This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. INFO-DIR-SECTION XEmacs Editor START-INFO-DIR-ENTRY * Lispref: (lispref). XEmacs Lisp Reference Manual. END-INFO-DIR-ENTRY Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May, November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. 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: lispref.info, Node: Backquote, Next: Problems with Macros, Prev: Defining Macros, Up: Macros Backquote ========= Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the macro ``' (often called "backquote"). Backquote allows you to quote a list, but selectively evaluate elements of that list. In the simplest case, it is identical to the special form `quote' (*note Quoting::.). For example, these two forms yield identical results: `(a list of (+ 2 3) elements) => (a list of (+ 2 3) elements) '(a list of (+ 2 3) elements) => (a list of (+ 2 3) elements) The special marker `,' inside of the argument to backquote indicates a value that isn't constant. Backquote evaluates the argument of `,' and puts the value in the list structure: (list 'a 'list 'of (+ 2 3) 'elements) => (a list of 5 elements) `(a list of ,(+ 2 3) elements) => (a list of 5 elements) You can also "splice" an evaluated value into the resulting list, using the special marker `,@'. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ``' is often unreadable. Here are some examples: (setq some-list '(2 3)) => (2 3) (cons 1 (append some-list '(4) some-list)) => (1 2 3 4 2 3) `(1 ,@some-list 4 ,@some-list) => (1 2 3 4 2 3) (setq list '(hack foo bar)) => (hack foo bar) (cons 'use (cons 'the (cons 'words (append (cdr list) '(as elements))))) => (use the words foo bar as elements) `(use the words ,@(cdr list) as elements) => (use the words foo bar as elements) In older versions of Emacs (before XEmacs 19.12 or FSF Emacs version 19.29), ``' used a different syntax which required an extra level of parentheses around the entire backquote construct. Likewise, each `,' or `,@' substitution required an extra level of parentheses surrounding both the `,' or `,@' and the following expression. The old syntax required whitespace between the ``', `,' or `,@' and the following expression. This syntax is still accepted, but no longer recommended except for compatibility with old Emacs versions.  File: lispref.info, Node: Problems with Macros, Prev: Backquote, Up: Macros Common Problems Using Macros ============================ The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble. * Menu: * Argument Evaluation:: The expansion should evaluate each macro arg once. * Surprising Local Vars:: Local variable bindings in the expansion require special care. * Eval During Expansion:: Don't evaluate them; put them in the expansion. * Repeated Expansion:: Avoid depending on how many times expansion is done.  File: lispref.info, Node: Argument Evaluation, Next: Surprising Local Vars, Up: Problems with Macros Evaluating Macro Arguments Repeatedly ------------------------------------- When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple "for" loop such as one might find in Pascal. (defmacro for (var from init to final do &rest body) "Execute a simple \"for\" loop. For example, (for i from 1 to 10 do (print i))." (list 'let (list (list var init)) (cons 'while (cons (list '<= var final) (append body (list (list 'inc var))))))) => for (for i from 1 to 3 do (setq square (* i i)) (princ (format "\n%d %d" i square))) ==> (let ((i 1)) (while (<= i 3) (setq square (* i i)) (princ (format "%d %d" i square)) (inc i))) -|1 1 -|2 4 -|3 9 => nil (The arguments `from', `to', and `do' in this macro are "syntactic sugar"; they are entirely ignored. The idea is that you will write noise words (such as `from', `to', and `do') in those positions in the macro call.) Here's an equivalent definition simplified through use of backquote: (defmacro for (var from init to final do &rest body) "Execute a simple \"for\" loop. For example, (for i from 1 to 10 do (print i))." `(let ((,var ,init)) (while (<= ,var ,final) ,@body (inc ,var)))) Both forms of this definition (with backquote and without) suffer from the defect that FINAL is evaluated on every iteration. If FINAL is a constant, this is not a problem. If it is a more complex form, say `(long-complex-calculation x)', this can slow down the execution significantly. If FINAL has side effects, executing it more than once is probably incorrect. A well-designed macro definition takes steps to avoid this problem by producing an expansion that evaluates the argument expressions exactly once unless repeated evaluation is part of the intended purpose of the macro. Here is a correct expansion for the `for' macro: (let ((i 1) (max 3)) (while (<= i max) (setq square (* i i)) (princ (format "%d %d" i square)) (inc i))) Here is a macro definition that creates this expansion: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." `(let ((,var ,init) (max ,final)) (while (<= ,var max) ,@body (inc ,var)))) Unfortunately, this introduces another problem. Proceed to the following node.  File: lispref.info, Node: Surprising Local Vars, Next: Eval During Expansion, Prev: Argument Evaluation, Up: Problems with Macros Local Variables in Macro Expansions ----------------------------------- In the previous section, the definition of `for' was fixed as follows to make the expansion evaluate the macro arguments the proper number of times: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." `(let ((,var ,init) (max ,final)) (while (<= ,var max) ,@body (inc ,var)))) The new definition of `for' has a new problem: it introduces a local variable named `max' which the user does not expect. This causes trouble in examples such as the following: (let ((max 0)) (for x from 0 to 10 do (let ((this (frob x))) (if (< max this) (setq max this))))) The references to `max' inside the body of the `for', which are supposed to refer to the user's binding of `max', really access the binding made by `for'. The way to correct this is to use an uninterned symbol instead of `max' (*note Creating Symbols::.). The uninterned symbol can be bound and referred to just like any other symbol, but since it is created by `for', we know that it cannot already appear in the user's program. Since it is not interned, there is no way the user can put it into the program later. It will never appear anywhere except where put by `for'. Here is a definition of `for' that works this way: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." (let ((tempvar (make-symbol "max"))) `(let ((,var ,init) (,tempvar ,final)) (while (<= ,var ,tempvar) ,@body (inc ,var))))) This creates an uninterned symbol named `max' and puts it in the expansion instead of the usual interned symbol `max' that appears in expressions ordinarily.  File: lispref.info, Node: Eval During Expansion, Next: Repeated Expansion, Prev: Surprising Local Vars, Up: Problems with Macros Evaluating Macro Arguments in Expansion --------------------------------------- Another problem can happen if you evaluate any of the macro argument expressions during the computation of the expansion, such as by calling `eval' (*note Eval::.). If the argument is supposed to refer to the user's variables, you may have trouble if the user happens to use a variable with the same name as one of the macro arguments. Inside the macro body, the macro argument binding is the most local binding of this variable, so any references inside the form being evaluated do refer to it. Here is an example: (defmacro foo (a) (list 'setq (eval a) t)) => foo (setq x 'b) (foo x) ==> (setq b t) => t ; and `b' has been set. ;; but (setq a 'c) (foo a) ==> (setq a t) => t ; but this set `a', not `c'. It makes a difference whether the user's variable is named `a' or `x', because `a' conflicts with the macro argument variable `a'. Another reason not to call `eval' in a macro definition is that it probably won't do what you intend in a compiled program. The byte-compiler runs macro definitions while compiling the program, when the program's own computations (which you might have wished to access with `eval') don't occur and its local variable bindings don't exist. The safe way to work with the run-time value of an expression is to put the expression into the macro expansion, so that its value is computed as part of executing the expansion.  File: lispref.info, Node: Repeated Expansion, Prev: Eval During Expansion, Up: Problems with Macros How Many Times is the Macro Expanded? ------------------------------------- Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded. In particular, constructing objects is a kind of side effect. If the macro is called once, then the objects are constructed only once. In other words, the same structure of objects is used each time the macro call is executed. In interpreted operation, the macro is reexpanded each time, producing a fresh collection of objects each time. Usually this does not matter--the objects have the same contents whether they are shared or not. But if the surrounding program does side effects on the objects, it makes a difference whether they are shared. Here is an example: (defmacro empty-object () (list 'quote (cons nil nil))) (defun initialize (condition) (let ((object (empty-object))) (if condition (setcar object condition)) object)) If `initialize' is interpreted, a new list `(nil)' is constructed each time `initialize' is called. Thus, no side effect survives between calls. If `initialize' is compiled, then the macro `empty-object' is expanded during compilation, producing a single "constant" `(nil)' that is reused and altered each time `initialize' is called. One way to avoid pathological cases like this is to think of `empty-object' as a funny kind of constant, not as a memory allocation construct. You wouldn't use `setcar' on a constant such as `'(nil)', so naturally you won't use it on `(empty-object)' either.  File: lispref.info, Node: Customization, Up: Top Writing Customization Definitions ********************************* This chapter describes how to declare user options for customization, and also customization groups for classifying them. We use the term "customization item" to include both kinds of customization definitions--as well as face definitions. * Menu: * Common Keywords:: * Group Definitions:: * Variable Definitions:: * Customization Types::  File: lispref.info, Node: Common Keywords, Next: Group Definitions, Up: Customization Common Keywords for All Kinds of Items ====================================== All kinds of customization declarations (for variables and groups, and for faces) accept keyword arguments for specifying various information. This section describes some keywords that apply to all kinds. All of these keywords, except `:tag', can be used more than once in a given item. Each use of the keyword has an independent effect. The keyword `:tag' is an exception because any given item can only display one name. `:tag NAME' Use NAME, a string, instead of the item's name, to label the item in customization menus and buffers. `:group GROUP' Put this customization item in group GROUP. When you use `:group' in a `defgroup', it makes the new group a subgroup of GROUP. If you use this keyword more than once, you can put a single item into more than one group. Displaying any of those groups will show this item. Be careful not to overdo this! `:link LINK-DATA' Include an external link after the documentation string for this item. This is a sentence containing an active field which references some other documentation. There are three alternatives you can use for LINK-DATA: `(custom-manual INFO-NODE)' Link to an Info node; INFO-NODE is a string which specifies the node name, as in `"(emacs)Top"'. The link appears as `[manual]' in the customization buffer. `(info-link INFO-NODE)' Like `custom-manual' except that the link appears in the customization buffer with the Info node name. `(url-link URL)' Link to a web page; URL is a string which specifies the URL. The link appears in the customization buffer as URL. You can specify the text to use in the customization buffer by adding `:tag NAME' after the first element of the LINK-DATA; for example, `(info-link :tag "foo" "(emacs)Top")' makes a link to the Emacs manual which appears in the buffer as `foo'. An item can have more than one external link; however, most items have none at all. `:load FILE' Load file FILE (a string) before displaying this customization item. Loading is done with `load-library', and only if the file is not already loaded. `:require FEATURE' Require feature FEATURE (a symbol) when installing a value for this item (an option or a face) that was saved using the customization feature. This is done by calling `require'. The most common reason to use `:require' is when a variable enables a feature such as a minor mode, and just setting the variable won't have any effect unless the code which implements the mode is loaded.  File: lispref.info, Node: Group Definitions, Next: Variable Definitions, Prev: Common Keywords, Up: Customization Defining Custom Groups ====================== Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twelve or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups. The package's main or only group should be a member of one or more of the standard customization groups. (To display the full list of them, use `M-x customize'.) Choose one or more of them (but not too many), and add your group to each of them using the `:group' keyword. The way to declare new customization groups is with `defgroup'. - Macro: defgroup GROUP MEMBERS DOC [KEYWORD VALUE]... Declare GROUP as a customization group containing MEMBERS. Do not quote the symbol GROUP. The argument DOC specifies the documentation string for the group. The argument MEMBERS is a list specifying an initial set of customization items to be members of the group. However, most often MEMBERS is `nil', and you specify the group's members by using the `:group' keyword when defining those members. If you want to specify group members through MEMBERS, each element should have the form `(NAME WIDGET)'. Here NAME is a symbol, and WIDGET is a widget type for editing that symbol. Useful widgets are `custom-variable' for a variable, `custom-face' for a face, and `custom-group' for a group. In addition to the common keywords (*note Common Keywords::.), you can use this keyword in `defgroup': `:prefix PREFIX' If the name of an item in the group starts with PREFIX, then the tag for that item is constructed (by default) by omitting PREFIX. One group can have any number of prefixes.  File: lispref.info, Node: Variable Definitions, Next: Customization Types, Prev: Group Definitions, Up: Customization Defining Customization Variables ================================ Use `defcustom' to declare user-editable variables. - Macro: defcustom OPTION DEFAULT DOC [KEYWORD VALUE]... Declare OPTION as a customizable user option variable. Do not quote OPTION. The argument DOC specifies the documentation string for the variable. If OPTION is void, `defcustom' initializes it to DEFAULT. DEFAULT should be an expression to compute the value; be careful in writing it, because it can be evaluated on more than one occasion. The following additional keywords are defined: `:type TYPE' Use TYPE as the data type for this option. It specifies which values are legitimate, and how to display the value. *Note Customization Types::, for more information. `:options LIST' Specify LIST as the list of reasonable values for use in this option. Currently this is meaningful only when the type is `hook'. In that case, the elements of LIST should be functions that are useful as elements of the hook value. The user is not restricted to using only these functions, but they are offered as convenient alternatives. `:version VERSION' This option specifies that the variable was first introduced, or its default value was changed, in Emacs version VERSION. The value VERSION must be a string. For example, (defcustom foo-max 34 "*Maximum number of foo's allowed." :type 'integer :group 'foo :version "20.3") `:set SETFUNCTION' Specify SETFUNCTION as the way to change the value of this option. The function SETFUNCTION should take two arguments, a symbol and the new value, and should do whatever is necessary to update the value properly for this option (which may not mean simply setting the option as a Lisp variable). The default for SETFUNCTION is `set-default'. `:get GETFUNCTION' Specify GETFUNCTION as the way to extract the value of this option. The function GETFUNCTION should take one argument, a symbol, and should return the "current value" for that symbol (which need not be the symbol's Lisp value). The default is `default-value'. `:initialize FUNCTION' FUNCTION should be a function used to initialize the variable when the `defcustom' is evaluated. It should take two arguments, the symbol and value. Here are some predefined functions meant for use in this way: `custom-initialize-set' Use the variable's `:set' function to initialize the variable, but do not reinitialize it if it is already non-void. This is the default `:initialize' function. `custom-initialize-default' Like `custom-initialize-set', but use the function `set-default' to set the variable, instead of the variable's `:set' function. This is the usual choice for a variable whose `:set' function enables or disables a minor mode; with this choice, defining the variable will not call the minor mode function, but customizing the variable will do so. `custom-initialize-reset' Always use the `:set' function to initialize the variable. If the variable is already non-void, reset it by calling the `:set' function using the current value (returned by the `:get' method). `custom-initialize-changed' Use the `:set' function to initialize the variable, if it is already set or has been customized; otherwise, just use `set-default'. The `:require' option is useful for an option that turns on the operation of a certain feature. Assuming that the package is coded to check the value of the option, you still need to arrange for the package to be loaded. You can do that with `:require'. *Note Common Keywords::. Here is an example, from the library `paren.el': (defcustom show-paren-mode nil "Toggle Show Paren mode...." :set (lambda (symbol value) (show-paren-mode (or value 0))) :initialize 'custom-initialize-default :type 'boolean :group 'paren-showing :require 'paren) Internally, `defcustom' uses the symbol property `standard-value' to record the expression for the default value, and `saved-value' to record the value saved by the user with the customization buffer. The `saved-value' property is actually a list whose car is an expression which evaluates to the value.  File: lispref.info, Node: Customization Types, Prev: Variable Definitions, Up: Customization Customization Types =================== When you define a user option with `defcustom', you must specify its "customization type". That is a Lisp object which describes (1) which values are legitimate and (2) how to display the value in the customization buffer for editing. You specify the customization type in `defcustom' with the `:type' keyword. The argument of `:type' is evaluated; since types that vary at run time are rarely useful, normally you use a quoted constant. For example: (defcustom diff-command "diff" "*The command to use to run diff." :type '(string) :group 'diff) In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (*note Type Keywords::.). Some of the type symbols do not use any arguments; those are called "simple types". For a simple type, if you do not use any keyword-value pairs, you can omit the parentheses around the type symbol. For example just `string' as a customization type is equivalent to `(string)'. * Menu: * Simple Types:: * Composite Types:: * Splicing into Lists:: * Type Keywords::  File: lispref.info, Node: Simple Types, Next: Composite Types, Up: Customization Types Simple Types ------------ This section describes all the simple customization types. `sexp' The value may be any Lisp object that can be printed and read back. You can use `sexp' as a fall-back for any option, if you don't want to take the time to work out a more specific type to use. `integer' The value must be an integer, and is represented textually in the customization buffer. `number' The value must be a number, and is represented textually in the customization buffer. `string' The value must be a string, and the customization buffer shows just the contents, with no delimiting `"' characters and no quoting with `\'. `regexp' Like `string' except that the string must be a valid regular expression. `character' The value must be a character code. A character code is actually an integer, but this type shows the value by inserting the character in the buffer, rather than by showing the number. `file' The value must be a file name, and you can do completion with `M-'. `(file :must-match t)' The value must be a file name for an existing file, and you can do completion with `M-'. `directory' The value must be a directory name, and you can do completion with `M-'. `symbol' The value must be a symbol. It appears in the customization buffer as the name of the symbol. `function' The value must be either a lambda expression or a function name. When it is a function name, you can do completion with `M-'. `variable' The value must be a variable name, and you can do completion with `M-'. `face' The value must be a symbol which is a face name. `boolean' The value is boolean--either `nil' or `t'. Note that by using `choice' and `const' together (see the next section), you can specify that the value must be `nil' or `t', but also specify the text to describe each value in a way that fits the specific meaning of the alternative.  File: lispref.info, Node: Composite Types, Next: Splicing into Lists, Prev: Simple Types, Up: Customization Types Composite Types --------------- When none of the simple types is appropriate, you can use composite types, which build new types from other types. Here are several ways of doing that: `(restricted-sexp :match-alternatives CRITERIA)' The value may be any Lisp object that satisfies one of CRITERIA. CRITERIA should be a list, and each elements should be one of these possibilities: * A predicate--that is, a function of one argument that returns non-`nil' if the argument fits a certain type. This means that objects of that type are acceptable. * A quoted constant--that is, `'OBJECT'. This means that OBJECT itself is an acceptable value. For example, (restricted-sexp :match-alternatives (integerp 't 'nil)) allows integers, `t' and `nil' as legitimate values. The customization buffer shows all legitimate values using their read syntax, and the user edits them textually. `(cons CAR-TYPE CDR-TYPE)' The value must be a cons cell, its CAR must fit CAR-TYPE, and its CDR must fit CDR-TYPE. For example, `(cons string symbol)' is a customization type which matches values such as `("foo" . foo)'. In the customization buffer, the CAR and the CDR are displayed and edited separately, each according to the type that you specify for it. `(list ELEMENT-TYPES...)' The value must be a list with exactly as many elements as the ELEMENT-TYPES you have specified; and each element must fit the corresponding ELEMENT-TYPE. For example, `(list integer string function)' describes a list of three elements; the first element must be an integer, the second a string, and the third a function. In the customization buffer, the each element is displayed and edited separately, according to the type specified for it. `(vector ELEMENT-TYPES...)' Like `list' except that the value must be a vector instead of a list. The elements work the same as in `list'. `(choice ALTERNATIVE-TYPES...)' The value must fit at least one of ALTERNATIVE-TYPES. For example, `(choice integer string)' allows either an integer or a string. In the customization buffer, the user selects one of the alternatives using a menu, and can then edit the value in the usual way for that alternative. Normally the strings in this menu are determined automatically from the choices; however, you can specify different strings for the menu by including the `:tag' keyword in the alternatives. For example, if an integer stands for a number of spaces, while a string is text to use verbatim, you might write the customization type this way, (choice (integer :tag "Number of spaces") (string :tag "Literal text")) so that the menu offers `Number of spaces' and `Literal Text'. In any alternative for which `nil' is not a valid value, other than a `const', you should specify a valid default for that alternative using the `:value' keyword. *Note Type Keywords::. `(const VALUE)' The value must be VALUE--nothing else is allowed. The main use of `const' is inside of `choice'. For example, `(choice integer (const nil))' allows either an integer or `nil'. `:tag' is often used with `const', inside of `choice'. For example, (choice (const :tag "Yes" t) (const :tag "No" nil) (const :tag "Ask" foo)) `(function-item FUNCTION)' Like `const', but used for values which are functions. This displays the documentation string as well as the function name. The documentation string is either the one you specify with `:doc', or FUNCTION's own documentation string. `(variable-item VARIABLE)' Like `const', but used for values which are variable names. This displays the documentation string as well as the variable name. The documentation string is either the one you specify with `:doc', or VARIABLE's own documentation string. `(set ELEMENTS...)' The value must be a list and each element of the list must be one of the ELEMENTS specified. This appears in the customization buffer as a checklist. `(repeat ELEMENT-TYPE)' The value must be a list and each element of the list must fit the type ELEMENT-TYPE. This appears in the customization buffer as a list of elements, with `[INS]' and `[DEL]' buttons for adding more elements or removing elements.  File: lispref.info, Node: Splicing into Lists, Next: Type Keywords, Prev: Composite Types, Up: Customization Types Splicing into Lists ------------------- The `:inline' feature lets you splice a variable number of elements into the middle of a list or vector. You use it in a `set', `choice' or `repeat' type which appears among the element-types of a `list' or `vector'. Normally, each of the element-types in a `list' or `vector' describes one and only one element of the list or vector. Thus, if an element-type is a `repeat', that specifies a list of unspecified length which appears as one element. But when the element-type uses `:inline', the value it matches is merged directly into the containing sequence. For example, if it matches a list with three elements, those become three elements of the overall sequence. This is analogous to using `,@' in the backquote construct. For example, to specify a list whose first element must be `t' and whose remaining arguments should be zero or more of `foo' and `bar', use this customization type: (list (const t) (set :inline t foo bar)) This matches values such as `(t)', `(t foo)', `(t bar)' and `(t foo bar)'. When the element-type is a `choice', you use `:inline' not in the `choice' itself, but in (some of) the alternatives of the `choice'. For example, to match a list which must start with a file name, followed either by the symbol `t' or two strings, use this customization type: (list file (choice (const t) (list :inline t string string))) If the user chooses the first alternative in the choice, then the overall list has two elements and the second element is `t'. If the user chooses the second alternative, then the overall list has three elements and the second and third must be strings.  File: lispref.info, Node: Type Keywords, Prev: Splicing into Lists, Up: Customization Types Type Keywords ------------- You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings: `:value DEFAULT' This is used for a type that appears as an alternative inside of `choice'; it specifies the default value to use, at first, if and when the user selects this alternative with the menu in the customization buffer. Of course, if the actual value of the option fits this alternative, it will appear showing the actual value, not DEFAULT. If `nil' is not a valid value for the alternative, then it is essential to specify a valid default with `:value'. `:format FORMAT-STRING' This string will be inserted in the buffer to represent the value corresponding to the type. The following `%' escapes are available for use in FORMAT-STRING: `%[BUTTON%]' Display the text BUTTON marked as a button. The `:action' attribute specifies what the button will do if the user invokes it; its value is a function which takes two arguments--the widget which the button appears in, and the event. There is no way to specify two different buttons with different actions. `%{SAMPLE%}' Show SAMPLE in a special face specified by `:sample-face'. `%v' Substitute the item's value. How the value is represented depends on the kind of item, and (for variables) on the customization type. `%d' Substitute the item's documentation string. `%h' Like `%d', but if the documentation string is more than one line, add an active field to control whether to show all of it or just the first line. `%t' Substitute the tag here. You specify the tag with the `:tag' keyword. `%%' Display a literal `%'. `:action ACTION' Perform ACTION if the user clicks on a button. `:button-face FACE' Use the face FACE (a face name or a list of face names) for button text displayed with `%[...%]'. `:button-prefix PREFIX' `:button-suffix SUFFIX' These specify the text to display before and after a button. Each can be: `nil' No text is inserted. a string The string is inserted literally. a symbol The symbol's value is used. `:tag TAG' Use TAG (a string) as the tag for the value (or part of the value) that corresponds to this type. `:doc DOC' Use DOC as the documentation string for this value (or part of the value) that corresponds to this type. In order for this to work, you must specify a value for `:format', and use `%d' or `%h' in that value. The usual reason to specify a documentation string for a type is to provide more information about the meanings of alternatives inside a `:choice' type or the parts of some other composite type. `:help-echo MOTION-DOC' When you move to this item with `widget-forward' or `widget-backward', it will display the string MOTION-DOC in the echo area. `:match FUNCTION' Specify how to decide whether a value matches the type. The corresponding value, FUNCTION, should be a function that accepts two arguments, a widget and a value; it should return non-`nil' if the value is acceptable.  File: lispref.info, Node: Loading, Next: Byte Compilation, Prev: Macros, Up: Top Loading ******* Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. XEmacs finds and opens the file, reads the text, evaluates each form, and then closes the file. The load functions evaluate all the expressions in a file just as the `eval-current-buffer' function evaluates all the expressions in a buffer. The difference is that the load functions read and evaluate the text in the file as found on disk, not the text in an Emacs buffer. The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a "top-level form". There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions. A file containing Lisp code is often called a "library". Thus, the "Rmail library" is a file containing code for Rmail mode. Similarly, a "Lisp library directory" is a directory of files containing Lisp code. * Menu: * How Programs Do Loading:: The `load' function and others. * Autoload:: Setting up a function to autoload. * Repeated Loading:: Precautions about loading a file twice. * Named Features:: Loading a library if it isn't already loaded. * Unloading:: How to "unload" a library that was loaded. * Hooks for Loading:: Providing code to be run when particular libraries are loaded.  File: lispref.info, Node: How Programs Do Loading, Next: Autoload, Up: Loading How Programs Do Loading ======================= XEmacs Lisp has several interfaces for loading. For example, `autoload' creates a placeholder object for a function in a file; trying to call the autoloading function loads the file to get the function's real definition (*note Autoload::.). `require' loads a file if it isn't already loaded (*note Named Features::.). Ultimately, all these facilities call the `load' function to do the work. - Function: load FILENAME &optional MISSING-OK NOMESSAGE NOSUFFIX This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file. To find the file, `load' first looks for a file named `FILENAME.elc', that is, for a file whose name is FILENAME with `.elc' appended. If such a file exists, it is loaded. If there is no file by that name, then `load' looks for a file named `FILENAME.el'. If that file exists, it is loaded. Finally, if neither of those names is found, `load' looks for a file named FILENAME with nothing appended, and loads it if it exists. (The `load' function is not clever about looking at FILENAME. In the perverse case of a file named `foo.el.el', evaluation of `(load "foo.el")' will indeed find it.) If the optional argument NOSUFFIX is non-`nil', then the suffixes `.elc' and `.el' are not tried. In this case, you must specify the precise file name you want. If FILENAME is a relative file name, such as `foo' or `baz/foo.bar', `load' searches for the file using the variable `load-path'. It appends FILENAME to each of the directories listed in `load-path', and loads the first file it finds whose name matches. The current default directory is tried only if it is specified in `load-path', where `nil' stands for the default directory. `load' tries all three possible suffixes in the first directory in `load-path', then all three suffixes in the second directory, and so on. If you get a warning that `foo.elc' is older than `foo.el', it means you should consider recompiling `foo.el'. *Note Byte Compilation::. Messages like `Loading foo...' and `Loading foo...done' appear in the echo area during loading unless NOMESSAGE is non-`nil'. Any unhandled errors while loading a file terminate loading. If the load was done for the sake of `autoload', any function definitions made during the loading are undone. If `load' can't find the file to load, then normally it signals the error `file-error' (with `Cannot open load file FILENAME'). But if MISSING-OK is non-`nil', then `load' just returns `nil'. You can use the variable `load-read-function' to specify a function for `load' to use instead of `read' for reading expressions. See below. `load' returns `t' if the file loads successfully. - User Option: load-path The value of this variable is a list of directories to search when loading files with `load'. Each element is a string (which must be a directory name) or `nil' (which stands for the current working directory). The value of `load-path' is initialized from the environment variable `EMACSLOADPATH', if that exists; otherwise its default value is specified in `emacs/src/paths.h' when XEmacs is built. The syntax of `EMACSLOADPATH' is the same as used for `PATH'; `:' (or `;', according to the operating system) separates directory names, and `.' is used for the current default directory. Here is an example of how to set your `EMACSLOADPATH' variable from a `csh' `.login' file: setenv EMACSLOADPATH .:/user/bil/emacs:/usr/lib/emacs/lisp Here is how to set it using `sh': export EMACSLOADPATH EMACSLOADPATH=.:/user/bil/emacs:/usr/local/lib/emacs/lisp Here is an example of code you can place in a `.emacs' file to add several directories to the front of your default `load-path': (setq load-path (append (list nil "/user/bil/emacs" "/usr/local/lisplib" "~/emacs") load-path)) In this example, the path searches the current working directory first, followed then by the `/user/bil/emacs' directory, the `/usr/local/lisplib' directory, and the `~/emacs' directory, which are then followed by the standard directories for Lisp code. The command line options `-l' or `-load' specify a Lisp library to load as part of Emacs startup. Since this file might be in the current directory, Emacs 18 temporarily adds the current directory to the front of `load-path' so the file can be found there. Newer Emacs versions also find such files in the current directory, but without altering `load-path'. Dumping Emacs uses a special value of `load-path'. If the value of `load-path' at the end of dumping is unchanged (that is, still the same special value), the dumped Emacs switches to the ordinary `load-path' value when it starts up, as described above. But if `load-path' has any other value at the end of dumping, that value is used for execution of the dumped Emacs also. Therefore, if you want to change `load-path' temporarily for loading a few libraries in `site-init.el' or `site-load.el', you should bind `load-path' locally with `let' around the calls to `load'. - Function: locate-file FILENAME PATH-LIST &optional SUFFIXES MODE This function searches for a file in the same way that `load' does, and returns the file found (if any). (In fact, `load' uses this function to search through `load-path'.) It searches for FILENAME through PATH-LIST, expanded by one of the optional SUFFIXES (string of suffixes separated by `:'s), checking for access MODE (0|1|2|4 = exists|executable|writeable|readable), default readable. `locate-file' keeps hash tables of the directories it searches through, in order to speed things up. It tries valiantly to not get confused in the face of a changing and unpredictable environment, but can occasionally get tripped up. In this case, you will have to call `locate-file-clear-hashing' to get it back on track. See that function for details. - Function: locate-file-clear-hashing PATH This function clears the hash records for the specified list of directories. `locate-file' uses a hashing scheme to speed lookup, and will correctly track the following environmental changes: * changes of any sort to the list of directories to be searched. * addition and deletion of non-shadowing files (see below) from the directories in the list. * byte-compilation of a .el file into a .elc file. `locate-file' will primarily get confused if you add a file that shadows (i.e. has the same name as) another file further down in the directory list. In this case, you must call `locate-file-clear-hashing'. - Variable: load-in-progress This variable is non-`nil' if Emacs is in the process of loading a file, and it is `nil' otherwise. - Variable: load-read-function This variable specifies an alternate expression-reading function for `load' and `eval-region' to use instead of `read'. The function should accept one argument, just as `read' does. Normally, the variable's value is `nil', which means those functions should use `read'. - User Option: load-warn-when-source-newer This variable specifies whether `load' should check whether the source is newer than the binary. If this variable is true, then when a `.elc' file is being loaded and the corresponding `.el' is newer, a warning message will be printed. The default is `nil', but it is bound to `t' during the initial loadup. - User Option: load-warn-when-source-only This variable specifies whether `load' should warn when loading a `.el' file instead of an `.elc'. If this variable is true, then when `load' is called with a filename without an extension, and the `.elc' version doesn't exist but the `.el' version does, then a message will be printed. If an explicit extension is passed to `load', no warning will be printed. The default is `nil', but it is bound to `t' during the initial loadup. - User Option: load-ignore-elc-files This variable specifies whether `load' should ignore `.elc' files when a suffix is not given. This is normally used only to bootstrap the `.elc' files when building XEmacs, when you use the command `make all-elc'. (This forces the `.el' versions to be loaded in the process of compiling those same files, so that existing out-of-date `.elc' files do not make it mess things up.) To learn how `load' is used to build XEmacs, see *Note Building XEmacs::.