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  ANSI Common Lisp   10 Symbols   10.2 Dictionary of Symbols

10.2.10 symbol-function Accessor

symbol-function symbol    contents

(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.

Accesses the symbol's function cell.

 (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)
 (functionp (symbol-function 'defun))
 (defun symbol-function-or-nil (symbol)
   (if (and (fboundp symbol) 
            (not (macro-function symbol))
            (not (special-operator-p symbol)))
       (symbol-function symbol)
 (symbol-function-or-nil 'car)  #<FUNCTION CAR>
 (symbol-function-or-nil 'defun)   NIL

Affected By:

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

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.

Allegro CL Implementation Details:

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