@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 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2003
+@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/objects
@node Lisp Data Types, Numbers, Introduction, Top
@cindex primitive type
A few fundamental object types are built into Emacs. These, from
-which all other types are constructed, are called @dfn{primitive
-types}. Each object belongs to one and only one primitive type. These
-types include @dfn{integer}, @dfn{float}, @dfn{cons}, @dfn{symbol},
-@dfn{string}, @dfn{vector}, @dfn{subr}, @dfn{byte-code function}, plus
-several special types, such as @dfn{buffer}, that are related to
-editing. (@xref{Editing Types}.)
+which all other types are constructed, are called @dfn{primitive types}.
+Each object belongs to one and only one primitive type. These types
+include @dfn{integer}, @dfn{float}, @dfn{cons}, @dfn{symbol},
+@dfn{string}, @dfn{vector}, @dfn{hash-table}, @dfn{subr}, and
+@dfn{byte-code function}, plus several special types, such as
+@dfn{buffer}, that are related to editing. (@xref{Editing Types}.)
Each primitive type has a corresponding Lisp function that checks
whether an object is a member of that type.
variable, and the type is known by the compiler but not represented in
the data. Such type declarations do not exist in Emacs Lisp. A Lisp
variable can have any type of value, and it remembers whatever value
-you store in it, type and all.
+you store in it, type and all. (Actually, a small number of Emacs
+Lisp variables can only take on values of a certain type.
+@xref{Variables with Restricted Values}.)
This chapter describes the purpose, printed representation, and read
syntax of each of the standard types in GNU Emacs Lisp. Details on how
* Comments:: Comments and their formatting conventions.
* Programming Types:: Types found in all Lisp systems.
* Editing Types:: Types specific to Emacs.
+* Circular Objects:: Read syntax for circular structure.
* Type Predicates:: Tests related to types.
* Equality Predicates:: Tests of equality between any two objects.
@end menu
* Vector Type:: One-dimensional arrays.
* Char-Table Type:: One-dimensional sparse arrays indexed by characters.
* Bool-Vector Type:: One-dimensional arrays of @code{t} or @code{nil}.
+* Hash Table Type:: Super-fast lookup tables.
* Function Type:: A piece of executable code you can call from elsewhere.
* Macro Type:: A method of expanding an expression into another
expression, more fundamental but less pretty.
@node Integer Type
@subsection Integer Type
- The range of values for integers in Emacs Lisp is @minus{}134217728 to
-134217727 (28 bits; i.e.,
-@ifinfo
--2**27
-@end ifinfo
+ The range of values for integers in Emacs Lisp is @minus{}268435456 to
+268435455 (29 bits; i.e.,
+@ifnottex
+-2**28
+@end ifnottex
@tex
-$-2^{27}$
+@math{-2^{28}}
@end tex
to
-@ifinfo
-2**27 - 1)
-@end ifinfo
+@ifnottex
+2**28 - 1)
+@end ifnottex
@tex
-$2^{28}-1$)
+@math{2^{28}-1})
@end tex
on most machines. (Some machines may provide a wider range.) It is
important to note that the Emacs Lisp arithmetic functions do not check
-for overflow. Thus @code{(1+ 134217727)} is @minus{}134217728 on most
+for overflow. Thus @code{(1+ 268435455)} is @minus{}268435456 on most
machines.
The read syntax for integers is a sequence of (base ten) digits with an
@group
-1 ; @r{The integer -1.}
1 ; @r{The integer 1.}
-1. ; @r{Also The integer 1.}
+1. ; @r{Also the integer 1.}
+1 ; @r{Also the integer 1.}
-268435457 ; @r{Also the integer 1 on a 28-bit implementation.}
+536870913 ; @r{Also the integer 1 on a 29-bit implementation.}
@end group
@end example
@node Floating Point Type
@subsection Floating Point Type
- Emacs supports floating point numbers (though there is a compilation
-option to disable them). The precise range of floating point numbers is
-machine-specific.
+ Floating point numbers are the computer equivalent of scientific
+notation. The precise number of significant figures and the range of
+possible exponents is machine-specific; Emacs always uses the C data
+type @code{double} to store the value.
The printed representation for floating point numbers requires either
a decimal point (with at least one digit following), an exponent, or
@node Character Type
@subsection Character Type
-@cindex @sc{ASCII} character codes
+@cindex @acronym{ASCII} character codes
A @dfn{character} in Emacs Lisp is nothing more than an integer. In
other words, characters are represented by their character codes. For
common to work with @emph{strings}, which are sequences composed of
characters. @xref{String Type}.
- Characters in strings, buffers, and files are currently limited to the
-range of 0 to 524287---nineteen bits. But not all values in that range
-are valid character codes. Codes 0 through 127 are ASCII codes; the
-rest are non-ASCII (@pxref{Non-ASCII Characters}). Characters that represent
-keyboard input have a much wider range, to encode modifier keys such as
+ Characters in strings, buffers, and files are currently limited to
+the range of 0 to 524287---nineteen bits. But not all values in that
+range are valid character codes. Codes 0 through 127 are
+@acronym{ASCII} codes; the rest are non-@acronym{ASCII}
+(@pxref{Non-ASCII Characters}). Characters that represent keyboard
+input have a much wider range, to encode modifier keys such as
Control, Meta and Shift.
@cindex read syntax for characters
The usual read syntax for alphanumeric characters is a question mark
followed by the character; thus, @samp{?A} for the character
@kbd{A}, @samp{?B} for the character @kbd{B}, and @samp{?a} for the
-character @kbd{a}.
+character @kbd{a}.
For example:
You can use the same syntax for punctuation characters, but it is
often a good idea to add a @samp{\} so that the Emacs commands for
-editing Lisp code don't get confused. For example, @samp{?\ } is the
-way to write the space character. If the character is @samp{\}, you
-@emph{must} use a second @samp{\} to quote it: @samp{?\\}.
+editing Lisp code don't get confused. For example, @samp{?\(} is the
+way to write the open-paren character. If the character is @samp{\},
+you @emph{must} use a second @samp{\} to quote it: @samp{?\\}.
@cindex whitespace
@cindex bell character
@cindex @samp{\r}
@cindex escape
@cindex @samp{\e}
- You can express the characters Control-g, backspace, tab, newline,
-vertical tab, formfeed, return, and escape as @samp{?\a}, @samp{?\b},
-@samp{?\t}, @samp{?\n}, @samp{?\v}, @samp{?\f}, @samp{?\r}, @samp{?\e},
-respectively. Thus,
+@cindex space
+@cindex @samp{\s}
+ You can express the characters control-g, backspace, tab, newline,
+vertical tab, formfeed, space, return, del, and escape as @samp{?\a},
+@samp{?\b}, @samp{?\t}, @samp{?\n}, @samp{?\v}, @samp{?\f},
+@samp{?\s}, @samp{?\r}, @samp{?\d}, and @samp{?\e}, respectively.
+Thus,
@example
-?\a @result{} 7 ; @r{@kbd{C-g}}
+?\a @result{} 7 ; @r{control-g, @kbd{C-g}}
?\b @result{} 8 ; @r{backspace, @key{BS}, @kbd{C-h}}
?\t @result{} 9 ; @r{tab, @key{TAB}, @kbd{C-i}}
?\n @result{} 10 ; @r{newline, @kbd{C-j}}
?\f @result{} 12 ; @r{formfeed character, @kbd{C-l}}
?\r @result{} 13 ; @r{carriage return, @key{RET}, @kbd{C-m}}
?\e @result{} 27 ; @r{escape character, @key{ESC}, @kbd{C-[}}
+?\s @result{} 32 ; @r{space character, @key{SPC}}
?\\ @result{} 92 ; @r{backslash character, @kbd{\}}
+?\d @result{} 127 ; @r{delete character, @key{DEL}}
@end example
@cindex escape sequence
These sequences which start with backslash are also known as
-@dfn{escape sequences}, because backslash plays the role of an escape
-character; this usage has nothing to do with the character @key{ESC}.
+@dfn{escape sequences}, because backslash plays the role of an
+``escape character''; this terminology has nothing to do with the
+character @key{ESC}. @samp{\s} is meant for use only in character
+constants; in string constants, just write the space.
@cindex control characters
Control characters may be represented using yet another read syntax.
@end example
In strings and buffers, the only control characters allowed are those
-that exist in @sc{ASCII}; but for keyboard input purposes, you can turn
+that exist in @acronym{ASCII}; but for keyboard input purposes, you can turn
any character into a control character with @samp{C-}. The character
-codes for these non-@sc{ASCII} control characters include the
+codes for these non-@acronym{ASCII} control characters include the
@tex
-$2^{26}$
+@math{2^{26}}
@end tex
-@ifinfo
+@ifnottex
2**26
-@end ifinfo
+@end ifnottex
bit as well as the code for the corresponding non-control
-character. Ordinary terminals have no way of generating non-@sc{ASCII}
+character. Ordinary terminals have no way of generating non-@acronym{ASCII}
control characters, but you can generate them straightforwardly using X
and other window systems.
A @dfn{meta character} is a character typed with the @key{META}
modifier key. The integer that represents such a character has the
@tex
-$2^{27}$
+@math{2^{27}}
@end tex
-@ifinfo
+@ifnottex
2**27
-@end ifinfo
-bit set (which on most machines makes it a negative number). We
-use high bits for this and other modifiers to make possible a wide range
-of basic character codes.
+@end ifnottex
+bit set. We use high bits for this and other modifiers to make
+possible a wide range of basic character codes.
In a string, the
@tex
-$2^{7}$
+@math{2^{7}}
@end tex
-@ifinfo
+@ifnottex
2**7
-@end ifinfo
-bit attached to an ASCII character indicates a meta character; thus, the
-meta characters that can fit in a string have codes in the range from
-128 to 255, and are the meta versions of the ordinary @sc{ASCII}
-characters. (In Emacs versions 18 and older, this convention was used
-for characters outside of strings as well.)
+@end ifnottex
+bit attached to an @acronym{ASCII} character indicates a meta
+character; thus, the meta characters that can fit in a string have
+codes in the range from 128 to 255, and are the meta versions of the
+ordinary @acronym{ASCII} characters. (In Emacs versions 18 and older,
+this convention was used for characters outside of strings as well.)
The read syntax for meta characters uses @samp{\M-}. For example,
@samp{?\M-A} stands for @kbd{M-A}. You can use @samp{\M-} together with
@samp{?\M-\C-b}, @samp{?\C-\M-b}, or @samp{?\M-\002}.
The case of a graphic character is indicated by its character code;
-for example, @sc{ASCII} distinguishes between the characters @samp{a}
-and @samp{A}. But @sc{ASCII} has no way to represent whether a control
+for example, @acronym{ASCII} distinguishes between the characters @samp{a}
+and @samp{A}. But @acronym{ASCII} has no way to represent whether a control
character is upper case or lower case. Emacs uses the
@tex
-$2^{25}$
+@math{2^{25}}
@end tex
-@ifinfo
+@ifnottex
2**25
-@end ifinfo
+@end ifnottex
bit to indicate that the shift key was used in typing a control
character. This distinction is possible only when you use X terminals
or other special terminals; ordinary terminals do not report the
distinction to the computer in any way. The Lisp syntax for
-the shift bit is @samp{\S-}; thus, @samp{?\C-\S-o} or @samp{?\C-\S-O}
+the shift bit is @samp{\S-}; thus, @samp{?\C-\S-o} or @samp{?\C-\S-O}
represents the shifted-control-o character.
@cindex hyper characters
@cindex super characters
@cindex alt characters
- The X Window System defines three other modifier bits that can be set
+ The X Window System defines three other @anchor{modifier bits}
+modifier bits that can be set
in a character: @dfn{hyper}, @dfn{super} and @dfn{alt}. The syntaxes
for these bits are @samp{\H-}, @samp{\s-} and @samp{\A-}. (Case is
significant in these prefixes.) Thus, @samp{?\H-\M-\A-x} represents
-@kbd{Alt-Hyper-Meta-x}.
+@kbd{Alt-Hyper-Meta-x}. (Note that @samp{\s} with no following @samp{-}
+represents the space character.)
@tex
-Numerically, the
-bit values are $2^{22}$ for alt, $2^{23}$ for super and $2^{24}$ for hyper.
+Numerically, the bit values are @math{2^{22}} for alt, @math{2^{23}}
+for super and @math{2^{24}} for hyper.
@end tex
-@ifinfo
+@ifnottex
Numerically, the
bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper.
-@end ifinfo
+@end ifnottex
@cindex @samp{\} in character constant
@cindex backslash in character constant
mark followed by a backslash and the octal character code (up to three
octal digits); thus, @samp{?\101} for the character @kbd{A},
@samp{?\001} for the character @kbd{C-a}, and @code{?\002} for the
-character @kbd{C-b}. Although this syntax can represent any @sc{ASCII}
+character @kbd{C-b}. Although this syntax can represent any @acronym{ASCII}
character, it is preferred only when the precise octal value is more
-important than the @sc{ASCII} representation.
+important than the @acronym{ASCII} representation.
@example
@group
and the hexadecimal character code. You can use any number of hex
digits, so you can represent any character code in this way.
Thus, @samp{?\x41} for the character @kbd{A}, @samp{?\x1} for the
-character @kbd{C-a}, and @code{?\x8e0} for the character
+character @kbd{C-a}, and @code{?\x8e0} for the Latin-1 character
@iftex
@samp{@`a}.
@end iftex
-@ifinfo
+@ifnottex
@samp{a} with grave accent.
-@end ifinfo
+@end ifnottex
A backslash is allowed, and harmless, preceding any character without
a special escape meaning; thus, @samp{?\+} is equivalent to @samp{?+}.
There is no reason to add a backslash before most characters. However,
you should add a backslash before any of the characters
@samp{()\|;'`"#.,} to avoid confusing the Emacs commands for editing
-Lisp code. Also add a backslash before whitespace characters such as
+Lisp code. You can also add a backslash before whitespace characters such as
space, tab, newline and formfeed. However, it is cleaner to use one of
-the easily readable escape sequences, such as @samp{\t}, instead of an
-actual whitespace character such as a tab.
+the easily readable escape sequences, such as @samp{\t} or @samp{\s},
+instead of an actual whitespace character such as a tab or a space.
+(If you do write backslash followed by a space, you should write
+an extra space after the character constant to separate it from the
+following text.)
@node Symbol Type
@subsection Symbol Type
intended. But you can use one symbol in all of these ways,
independently.
+ A symbol whose name starts with a colon (@samp{:}) is called a
+@dfn{keyword symbol}. These symbols automatically act as constants, and
+are normally used only by comparing an unknown symbol with a few
+specific alternatives.
+
@cindex @samp{\} in symbols
@cindex backslash in symbols
A symbol name can contain any characters whatever. Most symbol names
@samp{-+=*/}. Such names require no special punctuation; the characters
of the name suffice as long as the name does not look like a number.
(If it does, write a @samp{\} at the beginning of the name to force
-interpretation as a symbol.) The characters @samp{_~!@@$%^&:<>@{@}} are
+interpretation as a symbol.) The characters @samp{_~!@@$%^&:<>@{@}?} are
less often used but also require no special punctuation. Any other
characters may be included in a symbol's name by escaping them with a
backslash. In contrast to its use in strings, however, a backslash in
Here are several examples of symbol names. Note that the @samp{+} in
the fifth example is escaped to prevent it from being read as a number.
-This is not necessary in the sixth example because the rest of the name
+This is not necessary in the seventh example because the rest of the name
makes it invalid as a number.
@example
@end group
@end example
+@ifinfo
+@c This uses ``colon'' instead of a literal `:' because Info cannot
+@c cope with a `:' in a menu
+@cindex @samp{#@var{colon}} read syntax
+@end ifinfo
+@ifnotinfo
+@cindex @samp{#:} read syntax
+@end ifnotinfo
+ Normally the Lisp reader interns all symbols (@pxref{Creating
+Symbols}). To prevent interning, you can write @samp{#:} before the
+name of the symbol.
+
@node Sequence Type
@subsection Sequence Types
Arrays are further subdivided into strings, vectors, char-tables and
bool-vectors. Vectors can hold elements of any type, but string
elements must be characters, and bool-vector elements must be @code{t}
-or @code{nil}. The characters in a string can have text properties like
-characters in a buffer (@pxref{Text Properties}); vectors and
-bool-vectors do not support text properties even when their elements
-happen to be characters. Char-tables are like vectors except that they
-are indexed by any valid character code.
+or @code{nil}. Char-tables are like vectors except that they are
+indexed by any valid character code. The characters in a string can
+have text properties like characters in a buffer (@pxref{Text
+Properties}), but vectors do not support text properties, even when
+their elements happen to be characters.
Lists, strings and the other array types are different, but they have
important similarities. For example, all have a length @var{l}, and all
A @dfn{cons cell} is an object that consists of two slots, called the
@sc{car} slot and the @sc{cdr} slot. Each slot can @dfn{hold} or
-@dfn{refer to} any Lisp object. We also say that the ``the @sc{car} of
+@dfn{refer to} any Lisp object. We also say that ``the @sc{car} of
this cons cell is'' whatever object its @sc{car} slot currently holds,
and likewise for the @sc{cdr}.
@code{(@var{a} .@: @var{b})} stands for a cons cell whose @sc{car} is
the object @var{a}, and whose @sc{cdr} is the object @var{b}. Dotted
pair notation is therefore more general than list syntax. In the dotted
-pair notation, the list @samp{(1 2 3)} is written as @samp{(1 . (2 . (3
+pair notation, the list @samp{(1 2 3)} is written as @samp{(1 . (2 . (3
. nil)))}. For @code{nil}-terminated lists, you can use either
notation, but list notation is usually clearer and more convenient.
When printing a list, the dotted pair notation is only used if the
Similarly, the three-element list @code{(rose violet buttercup)}
is equivalent to @code{(rose . (violet . (buttercup)))}.
-@ifinfo
+@ifnottex
It looks like this:
@example
--> rose --> violet --> buttercup
@end group
@end example
-@end ifinfo
+@end ifnottex
@node Association List Type
@comment node-name, next, previous, up
@example
(setq alist-of-colors
- '((rose . red) (lily . white) (buttercup . yellow)))
+ '((rose . red) (lily . white) (buttercup . yellow)))
@end example
@noindent
first element, @code{rose} is the key and @code{red} is the value.
@xref{Association Lists}, for a further explanation of alists and for
-functions that work on alists.
+functions that work on alists. @xref{Hash Tables}, for another kind of
+lookup table, which is much faster for handling a large number of keys.
@node Array Type
@subsection Array Type
in documentation strings,
but the newline is \
ignored if escaped."
- @result{} "It is useful to include newlines
-in documentation strings,
+ @result{} "It is useful to include newlines
+in documentation strings,
but the newline is ignored if escaped."
@end example
@node Non-ASCII in Strings
-@subsubsection Non-ASCII Characters in Strings
+@subsubsection Non-@acronym{ASCII} Characters in Strings
- You can include a non-@sc{ASCII} international character in a string
+ You can include a non-@acronym{ASCII} international character in a string
constant by writing it literally. There are two text representations
-for non-@sc{ASCII} characters in Emacs strings (and in buffers): unibyte
+for non-@acronym{ASCII} characters in Emacs strings (and in buffers): unibyte
and multibyte. If the string constant is read from a multibyte source,
such as a multibyte buffer or string, or a file that would be visited as
multibyte, then the character is read as a multibyte character, and that
unibyte source, then the character is read as unibyte and that makes the
string unibyte.
- You can also represent a multibyte non-@sc{ASCII} character with its
-character code, using a hex escape, @samp{\x@var{nnnnnnn}}, with as many
-digits as necessary. (Multibyte non-@sc{ASCII} character codes are all
+ You can also represent a multibyte non-@acronym{ASCII} character with its
+character code: use a hex escape, @samp{\x@var{nnnnnnn}}, with as many
+digits as necessary. (Multibyte non-@acronym{ASCII} character codes are all
greater than 256.) Any character which is not a valid hex digit
terminates this construct. If the next character in the string could be
interpreted as a hex digit, write @w{@samp{\ }} (backslash and space) to
constant is just like backslash-newline; it does not contribute any
character to the string, but it does terminate the preceding hex escape.
- Using a multibyte hex escape forces the string to multibyte. You can
-represent a unibyte non-@sc{ASCII} character with its character code,
-which must be in the range from 128 (0200 octal) to 255 (0377 octal).
-This forces a unibyte string.
-
+ You can represent a unibyte non-@acronym{ASCII} character with its
+character code, which must be in the range from 128 (0200 octal) to
+255 (0377 octal). If you write all such character codes in octal and
+the string contains no other characters forcing it to be multibyte,
+this produces a unibyte string. However, using any hex escape in a
+string (even for an @acronym{ASCII} character) forces the string to be
+multibyte.
+
@xref{Text Representations}, for more information about the two
text representations.
However, not all of the characters you can write with backslash
escape-sequences are valid in strings. The only control characters that
-a string can hold are the @sc{ASCII} control characters. Strings do not
-distinguish case in @sc{ASCII} control characters.
+a string can hold are the @acronym{ASCII} control characters. Strings do not
+distinguish case in @acronym{ASCII} control characters.
Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
-that provides a way to represent meta versions of @sc{ASCII} characters in a
-string. If you use the @samp{\M-} syntax to indicate a meta character
-in a string constant, this sets the
+that provides a way to represent meta versions of @acronym{ASCII}
+characters in a string. If you use the @samp{\M-} syntax to indicate
+a meta character in a string constant, this sets the
@tex
-$2^{7}$
+@math{2^{7}}
@end tex
-@ifinfo
+@ifnottex
2**7
-@end ifinfo
+@end ifnottex
bit of the character in the string. If the string is used in
@code{define-key} or @code{lookup-key}, this numeric code is translated
into the equivalent meta character. @xref{Character Type}.
Character category tables (@pxref{Categories}).
@item
-Display Tables (@pxref{Display Tables}).
+Display tables (@pxref{Display Tables}).
@item
Syntax tables (@pxref{Syntax Tables}).
A @dfn{bool-vector} is a one-dimensional array of elements that
must be @code{t} or @code{nil}.
- The printed representation of a Bool-vector is like a string, except
+ The printed representation of a bool-vector is like a string, except
that it begins with @samp{#&} followed by the length. The string
constant that follows actually specifies the contents of the bool-vector
as a bitmap---each ``character'' in the string contains 8 bits, which
specify the next 8 elements of the bool-vector (1 stands for @code{t},
-and 0 for @code{nil}). The least significant bits of the character
-correspond to the lowest indices in the bool-vector. If the length is not a
-multiple of 8, the printed representation shows extra elements, but
-these extras really make no difference.
+and 0 for @code{nil}). The least significant bits of the character
+correspond to the lowest indices in the bool-vector.
@example
(make-bool-vector 3 t)
- @result{} #&3"\007"
+ @result{} #&3"^G"
(make-bool-vector 3 nil)
- @result{} #&3"\0"
-;; @r{These are equal since only the first 3 bits are used.}
+ @result{} #&3"^@@"
+@end example
+
+@noindent
+These results make sense, because the binary code for @samp{C-g} is
+111 and @samp{C-@@} is the character with code 0.
+
+ If the length is not a multiple of 8, the printed representation
+shows extra elements, but these extras really make no difference. For
+instance, in the next example, the two bool-vectors are equal, because
+only the first 3 bits are used:
+
+@example
(equal #&3"\377" #&3"\007")
@result{} t
@end example
+@node Hash Table Type
+@subsection Hash Table Type
+
+ A hash table is a very fast kind of lookup table, somewhat like an
+alist in that it maps keys to corresponding values, but much faster.
+Hash tables are a new feature in Emacs 21; they have no read syntax, and
+print using hash notation. @xref{Hash Tables}.
+
+@example
+(make-hash-table)
+ @result{} #<hash-table 'eql nil 0/65 0x83af980>
+@end example
+
@node Function Type
@subsection Function Type
@subsection Autoload Type
An @dfn{autoload object} is a list whose first element is the symbol
-@code{autoload}. It is stored as the function definition of a symbol as
-a placeholder for the real definition; it says that the real definition
-is found in a file of Lisp code that should be loaded when necessary.
-The autoload object contains the name of the file, plus some other
-information about the real definition.
+@code{autoload}. It is stored as the function definition of a symbol,
+where it serves as a placeholder for the real definition. The autoload
+object says that the real definition is found in a file of Lisp code
+that should be loaded when necessary. It contains the name of the file,
+plus some other information about the real definition.
After the file has been loaded, the symbol should have a new function
definition that is not an autoload object. The new definition is then
The contents of a buffer are much like a string, but buffers are not
used like strings in Emacs Lisp, and the available operations are
different. For example, you can insert text efficiently into an
-existing buffer, whereas ``inserting'' text into a string requires
-concatenating substrings, and the result is an entirely new string
-object.
+existing buffer, altering the buffer's contents, whereas ``inserting''
+text into a string requires concatenating substrings, and the result is
+an entirely new string object.
Each buffer has a designated position called @dfn{point}
(@pxref{Positions}). At any time, one buffer is the @dfn{current
@xref{Overlays}, for how to create and use overlays.
+@node Circular Objects
+@section Read Syntax for Circular Objects
+@cindex circular structure, read syntax
+@cindex shared structure, read syntax
+@cindex @samp{#@var{n}=} read syntax
+@cindex @samp{#@var{n}#} read syntax
+
+ In Emacs 21, to represent shared or circular structures within a
+complex of Lisp objects, you can use the reader constructs
+@samp{#@var{n}=} and @samp{#@var{n}#}.
+
+ Use @code{#@var{n}=} before an object to label it for later reference;
+subsequently, you can use @code{#@var{n}#} to refer the same object in
+another place. Here, @var{n} is some integer. For example, here is how
+to make a list in which the first element recurs as the third element:
+
+@example
+(#1=(a) b #1#)
+@end example
+
+@noindent
+This differs from ordinary syntax such as this
+
+@example
+((a) b (a))
+@end example
+
+@noindent
+which would result in a list whose first and third elements
+look alike but are not the same Lisp object. This shows the difference:
+
+@example
+(prog1 nil
+ (setq x '(#1=(a) b #1#)))
+(eq (nth 0 x) (nth 2 x))
+ @result{} t
+(setq x '((a) b (a)))
+(eq (nth 0 x) (nth 2 x))
+ @result{} nil
+@end example
+
+ You can also use the same syntax to make a circular structure, which
+appears as an ``element'' within itself. Here is an example:
+
+@example
+#1=(a #1#)
+@end example
+
+@noindent
+This makes a list whose second element is the list itself.
+Here's how you can see that it really works:
+
+@example
+(prog1 nil
+ (setq x '#1=(a #1#)))
+(eq x (cadr x))
+ @result{} t
+@end example
+
+ The Lisp printer can produce this syntax to record circular and shared
+structure in a Lisp object, if you bind the variable @code{print-circle}
+to a non-@code{nil} value. @xref{Output Variables}.
+
@node Type Predicates
@section Type Predicates
@cindex predicates
@item keymapp
@xref{Creating Keymaps, keymapp}.
+@item keywordp
+@xref{Constant Variables}.
+
@item listp
@xref{List-related Predicates, listp}.
This function returns a symbol naming the primitive type of
@var{object}. The value is one of the symbols @code{symbol},
@code{integer}, @code{float}, @code{string}, @code{cons}, @code{vector},
-@code{char-table}, @code{bool-vector}, @code{subr},
+@code{char-table}, @code{bool-vector}, @code{hash-table}, @code{subr},
@code{compiled-function}, @code{marker}, @code{overlay}, @code{window},
@code{buffer}, @code{frame}, @code{process}, or
@code{window-configuration}.
This function returns @code{t} if @var{object1} and @var{object2} have
equal components, @code{nil} otherwise. Whereas @code{eq} tests if its
arguments are the same object, @code{equal} looks inside nonidentical
-arguments to see if their elements are the same. So, if two objects are
-@code{eq}, they are @code{equal}, but the converse is not always true.
+arguments to see if their elements or contents are the same. So, if two
+objects are @code{eq}, they are @code{equal}, but the converse is not
+always true.
@example
@group
@end example
Comparison of strings is case-sensitive, but does not take account of
-text properties---it compares only the characters in the strings.
-A unibyte string never equals a multibyte string unless the
-contents are entirely @sc{ASCII} (@pxref{Text Representations}).
+text properties---it compares only the characters in the strings. For
+technical reasons, a unibyte string and a multibyte string are
+@code{equal} if and only if they contain the same sequence of
+character codes and all these codes are either in the range 0 through
+127 (@acronym{ASCII}) or 160 through 255 (@code{eight-bit-graphic}).
+(@pxref{Text Representations}).
@example
@group
@end group
@end example
-Two distinct buffers are never @code{equal}, even if their contents
-are the same.
+However, two distinct buffers are never considered @code{equal}, even if
+their textual contents are the same.
@end defun
- The test for equality is implemented recursively, and circular lists may
-therefore cause infinite recursion (leading to an error).
+ The test for equality is implemented recursively; for example, given
+two cons cells @var{x} and @var{y}, @code{(equal @var{x} @var{y})}
+returns @code{t} if and only if both the expressions below return
+@code{t}:
+
+@example
+(equal (car @var{x}) (car @var{y}))
+(equal (cdr @var{x}) (cdr @var{y}))
+@end example
+
+Because of this recursive method, circular lists may therefore cause
+infinite recursion (leading to an error).
+
+@ignore
+ arch-tag: 9711a66e-4749-4265-9e8c-972d55b67096
+@end ignore
HCoop / bpt / emacs.git / blobdiff