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 predicate sequence
561 This function returns non-@code{nil} if @var{predicate} returns
562 non-@code{nil} for any element of @var{sequence}. If so, the returned
563 value is the value returned by @var{predicate}.
567 (seq-some #'numberp ["abc" 1 nil])
571 (seq-some #'numberp ["abc" "def"])
575 (seq-some #'null ["abc" 1 nil])
581 @defun seq-every-p predicate sequence
582 This function returns non-@code{nil} if applying @var{predicate}
583 to every element of @var{sequence} returns non-@code{nil}.
587 (seq-every-p #'numberp [2 4 6])
591 (seq-some #'numberp [2 4 "6"])
597 @defun seq-empty-p sequence
598 This function returns non-@code{nil} if @var{sequence} is empty.
602 (seq-empty-p "not empty")
612 @defun seq-count predicate sequence
613 This function returns the number of elements in @var{sequence} for which
614 @var{predicate} returns non-@code{nil}.
617 (seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
622 @cindex sorting sequences
623 @defun seq-sort function sequence
624 This function returns a copy of @var{sequence} that is sorted
625 according to @var{function}, a function of two arguments that returns
626 non-@code{nil} if the first argument should sort before the second.
629 @defun seq-contains sequence elt &optional function
630 This function returns the first element in @var{sequence} that is equal to
631 @var{elt}. If the optional argument @var{function} is non-@code{nil},
632 it is a function of two arguments to use instead of the default @code{equal}.
636 (seq-contains '(symbol1 symbol2) 'symbol1)
640 (seq-contains '(symbol1 symbol2) 'symbol3)
647 @defun seq-uniq sequence &optional function
648 This function returns a list of the elements of @var{sequence} with
649 duplicates removed. If the optional argument @var{function} is non-@code{nil},
650 it is a function of two arguments to use instead of the default @code{equal}.
654 (seq-uniq '(1 2 2 1 3))
658 (seq-uniq '(1 2 2.0 1.0) #'=)
664 @defun seq-subseq sequence start &optional end
665 This function returns a subset of @var{sequence} from @var{start}
666 to @var{end}, both integers (@var{end} defaults to the last element).
667 If @var{start} or @var{end} is negative, it counts from the end of
672 (seq-subseq '(1 2 3 4 5) 1)
676 (seq-subseq '[1 2 3 4 5] 1 3)
680 (seq-subseq '[1 2 3 4 5] -3 -1)
686 @defun seq-concatenate type &rest sequences
687 This function returns a sequence of type @var{type} made of the
688 concatenation of @var{sequences}. @var{type} may be: @code{vector},
689 @code{list} or @code{string}.
693 (seq-concatenate 'list '(1 2) '(3 4) [5 6])
694 @result{} (1 2 3 5 6)
697 (seq-concatenate 'string "Hello " "world")
698 @result{} "Hello world"
703 @defun seq-mapcat function sequence &optional type
704 This function returns the result of applying @code{seq-concatenate}
705 to the result of applying @var{function} to each element of
706 @var{sequence}. The result is a sequence of type @var{type}, or a
707 list if @var{type} is @code{nil}.
711 (seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))
712 @result{} (1 2 3 4 5 6)
717 @defun seq-partition sequence n
718 This function returns a list of the elements of @var{sequence}
719 grouped into sub-sequences of length @var{n}. The last sequence may
720 contain less elements than @var{n}. @var{n} must be an integer. If
721 @var{n} is a negative integer or 0, nil is returned.
725 (seq-partition '(0 1 2 3 4 5 6 7) 3)
726 @result{} ((0 1 2) (3 4 5) (6 7))
731 @defun seq-intersection sequence1 sequence2 &optional function
732 This function returns a list of the elements that appear both in
733 @var{sequence1} and @var{sequence2}. If the optional argument
734 @var{function} is non-@code{nil}, it is a function of two arguments to
735 use to compare elements instead of the default @code{equal}.
739 (seq-intersection [2 3 4 5] [1 3 5 6 7])
746 @defun seq-difference sequence1 sequence2 &optional function
747 This function returns a list of the elements that appear in
748 @var{sequence1} but not in @var{sequence2}. If the optional argument
749 @var{function} is non-@code{nil}, it is a function of two arguments to
750 use to compare elements instead of the default @code{equal}.
754 (seq-difference '(2 3 4 5) [1 3 5 6 7])
760 @defun seq-group-by function sequence
761 This function separates the elements of @var{sequence} into an alist
762 whose keys are the result of applying @var{function} to each element
763 of @var{sequence}. Keys are compared using @code{equal}.
767 (seq-group-by #'integerp '(1 2.1 3 2 3.2))
768 @result{} ((t 1 3 2) (nil 2.1 3.2))
771 (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))
772 @result{} ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
777 @defun seq-into sequence type
778 This function converts the sequence @var{sequence} into a sequence
779 of type @var{type}. @var{type} can be one of the following symbols:
780 @code{vector}, @code{string} or @code{list}.
784 (seq-into [1 2 3] 'list)
788 (seq-into nil 'vector)
792 (seq-into "hello" 'vector)
793 @result{} [104 101 108 108 111]
798 @defun seq-min sequence
799 This function returns the smallest element of
800 @var{sequence}. @var{sequence} must be a sequence of numbers or
815 @defun seq-max sequence
816 This function returns the largest element of
817 @var{sequence}. @var{sequence} must be a sequence of numbers or
832 @defmac seq-doseq (var sequence) body@dots{}
833 @cindex sequence iteration
834 This macro is like @code{dolist}, except that @var{sequence} can be a list,
835 vector or string (@pxref{Iteration} for more information about the
836 @code{dolist} macro). This is primarily useful for side-effects.
839 @defmac seq-let arguments sequence body@dots{}
840 @cindex sequence destructuring
841 This macro binds the variables defined in @var{arguments} to the
842 elements of the sequence @var{sequence}. @var{arguments} can itself
843 include sequences allowing for nested destructuring.
845 The @var{arguments} sequence can also include the @code{&rest} marker
846 followed by a variable name to be bound to the rest of
851 (seq-let [first second] [1 2 3 4]
856 (seq-let (_ a _ b) '(1 2 3 4)
861 (seq-let [a [b [c]]] [1 [2 [3]]]
866 (seq-let [a b &rest others] [1 2 3 4]
878 An @dfn{array} object has slots that hold a number of other Lisp
879 objects, called the elements of the array. Any element of an array
880 may be accessed in constant time. In contrast, the time to access an
881 element of a list is proportional to the position of that element in
884 Emacs defines four types of array, all one-dimensional:
885 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
886 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
887 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
888 can hold elements of any type, but strings can only hold characters,
889 and bool-vectors can only hold @code{t} and @code{nil}.
891 All four kinds of array share these characteristics:
895 The first element of an array has index zero, the second element has
896 index 1, and so on. This is called @dfn{zero-origin} indexing. For
897 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
900 The length of the array is fixed once you create it; you cannot
901 change the length of an existing array.
904 For purposes of evaluation, the array is a constant---i.e.,
905 it evaluates to itself.
908 The elements of an array may be referenced or changed with the functions
909 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
912 When you create an array, other than a char-table, you must specify
913 its length. You cannot specify the length of a char-table, because that
914 is determined by the range of character codes.
916 In principle, if you want an array of text characters, you could use
917 either a string or a vector. In practice, we always choose strings for
918 such applications, for four reasons:
922 They occupy one-fourth the space of a vector of the same elements.
925 Strings are printed in a way that shows the contents more clearly
929 Strings can hold text properties. @xref{Text Properties}.
932 Many of the specialized editing and I/O facilities of Emacs accept only
933 strings. For example, you cannot insert a vector of characters into a
934 buffer the way you can insert a string. @xref{Strings and Characters}.
937 By contrast, for an array of keyboard input characters (such as a key
938 sequence), a vector may be necessary, because many keyboard input
939 characters are outside the range that will fit in a string. @xref{Key
942 @node Array Functions
943 @section Functions that Operate on Arrays
945 In this section, we describe the functions that accept all types of
949 This function returns @code{t} if @var{object} is an array (i.e., a
950 vector, a string, a bool-vector or a char-table).
958 (arrayp (syntax-table)) ;; @r{A char-table.}
964 @defun aref array index
965 @cindex array elements
966 This function returns the @var{index}th element of @var{array}. The
967 first element is at index zero.
971 (setq primes [2 3 5 7 11 13])
972 @result{} [2 3 5 7 11 13]
978 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
982 See also the function @code{elt}, in @ref{Sequence Functions}.
985 @defun aset array index object
986 This function sets the @var{index}th element of @var{array} to be
987 @var{object}. It returns @var{object}.
991 (setq w [foo bar baz])
992 @result{} [foo bar baz]
996 @result{} [fu bar baz]
1001 @result{} "asdfasfd"
1005 @result{} "asdZasfd"
1009 If @var{array} is a string and @var{object} is not a character, a
1010 @code{wrong-type-argument} error results. The function converts a
1011 unibyte string to multibyte if necessary to insert a character.
1014 @defun fillarray array object
1015 This function fills the array @var{array} with @var{object}, so that
1016 each element of @var{array} is @var{object}. It returns @var{array}.
1020 (setq a [a b c d e f g])
1021 @result{} [a b c d e f g]
1023 @result{} [0 0 0 0 0 0 0]
1025 @result{} [0 0 0 0 0 0 0]
1028 (setq s "When in the course")
1029 @result{} "When in the course"
1031 @result{} "------------------"
1035 If @var{array} is a string and @var{object} is not a character, a
1036 @code{wrong-type-argument} error results.
1039 The general sequence functions @code{copy-sequence} and @code{length}
1040 are often useful for objects known to be arrays. @xref{Sequence Functions}.
1044 @cindex vector (type)
1046 A @dfn{vector} is a general-purpose array whose elements can be any
1047 Lisp objects. (By contrast, the elements of a string can only be
1048 characters. @xref{Strings and Characters}.) Vectors are used in
1049 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
1050 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
1051 representation of a byte-compiled function (@pxref{Byte Compilation}),
1054 Like other arrays, vectors use zero-origin indexing: the first
1055 element has index 0.
1057 Vectors are printed with square brackets surrounding the elements.
1058 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
1059 @code{a} is printed as @code{[a b a]}. You can write vectors in the
1060 same way in Lisp input.
1062 A vector, like a string or a number, is considered a constant for
1063 evaluation: the result of evaluating it is the same vector. This does
1064 not evaluate or even examine the elements of the vector.
1065 @xref{Self-Evaluating Forms}.
1067 Here are examples illustrating these principles:
1071 (setq avector [1 two '(three) "four" [five]])
1072 @result{} [1 two (quote (three)) "four" [five]]
1074 @result{} [1 two (quote (three)) "four" [five]]
1075 (eq avector (eval avector))
1080 @node Vector Functions
1081 @section Functions for Vectors
1083 Here are some functions that relate to vectors:
1085 @defun vectorp object
1086 This function returns @code{t} if @var{object} is a vector.
1098 @defun vector &rest objects
1099 This function creates and returns a vector whose elements are the
1100 arguments, @var{objects}.
1104 (vector 'foo 23 [bar baz] "rats")
1105 @result{} [foo 23 [bar baz] "rats"]
1112 @defun make-vector length object
1113 This function returns a new vector consisting of @var{length} elements,
1114 each initialized to @var{object}.
1118 (setq sleepy (make-vector 9 'Z))
1119 @result{} [Z Z Z Z Z Z Z Z Z]
1124 @defun vconcat &rest sequences
1125 @cindex copying vectors
1126 This function returns a new vector containing all the elements of
1127 @var{sequences}. The arguments @var{sequences} may be true lists,
1128 vectors, strings or bool-vectors. If no @var{sequences} are given,
1129 the empty vector is returned.
1131 The value is either the empty vector, or is a newly constructed
1132 nonempty vector that is not @code{eq} to any existing vector.
1136 (setq a (vconcat '(A B C) '(D E F)))
1137 @result{} [A B C D E F]
1144 (vconcat [A B C] "aa" '(foo (6 7)))
1145 @result{} [A B C 97 97 foo (6 7)]
1149 The @code{vconcat} function also allows byte-code function objects as
1150 arguments. This is a special feature to make it easy to access the entire
1151 contents of a byte-code function object. @xref{Byte-Code Objects}.
1153 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
1154 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
1155 in @ref{Building Lists}.
1158 The @code{append} function also provides a way to convert a vector into a
1159 list with the same elements:
1163 (setq avector [1 two (quote (three)) "four" [five]])
1164 @result{} [1 two (quote (three)) "four" [five]]
1165 (append avector nil)
1166 @result{} (1 two (quote (three)) "four" [five])
1171 @section Char-Tables
1173 @cindex extra slots of char-table
1175 A char-table is much like a vector, except that it is indexed by
1176 character codes. Any valid character code, without modifiers, can be
1177 used as an index in a char-table. You can access a char-table's
1178 elements with @code{aref} and @code{aset}, as with any array. In
1179 addition, a char-table can have @dfn{extra slots} to hold additional
1180 data not associated with particular character codes. Like vectors,
1181 char-tables are constants when evaluated, and can hold elements of any
1184 @cindex subtype of char-table
1185 Each char-table has a @dfn{subtype}, a symbol, which serves two
1190 The subtype provides an easy way to tell what the char-table is for.
1191 For instance, display tables are char-tables with @code{display-table}
1192 as the subtype, and syntax tables are char-tables with
1193 @code{syntax-table} as the subtype. The subtype can be queried using
1194 the function @code{char-table-subtype}, described below.
1197 The subtype controls the number of @dfn{extra slots} in the
1198 char-table. This number is specified by the subtype's
1199 @code{char-table-extra-slots} symbol property (@pxref{Symbol
1200 Properties}), whose value should be an integer between 0 and 10. If
1201 the subtype has no such symbol property, the char-table has no extra
1205 @cindex parent of char-table
1206 A char-table can have a @dfn{parent}, which is another char-table. If
1207 it does, then whenever the char-table specifies @code{nil} for a
1208 particular character @var{c}, it inherits the value specified in the
1209 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
1210 the value from the parent of @var{char-table} if @var{char-table} itself
1211 specifies @code{nil}.
1213 @cindex default value of char-table
1214 A char-table can also have a @dfn{default value}. If so, then
1215 @code{(aref @var{char-table} @var{c})} returns the default value
1216 whenever the char-table does not specify any other non-@code{nil} value.
1218 @defun make-char-table subtype &optional init
1219 Return a newly-created char-table, with subtype @var{subtype} (a
1220 symbol). Each element is initialized to @var{init}, which defaults to
1221 @code{nil}. You cannot alter the subtype of a char-table after the
1222 char-table is created.
1224 There is no argument to specify the length of the char-table, because
1225 all char-tables have room for any valid character code as an index.
1227 If @var{subtype} has the @code{char-table-extra-slots} symbol
1228 property, that specifies the number of extra slots in the char-table.
1229 This should be an integer between 0 and 10; otherwise,
1230 @code{make-char-table} raises an error. If @var{subtype} has no
1231 @code{char-table-extra-slots} symbol property (@pxref{Property
1232 Lists}), the char-table has no extra slots.
1235 @defun char-table-p object
1236 This function returns @code{t} if @var{object} is a char-table, and
1237 @code{nil} otherwise.
1240 @defun char-table-subtype char-table
1241 This function returns the subtype symbol of @var{char-table}.
1244 There is no special function to access default values in a char-table.
1245 To do that, use @code{char-table-range} (see below).
1247 @defun char-table-parent char-table
1248 This function returns the parent of @var{char-table}. The parent is
1249 always either @code{nil} or another char-table.
1252 @defun set-char-table-parent char-table new-parent
1253 This function sets the parent of @var{char-table} to @var{new-parent}.
1256 @defun char-table-extra-slot char-table n
1257 This function returns the contents of extra slot @var{n} of
1258 @var{char-table}. The number of extra slots in a char-table is
1259 determined by its subtype.
1262 @defun set-char-table-extra-slot char-table n value
1263 This function stores @var{value} in extra slot @var{n} of
1267 A char-table can specify an element value for a single character code;
1268 it can also specify a value for an entire character set.
1270 @defun char-table-range char-table range
1271 This returns the value specified in @var{char-table} for a range of
1272 characters @var{range}. Here are the possibilities for @var{range}:
1276 Refers to the default value.
1279 Refers to the element for character @var{char}
1280 (supposing @var{char} is a valid character code).
1282 @item @code{(@var{from} . @var{to})}
1283 A cons cell refers to all the characters in the inclusive range
1284 @samp{[@var{from}..@var{to}]}.
1288 @defun set-char-table-range char-table range value
1289 This function sets the value in @var{char-table} for a range of
1290 characters @var{range}. Here are the possibilities for @var{range}:
1294 Refers to the default value.
1297 Refers to the whole range of character codes.
1300 Refers to the element for character @var{char}
1301 (supposing @var{char} is a valid character code).
1303 @item @code{(@var{from} . @var{to})}
1304 A cons cell refers to all the characters in the inclusive range
1305 @samp{[@var{from}..@var{to}]}.
1309 @defun map-char-table function char-table
1310 This function calls its argument @var{function} for each element of
1311 @var{char-table} that has a non-@code{nil} value. The call to
1312 @var{function} is with two arguments, a key and a value. The key
1313 is a possible @var{range} argument for @code{char-table-range}---either
1314 a valid character or a cons cell @code{(@var{from} . @var{to})},
1315 specifying a range of characters that share the same value. The value is
1316 what @code{(char-table-range @var{char-table} @var{key})} returns.
1318 Overall, the key-value pairs passed to @var{function} describe all the
1319 values stored in @var{char-table}.
1321 The return value is always @code{nil}; to make calls to
1322 @code{map-char-table} useful, @var{function} should have side effects.
1323 For example, here is how to examine the elements of the syntax table:
1328 #'(lambda (key value)
1332 (list (car key) (cdr key))
1339 (((2597602 4194303) (2)) ((2597523 2597601) (3))
1340 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
1341 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
1346 @section Bool-vectors
1347 @cindex Bool-vectors
1349 A bool-vector is much like a vector, except that it stores only the
1350 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
1351 value into an element of the bool-vector, the effect is to store
1352 @code{t} there. As with all arrays, bool-vector indices start from 0,
1353 and the length cannot be changed once the bool-vector is created.
1354 Bool-vectors are constants when evaluated.
1356 Several functions work specifically with bool-vectors; aside
1357 from that, you manipulate them with same functions used for other kinds
1360 @defun make-bool-vector length initial
1361 Return a new bool-vector of @var{length} elements,
1362 each one initialized to @var{initial}.
1365 @defun bool-vector &rest objects
1366 This function creates and returns a bool-vector whose elements are the
1367 arguments, @var{objects}.
1370 @defun bool-vector-p object
1371 This returns @code{t} if @var{object} is a bool-vector,
1372 and @code{nil} otherwise.
1375 There are also some bool-vector set operation functions, described below:
1377 @defun bool-vector-exclusive-or a b &optional c
1378 Return @dfn{bitwise exclusive or} of bool vectors @var{a} and @var{b}.
1379 If optional argument @var{c} is given, the result of this operation is
1380 stored into @var{c}. All arguments should be bool vectors of the same length.
1383 @defun bool-vector-union a b &optional c
1384 Return @dfn{bitwise or} of bool vectors @var{a} and @var{b}. If
1385 optional argument @var{c} is given, the result of this operation is
1386 stored into @var{c}. All arguments should be bool vectors of the same length.
1389 @defun bool-vector-intersection a b &optional c
1390 Return @dfn{bitwise and} of bool vectors @var{a} and @var{b}. If
1391 optional argument @var{c} is given, the result of this operation is
1392 stored into @var{c}. All arguments should be bool vectors of the same length.
1395 @defun bool-vector-set-difference a b &optional c
1396 Return @dfn{set difference} of bool vectors @var{a} and @var{b}. If
1397 optional argument @var{c} is given, the result of this operation is
1398 stored into @var{c}. All arguments should be bool vectors of the same length.
1401 @defun bool-vector-not a &optional b
1402 Return @dfn{set complement} of bool vector @var{a}. If optional
1403 argument @var{b} is given, the result of this operation is stored into
1404 @var{b}. All arguments should be bool vectors of the same length.
1407 @defun bool-vector-subsetp a b
1408 Return @code{t} if every @code{t} value in @var{a} is also t in
1409 @var{b}, @code{nil} otherwise. All arguments should be bool vectors of the
1413 @defun bool-vector-count-consecutive a b i
1414 Return the number of consecutive elements in @var{a} equal @var{b}
1415 starting at @var{i}. @code{a} is a bool vector, @var{b} is @code{t}
1416 or @code{nil}, and @var{i} is an index into @code{a}.
1419 @defun bool-vector-count-population a
1420 Return the number of elements that are @code{t} in bool vector @var{a}.
1423 The printed form represents up to 8 boolean values as a single
1428 (bool-vector t nil t nil)
1435 You can use @code{vconcat} to print a bool-vector like other vectors:
1439 (vconcat (bool-vector nil t nil t))
1440 @result{} [nil t nil t]
1444 Here is another example of creating, examining, and updating a
1448 (setq bv (make-bool-vector 5 t))
1459 These results make sense because the binary codes for control-_ and
1460 control-W are 11111 and 10111, respectively.
1463 @section Managing a Fixed-Size Ring of Objects
1465 @cindex ring data structure
1466 A @dfn{ring} is a fixed-size data structure that supports insertion,
1467 deletion, rotation, and modulo-indexed reference and traversal. An
1468 efficient ring data structure is implemented by the @code{ring}
1469 package. It provides the functions listed in this section.
1471 Note that several ``rings'' in Emacs, like the kill ring and the
1472 mark ring, are actually implemented as simple lists, @emph{not} using
1473 the @code{ring} package; thus the following functions won't work on
1476 @defun make-ring size
1477 This returns a new ring capable of holding @var{size} objects.
1478 @var{size} should be an integer.
1481 @defun ring-p object
1482 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
1485 @defun ring-size ring
1486 This returns the maximum capacity of the @var{ring}.
1489 @defun ring-length ring
1490 This returns the number of objects that @var{ring} currently contains.
1491 The value will never exceed that returned by @code{ring-size}.
1494 @defun ring-elements ring
1495 This returns a list of the objects in @var{ring}, in order, newest first.
1498 @defun ring-copy ring
1499 This returns a new ring which is a copy of @var{ring}.
1500 The new ring contains the same (@code{eq}) objects as @var{ring}.
1503 @defun ring-empty-p ring
1504 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
1507 The newest element in the ring always has index 0. Higher indices
1508 correspond to older elements. Indices are computed modulo the ring
1509 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
1510 to the next-oldest, and so forth.
1512 @defun ring-ref ring index
1513 This returns the object in @var{ring} found at index @var{index}.
1514 @var{index} may be negative or greater than the ring length. If
1515 @var{ring} is empty, @code{ring-ref} signals an error.
1518 @defun ring-insert ring object
1519 This inserts @var{object} into @var{ring}, making it the newest
1520 element, and returns @var{object}.
1522 If the ring is full, insertion removes the oldest element to
1523 make room for the new element.
1526 @defun ring-remove ring &optional index
1527 Remove an object from @var{ring}, and return that object. The
1528 argument @var{index} specifies which item to remove; if it is
1529 @code{nil}, that means to remove the oldest item. If @var{ring} is
1530 empty, @code{ring-remove} signals an error.
1533 @defun ring-insert-at-beginning ring object
1534 This inserts @var{object} into @var{ring}, treating it as the oldest
1535 element. The return value is not significant.
1537 If the ring is full, this function removes the newest element to make
1538 room for the inserted element.
1541 @cindex fifo data structure
1542 If you are careful not to exceed the ring size, you can
1543 use the ring as a first-in-first-out queue. For example:
1546 (let ((fifo (make-ring 5)))
1547 (mapc (lambda (obj) (ring-insert fifo obj))
1549 (list (ring-remove fifo) t
1550 (ring-remove fifo) t
1551 (ring-remove fifo)))
1552 @result{} (0 t one t "two")