Accessor symbol-function

Syntax:

Arguments and Values:

The symbol need not be fbound for the SETF form. --sjl 16 Mar 92 \param{symbol}---an \term{fbound} \term{symbol}.symbol—a symbol.

contents— If the symbol is globally defined as a macro or a special operator, Removed per Barrett. -kmp 14-Feb-92 and if the \param{symbol} is \term{fbound},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. This shouldn't be needed, actually. \issue{FUNCTION-TYPE:X3J13-MARCH-88} The consequences of attempting to make the global \term{function} definition of a \term{symbol} be a \term{symbol}, a \term{list}, or the value returned by \funref{symbol-function} on the name of a \term{macro} or a \term{special form} are unspecified. \endissue{FUNCTION-TYPE:X3J13-MARCH-88}

Description:

7.1.1 14Accesses the symbol's function cell.

Examples:

Some examples involving FBOUNDP simplified/corrected per Moore #2 (first public review) -kmp 12-May-93

 (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

Side Effects:

None.

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:

!!! Sandra thinks this should be in the Description. I'm not so sure. -kmp 13-Dec-91setf 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)