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.
This function does not check that the returned object is a legitimate function.(defun bar (n) (+ n 2)) (symbol-function 'bar) ⇒ (lambda (n) (+ n 2)) (fset 'baz 'bar) ⇒ bar (symbol-function '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 such a symbol
as a function, it 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
This function returns
tif the symbol has an object in its function cell,
nilotherwise. It does not check that the object is a legitimate function.
This function makes symbol's function cell void, so that a subsequent attempt to access this cell will cause a
void-functionerror. It returns symbol. (See also
makunbound, in Void Variables.)(defun foo (x) x) (foo 1) ⇒1 (fmakunbound 'foo) ⇒ foo (foo 1) error--> Symbol's function definition is void: foo
This function stores definition in the function cell of symbol. The result is definition. Normally 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
defadvice(see Advising Functions). (If
defunwere not a primitive, it could be written as a Lisp macro using
fset.) You can also use it to give a symbol a function definition that is not a list, e.g., a keyboard macro (see Keyboard Macros):;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") ⇒ "\^u2\^k"
It you wish to use
fsetto make an alternate name for a function, consider using
defaliasinstead. See Definition of defalias.