[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Emacs-diffs] Changes to objects.texi
|
From: |
Glenn Morris |
|
Subject: |
[Emacs-diffs] Changes to objects.texi |
|
Date: |
Thu, 06 Sep 2007 04:13:37 +0000 |
CVSROOT: /sources/emacs
Module name: emacs
Changes by: Glenn Morris <gm> 07/09/06 04:13:36
Index: objects.texi
===================================================================
RCS file: objects.texi
diff -N objects.texi
--- objects.texi 7 Apr 2007 01:53:53 -0000 1.63
+++ /dev/null 1 Jan 1970 00:00:00 -0000
@@ -1,2036 +0,0 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999,
2001,
address@hidden 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation,
Inc.
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/objects
address@hidden Lisp Data Types, Numbers, Introduction, Top
address@hidden Lisp Data Types
address@hidden object
address@hidden Lisp object
address@hidden type
address@hidden data type
-
- A Lisp @dfn{object} is a piece of data used and manipulated by Lisp
-programs. For our purposes, a @dfn{type} or @dfn{data type} is a set of
-possible objects.
-
- Every object belongs to at least one type. Objects of the same type
-have similar structures and may usually be used in the same contexts.
-Types can overlap, and objects can belong to two or more types.
-Consequently, we can ask whether an object belongs to a particular type,
-but not for ``the'' type of an object.
-
address@hidden 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},
address@hidden, @dfn{vector}, @dfn{hash-table}, @dfn{subr}, and
address@hidden function}, plus several special types, such as
address@hidden, 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.
-
- Note that Lisp is unlike many other languages in that Lisp objects are
address@hidden: the primitive type of the object is implicit in the
-object itself. For example, if an object is a vector, nothing can treat
-it as a number; Lisp knows it is a vector, not a number.
-
- In most languages, the programmer must declare the data type of each
-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. (Actually, a small number of Emacs
-Lisp variables can only take on values of a certain type.
address@hidden 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
-to use these types can be found in later chapters.
-
address@hidden
-* Printed Representation:: How Lisp objects are represented as text.
-* 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.
address@hidden menu
-
address@hidden Printed Representation
address@hidden node-name, next, previous, up
address@hidden Printed Representation and Read Syntax
address@hidden printed representation
address@hidden read syntax
-
- The @dfn{printed representation} of an object is the format of the
-output generated by the Lisp printer (the function @code{prin1}) for
-that object. Every data type has a unique printed representation.
-The @dfn{read syntax} of an object is the format of the input accepted
-by the Lisp reader (the function @code{read}) for that object. This
-is not necessarily unique; many kinds of object have more than one
-syntax. @xref{Read and Print}.
-
address@hidden hash notation
- In most cases, an object's printed representation is also a read
-syntax for the object. However, some types have no read syntax, since
-it does not make sense to enter objects of these types as constants in
-a Lisp program. These objects are printed in @dfn{hash notation},
-which consists of the characters @samp{#<}, a descriptive string
-(typically the type name followed by the name of the object), and a
-closing @samp{>}. For example:
-
address@hidden
-(current-buffer)
- @result{} #<buffer objects.texi>
address@hidden example
-
address@hidden
-Hash notation cannot be read at all, so the Lisp reader signals the
-error @code{invalid-read-syntax} whenever it encounters @samp{#<}.
address@hidden invalid-read-syntax
-
- In other languages, an expression is text; it has no other form. In
-Lisp, an expression is primarily a Lisp object and only secondarily the
-text that is the object's read syntax. Often there is no need to
-emphasize this distinction, but you must keep it in the back of your
-mind, or you will occasionally be very confused.
-
- When you evaluate an expression interactively, the Lisp interpreter
-first reads the textual representation of it, producing a Lisp object,
-and then evaluates that object (@pxref{Evaluation}). However,
-evaluation and reading are separate activities. Reading returns the
-Lisp object represented by the text that is read; the object may or may
-not be evaluated later. @xref{Input Functions}, for a description of
address@hidden, the basic function for reading objects.
-
address@hidden Comments
address@hidden node-name, next, previous, up
address@hidden Comments
address@hidden comments
address@hidden @samp{;} in comment
-
- A @dfn{comment} is text that is written in a program only for the sake
-of humans that read the program, and that has no effect on the meaning
-of the program. In Lisp, a semicolon (@samp{;}) starts a comment if it
-is not within a string or character constant. The comment continues to
-the end of line. The Lisp reader discards comments; they do not become
-part of the Lisp objects which represent the program within the Lisp
-system.
-
- The @samp{#@@@var{count}} construct, which skips the next @var{count}
-characters, is useful for program-generated comments containing binary
-data. The Emacs Lisp byte compiler uses this in its output files
-(@pxref{Byte Compilation}). It isn't meant for source files, however.
-
- @xref{Comment Tips}, for conventions for formatting comments.
-
address@hidden Programming Types
address@hidden Programming Types
address@hidden programming types
-
- There are two general categories of types in Emacs Lisp: those having
-to do with Lisp programming, and those having to do with editing. The
-former exist in many Lisp implementations, in one form or another. The
-latter are unique to Emacs Lisp.
-
address@hidden
-* Integer Type:: Numbers without fractional parts.
-* Floating Point Type:: Numbers with fractional parts and with a large range.
-* Character Type:: The representation of letters, numbers and
- control characters.
-* Symbol Type:: A multi-use object that refers to a function,
- variable, or property list, and has a unique identity.
-* Sequence Type:: Both lists and arrays are classified as sequences.
-* Cons Cell Type:: Cons cells, and lists (which are made from cons cells).
-* Array Type:: Arrays include strings and vectors.
-* String Type:: An (efficient) array of characters.
-* 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.
-* Primitive Function Type:: A function written in C, callable from Lisp.
-* Byte-Code Type:: A function written in Lisp, then compiled.
-* Autoload Type:: A type used for automatically loading seldom-used
- functions.
address@hidden menu
-
address@hidden Integer Type
address@hidden Integer Type
-
- The range of values for integers in Emacs Lisp is @minus{}268435456 to
-268435455 (29 bits; i.e.,
address@hidden
--2**28
address@hidden ifnottex
address@hidden
address@hidden
address@hidden tex
-to
address@hidden
-2**28 - 1)
address@hidden ifnottex
address@hidden
address@hidden)
address@hidden 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+ 268435455)} is @minus{}268435456 on most
-machines.
-
- The read syntax for integers is a sequence of (base ten) digits with an
-optional sign at the beginning and an optional period at the end. The
-printed representation produced by the Lisp interpreter never has a
-leading @samp{+} or a final @samp{.}.
-
address@hidden
address@hidden
--1 ; @r{The integer -1.}
-1 ; @r{The integer 1.}
-1. ; @r{Also the integer 1.}
-+1 ; @r{Also the integer 1.}
-536870913 ; @r{Also the integer 1 on a 29-bit implementation.}
address@hidden group
address@hidden example
-
- @xref{Numbers}, for more information.
-
address@hidden Floating Point Type
address@hidden Floating Point Type
-
- Floating point numbers are the computer equivalent of scientific
-notation; you can think of a floating point number as a fraction
-together with a power of ten. The precise number of significant
-figures and the range of possible exponents is machine-specific; Emacs
-uses the C data type @code{double} to store the value, and internally
-this records a power of 2 rather than a power of 10.
-
- The printed representation for floating point numbers requires either
-a decimal point (with at least one digit following), an exponent, or
-both. For example, @samp{1500.0}, @samp{15e2}, @samp{15.0e2},
address@hidden, and @samp{.15e4} are five ways of writing a floating point
-number whose value is 1500. They are all equivalent.
-
- @xref{Numbers}, for more information.
-
address@hidden Character Type
address@hidden Character Type
address@hidden @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
-example, the character @kbd{A} is represented as the @w{integer 65}.
-
- Individual characters are used occasionally in programs, but it is
-more 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
address@hidden codes; the rest are address@hidden
-(@pxref{Non-ASCII Characters}). Characters that represent keyboard
-input have a much wider range, to encode modifier keys such as
-Control, Meta and Shift.
-
- There are special functions for producing a human-readable textual
-description of a character for the sake of messages. @xref{Describing
-Characters}.
-
address@hidden
-* Basic Char Syntax::
-* General Escape Syntax::
-* Ctl-Char Syntax::
-* Meta-Char Syntax::
-* Other Char Bits::
address@hidden menu
-
address@hidden Basic Char Syntax
address@hidden Basic Char Syntax
address@hidden read syntax for characters
address@hidden printed representation for characters
address@hidden syntax for characters
address@hidden @samp{?} in character constant
address@hidden question mark in character constant
-
- Since characters are really integers, the printed representation of
-a character is a decimal number. This is also a possible read syntax
-for a character, but writing characters that way in Lisp programs is
-not clear programming. You should @emph{always} use the special read
-syntax formats that Emacs Lisp provides for characters. These syntax
-formats start with a question mark.
-
- The usual read syntax for alphanumeric characters is a question mark
-followed by the character; thus, @samp{?A} for the character
address@hidden, @samp{?B} for the character @kbd{B}, and @samp{?a} for the
-character @kbd{a}.
-
- For example:
-
address@hidden
-?Q @result{} 81 ?q @result{} 113
address@hidden 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 open-paren character. If the character is @samp{\},
-you @emph{must} use a second @samp{\} to quote it: @samp{?\\}.
-
address@hidden whitespace
address@hidden bell character
address@hidden @samp{\a}
address@hidden backspace
address@hidden @samp{\b}
address@hidden tab (ASCII character)
address@hidden @samp{\t}
address@hidden vertical tab
address@hidden @samp{\v}
address@hidden formfeed
address@hidden @samp{\f}
address@hidden newline
address@hidden @samp{\n}
address@hidden return (ASCII character)
address@hidden @samp{\r}
address@hidden escape (ASCII character)
address@hidden @samp{\e}
address@hidden space (ASCII character)
address@hidden @samp{\s}
- You can express the characters control-g, backspace, tab, newline,
-vertical tab, formfeed, space, return, del, and escape as @samp{?\a},
address@hidden, @samp{?\t}, @samp{?\n}, @samp{?\v}, @samp{?\f},
address@hidden, @samp{?\r}, @samp{?\d}, and @samp{?\e}, respectively.
-(@samp{?\s} followed by a dash has a different meaning---it applies
-the ``super'' modifier to the following character.) Thus,
-
address@hidden
-?\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}}
-?\v @result{} 11 ; @r{vertical tab, @kbd{C-k}}
-?\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}}
address@hidden example
-
address@hidden escape sequence
- These sequences which start with backslash are also known as
address@hidden 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 in character
-constants; in string constants, just write the space.
-
- 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
address@hidden()\|;'`"#.,} to avoid confusing the Emacs commands for editing
-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} 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.)
-
address@hidden General Escape Syntax
address@hidden General Escape Syntax
-
- In addition to the specific excape sequences for special important
-control characters, Emacs provides general categories of escape syntax
-that you can use to specify non-ASCII text characters.
-
address@hidden unicode character escape
- For instance, you can specify characters by their Unicode values.
address@hidden@var{nnnn}} represents a character that maps to the Unicode
-code point @address@hidden There is a slightly different syntax
-for specifying characters with code points above @code{#xFFFF};
address@hidden@var{nnnnnn}} represents the character whose Unicode code
-point is @address@hidden, if such a character is supported by
-Emacs. If the corresponding character is not supported, Emacs signals
-an error.
-
- This peculiar and inconvenient syntax was adopted for compatibility
-with other programming languages. Unlike some other languages, Emacs
-Lisp supports this syntax in only character literals and strings.
-
address@hidden @samp{\} in character constant
address@hidden backslash in character constant
address@hidden octal character code
- The most general read syntax for a character represents the
-character code in either octal or hex. To use octal, write a question
-mark followed by a backslash and the octal character code (up to three
-octal digits); thus, @samp{?\101} for the character @kbd{A},
address@hidden for the character @kbd{C-a}, and @code{?\002} for the
-character @kbd{C-b}. Although this syntax can represent any
address@hidden character, it is preferred only when the precise octal
-value is more important than the @acronym{ASCII} representation.
-
address@hidden
address@hidden
-?\012 @result{} 10 ?\n @result{} 10 ?\C-j @result{} 10
-?\101 @result{} 65 ?A @result{} 65
address@hidden group
address@hidden example
-
- To use hex, write a question mark followed by a backslash, @samp{x},
-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 Latin-1 character
address@hidden
address@hidden@`a}.
address@hidden iftex
address@hidden
address@hidden with grave accent.
address@hidden ifnottex
-
address@hidden Ctl-Char Syntax
address@hidden Control-Character Syntax
-
address@hidden control characters
- Control characters can be represented using yet another read syntax.
-This consists of a question mark followed by a backslash, caret, and the
-corresponding non-control character, in either upper or lower case. For
-example, both @samp{?\^I} and @samp{?\^i} are valid read syntax for the
-character @kbd{C-i}, the character whose value is 9.
-
- Instead of the @samp{^}, you can use @samp{C-}; thus, @samp{?\C-i} is
-equivalent to @samp{?\^I} and to @samp{?\^i}:
-
address@hidden
-?\^I @result{} 9 ?\C-I @result{} 9
address@hidden example
-
- In strings and buffers, the only control characters allowed are those
-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 address@hidden control characters include the
address@hidden
address@hidden
address@hidden tex
address@hidden
-2**26
address@hidden ifnottex
-bit as well as the code for the corresponding non-control
-character. Ordinary terminals have no way of generating address@hidden
-control characters, but you can generate them straightforwardly using X
-and other window systems.
-
- For historical reasons, Emacs treats the @key{DEL} character as
-the control equivalent of @kbd{?}:
-
address@hidden
-?\^? @result{} 127 ?\C-? @result{} 127
address@hidden example
-
address@hidden
-As a result, it is currently not possible to represent the character
address@hidden, which is a meaningful input character under X, using
address@hidden It is not easy to change this, as various Lisp files refer
-to @key{DEL} in this way.
-
- For representing control characters to be found in files or strings,
-we recommend the @samp{^} syntax; for control characters in keyboard
-input, we prefer the @samp{C-} syntax. Which one you use does not
-affect the meaning of the program, but may guide the understanding of
-people who read it.
-
address@hidden Meta-Char Syntax
address@hidden Meta-Character Syntax
-
address@hidden meta characters
- A @dfn{meta character} is a character typed with the @key{META}
-modifier key. The integer that represents such a character has the
address@hidden
address@hidden
address@hidden tex
address@hidden
-2**27
address@hidden 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
address@hidden
address@hidden
address@hidden tex
address@hidden
-2**7
address@hidden 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,
address@hidden stands for @kbd{M-A}. You can use @samp{\M-} together with
-octal character codes (see below), with @samp{\C-}, or with any other
-syntax for a character. Thus, you can write @kbd{M-A} as @samp{?\M-A},
-or as @samp{?\M-\101}. Likewise, you can write @kbd{C-M-b} as
address@hidden, @samp{?\C-\M-b}, or @samp{?\M-\002}.
-
address@hidden Other Char Bits
address@hidden Other Character Modifier Bits
-
- The case of a graphic character is indicated by its character code;
-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
address@hidden
address@hidden
address@hidden tex
address@hidden
-2**25
address@hidden 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}
-represents the shifted-control-o character.
-
address@hidden hyper characters
address@hidden super characters
address@hidden alt characters
- The X Window System defines three other
address@hidden 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
address@hidden (Note that @samp{\s} with no following @samp{-}
-represents the space character.)
address@hidden
-Numerically, the bit values are @math{2^{22}} for alt, @math{2^{23}}
-for super and @math{2^{24}} for hyper.
address@hidden tex
address@hidden
-Numerically, the
-bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper.
address@hidden ifnottex
-
address@hidden Symbol Type
address@hidden Symbol Type
-
- A @dfn{symbol} in GNU Emacs Lisp is an object with a name. The
-symbol name serves as the printed representation of the symbol. In
-ordinary Lisp use, with one single obarray (@pxref{Creating Symbols},
-a symbol's name is unique---no two symbols have the same name.
-
- A symbol can serve as a variable, as a function name, or to hold a
-property list. Or it may serve only to be distinct from all other Lisp
-objects, so that its presence in a data structure may be recognized
-reliably. In a given context, usually only one of these uses is
-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
address@hidden symbol}. These symbols automatically act as constants, and
-are normally used only by comparing an unknown symbol with a few
-specific alternatives.
-
address@hidden @samp{\} in symbols
address@hidden backslash in symbols
- A symbol name can contain any characters whatever. Most symbol names
-are written with letters, digits, and the punctuation characters
address@hidden/}. 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{_~!@@$%^&:<>@address@hidden
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
-the name of a symbol simply quotes the single character that follows the
-backslash. For example, in a string, @samp{\t} represents a tab
-character; in the name of a symbol, however, @samp{\t} merely quotes the
-letter @samp{t}. To have a symbol with a tab character in its name, you
-must actually use a tab (preceded with a backslash). But it's rare to
-do such a thing.
-
address@hidden CL note---case of letters
address@hidden
address@hidden Lisp note:} In Common Lisp, lower case letters are always
-``folded'' to upper case, unless they are explicitly escaped. In Emacs
-Lisp, upper case and lower case letters are distinct.
address@hidden quotation
-
- 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 fourth example because the rest of the name
-makes it invalid as a number.
-
address@hidden
address@hidden
-foo ; @r{A symbol named @samp{foo}.}
-FOO ; @r{A symbol named @samp{FOO}, different from @samp{foo}.}
-char-to-string ; @r{A symbol named @samp{char-to-string}.}
address@hidden group
address@hidden
-1+ ; @r{A symbol named @samp{1+}}
- ; @r{(not @samp{+1}, which is an integer).}
address@hidden group
address@hidden
-\+1 ; @r{A symbol named @samp{+1}}
- ; @r{(not a very readable name).}
address@hidden group
address@hidden
-\(*\ 1\ 2\) ; @r{A symbol named @samp{(* 1 2)} (a worse name).}
address@hidden the @'s in this next line use up three characters, hence the
address@hidden apparent misalignment of the comment.
-+-*/_~!@@$%^&=:<>@address@hidden ; @r{A symbol named
@samp{+-*/_~!@@$%^&=:<>@address@hidden
- ; @r{These characters need not be escaped.}
address@hidden group
address@hidden example
-
address@hidden
address@hidden This uses ``colon'' instead of a literal `:' because Info cannot
address@hidden cope with a `:' in a menu
address@hidden @address@hidden read syntax
address@hidden ifinfo
address@hidden
address@hidden @samp{#:} read syntax
address@hidden ifnotinfo
- Normally the Lisp reader interns all symbols (@pxref{Creating
-Symbols}). To prevent interning, you can write @samp{#:} before the
-name of the symbol.
-
address@hidden Sequence Type
address@hidden Sequence Types
-
- A @dfn{sequence} is a Lisp object that represents an ordered set of
-elements. There are two kinds of sequence in Emacs Lisp, lists and
-arrays. Thus, an object of type list or of type array is also
-considered a sequence.
-
- 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}. 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
-have elements which can be indexed from zero to @var{l} minus one.
-Several functions, called sequence functions, accept any kind of
-sequence. For example, the function @code{elt} can be used to extract
-an element of a sequence, given its index. @xref{Sequences Arrays
-Vectors}.
-
- It is generally impossible to read the same sequence twice, since
-sequences are always created anew upon reading. If you read the read
-syntax for a sequence twice, you get two sequences with equal contents.
-There is one exception: the empty list @code{()} always stands for the
-same object, @code{nil}.
-
address@hidden Cons Cell Type
address@hidden Cons Cell and List Types
address@hidden address field of register
address@hidden decrement field of register
address@hidden pointers
-
- A @dfn{cons cell} is an object that consists of two slots, called the
address@hidden slot and the @sc{cdr} slot. Each slot can @dfn{hold} or
address@hidden 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}.
-
address@hidden
-A note to C programmers: in Lisp, we do not distinguish between
-``holding'' a value and ``pointing to'' the value, because pointers in
-Lisp are implicit.
address@hidden quotation
-
- A @dfn{list} is a series of cons cells, linked together so that the
address@hidden slot of each cons cell holds either the next cons cell or the
-empty list. The empty list is actually the symbol @code{nil}.
address@hidden, for functions that work on lists. Because most cons
-cells are used as part of lists, the phrase @dfn{list structure} has
-come to refer to any structure made out of cons cells.
-
address@hidden atoms
- Because cons cells are so central to Lisp, we also have a word for
-``an object which is not a cons cell.'' These objects are called
address@hidden
-
address@hidden parenthesis
address@hidden @samp{(@dots{})} in lists
- The read syntax and printed representation for lists are identical, and
-consist of a left parenthesis, an arbitrary number of elements, and a
-right parenthesis. Here are examples of lists:
-
address@hidden
-(A 2 "A") ; @r{A list of three elements.}
-() ; @r{A list of no elements (the empty list).}
-nil ; @r{A list of no elements (the empty list).}
-("A ()") ; @r{A list of one element: the string @code{"A ()"}.}
-(A ()) ; @r{A list of two elements: @code{A} and the empty list.}
-(A nil) ; @r{Equivalent to the previous.}
-((A B C)) ; @r{A list of one element}
- ; @r{(which is a list of three elements).}
address@hidden example
-
- Upon reading, each object inside the parentheses becomes an element
-of the list. That is, a cons cell is made for each element. The
address@hidden slot of the cons cell holds the element, and its @sc{cdr}
-slot refers to the next cons cell of the list, which holds the next
-element in the list. The @sc{cdr} slot of the last cons cell is set to
-hold @code{nil}.
-
- The names @sc{car} and @sc{cdr} derive from the history of Lisp. The
-original Lisp implementation ran on an @w{IBM 704} computer which
-divided words into two parts, called the ``address'' part and the
-``decrement''; @sc{car} was an instruction to extract the contents of
-the address part of a register, and @sc{cdr} an instruction to extract
-the contents of the decrement. By contrast, ``cons cells'' are named
-for the function @code{cons} that creates them, which in turn was named
-for its purpose, the construction of cells.
-
address@hidden
-* Box Diagrams:: Drawing pictures of lists.
-* Dotted Pair Notation:: A general syntax for cons cells.
-* Association List Type:: A specially constructed list.
address@hidden menu
-
address@hidden Box Diagrams
address@hidden Drawing Lists as Box Diagrams
address@hidden box diagrams, for lists
address@hidden diagrams, boxed, for lists
-
- A list can be illustrated by a diagram in which the cons cells are
-shown as pairs of boxes, like dominoes. (The Lisp reader cannot read
-such an illustration; unlike the textual notation, which can be
-understood by both humans and computers, the box illustrations can be
-understood only by humans.) This picture represents the three-element
-list @code{(rose violet buttercup)}:
-
address@hidden
address@hidden
- --- --- --- --- --- ---
- | | |--> | | |--> | | |--> nil
- --- --- --- --- --- ---
- | | |
- | | |
- --> rose --> violet --> buttercup
address@hidden group
address@hidden example
-
- In this diagram, each box represents a slot that can hold or refer to
-any Lisp object. Each pair of boxes represents a cons cell. Each arrow
-represents a reference to a Lisp object, either an atom or another cons
-cell.
-
- In this example, the first box, which holds the @sc{car} of the first
-cons cell, refers to or ``holds'' @code{rose} (a symbol). The second
-box, holding the @sc{cdr} of the first cons cell, refers to the next
-pair of boxes, the second cons cell. The @sc{car} of the second cons
-cell is @code{violet}, and its @sc{cdr} is the third cons cell. The
address@hidden of the third (and last) cons cell is @code{nil}.
-
- Here is another diagram of the same list, @code{(rose violet
-buttercup)}, sketched in a different manner:
-
address@hidden
address@hidden
- --------------- ---------------- -------------------
-| car | cdr | | car | cdr | | car | cdr |
-| rose | o-------->| violet | o-------->| buttercup | nil |
-| | | | | | | | |
- --------------- ---------------- -------------------
address@hidden group
address@hidden smallexample
-
address@hidden @code{nil} as a list
address@hidden empty list
- A list with no elements in it is the @dfn{empty list}; it is identical
-to the symbol @code{nil}. In other words, @code{nil} is both a symbol
-and a list.
-
- Here is the list @code{(A ())}, or equivalently @code{(A nil)},
-depicted with boxes and arrows:
-
address@hidden
address@hidden
- --- --- --- ---
- | | |--> | | |--> nil
- --- --- --- ---
- | |
- | |
- --> A --> nil
address@hidden group
address@hidden example
-
- Here is a more complex illustration, showing the three-element list,
address@hidden((pine needles) oak maple)}, the first element of which is a
-two-element list:
-
address@hidden
address@hidden
- --- --- --- --- --- ---
- | | |--> | | |--> | | |--> nil
- --- --- --- --- --- ---
- | | |
- | | |
- | --> oak --> maple
- |
- | --- --- --- ---
- --> | | |--> | | |--> nil
- --- --- --- ---
- | |
- | |
- --> pine --> needles
address@hidden group
address@hidden example
-
- The same list represented in the second box notation looks like this:
-
address@hidden
address@hidden
- -------------- -------------- --------------
-| car | cdr | | car | cdr | | car | cdr |
-| o | o------->| oak | o------->| maple | nil |
-| | | | | | | | | |
- -- | --------- -------------- --------------
- |
- |
- | -------------- ----------------
- | | car | cdr | | car | cdr |
- ------>| pine | o------->| needles | nil |
- | | | | | |
- -------------- ----------------
address@hidden group
address@hidden example
-
address@hidden Dotted Pair Notation
address@hidden Dotted Pair Notation
address@hidden dotted pair notation
address@hidden @samp{.} in lists
-
- @dfn{Dotted pair notation} is a general syntax for cons cells that
-represents the @sc{car} and @sc{cdr} explicitly. In this syntax,
address@hidden(@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 more general than list syntax because the @sc{cdr}
-does not have to be a list. However, it is more cumbersome in cases
-where list syntax would work. In dotted pair notation, the list
address@hidden(1 2 3)} is written as @samp{(1 . (2 . (3 . nil)))}. For
address@hidden 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 @sc{cdr} of a cons
-cell is not a list.
-
- Here's an example using boxes to illustrate dotted pair notation.
-This example shows the pair @code{(rose . violet)}:
-
address@hidden
address@hidden
- --- ---
- | | |--> violet
- --- ---
- |
- |
- --> rose
address@hidden group
address@hidden example
-
- You can combine dotted pair notation with list notation to represent
-conveniently a chain of cons cells with a address@hidden final @sc{cdr}.
-You write a dot after the last element of the list, followed by the
address@hidden of the final cons cell. For example, @code{(rose violet
-. buttercup)} is equivalent to @code{(rose . (violet . buttercup))}.
-The object looks like this:
-
address@hidden
address@hidden
- --- --- --- ---
- | | |--> | | |--> buttercup
- --- --- --- ---
- | |
- | |
- --> rose --> violet
address@hidden group
address@hidden example
-
- The syntax @code{(rose .@: violet .@: buttercup)} is invalid because
-there is nothing that it could mean. If anything, it would say to put
address@hidden in the @sc{cdr} of a cons cell whose @sc{cdr} is already
-used for @code{violet}.
-
- The list @code{(rose violet)} is equivalent to @code{(rose . (violet))},
-and looks like this:
-
address@hidden
address@hidden
- --- --- --- ---
- | | |--> | | |--> nil
- --- --- --- ---
- | |
- | |
- --> rose --> violet
address@hidden group
address@hidden example
-
- Similarly, the three-element list @code{(rose violet buttercup)}
-is equivalent to @code{(rose . (violet . (buttercup)))}.
address@hidden
-It looks like this:
-
address@hidden
address@hidden
- --- --- --- --- --- ---
- | | |--> | | |--> | | |--> nil
- --- --- --- --- --- ---
- | | |
- | | |
- --> rose --> violet --> buttercup
address@hidden group
address@hidden example
address@hidden ifnottex
-
address@hidden Association List Type
address@hidden node-name, next, previous, up
address@hidden Association List Type
-
- An @dfn{association list} or @dfn{alist} is a specially-constructed
-list whose elements are cons cells. In each element, the @sc{car} is
-considered a @dfn{key}, and the @sc{cdr} is considered an
address@hidden value}. (In some cases, the associated value is stored
-in the @sc{car} of the @sc{cdr}.) Association lists are often used as
-stacks, since it is easy to add or remove associations at the front of
-the list.
-
- For example,
-
address@hidden
-(setq alist-of-colors
- '((rose . red) (lily . white) (buttercup . yellow)))
address@hidden example
-
address@hidden
-sets the variable @code{alist-of-colors} to an alist of three elements. In the
-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. @xref{Hash Tables}, for another kind of
-lookup table, which is much faster for handling a large number of keys.
-
address@hidden Array Type
address@hidden Array Type
-
- An @dfn{array} is composed of an arbitrary number of slots for
-holding or referring to other Lisp objects, arranged in a contiguous block of
-memory. Accessing any element of an array takes approximately the same
-amount of time. In contrast, accessing an element of a list requires
-time proportional to the position of the element in the list. (Elements
-at the end of a list take longer to access than elements at the
-beginning of a list.)
-
- Emacs defines four types of array: strings, vectors, bool-vectors, and
-char-tables.
-
- A string is an array of characters and a vector is an array of
-arbitrary objects. A bool-vector can hold only @code{t} or @code{nil}.
-These kinds of array may have any length up to the largest integer.
-Char-tables are sparse arrays indexed by any valid character code; they
-can hold arbitrary objects.
-
- 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}. The
-largest possible index value is one less than the length of the array.
-Once an array is created, its length is fixed.
-
- All Emacs Lisp arrays are one-dimensional. (Most other programming
-languages support multidimensional arrays, but they are not essential;
-you can get the same effect with nested one-dimensional arrays.) Each
-type of array has its own read syntax; see the following sections for
-details.
-
- The array type is a subset of the sequence type, and contains the
-string type, the vector type, the bool-vector type, and the char-table
-type.
-
address@hidden String Type
address@hidden String Type
-
- A @dfn{string} is an array of characters. Strings are used for many
-purposes in Emacs, as can be expected in a text editor; for example, as
-the names of Lisp symbols, as messages for the user, and to represent
-text extracted from buffers. Strings in Lisp are constants: evaluation
-of a string returns the same string.
-
- @xref{Strings and Characters}, for functions that operate on strings.
-
address@hidden
-* Syntax for Strings::
-* Non-ASCII in Strings::
-* Nonprinting Characters::
-* Text Props and Strings::
address@hidden menu
-
address@hidden Syntax for Strings
address@hidden Syntax for Strings
-
address@hidden @samp{"} in strings
address@hidden double-quote in strings
address@hidden @samp{\} in strings
address@hidden backslash in strings
- The read syntax for strings is a double-quote, an arbitrary number of
-characters, and another double-quote, @code{"like this"}. To include a
-double-quote in a string, precede it with a backslash; thus, @code{"\""}
-is a string containing just a single double-quote character. Likewise,
-you can include a backslash by preceding it with another backslash, like
-this: @code{"this \\ is a single embedded backslash"}.
-
address@hidden newline in strings
- The newline character is not special in the read syntax for strings;
-if you write a new line between the double-quotes, it becomes a
-character in the string. But an escaped newline---one that is preceded
-by @samp{\}---does not become part of the string; i.e., the Lisp reader
-ignores an escaped newline while reading a string. An escaped space
address@hidden@samp{\ }} is likewise ignored.
-
address@hidden
-"It is useful to include newlines
-in documentation strings,
-but the newline is \
-ignored if escaped."
- @result{} "It is useful to include newlines
-in documentation strings,
-but the newline is ignored if escaped."
address@hidden example
-
address@hidden Non-ASCII in Strings
address@hidden address@hidden Characters in Strings
-
- You can include a address@hidden international character in a string
-constant by writing it literally. There are two text representations
-for address@hidden 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
-makes the string multibyte. If the string constant is read from a
-unibyte source, then the character is read as unibyte and that makes the
-string unibyte.
-
- You can also represent a multibyte address@hidden character with its
-character code: use a hex escape, @address@hidden, with as many
-digits as necessary. (Multibyte address@hidden 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 @address@hidden }} (backslash and space) to
-terminate the hex escape---for example, @address@hidden }} represents
-one character, @samp{a} with grave accent. @address@hidden }} in a string
-constant is just like backslash-newline; it does not contribute any
-character to the string, but it does terminate the preceding hex escape.
-
- You can represent a unibyte address@hidden 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.
-
- You can also specify characters in a string by their numeric values
-in Unicode, using @samp{\u} and @samp{\U} (@pxref{Character Type}).
-
- @xref{Text Representations}, for more information about the two
-text representations.
-
address@hidden Nonprinting Characters
address@hidden Nonprinting Characters in Strings
-
- You can use the same backslash escape-sequences in a string constant
-as in character literals (but do not use the question mark that begins a
-character constant). For example, you can write a string containing the
-nonprinting characters tab and @kbd{C-a}, with commas and spaces between
-them, like this: @code{"\t, \C-a"}. @xref{Character Type}, for a
-description of the read syntax for characters.
-
- 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 @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 @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
address@hidden
address@hidden
address@hidden tex
address@hidden
-2**7
address@hidden ifnottex
-bit of the character in the string. If the string is used in
address@hidden or @code{lookup-key}, this numeric code is translated
-into the equivalent meta character. @xref{Character Type}.
-
- Strings cannot hold characters that have the hyper, super, or alt
-modifiers.
-
address@hidden Text Props and Strings
address@hidden Text Properties in Strings
-
- A string can hold properties for the characters it contains, in
-addition to the characters themselves. This enables programs that copy
-text between strings and buffers to copy the text's properties with no
-special effort. @xref{Text Properties}, for an explanation of what text
-properties mean. Strings with text properties use a special read and
-print syntax:
-
address@hidden
-#("@var{characters}" @var{property-data}...)
address@hidden example
-
address@hidden
-where @var{property-data} consists of zero or more elements, in groups
-of three as follows:
-
address@hidden
address@hidden @var{end} @var{plist}
address@hidden example
-
address@hidden
-The elements @var{beg} and @var{end} are integers, and together specify
-a range of indices in the string; @var{plist} is the property list for
-that range. For example,
-
address@hidden
-#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
address@hidden example
-
address@hidden
-represents a string whose textual contents are @samp{foo bar}, in which
-the first three characters have a @code{face} property with value
address@hidden, and the last three have a @code{face} property with value
address@hidden (The fourth character has no text properties, so its
-property list is @code{nil}. It is not actually necessary to mention
-ranges with @code{nil} as the property list, since any characters not
-mentioned in any range will default to having no properties.)
-
address@hidden Vector Type
address@hidden Vector Type
-
- A @dfn{vector} is a one-dimensional array of elements of any type. It
-takes a constant amount of time to access any element of a vector. (In
-a list, the access time of an element is proportional to the distance of
-the element from the beginning of the list.)
-
- The printed representation of a vector consists of a left square
-bracket, the elements, and a right square bracket. This is also the
-read syntax. Like numbers and strings, vectors are considered constants
-for evaluation.
-
address@hidden
-[1 "two" (three)] ; @r{A vector of three elements.}
- @result{} [1 "two" (three)]
address@hidden example
-
- @xref{Vectors}, for functions that work with vectors.
-
address@hidden Char-Table Type
address@hidden Char-Table Type
-
- A @dfn{char-table} is a one-dimensional array of elements of any type,
-indexed by character codes. Char-tables have certain extra features to
-make them more useful for many jobs that involve assigning information
-to character codes---for example, a char-table can have a parent to
-inherit from, a default value, and a small number of extra slots to use for
-special purposes. A char-table can also specify a single value for
-a whole character set.
-
- The printed representation of a char-table is like a vector
-except that there is an extra @samp{#^} at the beginning.
-
- @xref{Char-Tables}, for special functions to operate on char-tables.
-Uses of char-tables include:
-
address@hidden @bullet
address@hidden
-Case tables (@pxref{Case Tables}).
-
address@hidden
-Character category tables (@pxref{Categories}).
-
address@hidden
-Display tables (@pxref{Display Tables}).
-
address@hidden
-Syntax tables (@pxref{Syntax Tables}).
address@hidden itemize
-
address@hidden Bool-Vector Type
address@hidden Bool-Vector Type
-
- 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
-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.
-
address@hidden
-(make-bool-vector 3 t)
- @result{} #&3"^G"
-(make-bool-vector 3 nil)
- @result{} #&3"^@@"
address@hidden example
-
address@hidden
-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:
-
address@hidden
-(equal #&3"\377" #&3"\007")
- @result{} t
address@hidden example
-
address@hidden Hash Table Type
address@hidden 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 have no read syntax, and print using hash notation.
address@hidden Tables}, for functions that operate on hash tables.
-
address@hidden
-(make-hash-table)
- @result{} #<hash-table 'eql nil 0/65 0x83af980>
address@hidden example
-
address@hidden Function Type
address@hidden Function Type
-
- Lisp functions are executable code, just like functions in other
-programming languages. In Lisp, unlike most languages, functions are
-also Lisp objects. A non-compiled function in Lisp is a lambda
-expression: that is, a list whose first element is the symbol
address@hidden (@pxref{Lambda Expressions}).
-
- In most programming languages, it is impossible to have a function
-without a name. In Lisp, a function has no intrinsic name. A lambda
-expression can be called as a function even though it has no name; to
-emphasize this, we also call it an @dfn{anonymous function}
-(@pxref{Anonymous Functions}). A named function in Lisp is just a
-symbol with a valid function in its function cell (@pxref{Defining
-Functions}).
-
- Most of the time, functions are called when their names are written in
-Lisp expressions in Lisp programs. However, you can construct or obtain
-a function object at run time and then call it with the primitive
-functions @code{funcall} and @code{apply}. @xref{Calling Functions}.
-
address@hidden Macro Type
address@hidden Macro Type
-
- A @dfn{Lisp macro} is a user-defined construct that extends the Lisp
-language. It is represented as an object much like a function, but with
-different argument-passing semantics. A Lisp macro has the form of a
-list whose first element is the symbol @code{macro} and whose @sc{cdr}
-is a Lisp function object, including the @code{lambda} symbol.
-
- Lisp macro objects are usually defined with the built-in
address@hidden function, but any list that begins with @code{macro} is
-a macro as far as Emacs is concerned. @xref{Macros}, for an explanation
-of how to write a macro.
-
- @strong{Warning}: Lisp macros and keyboard macros (@pxref{Keyboard
-Macros}) are entirely different things. When we use the word ``macro''
-without qualification, we mean a Lisp macro, not a keyboard macro.
-
address@hidden Primitive Function Type
address@hidden Primitive Function Type
address@hidden special forms
-
- A @dfn{primitive function} is a function callable from Lisp but
-written in the C programming language. Primitive functions are also
-called @dfn{subrs} or @dfn{built-in functions}. (The word ``subr'' is
-derived from ``subroutine.'') Most primitive functions evaluate all
-their arguments when they are called. A primitive function that does
-not evaluate all its arguments is called a @dfn{special form}
-(@pxref{Special Forms})address@hidden
-
- It does not matter to the caller of a function whether the function is
-primitive. However, this does matter if you try to redefine a primitive
-with a function written in Lisp. The reason is that the primitive
-function may be called directly from C code. Calls to the redefined
-function from Lisp will use the new definition, but calls from C code
-may still use the built-in definition. Therefore, @strong{we discourage
-redefinition of primitive functions}.
-
- The term @dfn{function} refers to all Emacs functions, whether written
-in Lisp or C. @xref{Function Type}, for information about the
-functions written in Lisp.
-
- Primitive functions have no read syntax and print in hash notation
-with the name of the subroutine.
-
address@hidden
address@hidden
-(symbol-function 'car) ; @r{Access the function cell}
- ; @r{of the symbol.}
- @result{} #<subr car>
-(subrp (symbol-function 'car)) ; @r{Is this a primitive function?}
- @result{} t ; @r{Yes.}
address@hidden group
address@hidden example
-
address@hidden Byte-Code Type
address@hidden Byte-Code Function Type
-
-The byte compiler produces @dfn{byte-code function objects}.
-Internally, a byte-code function object is much like a vector; however,
-the evaluator handles this data type specially when it appears as a
-function to be called. @xref{Byte Compilation}, for information about
-the byte compiler.
-
-The printed representation and read syntax for a byte-code function
-object is like that for a vector, with an additional @samp{#} before the
-opening @samp{[}.
-
address@hidden Autoload Type
address@hidden Autoload Type
-
- An @dfn{autoload object} is a list whose first element is the symbol
address@hidden 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
-called as if it had been there to begin with. From the user's point of
-view, the function call works as expected, using the function definition
-in the loaded file.
-
- An autoload object is usually created with the function
address@hidden, which stores the object in the function cell of a
-symbol. @xref{Autoload}, for more details.
-
address@hidden Editing Types
address@hidden Editing Types
address@hidden editing types
-
- The types in the previous section are used for general programming
-purposes, and most of them are common to most Lisp dialects. Emacs Lisp
-provides several additional data types for purposes connected with
-editing.
-
address@hidden
-* Buffer Type:: The basic object of editing.
-* Marker Type:: A position in a buffer.
-* Window Type:: Buffers are displayed in windows.
-* Frame Type:: Windows subdivide frames.
-* Window Configuration Type:: Recording the way a frame is subdivided.
-* Frame Configuration Type:: Recording the status of all frames.
-* Process Type:: A process running on the underlying OS.
-* Stream Type:: Receive or send characters.
-* Keymap Type:: What function a keystroke invokes.
-* Overlay Type:: How an overlay is represented.
address@hidden menu
-
address@hidden Buffer Type
address@hidden Buffer Type
-
- A @dfn{buffer} is an object that holds text that can be edited
-(@pxref{Buffers}). Most buffers hold the contents of a disk file
-(@pxref{Files}) so they can be edited, but some are used for other
-purposes. Most buffers are also meant to be seen by the user, and
-therefore displayed, at some time, in a window (@pxref{Windows}). But a
-buffer need not be displayed in any window.
-
- 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, 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
-buffer}. Most editing commands act on the contents of the current
-buffer in the neighborhood of point. Many of the standard Emacs
-functions manipulate or test the characters in the current buffer; a
-whole chapter in this manual is devoted to describing these functions
-(@pxref{Text}).
-
- Several other data structures are associated with each buffer:
-
address@hidden @bullet
address@hidden
-a local syntax table (@pxref{Syntax Tables});
-
address@hidden
-a local keymap (@pxref{Keymaps}); and,
-
address@hidden
-a list of buffer-local variable bindings (@pxref{Buffer-Local Variables}).
-
address@hidden
-overlays (@pxref{Overlays}).
-
address@hidden
-text properties for the text in the buffer (@pxref{Text Properties}).
address@hidden itemize
-
address@hidden
-The local keymap and variable list contain entries that individually
-override global bindings or values. These are used to customize the
-behavior of programs in different buffers, without actually changing the
-programs.
-
- A buffer may be @dfn{indirect}, which means it shares the text
-of another buffer, but presents it differently. @xref{Indirect Buffers}.
-
- Buffers have no read syntax. They print in hash notation, showing the
-buffer name.
-
address@hidden
address@hidden
-(current-buffer)
- @result{} #<buffer objects.texi>
address@hidden group
address@hidden example
-
address@hidden Marker Type
address@hidden Marker Type
-
- A @dfn{marker} denotes a position in a specific buffer. Markers
-therefore have two components: one for the buffer, and one for the
-position. Changes in the buffer's text automatically relocate the
-position value as necessary to ensure that the marker always points
-between the same two characters in the buffer.
-
- Markers have no read syntax. They print in hash notation, giving the
-current character position and the name of the buffer.
-
address@hidden
address@hidden
-(point-marker)
- @result{} #<marker at 10779 in objects.texi>
address@hidden group
address@hidden example
-
address@hidden, for information on how to test, create, copy, and move
-markers.
-
address@hidden Window Type
address@hidden Window Type
-
- A @dfn{window} describes the portion of the terminal screen that Emacs
-uses to display a buffer. Every window has one associated buffer, whose
-contents appear in the window. By contrast, a given buffer may appear
-in one window, no window, or several windows.
-
- Though many windows may exist simultaneously, at any time one window
-is designated the @dfn{selected window}. This is the window where the
-cursor is (usually) displayed when Emacs is ready for a command. The
-selected window usually displays the current buffer, but this is not
-necessarily the case.
-
- Windows are grouped on the screen into frames; each window belongs to
-one and only one frame. @xref{Frame Type}.
-
- Windows have no read syntax. They print in hash notation, giving the
-window number and the name of the buffer being displayed. The window
-numbers exist to identify windows uniquely, since the buffer displayed
-in any given window can change frequently.
-
address@hidden
address@hidden
-(selected-window)
- @result{} #<window 1 on objects.texi>
address@hidden group
address@hidden example
-
- @xref{Windows}, for a description of the functions that work on windows.
-
address@hidden Frame Type
address@hidden Frame Type
-
- A @dfn{frame} is a screen area that contains one or more Emacs
-windows; we also use the term ``frame'' to refer to the Lisp object
-that Emacs uses to refer to the screen area.
-
- Frames have no read syntax. They print in hash notation, giving the
-frame's title, plus its address in core (useful to identify the frame
-uniquely).
-
address@hidden
address@hidden
-(selected-frame)
- @result{} #<frame emacs@@psilocin.gnu.org 0xdac80>
address@hidden group
address@hidden example
-
- @xref{Frames}, for a description of the functions that work on frames.
-
address@hidden Window Configuration Type
address@hidden Window Configuration Type
address@hidden window layout in a frame
-
- A @dfn{window configuration} stores information about the positions,
-sizes, and contents of the windows in a frame, so you can recreate the
-same arrangement of windows later.
-
- Window configurations do not have a read syntax; their print syntax
-looks like @samp{#<window-configuration>}. @xref{Window
-Configurations}, for a description of several functions related to
-window configurations.
-
address@hidden Frame Configuration Type
address@hidden Frame Configuration Type
address@hidden screen layout
address@hidden window layout, all frames
-
- A @dfn{frame configuration} stores information about the positions,
-sizes, and contents of the windows in all frames. It is actually
-a list whose @sc{car} is @code{frame-configuration} and whose
address@hidden is an alist. Each alist element describes one frame,
-which appears as the @sc{car} of that element.
-
- @xref{Frame Configurations}, for a description of several functions
-related to frame configurations.
-
address@hidden Process Type
address@hidden Process Type
-
- The word @dfn{process} usually means a running program. Emacs itself
-runs in a process of this sort. However, in Emacs Lisp, a process is a
-Lisp object that designates a subprocess created by the Emacs process.
-Programs such as shells, GDB, ftp, and compilers, running in
-subprocesses of Emacs, extend the capabilities of Emacs.
-
- An Emacs subprocess takes textual input from Emacs and returns textual
-output to Emacs for further manipulation. Emacs can also send signals
-to the subprocess.
-
- Process objects have no read syntax. They print in hash notation,
-giving the name of the process:
-
address@hidden
address@hidden
-(process-list)
- @result{} (#<process shell>)
address@hidden group
address@hidden example
-
address@hidden, for information about functions that create, delete,
-return information about, send input or signals to, and receive output
-from processes.
-
address@hidden Stream Type
address@hidden Stream Type
-
- A @dfn{stream} is an object that can be used as a source or sink for
-characters---either to supply characters for input or to accept them as
-output. Many different types can be used this way: markers, buffers,
-strings, and functions. Most often, input streams (character sources)
-obtain characters from the keyboard, a buffer, or a file, and output
-streams (character sinks) send characters to a buffer, such as a
address@hidden buffer, or to the echo area.
-
- The object @code{nil}, in addition to its other meanings, may be used
-as a stream. It stands for the value of the variable
address@hidden or @code{standard-output}. Also, the object
address@hidden as a stream specifies input using the minibuffer
-(@pxref{Minibuffers}) or output in the echo area (@pxref{The Echo
-Area}).
-
- Streams have no special printed representation or read syntax, and
-print as whatever primitive type they are.
-
- @xref{Read and Print}, for a description of functions
-related to streams, including parsing and printing functions.
-
address@hidden Keymap Type
address@hidden Keymap Type
-
- A @dfn{keymap} maps keys typed by the user to commands. This mapping
-controls how the user's command input is executed. A keymap is actually
-a list whose @sc{car} is the symbol @code{keymap}.
-
- @xref{Keymaps}, for information about creating keymaps, handling prefix
-keys, local as well as global keymaps, and changing key bindings.
-
address@hidden Overlay Type
address@hidden Overlay Type
-
- An @dfn{overlay} specifies properties that apply to a part of a
-buffer. Each overlay applies to a specified range of the buffer, and
-contains a property list (a list whose elements are alternating property
-names and values). Overlay properties are used to present parts of the
-buffer temporarily in a different display style. Overlays have no read
-syntax, and print in hash notation, giving the buffer name and range of
-positions.
-
- @xref{Overlays}, for how to create and use overlays.
-
address@hidden Circular Objects
address@hidden Read Syntax for Circular Objects
address@hidden circular structure, read syntax
address@hidden shared structure, read syntax
address@hidden @address@hidden read syntax
address@hidden @address@hidden read syntax
-
- To represent shared or circular structures within a complex of Lisp
-objects, you can use the reader constructs @address@hidden and
address@hidden@var{n}#}.
-
- Use @address@hidden before an object to label it for later reference;
-subsequently, you can use @address@hidden 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:
-
address@hidden
-(#1=(a) b #1#)
address@hidden example
-
address@hidden
-This differs from ordinary syntax such as this
-
address@hidden
-((a) b (a))
address@hidden example
-
address@hidden
-which would result in a list whose first and third elements
-look alike but are not the same Lisp object. This shows the difference:
-
address@hidden
-(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
address@hidden example
-
- You can also use the same syntax to make a circular structure, which
-appears as an ``element'' within itself. Here is an example:
-
address@hidden
-#1=(a #1#)
address@hidden example
-
address@hidden
-This makes a list whose second element is the list itself.
-Here's how you can see that it really works:
-
address@hidden
-(prog1 nil
- (setq x '#1=(a #1#)))
-(eq x (cadr x))
- @result{} t
address@hidden 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 address@hidden value. @xref{Output Variables}.
-
address@hidden Type Predicates
address@hidden Type Predicates
address@hidden type checking
address@hidden wrong-type-argument
-
- The Emacs Lisp interpreter itself does not perform type checking on
-the actual arguments passed to functions when they are called. It could
-not do so, since function arguments in Lisp do not have declared data
-types, as they do in other programming languages. It is therefore up to
-the individual function to test whether each actual argument belongs to
-a type that the function can use.
-
- All built-in functions do check the types of their actual arguments
-when appropriate, and signal a @code{wrong-type-argument} error if an
-argument is of the wrong type. For example, here is what happens if you
-pass an argument to @code{+} that it cannot handle:
-
address@hidden
address@hidden
-(+ 2 'a)
- @error{} Wrong type argument: number-or-marker-p, a
address@hidden group
address@hidden example
-
address@hidden type predicates
address@hidden testing types
- If you want your program to handle different types differently, you
-must do explicit type checking. The most common way to check the type
-of an object is to call a @dfn{type predicate} function. Emacs has a
-type predicate for each type, as well as some predicates for
-combinations of types.
-
- A type predicate function takes one argument; it returns @code{t} if
-the argument belongs to the appropriate type, and @code{nil} otherwise.
-Following a general Lisp convention for predicate functions, most type
-predicates' names end with @samp{p}.
-
- Here is an example which uses the predicates @code{listp} to check for
-a list and @code{symbolp} to check for a symbol.
-
address@hidden
-(defun add-on (x)
- (cond ((symbolp x)
- ;; If X is a symbol, put it on LIST.
- (setq list (cons x list)))
- ((listp x)
- ;; If X is a list, add its elements to LIST.
- (setq list (append x list)))
- (t
- ;; We handle only symbols and lists.
- (error "Invalid argument %s in add-on" x))))
address@hidden example
-
- Here is a table of predefined type predicates, in alphabetical order,
-with references to further information.
-
address@hidden @code
address@hidden atom
address@hidden Predicates, atom}.
-
address@hidden arrayp
address@hidden Functions, arrayp}.
-
address@hidden bool-vector-p
address@hidden, bool-vector-p}.
-
address@hidden bufferp
address@hidden Basics, bufferp}.
-
address@hidden byte-code-function-p
address@hidden Type, byte-code-function-p}.
-
address@hidden case-table-p
address@hidden Tables, case-table-p}.
-
address@hidden char-or-string-p
address@hidden for Strings, char-or-string-p}.
-
address@hidden char-table-p
address@hidden, char-table-p}.
-
address@hidden commandp
address@hidden Call, commandp}.
-
address@hidden consp
address@hidden Predicates, consp}.
-
address@hidden display-table-p
address@hidden Tables, display-table-p}.
-
address@hidden floatp
address@hidden on Numbers, floatp}.
-
address@hidden frame-configuration-p
address@hidden Configurations, frame-configuration-p}.
-
address@hidden frame-live-p
address@hidden Frames, frame-live-p}.
-
address@hidden framep
address@hidden, framep}.
-
address@hidden functionp
address@hidden, functionp}.
-
address@hidden hash-table-p
address@hidden Hash, hash-table-p}.
-
address@hidden integer-or-marker-p
address@hidden on Markers, integer-or-marker-p}.
-
address@hidden integerp
address@hidden on Numbers, integerp}.
-
address@hidden keymapp
address@hidden Keymaps, keymapp}.
-
address@hidden keywordp
address@hidden Variables}.
-
address@hidden listp
address@hidden Predicates, listp}.
-
address@hidden markerp
address@hidden on Markers, markerp}.
-
address@hidden wholenump
address@hidden on Numbers, wholenump}.
-
address@hidden nlistp
address@hidden Predicates, nlistp}.
-
address@hidden numberp
address@hidden on Numbers, numberp}.
-
address@hidden number-or-marker-p
address@hidden on Markers, number-or-marker-p}.
-
address@hidden overlayp
address@hidden, overlayp}.
-
address@hidden processp
address@hidden, processp}.
-
address@hidden sequencep
address@hidden Functions, sequencep}.
-
address@hidden stringp
address@hidden for Strings, stringp}.
-
address@hidden subrp
address@hidden Cells, subrp}.
-
address@hidden symbolp
address@hidden, symbolp}.
-
address@hidden syntax-table-p
address@hidden Tables, syntax-table-p}.
-
address@hidden user-variable-p
address@hidden Variables, user-variable-p}.
-
address@hidden vectorp
address@hidden, vectorp}.
-
address@hidden window-configuration-p
address@hidden Configurations, window-configuration-p}.
-
address@hidden window-live-p
address@hidden Windows, window-live-p}.
-
address@hidden windowp
address@hidden Windows, windowp}.
-
address@hidden booleanp
address@hidden and t, booleanp}.
-
address@hidden string-or-null-p
address@hidden for Strings, string-or-null-p}.
address@hidden table
-
- The most general way to check the type of an object is to call the
-function @code{type-of}. Recall that each object belongs to one and
-only one primitive type; @code{type-of} tells you which one (@pxref{Lisp
-Data Types}). But @code{type-of} knows nothing about non-primitive
-types. In most cases, it is more convenient to use type predicates than
address@hidden
-
address@hidden type-of object
-This function returns a symbol naming the primitive type of
address@hidden The value is one of the symbols @code{symbol},
address@hidden, @code{float}, @code{string}, @code{cons}, @code{vector},
address@hidden, @code{bool-vector}, @code{hash-table}, @code{subr},
address@hidden, @code{marker}, @code{overlay}, @code{window},
address@hidden, @code{frame}, @code{process}, or
address@hidden
-
address@hidden
-(type-of 1)
- @result{} integer
address@hidden
-(type-of 'nil)
- @result{} symbol
-(type-of '()) ; @address@hidden()} is @code{nil}.}
- @result{} symbol
-(type-of '(x))
- @result{} cons
address@hidden group
address@hidden example
address@hidden defun
-
address@hidden Equality Predicates
address@hidden Equality Predicates
address@hidden equality
-
- Here we describe two functions that test for equality between any two
-objects. Other functions test equality between objects of specific
-types, e.g., strings. For these predicates, see the appropriate chapter
-describing the data type.
-
address@hidden eq object1 object2
-This function returns @code{t} if @var{object1} and @var{object2} are
-the same object, @code{nil} otherwise.
-
address@hidden returns @code{t} if @var{object1} and @var{object2} are
-integers with the same value. Also, since symbol names are normally
-unique, if the arguments are symbols with the same name, they are
address@hidden For other types (e.g., lists, vectors, strings), two
-arguments with the same contents or elements are not necessarily
address@hidden to each other: they are @code{eq} only if they are the same
-object, meaning that a change in the contents of one will be reflected
-by the same change in the contents of the other.
-
address@hidden
address@hidden
-(eq 'foo 'foo)
- @result{} t
address@hidden group
-
address@hidden
-(eq 456 456)
- @result{} t
address@hidden group
-
address@hidden
-(eq "asdf" "asdf")
- @result{} nil
address@hidden group
-
address@hidden
-(eq '(1 (2 (3))) '(1 (2 (3))))
- @result{} nil
address@hidden group
-
address@hidden
-(setq foo '(1 (2 (3))))
- @result{} (1 (2 (3)))
-(eq foo foo)
- @result{} t
-(eq foo '(1 (2 (3))))
- @result{} nil
address@hidden group
-
address@hidden
-(eq [(1 2) 3] [(1 2) 3])
- @result{} nil
address@hidden group
-
address@hidden
-(eq (point-marker) (point-marker))
- @result{} nil
address@hidden group
address@hidden example
-
-The @code{make-symbol} function returns an uninterned symbol, distinct
-from the symbol that is used if you write the name in a Lisp expression.
-Distinct symbols with the same name are not @code{eq}. @xref{Creating
-Symbols}.
-
address@hidden
address@hidden
-(eq (make-symbol "foo") 'foo)
- @result{} nil
address@hidden group
address@hidden example
address@hidden defun
-
address@hidden equal object1 object2
-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 or contents are the same. So, if two
-objects are @code{eq}, they are @code{equal}, but the converse is not
-always true.
-
address@hidden
address@hidden
-(equal 'foo 'foo)
- @result{} t
address@hidden group
-
address@hidden
-(equal 456 456)
- @result{} t
address@hidden group
-
address@hidden
-(equal "asdf" "asdf")
- @result{} t
address@hidden group
address@hidden
-(eq "asdf" "asdf")
- @result{} nil
address@hidden group
-
address@hidden
-(equal '(1 (2 (3))) '(1 (2 (3))))
- @result{} t
address@hidden group
address@hidden
-(eq '(1 (2 (3))) '(1 (2 (3))))
- @result{} nil
address@hidden group
-
address@hidden
-(equal [(1 2) 3] [(1 2) 3])
- @result{} t
address@hidden group
address@hidden
-(eq [(1 2) 3] [(1 2) 3])
- @result{} nil
address@hidden group
-
address@hidden
-(equal (point-marker) (point-marker))
- @result{} t
address@hidden group
-
address@hidden
-(eq (point-marker) (point-marker))
- @result{} nil
address@hidden group
address@hidden example
-
-Comparison of strings is case-sensitive, but does not take account of
-text properties---it compares only the characters in the strings. For
-technical reasons, a unibyte string and a multibyte string are
address@hidden 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}).
-
address@hidden
address@hidden
-(equal "asdf" "ASDF")
- @result{} nil
address@hidden group
address@hidden example
-
-However, two distinct buffers are never considered @code{equal}, even if
-their textual contents are the same.
address@hidden defun
-
- 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
address@hidden:
-
address@hidden
-(equal (car @var{x}) (car @var{y}))
-(equal (cdr @var{x}) (cdr @var{y}))
address@hidden example
-
-Because of this recursive method, circular lists may therefore cause
-infinite recursion (leading to an error).
-
address@hidden
- arch-tag: 9711a66e-4749-4265-9e8c-972d55b67096
address@hidden ignore
- [Emacs-diffs] Changes to objects.texi,
Glenn Morris <=