2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2015 Free Software
5 @c See the file elisp.texi for copying conditions.
6 @node Sequences Arrays Vectors
7 @chapter Sequences, Arrays, and Vectors
10 The @dfn{sequence} type is the union of two other Lisp types: lists
11 and arrays. In other words, any list is a sequence, and any array is
12 a sequence. The common property that all sequences have is that each
13 is an ordered collection of elements.
15 An @dfn{array} is a fixed-length object with a slot for each of its
16 elements. All the elements are accessible in constant time. The four
17 types of arrays are strings, vectors, char-tables and bool-vectors.
19 A list is a sequence of elements, but it is not a single primitive
20 object; it is made of cons cells, one cell per element. Finding the
21 @var{n}th element requires looking through @var{n} cons cells, so
22 elements farther from the beginning of the list take longer to access.
23 But it is possible to add elements to the list, or remove elements.
25 The following diagram shows the relationship between these types:
29 _____________________________________________
32 | ______ ________________________________ |
34 | | List | | Array | |
35 | | | | ________ ________ | |
36 | |______| | | | | | | |
37 | | | Vector | | String | | |
38 | | |________| |________| | |
39 | | ____________ _____________ | |
41 | | | Char-table | | Bool-vector | | |
42 | | |____________| |_____________| | |
43 | |________________________________| |
44 |_____________________________________________|
49 * Sequence Functions:: Functions that accept any kind of sequence.
50 * Arrays:: Characteristics of arrays in Emacs Lisp.
51 * Array Functions:: Functions specifically for arrays.
52 * Vectors:: Special characteristics of Emacs Lisp vectors.
53 * Vector Functions:: Functions specifically for vectors.
54 * Char-Tables:: How to work with char-tables.
55 * Bool-Vectors:: How to work with bool-vectors.
56 * Rings:: Managing a fixed-size ring of objects.
59 @node Sequence Functions
62 This section describes functions that accept any kind of sequence.
64 @defun sequencep object
65 This function returns @code{t} if @var{object} is a list, vector,
66 string, bool-vector, or char-table, @code{nil} otherwise.
69 @defun length sequence
73 @cindex sequence length
74 @cindex char-table length
75 This function returns the number of elements in @var{sequence}. If
76 @var{sequence} is a dotted list, a @code{wrong-type-argument} error is
77 signaled. Circular lists may cause an infinite loop. For a
78 char-table, the value returned is always one more than the maximum
81 @xref{Definition of safe-length}, for the related function @code{safe-length}.
101 (length (make-bool-vector 5 nil))
108 See also @code{string-bytes}, in @ref{Text Representations}.
110 If you need to compute the width of a string on display, you should use
111 @code{string-width} (@pxref{Size of Displayed Text}), not @code{length},
112 since @code{length} only counts the number of characters, but does not
113 account for the display width of each character.
115 @defun elt sequence index
116 @cindex elements of sequences
117 This function returns the element of @var{sequence} indexed by
118 @var{index}. Legitimate values of @var{index} are integers ranging
119 from 0 up to one less than the length of @var{sequence}. If
120 @var{sequence} is a list, out-of-range values behave as for
121 @code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
122 trigger an @code{args-out-of-range} error.
134 ;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
135 (string (elt "1234" 2))
140 @error{} Args out of range: [1 2 3 4], 4
144 @error{} Args out of range: [1 2 3 4], -1
148 This function generalizes @code{aref} (@pxref{Array Functions}) and
149 @code{nth} (@pxref{Definition of nth}).
152 @defun copy-sequence sequence
153 @cindex copying sequences
154 This function returns a copy of @var{sequence}. The copy is the same
155 type of object as the original sequence, and it has the same elements
158 Storing a new element into the copy does not affect the original
159 @var{sequence}, and vice versa. However, the elements of the new
160 sequence are not copies; they are identical (@code{eq}) to the elements
161 of the original. Therefore, changes made within these elements, as
162 found via the copied sequence, are also visible in the original
165 If the sequence is a string with text properties, the property list in
166 the copy is itself a copy, not shared with the original's property
167 list. However, the actual values of the properties are shared.
168 @xref{Text Properties}.
170 This function does not work for dotted lists. Trying to copy a
171 circular list may cause an infinite loop.
173 See also @code{append} in @ref{Building Lists}, @code{concat} in
174 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
175 for other ways to copy sequences.
183 (setq x (vector 'foo bar))
184 @result{} [foo (1 2)]
187 (setq y (copy-sequence x))
188 @result{} [foo (1 2)]
200 (eq (elt x 1) (elt y 1))
205 ;; @r{Replacing an element of one sequence.}
207 x @result{} [quux (1 2)]
208 y @result{} [foo (1 2)]
212 ;; @r{Modifying the inside of a shared element.}
213 (setcar (aref x 1) 69)
214 x @result{} [quux (69 2)]
215 y @result{} [foo (69 2)]
220 @defun reverse sequence
221 @cindex string reverse
223 @cindex vector reverse
224 @cindex sequence reverse
225 This function creates a new sequence whose elements are the elements
226 of @var{sequence}, but in reverse order. The original argument @var{sequence}
227 is @emph{not} altered. Note that char-tables cannot be reversed.
263 @defun nreverse sequence
264 @cindex reversing a string
265 @cindex reversing a list
266 @cindex reversing a vector
267 This function reverses the order of the elements of @var{sequence}.
268 Unlike @code{reverse} the original @var{sequence} may be modified.
284 ;; @r{The cons cell that was first is now last.}
290 To avoid confusion, we usually store the result of @code{nreverse}
291 back in the same variable which held the original list:
294 (setq x (nreverse x))
297 Here is the @code{nreverse} of our favorite example, @code{(a b c)},
298 presented graphically:
302 @r{Original list head:} @r{Reversed list:}
303 ------------- ------------- ------------
304 | car | cdr | | car | cdr | | car | cdr |
305 | a | nil |<-- | b | o |<-- | c | o |
306 | | | | | | | | | | | | |
307 ------------- | --------- | - | -------- | -
309 ------------- ------------
313 For the vector, it is even simpler because you don't need setq:
324 Note that unlike @code{reverse}, this function doesn't work with strings.
325 Although you can alter string data by using @code{aset}, it is strongly
326 encouraged to treat strings as immutable.
330 @defun sort sequence predicate
332 @cindex sorting lists
333 @cindex sorting vectors
334 This function sorts @var{sequence} stably. Note that this function doesn't work
335 for all sequences; it may be used only for lists and vectors. If @var{sequence}
336 is a list, it is modified destructively. This functions returns the sorted
337 @var{sequence} and compares elements using @var{predicate}. A stable sort is
338 one in which elements with equal sort keys maintain their relative order before
339 and after the sort. Stability is important when successive sorts are used to
340 order elements according to different criteria.
342 The argument @var{predicate} must be a function that accepts two
343 arguments. It is called with two elements of @var{sequence}. To get an
344 increasing order sort, the @var{predicate} should return non-@code{nil} if the
345 first element is ``less than'' the second, or @code{nil} if not.
347 The comparison function @var{predicate} must give reliable results for
348 any given pair of arguments, at least within a single call to
349 @code{sort}. It must be @dfn{antisymmetric}; that is, if @var{a} is
350 less than @var{b}, @var{b} must not be less than @var{a}. It must be
351 @dfn{transitive}---that is, if @var{a} is less than @var{b}, and @var{b}
352 is less than @var{c}, then @var{a} must be less than @var{c}. If you
353 use a comparison function which does not meet these requirements, the
354 result of @code{sort} is unpredictable.
356 The destructive aspect of @code{sort} for lists is that it rearranges the
357 cons cells forming @var{sequence} by changing @sc{cdr}s. A nondestructive
358 sort function would create new cons cells to store the elements in their
359 sorted order. If you wish to make a sorted copy without destroying the
360 original, copy it first with @code{copy-sequence} and then sort.
362 Sorting does not change the @sc{car}s of the cons cells in @var{sequence};
363 the cons cell that originally contained the element @code{a} in
364 @var{sequence} still has @code{a} in its @sc{car} after sorting, but it now
365 appears in a different position in the list due to the change of
366 @sc{cdr}s. For example:
370 (setq nums '(1 3 2 6 5 4 0))
371 @result{} (1 3 2 6 5 4 0)
375 @result{} (0 1 2 3 4 5 6)
379 @result{} (1 2 3 4 5 6)
384 @strong{Warning}: Note that the list in @code{nums} no longer contains
385 0; this is the same cons cell that it was before, but it is no longer
386 the first one in the list. Don't assume a variable that formerly held
387 the argument now holds the entire sorted list! Instead, save the result
388 of @code{sort} and use that. Most often we store the result back into
389 the variable that held the original list:
392 (setq nums (sort nums '<))
395 For the better understanding of what stable sort is, consider the following
396 vector example. After sorting, all items whose @code{car} is 8 are grouped
397 at the beginning of @code{vector}, but their relative order is preserved.
398 All items whose @code{car} is 9 are grouped at the end of @code{vector},
399 but their relative order is also preserved:
405 (vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")
406 '(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))
407 @result{} [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")
408 (9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]
411 (sort vector (lambda (x y) (< (car x) (car y))))
412 @result{} [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")
413 (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
417 @xref{Sorting}, for more functions that perform sorting.
418 See @code{documentation} in @ref{Accessing Documentation}, for a
419 useful example of @code{sort}.
422 @cindex sequence functions in seq
424 The @file{seq.el} library provides the following additional sequence
425 manipulation macros and functions, prefixed with @code{seq-}. To use
426 them, you must first load the @file{seq} library.
428 All functions defined in this library are free of side-effects;
429 i.e., they do not modify any sequence (list, vector, or string) that
430 you pass as an argument. Unless otherwise stated, the result is a
431 sequence of the same type as the input. For those functions that take
432 a predicate, this should be a function of one argument.
434 @defun seq-drop sequence n
435 This function returns all but the first @var{n} (an integer)
436 elements of @var{sequence}. If @var{n} is negative or zero,
437 the result is @var{sequence}.
441 (seq-drop [1 2 3 4 5 6] 3)
445 (seq-drop "hello world" -4)
446 @result{} "hello world"
451 @defun seq-take sequence n
452 This function returns the first @var{n} (an integer) elements of
453 @var{sequence}. If @var{n} is negative or zero, the result
458 (seq-take '(1 2 3 4) 3)
462 (seq-take [1 2 3 4] 0)
468 @defun seq-take-while predicate sequence
469 This function returns the members of @var{sequence} in order,
470 stopping before the first one for which @var{predicate} returns @code{nil}.
474 (seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
478 (seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])
484 @defun seq-drop-while predicate sequence
485 This function returns the members of @var{sequence} in order,
486 starting from the first one for which @var{predicate} returns @code{nil}.
490 (seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
494 (seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])
500 @defun seq-filter predicate sequence
501 @cindex filtering sequences
502 This function returns a list of all the elements in @var{sequence}
503 for which @var{predicate} returns non-@code{nil}.
507 (seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
511 (seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
517 @defun seq-remove predicate sequence
518 @cindex removing from sequences
519 This function returns a list of all the elements in @var{sequence}
520 for which @var{predicate} returns @code{nil}.
524 (seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
528 (seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
534 @defun seq-reduce function sequence initial-value
535 @cindex reducing sequences
536 This function returns the result of calling @var{function} with
537 @var{initial-value} and the first element of @var{sequence}, then calling
538 @var{function} with that result and the second element of @var{sequence},
539 then with that result and the third element of @var{sequence}, etc.
540 @var{function} should be a function of two arguments. If
541 @var{sequence} is empty, this returns @var{initial-value} without
542 calling @var{function}.
546 (seq-reduce #'+ [1 2 3 4] 0)
550 (seq-reduce #'+ '(1 2 3 4) 5)
554 (seq-reduce #'+ '() 3)
560 @defun seq-some-p predicate sequence
561 This function returns the first member of sequence for which @var{predicate}
562 returns non-@code{nil}.
566 (seq-some-p #'numberp ["abc" 1 nil])
570 (seq-some-p #'numberp ["abc" "def"])
576 @defun seq-every-p predicate sequence
577 This function returns non-@code{nil} if applying @var{predicate}
578 to every element of @var{sequence} returns non-@code{nil}.
582 (seq-every-p #'numberp [2 4 6])
586 (seq-some-p #'numberp [2 4 "6"])
592 @defun seq-empty-p sequence
593 This function returns non-@code{nil} if @var{sequence} is empty.
597 (seq-empty-p "not empty")
607 @defun seq-count predicate sequence
608 This function returns the number of elements in @var{sequence} for which
609 @var{predicate} returns non-@code{nil}.
612 (seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
617 @cindex sorting sequences
618 @defun seq-sort function sequence
619 This function returns a copy of @var{sequence} that is sorted
620 according to @var{function}, a function of two arguments that returns
621 non-@code{nil} if the first argument should sort before the second.
624 @defun seq-contains-p sequence elt &optional function
625 This function returns the first element in @var{sequence} that is equal to
626 @var{elt}. If the optional argument @var{function} is non-@code{nil},
627 it is a function of two arguments to use instead of the default @code{equal}.
631 (seq-contains-p '(symbol1 symbol2) 'symbol1)
635 (seq-contains-p '(symbol1 symbol2) 'symbol3)
642 @defun seq-uniq sequence &optional function
643 This function returns a list of the elements of @var{sequence} with
644 duplicates removed. If the optional argument @var{function} is non-@code{nil},
645 it is a function of two arguments to use instead of the default @code{equal}.
649 (seq-uniq '(1 2 2 1 3))
653 (seq-uniq '(1 2 2.0 1.0) #'=)
659 @defun seq-subseq sequence start &optional end
660 This function returns a subset of @var{sequence} from @var{start}
661 to @var{end}, both integers (@var{end} defaults to the last element).
662 If @var{start} or @var{end} is negative, it counts from the end of
667 (seq-subseq '(1 2 3 4 5) 1)
671 (seq-subseq '[1 2 3 4 5] 1 3)
675 (seq-subseq '[1 2 3 4 5] -3 -1)
681 @defun seq-concatenate type &rest sequences
682 This function returns a sequence of type @var{type} made of the
683 concatenation of @var{sequences}. @var{type} may be: @code{vector},
684 @code{list} or @code{string}.
688 (seq-concatenate 'list '(1 2) '(3 4) [5 6])
689 @result{} (1 2 3 5 6)
692 (seq-concatenate 'string "Hello " "world")
693 @result{} "Hello world"
698 @defun seq-mapcat function sequence &optional type
699 This function returns the result of applying @code{seq-concatenate}
700 to the result of applying @var{function} to each element of
701 @var{sequence}. The result is a sequence of type @var{type}, or a
702 list if @var{type} is @code{nil}.
706 (seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
707 @result{} (1 2 3 4 5 6)
712 @defun seq-partition sequence n
713 This function returns a list of the elements of @var{sequence}
714 grouped into sub-sequences of length @var{n}. The last sequence may
715 contain less elements than @var{n}. @var{n} must be an integer. If
716 @var{n} is a negative integer or 0, nil is returned.
720 (seq-partition '(0 1 2 3 4 5 6 7) 3)
721 @result{} ((0 1 2) (3 4 5) (6 7))
726 @defun seq-group-by function sequence
727 This function separates the elements of @var{sequence} into an alist
728 whose keys are the result of applying @var{function} to each element
729 of @var{sequence}. Keys are compared using @code{equal}.
733 (seq-group-by #'integerp '(1 2.1 3 2 3.2))
734 @result{} ((t 1 3 2) (nil 2.1 3.2))
737 (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
738 @result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
743 @defun seq-into sequence type
744 This function converts the sequence @var{sequence} into a sequence
745 of type @var{type}. @var{type} can be one of the following symbols:
746 @code{vector}, @code{string} or @code{list}.
750 (seq-into [1 2 3] 'list)
754 (seq-into nil 'vector)
758 (seq-into "hello" 'vector)
759 @result{} [104 101 108 108 111]
765 @defmac seq-doseq (var sequence [result]) body@dots{}
766 @cindex sequence iteration
767 This macro is like @code{dolist}, except that @var{sequence} can be a list,
768 vector or string (@pxref{Iteration} for more information about the
769 @code{dolist} macro). This is primarily useful for side-effects.
776 An @dfn{array} object has slots that hold a number of other Lisp
777 objects, called the elements of the array. Any element of an array
778 may be accessed in constant time. In contrast, the time to access an
779 element of a list is proportional to the position of that element in
782 Emacs defines four types of array, all one-dimensional:
783 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
784 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
785 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
786 can hold elements of any type, but strings can only hold characters,
787 and bool-vectors can only hold @code{t} and @code{nil}.
789 All four kinds of array share these characteristics:
793 The first element of an array has index zero, the second element has
794 index 1, and so on. This is called @dfn{zero-origin} indexing. For
795 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
798 The length of the array is fixed once you create it; you cannot
799 change the length of an existing array.
802 For purposes of evaluation, the array is a constant---i.e.,
803 it evaluates to itself.
806 The elements of an array may be referenced or changed with the functions
807 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
810 When you create an array, other than a char-table, you must specify
811 its length. You cannot specify the length of a char-table, because that
812 is determined by the range of character codes.
814 In principle, if you want an array of text characters, you could use
815 either a string or a vector. In practice, we always choose strings for
816 such applications, for four reasons:
820 They occupy one-fourth the space of a vector of the same elements.
823 Strings are printed in a way that shows the contents more clearly
827 Strings can hold text properties. @xref{Text Properties}.
830 Many of the specialized editing and I/O facilities of Emacs accept only
831 strings. For example, you cannot insert a vector of characters into a
832 buffer the way you can insert a string. @xref{Strings and Characters}.
835 By contrast, for an array of keyboard input characters (such as a key
836 sequence), a vector may be necessary, because many keyboard input
837 characters are outside the range that will fit in a string. @xref{Key
840 @node Array Functions
841 @section Functions that Operate on Arrays
843 In this section, we describe the functions that accept all types of
847 This function returns @code{t} if @var{object} is an array (i.e., a
848 vector, a string, a bool-vector or a char-table).
856 (arrayp (syntax-table)) ;; @r{A char-table.}
862 @defun aref array index
863 @cindex array elements
864 This function returns the @var{index}th element of @var{array}. The
865 first element is at index zero.
869 (setq primes [2 3 5 7 11 13])
870 @result{} [2 3 5 7 11 13]
876 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
880 See also the function @code{elt}, in @ref{Sequence Functions}.
883 @defun aset array index object
884 This function sets the @var{index}th element of @var{array} to be
885 @var{object}. It returns @var{object}.
889 (setq w [foo bar baz])
890 @result{} [foo bar baz]
894 @result{} [fu bar baz]
907 If @var{array} is a string and @var{object} is not a character, a
908 @code{wrong-type-argument} error results. The function converts a
909 unibyte string to multibyte if necessary to insert a character.
912 @defun fillarray array object
913 This function fills the array @var{array} with @var{object}, so that
914 each element of @var{array} is @var{object}. It returns @var{array}.
918 (setq a [a b c d e f g])
919 @result{} [a b c d e f g]
921 @result{} [0 0 0 0 0 0 0]
923 @result{} [0 0 0 0 0 0 0]
926 (setq s "When in the course")
927 @result{} "When in the course"
929 @result{} "------------------"
933 If @var{array} is a string and @var{object} is not a character, a
934 @code{wrong-type-argument} error results.
937 The general sequence functions @code{copy-sequence} and @code{length}
938 are often useful for objects known to be arrays. @xref{Sequence Functions}.
942 @cindex vector (type)
944 A @dfn{vector} is a general-purpose array whose elements can be any
945 Lisp objects. (By contrast, the elements of a string can only be
946 characters. @xref{Strings and Characters}.) Vectors are used in
947 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
948 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
949 representation of a byte-compiled function (@pxref{Byte Compilation}),
952 Like other arrays, vectors use zero-origin indexing: the first
955 Vectors are printed with square brackets surrounding the elements.
956 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
957 @code{a} is printed as @code{[a b a]}. You can write vectors in the
958 same way in Lisp input.
960 A vector, like a string or a number, is considered a constant for
961 evaluation: the result of evaluating it is the same vector. This does
962 not evaluate or even examine the elements of the vector.
963 @xref{Self-Evaluating Forms}.
965 Here are examples illustrating these principles:
969 (setq avector [1 two '(three) "four" [five]])
970 @result{} [1 two (quote (three)) "four" [five]]
972 @result{} [1 two (quote (three)) "four" [five]]
973 (eq avector (eval avector))
978 @node Vector Functions
979 @section Functions for Vectors
981 Here are some functions that relate to vectors:
983 @defun vectorp object
984 This function returns @code{t} if @var{object} is a vector.
996 @defun vector &rest objects
997 This function creates and returns a vector whose elements are the
998 arguments, @var{objects}.
1002 (vector 'foo 23 [bar baz] "rats")
1003 @result{} [foo 23 [bar baz] "rats"]
1010 @defun make-vector length object
1011 This function returns a new vector consisting of @var{length} elements,
1012 each initialized to @var{object}.
1016 (setq sleepy (make-vector 9 'Z))
1017 @result{} [Z Z Z Z Z Z Z Z Z]
1022 @defun vconcat &rest sequences
1023 @cindex copying vectors
1024 This function returns a new vector containing all the elements of
1025 @var{sequences}. The arguments @var{sequences} may be true lists,
1026 vectors, strings or bool-vectors. If no @var{sequences} are given,
1027 the empty vector is returned.
1029 The value is either the empty vector, or is a newly constructed
1030 nonempty vector that is not @code{eq} to any existing vector.
1034 (setq a (vconcat '(A B C) '(D E F)))
1035 @result{} [A B C D E F]
1042 (vconcat [A B C] "aa" '(foo (6 7)))
1043 @result{} [A B C 97 97 foo (6 7)]
1047 The @code{vconcat} function also allows byte-code function objects as
1048 arguments. This is a special feature to make it easy to access the entire
1049 contents of a byte-code function object. @xref{Byte-Code Objects}.
1051 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
1052 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
1053 in @ref{Building Lists}.
1056 The @code{append} function also provides a way to convert a vector into a
1057 list with the same elements:
1061 (setq avector [1 two (quote (three)) "four" [five]])
1062 @result{} [1 two (quote (three)) "four" [five]]
1063 (append avector nil)
1064 @result{} (1 two (quote (three)) "four" [five])
1069 @section Char-Tables
1071 @cindex extra slots of char-table
1073 A char-table is much like a vector, except that it is indexed by
1074 character codes. Any valid character code, without modifiers, can be
1075 used as an index in a char-table. You can access a char-table's
1076 elements with @code{aref} and @code{aset}, as with any array. In
1077 addition, a char-table can have @dfn{extra slots} to hold additional
1078 data not associated with particular character codes. Like vectors,
1079 char-tables are constants when evaluated, and can hold elements of any
1082 @cindex subtype of char-table
1083 Each char-table has a @dfn{subtype}, a symbol, which serves two
1088 The subtype provides an easy way to tell what the char-table is for.
1089 For instance, display tables are char-tables with @code{display-table}
1090 as the subtype, and syntax tables are char-tables with
1091 @code{syntax-table} as the subtype. The subtype can be queried using
1092 the function @code{char-table-subtype}, described below.
1095 The subtype controls the number of @dfn{extra slots} in the
1096 char-table. This number is specified by the subtype's
1097 @code{char-table-extra-slots} symbol property (@pxref{Symbol
1098 Properties}), whose value should be an integer between 0 and 10. If
1099 the subtype has no such symbol property, the char-table has no extra
1103 @cindex parent of char-table
1104 A char-table can have a @dfn{parent}, which is another char-table. If
1105 it does, then whenever the char-table specifies @code{nil} for a
1106 particular character @var{c}, it inherits the value specified in the
1107 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
1108 the value from the parent of @var{char-table} if @var{char-table} itself
1109 specifies @code{nil}.
1111 @cindex default value of char-table
1112 A char-table can also have a @dfn{default value}. If so, then
1113 @code{(aref @var{char-table} @var{c})} returns the default value
1114 whenever the char-table does not specify any other non-@code{nil} value.
1116 @defun make-char-table subtype &optional init
1117 Return a newly-created char-table, with subtype @var{subtype} (a
1118 symbol). Each element is initialized to @var{init}, which defaults to
1119 @code{nil}. You cannot alter the subtype of a char-table after the
1120 char-table is created.
1122 There is no argument to specify the length of the char-table, because
1123 all char-tables have room for any valid character code as an index.
1125 If @var{subtype} has the @code{char-table-extra-slots} symbol
1126 property, that specifies the number of extra slots in the char-table.
1127 This should be an integer between 0 and 10; otherwise,
1128 @code{make-char-table} raises an error. If @var{subtype} has no
1129 @code{char-table-extra-slots} symbol property (@pxref{Property
1130 Lists}), the char-table has no extra slots.
1133 @defun char-table-p object
1134 This function returns @code{t} if @var{object} is a char-table, and
1135 @code{nil} otherwise.
1138 @defun char-table-subtype char-table
1139 This function returns the subtype symbol of @var{char-table}.
1142 There is no special function to access default values in a char-table.
1143 To do that, use @code{char-table-range} (see below).
1145 @defun char-table-parent char-table
1146 This function returns the parent of @var{char-table}. The parent is
1147 always either @code{nil} or another char-table.
1150 @defun set-char-table-parent char-table new-parent
1151 This function sets the parent of @var{char-table} to @var{new-parent}.
1154 @defun char-table-extra-slot char-table n
1155 This function returns the contents of extra slot @var{n} of
1156 @var{char-table}. The number of extra slots in a char-table is
1157 determined by its subtype.
1160 @defun set-char-table-extra-slot char-table n value
1161 This function stores @var{value} in extra slot @var{n} of
1165 A char-table can specify an element value for a single character code;
1166 it can also specify a value for an entire character set.
1168 @defun char-table-range char-table range
1169 This returns the value specified in @var{char-table} for a range of
1170 characters @var{range}. Here are the possibilities for @var{range}:
1174 Refers to the default value.
1177 Refers to the element for character @var{char}
1178 (supposing @var{char} is a valid character code).
1180 @item @code{(@var{from} . @var{to})}
1181 A cons cell refers to all the characters in the inclusive range
1182 @samp{[@var{from}..@var{to}]}.
1186 @defun set-char-table-range char-table range value
1187 This function sets the value in @var{char-table} for a range of
1188 characters @var{range}. Here are the possibilities for @var{range}:
1192 Refers to the default value.
1195 Refers to the whole range of character codes.
1198 Refers to the element for character @var{char}
1199 (supposing @var{char} is a valid character code).
1201 @item @code{(@var{from} . @var{to})}
1202 A cons cell refers to all the characters in the inclusive range
1203 @samp{[@var{from}..@var{to}]}.
1207 @defun map-char-table function char-table
1208 This function calls its argument @var{function} for each element of
1209 @var{char-table} that has a non-@code{nil} value. The call to
1210 @var{function} is with two arguments, a key and a value. The key
1211 is a possible @var{range} argument for @code{char-table-range}---either
1212 a valid character or a cons cell @code{(@var{from} . @var{to})},
1213 specifying a range of characters that share the same value. The value is
1214 what @code{(char-table-range @var{char-table} @var{key})} returns.
1216 Overall, the key-value pairs passed to @var{function} describe all the
1217 values stored in @var{char-table}.
1219 The return value is always @code{nil}; to make calls to
1220 @code{map-char-table} useful, @var{function} should have side effects.
1221 For example, here is how to examine the elements of the syntax table:
1226 #'(lambda (key value)
1230 (list (car key) (cdr key))
1237 (((2597602 4194303) (2)) ((2597523 2597601) (3))
1238 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
1239 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
1244 @section Bool-vectors
1245 @cindex Bool-vectors
1247 A bool-vector is much like a vector, except that it stores only the
1248 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
1249 value into an element of the bool-vector, the effect is to store
1250 @code{t} there. As with all arrays, bool-vector indices start from 0,
1251 and the length cannot be changed once the bool-vector is created.
1252 Bool-vectors are constants when evaluated.
1254 Several functions work specifically with bool-vectors; aside
1255 from that, you manipulate them with same functions used for other kinds
1258 @defun make-bool-vector length initial
1259 Return a new bool-vector of @var{length} elements,
1260 each one initialized to @var{initial}.
1263 @defun bool-vector &rest objects
1264 This function creates and returns a bool-vector whose elements are the
1265 arguments, @var{objects}.
1268 @defun bool-vector-p object
1269 This returns @code{t} if @var{object} is a bool-vector,
1270 and @code{nil} otherwise.
1273 There are also some bool-vector set operation functions, described below:
1275 @defun bool-vector-exclusive-or a b &optional c
1276 Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
1277 If optional argument @var{c} is given, the result of this operation is
1278 stored into @var{c}. All arguments should be bool vectors of the same length.
1281 @defun bool-vector-union a b &optional c
1282 Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
1283 optional argument @var{c} is given, the result of this operation is
1284 stored into @var{c}. All arguments should be bool vectors of the same length.
1287 @defun bool-vector-intersection a b &optional c
1288 Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
1289 optional argument @var{c} is given, the result of this operation is
1290 stored into @var{c}. All arguments should be bool vectors of the same length.
1293 @defun bool-vector-set-difference a b &optional c
1294 Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
1295 optional argument @var{c} is given, the result of this operation is
1296 stored into @var{c}. All arguments should be bool vectors of the same length.
1299 @defun bool-vector-not a &optional b
1300 Return @dfn{set complement} of bool vector @var{a}. If optional
1301 argument @var{b} is given, the result of this operation is stored into
1302 @var{b}. All arguments should be bool vectors of the same length.
1305 @defun bool-vector-subsetp a b
1306 Return @code{t} if every @code{t} value in @var{a} is also t in
1307 @var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
1311 @defun bool-vector-count-consecutive a b i
1312 Return the number of consecutive elements in @var{a} equal @var{b}
1313 starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
1314 or @code{nil}, and @var{i} is an index into @code{a}.
1317 @defun bool-vector-count-population a
1318 Return the number of elements that are @code{t} in bool vector @var{a}.
1321 The printed form represents up to 8 boolean values as a single
1326 (bool-vector t nil t nil)
1333 You can use @code{vconcat} to print a bool-vector like other vectors:
1337 (vconcat (bool-vector nil t nil t))
1338 @result{} [nil t nil t]
1342 Here is another example of creating, examining, and updating a
1346 (setq bv (make-bool-vector 5 t))
1357 These results make sense because the binary codes for control-_ and
1358 control-W are 11111 and 10111, respectively.
1361 @section Managing a Fixed-Size Ring of Objects
1363 @cindex ring data structure
1364 A @dfn{ring} is a fixed-size data structure that supports insertion,
1365 deletion, rotation, and modulo-indexed reference and traversal. An
1366 efficient ring data structure is implemented by the @code{ring}
1367 package. It provides the functions listed in this section.
1369 Note that several ``rings'' in Emacs, like the kill ring and the
1370 mark ring, are actually implemented as simple lists, @emph{not} using
1371 the @code{ring} package; thus the following functions won't work on
1374 @defun make-ring size
1375 This returns a new ring capable of holding @var{size} objects.
1376 @var{size} should be an integer.
1379 @defun ring-p object
1380 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
1383 @defun ring-size ring
1384 This returns the maximum capacity of the @var{ring}.
1387 @defun ring-length ring
1388 This returns the number of objects that @var{ring} currently contains.
1389 The value will never exceed that returned by @code{ring-size}.
1392 @defun ring-elements ring
1393 This returns a list of the objects in @var{ring}, in order, newest first.
1396 @defun ring-copy ring
1397 This returns a new ring which is a copy of @var{ring}.
1398 The new ring contains the same (@code{eq}) objects as @var{ring}.
1401 @defun ring-empty-p ring
1402 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
1405 The newest element in the ring always has index 0. Higher indices
1406 correspond to older elements. Indices are computed modulo the ring
1407 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
1408 to the next-oldest, and so forth.
1410 @defun ring-ref ring index
1411 This returns the object in @var{ring} found at index @var{index}.
1412 @var{index} may be negative or greater than the ring length. If
1413 @var{ring} is empty, @code{ring-ref} signals an error.
1416 @defun ring-insert ring object
1417 This inserts @var{object} into @var{ring}, making it the newest
1418 element, and returns @var{object}.
1420 If the ring is full, insertion removes the oldest element to
1421 make room for the new element.
1424 @defun ring-remove ring &optional index
1425 Remove an object from @var{ring}, and return that object. The
1426 argument @var{index} specifies which item to remove; if it is
1427 @code{nil}, that means to remove the oldest item. If @var{ring} is
1428 empty, @code{ring-remove} signals an error.
1431 @defun ring-insert-at-beginning ring object
1432 This inserts @var{object} into @var{ring}, treating it as the oldest
1433 element. The return value is not significant.
1435 If the ring is full, this function removes the newest element to make
1436 room for the inserted element.
1439 @cindex fifo data structure
1440 If you are careful not to exceed the ring size, you can
1441 use the ring as a first-in-first-out queue. For example:
1444 (let ((fifo (make-ring 5)))
1445 (mapc (lambda (obj) (ring-insert fifo obj))
1447 (list (ring-remove fifo) t
1448 (ring-remove fifo) t
1449 (ring-remove fifo)))
1450 @result{} (0 t one t "two")