commonly used to find patterns in one string and
1933 replace them with the contents of another string.
1935 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
1936 @deffn procedure regexp-substitute port match [item@dots{}]
1937 Write to the output port @var{port} selected contents of the match
1938 structure @var{match}. Each @var{item} specifies what should be
1939 written, and may be one of the following arguments:
1943 A string. String arguments are written out verbatim.
1946 An integer. The submatch with that number is written.
1949 The symbol @samp{pre}. The portion of the matched string preceding
1950 the regexp match is written.
1953 The symbol @samp{post}. The portion of the matched string following
1954 the regexp match is written.
1957 @var{port} may be @code{#f}, in which case nothing is written; instead,
1958 @code{regexp-substitute} constructs a string from the specified
1959 @var{item}s and returns that.
1962 @c begin (scm-doc-string "regex.scm" "regexp-substitute")
1963 @deffn procedure regexp-substitute/global port regexp target [item@dots{}]
1964 Similar to @code{regexp-substitute}, but can be used to perform global
1965 substitutions on @var{str}. Instead of taking a match structure as an
1966 argument, @code{regexp-substitute/global} takes two string arguments: a
1967 @var{regexp} string describing a regular expression, and a @var{target}
1968 string which should be matched against this regular expression.
1970 Each @var{item} behaves as in @var{regexp-substitute}, with the
1971 following exceptions:
1975 A function may be supplied. When this function is called, it will be
1976 passed one argument: a match structure for a given regular expression
1977 match. It should return a string to be written out to @var{port}.
1980 The @samp{post} symbol causes @code{regexp-substitute/global} to recurse
1981 on the unmatched portion of @var{str}. This @emph{must} be supplied in
1982 order to perform global search-and-replace on @var{str}; if it is not
1983 present among the @var{item}s, then @code{regexp-substitute/global} will
1984 return after processing a single match.
1988 @node Match Structures
1989 @subsection Match Structures
1991 @cindex match structures
1993 A @dfn{match structure} is the object returned by @code{string-match} and
1994 @code{regexp-exec}. It describes which portion of a string, if any,
1995 matched the given regular expression. Match structures include: a
1996 reference to the string that was checked for matches; the starting and
1997 ending positions of the regexp match; and, if the regexp included any
1998 parenthesized subexpressions, the starting and ending positions of each
2001 In each of the regexp match functions described below, the @code{match}
2002 argument must be a match structure returned by a previous call to
2003 @code{string-match} or @code{regexp-exec}. Most of these functions
2004 return some information about the original target string that was
2005 matched against a regular expression; we will call that string
2006 @var{target} for easy reference.
2008 @c begin (scm-doc-string "regex.scm" "regexp-match?")
2009 @deffn procedure regexp-match? obj
2010 Return @code{#t} if @var{obj} is a match structure returned by a
2011 previous call to @code{regexp-exec}, or @code{#f} otherwise.
2014 @c begin (scm-doc-string "regex.scm" "match:substring")
2015 @deffn procedure match:substring match [n]
2016 Return the portion of @var{target} matched by subexpression number
2017 @var{n}. Submatch 0 (the default) represents the entire regexp match.
2018 If the regular expression as a whole matched, but the subexpression
2019 number @var{n} did not match, return @code{#f}.
2022 @c begin (scm-doc-string "regex.scm" "match:start")
2023 @deffn procedure match:start match [n]
2024 Return the starting position of submatch number @var{n}.
2027 @c begin (scm-doc-string "regex.scm" "match:end")
2028 @deffn procedure match:end match [n]
2029 Return the ending position of submatch number @var{n}.
2032 @c begin (scm-doc-string "regex.scm" "match:prefix")
2033 @deffn procedure match:prefix match
2034 Return the unmatched portion of @var{target} preceding the regexp match.
2037 @c begin (scm-doc-string "regex.scm" "match:suffix")
2038 @deffn procedure match:suffix match
2039 Return the unmatched portion of @var{target} following the regexp match.
2042 @c begin (scm-doc-string "regex.scm" "match:count")
2043 @deffn procedure match:count match
2044 Return the number of parenthesized subexpressions from @var{match}.
2045 Note that the entire regular expression match itself counts as a
2046 subexpression, and failed submatches are included in the count.
2049 @c begin (scm-doc-string "regex.scm" "match:string")
2050 @deffn procedure match:string match
2051 Return the original @var{target} string.
2054 @node Backslash Escapes
2055 @subsection Backslash Escapes
2057 Sometimes you will want a regexp to match characters like @samp{*} or
2058 @samp{$} exactly. For example, to check whether a particular string
2059 represents a menu entry from an Info node, it would be useful to match
2060 it against a regexp like @samp{^* [^:]*::}. However, this won't work;
2061 because the asterisk is a metacharacter, it won't match the @samp{*} at
2062 the beginning of the string. In this case, we want to make the first
2065 You can do this by preceding the metacharacter with a backslash
2066 character @samp{\}. (This is also called @dfn{quoting} the
2067 metacharacter, and is known as a @dfn{backslash escape}.) When Guile
2068 sees a backslash in a regular expression, it considers the following
2069 glyph to be an ordinary character, no matter what special meaning it
2070 would ordinarily have. Therefore, we can make the above example work by
2071 changing the regexp to @samp{^\* [^:]*::}. The @samp{\*} sequence tells
2072 the regular expression engine to match only a single asterisk in the
2075 Since the backslash is itself a metacharacter, you may force a regexp to
2076 match a backslash in the target string by preceding the backslash with
2077 itself. For example, to find variable references in a @TeX{} program,
2078 you might want to find occurrences of the string @samp{\let\} followed
2079 by any number of alphabetic characters. The regular expression
2080 @samp{\\let\\[A-Za-z]*} would do this: the double backslashes in the
2081 regexp each match a single backslash in the target string.
2083 @c begin (scm-doc-string "regex.scm" "regexp-quote")
2084 @deffn procedure regexp-quote str
2085 Quote each special character found in @var{str} with a backslash, and
2086 return the resulting string.
2089 @strong{Very important:} Using backslash escapes in Guile source code
2090 (as in Emacs Lisp or C) can be tricky, because the backslash character
2091 has special meaning for the Guile reader. For example, if Guile
2092 encounters the character sequence @samp{\n} in the middle of a string
2093 while processing Scheme code, it replaces those characters with a
2094 newline character. Similarly, the character sequence @samp{\t} is
2095 replaced by a horizontal tab. Several of these @dfn{escape sequences}
2096 are processed by the Guile reader before your code is executed.
2097 Unrecognized escape sequences are ignored: if the characters @samp{\*}
2098 appear in a string, they will be translated to the single character
2101 This translation is obviously undesirable for regular expressions, since
2102 we want to be able to include backslashes in a string in order to
2103 escape regexp metacharacters. Therefore, to make sure that a backslash
2104 is preserved in a string in your Guile program, you must use @emph{two}
2105 consecutive backslashes:
2108 (define Info-menu-entry-pattern (make-regexp "^\\* [^:]*"))
2111 The string in this example is preprocessed by the Guile reader before
2112 any code is executed. The resulting argument to @code{make-regexp} is
2113 the string @samp{^\* [^:]*}, which is what we really want.
2115 This also means that in order to write a regular expression that matches
2116 a single backslash character, the regular expression string in the
2117 source code must include @emph{four} backslashes. Each consecutive pair
2118 of backslashes gets translated by the Guile reader to a single
2119 backslash, and the resulting double-backslash is interpreted by the
2120 regexp engine as matching a single backslash character. Hence:
2123 (define tex-variable-pattern (make-regexp "\\\\let\\\\=[A-Za-z]*"))
2126 The reason for the unwieldiness of this syntax is historical. Both
2127 regular expression pattern matchers and Unix string processing systems
2128 have traditionally used backslashes with the special meanings
2129 described above. The POSIX regular expression specification and ANSI C
2130 standard both require these semantics. Attempting to abandon either
2131 convention would cause other kinds of compatibility problems, possibly
2132 more severe ones. Therefore, without extending the Scheme reader to
2133 support strings with different quoting conventions (an ungainly and
2134 confusing extension when implemented in other languages), we must adhere
2135 to this cumbersome escape syntax.
2138 @subsection Rx Interface
2140 @c FIXME::martin: Shouldn't this be removed or moved to the
2141 @c ``Guile Modules'' chapter? The functions are not available in
2144 [FIXME: this is taken from Gary and Mark's quick summaries and should be
2145 reviewed and expanded. Rx is pretty stable, so could already be done!]
2148 @cindex finite automaton
2150 Guile includes an interface to Tom Lord's Rx library (currently only to
2151 POSIX regular expressions). Use of the library requires a two step
2152 process: compile a regular expression into an efficient structure, then
2153 use the structure in any number of string comparisons.
2155 For example, given the
2156 regular expression @samp{abc.} (which matches any string containing
2157 @samp{abc} followed by any single character):
2160 guile> @kbd{(define r (regcomp "abc."))}
2163 guile> @kbd{(regexec r "abc")}
2165 guile> @kbd{(regexec r "abcd")}
2170 The definitions of @code{regcomp} and @code{regexec} are as follows:
2172 @c NJFIXME not in libguile!
2173 @deffn primitive regcomp pattern [flags]
2174 Compile the regular expression pattern using POSIX rules. Flags is
2175 optional and should be specified using symbolic names:
2176 @defvar REG_EXTENDED
2177 use extended POSIX syntax
2180 use case-insensitive matching
2183 allow anchors to match after newline characters in the
2184 string and prevents @code{.} or @code{[^...]} from matching newlines.
2187 The @code{logior} procedure can be used to combine multiple flags.
2188 The default is to use
2189 POSIX basic syntax, which makes @code{+} and @code{?} literals and @code{\+}
2191 operators. Backslashes in @var{pattern} must be escaped if specified in a
2192 literal string e.g., @code{"\\(a\\)\\?"}.
2195 @c NJFIXME not in libguile!
2196 @deffn primitive regexec regex string [match-pick] [flags]
2198 Match @var{string} against the compiled POSIX regular expression
2200 @var{match-pick} and @var{flags} are optional. Possible flags (which can be
2201 combined using the logior procedure) are:
2204 The beginning of line operator won't match the beginning of
2205 @var{string} (presumably because it's not the beginning of a line)
2209 Similar to REG_NOTBOL, but prevents the end of line operator
2210 from matching the end of @var{string}.
2213 If no match is possible, regexec returns #f. Otherwise @var{match-pick}
2214 determines the return value:
2216 @code{#t} or unspecified: a newly-allocated vector is returned,
2217 containing pairs with the indices of the matched part of @var{string} and any
2220 @code{""}: a list is returned: the first element contains a nested list
2221 with the matched part of @var{string} surrounded by the the unmatched parts.
2222 Remaining elements are matched substrings (if any). All returned
2223 substrings share memory with @var{string}.
2225 @code{#f}: regexec returns #t if a match is made, otherwise #f.
2227 vector: the supplied vector is returned, with the first element replaced
2228 by a pair containing the indices of the matched portion of @var{string} and
2229 further elements replaced by pairs containing the indices of matched
2230 substrings (if any).
2232 list: a list will be returned, with each member of the list
2233 specified by a code in the corresponding position of the supplied list:
2235 a number: the numbered matching substring (0 for the entire match).
2237 @code{#\<}: the beginning of @var{string} to the beginning of the part matched
2240 @code{#\>}: the end of the matched part of @var{string} to the end of
2243 @code{#\c}: the "final tag", which seems to be associated with the "cut
2244 operator", which doesn't seem to be available through the posix
2247 e.g., @code{(list #\< 0 1 #\>)}. The returned substrings share memory with
2251 Here are some other procedures that might be used when using regular
2254 @c NJFIXME not in libguile!
2255 @deffn primitive compiled-regexp? obj
2256 Test whether obj is a compiled regular expression.
2259 @c NJFIXME not in libguile!
2260 @deffn primitive regexp->dfa regex [flags]
2263 @c NJFIXME not in libguile!
2264 @deffn primitive dfa-fork dfa
2267 @c NJFIXME not in libguile!
2268 @deffn primitive reset-dfa! dfa
2271 @c NJFIXME not in libguile!
2272 @deffn primitive dfa-final-tag dfa
2275 @c NJFIXME not in libguile!
2276 @deffn primitive dfa-continuable? dfa
2279 @c NJFIXME not in libguile!
2280 @deffn primitive advance-dfa! dfa string
2284 @node Symbols and Variables
2285 @section Symbols and Variables
2287 @c FIXME::martin: Review me!
2289 Symbols are a data type with a special property. On the one hand,
2290 symbols are used for denoting variables in a Scheme program, on the
2291 other they can be used as literal data as well.
2293 The association between symbols and values is maintained in special data
2294 structures, the symbol tables.
2296 In addition, Guile offers variables as first-class objects. They can
2297 be used for interacting with the module system.
2300 * Symbols:: All about symbols as a data type.
2301 * Symbol Tables:: Tables for mapping symbols to values.
2302 * Variables:: First-class variables.
2308 @c FIXME::martin: Review me!
2310 Symbols are especially useful because two symbols which are spelled the
2311 same way are equivalent in the sense of @code{eq?}. That means that
2312 they are actually the same Scheme object. The advantage is that symbols
2313 can be compared extremely efficiently, although they carry more
2314 information for the human reader than, say, numbers.
2316 It is very common in Scheme programs to use symbols as keys in
2317 association lists (@pxref{Association Lists}) or hash tables
2318 (@pxref{Hash Tables}), because this usage improves the readability a
2319 lot, and does not cause any performance loss.
2321 The read syntax for symbols is a sequence of letters, digits, and
2322 @emph{extended alphabetic characters} that begins with a character that
2323 cannot begin a number is an identifier. In addition, @code{+},
2324 @code{-}, and @code{...} are identifiers.
2326 Extended alphabetic characters may be used within identifiers as if
2327 they were letters. The following are extended alphabetic characters:
2330 ! $ % & * + - . / : < = > ? @@ ^ _ ~
2333 In addition to the read syntax defined above (which is taken from R5RS
2334 (@pxref{Formal syntax,,,r5rs,The Revised^5 Report on Scheme})), Guile
2335 provides a method for writing symbols with unusual characters, such as
2336 space characters. If you (for whatever reason) need to write a symbol
2337 containing characters not mentioned above, you write symbols as follows:
2341 Begin the symbol with the two character @code{#@{},
2344 write the characters of the symbol and
2347 finish the symbol with the characters @code{@}#}.
2350 Here are a few examples of this form of read syntax; the first
2351 containing a space character, the second containing a line break and the
2352 last one looks like a number.
2361 Usage of this form of read syntax is discouraged, because it is not
2362 portable at all, and is not very readable.
2365 @deffn primitive symbol? obj
2366 Return @code{#t} if @var{obj} is a symbol, otherwise return
2370 @rnindex string->symbol
2371 @deffn primitive string->symbol string
2372 Return the symbol whose name is @var{string}. This procedure
2373 can create symbols with names containing special characters or
2374 letters in the non-standard case, but it is usually a bad idea
2375 to create such symbols because in some implementations of
2376 Scheme they cannot be read as themselves. See
2377 @code{symbol->string}.
2379 The following examples assume that the implementation's
2380 standard case is lower case:
2383 (eq? 'mISSISSIppi 'mississippi) @result{} #t
2384 (string->symbol "mISSISSIppi") @result{} @r{the symbol with name "mISSISSIppi"}
2385 (eq? 'bitBlt (string->symbol "bitBlt")) @result{} #f
2387 (string->symbol (symbol->string 'JollyWog))) @result{} #t
2388 (string=? "K. Harper, M.D."
2390 (string->symbol "K. Harper, M.D."))) @result{}#t
2394 @rnindex symbol->string
2395 @deffn primitive symbol->string s
2396 Return the name of @var{symbol} as a string. If the symbol was
2397 part of an object returned as the value of a literal expression
2398 (section @pxref{Literal expressions,,,r5rs, The Revised^5
2399 Report on Scheme}) or by a call to the @code{read} procedure,
2400 and its name contains alphabetic characters, then the string
2401 returned will contain characters in the implementation's
2402 preferred standard case--some implementations will prefer
2403 upper case, others lower case. If the symbol was returned by
2404 @code{string->symbol}, the case of characters in the string
2405 returned will be the same as the case in the string that was
2406 passed to @code{string->symbol}. It is an error to apply
2407 mutation procedures like @code{string-set!} to strings returned
2410 The following examples assume that the implementation's
2411 standard case is lower case:
2414 (symbol->string 'flying-fish) @result{} "flying-fish"
2415 (symbol->string 'Martin) @result{} "martin"
2417 (string->symbol "Malvina")) @result{} "Malvina"
2422 @subsection Symbol Tables
2424 @c FIXME::martin: Review me!
2426 @c FIXME::martin: Are all these procedures still relevant?
2428 Guile symbol tables are hash tables. Each hash table, also called an
2429 @dfn{obarray} (for `object array'), is a vector of association lists.
2430 Each entry in the alists is a pair (@var{SYMBOL} . @var{VALUE}). To
2431 @dfn{intern} a symbol in a symbol table means to return its
2432 (@var{SYMBOL} . @var{VALUE}) pair, adding a new entry to the symbol
2433 table (with an undefined value) if none is yet present.
2435 @c FIXME::martin: According to NEWS, removed. Remove here too, or
2436 @c leave for compatibility?
2437 @c @c docstring begin (texi-doc-string "guile" "builtin-bindings")
2438 @c @deffn primitive builtin-bindings
2439 @c Create and return a copy of the global symbol table, removing all
2443 @deffn primitive gensym [prefix]
2444 Create a new symbol with a name constructed from a prefix and
2445 a counter value. The string @var{prefix} can be specified as
2446 an optional argument. Default prefix is @code{g}. The counter
2447 is increased by 1 at each call. There is no provision for
2448 resetting the counter.
2451 @deffn primitive gentemp [prefix [obarray]]
2452 Create a new symbol with a name unique in an obarray.
2453 The name is constructed from an optional string @var{prefix}
2454 and a counter value. The default prefix is @code{t}. The
2455 @var{obarray} is specified as a second optional argument.
2456 Default is the system obarray where all normal symbols are
2457 interned. The counter is increased by 1 at each
2458 call. There is no provision for resetting the counter.
2461 @deffn primitive intern-symbol obarray string
2462 Add a new symbol to @var{obarray} with name @var{string}, bound to an
2463 unspecified initial value. The symbol table is not modified if a symbol
2464 with this name is already present.
2467 @deffn primitive string->obarray-symbol obarray string [soft?]
2468 Intern a new symbol in @var{obarray}, a symbol table, with name
2472 @deffn primitive symbol-binding obarray string
2473 Look up in @var{obarray} the symbol whose name is @var{string}, and
2474 return the value to which it is bound. If @var{obarray} is @code{#f},
2475 use the global symbol table. If @var{string} is not interned in
2476 @var{obarray}, an error is signalled.
2479 @deffn primitive symbol-bound? obarray string
2480 Return @code{#t} if @var{obarray} contains a symbol with name
2481 @var{string} bound to a defined value. This differs from
2482 @var{symbol-interned?} in that the mere mention of a symbol
2483 usually causes it to be interned; @code{symbol-bound?}
2484 determines whether a symbol has been given any meaningful
2488 @deffn primitive symbol-fref symbol
2489 Return the contents of @var{symbol}'s @dfn{function slot}.
2492 @deffn primitive symbol-fset! symbol value
2493 Change the binding of @var{symbol}'s function slot.
2496 @deffn primitive symbol-hash symbol
2497 Return a hash value for @var{symbol}.
2500 @deffn primitive symbol-interned? obarray string
2501 Return @code{#t} if @var{obarray} contains a symbol with name
2502 @var{string}, and @code{#f} otherwise.
2505 @deffn primitive symbol-pref symbol
2506 Return the @dfn{property list} currently associated with @var{symbol}.
2509 @deffn primitive symbol-pset! symbol value
2510 Change the binding of @var{symbol}'s property slot.
2513 @deffn primitive symbol-set! obarray string value
2514 Find the symbol in @var{obarray} whose name is @var{string}, and rebind
2515 it to @var{value}. An error is signalled if @var{string} is not present
2519 @deffn primitive unintern-symbol obarray string
2520 Remove the symbol with name @var{string} from @var{obarray}. This
2521 function returns @code{#t} if the symbol was present and @code{#f}
2526 @subsection Variables
2528 @c FIXME::martin: Review me!
2530 Variables are objects with two fields. They contain a value and they
2531 can contain a symbol, which is the name of the variable. A variable is
2532 said to be bound if it does not contain the object denoting unbound
2533 variables in the value slot.
2535 Variables do not have a read syntax, they have to be created by calling
2536 one of the constructor procedures @code{make-variable} or
2537 @code{make-undefined-variable} or retrieved by @code{builtin-variable}.
2539 First-class variables are especially useful for interacting with the
2540 current module system (@pxref{The Guile module system}).
2542 @deffn primitive builtin-variable name
2543 Return the built-in variable with the name @var{name}.
2544 @var{name} must be a symbol (not a string).
2545 Then use @code{variable-ref} to access its value.
2548 @deffn primitive make-undefined-variable [name-hint]
2549 Return a variable object initialized to an undefined value.
2550 If given, uses @var{name-hint} as its internal (debugging)
2551 name, otherwise just treat it as an anonymous variable.
2552 Remember, of course, that multiple bindings to the same
2553 variable may exist, so @var{name-hint} is just that---a hint.
2556 @deffn primitive make-variable init [name-hint]
2557 Return a variable object initialized to value @var{init}.
2558 If given, uses @var{name-hint} as its internal (debugging)
2559 name, otherwise just treat it as an anonymous variable.
2560 Remember, of course, that multiple bindings to the same
2561 variable may exist, so @var{name-hint} is just that---a hint.
2564 @deffn primitive variable-bound? var
2565 Return @code{#t} iff @var{var} is bound to a value.
2566 Throws an error if @var{var} is not a variable object.
2569 @deffn primitive variable-ref var
2570 Dereference @var{var} and return its value.
2571 @var{var} must be a variable object; see @code{make-variable}
2572 and @code{make-undefined-variable}.
2575 @deffn primitive variable-set! var val
2576 Set the value of the variable @var{var} to @var{val}.
2577 @var{var} must be a variable object, @var{val} can be any
2578 value. Return an unspecified value.
2581 @deffn primitive variable? obj
2582 Return @code{#t} iff @var{obj} is a variable object, else
2590 Keywords are self-evaluating objects with a convenient read syntax that
2591 makes them easy to type.
2593 Guile's keyword support conforms to R5RS, and adds a (switchable) read
2594 syntax extension to permit keywords to begin with @code{:} as well as
2598 * Why Use Keywords?:: Motivation for keyword usage.
2599 * Coding With Keywords:: How to use keywords.
2600 * Keyword Read Syntax:: Read syntax for keywords.
2601 * Keyword Primitives:: Procedures for dealing with keywords.
2604 @node Why Use Keywords?
2605 @subsection Why Use Keywords?
2607 Keywords are useful in contexts where a program or procedure wants to be
2608 able to accept a large number of optional arguments without making its
2609 interface unmanageable.
2611 To illustrate this, consider a hypothetical @code{make-window}
2612 procedure, which creates a new window on the screen for drawing into
2613 using some graphical toolkit. There are many parameters that the caller
2614 might like to specify, but which could also be sensibly defaulted, for
2619 colour depth -- Default: the colour depth for the screen
2622 background colour -- Default: white
2625 width -- Default: 600
2628 height -- Default: 400
2631 If @code{make-window} did not use keywords, the caller would have to
2632 pass in a value for each possible argument, remembering the correct
2633 argument order and using a special value to indicate the default value
2637 (make-window 'default ;; Colour depth
2638 'default ;; Background colour
2641 @dots{}) ;; More make-window arguments
2644 With keywords, on the other hand, defaulted arguments are omitted, and
2645 non-default arguments are clearly tagged by the appropriate keyword. As
2646 a result, the invocation becomes much clearer:
2649 (make-window #:width 800 #:height 100)
2652 On the other hand, for a simpler procedure with few arguments, the use
2653 of keywords would be a hindrance rather than a help. The primitive
2654 procedure @code{cons}, for example, would not be improved if it had to
2658 (cons #:car x #:cdr y)
2661 So the decision whether to use keywords or not is purely pragmatic: use
2662 them if they will clarify the procedure invocation at point of call.
2664 @node Coding With Keywords
2665 @subsection Coding With Keywords
2667 If a procedure wants to support keywords, it should take a rest argument
2668 and then use whatever means is convenient to extract keywords and their
2669 corresponding arguments from the contents of that rest argument.
2671 The following example illustrates the principle: the code for
2672 @code{make-window} uses a helper procedure called
2673 @code{get-keyword-value} to extract individual keyword arguments from
2677 (define (get-keyword-value args keyword default)
2678 (let ((kv (memq keyword args)))
2679 (if (and kv (>= (length kv) 2))
2683 (define (make-window . args)
2684 (let ((depth (get-keyword-value args #:depth screen-depth))
2685 (bg (get-keyword-value args #:bg "white"))
2686 (width (get-keyword-value args #:width 800))
2687 (height (get-keyword-value args #:height 100))
2692 But you don't need to write @code{get-keyword-value}. The @code{(ice-9
2693 optargs)} module provides a set of powerful macros that you can use to
2694 implement keyword-supporting procedures like this:
2697 (use-modules (ice-9 optargs))
2699 (define (make-window . args)
2700 (let-keywords args #f ((depth screen-depth)
2708 Or, even more economically, like this:
2711 (use-modules (ice-9 optargs))
2713 (define* (make-window #:key (depth screen-depth)
2720 For further details on @code{let-keywords}, @code{define*} and other
2721 facilities provided by the @code{(ice-9 optargs)} module, @ref{Optional
2725 @node Keyword Read Syntax
2726 @subsection Keyword Read Syntax
2728 Guile, by default, only recognizes the keyword syntax specified by R5RS.
2729 A token of the form @code{#:NAME}, where @code{NAME} has the same syntax
2730 as a Scheme symbol, is the external representation of the keyword named
2731 @code{NAME}. Keyword objects print using this syntax as well, so values
2732 containing keyword objects can be read back into Guile. When used in an
2733 expression, keywords are self-quoting objects.
2735 If the @code{keyword} read option is set to @code{'prefix}, Guile also
2736 recognizes the alternative read syntax @code{:NAME}. Otherwise, tokens
2737 of the form @code{:NAME} are read as symbols, as required by R5RS.
2739 To enable and disable the alternative non-R5RS keyword syntax, you use
2740 the @code{read-options} procedure documented in @ref{General option
2741 interface} and @ref{Reader options}.
2744 (read-set! keywords 'prefix)
2754 (read-set! keywords #f)
2762 ERROR: In expression :type:
2763 ERROR: Unbound variable: :type
2764 ABORT: (unbound-variable)
2767 @node Keyword Primitives
2768 @subsection Keyword Primitives
2770 Internally, a keyword is implemented as something like a tagged symbol,
2771 where the tag identifies the keyword as being self-evaluating, and the
2772 symbol, known as the keyword's @dfn{dash symbol} has the same name as
2773 the keyword name but prefixed by a single dash. For example, the
2774 keyword @code{#:name} has the corresponding dash symbol @code{-name}.
2776 Most keyword objects are constructed automatically by the reader when it
2777 reads a token beginning with @code{#:}. However, if you need to
2778 construct a keyword object programmatically, you can do so by calling
2779 @code{make-keyword-from-dash-symbol} with the corresponding dash symbol
2780 (as the reader does). The dash symbol for a keyword object can be
2781 retrieved using the @code{keyword-dash-symbol} procedure.
2783 @deffn primitive make-keyword-from-dash-symbol symbol
2784 Make a keyword object from a @var{symbol} that starts with a dash.
2787 @deffn primitive keyword? obj
2788 Return @code{#t} if the argument @var{obj} is a keyword, else
2792 @deffn primitive keyword-dash-symbol keyword
2793 Return the dash symbol for @var{keyword}.
2794 This is the inverse of @code{make-keyword-from-dash-symbol}.
2801 @c FIXME::martin: Review me!
2803 Pairs are used to combine two Scheme objects into one compound object.
2804 Hence the name: A pair stores a pair of objects.
2806 The data type @emph{pair} is extremely important in Scheme, just like in
2807 any other Lisp dialect. The reason is that pairs are not only used to
2808 make two values available as one object, but that pairs are used for
2809 constructing lists of values. Because lists are so important in Scheme,
2810 they are described in a section of their own (@pxref{Lists}).
2812 Pairs can literally get entered in source code or at the REPL, in the
2813 so-called @dfn{dotted list} syntax. This syntax consists of an opening
2814 parentheses, the first element of the pair, a dot, the second element
2815 and a closing parentheses. The following example shows how a pair
2816 consisting of the two numbers 1 and 2, and a pair containing the symbols
2817 @code{foo} and @code{bar} can be entered. It is very important to write
2818 the whitespace before and after the dot, because otherwise the Scheme
2819 parser whould not be able to figure out where to split the tokens.
2826 But beware, if you want to try out these examples, you have to
2827 @dfn{quote} the expressions. More information about quotation is
2828 available in the section (REFFIXME). The correct way to try these
2829 examples is as follows.
2840 A new pair is made by calling the procedure @code{cons} with two
2841 arguments. Then the argument values are stored into a newly allocated
2842 pair, and the pair is returned. The name @code{cons} stands for
2843 @emph{construct}. Use the procedure @code{pair?} to test whether a
2844 given Scheme object is a pair or not.
2847 @deffn primitive cons x y
2848 Return a newly allocated pair whose car is @var{x} and whose
2849 cdr is @var{y}. The pair is guaranteed to be different (in the
2850 sense of @code{eq?}) from every previously existing object.
2854 @deffn primitive pair? x
2855 Return @code{#t} if @var{x} is a pair; otherwise return
2859 The two parts of a pair are traditionally called @emph{car} and
2860 @emph{cdr}. They can be retrieved with procedures of the same name
2861 (@code{car} and @code{cdr}), and can be modified with the procedures
2862 @code{set-car!} and @code{set-cdr!}. Since a very common operation in
2863 Scheme programs is to access the car of a pair, or the car of the cdr of
2864 a pair, etc., the procedures called @code{caar}, @code{cadr} and so on
2865 are also predefined.
2869 @deffn primitive car pair
2870 @deffnx primitive cdr pair
2871 Return the car or the cdr of @var{pair}, respectively.
2874 @deffn primitive caar pair
2875 @deffnx primitive cadr pair @dots{}
2876 @deffnx primitive cdddar pair
2877 @deffnx primitive cddddr pair
2878 These procedures are compositions of @code{car} and @code{cdr}, where
2879 for example @code{caddr} could be defined by
2882 (define caddr (lambda (x) (car (cdr (cdr x)))))
2887 @deffn primitive set-car! pair value
2888 Stores @var{value} in the car field of @var{pair}. The value returned
2889 by @code{set-car!} is unspecified.
2893 @deffn primitive set-cdr! pair value
2894 Stores @var{value} in the cdr field of @var{pair}. The value returned
2895 by @code{set-cdr!} is unspecified.
2902 @c FIXME::martin: Review me!
2904 A very important data type in Scheme---as well as in all other Lisp
2905 dialects---is the data type @dfn{list}.@footnote{Strictly speaking,
2906 Scheme does not have a real datatype @emph{list}. Lists are made up of
2907 chained @emph{pairs}, and only exist by definition---a list is a chain
2908 of pairs which looks like a list.}
2910 This is the short definition of what a list is:
2914 Either the empty list @code{()},
2917 or a pair which has a list in its cdr.
2920 @c FIXME::martin: Describe the pair chaining in more detail.
2922 @c FIXME::martin: What is a proper, what an improper list?
2923 @c What is a circular list?
2925 @c FIXME::martin: Maybe steal some graphics from the Elisp reference
2929 * List Syntax:: Writing literal lists.
2930 * List Predicates:: Testing lists.
2931 * List Constructors:: Creating new lists.
2932 * List Selection:: Selecting from lists, getting their length.
2933 * Append/Reverse:: Appending and reversing lists.
2934 * List Modifification:: Modifying list structure.
2935 * List Searching:: Searching for list elements
2936 * List Mapping:: Applying procedures to lists.
2940 @subsection List Read Syntax
2942 @c FIXME::martin: Review me!
2944 The syntax for lists is an opening parentheses, then all the elements of
2945 the list (separated by whitespace) and finally a closing
2946 parentheses.@footnote{Note that there is no separation character between
2947 the list elements, like a comma or a semicolon.}.
2950 (1 2 3) ; @r{a list of the numbers 1, 2 and 3}
2951 ("foo" bar 3.1415) ; @r{a string, a symbol and a real number}
2952 () ; @r{the empty list}
2955 The last example needs a bit more explanation. A list with no elements,
2956 called the @dfn{empty list}, is special in some ways. It is used for
2957 terminating lists by storing it into the cdr of the last pair that makes
2958 up a list. An example will clear that up:
2969 This example also shows that lists have to be quoted (REFFIXME) when
2970 written, because they would otherwise be mistakingly taken as procedure
2971 applications (@pxref{Simple Invocation}).
2974 @node List Predicates
2975 @subsection List Predicates
2977 @c FIXME::martin: Review me!
2979 Often it is useful to test whether a given Scheme object is a list or
2980 not. List-processing procedures could use this information to test
2981 whether their input is valid, or they could do different things
2982 depending on the datatype of their arguments.
2985 @deffn primitive list? x
2986 Return @code{#t} iff @var{x} is a proper list, else @code{#f}.
2989 The predicate @code{null?} is often used in list-processing code to
2990 tell whether a given list has run out of elements. That is, a loop
2991 somehow deals with the elements of a list until the list satisfies
2992 @code{null?}. Then, teh algorithm terminates.
2995 @deffn primitive null? x
2996 Return @code{#t} iff @var{x} is the empty list, else @code{#f}.
2999 @node List Constructors
3000 @subsection List Constructors
3002 This section describes the procedures for constructing new lists.
3003 @code{list} simply returns a list where the elements are the arguments,
3004 @code{cons*} is similar, but the last argument is stored in the cdr of
3005 the last pair of the list.
3008 @deffn primitive list arg1 @dots{}
3009 Return a list containing @var{objs}, the arguments to
3013 @deffn primitive cons* arg1 arg2 @dots{}
3014 Like @code{list}, but the last arg provides the tail of the
3015 constructed list, returning @code{(cons @var{arg1} (cons
3016 @var{arg2} (cons @dots{} @var{argn})))}. Requires at least one
3017 argument. If given one argument, that argument is returned as
3018 result. This function is called @code{list*} in some other
3019 Schemes and in Common LISP.
3022 @deffn primitive list-copy lst
3023 Return a (newly-created) copy of @var{lst}.
3026 Note that @code{list-copy} only makes a copy of the pairs which make up
3027 the spine of the lists. The list elements are not copied, which means
3028 that modifying the elements of the new list also modyfies the elements
3029 of the old list. On the other hand, applying procedures like
3030 @code{set-cdr!} or @code{delv!} to the new list will not alter the old
3031 list. If you also need to copy the list elements (making a deep copy),
3032 use the procedure @code{copy-tree} (@pxref{Copying}).
3034 @node List Selection
3035 @subsection List Selection
3037 @c FIXME::martin: Review me!
3039 These procedures are used to get some information about a list, or to
3040 retrieve one or more elements of a list.
3043 @deffn primitive length lst
3044 Return the number of elements in list @var{lst}.
3047 @deffn primitive last-pair lst
3048 Return a pointer to the last pair in @var{lst}, signalling an error if
3049 @var{lst} is circular.
3053 @deffn primitive list-ref list k
3054 Return the @var{k}th element from @var{list}.
3058 @deffn primitive list-tail lst k
3059 @deffnx primitive list-cdr-ref lst k
3060 Return the "tail" of @var{lst} beginning with its @var{k}th element.
3061 The first element of the list is considered to be element 0.
3063 @code{list-tail} and @code{list-cdr-ref} are identical. It may help to
3064 think of @code{list-cdr-ref} as accessing the @var{k}th cdr of the list,
3065 or returning the results of cdring @var{k} times down @var{lst}.
3068 @deffn primitive list-head lst k
3069 Copy the first @var{k} elements from @var{lst} into a new list, and
3073 @node Append/Reverse
3074 @subsection Append and Reverse
3076 @c FIXME::martin: Review me!
3078 @code{append} and @code{append!} are used to concatenate two or more
3079 lists in order to form a new list. @code{reverse} and @code{reverse!}
3080 return lists with the same elements as their arguments, but in reverse
3081 order. The procedure variants with an @code{!} directly modify the
3082 pairs which form the list, whereas the other procedures create new
3083 pairs. This is why you should be careful when using the side-effecting
3087 @deffn primitive append . args
3088 Return a list consisting of the elements the lists passed as
3091 (append '(x) '(y)) @result{} (x y)
3092 (append '(a) '(b c d)) @result{} (a b c d)
3093 (append '(a (b)) '((c))) @result{} (a (b) (c))
3095 The resulting list is always newly allocated, except that it
3096 shares structure with the last list argument. The last
3097 argument may actually be any object; an improper list results
3098 if the last argument is not a proper list.
3100 (append '(a b) '(c . d)) @result{} (a b c . d)
3101 (append '() 'a) @result{} a
3105 @deffn primitive append! . lists
3106 A destructive version of @code{append} (@pxref{Pairs and
3107 lists,,,r5rs, The Revised^5 Report on Scheme}). The cdr field
3108 of each list's final pair is changed to point to the head of
3109 the next list, so no consing is performed. Return a pointer to
3114 @deffn primitive reverse lst
3115 Return a new list that contains the elements of @var{lst} but
3119 @c NJFIXME explain new_tail
3120 @deffn primitive reverse! lst [new_tail]
3121 A destructive version of @code{reverse} (@pxref{Pairs and lists,,,r5rs,
3122 The Revised^5 Report on Scheme}). The cdr of each cell in @var{lst} is
3123 modified to point to the previous list element. Return a pointer to the
3124 head of the reversed list.
3126 Caveat: because the list is modified in place, the tail of the original
3127 list now becomes its head, and the head of the original list now becomes
3128 the tail. Therefore, the @var{lst} symbol to which the head of the
3129 original list was bound now points to the tail. To ensure that the head
3130 of the modified list is not lost, it is wise to save the return value of
3134 @node List Modifification
3135 @subsection List Modification
3137 @c FIXME::martin: Review me!
3139 The following procedures modify existing list. @code{list-set!} and
3140 @code{list-cdr-set!} change which elements a list contains, the various
3141 deletion procedures @code{delq}, @code{delv} etc.
3143 @deffn primitive list-set! list k val
3144 Set the @var{k}th element of @var{list} to @var{val}.
3147 @deffn primitive list-cdr-set! list k val
3148 Set the @var{k}th cdr of @var{list} to @var{val}.
3151 @deffn primitive delq item lst
3152 Return a newly-created copy of @var{lst} with elements
3153 @code{eq?} to @var{item} removed. This procedure mirrors
3154 @code{memq}: @code{delq} compares elements of @var{lst} against
3155 @var{item} with @code{eq?}.
3158 @deffn primitive delv item lst
3159 Return a newly-created copy of @var{lst} with elements
3160 @code{eqv?} to @var{item} removed. This procedure mirrors
3161 @code{memv}: @code{delv} compares elements of @var{lst} against
3162 @var{item} with @code{eqv?}.
3165 @deffn primitive delete item lst
3166 Return a newly-created copy of @var{lst} with elements
3167 @code{equal?} to @var{item} removed. This procedure mirrors
3168 @code{member}: @code{delete} compares elements of @var{lst}
3169 against @var{item} with @code{equal?}.
3172 @deffn primitive delq! item lst
3173 @deffnx primitive delv! item lst
3174 @deffnx primitive delete! item lst
3175 These procedures are destructive versions of @code{delq}, @code{delv}
3176 and @code{delete}: they modify the pointers in the existing @var{lst}
3177 rather than creating a new list. Caveat evaluator: Like other
3178 destructive list functions, these functions cannot modify the binding of
3179 @var{lst}, and so cannot be used to delete the first element of
3180 @var{lst} destructively.
3183 @deffn primitive delq1! item lst
3184 Like @code{delq!}, but only deletes the first occurrence of
3185 @var{item} from @var{lst}. Tests for equality using
3186 @code{eq?}. See also @code{delv1!} and @code{delete1!}.
3189 @deffn primitive delv1! item lst
3190 Like @code{delv!}, but only deletes the first occurrence of
3191 @var{item} from @var{lst}. Tests for equality using
3192 @code{eqv?}. See also @code{delq1!} and @code{delete1!}.
3195 @deffn primitive delete1! item lst
3196 Like @code{delete!}, but only deletes the first occurrence of
3197 @var{item} from @var{lst}. Tests for equality using
3198 @code{equal?}. See also @code{delq1!} and @code{delv1!}.
3201 @node List Searching
3202 @subsection List Searching
3204 @c FIXME::martin: Review me!
3206 The following procedures search lists for particular elements. They use
3207 different comparison predicates for comparing list elements with the
3208 object to be seached. When they fail, they return @code{#f}, otherwise
3209 they return the sublist whose car is equal to the search object, where
3210 equality depends on the equality predicate used.
3213 @deffn primitive memq x lst
3214 Return the first sublist of @var{lst} whose car is @code{eq?}
3215 to @var{x} where the sublists of @var{lst} are the non-empty
3216 lists returned by @code{(list-tail @var{lst} @var{k})} for
3217 @var{k} less than the length of @var{lst}. If @var{x} does not
3218 occur in @var{lst}, then @code{#f} (not the empty list) is
3223 @deffn primitive memv x lst
3224 Return the first sublist of @var{lst} whose car is @code{eqv?}
3225 to @var{x} where the sublists of @var{lst} are the non-empty
3226 lists returned by @code{(list-tail @var{lst} @var{k})} for
3227 @var{k} less than the length of @var{lst}. If @var{x} does not
3228 occur in @var{lst}, then @code{#f} (not the empty list) is
3233 @deffn primitive member x lst
3234 Return the first sublist of @var{lst} whose car is
3235 @code{equal?} to @var{x} where the sublists of @var{lst} are
3236 the non-empty lists returned by @code{(list-tail @var{lst}
3237 @var{k})} for @var{k} less than the length of @var{lst}. If
3238 @var{x} does not occur in @var{lst}, then @code{#f} (not the
3239 empty list) is returned.
3242 [FIXME: is there any reason to have the `sloppy' functions available at
3243 high level at all? Maybe these docs should be relegated to a "Guile
3244 Internals" node or something. -twp]
3246 @deffn primitive sloppy-memq x lst
3247 This procedure behaves like @code{memq}, but does no type or error checking.
3248 Its use is recommended only in writing Guile internals,
3249 not for high-level Scheme programs.
3252 @deffn primitive sloppy-memv x lst
3253 This procedure behaves like @code{memv}, but does no type or error checking.
3254 Its use is recommended only in writing Guile internals,
3255 not for high-level Scheme programs.
3258 @deffn primitive sloppy-member x lst
3259 This procedure behaves like @code{member}, but does no type or error checking.
3260 Its use is recommended only in writing Guile internals,
3261 not for high-level Scheme programs.
3265 @subsection List Mapping
3267 @c FIXME::martin: Review me!
3269 List processing is very convenient in Scheme because the process of
3270 iterating over the elements of a list can be highly abstracted. The
3271 procedures in this section are the most basic iterating procedures for
3272 lists. They take a procedure and one or more lists as arguments, and
3273 apply the procedure to each element of the list. They differ in what
3274 the result of the invocation is.
3277 @c begin (texi-doc-string "guile" "map")
3278 @deffn primitive map proc arg1 arg2 @dots{}
3279 @deffnx primitive map-in-order proc arg1 arg2 @dots{}
3280 Apply @var{proc} to each element of the list @var{arg1} (if only two
3281 arguments are given), or to the corresponding elements of the argument
3282 lists (if more than two arguments are given). The result(s) of the
3283 procedure applications are saved and returned in a list. For
3284 @code{map}, the order of procedure applications is not specified,
3285 @code{map-in-order} applies the procedure from left to right to the list
3290 @c begin (texi-doc-string "guile" "for-each")
3291 @deffn primitive for-each proc arg1 arg2 @dots{}
3292 Like @code{map}, but the procedure is always applied from left to right,
3293 and the result(s) of the procedure applications are thrown away. The
3294 return value is not specified.
3301 [FIXME: this is pasted in from Tom Lord's original guile.texi and should
3304 A @dfn{record type} is a first class object representing a user-defined
3305 data type. A @dfn{record} is an instance of a record type.
3307 @deffn procedure record? obj
3308 Returns @code{#t} if @var{obj} is a record of any type and @code{#f}
3311 Note that @code{record?} may be true of any Scheme value; there is no
3312 promise that records are disjoint with other Scheme types.
3315 @deffn procedure make-record-type type-name field-names
3316 Returns a @dfn{record-type descriptor}, a value representing a new data
3317 type disjoint from all others. The @var{type-name} argument must be a
3318 string, but is only used for debugging purposes (such as the printed
3319 representation of a record of the new type). The @var{field-names}
3320 argument is a list of symbols naming the @dfn{fields} of a record of the
3321 new type. It is an error if the list contains any duplicates. It is
3322 unspecified how record-type descriptors are represented.@refill
3325 @deffn procedure record-constructor rtd [field-names]
3326 Returns a procedure for constructing new members of the type represented
3327 by @var{rtd}. The returned procedure accepts exactly as many arguments
3328 as there are symbols in the given list, @var{field-names}; these are
3329 used, in order, as the initial values of those fields in a new record,
3330 which is returned by the constructor procedure. The values of any
3331 fields not named in that list are unspecified. The @var{field-names}
3332 argument defaults to the list of field names in the call to
3333 @code{make-record-type} that created the type represented by @var{rtd};
3334 if the @var{field-names} argument is provided, it is an error if it
3335 contains any duplicates or any symbols not in the default list.@refill
3338 @deffn procedure record-predicate rtd
3339 Returns a procedure for testing membership in the type represented by
3340 @var{rtd}. The returned procedure accepts exactly one argument and
3341 returns a true value if the argument is a member of the indicated record
3342 type; it returns a false value otherwise.@refill
3345 @deffn procedure record-accessor rtd field-name
3346 Returns a procedure for reading the value of a particular field of a
3347 member of the type represented by @var{rtd}. The returned procedure
3348 accepts exactly one argument which must be a record of the appropriate
3349 type; it returns the current value of the field named by the symbol
3350 @var{field-name} in that record. The symbol @var{field-name} must be a
3351 member of the list of field-names in the call to @code{make-record-type}
3352 that created the type represented by @var{rtd}.@refill
3355 @deffn procedure record-modifier rtd field-name
3356 Returns a procedure for writing the value of a particular field of a
3357 member of the type represented by @var{rtd}. The returned procedure
3358 accepts exactly two arguments: first, a record of the appropriate type,
3359 and second, an arbitrary Scheme value; it modifies the field named by
3360 the symbol @var{field-name} in that record to contain the given value.
3361 The returned value of the modifier procedure is unspecified. The symbol
3362 @var{field-name} must be a member of the list of field-names in the call
3363 to @code{make-record-type} that created the type represented by
3367 @deffn procedure record-type-descriptor record
3368 Returns a record-type descriptor representing the type of the given
3369 record. That is, for example, if the returned descriptor were passed to
3370 @code{record-predicate}, the resulting predicate would return a true
3371 value when passed the given record. Note that it is not necessarily the
3372 case that the returned descriptor is the one that was passed to
3373 @code{record-constructor} in the call that created the constructor
3374 procedure that created the given record.@refill
3377 @deffn procedure record-type-name rtd
3378 Returns the type-name associated with the type represented by rtd. The
3379 returned value is @code{eqv?} to the @var{type-name} argument given in
3380 the call to @code{make-record-type} that created the type represented by
3384 @deffn procedure record-type-fields rtd
3385 Returns a list of the symbols naming the fields in members of the type
3386 represented by @var{rtd}. The returned value is @code{equal?} to the
3387 field-names argument given in the call to @code{make-record-type} that
3388 created the type represented by @var{rtd}.@refill
3395 [FIXME: this is pasted in from Tom Lord's original guile.texi and should
3398 A @dfn{structure type} is a first class user-defined data type. A
3399 @dfn{structure} is an instance of a structure type. A structure type is
3402 Structures are less abstract and more general than traditional records.
3403 In fact, in Guile Scheme, records are implemented using structures.
3406 * Structure Concepts:: The structure of Structures
3407 * Structure Layout:: Defining the layout of structure types
3408 * Structure Basics:: make-, -ref and -set! procedures for structs
3409 * Vtables:: Accessing type-specific data
3412 @node Structure Concepts
3413 @subsection Structure Concepts
3415 A structure object consists of a handle, structure data, and a vtable.
3416 The handle is a Scheme value which points to both the vtable and the
3417 structure's data. Structure data is a dynamically allocated region of
3418 memory, private to the structure, divided up into typed fields. A
3419 vtable is another structure used to hold type-specific data. Multiple
3420 structures can share a common vtable.
3422 Three concepts are key to understanding structures.
3425 @item @dfn{layout specifications}
3427 Layout specifications determine how memory allocated to structures is
3428 divided up into fields. Programmers must write a layout specification
3429 whenever a new type of structure is defined.
3431 @item @dfn{structural accessors}
3433 Structure access is by field number. There is only one set of
3434 accessors common to all structure objects.
3438 Vtables, themselves structures, are first class representations of
3439 disjoint sub-types of structures in general. In most cases, when a
3440 new structure is created, programmers must specifiy a vtable for the
3441 new structure. Each vtable has a field describing the layout of its
3442 instances. Vtables can have additional, user-defined fields as well.
3447 @node Structure Layout
3448 @subsection Structure Layout
3450 When a structure is created, a region of memory is allocated to hold its
3451 state. The @dfn{layout} of the structure's type determines how that
3452 memory is divided into fields.
3454 Each field has a specified type. There are only three types allowed, each
3455 corresponding to a one letter code. The allowed types are:
3458 @item 'u' -- unprotected
3460 The field holds binary data that is not GC protected.
3462 @item 'p' -- protected
3464 The field holds a Scheme value and is GC protected.
3468 The field holds a Scheme value and is GC protected. When a structure is
3469 created with this type of field, the field is initialized to refer to
3470 the structure's own handle. This kind of field is mainly useful when
3471 mixing Scheme and C code in which the C code may need to compute a
3472 structure's handle given only the address of its malloced data.
3476 Each field also has an associated access protection. There are only
3477 three kinds of protection, each corresponding to a one letter code.
3478 The allowed protections are:
3481 @item 'w' -- writable
3483 The field can be read and written.
3485 @item 'r' -- readable
3487 The field can be read, but not written.
3491 The field can be neither read nor written. This kind
3492 of protection is for fields useful only to built-in routines.
3495 A layout specification is described by stringing together pairs
3496 of letters: one to specify a field type and one to specify a field
3497 protection. For example, a traditional cons pair type object could
3501 ; cons pairs have two writable fields of Scheme data
3505 A pair object in which the first field is held constant could be:
3511 Binary fields, (fields of type "u"), hold one @emph{word} each. The
3512 size of a word is a machine dependent value defined to be equal to the
3513 value of the C expression: @code{sizeof (long)}.
3515 The last field of a structure layout may specify a tail array.
3516 A tail array is indicated by capitalizing the field's protection
3517 code ('W', 'R' or 'O'). A tail-array field is replaced by
3518 a read-only binary data field containing an array size. The array
3519 size is determined at the time the structure is created. It is followed
3520 by a corresponding number of fields of the type specified for the
3521 tail array. For example, a conventional Scheme vector can be
3525 ; A vector is an arbitrary number of writable fields holding Scheme
3530 In the above example, field 0 contains the size of the vector and
3531 fields beginning at 1 contain the vector elements.
3533 A kind of tagged vector (a constant tag followed by conventioal
3534 vector elements) might be:
3541 Structure layouts are represented by specially interned symbols whose
3542 name is a string of type and protection codes. To create a new
3543 structure layout, use this procedure:
3545 @deffn primitive make-struct-layout fields
3546 Return a new structure layout object.
3548 @var{fields} must be a string made up of pairs of characters
3549 strung together. The first character of each pair describes a field
3550 type, the second a field protection. Allowed types are 'p' for
3551 GC-protected Scheme data, 'u' for unprotected binary data, and 's' for
3552 a field that points to the structure itself. Allowed protections
3553 are 'w' for mutable fields, 'r' for read-only fields, and 'o' for opaque
3554 fields. The last field protection specification may be capitalized to
3555 indicate that the field is a tail-array.
3560 @node Structure Basics
3561 @subsection Structure Basics
3563 This section describes the basic procedures for creating and accessing
3566 @deffn primitive make-struct vtable tail_array_size . init
3567 Create a new structure.
3569 @var{type} must be a vtable structure (@pxref{Vtables}).
3571 @var{tail-elts} must be a non-negative integer. If the layout
3572 specification indicated by @var{type} includes a tail-array,
3573 this is the number of elements allocated to that array.
3575 The @var{init1}, @dots{} are optional arguments describing how
3576 successive fields of the structure should be initialized. Only fields
3577 with protection 'r' or 'w' can be initialized, except for fields of
3578 type 's', which are automatically initialized to point to the new
3579 structure itself; fields with protection 'o' can not be initialized by
3582 If fewer optional arguments than initializable fields are supplied,
3583 fields of type 'p' get default value #f while fields of type 'u' are
3586 Structs are currently the basic representation for record-like data
3587 structures in Guile. The plan is to eventually replace them with a
3588 new representation which will at the same time be easier to use and
3591 For more information, see the documentation for @code{make-vtable-vtable}.
3594 @deffn primitive struct? x
3595 Return @code{#t} iff @var{obj} is a structure object, else
3600 @deffn primitive struct-ref handle pos
3601 @deffnx primitive struct-set! struct n value
3602 Access (or modify) the @var{n}th field of @var{struct}.
3604 If the field is of type 'p', then it can be set to an arbitrary value.
3606 If the field is of type 'u', then it can only be set to a non-negative
3607 integer value small enough to fit in one machine word.
3615 Vtables are structures that are used to represent structure types. Each
3616 vtable contains a layout specification in field
3617 @code{vtable-index-layout} -- instances of the type are laid out
3618 according to that specification. Vtables contain additional fields
3619 which are used only internally to libguile. The variable
3620 @code{vtable-offset-user} is bound to a field number. Vtable fields
3621 at that position or greater are user definable.
3623 @deffn primitive struct-vtable handle
3624 Return the vtable structure that describes the type of @var{struct}.
3627 @deffn primitive struct-vtable? x
3628 Return @code{#t} iff obj is a vtable structure.
3631 If you have a vtable structure, @code{V}, you can create an instance of
3632 the type it describes by using @code{(make-struct V ...)}. But where
3633 does @code{V} itself come from? One possibility is that @code{V} is an
3634 instance of a user-defined vtable type, @code{V'}, so that @code{V} is
3635 created by using @code{(make-struct V' ...)}. Another possibility is
3636 that @code{V} is an instance of the type it itself describes. Vtable
3637 structures of the second sort are created by this procedure:
3639 @deffn primitive make-vtable-vtable user_fields tail_array_size . init
3640 Return a new, self-describing vtable structure.
3642 @var{user-fields} is a string describing user defined fields of the
3643 vtable beginning at index @code{vtable-offset-user}
3644 (see @code{make-struct-layout}).
3646 @var{tail-size} specifies the size of the tail-array (if any) of
3649 @var{init1}, @dots{} are the optional initializers for the fields of
3652 Vtables have one initializable system field---the struct printer.
3653 This field comes before the user fields in the initializers passed
3654 to @code{make-vtable-vtable} and @code{make-struct}, and thus works as
3655 a third optional argument to @code{make-vtable-vtable} and a fourth to
3656 @code{make-struct} when creating vtables:
3658 If the value is a procedure, it will be called instead of the standard
3659 printer whenever a struct described by this vtable is printed.
3660 The procedure will be called with arguments STRUCT and PORT.
3662 The structure of a struct is described by a vtable, so the vtable is
3663 in essence the type of the struct. The vtable is itself a struct with
3664 a vtable. This could go on forever if it weren't for the
3665 vtable-vtables which are self-describing vtables, and thus terminate
3668 There are several potential ways of using structs, but the standard
3669 one is to use three kinds of structs, together building up a type
3670 sub-system: one vtable-vtable working as the root and one or several
3671 "types", each with a set of "instances". (The vtable-vtable should be
3672 compared to the class <class> which is the class of itself.)
3675 (define ball-root (make-vtable-vtable "pr" 0))
3677 (define (make-ball-type ball-color)
3678 (make-struct ball-root 0
3679 (make-struct-layout "pw")
3681 (format port "#<a ~A ball owned by ~A>"
3685 (define (color ball) (struct-ref (struct-vtable ball) vtable-offset-user))
3686 (define (owner ball) (struct-ref ball 0))
3688 (define red (make-ball-type 'red))
3689 (define green (make-ball-type 'green))
3691 (define (make-ball type owner) (make-struct type 0 owner))
3693 (define ball (make-ball green 'Nisse))
3694 ball @result{} #<a green ball owned by Nisse>
3698 @deffn primitive struct-vtable-name vtable
3699 Return the name of the vtable @var{vtable}.
3702 @deffn primitive set-struct-vtable-name! vtable name
3703 Set the name of the vtable @var{vtable} to @var{name}.
3706 @deffn primitive struct-vtable-tag handle
3707 Return the vtable tag of the structure @var{handle}.
3715 * Conventional Arrays:: Arrays with arbitrary data.
3716 * Array Mapping:: Applying a procedure to the contents of an array.
3717 * Uniform Arrays:: Arrays with data of a single type.
3718 * Bit Vectors:: Vectors of bits.
3721 @node Conventional Arrays
3722 @subsection Conventional Arrays
3724 @dfn{Conventional arrays} are a collection of cells organised into an
3725 arbitrary number of dimensions. Each cell can hold any kind of Scheme
3726 value and can be accessed in constant time by supplying an index for
3727 each dimension. This contrasts with uniform arrays, which use memory
3728 more efficiently but can hold data of only a single type, and lists
3729 where inserting and deleting cells is more efficient, but more time
3730 is usually required to access a particular cell.
3732 A conventional array is displayed as @code{#} followed by the @dfn{rank}
3733 (number of dimensions) followed by the cells, organised into dimensions
3734 using parentheses. The nesting depth of the parentheses is equal to
3737 When an array is created, the number of dimensions and range of each
3738 dimension must be specified, e.g., to create a 2x3 array with a
3742 (make-array 'ho 2 3) @result{}
3743 #2((ho ho ho) (ho ho ho))
3746 The range of each dimension can also be given explicitly, e.g., another
3747 way to create the same array:
3750 (make-array 'ho '(0 1) '(0 2)) @result{}
3751 #2((ho ho ho) (ho ho ho))
3754 A conventional array with one dimension based at zero is identical to
3758 (make-array 'ho 3) @result{}
3762 The following procedures can be used with conventional arrays (or vectors).
3764 @deffn primitive array? v [prot]
3765 Return @code{#t} if the @var{obj} is an array, and @code{#f} if
3766 not. The @var{prototype} argument is used with uniform arrays
3767 and is described elsewhere.
3770 @deffn procedure make-array initial-value bound1 bound2 @dots{}
3771 Creates and returns an array that has as many dimensions as there are
3772 @var{bound}s and fills it with @var{initial-value}.
3775 @c array-ref's type is `compiled-closure'. There's some weird stuff
3776 @c going on in array.c, too. Let's call it a primitive. -twp
3778 @deffn primitive uniform-vector-ref v args
3779 @deffnx primitive array-ref v . args
3780 Return the element at the @code{(index1, index2)} element in
3784 @deffn primitive array-in-bounds? v . args
3785 Return @code{#t} if its arguments would be acceptable to
3789 @deffn primitive array-set! v obj . args
3790 @deffnx primitive uniform-array-set1! v obj args
3791 Sets the element at the @code{(index1, index2)} element in @var{array} to
3792 @var{new-value}. The value returned by array-set! is unspecified.
3795 @deffn primitive make-shared-array oldra mapfunc . dims
3796 @code{make-shared-array} can be used to create shared subarrays of other
3797 arrays. The @var{mapper} is a function that translates coordinates in
3798 the new array into coordinates in the old array. A @var{mapper} must be
3799 linear, and its range must stay within the bounds of the old array, but
3800 it can be otherwise arbitrary. A simple example:
3802 (define fred (make-array #f 8 8))
3803 (define freds-diagonal
3804 (make-shared-array fred (lambda (i) (list i i)) 8))
3805 (array-set! freds-diagonal 'foo 3)
3806 (array-ref fred 3 3) @result{} foo
3807 (define freds-center
3808 (make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j))) 2 2))
3809 (array-ref freds-center 0 0) @result{} foo
3813 @deffn primitive shared-array-increments ra
3814 For each dimension, return the distance between elements in the root vector.
3817 @deffn primitive shared-array-offset ra
3818 Return the root vector index of the first element in the array.
3821 @deffn primitive shared-array-root ra
3822 Return the root vector of a shared array.
3825 @deffn primitive transpose-array ra . args
3826 Return an array sharing contents with @var{array}, but with
3827 dimensions arranged in a different order. There must be one
3828 @var{dim} argument for each dimension of @var{array}.
3829 @var{dim0}, @var{dim1}, @dots{} should be integers between 0
3830 and the rank of the array to be returned. Each integer in that
3831 range must appear at least once in the argument list.
3833 The values of @var{dim0}, @var{dim1}, @dots{} correspond to
3834 dimensions in the array to be returned, their positions in the
3835 argument list to dimensions of @var{array}. Several @var{dim}s
3836 may have the same value, in which case the returned array will
3837 have smaller rank than @var{array}.
3840 (transpose-array '#2((a b) (c d)) 1 0) @result{} #2((a c) (b d))
3841 (transpose-array '#2((a b) (c d)) 0 0) @result{} #1(a d)
3842 (transpose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 1 0) @result{}
3843 #2((a 4) (b 5) (c 6))
3847 @deffn primitive enclose-array ra . axes
3848 @var{dim0}, @var{dim1} @dots{} should be nonnegative integers less than
3849 the rank of @var{array}. @var{enclose-array} returns an array
3850 resembling an array of shared arrays. The dimensions of each shared
3851 array are the same as the @var{dim}th dimensions of the original array,
3852 the dimensions of the outer array are the same as those of the original
3853 array that did not match a @var{dim}.
3855 An enclosed array is not a general Scheme array. Its elements may not
3856 be set using @code{array-set!}. Two references to the same element of
3857 an enclosed array will be @code{equal?} but will not in general be
3858 @code{eq?}. The value returned by @var{array-prototype} when given an
3859 enclosed array is unspecified.
3863 (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1) @result{}
3864 #<enclosed-array (#1(a d) #1(b e) #1(c f)) (#1(1 4) #1(2 5) #1(3 6))>
3866 (enclose-array '#3(((a b c) (d e f)) ((1 2 3) (4 5 6))) 1 0) @result{}
3867 #<enclosed-array #2((a 1) (d 4)) #2((b 2) (e 5)) #2((c 3) (f 6))>
3871 @deffn procedure array-shape array
3872 Returns a list of inclusive bounds of integers.
3874 (array-shape (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) (0 4))
3878 @deffn primitive array-dimensions ra
3879 @code{Array-dimensions} is similar to @code{array-shape} but replaces
3880 elements with a @code{0} minimum with one greater than the maximum. So:
3882 (array-dimensions (make-array 'foo '(-1 3) 5)) @result{} ((-1 3) 5)
3886 @deffn primitive array-rank ra
3887 Return the number of dimensions of @var{obj}. If @var{obj} is
3888 not an array, @code{0} is returned.
3891 @deffn primitive array->list v
3892 Return a list consisting of all the elements, in order, of
3896 @deffn primitive array-copy! src dst
3897 @deffnx primitive array-copy-in-order! src dst
3898 Copies every element from vector or array @var{source} to the
3899 corresponding element of @var{destination}. @var{destination} must have
3900 the same rank as @var{source}, and be at least as large in each
3901 dimension. The order is unspecified.
3904 @deffn primitive array-fill! ra fill
3905 Stores @var{fill} in every element of @var{array}. The value returned
3909 @c begin (texi-doc-string "guile" "array-equal?")
3910 @deffn primitive array-equal? ra0 ra1
3911 Returns @code{#t} iff all arguments are arrays with the same shape, the
3912 same type, and have corresponding elements which are either
3913 @code{equal?} or @code{array-equal?}. This function differs from
3914 @code{equal?} in that a one dimensional shared array may be
3915 @var{array-equal?} but not @var{equal?} to a vector or uniform vector.
3918 @deffn primitive array-contents ra [strict]
3919 @deffnx primitive array-contents array strict
3920 If @var{array} may be @dfn{unrolled} into a one dimensional shared array
3921 without changing their order (last subscript changing fastest), then
3922 @code{array-contents} returns that shared array, otherwise it returns
3923 @code{#f}. All arrays made by @var{make-array} and
3924 @var{make-uniform-array} may be unrolled, some arrays made by
3925 @var{make-shared-array} may not be.
3927 If the optional argument @var{strict} is provided, a shared array will
3928 be returned only if its elements are stored internally contiguous in
3933 @subsection Array Mapping
3935 @deffn primitive array-map! ra0 proc . lra
3936 @deffnx primitive array-map-in-order! ra0 proc . lra
3937 @var{array1}, @dots{} must have the same number of dimensions as
3938 @var{array0} and have a range for each index which includes the range
3939 for the corresponding index in @var{array0}. @var{proc} is applied to
3940 each tuple of elements of @var{array1} @dots{} and the result is stored
3941 as the corresponding element in @var{array0}. The value returned is
3942 unspecified. The order of application is unspecified.
3945 @deffn primitive array-for-each proc ra0 . lra
3946 @var{proc} is applied to each tuple of elements of @var{array0} @dots{}
3947 in row-major order. The value returned is unspecified.
3950 @deffn primitive array-index-map! ra proc
3951 applies @var{proc} to the indices of each element of @var{array} in
3952 turn, storing the result in the corresponding element. The value
3953 returned and the order of application are unspecified.
3955 One can implement @var{array-indexes} as
3957 (define (array-indexes array)
3958 (let ((ra (apply make-array #f (array-shape array))))
3959 (array-index-map! ra (lambda x x))
3964 (define (apl:index-generator n)
3965 (let ((v (make-uniform-vector n 1)))
3966 (array-index-map! v (lambda (i) i))
3971 @node Uniform Arrays
3972 @subsection Uniform Arrays
3975 @dfn{Uniform arrays} have elements all of the
3976 same type and occupy less storage than conventional
3977 arrays. Uniform arrays with a single zero-based dimension
3978 are also known as @dfn{uniform vectors}. The procedures in
3979 this section can also be used on conventional arrays, vectors,
3980 bit-vectors and strings.
3983 When creating a uniform array, the type of data to be stored
3984 is indicated with a @var{prototype} argument. The following table
3985 lists the types available and example prototypes:
3988 prototype type printing character
3990 #t boolean (bit-vector) b
3992 #\nul byte (integer) y
3993 's short (integer) h
3994 1 unsigned long (integer) u
3995 -1 signed long (integer) e
3996 'l signed long long (integer) l
3997 1.0 float (single precision) s
3998 1/3 double (double precision float) i
3999 0+i complex (double precision) c
4000 () conventional vector
4004 Unshared uniform arrays of characters with a single zero-based dimension
4005 are identical to strings:
4008 (make-uniform-array #\a 3) @result{}
4013 Unshared uniform arrays of booleans with a single zero-based dimension
4014 are identical to @ref{Bit Vectors, bit-vectors}.
4017 (make-uniform-array #t 3) @result{}
4022 Other uniform vectors are written in a form similar to that of vectors,
4023 except that a single character from the above table is put between
4024 @code{#} and @code{(}. For example, a uniform vector of signed
4025 long integers is displayed in the form @code{'#e(3 5 9)}.
4027 @deffn primitive array? v [prot]
4028 Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not.
4030 The @var{prototype} argument is used with uniform arrays and is described
4034 @deffn procedure make-uniform-array prototype bound1 bound2 @dots{}
4035 Creates and returns a uniform array of type corresponding to
4036 @var{prototype} that has as many dimensions as there are @var{bound}s
4037 and fills it with @var{prototype}.
4040 @deffn primitive array-prototype ra
4041 Return an object that would produce an array of the same type
4042 as @var{array}, if used as the @var{prototype} for
4043 @code{make-uniform-array}.
4046 @deffn primitive list->uniform-array ndim prot lst
4047 @deffnx procedure list->uniform-vector prot lst
4048 Return a uniform array of the type indicated by prototype
4049 @var{prot} with elements the same as those of @var{lst}.
4050 Elements must be of the appropriate type, no coercions are
4054 @deffn primitive uniform-vector-fill! uve fill
4055 Stores @var{fill} in every element of @var{uve}. The value returned is
4059 @deffn primitive uniform-vector-length v
4060 Return the number of elements in @var{uve}.
4063 @deffn primitive dimensions->uniform-array dims prot [fill]
4064 @deffnx primitive make-uniform-vector length prototype [fill]
4065 Create and return a uniform array or vector of type
4066 corresponding to @var{prototype} with dimensions @var{dims} or
4067 length @var{length}. If @var{fill} is supplied, it's used to
4068 fill the array, otherwise @var{prototype} is used.
4071 @c Another compiled-closure. -twp
4073 @deffn primitive uniform-array-read! ra [port_or_fd [start [end]]]
4074 @deffnx primitive uniform-vector-read! uve [port-or-fdes] [start] [end]
4075 Attempts to read all elements of @var{ura}, in lexicographic order, as
4076 binary objects from @var{port-or-fdes}.
4077 If an end of file is encountered during
4078 uniform-array-read! the objects up to that point only are put into @var{ura}
4079 (starting at the beginning) and the remainder of the array is
4082 The optional arguments @var{start} and @var{end} allow
4083 a specified region of a vector (or linearized array) to be read,
4084 leaving the remainder of the vector unchanged.
4086 @code{uniform-array-read!} returns the number of objects read.
4087 @var{port-or-fdes} may be omitted, in which case it defaults to the value
4088 returned by @code{(current-input-port)}.
4091 @deffn primitive uniform-array-write v [port_or_fd [start [end]]]
4092 @deffnx primitive uniform-vector-write uve [port-or-fdes] [start] [end]
4093 Writes all elements of @var{ura} as binary objects to
4096 The optional arguments @var{start}
4098 a specified region of a vector (or linearized array) to be written.
4100 The number of objects actually written is returned.
4101 @var{port-or-fdes} may be
4102 omitted, in which case it defaults to the value returned by
4103 @code{(current-output-port)}.
4107 @subsection Bit Vectors
4110 Bit vectors are a specific type of uniform array: an array of booleans
4111 with a single zero-based index.
4114 They are displayed as a sequence of @code{0}s and
4115 @code{1}s prefixed by @code{#*}, e.g.,
4118 (make-uniform-vector 8 #t #f) @result{}
4121 #b(#t #f #t) @result{}
4125 @deffn primitive bit-count b bitvector
4126 Return the number of occurrences of the boolean @var{b} in
4130 @deffn primitive bit-position item v k
4131 Return the minimum index of an occurrence of @var{bool} in
4132 @var{bv} which is at least @var{k}. If no @var{bool} occurs
4133 within the specified range @code{#f} is returned.
4136 @deffn primitive bit-invert! v
4137 Modifies @var{bv} by replacing each element with its negation.
4140 @deffn primitive bit-set*! v kv obj
4141 If uve is a bit-vector @var{bv} and uve must be of the same
4142 length. If @var{bool} is @code{#t}, uve is OR'ed into
4143 @var{bv}; If @var{bool} is @code{#f}, the inversion of uve is
4144 AND'ed into @var{bv}.
4146 If uve is a unsigned integer vector all the elements of uve
4147 must be between 0 and the @code{length} of @var{bv}. The bits
4148 of @var{bv} corresponding to the indexes in uve are set to
4149 @var{bool}. The return value is unspecified.
4152 @deffn primitive bit-count* v kv obj
4155 (bit-count (bit-set*! (if bool bv (bit-invert! bv)) uve #t) #t).
4157 @var{bv} is not modified.
4161 @node Association Lists and Hash Tables
4162 @section Association Lists and Hash Tables
4164 This chapter discusses dictionary objects: data structures that are
4165 useful for organizing and indexing large bodies of information.
4168 * Dictionary Types:: About dictionary types; what they're good for.
4169 * Association Lists::
4173 @node Dictionary Types
4174 @subsection Dictionary Types
4176 A @dfn{dictionary} object is a data structure used to index
4177 information in a user-defined way. In standard Scheme, the main
4178 aggregate data types are lists and vectors. Lists are not really
4179 indexed at all, and vectors are indexed only by number
4180 (e.g. @code{(vector-ref foo 5)}). Often you will find it useful
4181 to index your data on some other type; for example, in a library
4182 catalog you might want to look up a book by the name of its
4183 author. Dictionaries are used to help you organize information in
4186 An @dfn{association list} (or @dfn{alist} for short) is a list of
4187 key-value pairs. Each pair represents a single quantity or
4188 object; the @code{car} of the pair is a key which is used to
4189 identify the object, and the @code{cdr} is the object's value.
4191 A @dfn{hash table} also permits you to index objects with
4192 arbitrary keys, but in a way that makes looking up any one object
4193 extremely fast. A well-designed hash system makes hash table
4194 lookups almost as fast as conventional array or vector references.
4196 Alists are popular among Lisp programmers because they use only
4197 the language's primitive operations (lists, @dfn{car}, @dfn{cdr}
4198 and the equality primitives). No changes to the language core are
4199 necessary. Therefore, with Scheme's built-in list manipulation
4200 facilities, it is very convenient to handle data stored in an
4201 association list. Also, alists are highly portable and can be
4202 easily implemented on even the most minimal Lisp systems.
4204 However, alists are inefficient, especially for storing large
4205 quantities of data. Because we want Guile to be useful for large
4206 software systems as well as small ones, Guile provides a rich set
4207 of tools for using either association lists or hash tables.
4209 @node Association Lists
4210 @subsection Association Lists
4211 @cindex Association List
4215 An association list is a conventional data structure that is often used
4216 to implement simple key-value databases. It consists of a list of
4217 entries in which each entry is a pair. The @dfn{key} of each entry is
4218 the @code{car} of the pair and the @dfn{value} of each entry is the
4222 ASSOCIATION LIST ::= '( (KEY1 . VALUE1)
4230 Association lists are also known, for short, as @dfn{alists}.
4232 The structure of an association list is just one example of the infinite
4233 number of possible structures that can be built using pairs and lists.
4234 As such, the keys and values in an association list can be manipulated
4235 using the general list structure procedures @code{cons}, @code{car},
4236 @code{cdr}, @code{set-car!}, @code{set-cdr!} and so on. However,
4237 because association lists are so useful, Guile also provides specific
4238 procedures for manipulating them.
4241 * Alist Key Equality::
4242 * Adding or Setting Alist Entries::
4243 * Retrieving Alist Entries::
4244 * Removing Alist Entries::
4245 * Sloppy Alist Functions::
4249 @node Alist Key Equality
4250 @subsubsection Alist Key Equality
4252 All of Guile's dedicated association list procedures, apart from
4253 @code{acons}, come in three flavours, depending on the level of equality
4254 that is required to decide whether an existing key in the association
4255 list is the same as the key that the procedure call uses to identify the
4260 Procedures with @dfn{assq} in their name use @code{eq?} to determine key
4264 Procedures with @dfn{assv} in their name use @code{eqv?} to determine
4268 Procedures with @dfn{assoc} in their name use @code{equal?} to
4269 determine key equality.
4272 @code{acons} is an exception because it is used to build association
4273 lists which do not require their entries' keys to be unique.
4275 @node Adding or Setting Alist Entries
4276 @subsubsection Adding or Setting Alist Entries
4278 @code{acons} adds a new entry to an association list and returns the
4279 combined association list. The combined alist is formed by consing the
4280 new entry onto the head of the alist specified in the @code{acons}
4281 procedure call. So the specified alist is not modified, but its
4282 contents become shared with the tail of the combined alist that
4283 @code{acons} returns.
4285 In the most common usage of @code{acons}, a variable holding the
4286 original association list is updated with the combined alist:
4289 (set! address-list (acons name address address-list))
4292 In such cases, it doesn't matter that the old and new values of
4293 @code{address-list} share some of their contents, since the old value is
4294 usually no longer independently accessible.
4296 Note that @code{acons} adds the specified new entry regardless of
4297 whether the alist may already contain entries with keys that are, in
4298 some sense, the same as that of the new entry. Thus @code{acons} is
4299 ideal for building alists where there is no concept of key uniqueness.
4302 (set! task-list (acons 3 "pay gas bill" '()))
4305 ((3 . "pay gas bill"))
4307 (set! task-list (acons 3 "tidy bedroom" task-list))
4310 ((3 . "tidy bedroom") (3 . "pay gas bill"))
4313 @code{assq-set!}, @code{assv-set!} and @code{assoc-set!} are used to add
4314 or replace an entry in an association list where there @emph{is} a
4315 concept of key uniqueness. If the specified association list already
4316 contains an entry whose key is the same as that specified in the
4317 procedure call, the existing entry is replaced by the new one.
4318 Otherwise, the new entry is consed onto the head of the old association
4319 list to create the combined alist. In all cases, these procedures
4320 return the combined alist.
4322 @code{assq-set!} and friends @emph{may} destructively modify the
4323 structure of the old association list in such a way that an existing
4324 variable is correctly updated without having to @code{set!} it to the
4330 (("mary" . "34 Elm Road") ("james" . "16 Bow Street"))
4332 (assoc-set! address-list "james" "1a London Road")
4334 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4338 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4344 (assoc-set! address-list "bob" "11 Newington Avenue")
4346 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4347 ("james" . "1a London Road"))
4351 (("mary" . "34 Elm Road") ("james" . "1a London Road"))
4354 The only safe way to update an association list variable when adding or
4355 replacing an entry like this is to @code{set!} the variable to the
4360 (assoc-set! address-list "bob" "11 Newington Avenue"))
4363 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4364 ("james" . "1a London Road"))
4367 Because of this slight inconvenience, you may find it more convenient to
4368 use hash tables to store dictionary data. If your application will not
4369 be modifying the contents of an alist very often, this may not make much
4372 If you need to keep the old value of an association list in a form
4373 independent from the list that results from modification by
4374 @code{acons}, @code{assq-set!}, @code{assv-set!} or @code{assoc-set!},
4375 use @code{list-copy} to copy the old association list before modifying
4378 @deffn primitive acons key value alist
4379 Adds a new key-value pair to @var{alist}. A new pair is
4380 created whose car is @var{key} and whose cdr is @var{value}, and the
4381 pair is consed onto @var{alist}, and the new list is returned. This
4382 function is @emph{not} destructive; @var{alist} is not modified.
4385 @deffn primitive assq-set! alist key val
4386 @deffnx primitive assv-set! alist key value
4387 @deffnx primitive assoc-set! alist key value
4388 Reassociate @var{key} in @var{alist} with @var{value}: find any existing
4389 @var{alist} entry for @var{key} and associate it with the new
4390 @var{value}. If @var{alist} does not contain an entry for @var{key},
4391 add a new one. Return the (possibly new) alist.
4393 These functions do not attempt to verify the structure of @var{alist},
4394 and so may cause unusual results if passed an object that is not an
4398 @node Retrieving Alist Entries
4399 @subsubsection Retrieving Alist Entries
4404 @code{assq}, @code{assv} and @code{assoc} take an alist and a key as
4405 arguments and return the entry for that key if an entry exists, or
4406 @code{#f} if there is no entry for that key. Note that, in the cases
4407 where an entry exists, these procedures return the complete entry, that
4408 is @code{(KEY . VALUE)}, not just the value.
4410 @deffn primitive assq key alist
4411 @deffnx primitive assv key alist
4412 @deffnx primitive assoc key alist
4413 Fetches the entry in @var{alist} that is associated with @var{key}. To
4414 decide whether the argument @var{key} matches a particular entry in
4415 @var{alist}, @code{assq} compares keys with @code{eq?}, @code{assv}
4416 uses @code{eqv?} and @code{assoc} uses @code{equal?}. If @var{key}
4417 cannot be found in @var{alist} (according to whichever equality
4418 predicate is in use), then @code{#f} is returned. These functions
4419 return the entire alist entry found (i.e. both the key and the value).
4422 @code{assq-ref}, @code{assv-ref} and @code{assoc-ref}, on the other
4423 hand, take an alist and a key and return @emph{just the value} for that
4424 key, if an entry exists. If there is no entry for the specified key,
4425 these procedures return @code{#f}.
4427 This creates an ambiguity: if the return value is @code{#f}, it means
4428 either that there is no entry with the specified key, or that there
4429 @emph{is} an entry for the specified key, with value @code{#f}.
4430 Consequently, @code{assq-ref} and friends should only be used where it
4431 is known that an entry exists, or where the ambiguity doesn't matter
4432 for some other reason.
4434 @deffn primitive assq-ref alist key
4435 @deffnx primitive assv-ref alist key
4436 @deffnx primitive assoc-ref alist key
4437 Like @code{assq}, @code{assv} and @code{assoc}, except that only the
4438 value associated with @var{key} in @var{alist} is returned. These
4439 functions are equivalent to
4442 (let ((ent (@var{associator} @var{key} @var{alist})))
4443 (and ent (cdr ent)))
4446 where @var{associator} is one of @code{assq}, @code{assv} or @code{assoc}.
4449 @node Removing Alist Entries
4450 @subsubsection Removing Alist Entries
4452 To remove the element from an association list whose key matches a
4453 specified key, use @code{assq-remove!}, @code{assv-remove!} or
4454 @code{assoc-remove!} (depending, as usual, on the level of equality
4455 required between the key that you specify and the keys in the
4458 As with @code{assq-set!} and friends, the specified alist may or may not
4459 be modified destructively, and the only safe way to update a variable
4460 containing the alist is to @code{set!} it to the value that
4461 @code{assq-remove!} and friends return.
4466 (("bob" . "11 Newington Avenue") ("mary" . "34 Elm Road")
4467 ("james" . "1a London Road"))
4469 (set! address-list (assoc-remove! address-list "mary"))
4472 (("bob" . "11 Newington Avenue") ("james" . "1a London Road"))
4475 Note that, when @code{assq/v/oc-remove!} is used to modify an
4476 association list that has been constructed only using the corresponding
4477 @code{assq/v/oc-set!}, there can be at most one matching entry in the
4478 alist, so the question of multiple entries being removed in one go does
4479 not arise. If @code{assq/v/oc-remove!} is applied to an association
4480 list that has been constructed using @code{acons}, or an
4481 @code{assq/v/oc-set!} with a different level of equality, or any mixture
4482 of these, it removes only the first matching entry from the alist, even
4483 if the alist might contain further matching entries. For example:
4486 (define address-list '())
4487 (set! address-list (assq-set! address-list "mary" "11 Elm Street"))
4488 (set! address-list (assq-set! address-list "mary" "57 Pine Drive"))
4491 (("mary" . "57 Pine Drive") ("mary" . "11 Elm Street"))
4493 (set! address-list (assoc-remove! address-list "mary"))
4496 (("mary" . "11 Elm Street"))
4499 In this example, the two instances of the string "mary" are not the same
4500 when compared using @code{eq?}, so the two @code{assq-set!} calls add
4501 two distinct entries to @code{address-list}. When compared using
4502 @code{equal?}, both "mary"s in @code{address-list} are the same as the
4503 "mary" in the @code{assoc-remove!} call, but @code{assoc-remove!} stops
4504 after removing the first matching entry that it finds, and so one of the
4505 "mary" entries is left in place.
4507 @deffn primitive assq-remove! alist key
4508 @deffnx primitive assv-remove! alist key
4509 @deffnx primitive assoc-remove! alist key
4510 Delete the first entry in @var{alist} associated with @var{key}, and return
4511 the resulting alist.
4514 @node Sloppy Alist Functions
4515 @subsubsection Sloppy Alist Functions
4517 @code{sloppy-assq}, @code{sloppy-assv} and @code{sloppy-assoc} behave
4518 like the corresponding non-@code{sloppy-} procedures, except that they
4519 return @code{#f} when the specified association list is not well-formed,
4520 where the non-@code{sloppy-} versions would signal an error.
4522 Specifically, there are two conditions for which the non-@code{sloppy-}
4523 procedures signal an error, which the @code{sloppy-} procedures handle
4524 instead by returning @code{#f}. Firstly, if the specified alist as a
4525 whole is not a proper list:
4528 (assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
4530 ERROR: In procedure assoc in expression (assoc "mary" (quote #)):
4531 ERROR: Wrong type argument in position 2 (expecting NULLP): "open sesame"
4532 ABORT: (wrong-type-arg)
4534 (sloppy-assoc "mary" '((1 . 2) ("key" . "door") . "open sesame"))
4540 Secondly, if one of the entries in the specified alist is not a pair:
4543 (assoc 2 '((1 . 1) 2 (3 . 9)))
4545 ERROR: In procedure assoc in expression (assoc 2 (quote #)):
4546 ERROR: Wrong type argument in position 2 (expecting CONSP): 2
4547 ABORT: (wrong-type-arg)
4549 (sloppy-assoc 2 '((1 . 1) 2 (3 . 9)))
4554 Unless you are explicitly working with badly formed association lists,
4555 it is much safer to use the non-@code{sloppy-} procedures, because they
4556 help to highlight coding and data errors that the @code{sloppy-}
4557 versions would silently cover up.
4559 @deffn primitive sloppy-assq key alist
4560 Behaves like @code{assq} but does not do any error checking.
4561 Recommended only for use in Guile internals.
4564 @deffn primitive sloppy-assv key alist
4565 Behaves like @code{assv} but does not do any error checking.
4566 Recommended only for use in Guile internals.
4569 @deffn primitive sloppy-assoc key alist
4570 Behaves like @code{assoc} but does not do any error checking.
4571 Recommended only for use in Guile internals.
4575 @subsubsection Alist Example
4577 Here is a longer example of how alists may be used in practice.
4580 (define capitals '(("New York" . "Albany")
4581 ("Oregon" . "Salem")
4582 ("Florida" . "Miami")))
4584 ;; What's the capital of Oregon?
4585 (assoc "Oregon" capitals) @result{} ("Oregon" . "Salem")
4586 (assoc-ref capitals "Oregon") @result{} "Salem"
4588 ;; We left out South Dakota.
4590 (assoc-set! capitals "South Dakota" "Bismarck"))
4592 @result{} (("South Dakota" . "Bismarck")
4593 ("New York" . "Albany")
4594 ("Oregon" . "Salem")
4595 ("Florida" . "Miami"))
4597 ;; And we got Florida wrong.
4599 (assoc-set! capitals "Florida" "Tallahassee"))
4601 @result{} (("South Dakota" . "Bismarck")
4602 ("New York" . "Albany")
4603 ("Oregon" . "Salem")
4604 ("Florida" . "Tallahassee"))
4606 ;; After Oregon secedes, we can remove it.
4608 (assoc-remove! capitals "Oregon"))
4610 @result{} (("South Dakota" . "Bismarck")
4611 ("New York" . "Albany")
4612 ("Florida" . "Tallahassee"))
4616 @subsection Hash Tables
4618 Like the association list functions, the hash table functions come
4619 in several varieties: @code{hashq}, @code{hashv}, and @code{hash}.
4620 The @code{hashq} functions use @code{eq?} to determine whether two
4621 keys match. The @code{hashv} functions use @code{eqv?}, and the
4622 @code{hash} functions use @code{equal?}.
4624 In each of the functions that follow, the @var{table} argument
4625 must be a vector. The @var{key} and @var{value} arguments may be
4628 @deffn primitive hashq-ref table key [dflt]
4629 Look up @var{key} in the hash table @var{table}, and return the
4630 value (if any) associated with it. If @var{key} is not found,
4631 return @var{default} (or @code{#f} if no @var{default} argument
4632 is supplied). Uses @code{eq?} for equality testing.
4635 @deffn primitive hashv-ref table key [dflt]
4636 Look up @var{key} in the hash table @var{table}, and return the
4637 value (if any) associated with it. If @var{key} is not found,
4638 return @var{default} (or @code{#f} if no @var{default} argument
4639 is supplied). Uses @code{eqv?} for equality testing.
4642 @deffn primitive hash-ref table key [dflt]
4643 Look up @var{key} in the hash table @var{table}, and return the
4644 value (if any) associated with it. If @var{key} is not found,
4645 return @var{default} (or @code{#f} if no @var{default} argument
4646 is supplied). Uses @code{equal?} for equality testing.
4649 @deffn primitive hashq-set! table key val
4650 Find the entry in @var{table} associated with @var{key}, and
4651 store @var{value} there. Uses @code{eq?} for equality testing.
4654 @deffn primitive hashv-set! table key val
4655 Find the entry in @var{table} associated with @var{key}, and
4656 store @var{value} there. Uses @code{eqv?} for equality testing.
4659 @deffn primitive hash-set! table key val
4660 Find the entry in @var{table} associated with @var{key}, and
4661 store @var{value} there. Uses @code{equal?} for equality
4665 @deffn primitive hashq-remove! table key
4666 Remove @var{key} (and any value associated with it) from
4667 @var{table}. Uses @code{eq?} for equality tests.
4670 @deffn primitive hashv-remove! table key
4671 Remove @var{key} (and any value associated with it) from
4672 @var{table}. Uses @code{eqv?} for equality tests.
4675 @deffn primitive hash-remove! table key
4676 Remove @var{key} (and any value associated with it) from
4677 @var{table}. Uses @code{equal?} for equality tests.
4680 The standard hash table functions may be too limited for some
4681 applications. For example, you may want a hash table to store
4682 strings in a case-insensitive manner, so that references to keys
4683 named ``foobar'', ``FOOBAR'' and ``FooBaR'' will all yield the
4684 same item. Guile provides you with @dfn{extended} hash tables
4685 that permit you to specify a hash function and associator function
4686 of your choosing. The functions described in the rest of this section
4687 can be used to implement such custom hash table structures.
4689 If you are unfamiliar with the inner workings of hash tables, then
4690 this facility will probably be a little too abstract for you to
4691 use comfortably. If you are interested in learning more, see an
4692 introductory textbook on data structures or algorithms for an
4693 explanation of how hash tables are implemented.
4695 @deffn primitive hashq key size
4696 Determine a hash value for @var{key} that is suitable for
4697 lookups in a hashtable of size @var{size}, where @code{eq?} is
4698 used as the equality predicate. The function returns an
4699 integer in the range 0 to @var{size} - 1. Note that
4700 @code{hashq} may use internal addresses. Thus two calls to
4701 hashq where the keys are @code{eq?} are not guaranteed to
4702 deliver the same value if the key object gets garbage collected
4703 in between. This can happen, for example with symbols:
4704 @code{(hashq 'foo n) (gc) (hashq 'foo n)} may produce two
4705 different values, since @code{foo} will be garbage collected.
4708 @deffn primitive hashv key size
4709 Determine a hash value for @var{key} that is suitable for
4710 lookups in a hashtable of size @var{size}, where @code{eqv?} is
4711 used as the equality predicate. The function returns an
4712 integer in the range 0 to @var{size} - 1. Note that
4713 @code{(hashv key)} may use internal addresses. Thus two calls
4714 to hashv where the keys are @code{eqv?} are not guaranteed to
4715 deliver the same value if the key object gets garbage collected
4716 in between. This can happen, for example with symbols:
4717 @code{(hashv 'foo n) (gc) (hashv 'foo n)} may produce two
4718 different values, since @code{foo} will be garbage collected.
4721 @deffn primitive hash key size
4722 Determine a hash value for @var{key} that is suitable for
4723 lookups in a hashtable of size @var{size}, where @code{equal?}
4724 is used as the equality predicate. The function returns an
4725 integer in the range 0 to @var{size} - 1.
4728 @deffn primitive hashx-ref hash assoc table key [dflt]
4729 This behaves the same way as the corresponding @code{ref}
4730 function, but uses @var{hash} as a hash function and
4731 @var{assoc} to compare keys. @code{hash} must be a function
4732 that takes two arguments, a key to be hashed and a table size.
4733 @code{assoc} must be an associator function, like @code{assoc},
4734 @code{assq} or @code{assv}.
4736 By way of illustration, @code{hashq-ref table key} is
4737 equivalent to @code{hashx-ref hashq assq table key}.
4740 @deffn primitive hashx-set! hash assoc table key val
4741 This behaves the same way as the corresponding @code{set!}
4742 function, but uses @var{hash} as a hash function and
4743 @var{assoc} to compare keys. @code{hash} must be a function
4744 that takes two arguments, a key to be hashed and a table size.
4745 @code{assoc} must be an associator function, like @code{assoc},
4746 @code{assq} or @code{assv}.
4748 By way of illustration, @code{hashq-set! table key} is
4749 equivalent to @code{hashx-set! hashq assq table key}.
4752 @deffn primitive hashq-get-handle table key
4753 This procedure returns the @code{(key . value)} pair from the
4754 hash table @var{table}. If @var{table} does not hold an
4755 associated value for @var{key}, @code{#f} is returned.
4756 Uses @code{eq?} for equality testing.
4759 @deffn primitive hashv-get-handle table key
4760 This procedure returns the @code{(key . value)} pair from the
4761 hash table @var{table}. If @var{table} does not hold an
4762 associated value for @var{key}, @code{#f} is returned.
4763 Uses @code{eqv?} for equality testing.
4766 @deffn primitive hash-get-handle table key
4767 This procedure returns the @code{(key . value)} pair from the
4768 hash table @var{table}. If @var{table} does not hold an
4769 associated value for @var{key}, @code{#f} is returned.
4770 Uses @code{equal?} for equality testing.
4773 @deffn primitive hashx-get-handle hash assoc table key
4774 This behaves the same way as the corresponding
4775 @code{-get-handle} function, but uses @var{hash} as a hash
4776 function and @var{assoc} to compare keys. @code{hash} must be
4777 a function that takes two arguments, a key to be hashed and a
4778 table size. @code{assoc} must be an associator function, like
4779 @code{assoc}, @code{assq} or @code{assv}.
4782 @deffn primitive hashq-create-handle! table key init
4783 This function looks up @var{key} in @var{table} and returns its handle.
4784 If @var{key} is not already present, a new handle is created which
4785 associates @var{key} with @var{init}.
4788 @deffn primitive hashv-create-handle! table key init
4789 This function looks up @var{key} in @var{table} and returns its handle.
4790 If @var{key} is not already present, a new handle is created which
4791 associates @var{key} with @var{init}.
4794 @deffn primitive hash-create-handle! table key init
4795 This function looks up @var{key} in @var{table} and returns its handle.
4796 If @var{key} is not already present, a new handle is created which
4797 associates @var{key} with @var{init}.
4800 @deffn primitive hashx-create-handle! hash assoc table key init
4801 This behaves the same way as the corresponding
4802 @code{-create-handle} function, but uses @var{hash} as a hash
4803 function and @var{assoc} to compare keys. @code{hash} must be
4804 a function that takes two arguments, a key to be hashed and a
4805 table size. @code{assoc} must be an associator function, like
4806 @code{assoc}, @code{assq} or @code{assv}.
4809 @deffn primitive hash-fold proc init table
4810 An iterator over hash-table elements.
4811 Accumulates and returns a result by applying PROC successively.
4812 The arguments to PROC are "(key value prior-result)" where key
4813 and value are successive pairs from the hash table TABLE, and
4814 prior-result is either INIT (for the first application of PROC)
4815 or the return value of the previous application of PROC.
4816 For example, @code{(hash-fold acons () tab)} will convert a hash
4817 table into an a-list of key-value pairs.
4824 @c FIXME::martin: Review me!
4826 @c FIXME::martin: This node should come before the non-standard data types.
4828 @c FIXME::martin: Should the subsections of this section be nodes
4829 @c of their own, or are the resulting nodes too short, then?
4831 Vectors are sequences of Scheme objects. Unlike lists, the length of a
4832 vector, once the vector is created, cannot be changed. The advantage of
4833 vectors over lists is that the time required to access one element of a
4834 vector is constant, whereas lists have an access time linear to the
4835 index of the accessed element in the list.
4837 Note that the vectors documented in this section can contain any kind of
4838 Scheme object, it is even possible to have different types of objects in
4841 @subsection Vector Read Syntax
4843 Vectors can literally be entered in source code, just like strings,
4844 characters or some of the other data types. The read syntax for vectors
4845 is as follows: A sharp sign (@code{#}), followed by an opening
4846 parentheses, all elements of the vector in their respective read syntax,
4847 and finally a closing parentheses. The following are examples of the
4848 read syntax for vectors; where the first vector only contains numbers
4849 and the second three different object types: a string, a symbol and a
4850 number in hexidecimal notation.
4854 #("Hello" foo #xdeadbeef)
4857 @subsection Vector Predicates
4860 @deffn primitive vector? obj
4861 Return @code{#t} if @var{obj} is a vector, otherwise return
4865 @subsection Vector Constructors
4867 @rnindex make-vector
4868 @deffn primitive make-vector k [fill]
4869 Return a newly allocated vector of @var{k} elements. If a
4870 second argument is given, then each element is initialized to
4871 @var{fill}. Otherwise the initial contents of each element is
4876 @rnindex list->vector
4877 @deffn primitive vector . l
4878 @deffnx primitive list->vector l
4879 Return a newly allocated vector whose elements contain the
4880 given arguments. Analogous to @code{list}.
4883 (vector 'a 'b 'c) @result{} #(a b c)
4887 @rnindex vector->list
4888 @deffn primitive vector->list v
4889 Return a newly allocated list of the objects contained in the
4890 elements of @var{vector}.
4893 (vector->list '#(dah dah didah)) @result{} (dah dah didah)
4894 (list->vector '(dididit dah)) @result{} #(dididit dah)
4898 @subsection Vector Modification
4900 A vector created by any of the vector constructor procedures
4901 (@pxref{Vectors}) documented above can be modified using the
4902 following procedures.
4904 According to R5RS, using any of these procedures on literally entered
4905 vectors is an error, because these vectors are considered to be
4906 constant, although Guile currently does not detect this error.
4908 @rnindex vector-set!
4909 @deffn primitive vector-set! vector k obj
4910 @var{k} must be a valid index of @var{vector}.
4911 @code{Vector-set!} stores @var{obj} in element @var{k} of @var{vector}.
4912 The value returned by @samp{vector-set!} is unspecified.
4914 (let ((vec (vector 0 '(2 2 2 2) "Anna")))
4915 (vector-set! vec 1 '("Sue" "Sue"))
4916 vec) @result{} #(0 ("Sue" "Sue") "Anna")
4917 (vector-set! '#(0 1 2) 1 "doe") @result{} @emph{error} ; constant vector
4921 @rnindex vector-fill!
4922 @deffn primitive vector-fill! v fill
4923 Store @var{fill} in every element of @var{vector}. The value
4924 returned by @code{vector-fill!} is unspecified.
4927 @deffn primitive vector-move-left! vec1 start1 end1 vec2 start2
4928 Vector version of @code{substring-move-left!}.
4931 @deffn primitive vector-move-right! vec1 start1 end1 vec2 start2
4932 Vector version of @code{substring-move-right!}.
4935 @subsection Vector Selection
4937 These procedures return information about a given vector, such as the
4938 size or what elements are contained in the vector.
4940 @rnindex vector-length
4941 @deffn primitive vector-length vector
4942 Returns the number of elements in @var{vector} as an exact integer.
4946 @deffn primitive vector-ref vector k
4947 @var{k} must be a valid index of @var{vector}.
4948 @samp{Vector-ref} returns the contents of element @var{k} of
4951 (vector-ref '#(1 1 2 3 5 8 13 21) 5) @result{} 8
4952 (vector-ref '#(1 1 2 3 5 8 13 21)
4953 (let ((i (round (* 2 (acos -1)))))
4963 @c FIXME::martin: Review me!
4965 A hook is basically a list of procedures to be called at well defined
4966 points in time. Hooks are used internally for several debugging
4967 facilities, but they can be used in user code, too.
4969 Hooks are created with @code{make-hook}, then procedures can be added to
4970 a hook with @code{add-hook!} or removed with @code{remove-hook!} or
4971 @code{reset-hook!}. The procedures stored in a hook can be invoked with
4975 * Hook Examples:: Hook usage by example.
4976 * Hook Reference:: Reference of all hook procedures.
4980 @subsection Hook Examples
4982 Hook usage is shown by some examples in this section. First, we will
4983 define a hook of arity 2 --- that is, the procedures stored in the hook
4984 will have to accept two arguments.
4987 (define hook (make-hook 2))
4989 @result{} #<hook 2 40286c90>
4992 Now we are ready to add some procedures to the newly created hook with
4993 @code{add-hook!}. In the following example, two procedures are added,
4994 which print different messages and do different things with their
4995 arguments. When the procedures have been added, we can invoke them
4996 using @code{run-hook}.
4999 (add-hook! hook (lambda (x y)
5003 (add-hook! hook (lambda (x y)
5012 Note that the procedures are called in reverse order than they were
5013 added. This can be changed by providing the optional third argument
5014 on the second call to @code{add-hook!}.
5017 (add-hook! hook (lambda (x y)
5021 (add-hook! hook (lambda (x y)
5025 #t) ; @r{<- Change here!}
5031 @node Hook Reference
5032 @subsection Hook Reference
5034 When a hook is created with @code{make-hook}, you can supply the arity
5035 of the procedures which can be added to the hook. The arity defaults to
5036 zero. All procedures of a hook must have the same arity, and when the
5037 procedures are invoked using @code{run-hook}, the number of arguments
5038 must match the arity of the procedures.
5040 The order in which procedures are added to a hook matters. If the third
5041 parameter to @var{add-hook!} is omitted or is equal to @code{#f}, the
5042 procedure is added in front of the procedures which might already be on
5043 that hook, otherwise the procedure is added at the end. The procedures
5044 are always called from first to last when they are invoked via
5047 When calling @code{hook->list}, the procedures in the resulting list are
5048 in the same order as they would have been called by @code{run-hook}.
5050 @deffn primitive make-hook-with-name name [n_args]
5051 Create a named hook with the name @var{name} for storing
5052 procedures of arity @var{n_args}. @var{n_args} defaults to
5056 @deffn primitive make-hook [n_args]
5057 Create a hook for storing procedure of arity
5058 @var{n_args}. @var{n_args} defaults to zero.
5061 @deffn primitive hook? x
5062 Return @code{#t} if @var{x} is a hook, @code{#f} otherwise.
5065 @deffn primitive hook-empty? hook
5066 Return @code{#t} if @var{hook} is an empty hook, @code{#f}
5070 @deffn primitive add-hook! hook proc [append_p]
5071 Add the procedure @var{proc} to the hook @var{hook}. The
5072 procedure is added to the end if @var{append_p} is true,
5073 otherwise it is added to the front.
5076 @deffn primitive remove-hook! hook proc
5077 Remove the procedure @var{proc} from the hook @var{hook}.
5080 @deffn primitive reset-hook! hook
5081 Remove all procedures from the hook @var{hook}.
5084 @deffn primitive run-hook hook . args
5085 Apply all procedures from the hook @var{hook} to the arguments
5086 @var{args}. The order of the procedure application is first to
5090 @deffn primitive hook->list hook
5091 Convert the procedure list of @var{hook} to a list.
5095 @node Other Data Types
5096 @section Other Core Guile Data Types
5100 @c TeX-master: "guile.texi"