2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../../info/sequences
7 @node Sequences Arrays Vectors, Hash Tables, Lists, Top
8 @chapter Sequences, Arrays, and Vectors
11 The @dfn{sequence} type is the union of two other Lisp types: lists
12 and arrays. In other words, any list is a sequence, and any array is
13 a sequence. The common property that all sequences have is that each
14 is an ordered collection of elements.
16 An @dfn{array} is a fixed-length object with a slot for each of its
17 elements. All the elements are accessible in constant time. The four
18 types of arrays are strings, vectors, char-tables and bool-vectors.
20 A list is a sequence of elements, but it is not a single primitive
21 object; it is made of cons cells, one cell per element. Finding the
22 @var{n}th element requires looking through @var{n} cons cells, so
23 elements farther from the beginning of the list take longer to access.
24 But it is possible to add elements to the list, or remove elements.
26 The following diagram shows the relationship between these types:
30 _____________________________________________
33 | ______ ________________________________ |
35 | | List | | Array | |
36 | | | | ________ ________ | |
37 | |______| | | | | | | |
38 | | | Vector | | String | | |
39 | | |________| |________| | |
40 | | ____________ _____________ | |
42 | | | Char-table | | Bool-vector | | |
43 | | |____________| |_____________| | |
44 | |________________________________| |
45 |_____________________________________________|
50 * Sequence Functions:: Functions that accept any kind of sequence.
51 * Arrays:: Characteristics of arrays in Emacs Lisp.
52 * Array Functions:: Functions specifically for arrays.
53 * Vectors:: Special characteristics of Emacs Lisp vectors.
54 * Vector Functions:: Functions specifically for vectors.
55 * Char-Tables:: How to work with char-tables.
56 * Bool-Vectors:: How to work with bool-vectors.
57 * Rings:: Managing a fixed-size ring of objects.
60 @node Sequence Functions
63 This section describes functions that accept any kind of sequence.
65 @defun sequencep object
66 This function returns @code{t} if @var{object} is a list, vector,
67 string, bool-vector, or char-table, @code{nil} otherwise.
70 @defun length sequence
74 @cindex sequence length
75 @cindex char-table 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 @defun elt sequence index
112 @cindex elements of sequences
113 This function returns the element of @var{sequence} indexed by
114 @var{index}. Legitimate values of @var{index} are integers ranging
115 from 0 up to one less than the length of @var{sequence}. If
116 @var{sequence} is a list, out-of-range values behave as for
117 @code{nth}. @xref{Definition of nth}. Otherwise, out-of-range values
118 trigger an @code{args-out-of-range} error.
130 ;; @r{We use @code{string} to show clearly which character @code{elt} returns.}
131 (string (elt "1234" 2))
136 @error{} Args out of range: [1 2 3 4], 4
140 @error{} Args out of range: [1 2 3 4], -1
144 This function generalizes @code{aref} (@pxref{Array Functions}) and
145 @code{nth} (@pxref{Definition of nth}).
148 @defun copy-sequence sequence
149 @cindex copying sequences
150 This function returns a copy of @var{sequence}. The copy is the same
151 type of object as the original sequence, and it has the same elements
154 Storing a new element into the copy does not affect the original
155 @var{sequence}, and vice versa. However, the elements of the new
156 sequence are not copies; they are identical (@code{eq}) to the elements
157 of the original. Therefore, changes made within these elements, as
158 found via the copied sequence, are also visible in the original
161 If the sequence is a string with text properties, the property list in
162 the copy is itself a copy, not shared with the original's property
163 list. However, the actual values of the properties are shared.
164 @xref{Text Properties}.
166 This function does not work for dotted lists. Trying to copy a
167 circular list may cause an infinite loop.
169 See also @code{append} in @ref{Building Lists}, @code{concat} in
170 @ref{Creating Strings}, and @code{vconcat} in @ref{Vector Functions},
171 for other ways to copy sequences.
179 (setq x (vector 'foo bar))
180 @result{} [foo (1 2)]
183 (setq y (copy-sequence x))
184 @result{} [foo (1 2)]
196 (eq (elt x 1) (elt y 1))
201 ;; @r{Replacing an element of one sequence.}
203 x @result{} [quux (1 2)]
204 y @result{} [foo (1 2)]
208 ;; @r{Modifying the inside of a shared element.}
209 (setcar (aref x 1) 69)
210 x @result{} [quux (69 2)]
211 y @result{} [foo (69 2)]
220 An @dfn{array} object has slots that hold a number of other Lisp
221 objects, called the elements of the array. Any element of an array
222 may be accessed in constant time. In contrast, the time to access an
223 element of a list is proportional to the position of that element in
226 Emacs defines four types of array, all one-dimensional:
227 @dfn{strings} (@pxref{String Type}), @dfn{vectors} (@pxref{Vector
228 Type}), @dfn{bool-vectors} (@pxref{Bool-Vector Type}), and
229 @dfn{char-tables} (@pxref{Char-Table Type}). Vectors and char-tables
230 can hold elements of any type, but strings can only hold characters,
231 and bool-vectors can only hold @code{t} and @code{nil}.
233 All four kinds of array share these characteristics:
237 The first element of an array has index zero, the second element has
238 index 1, and so on. This is called @dfn{zero-origin} indexing. For
239 example, an array of four elements has indices 0, 1, 2, @w{and 3}.
242 The length of the array is fixed once you create it; you cannot
243 change the length of an existing array.
246 For purposes of evaluation, the array is a constant---in other words,
247 it evaluates to itself.
250 The elements of an array may be referenced or changed with the functions
251 @code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
254 When you create an array, other than a char-table, you must specify
255 its length. You cannot specify the length of a char-table, because that
256 is determined by the range of character codes.
258 In principle, if you want an array of text characters, you could use
259 either a string or a vector. In practice, we always choose strings for
260 such applications, for four reasons:
264 They occupy one-fourth the space of a vector of the same elements.
267 Strings are printed in a way that shows the contents more clearly
271 Strings can hold text properties. @xref{Text Properties}.
274 Many of the specialized editing and I/O facilities of Emacs accept only
275 strings. For example, you cannot insert a vector of characters into a
276 buffer the way you can insert a string. @xref{Strings and Characters}.
279 By contrast, for an array of keyboard input characters (such as a key
280 sequence), a vector may be necessary, because many keyboard input
281 characters are outside the range that will fit in a string. @xref{Key
284 @node Array Functions
285 @section Functions that Operate on Arrays
287 In this section, we describe the functions that accept all types of
291 This function returns @code{t} if @var{object} is an array (i.e., a
292 vector, a string, a bool-vector or a char-table).
300 (arrayp (syntax-table)) ;; @r{A char-table.}
306 @defun aref array index
307 @cindex array elements
308 This function returns the @var{index}th element of @var{array}. The
309 first element is at index zero.
313 (setq primes [2 3 5 7 11 13])
314 @result{} [2 3 5 7 11 13]
320 @result{} 98 ; @r{@samp{b} is @acronym{ASCII} code 98.}
324 See also the function @code{elt}, in @ref{Sequence Functions}.
327 @defun aset array index object
328 This function sets the @var{index}th element of @var{array} to be
329 @var{object}. It returns @var{object}.
333 (setq w [foo bar baz])
334 @result{} [foo bar baz]
338 @result{} [fu bar baz]
351 If @var{array} is a string and @var{object} is not a character, a
352 @code{wrong-type-argument} error results. The function converts a
353 unibyte string to multibyte if necessary to insert a character.
356 @defun fillarray array object
357 This function fills the array @var{array} with @var{object}, so that
358 each element of @var{array} is @var{object}. It returns @var{array}.
362 (setq a [a b c d e f g])
363 @result{} [a b c d e f g]
365 @result{} [0 0 0 0 0 0 0]
367 @result{} [0 0 0 0 0 0 0]
370 (setq s "When in the course")
371 @result{} "When in the course"
373 @result{} "------------------"
377 If @var{array} is a string and @var{object} is not a character, a
378 @code{wrong-type-argument} error results.
381 The general sequence functions @code{copy-sequence} and @code{length}
382 are often useful for objects known to be arrays. @xref{Sequence Functions}.
386 @cindex vector (type)
388 A @dfn{vector} is a general-purpose array whose elements can be any
389 Lisp objects. (By contrast, the elements of a string can only be
390 characters. @xref{Strings and Characters}.) Vectors are used in
391 Emacs for many purposes: as key sequences (@pxref{Key Sequences}), as
392 symbol-lookup tables (@pxref{Creating Symbols}), as part of the
393 representation of a byte-compiled function (@pxref{Byte Compilation}),
396 Like other arrays, vectors use zero-origin indexing: the first
399 Vectors are printed with square brackets surrounding the elements.
400 Thus, a vector whose elements are the symbols @code{a}, @code{b} and
401 @code{a} is printed as @code{[a b a]}. You can write vectors in the
402 same way in Lisp input.
404 A vector, like a string or a number, is considered a constant for
405 evaluation: the result of evaluating it is the same vector. This does
406 not evaluate or even examine the elements of the vector.
407 @xref{Self-Evaluating Forms}.
409 Here are examples illustrating these principles:
413 (setq avector [1 two '(three) "four" [five]])
414 @result{} [1 two (quote (three)) "four" [five]]
416 @result{} [1 two (quote (three)) "four" [five]]
417 (eq avector (eval avector))
422 @node Vector Functions
423 @section Functions for Vectors
425 Here are some functions that relate to vectors:
427 @defun vectorp object
428 This function returns @code{t} if @var{object} is a vector.
440 @defun vector &rest objects
441 This function creates and returns a vector whose elements are the
442 arguments, @var{objects}.
446 (vector 'foo 23 [bar baz] "rats")
447 @result{} [foo 23 [bar baz] "rats"]
454 @defun make-vector length object
455 This function returns a new vector consisting of @var{length} elements,
456 each initialized to @var{object}.
460 (setq sleepy (make-vector 9 'Z))
461 @result{} [Z Z Z Z Z Z Z Z Z]
466 @defun vconcat &rest sequences
467 @cindex copying vectors
468 This function returns a new vector containing all the elements of
469 @var{sequences}. The arguments @var{sequences} may be true lists,
470 vectors, strings or bool-vectors. If no @var{sequences} are given, an
471 empty vector is returned.
473 The value is a newly constructed vector that is not @code{eq} to any
478 (setq a (vconcat '(A B C) '(D E F)))
479 @result{} [A B C D E F]
486 (vconcat [A B C] "aa" '(foo (6 7)))
487 @result{} [A B C 97 97 foo (6 7)]
491 The @code{vconcat} function also allows byte-code function objects as
492 arguments. This is a special feature to make it easy to access the entire
493 contents of a byte-code function object. @xref{Byte-Code Objects}.
495 For other concatenation functions, see @code{mapconcat} in @ref{Mapping
496 Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
497 in @ref{Building Lists}.
500 The @code{append} function also provides a way to convert a vector into a
501 list with the same elements:
505 (setq avector [1 two (quote (three)) "four" [five]])
506 @result{} [1 two (quote (three)) "four" [five]]
508 @result{} (1 two (quote (three)) "four" [five])
515 @cindex extra slots of char-table
517 A char-table is much like a vector, except that it is indexed by
518 character codes. Any valid character code, without modifiers, can be
519 used as an index in a char-table. You can access a char-table's
520 elements with @code{aref} and @code{aset}, as with any array. In
521 addition, a char-table can have @dfn{extra slots} to hold additional
522 data not associated with particular character codes. Like vectors,
523 char-tables are constants when evaluated, and can hold elements of any
526 @cindex subtype of char-table
527 Each char-table has a @dfn{subtype}, a symbol, which serves two
532 The subtype provides an easy way to tell what the char-table is for.
533 For instance, display tables are char-tables with @code{display-table}
534 as the subtype, and syntax tables are char-tables with
535 @code{syntax-table} as the subtype. The subtype can be queried using
536 the function @code{char-table-subtype}, described below.
539 The subtype controls the number of @dfn{extra slots} in the
540 char-table. This number is specified by the subtype's
541 @code{char-table-extra-slots} symbol property, which should be an
542 integer between 0 and 10. If the subtype has no such symbol property,
543 the char-table has no extra slots. @xref{Property Lists}, for
544 information about symbol properties.
547 @cindex parent of char-table
548 A char-table can have a @dfn{parent}, which is another char-table. If
549 it does, then whenever the char-table specifies @code{nil} for a
550 particular character @var{c}, it inherits the value specified in the
551 parent. In other words, @code{(aref @var{char-table} @var{c})} returns
552 the value from the parent of @var{char-table} if @var{char-table} itself
553 specifies @code{nil}.
555 @cindex default value of char-table
556 A char-table can also have a @dfn{default value}. If so, then
557 @code{(aref @var{char-table} @var{c})} returns the default value
558 whenever the char-table does not specify any other non-@code{nil} value.
560 @defun make-char-table subtype &optional init
561 Return a newly-created char-table, with subtype @var{subtype} (a
562 symbol). Each element is initialized to @var{init}, which defaults to
563 @code{nil}. You cannot alter the subtype of a char-table after the
564 char-table is created.
566 There is no argument to specify the length of the char-table, because
567 all char-tables have room for any valid character code as an index.
569 If @var{subtype} has the @code{char-table-extra-slots} symbol
570 property, that specifies the number of extra slots in the char-table.
571 This should be an integer between 0 and 10; otherwise,
572 @code{make-char-table} raises an error. If @var{subtype} has no
573 @code{char-table-extra-slots} symbol property (@pxref{Property
574 Lists}), the char-table has no extra slots.
577 @defun char-table-p object
578 This function returns @code{t} if @var{object} is a char-table, and
579 @code{nil} otherwise.
582 @defun char-table-subtype char-table
583 This function returns the subtype symbol of @var{char-table}.
586 There is no special function to access default values in a char-table.
587 To do that, use @code{char-table-range} (see below).
589 @defun char-table-parent char-table
590 This function returns the parent of @var{char-table}. The parent is
591 always either @code{nil} or another char-table.
594 @defun set-char-table-parent char-table new-parent
595 This function sets the parent of @var{char-table} to @var{new-parent}.
598 @defun char-table-extra-slot char-table n
599 This function returns the contents of extra slot @var{n} of
600 @var{char-table}. The number of extra slots in a char-table is
601 determined by its subtype.
604 @defun set-char-table-extra-slot char-table n value
605 This function stores @var{value} in extra slot @var{n} of
609 A char-table can specify an element value for a single character code;
610 it can also specify a value for an entire character set.
612 @defun char-table-range char-table range
613 This returns the value specified in @var{char-table} for a range of
614 characters @var{range}. Here are the possibilities for @var{range}:
618 Refers to the default value.
621 Refers to the element for character @var{char}
622 (supposing @var{char} is a valid character code).
624 @item @code{(@var{from} . @var{to})}
625 A cons cell refers to all the characters in the inclusive range
626 @samp{[@var{from}..@var{to}]}.
630 @defun set-char-table-range char-table range value
631 This function sets the value in @var{char-table} for a range of
632 characters @var{range}. Here are the possibilities for @var{range}:
636 Refers to the default value.
639 Refers to the whole range of character codes.
642 Refers to the element for character @var{char}
643 (supposing @var{char} is a valid character code).
645 @item @code{(@var{from} . @var{to})}
646 A cons cell refers to all the characters in the inclusive range
647 @samp{[@var{from}..@var{to}]}.
651 @defun map-char-table function char-table
652 This function calls its argument @var{function} for each element of
653 @var{char-table} that has a non-@code{nil} value. The call to
654 @var{function} is with two arguments, a key and a value. The key
655 is a possible @var{range} argument for @code{char-table-range}---either
656 a valid character or a cons cell @code{(@var{from} . @var{to})},
657 specifying a range of characters that share the same value. The value is
658 what @code{(char-table-range @var{char-table} @var{key})} returns.
660 Overall, the key-value pairs passed to @var{function} describe all the
661 values stored in @var{char-table}.
663 The return value is always @code{nil}; to make calls to
664 @code{map-char-table} useful, @var{function} should have side effects.
665 For example, here is how to examine the elements of the syntax table:
670 #'(lambda (key value)
674 (list (car key) (cdr key))
681 (((2597602 4194303) (2)) ((2597523 2597601) (3))
682 ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))
683 ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
688 @section Bool-vectors
691 A bool-vector is much like a vector, except that it stores only the
692 values @code{t} and @code{nil}. If you try to store any non-@code{nil}
693 value into an element of the bool-vector, the effect is to store
694 @code{t} there. As with all arrays, bool-vector indices start from 0,
695 and the length cannot be changed once the bool-vector is created.
696 Bool-vectors are constants when evaluated.
698 There are two special functions for working with bool-vectors; aside
699 from that, you manipulate them with same functions used for other kinds
702 @defun make-bool-vector length initial
703 Return a new bool-vector of @var{length} elements,
704 each one initialized to @var{initial}.
707 @defun bool-vector-p object
708 This returns @code{t} if @var{object} is a bool-vector,
709 and @code{nil} otherwise.
712 Here is an example of creating, examining, and updating a
713 bool-vector. Note that the printed form represents up to 8 boolean
714 values as a single character.
717 (setq bv (make-bool-vector 5 t))
728 These results make sense because the binary codes for control-_ and
729 control-W are 11111 and 10111, respectively.
732 @section Managing a Fixed-Size Ring of Objects
734 @cindex ring data structure
735 A @dfn{ring} is a fixed-size data structure that supports insertion,
736 deletion, rotation, and modulo-indexed reference and traversal. An
737 efficient ring data structure is implemented by the @code{ring}
738 package. It provides the functions listed in this section.
740 Note that several ``rings'' in Emacs, like the kill ring and the
741 mark ring, are actually implemented as simple lists, @emph{not} using
742 the @code{ring} package; thus the following functions won't work on
745 @defun make-ring size
746 This returns a new ring capable of holding @var{size} objects.
747 @var{size} should be an integer.
751 This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
754 @defun ring-size ring
755 This returns the maximum capacity of the @var{ring}.
758 @defun ring-length ring
759 This returns the number of objects that @var{ring} currently contains.
760 The value will never exceed that returned by @code{ring-size}.
763 @defun ring-elements ring
764 This returns a list of the objects in @var{ring}, in order, newest first.
767 @defun ring-copy ring
768 This returns a new ring which is a copy of @var{ring}.
769 The new ring contains the same (@code{eq}) objects as @var{ring}.
772 @defun ring-empty-p ring
773 This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
776 The newest element in the ring always has index 0. Higher indices
777 correspond to older elements. Indices are computed modulo the ring
778 length. Index @minus{}1 corresponds to the oldest element, @minus{}2
779 to the next-oldest, and so forth.
781 @defun ring-ref ring index
782 This returns the object in @var{ring} found at index @var{index}.
783 @var{index} may be negative or greater than the ring length. If
784 @var{ring} is empty, @code{ring-ref} signals an error.
787 @defun ring-insert ring object
788 This inserts @var{object} into @var{ring}, making it the newest
789 element, and returns @var{object}.
791 If the ring is full, insertion removes the oldest element to
792 make room for the new element.
795 @defun ring-remove ring &optional index
796 Remove an object from @var{ring}, and return that object. The
797 argument @var{index} specifies which item to remove; if it is
798 @code{nil}, that means to remove the oldest item. If @var{ring} is
799 empty, @code{ring-remove} signals an error.
802 @defun ring-insert-at-beginning ring object
803 This inserts @var{object} into @var{ring}, treating it as the oldest
804 element. The return value is not significant.
806 If the ring is full, this function removes the newest element to make
807 room for the inserted element.
810 @cindex fifo data structure
811 If you are careful not to exceed the ring size, you can
812 use the ring as a first-in-first-out queue. For example:
815 (let ((fifo (make-ring 5)))
816 (mapc (lambda (obj) (ring-insert fifo obj))
818 (list (ring-remove fifo) t
821 @result{} (0 t one t "two")