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This is Info file elisp, produced by Makeinfo-1.63 from the input file elisp.texi. This version is the edition 2.4.2 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.34. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: elisp, Node: Character Type, Next: Symbol Type, Prev: Floating Point Type, Up: Programming Types Character Type -------------- A "character" in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character `A' is represented as the integer 65. Individual characters are not often used in programs. It is far more common to work with *strings*, which are sequences composed of characters. *Note String Type::. Characters in strings, buffers, and files are currently limited to the range of 0 to 255--eight bits. If you store a larger integer into a string, buffer or file, it is truncated to that range. Characters that represent keyboard input have a much wider range. 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 a very bad idea. You should *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, `?A' for the character `A', `?B' for the character `B', and `?a' for the character `a'. For example: ?Q => 81 ?q => 113 You can use the same syntax for punctuation characters, but it is often a good idea to add a `\' so that the Emacs commands for editing Lisp code don't get confused. For example, `?\ ' is the way to write the space character. If the character is `\', you *must* use a second `\' to quote it: `?\\'. You can express the characters Control-g, backspace, tab, newline, vertical tab, formfeed, return, and escape as `?\a', `?\b', `?\t', `?\n', `?\v', `?\f', `?\r', `?\e', respectively. Those values are 7, 8, 9, 10, 11, 12, 13, and 27 in decimal. Thus, ?\a => 7 ; `C-g' ?\b => 8 ; backspace, BS, `C-h' ?\t => 9 ; tab, TAB, `C-i' ?\n => 10 ; newline, LFD, `C-j' ?\v => 11 ; vertical tab, `C-k' ?\f => 12 ; formfeed character, `C-l' ?\r => 13 ; carriage return, RET, `C-m' ?\e => 27 ; escape character, ESC, `C-[' ?\\ => 92 ; backslash character, `\' These sequences which start with backslash are also known as "escape sequences", because backslash plays the role of an escape character; this usage has nothing to do with the character ESC. Control characters may 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 `?\^I' and `?\^i' are valid read syntax for the character `C-i', the character whose value is 9. Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to `?\^I' and to `?\^i': ?\^I => 9 ?\C-I => 9 For use in strings and buffers, you are limited to the control characters that exist in ASCII, but for keyboard input purposes, you can turn any character into a control character with `C-'. The character codes for these non-ASCII control characters include the 2**26 bit as well as the code for the corresponding non-control character. Ordinary terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using an X terminal. For historical reasons, Emacs treats the DEL character as the control equivalent of `?': ?\^? => 127 ?\C-? => 127 As a result, it is currently not possible to represent the character `Control-?', which is a meaningful input character under X. It is not easy to change this as various Lisp files refer to DEL in this way. For representing control characters to be found in files or strings, we recommend the `^' syntax; for control characters in keyboard input, we prefer the `C-' syntax. This does not affect the meaning of the program, but may guide the understanding of people who read it. A "meta character" is a character typed with the META modifier key. The integer that represents such a character has the 2**27 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. In a string, the 2**7 bit indicates a meta character, so 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 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 `\M-'. For example, `?\M-A' stands for `M-A'. You can use `\M-' together with octal character codes (see below), with `\C-', or with any other syntax for a character. Thus, you can write `M-A' as `?\M-A', or as `?\M-\101'. Likewise, you can write `C-M-b' as `?\M-\C-b', `?\C-\M-b', or `?\M-\002'. The case of an ordinary letter is indicated by its character code as part of ASCII, but ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the 2**25 bit to indicate that the shift key was used for typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not indicate the distinction to the computer in any way. The X Window System defines three other modifier bits that can be set in a character: "hyper", "super" and "alt". The syntaxes for these bits are `\H-', `\s-' and `\A-'. Thus, `?\H-\M-\A-x' represents `Alt-Hyper-Meta-x'. Numerically, the bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper. Finally, the most general read syntax consists of a question mark followed by a backslash and the character code in octal (up to three octal digits); thus, `?\101' for the character `A', `?\001' for the character `C-a', and `?\002' for the character `C-b'. Although this syntax can represent any ASCII character, it is preferred only when the precise octal value is more important than the ASCII representation. ?\012 => 10 ?\n => 10 ?\C-j => 10 ?\101 => 65 ?A => 65 A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, `?\+' is equivalent to `?+'. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters `()\|;'`"#.,' to avoid confusing the Emacs commands for editing Lisp code. 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 `\t', instead of an actual whitespace character such as a tab. File: elisp, Node: Symbol Type, Next: Sequence Type, Prev: Character Type, Up: Programming Types Symbol Type ----------- A "symbol" in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the 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 name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. 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 `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}' 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, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter `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. Common 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. Here are several examples of symbol names. Note that the `+' 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 makes it invalid as a number. foo ; A symbol named `foo'. FOO ; A symbol named `FOO', different from `foo'. char-to-string ; A symbol named `char-to-string'. 1+ ; A symbol named `1+' ; (not `+1', which is an integer). \+1 ; A symbol named `+1' ; (not a very readable name). $*\ 1\ 2$ ; A symbol named `(* 1 2)' (a worse name). +-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'. ; These characters need not be escaped. File: elisp, Node: Sequence Type, Next: Cons Cell Type, Prev: Symbol Type, Up: Programming Types Sequence Types -------------- A "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 and vectors. Vectors can hold elements of any type, but string elements must be characters in the range from 0 to 255. However, the characters in a string can have text properties like characters in a buffer (*note Text Properties::.); vectors do not support text properties even when their elements happen to be characters. Lists, strings and vectors are different, but they have important similarities. For example, all have a length L, and all have elements which can be indexed from zero to L minus one. Also, several functions, called sequence functions, accept any kind of sequence. For example, the function `elt' can be used to extract an element of a sequence, given its index. *Note Sequences Arrays Vectors::. It is 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 `()' always stands for the same object, `nil'. File: elisp, Node: Cons Cell Type, Next: Array Type, Prev: Sequence Type, Up: Programming Types Cons Cell and List Types ------------------------ A "cons cell" is an object comprising two pointers named the CAR and the CDR. Each of them can point to any Lisp object. A "list" is a series of cons cells, linked together so that the CDR of each cons cell points either to another cons cell or to the empty list. *Note Lists::, for functions that work on lists. Because most cons cells are used as part of lists, the phrase "list structure" has come to refer to any structure made out of cons cells. The names CAR and CDR have only historical meaning now. The original Lisp implementation ran on an IBM 704 computer which divided words into two parts, called the "address" part and the "decrement"; CAR was an instruction to extract the contents of the address part of a register, and CDR an instruction to extract the contents of the decrement. By contrast, "cons cells" are named for the function `cons' that creates them, which in turn is named for its purpose, the construction of cells. 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 "atoms". 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. Upon reading, each object inside the parentheses becomes an element of the list. That is, a cons cell is made for each element. The CAR of the cons cell points to the element, and its CDR points to the next cons cell of the list, which holds the next element in the list. The CDR of the last cons cell is set to point to `nil'. A list can be illustrated by a diagram in which the cons cells are shown as pairs of boxes. (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.) The following represents the three-element list `(rose violet buttercup)': ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup In this diagram, each box represents a slot that can refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow is a reference to a Lisp object, either an atom or another cons cell. In this example, the first box, the CAR of the first cons cell, refers to or "contains" `rose' (a symbol). The second box, the CDR of the first cons cell, refers to the next pair of boxes, the second cons cell. The CAR of the second cons cell refers to `violet' and the CDR refers to the third cons cell. The CDR of the third (and last) cons cell refers to `nil'. Here is another diagram of the same list, `(rose violet buttercup)', sketched in a different manner: --------------- ---------------- ------------------- | car | cdr | | car | cdr | | car | cdr | | rose | o-------->| violet | o-------->| buttercup | nil | | | | | | | | | | --------------- ---------------- ------------------- A list with no elements in it is the "empty list"; it is identical to the symbol `nil'. In other words, `nil' is both a symbol and a list. Here are examples of lists written in Lisp syntax: (A 2 "A") ; A list of three elements. () ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string `"A ()"'. (A ()) ; A list of two elements: `A' and the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element ; (which is a list of three elements). Here is the list `(A ())', or equivalently `(A nil)', depicted with boxes and arrows: ___ ___ ___ ___ |___|___|--> |___|___|--> nil | | | | --> A --> nil * Menu: * Dotted Pair Notation:: An alternative syntax for lists. * Association List Type:: A specially constructed list. File: elisp, Node: Dotted Pair Notation, Next: Association List Type, Up: Cons Cell Type Dotted Pair Notation .................... "Dotted pair notation" is an alternative syntax for cons cells that represents the CAR and CDR explicitly. In this syntax, `(A . B)' stands for a cons cell whose CAR is the object A, and whose CDR is the object B. Dotted pair notation is therefore more general than list syntax. In the dotted pair notation, the list `(1 2 3)' is written as `(1 . (2 . (3 . nil)))'. For `nil'-terminated lists, the two notations produce the same result, but list notation is usually clearer and more convenient when it is applicable. When printing a list, the dotted pair notation is only used if the CDR of a cell is not a list. Here's how box notation can illustrate dotted pairs. This example shows the pair `(rose . violet)': ___ ___ |___|___|--> violet | | --> rose Dotted pair notation can be combined with list notation to represent a chain of cons cells with a non-`nil' final CDR. For example, `(rose violet . buttercup)' is equivalent to `(rose . (violet . buttercup))'. The object looks like this: ___ ___ ___ ___ |___|___|--> |___|___|--> buttercup | | | | --> rose --> violet These diagrams make it evident why `(rose . violet . buttercup)' is invalid syntax; it would require a cons cell that has three parts rather than two. The list `(rose violet)' is equivalent to `(rose . (violet))' and looks like this: ___ ___ ___ ___ |___|___|--> |___|___|--> nil | | | | --> rose --> violet Similarly, the three-element list `(rose violet buttercup)' is equivalent to `(rose . (violet . (buttercup)))'. It looks like this: ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup File: elisp, Node: Association List Type, Prev: Dotted Pair Notation, Up: Cons Cell Type Association List Type ..................... An "association list" or "alist" is a specially-constructed list whose elements are cons cells. In each element, the CAR is considered a "key", and the CDR is considered an "associated value". (In some cases, the associated value is stored in the CAR of the 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, (setq alist-of-colors '((rose . red) (lily . white) (buttercup . yellow))) sets the variable `alist-of-colors' to an alist of three elements. In the first element, `rose' is the key and `red' is the value. *Note Association Lists::, for a further explanation of alists and for functions that work on alists. File: elisp, Node: Array Type, Next: String Type, Prev: Cons Cell Type, Up: Programming Types Array Type ---------- An "array" is composed of an arbitrary number of slots for referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes 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 two types of array, strings and vectors. A string is an array of characters and a vector is an array of arbitrary objects. Both are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with an array of arrays.) Each type of array has its own read syntax; see *Note String Type::, and *Note Vector Type::. An array may have any length up to the largest integer; but once created, it has a fixed size. The first element of an array has index zero, the second element has index 1, and so on. This is called "zero-origin" indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The array type is contained in the sequence type and contains both the string type and the vector type. File: elisp, Node: String Type, Next: Vector Type, Prev: Array Type, Up: Programming Types String Type ----------- A "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. The read syntax for strings is a double-quote, an arbitrary number of characters, and another double-quote, `"like this"'. The Lisp reader accepts the same formats for reading the characters of a string as it does for reading single characters (without the question mark that begins a character literal). You can enter a nonprinting character such as tab, `C-a' or `M-C-A' using the convenient escape sequences, like this: `"\t, \C-a, \M-\C-a"'. You can include a double-quote in a string by preceding it with a backslash; thus, `"\""' is a string containing just a single double-quote character. (*Note Character Type::, for a description of the read syntax for characters.) If you use the `\M-' syntax to indicate a meta character in a string constant, this sets the 2**7 bit of the character in the string. This is not the same representation that the meta modifier has in a character on its own (not inside a string). *Note Character Type::. Strings cannot hold characters that have the hyper, super, or alt modifiers; they can hold ASCII control characters, but no others. They do not distinguish case in ASCII control characters. The printed representation of a string consists of a double-quote, the characters it contains, and another double-quote. However, you must escape any backslash or double-quote characters in the string with a backslash, like this: `"this \" is an embedded quote"'. 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 `\'--does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. "It is useful to include newlines in documentation strings, but the newline is \ ignored if escaped." => "It is useful to include newlines in documentation strings, but the newline is ignored if escaped." A string can hold properties of the text it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to preserve the properties with no special effort. *Note Text Properties::. Strings with text properties have a special read and print syntax: #("CHARACTERS" PROPERTY-DATA...) where PROPERTY-DATA consists of zero or more elements, in groups of three as follows: BEG END PLIST The elements BEG and END are integers, and together specify a range of indices in the string; PLIST is the property list for that range. *Note Strings and Characters::, for functions that work on strings. File: elisp, Node: Vector Type, Next: Function Type, Prev: String Type, Up: Programming Types Vector Type ----------- A "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. [1 "two" (three)] ; A vector of three elements. => [1 "two" (three)] *Note Vectors::, for functions that work with vectors. File: elisp, Node: Function Type, Next: Macro Type, Prev: Vector Type, Up: Programming Types Function Type ------------- Just as functions in other programming languages are executable, "Lisp function" objects are pieces of executable code. However, functions in Lisp are primarily Lisp objects, and only secondarily the text which represents them. These Lisp objects are lambda expressions: lists whose first element is the symbol `lambda' (*note 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 is also called an "anonymous function" (*note Anonymous Functions::.). A named function in Lisp is actually a symbol with a valid function in its function cell (*note 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 `funcall' and `apply'. *Note Calling Functions::. File: elisp, Node: Macro Type, Next: Primitive Function Type, Prev: Function Type, Up: Programming Types Macro Type ---------- A "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 parameter-passing semantics. A Lisp macro has the form of a list whose first element is the symbol `macro' and whose CDR is a Lisp function object, including the `lambda' symbol. Lisp macro objects are usually defined with the built-in `defmacro' function, but any list that begins with `macro' is a macro as far as Emacs is concerned. *Note Macros::, for an explanation of how to write a macro. File: elisp, Node: Primitive Function Type, Next: Byte-Code Type, Prev: Macro Type, Up: Programming Types Primitive Function Type ----------------------- A "primitive function" is a function callable from Lisp but written in the C programming language. Primitive functions are also called "subrs" or "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 "special form" (*note Special Forms::.). It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to substitute a function written in Lisp for a primitive of the same name. 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. The term "function" refers to all Emacs functions, whether written in Lisp or C. *Note 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. (symbol-function 'car) ; Access the function cell ; of the symbol. => #<subr car> (subrp (symbol-function 'car)) ; Is this a primitive function? => t ; Yes. File: elisp, Node: Byte-Code Type, Next: Autoload Type, Prev: Primitive Function Type, Up: Programming Types Byte-Code Function Type ----------------------- The byte compiler produces "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. *Note 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 `#' before the opening `['. File: elisp, Node: Autoload Type, Prev: Byte-Code Type, Up: Programming Types Autoload Type ------------- An "autoload object" is a list whose first element is the symbol `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. 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 `autoload', which stores the object in the function cell of a symbol. *Note Autoload::, for more details. File: elisp, Node: Editing Types, Next: Type Predicates, Prev: Programming Types, Up: Lisp Data Types Editing Types ============= The types in the previous section are common to many Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing. * Menu: * 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. * Process Type:: A process running on the underlying OS. * Stream Type:: Receive or send characters. * Keymap Type:: What function a keystroke invokes. * Syntax Table Type:: What a character means. * Display Table Type:: How display tables are represented. * Overlay Type:: How an overlay is represented. File: elisp, Node: Buffer Type, Next: Marker Type, Up: Editing Types Buffer Type ----------- A "buffer" is an object that holds text that can be edited (*note Buffers::.). Most buffers hold the contents of a disk file (*note 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 (*note 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, insertion of text into a buffer is very efficient, 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 "point" (*note Positions::.). At any time, one buffer is the "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 (*note Text::.). Several other data structures are associated with each buffer: * a local syntax table (*note Syntax Tables::.); * a local keymap (*note Keymaps::.); and, * a local variable binding list (*note Buffer-Local Variables::.). * a list of overlays (*note Overlays::.). * text properties for the text in the buffer (*note Text Properties::.). 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 "indirect", which means it shares the text of another buffer. *Note Indirect Buffers::. Buffers have no read syntax. They print in hash notation, showing the buffer name. (current-buffer) => #<buffer objects.texi> File: elisp, Node: Marker Type, Next: Window Type, Prev: Buffer Type, Up: Editing Types Marker Type ----------- A "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. (point-marker) => #<marker at 10779 in objects.texi> *Note Markers::, for information on how to test, create, copy, and move markers. File: elisp, Node: Window Type, Next: Frame Type, Prev: Marker Type, Up: Editing Types Window Type ----------- A "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 "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. *Note 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. (selected-window) => #<window 1 on objects.texi> *Note Windows::, for a description of the functions that work on windows. File: elisp, Node: Frame Type, Next: Window Configuration Type, Prev: Window Type, Up: Editing Types Frame Type ---------- A FRAME is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows. 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). (selected-frame) => #<frame xemacs@mole.gnu.ai.mit.edu 0xdac80> *Note Frames::, for a description of the functions that work on frames. File: elisp, Node: Window Configuration Type, Next: Process Type, Prev: Frame Type, Up: Editing Types Window Configuration Type ------------------------- A "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 `#<window-configuration>'. *Note Window Configurations::, for a description of several functions related to window configurations. File: elisp, Node: Process Type, Next: Stream Type, Prev: Window Configuration Type, Up: Editing Types Process Type ------------ The word "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: (process-list) => (#<process shell>) *Note Processes::, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes. File: elisp, Node: Stream Type, Next: Keymap Type, Prev: Process Type, Up: Editing Types Stream Type ----------- A "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 `*Help*' buffer, or to the echo area. The object `nil', in addition to its other meanings, may be used as a stream. It stands for the value of the variable `standard-input' or `standard-output'. Also, the object `t' as a stream specifies input using the minibuffer (*note Minibuffers::.) or output in the echo area (*note The Echo Area::.). Streams have no special printed representation or read syntax, and print as whatever primitive type they are. *Note Read and Print::, for a description of functions related to streams, including parsing and printing functions. File: elisp, Node: Keymap Type, Next: Syntax Table Type, Prev: Stream Type, Up: Editing Types Keymap Type ----------- A "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 CAR is the symbol `keymap'. *Note Keymaps::, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings. File: elisp, Node: Syntax Table Type, Next: Display Table Type, Prev: Keymap Type, Up: Editing Types Syntax Table Type ----------------- A "syntax table" is a vector of 256 integers. Each element of the vector defines how one character is interpreted when it appears in a buffer. For example, in C mode (*note Major Modes::.), the `+' character is punctuation, but in Lisp mode it is a valid character in a symbol. These modes specify different interpretations by changing the syntax table entry for `+', at index 43 in the syntax table. Syntax tables are used only for scanning text in buffers, not for reading Lisp expressions. The table the Lisp interpreter uses to read expressions is built into the Emacs source code and cannot be changed; thus, to change the list delimiters to be `{' and `}' instead of `(' and `)' would be impossible. *Note Syntax Tables::, for details about syntax classes and how to make and modify syntax tables. File: elisp, Node: Display Table Type, Next: Overlay Type, Prev: Syntax Table Type, Up: Editing Types Display Table Type ------------------ A "display table" specifies how to display each character code. Each buffer and each window can have its own display table. A display table is actually a vector of length 262. *Note Display Tables::. File: elisp, Node: Overlay Type, Prev: Display Table Type, Up: Editing Types Overlay Type ------------ An "overlay" specifies temporary alteration of the display appearance of a part of a buffer. It contains markers delimiting a range of the buffer, plus a property list (a list whose elements are alternating property names and values). Overlays are used to present parts of the buffer temporarily in a different display style. They have no read syntax, and print in hash notation, giving the buffer name and range of positions. *Note Overlays::, for how to create and use overlays. File: elisp, Node: Type Predicates, Next: Equality Predicates, Prev: Editing Types, Up: Lisp Data Types Type Predicates =============== 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 `wrong-type-argument' error if an argument is of the wrong type. For example, here is what happens if you pass an argument to `+' that it cannot handle: (+ 2 'a) error--> Wrong type argument: integer-or-marker-p, a 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 "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 `t' if the argument belongs to the appropriate type, and `nil' otherwise. Following a general Lisp convention for predicate functions, most type predicates' names end with `p'. Here is an example which uses the predicates `listp' to check for a list and `symbolp' to check for a symbol. (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 only handle symbols and lists. (error "Invalid argument %s in add-on" x)))) Here is a table of predefined type predicates, in alphabetical order, with references to further information. `atom' *Note atom: List-related Predicates. `arrayp' *Note arrayp: Array Functions. `bufferp' *Note bufferp: Buffer Basics. `byte-code-function-p' *Note byte-code-function-p: Byte-Code Type. `case-table-p' *Note case-table-p: Case Table. `char-or-string-p' *Note char-or-string-p: Predicates for Strings. `commandp' *Note commandp: Interactive Call. `consp' *Note consp: List-related Predicates. `floatp' *Note floatp: Predicates on Numbers. `frame-live-p' *Note frame-live-p: Deleting Frames. `framep' *Note framep: Frames. `integer-or-marker-p' *Note integer-or-marker-p: Predicates on Markers. `integerp' *Note integerp: Predicates on Numbers. `keymapp' *Note keymapp: Creating Keymaps. `listp' *Note listp: List-related Predicates. `markerp' *Note markerp: Predicates on Markers. `wholenump' *Note wholenump: Predicates on Numbers. `nlistp' *Note nlistp: List-related Predicates. `numberp' *Note numberp: Predicates on Numbers. `number-or-marker-p' *Note number-or-marker-p: Predicates on Markers. `overlayp' *Note overlayp: Overlays. `processp' *Note processp: Processes. `sequencep' *Note sequencep: Sequence Functions. `stringp' *Note stringp: Predicates for Strings. `subrp' *Note subrp: Function Cells. `symbolp' *Note symbolp: Symbols. `syntax-table-p' *Note syntax-table-p: Syntax Tables. `user-variable-p' *Note user-variable-p: Defining Variables. `vectorp' *Note vectorp: Vectors. `window-configuration-p' *Note window-configuration-p: Window Configurations. `window-live-p' *Note window-live-p: Deleting Windows. `windowp' *Note windowp: Basic Windows. The most general way to check the type of an object is to call the function `type-of'. Recall that each object belongs to one and only one primitive type; `type-of' tells you which one (*note Lisp Data Types::.). But `type-of' knows nothing about non-primitive types. In most cases, it is more convenient to use type predicates than `type-of'. - Function: type-of OBJECT This function returns a symbol naming the primitive type of OBJECT. The value is one of the symbols `symbol', `integer', `float', `string', `cons', `vector', `marker', `overlay', `window', `buffer', `subr', `compiled-function', `process', or `window-configuration'. (type-of 1) => integer (type-of 'nil) => symbol (type-of '()) ; `()' is `nil'. => symbol (type-of '(x)) => cons File: elisp, Node: Equality Predicates, Prev: Type Predicates, Up: Lisp Data Types Equality Predicates =================== 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. - Function: eq OBJECT1 OBJECT2 This function returns `t' if OBJECT1 and OBJECT2 are the same object, `nil' otherwise. The "same object" means that a change in one will be reflected by the same change in the other. `eq' returns `t' if OBJECT1 and 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 `eq'. For other types (e.g., lists, vectors, strings), two arguments with the same contents or elements are not necessarily `eq' to each other: they are `eq' only if they are the same object. (The `make-symbol' function returns an uninterned symbol that is not interned in the standard `obarray'. When uninterned symbols are in use, symbol names are no longer unique. Distinct symbols with the same name are not `eq'. *Note Creating Symbols::.) (eq 'foo 'foo) => t (eq 456 456) => t (eq "asdf" "asdf") => nil (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (setq foo '(1 (2 (3)))) => (1 (2 (3))) (eq foo foo) => t (eq foo '(1 (2 (3)))) => nil (eq [(1 2) 3] [(1 2) 3]) => nil (eq (point-marker) (point-marker)) => nil - Function: equal OBJECT1 OBJECT2 This function returns `t' if OBJECT1 and OBJECT2 have equal components, `nil' otherwise. Whereas `eq' tests if its arguments are the same object, `equal' looks inside nonidentical arguments to see if their elements are the same. So, if two objects are `eq', they are `equal', but the converse is not always true. (equal 'foo 'foo) => t (equal 456 456) => t (equal "asdf" "asdf") => t (eq "asdf" "asdf") => nil (equal '(1 (2 (3))) '(1 (2 (3)))) => t (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (equal [(1 2) 3] [(1 2) 3]) => t (eq [(1 2) 3] [(1 2) 3]) => nil (equal (point-marker) (point-marker)) => t (eq (point-marker) (point-marker)) => nil Comparison of strings is case-sensitive and takes account of text properties as well as the characters in the strings. To compare two strings' characters without comparing their text properties, use `string=' (*note Text Comparison::.). (equal "asdf" "ASDF") => nil Two distinct buffers are never `equal', even if their contents are the same. The test for equality is implemented recursively, and circular lists may therefore cause infinite recursion (leading to an error). File: elisp, Node: Numbers, Next: Strings and Characters, Prev: Lisp Data Types, Up: Top Numbers ******* GNU Emacs supports two numeric data types: "integers" and "floating point numbers". Integers are whole numbers such as -3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as -4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, `e2' stands for ten to the second power, and is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision. Support for floating point numbers is a new feature in Emacs 19, and it is controlled by a separate compilation option, so you may encounter a site where Emacs does not support them. * Menu: * Integer Basics:: Representation and range of integers. * Float Basics:: Representation and range of floating point. * Predicates on Numbers:: Testing for numbers. * Comparison of Numbers:: Equality and inequality predicates. * Numeric Conversions:: Converting float to integer and vice versa. * Arithmetic Operations:: How to add, subtract, multiply and divide. * Rounding Operations:: Explicitly rounding floating point numbers. * Bitwise Operations:: Logical and, or, not, shifting. * Math Functions:: Trig, exponential and logarithmic functions. * Random Numbers:: Obtaining random integers, predictable or not.