-This is Info file ../info/lispref.info, produced by Makeinfo version
-1.68 from the input file lispref/lispref.texi.
+This is ../info/lispref.info, produced by makeinfo version 4.0 from
+lispref/lispref.texi.
INFO-DIR-SECTION XEmacs Editor
START-INFO-DIR-ENTRY
Foundation instead of in the original English.
\1f
+File: lispref.info, Node: Default Value, Prev: Creating Buffer-Local, Up: Buffer-Local Variables
+
+The Default Value of a Buffer-Local Variable
+--------------------------------------------
+
+ The global value of a variable with buffer-local bindings is also
+called the "default" value, because it is the value that is in effect
+except when specifically overridden.
+
+ The functions `default-value' and `setq-default' access and change a
+variable's default value regardless of whether the current buffer has a
+buffer-local binding. For example, you could use `setq-default' to
+change the default setting of `paragraph-start' for most buffers; and
+this would work even when you are in a C or Lisp mode buffer that has a
+buffer-local value for this variable.
+
+ The special forms `defvar' and `defconst' also set the default value
+(if they set the variable at all), rather than any local value.
+
+ - Function: default-value symbol
+ This function returns SYMBOL's default value. This is the value
+ that is seen in buffers that do not have their own values for this
+ variable. If SYMBOL is not buffer-local, this is equivalent to
+ `symbol-value' (*note Accessing Variables::).
+
+ - Function: default-boundp symbol
+ The function `default-boundp' tells you whether SYMBOL's default
+ value is nonvoid. If `(default-boundp 'foo)' returns `nil', then
+ `(default-value 'foo)' would get an error.
+
+ `default-boundp' is to `default-value' as `boundp' is to
+ `symbol-value'.
+
+ - Special Form: setq-default symbol value
+ This sets the default value of SYMBOL to VALUE. It does not
+ evaluate SYMBOL, but does evaluate VALUE. The value of the
+ `setq-default' form is VALUE.
+
+ If a SYMBOL is not buffer-local for the current buffer, and is not
+ marked automatically buffer-local, `setq-default' has the same
+ effect as `setq'. If SYMBOL is buffer-local for the current
+ buffer, then this changes the value that other buffers will see
+ (as long as they don't have a buffer-local value), but not the
+ value that the current buffer sees.
+
+ ;; In buffer `foo':
+ (make-local-variable 'local)
+ => local
+ (setq local 'value-in-foo)
+ => value-in-foo
+ (setq-default local 'new-default)
+ => new-default
+ local
+ => value-in-foo
+ (default-value 'local)
+ => new-default
+
+ ;; In (the new) buffer `bar':
+ local
+ => new-default
+ (default-value 'local)
+ => new-default
+ (setq local 'another-default)
+ => another-default
+ (default-value 'local)
+ => another-default
+
+ ;; Back in buffer `foo':
+ local
+ => value-in-foo
+ (default-value 'local)
+ => another-default
+
+ - Function: set-default symbol value
+ This function is like `setq-default', except that SYMBOL is
+ evaluated.
+
+ (set-default (car '(a b c)) 23)
+ => 23
+ (default-value 'a)
+ => 23
+
+\1f
File: lispref.info, Node: Variable Aliases, Prev: Buffer-Local Variables, Up: Variables
Variable Aliases
returned. Any time you change the value of the former variable, the
value of the latter is actually changed. This is useful in cases where
you want to rename a variable but still make old code work (*note
-Obsoleteness::.).
+Obsoleteness::).
- - Function: defvaralias VARIABLE ALIAS
+ - Function: defvaralias variable alias
This function defines VARIABLE as an alias for ALIAS.
Thenceforth, any operations performed on VARIABLE will actually be
performed on ALIAS. Both VARIABLE and ALIAS should be symbols.
variable, a variable that has a buffer-local value in any buffer,
or the symbols `nil' or `t'.
- - Function: variable-alias VARIABLE
+ - Function: variable-alias variable
If VARIABLE is aliased to another variable, this function returns
that variable. VARIABLE should be a symbol. If VARIABLE is not
aliased, this function returns `nil'.
- - Function: indirect-variable OBJECT
+ - Function: indirect-variable object
This function returns the variable at the end of OBJECT's
variable-alias chain. If OBJECT is a symbol, follow all variable
aliases and return the final (non-aliased) symbol. If OBJECT is
A "command" is an object that `command-execute' can invoke; it is
a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
- interactive declaration (*note Defining Commands::.). Such a
+ interactive declaration (*note Defining Commands::). Such a
function can be called from Lisp expressions like other functions;
in this case, the fact that the function is a command makes no
difference.
A "compiled function" is a function that has been compiled by the
byte compiler. *Note Compiled-Function Type::.
- - Function: subrp OBJECT
+ - Function: subrp object
This function returns `t' if OBJECT is a built-in function (i.e.,
a Lisp primitive).
(subrp (symbol-function 'message))
=> t
- - Function: compiled-function-p OBJECT
+ - Function: compiled-function-p object
This function returns `t' if OBJECT is a compiled function. For
example:
It is not often useful to write a lambda expression as the CAR of a
form in this way. You can get the same result, of making local
variables and giving them values, using the special form `let' (*note
-Local Variables::.). And `let' is clearer and easier to use. In
+Local Variables::). And `let' is clearer and easier to use. In
practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
-arguments to other functions (*note Anonymous Functions::.).
+arguments to other functions (*note Anonymous Functions::).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form `let' was invented. At that
source file, but since these spaces come before the starting
double-quote, they are not part of the string. Some people make a
practice of indenting any additional lines of the string so that the
-text lines up in the program source. *This is a mistake.* The
+text lines up in the program source. _This is a mistake._ The
indentation of the following lines is inside the string; what looks
nice in the source code will look ugly when displayed by the help
commands.
However, a symbol can serve as the name of a function. This happens
when you put the function in the symbol's "function cell" (*note Symbol
-Components::.). Then the symbol itself becomes a valid, callable
+Components::). Then the symbol itself becomes a valid, callable
function, equivalent to the list or subr-object that its function cell
refers to. The contents of the function cell are also called the
symbol's "function definition". The procedure of using a symbol's
distinguish.
Even so, keep in mind that a function need not have a unique name.
-While a given function object *usually* appears in the function cell of
+While a given function object _usually_ appears in the function cell of
only one symbol, this is just a matter of convenience. It is easy to
store it in several symbols using `fset'; then each of the symbols is
equally well a name for the same function.
is called "defining a function", and it is done with the `defun'
special form.
- - Special Form: defun NAME ARGUMENT-LIST BODY-FORMS
+ - Special Form: defun name argument-list body-forms
`defun' is the usual way to define new Lisp functions. It defines
the symbol NAME as a function that looks like this:
`defun' stores this lambda expression in the function cell of
NAME. It returns the value NAME, but usually we ignore this value.
- As described previously (*note Lambda Expressions::.),
+ As described previously (*note Lambda Expressions::),
ARGUMENT-LIST is a list of argument names and may include the
keywords `&optional' and `&rest'. Also, the first two forms in
BODY-FORMS may be a documentation string and an interactive
distinguish deliberate redefinition from unintentional
redefinition.
- - Function: define-function NAME DEFINITION
- - Function: defalias NAME DEFINITION
+ - Function: define-function name definition
+ - Function: defalias name definition
These equivalent special forms define the symbol NAME as a
function, with definition DEFINITION (which can be any valid Lisp
function).
specific function name is being defined--especially where that
name appears explicitly in the source file being loaded. This is
because `define-function' and `defalias' record which file defined
- the function, just like `defun'. (*note Unloading::.).
+ the function, just like `defun'. (*note Unloading::).
By contrast, in programs that manipulate function definitions for
other purposes, it is better to use `fset', which does not keep
run time which function to call. To do that, use the functions
`funcall' and `apply'.
- - Function: funcall FUNCTION &rest ARGUMENTS
+ - Function: funcall function &rest arguments
`funcall' calls FUNCTION with ARGUMENTS, and returns whatever
FUNCTION returns.
that you can use any expression to obtain the function to be
called. It also means that `funcall' does not see the expressions
you write for the ARGUMENTS, only their values. These values are
- *not* evaluated a second time in the act of calling FUNCTION;
+ _not_ evaluated a second time in the act of calling FUNCTION;
`funcall' enters the normal procedure for calling a function at the
place where the arguments have already been evaluated.
Compare these example with the examples of `apply'.
- - Function: apply FUNCTION &rest ARGUMENTS
+ - Function: apply function &rest arguments
`apply' calls FUNCTION with ARGUMENTS, just like `funcall' but
with one difference: the last of ARGUMENTS is a list of arguments
to give to FUNCTION, rather than a single argument. We also say
function as the argument. Here are two different kinds of no-op
function:
- - Function: identity ARG
+ - Function: identity arg
This function returns ARG and has no side effects.
- - Function: ignore &rest ARGS
+ - Function: ignore &rest args
This function ignores any arguments and returns `nil'.
\1f
Mapping functions should never modify the sequence being mapped over.
The results are unpredictable.
- - Function: mapcar FUNCTION SEQUENCE
+ - Function: mapcar function sequence
`mapcar' applies FUNCTION to each element of SEQUENCE in turn, and
returns a list of the results.
=> (2 3 4)
(mapcar 'char-to-string "abc")
=> ("a" "b" "c")
-
+
;; Call each function in `my-hooks'.
(mapcar 'funcall my-hooks)
-
+
(defun mapcar* (f &rest args)
"Apply FUNCTION to successive cars of all ARGS.
Return the list of results."
(apply 'mapcar* f
;; Recurse for rest of elements.
(mapcar 'cdr args)))))
-
+
(mapcar* 'cons '(a b c) '(1 2 3 4))
=> ((a . 1) (b . 2) (c . 3))
- - Function: mapconcat FUNCTION SEQUENCE SEPARATOR
+ - Function: mapconcat function sequence separator
`mapconcat' applies FUNCTION to each element of SEQUENCE: the
results, which must be strings, are concatenated. Between each
pair of result strings, `mapconcat' inserts the string SEPARATOR.
'(The cat in the hat)
" ")
=> "The cat in the hat"
-
+
(mapconcat (function (lambda (x) (format "%c" (1+ x))))
"HAL-8000"
"")
=> (lambda (x) (+ 12 x))
This computes a list that looks like `(lambda (x) (+ 12 x))' and makes
-it the value (*not* the function definition!) of `silly'.
+it the value (_not_ the function definition!) of `silly'.
Here is how we might call this function:
(funcall silly 1)
=> 13
-(It does *not* work to write `(silly 1)', because this function is not
-the *function definition* of `silly'. We have not given `silly' any
+(It does _not_ work to write `(silly 1)', because this function is not
+the _function definition_ of `silly'. We have not given `silly' any
function definition, just a value as a variable.)
Most of the time, anonymous functions are constants that appear in
In such cases, we usually use the special form `function' instead of
simple quotation to quote the anonymous function.
- - Special Form: function FUNCTION-OBJECT
+ - Special Form: function function-object
This special form returns FUNCTION-OBJECT without evaluating it.
In this, it is equivalent to `quote'. However, it serves as a
note to the XEmacs Lisp compiler that FUNCTION-OBJECT is intended
See also the function `indirect-function' in *Note Function
Indirection::.
- - Function: symbol-function SYMBOL
+ - Function: symbol-function symbol
This returns the object in the function cell of SYMBOL. If the
symbol's function cell is void, a `void-function' error is
signaled.
`fboundp'. After you have given a symbol a function definition, you
can make it void once more using `fmakunbound'.
- - Function: fboundp SYMBOL
+ - Function: fboundp symbol
This function returns `t' if the symbol has an object in its
function cell, `nil' otherwise. It does not check that the object
is a legitimate function.
- - Function: fmakunbound SYMBOL
+ - Function: fmakunbound symbol
This function makes SYMBOL's function cell void, so that a
subsequent attempt to access this cell will cause a `void-function'
error. (See also `makunbound', in *Note Local Variables::.)
(foo 1)
error--> Symbol's function definition is void: foo
- - Function: fset SYMBOL OBJECT
+ - Function: fset symbol object
This function stores OBJECT in the function cell of SYMBOL. The
result is OBJECT. Normally OBJECT should be a function or the
name of a function, but this is not checked.
(list 'setq var (list '1+ var)))
When this is called with `(inc x)', the argument `var' has the value
-`x'--*not* the *value* of `x'. The body of the macro uses this to
+`x'--_not_ the _value_ of `x'. The body of the macro uses this to
construct the expansion, which is `(setq x (1+ x))'. Once the macro
definition returns this expansion, Lisp proceeds to evaluate it, thus
incrementing `x'.
You can see the expansion of a given macro call by calling
`macroexpand'.
- - Function: macroexpand FORM &optional ENVIRONMENT
+ - Function: macroexpand form &optional environment
This function expands FORM, if it is a macro call. If the result
is another macro call, it is expanded in turn, until something
which is not a macro call results. That is the value returned by
(defmacro inc (var)
(list 'setq var (list '1+ var)))
=> inc
-
+
(macroexpand '(inc r))
=> (setq r (1+ r))
-
+
(defmacro inc2 (var1 var2)
(list 'progn (list 'inc var1) (list 'inc var2)))
=> inc2
-
+
(macroexpand '(inc2 r s))
=> (progn (inc r) (inc s)) ; `inc' not expanded here.
-\1f
-File: lispref.info, Node: Compiling Macros, Next: Defining Macros, Prev: Expansion, Up: Macros
-
-Macros and Byte Compilation
-===========================
-
- You might ask why we take the trouble to compute an expansion for a
-macro and then evaluate the expansion. Why not have the macro body
-produce the desired results directly? The reason has to do with
-compilation.
-
- When a macro call appears in a Lisp program being compiled, the Lisp
-compiler calls the macro definition just as the interpreter would, and
-receives an expansion. But instead of evaluating this expansion, it
-compiles the expansion as if it had appeared directly in the program.
-As a result, the compiled code produces the value and side effects
-intended for the macro, but executes at full compiled speed. This would
-not work if the macro body computed the value and side effects
-itself--they would be computed at compile time, which is not useful.
-
- In order for compilation of macro calls to work, the macros must be
-defined in Lisp when the calls to them are compiled. The compiler has a
-special feature to help you do this: if a file being compiled contains a
-`defmacro' form, the macro is defined temporarily for the rest of the
-compilation of that file. To use this feature, you must define the
-macro in the same file where it is used and before its first use.
-
- Byte-compiling a file executes any `require' calls at top-level in
-the file. This is in case the file needs the required packages for
-proper compilation. One way to ensure that necessary macro definitions
-are available during compilation is to require the files that define
-them (*note Named Features::.). To avoid loading the macro definition
-files when someone *runs* the compiled program, write
-`eval-when-compile' around the `require' calls (*note Eval During
-Compile::.).
-
-\1f
-File: lispref.info, Node: Defining Macros, Next: Backquote, Prev: Compiling Macros, Up: Macros
-
-Defining Macros
-===============
-
- A Lisp macro is a list whose CAR is `macro'. Its CDR should be a
-function; expansion of the macro works by applying the function (with
-`apply') to the list of unevaluated argument-expressions from the macro
-call.
-
- It is possible to use an anonymous Lisp macro just like an anonymous
-function, but this is never done, because it does not make sense to pass
-an anonymous macro to functionals such as `mapcar'. In practice, all
-Lisp macros have names, and they are usually defined with the special
-form `defmacro'.
-
- - Special Form: defmacro NAME ARGUMENT-LIST BODY-FORMS...
- `defmacro' defines the symbol NAME as a macro that looks like this:
-
- (macro lambda ARGUMENT-LIST . BODY-FORMS)
-
- This macro object is stored in the function cell of NAME. The
- value returned by evaluating the `defmacro' form is NAME, but
- usually we ignore this value.
-
- The shape and meaning of ARGUMENT-LIST is the same as in a
- function, and the keywords `&rest' and `&optional' may be used
- (*note Argument List::.). Macros may have a documentation string,
- but any `interactive' declaration is ignored since macros cannot be
- called interactively.
-
projects / chise / xemacs-chise.git- / blobdiff