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[bpt/emacs.git] / lispref / sequences.texi

@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. 
@c See the file elisp.texi for copying conditions.
@setfilename ../info/sequences
@node Sequences Arrays Vectors, Symbols, Lists, Top
@chapter Sequences, Arrays, and Vectors
@cindex sequence

  Recall that the @dfn{sequence} type is the union of three other Lisp
types: lists, vectors, and strings.  In other words, any list is a
sequence, any vector is a sequence, and any string is a sequence.  The
common property that all sequences have is that each is an ordered
collection of elements.

  An @dfn{array} is a single primitive object that has a slot for each
elements.  All the elements are accessible in constant time, but the
length of an existing array cannot be changed.  Strings and vectors are
the two types of arrays.

  A list is a sequence of elements, but it is not a single primitive
object; it is made of cons cells, one cell per element.  Finding the
@var{n}th element requires looking through @var{n} cons cells, so
elements farther from the beginning of the list take longer to access.
But it is possible to add elements to the list, or remove elements.

  The following diagram shows the relationship between these types:

@example
@group
          ___________________________________
         |                                   |
         |          Sequence                 |
         |  ______   ______________________  |
         | |      | |                      | |
         | | List | |         Array        | |
         | |      | |  ________   _______  | |   
         | |______| | |        | |       | | |
         |          | | Vector | | String| | |
         |          | |________| |_______| | |
         |          |______________________| |
         |___________________________________|
@end group
@end example

  The elements of vectors and lists may be any Lisp objects.  The
elements of strings are all characters.

@menu
* Sequence Functions::    Functions that accept any kind of sequence.
* Arrays::                Characteristics of arrays in Emacs Lisp.
* Array Functions::       Functions specifically for arrays.
* Vectors::               Special characteristics of Emacs Lisp vectors.
* Vector Functions::      Functions specifically for vectors.
* Char-Tables::           How to work with char-tables.
* Bool-Vectors::          How to work with bool-vectors.
@end menu

@node Sequence Functions
@section Sequences

  In Emacs Lisp, a @dfn{sequence} is either a list, a vector or a
string.  The common property that all sequences have is that each is an
ordered collection of elements.  This section describes functions that
accept any kind of sequence.

@defun sequencep object
Returns @code{t} if @var{object} is a list, vector, or
string, @code{nil} otherwise.
@end defun

@defun copy-sequence sequence
@cindex copying sequences
Returns a copy of @var{sequence}.  The copy is the same type of object
as the original sequence, and it has the same elements in the same order.

Storing a new element into the copy does not affect the original
@var{sequence}, and vice versa.  However, the elements of the new
sequence are not copies; they are identical (@code{eq}) to the elements
of the original.  Therefore, changes made within these elements, as
found via the copied sequence, are also visible in the original
sequence.

If the sequence is a string with text properties, the property list in
the copy is itself a copy, not shared with the original's property
list.  However, the actual values of the properties are shared.
@xref{Text Properties}.

See also @code{append} in @ref{Building Lists}, @code{concat} in
@ref{Creating Strings}, and @code{vconcat} in @ref{Vectors}, for others
ways to copy sequences.

@example
@group
(setq bar '(1 2))
     @result{} (1 2)
@end group
@group
(setq x (vector 'foo bar))
     @result{} [foo (1 2)]
@end group
@group
(setq y (copy-sequence x))
     @result{} [foo (1 2)]
@end group

@group
(eq x y)
     @result{} nil
@end group
@group
(equal x y)
     @result{} t
@end group
@group
(eq (elt x 1) (elt y 1))
     @result{} t
@end group

@group
;; @r{Replacing an element of one sequence.}
(aset x 0 'quux)
x @result{} [quux (1 2)]
y @result{} [foo (1 2)]
@end group

@group
;; @r{Modifying the inside of a shared element.}
(setcar (aref x 1) 69)
x @result{} [quux (69 2)]
y @result{} [foo (69 2)]
@end group
@end example
@end defun

@defun length sequence
@cindex string length
@cindex list length
@cindex vector length
@cindex sequence length
Returns the number of elements in @var{sequence}.  If @var{sequence} is
a cons cell that is not a list (because the final @sc{cdr} is not
@code{nil}), a @code{wrong-type-argument} error is signaled.

@xref{List Elements}, for the related function @code{safe-list}.

@example
@group
(length '(1 2 3))
    @result{} 3
@end group
@group
(length ())
    @result{} 0
@end group
@group
(length "foobar")
    @result{} 6
@end group
@group
(length [1 2 3])
    @result{} 3
@end group
@end example
@end defun

@defun elt sequence index
@cindex elements of sequences
This function returns the element of @var{sequence} indexed by
@var{index}.  Legitimate values of @var{index} are integers ranging from
0 up to one less than the length of @var{sequence}.  If @var{sequence}
is a list, then out-of-range values of @var{index} return @code{nil};
otherwise, they trigger an @code{args-out-of-range} error.

@example
@group
(elt [1 2 3 4] 2)
     @result{} 3
@end group
@group
(elt '(1 2 3 4) 2)
     @result{} 3
@end group
@group
(char-to-string (elt "1234" 2))
     @result{} "3"
@end group
@group
(elt [1 2 3 4] 4)
     @error{}Args out of range: [1 2 3 4], 4
@end group
@group
(elt [1 2 3 4] -1)
     @error{}Args out of range: [1 2 3 4], -1
@end group
@end example

This function generalizes @code{aref} (@pxref{Array Functions}) and
@code{nth} (@pxref{List Elements}).
@end defun

@node Arrays
@section Arrays
@cindex array

  An @dfn{array} object has slots that hold a number of other Lisp
objects, called the elements of the array.  Any element of an array may
be accessed in constant time.  In contrast, an element of a list
requires access time that is proportional to the position of the element
in the list.

  When you create an array, you must specify how many elements it has.
The amount of space allocated depends on the number of elements.
Therefore, it is impossible to change the size of an array once it is
created; you cannot add or remove elements.  However, you can replace an
element with a different value.

  Emacs defines two types of array, both of which are one-dimensional:
@dfn{strings} and @dfn{vectors}.  A vector is a general array; its
elements can be any Lisp objects.  A string is a specialized array; its
elements must be characters (i.e., integers between 0 and 255).  Each
type of array has its own read syntax.  @xref{String Type}, and
@ref{Vector Type}.

  Both kinds of array share these characteristics:

@itemize @bullet
@item
The first element of an array has index zero, the second element has
index 1, and so on.  This is called @dfn{zero-origin} indexing.  For
example, an array of four elements has indices 0, 1, 2, @w{and 3}.

@item
The elements of an array may be referenced or changed with the functions
@code{aref} and @code{aset}, respectively (@pxref{Array Functions}).
@end itemize

  In principle, if you wish to have an array of text characters, you
could use either a string or a vector.  In practice, we always choose
strings for such applications, for four reasons:

@itemize @bullet
@item
They occupy one-fourth the space of a vector of the same elements.

@item
Strings are printed in a way that shows the contents more clearly
as text.

@item
Strings can hold text properties.  @xref{Text Properties}.

@item
Many of the specialized editing and I/O facilities of Emacs accept only
strings.  For example, you cannot insert a vector of characters into a
buffer the way you can insert a string.  @xref{Strings and Characters}.
@end itemize

  By contrast, for an array of keyboard input characters (such as a key
sequence), a vector may be necessary, because many keyboard input
characters are outside the range that will fit in a string.  @xref{Key
Sequence Input}.

@node Array Functions
@section Functions that Operate on Arrays

  In this section, we describe the functions that accept all types of
arrays.

@defun arrayp object
This function returns @code{t} if @var{object} is an array (i.e., a
vector, a string, a bool-vector or a char-table).

@example
@group
(arrayp [a])
@result{} t
(arrayp "asdf")
@result{} t
@end group
@end example
@end defun

@defun aref array index
@cindex array elements
This function returns the @var{index}th element of @var{array}.  The
first element is at index zero.

@example
@group
(setq primes [2 3 5 7 11 13])
     @result{} [2 3 5 7 11 13]
(aref primes 4)
     @result{} 11
(elt primes 4)
     @result{} 11
@end group

@group
(aref "abcdefg" 1)
     @result{} 98           ; @r{@samp{b} is @sc{ASCII} code 98.}
@end group
@end example

See also the function @code{elt}, in @ref{Sequence Functions}.
@end defun

@defun aset array index object
This function sets the @var{index}th element of @var{array} to be
@var{object}.  It returns @var{object}.

@example
@group
(setq w [foo bar baz])
     @result{} [foo bar baz]
(aset w 0 'fu)
     @result{} fu
w
     @result{} [fu bar baz]
@end group

@group
(setq x "asdfasfd")
     @result{} "asdfasfd"
(aset x 3 ?Z)
     @result{} 90
x
     @result{} "asdZasfd"
@end group
@end example

If @var{array} is a string and @var{object} is not a character, a
@code{wrong-type-argument} error results.  If @var{array} is a string
and @var{object} is character, but @var{object} does not use the same
number of bytes as the character currently stored in @code{(aref
@var{object} @var{index})}, that is also an error.  @xref{Chars and
Bytes}.
@end defun

@defun fillarray array object
This function fills the array @var{array} with @var{object}, so that
each element of @var{array} is @var{object}.  It returns @var{array}.

@example
@group
(setq a [a b c d e f g])
     @result{} [a b c d e f g]
(fillarray a 0)
     @result{} [0 0 0 0 0 0 0]
a
     @result{} [0 0 0 0 0 0 0]
@end group
@group
(setq s "When in the course")
     @result{} "When in the course"
(fillarray s ?-)
     @result{} "------------------"
@end group
@end example

If @var{array} is a string and @var{object} is not a character, a
@code{wrong-type-argument} error results.
@end defun

The general sequence functions @code{copy-sequence} and @code{length}
are often useful for objects known to be arrays.  @xref{Sequence Functions}.

@node Vectors
@section Vectors
@cindex vector

  Arrays in Lisp, like arrays in most languages, are blocks of memory
whose elements can be accessed in constant time.  A @dfn{vector} is a
general-purpose array; its elements can be any Lisp objects.  (By
contrast, a string can hold only characters as elements.)  Vectors in
Emacs are used for obarrays (vectors of symbols), and as part of keymaps
(vectors of commands).  They are also used internally as part of the
representation of a byte-compiled function; if you print such a
function, you will see a vector in it.

  In Emacs Lisp, the indices of the elements of a vector start from zero
and count up from there.

  Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols @code{a}, @code{b} and
@code{a} is printed as @code{[a b a]}.  You can write vectors in the
same way in Lisp input.

  A vector, like a string or a number, is considered a constant for
evaluation: the result of evaluating it is the same vector.  This does
not evaluate or even examine the elements of the vector.
@xref{Self-Evaluating Forms}.

  Here are examples illustrating these principles:

@example
@group
(setq avector [1 two '(three) "four" [five]])
     @result{} [1 two (quote (three)) "four" [five]]
(eval avector)
     @result{} [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
     @result{} t
@end group
@end example

@node Vector Functions
@section Functions That Operate on Vectors

  Here are some functions that relate to vectors:

@defun vectorp object
This function returns @code{t} if @var{object} is a vector.

@example
@group
(vectorp [a])
     @result{} t
(vectorp "asdf")
     @result{} nil
@end group
@end example
@end defun

@defun vector &rest objects
This function creates and returns a vector whose elements are the
arguments, @var{objects}.

@example
@group
(vector 'foo 23 [bar baz] "rats")
     @result{} [foo 23 [bar baz] "rats"]
(vector)
     @result{} []
@end group
@end example
@end defun

@defun make-vector length object
This function returns a new vector consisting of @var{length} elements,
each initialized to @var{object}.

@example
@group
(setq sleepy (make-vector 9 'Z))
     @result{} [Z Z Z Z Z Z Z Z Z]
@end group
@end example
@end defun

@defun vconcat &rest sequences
@cindex copying vectors
This function returns a new vector containing all the elements of the
@var{sequences}.  The arguments @var{sequences} may be any kind of
arrays, including lists, vectors, or strings.  If no @var{sequences} are
given, an empty vector is returned.

The value is a newly constructed vector that is not @code{eq} to any
existing vector.

@example
@group
(setq a (vconcat '(A B C) '(D E F)))
     @result{} [A B C D E F]
(eq a (vconcat a))
     @result{} nil
@end group
@group
(vconcat)
     @result{} []
(vconcat [A B C] "aa" '(foo (6 7)))
     @result{} [A B C 97 97 foo (6 7)]
@end group
@end example

The @code{vconcat} function also allows integers as arguments.  It
converts them to strings of digits, making up the decimal print
representation of the integer, and then uses the strings instead of the
original integers.  @strong{Don't use this feature; we plan to eliminate
it.  If you already use this feature, change your programs now!}  The
proper way to convert an integer to a decimal number in this way is with
@code{format} (@pxref{Formatting Strings}) or @code{number-to-string}
(@pxref{String Conversion}).

For other concatenation functions, see @code{mapconcat} in @ref{Mapping
Functions}, @code{concat} in @ref{Creating Strings}, and @code{append}
in @ref{Building Lists}.
@end defun

  The @code{append} function provides a way to convert a vector into a
list with the same elements (@pxref{Building Lists}):

@example
@group
(setq avector [1 two (quote (three)) "four" [five]])
     @result{} [1 two (quote (three)) "four" [five]]
(append avector nil)
     @result{} (1 two (quote (three)) "four" [five])
@end group
@end example

@node Char-Tables
@section Char-Tables
@cindex char-tables

  A char-table is much like a vector, except that it is indexed by
character codes.  Any valid character code, without modifiers, can be
used as an index in a char-table.  You can access a char-table with
@code{aref} and @code{aset}, just like a vector.

@cindex extra slots of char-table
@cindex subtype of char-table
  Each char-table has a @dfn{subtype} which is a symbol.  In order to be
a valid subtype, a symbol must have a @code{char-table-extra-slots}
property which is an integer between 0 and 10.  This integer specifies
the number of @dfn{extra slots} in the char-table.

@cindex parent of char-table
  A char-table can have a @dfn{parent}. which is another char-table.  If
it does, then whenever the char-table specifies @code{nil} for a
particular character @var{c}, it inherits the value specified in the
parent.  In other words, @code{(aref @var{char-table} @var{c})} returns
the value from the parent of @var{char-table} if @var{char-table} itself
specifies @code{nil}.

@cindex default value of char-table
  A char-table can also have a @dfn{default value}.  If so, then
@code{(aref @var{char-table} @var{c})} returns the default value
whenever the char-table does not specify any other non-@code{nil} value.

@tindex make-char-table
@defun make-char-table subtype &optional init
Return a newly created char-table, with subtype @var{subtype}.  Each
element is initialized to @var{init}, which defaults to @code{nil}.  You
cannot alter the subtype of a char-table after the char-table is
created.
@end defun

@tindex char-table-p
@defun char-table-p object
This function returns @code{t} if @code{object} is a char-table,
otherwise @code{nil}.
@end defun

@tindex char-table-subtype
@defun char-table-subtype char-table
This function returns the subtype symbol of @var{char-table}.
@end defun

@tindex set-char-table-default
@defun set-char-table-default char-table new-default
This function sets the default value of @var{char-table} to
@var{new-default}.

There is no special function to access the default value of a char-table.
To do that, use @code{(char-table-range @var{char-table} nil)}.
@end defun

@tindex char-table-parent
@defun char-table-parent char-table
This function returns the parent of @var{char-table}.  The parent is
always either @code{nil} or another char-table.
@end defun

@tindex set-char-table-parent
@defun set-char-table-parent char-table new-parent
This function sets the parent of @var{char-table} to @var{new-parent}.
@end defun

@tindex char-table-extra-slot
@defun char-table-extra-slot char-table n
This function returns the contents of extra slot @var{n} of
@var{char-table}.  The number of extra slots in a char-table is
determined by its subtype.
@end defun

@tindex set-char-table-extra-slot
@defun set-char-table-extra-slot char-table n value
This function stores @var{value} in extra slot @var{n} of
@var{char-table}.
@end defun

  A char-table can specify an element value for a single character code;
it can also specify a value for an entire character set.

@tindex char-table-range
@defun char-table-range char-table range
This returns the value specified in @var{char-table} for a range of
characters @var{range}.  Here @var{range} may be

@table @asis
@item @code{nil}
Refers to the default value.

@item @var{char}
Refers to the element for character @var{char}.

@item @var{charset}
Refers to the value specified for the whole character set
@var{charset} (@pxref{Character Sets}).
@end table
@end defun

@tindex set-char-table-range
@defun set-char-table-range char-table range value
This function set the value in @var{char-table} for a range of
characters @var{range}.  Here @var{range} may be

@table @asis
@item @code{nil}
Refers to the default value.

@item @code{t}
Refers to the whole range of character codes.

@item @var{char}
Refers to the element for character @var{char}.

@item @var{charset}
Refers to the value specified for the whole character set
@var{charset} (@pxref{Character Sets}).
@end table
@end defun

@tindex map-char-table
@defun map-char-table function char-table
This function calls @var{function} for each element of @var{char-table}.
@var{function} is called with two arguments, a key and a value.  The key
is a possible @var{range} argument for @code{char-table-range}, and the
value is @code{(char-table-range @var{char-table} @var{key})}.  Invalid
character codes are never used as the key.

Overall, the keys-value pairs passed to @var{function} describe all the
values stored in @var{char-table}.
@end defun

@node Bool-Vectors
@section Bool-vectors
@cindex Bool-vectors

  A bool-vector is much like a vector, except that it stores only the
values @code{t} and @code{nil}.  If you try to store any non-@code{nil}
value into an element of the bool-vector, that actually stores @code{t}
there.

  There are two special functions for working with bool-vectors; aside
from that, you manipulate them with same functions used for other kinds
of arrays.

@tindex make-bool-vector
@defun make-bool-vector length initial
Return a new book-vector of @var{length} elements,
each one initialized to @var{initial}.
@end defun

@defun bool-vector-p object
This returns @code{t} if @var{object} is a bool-vector,
and @code{nil} otherwise.
@end defun