2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2017 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 seqr
155 @cindex copying sequences
156 This function returns a copy of @var{seqr}, which should be either a
157 sequence or a record. The copy is the same type of object as the
158 original, and it has the same elements in the same order.
160 Storing a new element into the copy does not affect the original
161 @var{seqr}, and vice versa. However, the elements of the copy
162 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 copy, are also visible in the original.
166 If the argument is a string with text properties, the property list in
167 the copy is itself a copy, not shared with the original's property
168 list. However, the actual values of the properties are shared.
169 @xref{Text Properties}.
171 This function does not work for dotted lists. Trying to copy a
172 circular list may cause an infinite loop.
174 See also @code{append} in @ref{Building Lists}, @code{concat} in
175 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
176 for other ways to copy sequences.
184 (setq x (vector 'foo bar))
185 @result{} [foo (1 2)]
188 (setq y (copy-sequence x))
189 @result{} [foo (1 2)]
201 (eq (elt x 1) (elt y 1))
206 ;; @r{Replacing an element of one sequence.}
208 x @result{} [quux (1 2)]
209 y @result{} [foo (1 2)]
213 ;; @r{Modifying the inside of a shared element.}
214 (setcar (aref x 1) 69)
215 x @result{} [quux (69 2)]
216 y @result{} [foo (69 2)]
221 @defun reverse sequence
222 @cindex string reverse
224 @cindex vector reverse
225 @cindex sequence reverse
226 This function creates a new sequence whose elements are the elements
227 of @var{sequence}, but in reverse order. The original argument @var{sequence}
228 is @emph{not} altered. Note that char-tables cannot be reversed.
264 @defun nreverse sequence
265 @cindex reversing a string
266 @cindex reversing a list
267 @cindex reversing a vector
268 This function reverses the order of the elements of @var{sequence}.
269 Unlike @code{reverse} the original @var{sequence} may be modified.
285 ;; @r{The cons cell that was first is now last.}
291 To avoid confusion, we usually store the result of @code{nreverse}
292 back in the same variable which held the original list:
295 (setq x (nreverse x))
298 Here is the @code{nreverse} of our favorite example, @code{(a b c)},
299 presented graphically:
303 @r{Original list head:} @r{Reversed list:}
304 ------------- ------------- ------------
305 | car | cdr | | car | cdr | | car | cdr |
306 | a | nil |<-- | b | o |<-- | c | o |
307 | | | | | | | | | | | | |
308 ------------- | --------- | - | -------- | -
310 ------------- ------------
314 For the vector, it is even simpler because you don't need setq:
325 Note that unlike @code{reverse}, this function doesn't work with strings.
326 Although you can alter string data by using @code{aset}, it is strongly
327 encouraged to treat strings as immutable.
331 @defun sort sequence predicate
333 @cindex sorting lists
334 @cindex sorting vectors
335 This function sorts @var{sequence} stably. Note that this function doesn't work
336 for all sequences; it may be used only for lists and vectors. If @var{sequence}
337 is a list, it is modified destructively. This functions returns the sorted
338 @var{sequence} and compares elements using @var{predicate}. A stable sort is
339 one in which elements with equal sort keys maintain their relative order before
340 and after the sort. Stability is important when successive sorts are used to
341 order elements according to different criteria.
343 The argument @var{predicate} must be a function that accepts two
344 arguments. It is called with two elements of @var{sequence}. To get an
345 increasing order sort, the @var{predicate} should return non-@code{nil} if the
346 first element is ``less'' than the second, or @code{nil} if not.
348 The comparison function @var{predicate} must give reliable results for
349 any given pair of arguments, at least within a single call to
350 @code{sort}. It must be @dfn{antisymmetric}; that is, if @var{a} is
351 less than @var{b}, @var{b} must not be less than @var{a}. It must be
352 @dfn{transitive}---that is, if @var{a} is less than @var{b}, and @var{b}
353 is less than @var{c}, then @var{a} must be less than @var{c}. If you
354 use a comparison function which does not meet these requirements, the
355 result of @code{sort} is unpredictable.
357 The destructive aspect of @code{sort} for lists is that it rearranges the
358 cons cells forming @var{sequence} by changing @sc{cdr}s. A nondestructive
359 sort function would create new cons cells to store the elements in their
360 sorted order. If you wish to make a sorted copy without destroying the
361 original, copy it first with @code{copy-sequence} and then sort.
363 Sorting does not change the @sc{car}s of the cons cells in @var{sequence};
364 the cons cell that originally contained the element @code{a} in
365 @var{sequence} still has @code{a} in its @sc{car} after sorting, but it now
366 appears in a different position in the list due to the change of
367 @sc{cdr}s. For example:
371 (setq nums '(1 3 2 6 5 4 0))
372 @result{} (1 3 2 6 5 4 0)
376 @result{} (0 1 2 3 4 5 6)
380 @result{} (1 2 3 4 5 6)
385 @strong{Warning}: Note that the list in @code{nums} no longer contains
386 0; this is the same cons cell that it was before, but it is no longer
387 the first one in the list. Don't assume a variable that formerly held
388 the argument now holds the entire sorted list! Instead, save the result
389 of @code{sort} and use that. Most often we store the result back into
390 the variable that held the original list:
393 (setq nums (sort nums '<))
396 For the better understanding of what stable sort is, consider the following
397 vector example. After sorting, all items whose @code{car} is 8 are grouped
398 at the beginning of @code{vector}, but their relative order is preserved.
399 All items whose @code{car} is 9 are grouped at the end of @code{vector},
400 but their relative order is also preserved:
406 (vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")
407 '(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))
408 @result{} [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")
409 (9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]
412 (sort vector (lambda (x y) (< (car x) (car y))))
413 @result{} [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")
414 (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
418 @xref{Sorting}, for more functions that perform sorting.
419 See @code{documentation} in @ref{Accessing Documentation}, for a
420 useful example of @code{sort}.
423 @cindex sequence functions in seq
425 The @file{seq.el} library provides the following additional sequence
426 manipulation macros and functions, prefixed with @code{seq-}. To use
427 them, you must first load the @file{seq} library.
429 All functions defined in this library are free of side-effects;
430 i.e., they do not modify any sequence (list, vector, or string) that
431 you pass as an argument. Unless otherwise stated, the result is a
432 sequence of the same type as the input. For those functions that take
433 a predicate, this should be a function of one argument.
435 The @file{seq.el} library can be extended to work with additional
436 types of sequential data-structures. For that purpose, all functions
437 are defined using @code{cl-defgeneric}. @xref{Generic Functions}, for
438 more details about using @code{cl-defgeneric} for adding extensions.
440 @defun seq-elt sequence index
441 This function returns the element of @var{sequence} at the specified
442 @var{index}, which is an integer whose valid value range is zero to
443 one less than the length of @var{sequence}. For out-of-range values
444 on built-in sequence types, @code{seq-elt} behaves like @code{elt}.
445 For the details, see @ref{Definition of elt}.
449 (seq-elt [1 2 3 4] 2)
454 @code{seq-elt} returns places settable using @code{setf}
455 (@pxref{Setting Generalized Variables}).
460 (setf (seq-elt vec 2) 5)
467 @defun seq-length sequence
468 This function returns the number of elements in @var{sequence}. For
469 built-in sequence types, @code{seq-length} behaves like @code{length}.
470 @xref{Definition of length}.
474 This function returns non-@code{nil} if @var{sequence} is a sequence
475 (a list or array), or any additional type of sequence defined via
476 @file{seq.el} generic functions.
490 @defun seq-drop sequence n
491 This function returns all but the first @var{n} (an integer)
492 elements of @var{sequence}. If @var{n} is negative or zero,
493 the result is @var{sequence}.
497 (seq-drop [1 2 3 4 5 6] 3)
501 (seq-drop "hello world" -4)
502 @result{} "hello world"
507 @defun seq-take sequence n
508 This function returns the first @var{n} (an integer) elements of
509 @var{sequence}. If @var{n} is negative or zero, the result
514 (seq-take '(1 2 3 4) 3)
518 (seq-take [1 2 3 4] 0)
524 @defun seq-take-while predicate sequence
525 This function returns the members of @var{sequence} in order,
526 stopping before the first one for which @var{predicate} returns @code{nil}.
530 (seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
534 (seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])
540 @defun seq-drop-while predicate sequence
541 This function returns the members of @var{sequence} in order,
542 starting from the first one for which @var{predicate} returns @code{nil}.
546 (seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
550 (seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])
556 @defun seq-do function sequence
557 This function applies @var{function} to each element of
558 @var{sequence} in turn (presumably for side effects), and returns
562 @defun seq-map function sequence
563 This function returns the result of applying @var{function} to each
564 element of @var{sequence}. The returned value is a list.
568 (seq-map #'1+ '(2 4 6))
572 (seq-map #'symbol-name [foo bar])
573 @result{} ("foo" "bar")
578 @defun seq-map-indexed function sequence
579 This function returns the result of applying @var{function} to each
580 element of @var{sequence} and its index within @var{seq}. The
581 returned value is a list.
585 (seq-map-indexed (lambda (elt idx)
588 @result{} ((0 a) (b 1) (c 2))
593 @defun seq-mapn function &rest sequences
594 This function returns the result of applying @var{function} to each
595 element of @var{sequences}. The arity (@pxref{What Is a Function,
596 sub-arity}) of @var{function} must match the number of sequences.
597 Mapping stops at the end of the shortest sequence, and the returned
602 (seq-mapn #'+ '(2 4 6) '(20 40 60))
606 (seq-mapn #'concat '("moskito" "bite") ["bee" "sting"])
607 @result{} ("moskitobee" "bitesting")
612 @defun seq-filter predicate sequence
613 @cindex filtering sequences
614 This function returns a list of all the elements in @var{sequence}
615 for which @var{predicate} returns non-@code{nil}.
619 (seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
623 (seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
629 @defun seq-remove predicate sequence
630 @cindex removing from sequences
631 This function returns a list of all the elements in @var{sequence}
632 for which @var{predicate} returns @code{nil}.
636 (seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])
640 (seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
646 @defun seq-reduce function sequence initial-value
647 @cindex reducing sequences
648 This function returns the result of calling @var{function} with
649 @var{initial-value} and the first element of @var{sequence}, then calling
650 @var{function} with that result and the second element of @var{sequence},
651 then with that result and the third element of @var{sequence}, etc.
652 @var{function} should be a function of two arguments. If
653 @var{sequence} is empty, this returns @var{initial-value} without
654 calling @var{function}.
658 (seq-reduce #'+ [1 2 3 4] 0)
662 (seq-reduce #'+ '(1 2 3 4) 5)
666 (seq-reduce #'+ '() 3)
672 @defun seq-some predicate sequence
673 This function returns the first non-@code{nil} value returned by
674 applying @var{predicate} to each element of @var{sequence} in turn.
678 (seq-some #'numberp ["abc" 1 nil])
682 (seq-some #'numberp ["abc" "def"])
686 (seq-some #'null ["abc" 1 nil])
690 (seq-some #'1+ [2 4 6])
696 @defun seq-find predicate sequence &optional default
697 This function returns the first element in @var{sequence} for which
698 @var{predicate} returns non-@code{nil}. If no element matches
699 @var{predicate}, the function returns @var{default}.
701 Note that this function has an ambiguity if the found element is
702 identical to @var{default}, as in that case it cannot be known whether
703 an element was found or not.
707 (seq-find #'numberp ["abc" 1 nil])
711 (seq-find #'numberp ["abc" "def"])
717 @defun seq-every-p predicate sequence
718 This function returns non-@code{nil} if applying @var{predicate}
719 to every element of @var{sequence} returns non-@code{nil}.
723 (seq-every-p #'numberp [2 4 6])
727 (seq-some #'numberp [2 4 "6"])
733 @defun seq-empty-p sequence
734 This function returns non-@code{nil} if @var{sequence} is empty.
738 (seq-empty-p "not empty")
748 @defun seq-count predicate sequence
749 This function returns the number of elements in @var{sequence} for which
750 @var{predicate} returns non-@code{nil}.
753 (seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
758 @cindex sorting sequences
759 @defun seq-sort function sequence
760 This function returns a copy of @var{sequence} that is sorted
761 according to @var{function}, a function of two arguments that returns
762 non-@code{nil} if the first argument should sort before the second.
765 @defun seq-sort-by function predicate sequence
766 This function is similar to @code{seq-sort}, but the elements of
767 @var{sequence} are transformed by applying @var{function} on them
768 before being sorted. @var{function} is a function of one argument.
771 (seq-sort-by #'seq-length #'> ["a" "ab" "abc"])
772 @result{} ["abc" "ab" "a"]
777 @defun seq-contains sequence elt &optional function
778 This function returns the first element in @var{sequence} that is equal to
779 @var{elt}. If the optional argument @var{function} is non-@code{nil},
780 it is a function of two arguments to use instead of the default @code{equal}.
784 (seq-contains '(symbol1 symbol2) 'symbol1)
788 (seq-contains '(symbol1 symbol2) 'symbol3)
795 @defun seq-position sequence elt &optional function
796 This function returns the index of the first element in
797 @var{sequence} that is equal to @var{elt}. If the optional argument
798 @var{function} is non-@code{nil}, it is a function of two arguments to
799 use instead of the default @code{equal}.
803 (seq-position '(a b c) 'b)
807 (seq-position '(a b c) 'd)
814 @defun seq-uniq sequence &optional function
815 This function returns a list of the elements of @var{sequence} with
816 duplicates removed. If the optional argument @var{function} is non-@code{nil},
817 it is a function of two arguments to use instead of the default @code{equal}.
821 (seq-uniq '(1 2 2 1 3))
825 (seq-uniq '(1 2 2.0 1.0) #'=)
831 @defun seq-subseq sequence start &optional end
832 This function returns a subset of @var{sequence} from @var{start}
833 to @var{end}, both integers (@var{end} defaults to the last element).
834 If @var{start} or @var{end} is negative, it counts from the end of
839 (seq-subseq '(1 2 3 4 5) 1)
843 (seq-subseq '[1 2 3 4 5] 1 3)
847 (seq-subseq '[1 2 3 4 5] -3 -1)
853 @defun seq-concatenate type &rest sequences
854 This function returns a sequence of type @var{type} made of the
855 concatenation of @var{sequences}. @var{type} may be: @code{vector},
856 @code{list} or @code{string}.
860 (seq-concatenate 'list '(1 2) '(3 4) [5 6])
861 @result{} (1 2 3 4 5 6)
864 (seq-concatenate 'string "Hello " "world")
865 @result{} "Hello world"
870 @defun seq-mapcat function sequence &optional type
871 This function returns the result of applying @code{seq-concatenate}
872 to the result of applying @var{function} to each element of
873 @var{sequence}. The result is a sequence of type @var{type}, or a
874 list if @var{type} is @code{nil}.
878 (seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
879 @result{} (1 2 3 4 5 6)
884 @defun seq-partition sequence n
885 This function returns a list of the elements of @var{sequence}
886 grouped into sub-sequences of length @var{n}. The last sequence may
887 contain less elements than @var{n}. @var{n} must be an integer. If
888 @var{n} is a negative integer or 0, the return value is @code{nil}.
892 (seq-partition '(0 1 2 3 4 5 6 7) 3)
893 @result{} ((0 1 2) (3 4 5) (6 7))
898 @defun seq-intersection sequence1 sequence2 &optional function
899 This function returns a list of the elements that appear both in
900 @var{sequence1} and @var{sequence2}. If the optional argument
901 @var{function} is non-@code{nil}, it is a function of two arguments to
902 use to compare elements instead of the default @code{equal}.
906 (seq-intersection [2 3 4 5] [1 3 5 6 7])
913 @defun seq-difference sequence1 sequence2 &optional function
914 This function returns a list of the elements that appear in
915 @var{sequence1} but not in @var{sequence2}. If the optional argument
916 @var{function} is non-@code{nil}, it is a function of two arguments to
917 use to compare elements instead of the default @code{equal}.
921 (seq-difference '(2 3 4 5) [1 3 5 6 7])
927 @defun seq-group-by function sequence
928 This function separates the elements of @var{sequence} into an alist
929 whose keys are the result of applying @var{function} to each element
930 of @var{sequence}. Keys are compared using @code{equal}.
934 (seq-group-by #'integerp '(1 2.1 3 2 3.2))
935 @result{} ((t 1 3 2) (nil 2.1 3.2))
938 (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
939 @result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
944 @defun seq-into sequence type
945 This function converts the sequence @var{sequence} into a sequence
946 of type @var{type}. @var{type} can be one of the following symbols:
947 @code{vector}, @code{string} or @code{list}.
951 (seq-into [1 2 3] 'list)
955 (seq-into nil 'vector)
959 (seq-into "hello" 'vector)
960 @result{} [104 101 108 108 111]
965 @defun seq-min sequence
966 This function returns the smallest element of @var{sequence}. The
967 elements of @var{sequence} must be numbers or markers
982 @defun seq-max sequence
983 This function returns the largest element of @var{sequence}. The
984 elements of @var{sequence} must be numbers or markers.
998 @defmac seq-doseq (var sequence) body@dots{}
999 @cindex sequence iteration
1000 This macro is like @code{dolist} (@pxref{Iteration, dolist}), except
1001 that @var{sequence} can be a list, vector or string. This is
1002 primarily useful for side-effects.
1005 @defmac seq-let arguments sequence body@dots{}
1006 @cindex sequence destructuring
1007 This macro binds the variables defined in @var{arguments} to the
1008 elements of @var{sequence}. @var{arguments} can themselves include
1009 sequences, allowing for nested destructuring.
1011 The @var{arguments} sequence can also include the @code{&rest} marker
1012 followed by a variable name to be bound to the rest of
1017 (seq-let [first second] [1 2 3 4]
1018 (list first second))
1022 (seq-let (_ a _ b) '(1 2 3 4)
1027 (seq-let [a [b [c]]] [1 [2 [3]]]
1032 (seq-let [a b &rest others] [1 2 3 4]
1039 @defun seq-random-elt sequence
1040 This function returns an element of @var{sequence} taken at random.
1044 (seq-random-elt [1 2 3 4])
1046 (seq-random-elt [1 2 3 4])
1048 (seq-random-elt [1 2 3 4])
1050 (seq-random-elt [1 2 3 4])
1052 (seq-random-elt [1 2 3 4])
1057 If @var{sequence} is empty, this function signals an error.
1064 An @dfn{array} object has slots that hold a number of other Lisp
1065 objects, called the elements of the array. Any element of an array
1066 may be accessed in constant time. In contrast, the time to access an
1067 element of a list is proportional to the position of that element in
1070 Emacs defines four types of array, all one-dimensional:
1071 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
1072 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
1073 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
1074 can hold elements of any type, but strings can only hold characters,
1075 and bool-vectors can only hold @code{t} and @code{nil}.
1077 All four kinds of array share these characteristics:
1081 The first element of an array has index zero, the second element has
1082 index 1, and so on. This is called @dfn{zero-origin} indexing. For
1083 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
1086 The length of the array is fixed once you create it; you cannot
1087 change the length of an existing array.
1090 For purposes of evaluation, the array is a constant---i.e.,
1091 it evaluates to itself.
1094 The elements of an array may be referenced or changed with the functions
1095 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
1098 When you create an array, other than a char-table, you must specify
1099 its length. You cannot specify the length of a char-table, because that
1100 is determined by the range of character codes.
1102 In principle, if you want an array of text characters, you could use
1103 either a string or a vector. In practice, we always choose strings for
1104 such applications, for four reasons:
1108 They occupy one-fourth the space of a vector of the same elements.
1111 Strings are printed in a way that shows the contents more clearly
1115 Strings can hold text properties. @xref{Text Properties}.
1118 Many of the specialized editing and I/O facilities of Emacs accept only
1119 strings. For example, you cannot insert a vector of characters into a
1120 buffer the way you can insert a string. @xref{Strings and Characters}.
1123 By contrast, for an array of keyboard input characters (such as a key
1124 sequence), a vector may be necessary, because many keyboard input
1125 characters are outside the range that will fit in a string. @xref{Key
1128 @node Array Functions
1129 @section Functions that Operate on Arrays
1131 In this section, we describe the functions that accept all types of
1134 @defun arrayp object
1135 This function returns @code{t} if @var{object} is an array (i.e., a
1136 vector, a string, a bool-vector or a char-table).
1144 (arrayp (syntax-table)) ;; @r{A char-table.}
1150 @defun aref arr index
1151 @cindex array elements
1152 This function returns the @var{index}th element of the array or record
1153 @var{arr}. The first element is at index zero.
1157 (setq primes [2 3 5 7 11 13])
1158 @result{} [2 3 5 7 11 13]
1164 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
1168 See also the function @code{elt}, in @ref{Sequence Functions}.
1171 @defun aset array index object
1172 This function sets the @var{index}th element of @var{array} to be
1173 @var{object}. It returns @var{object}.
1177 (setq w [foo bar baz])
1178 @result{} [foo bar baz]
1182 @result{} [fu bar baz]
1187 @result{} "asdfasfd"
1191 @result{} "asdZasfd"
1195 If @var{array} is a string and @var{object} is not a character, a
1196 @code{wrong-type-argument} error results. The function converts a
1197 unibyte string to multibyte if necessary to insert a character.
1200 @defun fillarray array object
1201 This function fills the array @var{array} with @var{object}, so that
1202 each element of @var{array} is @var{object}. It returns @var{array}.
1206 (setq a [a b c d e f g])
1207 @result{} [a b c d e f g]
1209 @result{} [0 0 0 0 0 0 0]
1211 @result{} [0 0 0 0 0 0 0]
1214 (setq s "When in the course")
1215 @result{} "When in the course"
1217 @result{} "------------------"
1221 If @var{array} is a string and @var{object} is not a character, a
1222 @code{wrong-type-argument} error results.
1225 The general sequence functions @code{copy-sequence} and @code{length}
1226 are often useful for objects known to be arrays. @xref{Sequence Functions}.
1230 @cindex vector (type)
1232 A @dfn{vector} is a general-purpose array whose elements can be any
1233 Lisp objects. (By contrast, the elements of a string can only be
1234 characters. @xref{Strings and Characters}.) Vectors are used in
1235 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
1236 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
1237 representation of a byte-compiled function (@pxref{Byte Compilation}),
1240 Like other arrays, vectors use zero-origin indexing: the first
1241 element has index 0.
1243 Vectors are printed with square brackets surrounding the elements.
1244 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
1245 @code{a} is printed as @code{[a b a]}. You can write vectors in the
1246 same way in Lisp input.
1248 A vector, like a string or a number, is considered a constant for
1249 evaluation: the result of evaluating it is the same vector. This does
1250 not evaluate or even examine the elements of the vector.
1251 @xref{Self-Evaluating Forms}.
1253 Here are examples illustrating these principles:
1257 (setq avector [1 two '(three) "four" [five]])
1258 @result{} [1 two (quote (three)) "four" [five]]
1260 @result{} [1 two (quote (three)) "four" [five]]
1261 (eq avector (eval avector))
1266 @node Vector Functions
1267 @section Functions for Vectors
1269 Here are some functions that relate to vectors:
1271 @defun vectorp object
1272 This function returns @code{t} if @var{object} is a vector.
1284 @defun vector &rest objects
1285 This function creates and returns a vector whose elements are the
1286 arguments, @var{objects}.
1290 (vector 'foo 23 [bar baz] "rats")
1291 @result{} [foo 23 [bar baz] "rats"]
1298 @defun make-vector length object
1299 This function returns a new vector consisting of @var{length} elements,
1300 each initialized to @var{object}.
1304 (setq sleepy (make-vector 9 'Z))
1305 @result{} [Z Z Z Z Z Z Z Z Z]
1310 @defun vconcat &rest sequences
1311 @cindex copying vectors
1312 This function returns a new vector containing all the elements of
1313 @var{sequences}. The arguments @var{sequences} may be true lists,
1314 vectors, strings or bool-vectors. If no @var{sequences} are given,
1315 the empty vector is returned.
1317 The value is either the empty vector, or is a newly constructed
1318 nonempty vector that is not @code{eq} to any existing vector.
1322 (setq a (vconcat '(A B C) '(D E F)))
1323 @result{} [A B C D E F]
1330 (vconcat [A B C] "aa" '(foo (6 7)))
1331 @result{} [A B C 97 97 foo (6 7)]
1335 The @code{vconcat} function also allows byte-code function objects as
1336 arguments. This is a special feature to make it easy to access the entire
1337 contents of a byte-code function object. @xref{Byte-Code Objects}.
1339 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
1340 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
1341 in @ref{Building Lists}.
1344 The @code{append} function also provides a way to convert a vector into a
1345 list with the same elements:
1349 (setq avector [1 two (quote (three)) "four" [five]])
1350 @result{} [1 two (quote (three)) "four" [five]]
1351 (append avector nil)
1352 @result{} (1 two (quote (three)) "four" [five])
1357 @section Char-Tables
1359 @cindex extra slots of char-table
1361 A char-table is much like a vector, except that it is indexed by
1362 character codes. Any valid character code, without modifiers, can be
1363 used as an index in a char-table. You can access a char-table's
1364 elements with @code{aref} and @code{aset}, as with any array. In
1365 addition, a char-table can have @dfn{extra slots} to hold additional
1366 data not associated with particular character codes. Like vectors,
1367 char-tables are constants when evaluated, and can hold elements of any
1370 @cindex subtype of char-table
1371 Each char-table has a @dfn{subtype}, a symbol, which serves two
1376 The subtype provides an easy way to tell what the char-table is for.
1377 For instance, display tables are char-tables with @code{display-table}
1378 as the subtype, and syntax tables are char-tables with
1379 @code{syntax-table} as the subtype. The subtype can be queried using
1380 the function @code{char-table-subtype}, described below.
1383 The subtype controls the number of @dfn{extra slots} in the
1384 char-table. This number is specified by the subtype's
1385 @code{char-table-extra-slots} symbol property (@pxref{Symbol
1386 Properties}), whose value should be an integer between 0 and 10. If
1387 the subtype has no such symbol property, the char-table has no extra
1391 @cindex parent of char-table
1392 A char-table can have a @dfn{parent}, which is another char-table. If
1393 it does, then whenever the char-table specifies @code{nil} for a
1394 particular character @var{c}, it inherits the value specified in the
1395 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
1396 the value from the parent of @var{char-table} if @var{char-table} itself
1397 specifies @code{nil}.
1399 @cindex default value of char-table
1400 A char-table can also have a @dfn{default value}. If so, then
1401 @code{(aref @var{char-table} @var{c})} returns the default value
1402 whenever the char-table does not specify any other non-@code{nil} value.
1404 @defun make-char-table subtype &optional init
1405 Return a newly-created char-table, with subtype @var{subtype} (a
1406 symbol). Each element is initialized to @var{init}, which defaults to
1407 @code{nil}. You cannot alter the subtype of a char-table after the
1408 char-table is created.
1410 There is no argument to specify the length of the char-table, because
1411 all char-tables have room for any valid character code as an index.
1413 If @var{subtype} has the @code{char-table-extra-slots} symbol
1414 property, that specifies the number of extra slots in the char-table.
1415 This should be an integer between 0 and 10; otherwise,
1416 @code{make-char-table} raises an error. If @var{subtype} has no
1417 @code{char-table-extra-slots} symbol property (@pxref{Property
1418 Lists}), the char-table has no extra slots.
1421 @defun char-table-p object
1422 This function returns @code{t} if @var{object} is a char-table, and
1423 @code{nil} otherwise.
1426 @defun char-table-subtype char-table
1427 This function returns the subtype symbol of @var{char-table}.
1430 There is no special function to access default values in a char-table.
1431 To do that, use @code{char-table-range} (see below).
1433 @defun char-table-parent char-table
1434 This function returns the parent of @var{char-table}. The parent is
1435 always either @code{nil} or another char-table.
1438 @defun set-char-table-parent char-table new-parent
1439 This function sets the parent of @var{char-table} to @var{new-parent}.
1442 @defun char-table-extra-slot char-table n
1443 This function returns the contents of extra slot @var{n} (zero based)
1444 of @var{char-table}. The number of extra slots in a char-table is
1445 determined by its subtype.
1448 @defun set-char-table-extra-slot char-table n value
1449 This function stores @var{value} in extra slot @var{n} (zero based) of
1453 A char-table can specify an element value for a single character code;
1454 it can also specify a value for an entire character set.
1456 @defun char-table-range char-table range
1457 This returns the value specified in @var{char-table} for a range of
1458 characters @var{range}. Here are the possibilities for @var{range}:
1462 Refers to the default value.
1465 Refers to the element for character @var{char}
1466 (supposing @var{char} is a valid character code).
1468 @item @code{(@var{from} . @var{to})}
1469 A cons cell refers to all the characters in the inclusive range
1470 @samp{[@var{from}..@var{to}]}.
1474 @defun set-char-table-range char-table range value
1475 This function sets the value in @var{char-table} for a range of
1476 characters @var{range}. Here are the possibilities for @var{range}:
1480 Refers to the default value.
1483 Refers to the whole range of character codes.
1486 Refers to the element for character @var{char}
1487 (supposing @var{char} is a valid character code).
1489 @item @code{(@var{from} . @var{to})}
1490 A cons cell refers to all the characters in the inclusive range
1491 @samp{[@var{from}..@var{to}]}.
1495 @defun map-char-table function char-table
1496 This function calls its argument @var{function} for each element of
1497 @var{char-table} that has a non-@code{nil} value. The call to
1498 @var{function} is with two arguments, a key and a value. The key
1499 is a possible @var{range} argument for @code{char-table-range}---either
1500 a valid character or a cons cell @code{(@var{from} . @var{to})},
1501 specifying a range of characters that share the same value. The value is
1502 what @code{(char-table-range @var{char-table} @var{key})} returns.
1504 Overall, the key-value pairs passed to @var{function} describe all the
1505 values stored in @var{char-table}.
1507 The return value is always @code{nil}; to make calls to
1508 @code{map-char-table} useful, @var{function} should have side effects.
1509 For example, here is how to examine the elements of the syntax table:
1514 #'(lambda (key value)
1518 (list (car key) (cdr key))
1525 (((2597602 4194303) (2)) ((2597523 2597601) (3))
1526 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
1527 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
1532 @section Bool-vectors
1533 @cindex Bool-vectors
1535 A bool-vector is much like a vector, except that it stores only the
1536 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
1537 value into an element of the bool-vector, the effect is to store
1538 @code{t} there. As with all arrays, bool-vector indices start from 0,
1539 and the length cannot be changed once the bool-vector is created.
1540 Bool-vectors are constants when evaluated.
1542 Several functions work specifically with bool-vectors; aside
1543 from that, you manipulate them with same functions used for other kinds
1546 @defun make-bool-vector length initial
1547 Return a new bool-vector of @var{length} elements,
1548 each one initialized to @var{initial}.
1551 @defun bool-vector &rest objects
1552 This function creates and returns a bool-vector whose elements are the
1553 arguments, @var{objects}.
1556 @defun bool-vector-p object
1557 This returns @code{t} if @var{object} is a bool-vector,
1558 and @code{nil} otherwise.
1561 There are also some bool-vector set operation functions, described below:
1563 @defun bool-vector-exclusive-or a b &optional c
1564 Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
1565 If optional argument @var{c} is given, the result of this operation is
1566 stored into @var{c}. All arguments should be bool vectors of the same length.
1569 @defun bool-vector-union a b &optional c
1570 Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
1571 optional argument @var{c} is given, the result of this operation is
1572 stored into @var{c}. All arguments should be bool vectors of the same length.
1575 @defun bool-vector-intersection a b &optional c
1576 Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
1577 optional argument @var{c} is given, the result of this operation is
1578 stored into @var{c}. All arguments should be bool vectors of the same length.
1581 @defun bool-vector-set-difference a b &optional c
1582 Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
1583 optional argument @var{c} is given, the result of this operation is
1584 stored into @var{c}. All arguments should be bool vectors of the same length.
1587 @defun bool-vector-not a &optional b
1588 Return @dfn{set complement} of bool vector @var{a}. If optional
1589 argument @var{b} is given, the result of this operation is stored into
1590 @var{b}. All arguments should be bool vectors of the same length.
1593 @defun bool-vector-subsetp a b
1594 Return @code{t} if every @code{t} value in @var{a} is also t in
1595 @var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
1599 @defun bool-vector-count-consecutive a b i
1600 Return the number of consecutive elements in @var{a} equal @var{b}
1601 starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
1602 or @code{nil}, and @var{i} is an index into @code{a}.
1605 @defun bool-vector-count-population a
1606 Return the number of elements that are @code{t} in bool vector @var{a}.
1609 The printed form represents up to 8 boolean values as a single
1614 (bool-vector t nil t nil)
1621 You can use @code{vconcat} to print a bool-vector like other vectors:
1625 (vconcat (bool-vector nil t nil t))
1626 @result{} [nil t nil t]
1630 Here is another example of creating, examining, and updating a
1634 (setq bv (make-bool-vector 5 t))
1645 These results make sense because the binary codes for control-_ and
1646 control-W are 11111 and 10111, respectively.
1649 @section Managing a Fixed-Size Ring of Objects
1651 @cindex ring data structure
1652 A @dfn{ring} is a fixed-size data structure that supports insertion,
1653 deletion, rotation, and modulo-indexed reference and traversal. An
1654 efficient ring data structure is implemented by the @code{ring}
1655 package. It provides the functions listed in this section.
1657 Note that several rings in Emacs, like the kill ring and the
1658 mark ring, are actually implemented as simple lists, @emph{not} using
1659 the @code{ring} package; thus the following functions won't work on
1662 @defun make-ring size
1663 This returns a new ring capable of holding @var{size} objects.
1664 @var{size} should be an integer.
1667 @defun ring-p object
1668 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
1671 @defun ring-size ring
1672 This returns the maximum capacity of the @var{ring}.
1675 @defun ring-length ring
1676 This returns the number of objects that @var{ring} currently contains.
1677 The value will never exceed that returned by @code{ring-size}.
1680 @defun ring-elements ring
1681 This returns a list of the objects in @var{ring}, in order, newest first.
1684 @defun ring-copy ring
1685 This returns a new ring which is a copy of @var{ring}.
1686 The new ring contains the same (@code{eq}) objects as @var{ring}.
1689 @defun ring-empty-p ring
1690 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
1693 The newest element in the ring always has index 0. Higher indices
1694 correspond to older elements. Indices are computed modulo the ring
1695 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
1696 to the next-oldest, and so forth.
1698 @defun ring-ref ring index
1699 This returns the object in @var{ring} found at index @var{index}.
1700 @var{index} may be negative or greater than the ring length. If
1701 @var{ring} is empty, @code{ring-ref} signals an error.
1704 @defun ring-insert ring object
1705 This inserts @var{object} into @var{ring}, making it the newest
1706 element, and returns @var{object}.
1708 If the ring is full, insertion removes the oldest element to
1709 make room for the new element.
1712 @defun ring-remove ring &optional index
1713 Remove an object from @var{ring}, and return that object. The
1714 argument @var{index} specifies which item to remove; if it is
1715 @code{nil}, that means to remove the oldest item. If @var{ring} is
1716 empty, @code{ring-remove} signals an error.
1719 @defun ring-insert-at-beginning ring object
1720 This inserts @var{object} into @var{ring}, treating it as the oldest
1721 element. The return value is not significant.
1723 If the ring is full, this function removes the newest element to make
1724 room for the inserted element.
1727 @cindex fifo data structure
1728 If you are careful not to exceed the ring size, you can
1729 use the ring as a first-in-first-out queue. For example:
1732 (let ((fifo (make-ring 5)))
1733 (mapc (lambda (obj) (ring-insert fifo obj))
1735 (list (ring-remove fifo) t
1736 (ring-remove fifo) t
1737 (ring-remove fifo)))
1738 @result{} (0 t one t "two")