The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
See also the function
indirect-function. See Definition of indirect-function.
function symbol-function symbol
This returns the object in the function cell of
symbol. It does not check that the returned object is a legitimate function.
If the function cell is void, the return value is
nil. To distinguish between a function cell that is void and one set to
fboundp (see below).
(defun bar (n) (+ n 2))
⇒ (lambda (n) (+ n 2))
(fset 'baz 'bar)
If you have never given a symbol any function definition, we say that that symbol’s function cell is void. In other words, the function cell does not have any Lisp object in it. If you try to call the symbol as a function, Emacs signals a
Note that void is not the same as
nil or the symbol
void. The symbols
void are Lisp objects, and can be stored into a function cell just as any other object can be (and they can be valid functions if you define them in turn with
defun). A void function cell contains no object whatsoever.
You can test the voidness of a symbol’s function definition with
fboundp. After you have given a symbol a function definition, you can make it void once more using
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
This function makes
symbol’s function cell void, so that a subsequent attempt to access this cell will cause a
void-function error. It returns
symbol. (See also
makunbound, in Void Variables.)
(defun foo (x) x)
error→ Symbol's function definition is void: foo
function fset symbol definition
This function stores
definition in the function cell of
symbol. The result is
definition should be a function or the name of a function, but this is not checked. The argument
symbol is an ordinary evaluated argument.
The primary use of this function is as a subroutine by constructs that define or alter functions, like
advice-add (see Advising Functions). You can also use it to give a symbol a function definition that is not a function, e.g., a keyboard macro (see Keyboard Macros):
;; Define a named keyboard macro.
(fset 'kill-two-lines "\^u2\^k")
It you wish to use
fset to make an alternate name for a function, consider using
defalias instead. See Definition of defalias.