symbol-function (Accessor)

Syntax:

(setf (symbol-function symbol) new-contents)

Arguments and Values:

symbol—a symbol.

contents— If the symbol is globally defined as a macro or a special operator, an object of implementation-dependent nature and identity is returned. If the symbol is not globally defined as either a macro or a special operator, and if the symbol is fbound, a function object is returned.

new-contents—a function.

Description:

Accesses the symbol's function cell.

Examples:

 (symbol-function 'car) → #<FUNCTION CAR>
 (symbol-function 'twice) is an error   ;because TWICE isn't defined.
 (defun twice (n) (* n 2)) → TWICE
 (symbol-function 'twice) → #<FUNCTION TWICE>
 (list (twice 3)
       (funcall (function twice) 3)
       (funcall (symbol-function 'twice) 3))
→ (6 6 6)
 (flet ((twice (x) (list x x)))
   (list (twice 3)
         (funcall (function twice) 3)
         (funcall (symbol-function 'twice) 3)))
→ ((3 3) (3 3) 6)
 (setf (symbol-function 'twice) #'(lambda (x) (list x x)))
→ #<FUNCTION anonymous>
 (list (twice 3)
       (funcall (function twice) 3)
       (funcall (symbol-function 'twice) 3))
→ ((3 3) (3 3) (3 3))
 (fboundp 'defun) → true
 (symbol-function 'defun)
→ implementation-dependent
 (functionp (symbol-function 'defun))
→ implementation-dependent
 (defun symbol-function-or-nil (symbol)
   (if (and (fboundp symbol)
            (not (macro-function symbol))
            (not (special-operator-p symbol)))
       (symbol-function symbol)
       nil)) → SYMBOL-FUNCTION-OR-NIL
 (symbol-function-or-nil 'car) → #<FUNCTION CAR>
 (symbol-function-or-nil 'defun) → NIL

Affected By:

defun

Exceptional Situations:

Should signal an error of type type-error if symbol is not a symbol.

Should signal undefined-function if symbol is not fbound and an attempt is made to read its definition. (No such error is signaled on an attempt to write its definition.)

See Also:

fboundp, fmakunbound, macro-function, special-operator-p

Notes:

symbol-function cannot access the value of a lexical function name produced by flet or labels; it can access only the global function value.

setf may be used with symbol-function to replace a global function definition when the symbol's function definition does not represent a special operator.

(symbol-function symbol) ≡ (fdefinition symbol)

However, fdefinition accepts arguments other than just symbols.