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 @anchor{Definition of length}
76 This function returns the number of elements in @var{sequence}. If
77 @var{sequence} is a dotted list, a @code{wrong-type-argument} error is
78 signaled. Circular lists may cause an infinite loop. For a
79 char-table, the value returned is always one more than the maximum
82 @xref{Definition of safe-length}, for the related function @code{safe-length}.
102 (length (make-bool-vector 5 nil))
109 See also @code{string-bytes}, in @ref{Text Representations}.
111 If you need to compute the width of a string on display, you should use
112 @code{string-width} (@pxref{Size of Displayed Text}), not @code{length},
113 since @code{length} only counts the number of characters, but does not
114 account for the display width of each character.
116 @defun elt sequence index
117 @anchor{Definition of elt}
118 @cindex elements of sequences
119 This function returns the element of @var{sequence} indexed by
120 @var{index}. Legitimate values of @var{index} are integers ranging
121 from 0 up to one less than the length of @var{sequence}. If
122 @var{sequence} is a list, out-of-range values behave as for
123 @code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
124 trigger an @code{args-out-of-range} error.
136 ;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
137 (string (elt "1234" 2))
142 @error{} Args out of range: [1 2 3 4], 4
146 @error{} Args out of range: [1 2 3 4], -1
150 This function generalizes @code{aref} (@pxref{Array Functions}) and
151 @code{nth} (@pxref{Definition of nth}).
154 @defun copy-sequence sequence
155 @cindex copying sequences
156 This function returns a copy of @var{sequence}. The copy is the same
157 type of object as the original sequence, and it has the same elements
160 Storing a new element into the copy does not affect the original
161 @var{sequence}, and vice versa. However, the elements of the new
162 sequence are not copies; they are identical (@code{eq}) to the elements
163 of the original. Therefore, changes made within these elements, as
164 found via the copied sequence, are also visible in the original
167 If the sequence is a string with text properties, the property list in
168 the copy is itself a copy, not shared with the original's property
169 list. However, the actual values of the properties are shared.
170 @xref{Text Properties}.
172 This function does not work for dotted lists. Trying to copy a
173 circular list may cause an infinite loop.
175 See also @code{append} in @ref{Building Lists}, @code{concat} in
176 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
177 for other ways to copy sequences.
185 (setq x (vector 'foo bar))
186 @result{} [foo (1 2)]
189 (setq y (copy-sequence x))
190 @result{} [foo (1 2)]
202 (eq (elt x 1) (elt y 1))
207 ;; @r{Replacing an element of one sequence.}
209 x @result{} [quux (1 2)]
210 y @result{} [foo (1 2)]
214 ;; @r{Modifying the inside of a shared element.}
215 (setcar (aref x 1) 69)
216 x @result{} [quux (69 2)]
217 y @result{} [foo (69 2)]
222 @defun reverse sequence
223 @cindex string reverse
225 @cindex vector reverse
226 @cindex sequence reverse
227 This function creates a new sequence whose elements are the elements
228 of @var{sequence}, but in reverse order. The original argument @var{sequence}
229 is @emph{not} altered. Note that char-tables cannot be reversed.
265 @defun nreverse sequence
266 @cindex reversing a string
267 @cindex reversing a list
268 @cindex reversing a vector
269 This function reverses the order of the elements of @var{sequence}.
270 Unlike @code{reverse} the original @var{sequence} may be modified.
286 ;; @r{The cons cell that was first is now last.}
292 To avoid confusion, we usually store the result of @code{nreverse}
293 back in the same variable which held the original list:
296 (setq x (nreverse x))
299 Here is the @code{nreverse} of our favorite example, @code{(a b c)},
300 presented graphically:
304 @r{Original list head:} @r{Reversed list:}
305 ------------- ------------- ------------
306 | car | cdr | | car | cdr | | car | cdr |
307 | a | nil |<-- | b | o |<-- | c | o |
308 | | | | | | | | | | | | |
309 ------------- | --------- | - | -------- | -
311 ------------- ------------
315 For the vector, it is even simpler because you don't need setq:
326 Note that unlike @code{reverse}, this function doesn't work with strings.
327 Although you can alter string data by using @code{aset}, it is strongly
328 encouraged to treat strings as immutable.
332 @defun sort sequence predicate
334 @cindex sorting lists
335 @cindex sorting vectors
336 This function sorts @var{sequence} stably. Note that this function doesn't work
337 for all sequences; it may be used only for lists and vectors. If @var{sequence}
338 is a list, it is modified destructively. This functions returns the sorted
339 @var{sequence} and compares elements using @var{predicate}. A stable sort is
340 one in which elements with equal sort keys maintain their relative order before
341 and after the sort. Stability is important when successive sorts are used to
342 order elements according to different criteria.
344 The argument @var{predicate} must be a function that accepts two
345 arguments. It is called with two elements of @var{sequence}. To get an
346 increasing order sort, the @var{predicate} should return non-@code{nil} if the
347 first element is ``less'' than the second, or @code{nil} if not.
349 The comparison function @var{predicate} must give reliable results for
350 any given pair of arguments, at least within a single call to
351 @code{sort}. It must be @dfn{antisymmetric}; that is, if @var{a} is
352 less than @var{b}, @var{b} must not be less than @var{a}. It must be
353 @dfn{transitive}---that is, if @var{a} is less than @var{b}, and @var{b}
354 is less than @var{c}, then @var{a} must be less than @var{c}. If you
355 use a comparison function which does not meet these requirements, the
356 result of @code{sort} is unpredictable.
358 The destructive aspect of @code{sort} for lists is that it rearranges the
359 cons cells forming @var{sequence} by changing @sc{cdr}s. A nondestructive
360 sort function would create new cons cells to store the elements in their
361 sorted order. If you wish to make a sorted copy without destroying the
362 original, copy it first with @code{copy-sequence} and then sort.
364 Sorting does not change the @sc{car}s of the cons cells in @var{sequence};
365 the cons cell that originally contained the element @code{a} in
366 @var{sequence} still has @code{a} in its @sc{car} after sorting, but it now
367 appears in a different position in the list due to the change of
368 @sc{cdr}s. For example:
372 (setq nums '(1 3 2 6 5 4 0))
373 @result{} (1 3 2 6 5 4 0)
377 @result{} (0 1 2 3 4 5 6)
381 @result{} (1 2 3 4 5 6)
386 @strong{Warning}: Note that the list in @code{nums} no longer contains
387 0; this is the same cons cell that it was before, but it is no longer
388 the first one in the list. Don't assume a variable that formerly held
389 the argument now holds the entire sorted list! Instead, save the result
390 of @code{sort} and use that. Most often we store the result back into
391 the variable that held the original list:
394 (setq nums (sort nums '<))
397 For the better understanding of what stable sort is, consider the following
398 vector example. After sorting, all items whose @code{car} is 8 are grouped
399 at the beginning of @code{vector}, but their relative order is preserved.
400 All items whose @code{car} is 9 are grouped at the end of @code{vector},
401 but their relative order is also preserved:
407 (vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")
408 '(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))
409 @result{} [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")
410 (9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]
413 (sort vector (lambda (x y) (< (car x) (car y))))
414 @result{} [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")
415 (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
419 @xref{Sorting}, for more functions that perform sorting.
420 See @code{documentation} in @ref{Accessing Documentation}, for a
421 useful example of @code{sort}.
424 @cindex sequence functions in seq
426 The @file{seq.el} library provides the following additional sequence
427 manipulation macros and functions, prefixed with @code{seq-}. To use
428 them, you must first load the @file{seq} library.
430 All functions defined in this library are free of side-effects;
431 i.e., they do not modify any sequence (list, vector, or string) that
432 you pass as an argument. Unless otherwise stated, the result is a
433 sequence of the same type as the input. For those functions that take
434 a predicate, this should be a function of one argument.
436 The @file{seq.el} library can be extended to work with additional
437 types of sequential data-structures. For that purpose, all functions
438 are defined using @code{cl-defgeneric}.
440 @defun seq-elt sequence index
441 This function the element at the index @var{index} in
442 @var{sequence}. @var{index} can be an integer from zero up to the
443 length of @var{sequence} minus one. For out-of-range values on
444 built-in sequence types, @code{seq-elt} behaves like @code{elt}.
445 @xref{Definition of elt}.
449 (seq-elt [1 2 3 4] 2)
453 @code{seq-elt} returns settable places using @code{setf}.
457 (setf (seq-elt vec 2) 5)
464 @defun seq-length sequence
465 This function returns the number of elements in @var{sequence}. For
466 built-in sequence types, @code{seq-length} behaves like @code{length}.
467 @xref{Definition of length}.
470 @defun seq-p sequence
471 This function returns non-@code{nil} if @var{sequence} is a sequence
472 (a list or array), or any additional type of sequence defined via
473 @file{seq.el} generic functions.
487 @defun seq-drop sequence n
488 This function returns all but the first @var{n} (an integer)
489 elements of @var{sequence}. If @var{n} is negative or zero,
490 the result is @var{sequence}.
494 (seq-drop [1 2 3 4 5 6] 3)
498 (seq-drop "hello world" -4)
499 @result{} "hello world"
504 @defun seq-take sequence n
505 This function returns the first @var{n} (an integer) elements of
506 @var{sequence}. If @var{n} is negative or zero, the result
511 (seq-take '(1 2 3 4) 3)
515 (seq-take [1 2 3 4] 0)
521 @defun seq-take-while predicate sequence
522 This function returns the members of @var{sequence} in order,
523 stopping before the first one for which @var{predicate} returns @code{nil}.
527 (seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
531 (seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])
537 @defun seq-drop-while predicate sequence
538 This function returns the members of @var{sequence} in order,
539 starting from the first one for which @var{predicate} returns @code{nil}.
543 (seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
547 (seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])
553 @defun seq-do function sequence
554 This function applies @var{function} to each element of
555 @var{sequence} in turn (presumably for side effects) and returns
559 @defun seq-map function sequence
560 This function returns the result of applying @var{function} to each
561 element of @var{sequence}. The returned value is a list.
565 (seq-map #'1+ '(2 4 6))
569 (seq-map #'symbol-name [foo bar])
570 @result{} ("foo" "bar")
575 @defun seq-filter predicate sequence
576 @cindex filtering sequences
577 This function returns a list of all the elements in @var{sequence}
578 for which @var{predicate} returns non-@code{nil}.
582 (seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
586 (seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
592 @defun seq-remove predicate sequence
593 @cindex removing from sequences
594 This function returns a list of all the elements in @var{sequence}
595 for which @var{predicate} returns @code{nil}.
599 (seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
603 (seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
609 @defun seq-reduce function sequence initial-value
610 @cindex reducing sequences
611 This function returns the result of calling @var{function} with
612 @var{initial-value} and the first element of @var{sequence}, then calling
613 @var{function} with that result and the second element of @var{sequence},
614 then with that result and the third element of @var{sequence}, etc.
615 @var{function} should be a function of two arguments. If
616 @var{sequence} is empty, this returns @var{initial-value} without
617 calling @var{function}.
621 (seq-reduce #'+ [1 2 3 4] 0)
625 (seq-reduce #'+ '(1 2 3 4) 5)
629 (seq-reduce #'+ '() 3)
635 @defun seq-some predicate sequence
636 This function returns the first non-@code{nil} value returned by
637 applying @var{predicate} to each element of @var{sequence} in turn.
641 (seq-some #'numberp ["abc" 1 nil])
645 (seq-some #'numberp ["abc" "def"])
649 (seq-some #'null ["abc" 1 nil])
653 (seq-some #'1+ [2 4 6])
659 @defun seq-find predicate sequence &optional default
660 This function returns the first element for which @var{predicate}
661 returns non-@code{nil} in @var{sequence}. If no element matches
662 @var{predicate}, @var{default} is returned.
664 Note that this function has an ambiguity if the found element is
665 identical to @var{default}, as it cannot be known if an element was
670 (seq-find #'numberp ["abc" 1 nil])
674 (seq-find #'numberp ["abc" "def"])
680 @defun seq-every-p predicate sequence
681 This function returns non-@code{nil} if applying @var{predicate}
682 to every element of @var{sequence} returns non-@code{nil}.
686 (seq-every-p #'numberp [2 4 6])
690 (seq-some #'numberp [2 4 "6"])
696 @defun seq-empty-p sequence
697 This function returns non-@code{nil} if @var{sequence} is empty.
701 (seq-empty-p "not empty")
711 @defun seq-count predicate sequence
712 This function returns the number of elements in @var{sequence} for which
713 @var{predicate} returns non-@code{nil}.
716 (seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
721 @cindex sorting sequences
722 @defun seq-sort function sequence
723 This function returns a copy of @var{sequence} that is sorted
724 according to @var{function}, a function of two arguments that returns
725 non-@code{nil} if the first argument should sort before the second.
728 @defun seq-contains sequence elt &optional function
729 This function returns the first element in @var{sequence} that is equal to
730 @var{elt}. If the optional argument @var{function} is non-@code{nil},
731 it is a function of two arguments to use instead of the default @code{equal}.
735 (seq-contains '(symbol1 symbol2) 'symbol1)
739 (seq-contains '(symbol1 symbol2) 'symbol3)
746 @defun seq-uniq sequence &optional function
747 This function returns a list of the elements of @var{sequence} with
748 duplicates removed. If the optional argument @var{function} is non-@code{nil},
749 it is a function of two arguments to use instead of the default @code{equal}.
753 (seq-uniq '(1 2 2 1 3))
757 (seq-uniq '(1 2 2.0 1.0) #'=)
763 @defun seq-subseq sequence start &optional end
764 This function returns a subset of @var{sequence} from @var{start}
765 to @var{end}, both integers (@var{end} defaults to the last element).
766 If @var{start} or @var{end} is negative, it counts from the end of
771 (seq-subseq '(1 2 3 4 5) 1)
775 (seq-subseq '[1 2 3 4 5] 1 3)
779 (seq-subseq '[1 2 3 4 5] -3 -1)
785 @defun seq-concatenate type &rest sequences
786 This function returns a sequence of type @var{type} made of the
787 concatenation of @var{sequences}. @var{type} may be: @code{vector},
788 @code{list} or @code{string}.
792 (seq-concatenate 'list '(1 2) '(3 4) [5 6])
793 @result{} (1 2 3 5 6)
796 (seq-concatenate 'string "Hello " "world")
797 @result{} "Hello world"
802 @defun seq-mapcat function sequence &optional type
803 This function returns the result of applying @code{seq-concatenate}
804 to the result of applying @var{function} to each element of
805 @var{sequence}. The result is a sequence of type @var{type}, or a
806 list if @var{type} is @code{nil}.
810 (seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
811 @result{} (1 2 3 4 5 6)
816 @defun seq-partition sequence n
817 This function returns a list of the elements of @var{sequence}
818 grouped into sub-sequences of length @var{n}. The last sequence may
819 contain less elements than @var{n}. @var{n} must be an integer. If
820 @var{n} is a negative integer or 0, nil is returned.
824 (seq-partition '(0 1 2 3 4 5 6 7) 3)
825 @result{} ((0 1 2) (3 4 5) (6 7))
830 @defun seq-intersection sequence1 sequence2 &optional function
831 This function returns a list of the elements that appear both in
832 @var{sequence1} and @var{sequence2}. If the optional argument
833 @var{function} is non-@code{nil}, it is a function of two arguments to
834 use to compare elements instead of the default @code{equal}.
838 (seq-intersection [2 3 4 5] [1 3 5 6 7])
845 @defun seq-difference sequence1 sequence2 &optional function
846 This function returns a list of the elements that appear in
847 @var{sequence1} but not in @var{sequence2}. If the optional argument
848 @var{function} is non-@code{nil}, it is a function of two arguments to
849 use to compare elements instead of the default @code{equal}.
853 (seq-difference '(2 3 4 5) [1 3 5 6 7])
859 @defun seq-group-by function sequence
860 This function separates the elements of @var{sequence} into an alist
861 whose keys are the result of applying @var{function} to each element
862 of @var{sequence}. Keys are compared using @code{equal}.
866 (seq-group-by #'integerp '(1 2.1 3 2 3.2))
867 @result{} ((t 1 3 2) (nil 2.1 3.2))
870 (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
871 @result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
876 @defun seq-into sequence type
877 This function converts the sequence @var{sequence} into a sequence
878 of type @var{type}. @var{type} can be one of the following symbols:
879 @code{vector}, @code{string} or @code{list}.
883 (seq-into [1 2 3] 'list)
887 (seq-into nil 'vector)
891 (seq-into "hello" 'vector)
892 @result{} [104 101 108 108 111]
897 @defun seq-min sequence
898 This function returns the smallest element of
899 @var{sequence}. @var{sequence} must be a sequence of numbers or
914 @defun seq-max sequence
915 This function returns the largest element of
916 @var{sequence}. @var{sequence} must be a sequence of numbers or
931 @defmac seq-doseq (var sequence) body@dots{}
932 @cindex sequence iteration
933 This macro is like @code{dolist}, except that @var{sequence} can be a list,
934 vector or string (@pxref{Iteration} for more information about the
935 @code{dolist} macro). This is primarily useful for side-effects.
938 @defmac seq-let arguments sequence body@dots{}
939 @cindex sequence destructuring
940 This macro binds the variables defined in @var{arguments} to the
941 elements of the sequence @var{sequence}. @var{arguments} can itself
942 include sequences allowing for nested destructuring.
944 The @var{arguments} sequence can also include the @code{&rest} marker
945 followed by a variable name to be bound to the rest of
950 (seq-let [first second] [1 2 3 4]
955 (seq-let (_ a _ b) '(1 2 3 4)
960 (seq-let [a [b [c]]] [1 [2 [3]]]
965 (seq-let [a b &rest others] [1 2 3 4]
977 An @dfn{array} object has slots that hold a number of other Lisp
978 objects, called the elements of the array. Any element of an array
979 may be accessed in constant time. In contrast, the time to access an
980 element of a list is proportional to the position of that element in
983 Emacs defines four types of array, all one-dimensional:
984 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
985 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
986 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
987 can hold elements of any type, but strings can only hold characters,
988 and bool-vectors can only hold @code{t} and @code{nil}.
990 All four kinds of array share these characteristics:
994 The first element of an array has index zero, the second element has
995 index 1, and so on. This is called @dfn{zero-origin} indexing. For
996 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
999 The length of the array is fixed once you create it; you cannot
1000 change the length of an existing array.
1003 For purposes of evaluation, the array is a constant---i.e.,
1004 it evaluates to itself.
1007 The elements of an array may be referenced or changed with the functions
1008 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
1011 When you create an array, other than a char-table, you must specify
1012 its length. You cannot specify the length of a char-table, because that
1013 is determined by the range of character codes.
1015 In principle, if you want an array of text characters, you could use
1016 either a string or a vector. In practice, we always choose strings for
1017 such applications, for four reasons:
1021 They occupy one-fourth the space of a vector of the same elements.
1024 Strings are printed in a way that shows the contents more clearly
1028 Strings can hold text properties. @xref{Text Properties}.
1031 Many of the specialized editing and I/O facilities of Emacs accept only
1032 strings. For example, you cannot insert a vector of characters into a
1033 buffer the way you can insert a string. @xref{Strings and Characters}.
1036 By contrast, for an array of keyboard input characters (such as a key
1037 sequence), a vector may be necessary, because many keyboard input
1038 characters are outside the range that will fit in a string. @xref{Key
1041 @node Array Functions
1042 @section Functions that Operate on Arrays
1044 In this section, we describe the functions that accept all types of
1047 @defun arrayp object
1048 This function returns @code{t} if @var{object} is an array (i.e., a
1049 vector, a string, a bool-vector or a char-table).
1057 (arrayp (syntax-table)) ;; @r{A char-table.}
1063 @defun aref array index
1064 @cindex array elements
1065 This function returns the @var{index}th element of @var{array}. The
1066 first element is at index zero.
1070 (setq primes [2 3 5 7 11 13])
1071 @result{} [2 3 5 7 11 13]
1077 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
1081 See also the function @code{elt}, in @ref{Sequence Functions}.
1084 @defun aset array index object
1085 This function sets the @var{index}th element of @var{array} to be
1086 @var{object}. It returns @var{object}.
1090 (setq w [foo bar baz])
1091 @result{} [foo bar baz]
1095 @result{} [fu bar baz]
1100 @result{} "asdfasfd"
1104 @result{} "asdZasfd"
1108 If @var{array} is a string and @var{object} is not a character, a
1109 @code{wrong-type-argument} error results. The function converts a
1110 unibyte string to multibyte if necessary to insert a character.
1113 @defun fillarray array object
1114 This function fills the array @var{array} with @var{object}, so that
1115 each element of @var{array} is @var{object}. It returns @var{array}.
1119 (setq a [a b c d e f g])
1120 @result{} [a b c d e f g]
1122 @result{} [0 0 0 0 0 0 0]
1124 @result{} [0 0 0 0 0 0 0]
1127 (setq s "When in the course")
1128 @result{} "When in the course"
1130 @result{} "------------------"
1134 If @var{array} is a string and @var{object} is not a character, a
1135 @code{wrong-type-argument} error results.
1138 The general sequence functions @code{copy-sequence} and @code{length}
1139 are often useful for objects known to be arrays. @xref{Sequence Functions}.
1143 @cindex vector (type)
1145 A @dfn{vector} is a general-purpose array whose elements can be any
1146 Lisp objects. (By contrast, the elements of a string can only be
1147 characters. @xref{Strings and Characters}.) Vectors are used in
1148 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
1149 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
1150 representation of a byte-compiled function (@pxref{Byte Compilation}),
1153 Like other arrays, vectors use zero-origin indexing: the first
1154 element has index 0.
1156 Vectors are printed with square brackets surrounding the elements.
1157 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
1158 @code{a} is printed as @code{[a b a]}. You can write vectors in the
1159 same way in Lisp input.
1161 A vector, like a string or a number, is considered a constant for
1162 evaluation: the result of evaluating it is the same vector. This does
1163 not evaluate or even examine the elements of the vector.
1164 @xref{Self-Evaluating Forms}.
1166 Here are examples illustrating these principles:
1170 (setq avector [1 two '(three) "four" [five]])
1171 @result{} [1 two (quote (three)) "four" [five]]
1173 @result{} [1 two (quote (three)) "four" [five]]
1174 (eq avector (eval avector))
1179 @node Vector Functions
1180 @section Functions for Vectors
1182 Here are some functions that relate to vectors:
1184 @defun vectorp object
1185 This function returns @code{t} if @var{object} is a vector.
1197 @defun vector &rest objects
1198 This function creates and returns a vector whose elements are the
1199 arguments, @var{objects}.
1203 (vector 'foo 23 [bar baz] "rats")
1204 @result{} [foo 23 [bar baz] "rats"]
1211 @defun make-vector length object
1212 This function returns a new vector consisting of @var{length} elements,
1213 each initialized to @var{object}.
1217 (setq sleepy (make-vector 9 'Z))
1218 @result{} [Z Z Z Z Z Z Z Z Z]
1223 @defun vconcat &rest sequences
1224 @cindex copying vectors
1225 This function returns a new vector containing all the elements of
1226 @var{sequences}. The arguments @var{sequences} may be true lists,
1227 vectors, strings or bool-vectors. If no @var{sequences} are given,
1228 the empty vector is returned.
1230 The value is either the empty vector, or is a newly constructed
1231 nonempty vector that is not @code{eq} to any existing vector.
1235 (setq a (vconcat '(A B C) '(D E F)))
1236 @result{} [A B C D E F]
1243 (vconcat [A B C] "aa" '(foo (6 7)))
1244 @result{} [A B C 97 97 foo (6 7)]
1248 The @code{vconcat} function also allows byte-code function objects as
1249 arguments. This is a special feature to make it easy to access the entire
1250 contents of a byte-code function object. @xref{Byte-Code Objects}.
1252 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
1253 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
1254 in @ref{Building Lists}.
1257 The @code{append} function also provides a way to convert a vector into a
1258 list with the same elements:
1262 (setq avector [1 two (quote (three)) "four" [five]])
1263 @result{} [1 two (quote (three)) "four" [five]]
1264 (append avector nil)
1265 @result{} (1 two (quote (three)) "four" [five])
1270 @section Char-Tables
1272 @cindex extra slots of char-table
1274 A char-table is much like a vector, except that it is indexed by
1275 character codes. Any valid character code, without modifiers, can be
1276 used as an index in a char-table. You can access a char-table's
1277 elements with @code{aref} and @code{aset}, as with any array. In
1278 addition, a char-table can have @dfn{extra slots} to hold additional
1279 data not associated with particular character codes. Like vectors,
1280 char-tables are constants when evaluated, and can hold elements of any
1283 @cindex subtype of char-table
1284 Each char-table has a @dfn{subtype}, a symbol, which serves two
1289 The subtype provides an easy way to tell what the char-table is for.
1290 For instance, display tables are char-tables with @code{display-table}
1291 as the subtype, and syntax tables are char-tables with
1292 @code{syntax-table} as the subtype. The subtype can be queried using
1293 the function @code{char-table-subtype}, described below.
1296 The subtype controls the number of @dfn{extra slots} in the
1297 char-table. This number is specified by the subtype's
1298 @code{char-table-extra-slots} symbol property (@pxref{Symbol
1299 Properties}), whose value should be an integer between 0 and 10. If
1300 the subtype has no such symbol property, the char-table has no extra
1304 @cindex parent of char-table
1305 A char-table can have a @dfn{parent}, which is another char-table. If
1306 it does, then whenever the char-table specifies @code{nil} for a
1307 particular character @var{c}, it inherits the value specified in the
1308 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
1309 the value from the parent of @var{char-table} if @var{char-table} itself
1310 specifies @code{nil}.
1312 @cindex default value of char-table
1313 A char-table can also have a @dfn{default value}. If so, then
1314 @code{(aref @var{char-table} @var{c})} returns the default value
1315 whenever the char-table does not specify any other non-@code{nil} value.
1317 @defun make-char-table subtype &optional init
1318 Return a newly-created char-table, with subtype @var{subtype} (a
1319 symbol). Each element is initialized to @var{init}, which defaults to
1320 @code{nil}. You cannot alter the subtype of a char-table after the
1321 char-table is created.
1323 There is no argument to specify the length of the char-table, because
1324 all char-tables have room for any valid character code as an index.
1326 If @var{subtype} has the @code{char-table-extra-slots} symbol
1327 property, that specifies the number of extra slots in the char-table.
1328 This should be an integer between 0 and 10; otherwise,
1329 @code{make-char-table} raises an error. If @var{subtype} has no
1330 @code{char-table-extra-slots} symbol property (@pxref{Property
1331 Lists}), the char-table has no extra slots.
1334 @defun char-table-p object
1335 This function returns @code{t} if @var{object} is a char-table, and
1336 @code{nil} otherwise.
1339 @defun char-table-subtype char-table
1340 This function returns the subtype symbol of @var{char-table}.
1343 There is no special function to access default values in a char-table.
1344 To do that, use @code{char-table-range} (see below).
1346 @defun char-table-parent char-table
1347 This function returns the parent of @var{char-table}. The parent is
1348 always either @code{nil} or another char-table.
1351 @defun set-char-table-parent char-table new-parent
1352 This function sets the parent of @var{char-table} to @var{new-parent}.
1355 @defun char-table-extra-slot char-table n
1356 This function returns the contents of extra slot @var{n} (zero based)
1357 of @var{char-table}. The number of extra slots in a char-table is
1358 determined by its subtype.
1361 @defun set-char-table-extra-slot char-table n value
1362 This function stores @var{value} in extra slot @var{n} (zero based) of
1366 A char-table can specify an element value for a single character code;
1367 it can also specify a value for an entire character set.
1369 @defun char-table-range char-table range
1370 This returns the value specified in @var{char-table} for a range of
1371 characters @var{range}. Here are the possibilities for @var{range}:
1375 Refers to the default value.
1378 Refers to the element for character @var{char}
1379 (supposing @var{char} is a valid character code).
1381 @item @code{(@var{from} . @var{to})}
1382 A cons cell refers to all the characters in the inclusive range
1383 @samp{[@var{from}..@var{to}]}.
1387 @defun set-char-table-range char-table range value
1388 This function sets the value in @var{char-table} for a range of
1389 characters @var{range}. Here are the possibilities for @var{range}:
1393 Refers to the default value.
1396 Refers to the whole range of character codes.
1399 Refers to the element for character @var{char}
1400 (supposing @var{char} is a valid character code).
1402 @item @code{(@var{from} . @var{to})}
1403 A cons cell refers to all the characters in the inclusive range
1404 @samp{[@var{from}..@var{to}]}.
1408 @defun map-char-table function char-table
1409 This function calls its argument @var{function} for each element of
1410 @var{char-table} that has a non-@code{nil} value. The call to
1411 @var{function} is with two arguments, a key and a value. The key
1412 is a possible @var{range} argument for @code{char-table-range}---either
1413 a valid character or a cons cell @code{(@var{from} . @var{to})},
1414 specifying a range of characters that share the same value. The value is
1415 what @code{(char-table-range @var{char-table} @var{key})} returns.
1417 Overall, the key-value pairs passed to @var{function} describe all the
1418 values stored in @var{char-table}.
1420 The return value is always @code{nil}; to make calls to
1421 @code{map-char-table} useful, @var{function} should have side effects.
1422 For example, here is how to examine the elements of the syntax table:
1427 #'(lambda (key value)
1431 (list (car key) (cdr key))
1438 (((2597602 4194303) (2)) ((2597523 2597601) (3))
1439 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
1440 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
1445 @section Bool-vectors
1446 @cindex Bool-vectors
1448 A bool-vector is much like a vector, except that it stores only the
1449 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
1450 value into an element of the bool-vector, the effect is to store
1451 @code{t} there. As with all arrays, bool-vector indices start from 0,
1452 and the length cannot be changed once the bool-vector is created.
1453 Bool-vectors are constants when evaluated.
1455 Several functions work specifically with bool-vectors; aside
1456 from that, you manipulate them with same functions used for other kinds
1459 @defun make-bool-vector length initial
1460 Return a new bool-vector of @var{length} elements,
1461 each one initialized to @var{initial}.
1464 @defun bool-vector &rest objects
1465 This function creates and returns a bool-vector whose elements are the
1466 arguments, @var{objects}.
1469 @defun bool-vector-p object
1470 This returns @code{t} if @var{object} is a bool-vector,
1471 and @code{nil} otherwise.
1474 There are also some bool-vector set operation functions, described below:
1476 @defun bool-vector-exclusive-or a b &optional c
1477 Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
1478 If optional argument @var{c} is given, the result of this operation is
1479 stored into @var{c}. All arguments should be bool vectors of the same length.
1482 @defun bool-vector-union a b &optional c
1483 Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
1484 optional argument @var{c} is given, the result of this operation is
1485 stored into @var{c}. All arguments should be bool vectors of the same length.
1488 @defun bool-vector-intersection a b &optional c
1489 Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
1490 optional argument @var{c} is given, the result of this operation is
1491 stored into @var{c}. All arguments should be bool vectors of the same length.
1494 @defun bool-vector-set-difference a b &optional c
1495 Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
1496 optional argument @var{c} is given, the result of this operation is
1497 stored into @var{c}. All arguments should be bool vectors of the same length.
1500 @defun bool-vector-not a &optional b
1501 Return @dfn{set complement} of bool vector @var{a}. If optional
1502 argument @var{b} is given, the result of this operation is stored into
1503 @var{b}. All arguments should be bool vectors of the same length.
1506 @defun bool-vector-subsetp a b
1507 Return @code{t} if every @code{t} value in @var{a} is also t in
1508 @var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
1512 @defun bool-vector-count-consecutive a b i
1513 Return the number of consecutive elements in @var{a} equal @var{b}
1514 starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
1515 or @code{nil}, and @var{i} is an index into @code{a}.
1518 @defun bool-vector-count-population a
1519 Return the number of elements that are @code{t} in bool vector @var{a}.
1522 The printed form represents up to 8 boolean values as a single
1527 (bool-vector t nil t nil)
1534 You can use @code{vconcat} to print a bool-vector like other vectors:
1538 (vconcat (bool-vector nil t nil t))
1539 @result{} [nil t nil t]
1543 Here is another example of creating, examining, and updating a
1547 (setq bv (make-bool-vector 5 t))
1558 These results make sense because the binary codes for control-_ and
1559 control-W are 11111 and 10111, respectively.
1562 @section Managing a Fixed-Size Ring of Objects
1564 @cindex ring data structure
1565 A @dfn{ring} is a fixed-size data structure that supports insertion,
1566 deletion, rotation, and modulo-indexed reference and traversal. An
1567 efficient ring data structure is implemented by the @code{ring}
1568 package. It provides the functions listed in this section.
1570 Note that several rings in Emacs, like the kill ring and the
1571 mark ring, are actually implemented as simple lists, @emph{not} using
1572 the @code{ring} package; thus the following functions won't work on
1575 @defun make-ring size
1576 This returns a new ring capable of holding @var{size} objects.
1577 @var{size} should be an integer.
1580 @defun ring-p object
1581 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
1584 @defun ring-size ring
1585 This returns the maximum capacity of the @var{ring}.
1588 @defun ring-length ring
1589 This returns the number of objects that @var{ring} currently contains.
1590 The value will never exceed that returned by @code{ring-size}.
1593 @defun ring-elements ring
1594 This returns a list of the objects in @var{ring}, in order, newest first.
1597 @defun ring-copy ring
1598 This returns a new ring which is a copy of @var{ring}.
1599 The new ring contains the same (@code{eq}) objects as @var{ring}.
1602 @defun ring-empty-p ring
1603 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
1606 The newest element in the ring always has index 0. Higher indices
1607 correspond to older elements. Indices are computed modulo the ring
1608 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
1609 to the next-oldest, and so forth.
1611 @defun ring-ref ring index
1612 This returns the object in @var{ring} found at index @var{index}.
1613 @var{index} may be negative or greater than the ring length. If
1614 @var{ring} is empty, @code{ring-ref} signals an error.
1617 @defun ring-insert ring object
1618 This inserts @var{object} into @var{ring}, making it the newest
1619 element, and returns @var{object}.
1621 If the ring is full, insertion removes the oldest element to
1622 make room for the new element.
1625 @defun ring-remove ring &optional index
1626 Remove an object from @var{ring}, and return that object. The
1627 argument @var{index} specifies which item to remove; if it is
1628 @code{nil}, that means to remove the oldest item. If @var{ring} is
1629 empty, @code{ring-remove} signals an error.
1632 @defun ring-insert-at-beginning ring object
1633 This inserts @var{object} into @var{ring}, treating it as the oldest
1634 element. The return value is not significant.
1636 If the ring is full, this function removes the newest element to make
1637 room for the inserted element.
1640 @cindex fifo data structure
1641 If you are careful not to exceed the ring size, you can
1642 use the ring as a first-in-first-out queue. For example:
1645 (let ((fifo (make-ring 5)))
1646 (mapc (lambda (obj) (ring-insert fifo obj))
1648 (list (ring-remove fifo) t
1649 (ring-remove fifo) t
1650 (ring-remove fifo)))
1651 @result{} (0 t one t "two")