Next: Lambda Expressions, Up: Functions
In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other function-like objects.
car
or append
. These functions are also called
built-in functions or subrs. (Special forms are also
considered primitives.)
Usually the reason we implement a function as a primitive is either
because it is fundamental, because it provides a low-level interface to
operating system services, or because it needs to run fast. Primitives
can be modified or added only by changing the C sources and recompiling
the editor. See Writing Emacs Primitives.
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 (see 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.
Keyboard macros (strings and vectors) are commands also, even though
they are not functions. A symbol is a command if its function
definition is a command; such symbols can be invoked with M-x.
The symbol is a function as well if the definition is a function.
See Command Overview.
This function returns
t
if object is any kind of function, or a special form or macro.
This function returns
t
if object is a built-in function (i.e., a Lisp primitive).(subrp 'message) ;message
is a symbol, => nil ; not a subr object. (subrp (symbol-function 'message)) => t
This function returns
t
if object is a byte-code function. For example:(byte-code-function-p (symbol-function 'next-line)) => t
This function provides information about the argument list of a primitive, subr. The returned value is a pair
(
min.
max)
. min is the minimum number of args. max is the maximum number or the symbolmany
, for a function with&rest
arguments, or the symbolunevalled
if subr is a special form.