fdefinition

fdefinition Accessor

Syntax:

fdefinition function-name → definition

(setf (fdefinition function-name**)** new-definition**)**

Arguments and Values:

function-name—a function name. In the non-setf case, the name must be fbound in the global environment.

definition—Current global function definition named by function-name.

new-definition—a function.

Description:

fdefinition accesses the current global function definition named by function-name. The definition may be a function or may be an object representing a special form or macro. The value returned by fdefinition when fboundp returns true but the function-name denotes a macro or special form is not well-defined, but fdefinition does not signal an error.

Exceptional Situations:

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

An error of type undefined-function is signaled in the non-setf case if function-name is not fbound.

See Also:

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

Notes:

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

setf can be used with fdefinition to replace a global function definition when the function-name’s function definition does not represent a special form. setf of fdefinition requires a function as the new value. It is an error to set the fdefinition of a function-name to a symbol, a list, or the value returned by fdefinition on the name of a macro or special form.

Data and Control

fboundp

Expanded Reference: fdefinition

The function name that is set with (setf (fdefinition does not have to be fbound in the global environment. Therefore this can be useful for defining new functions programatically for them to be available in the global environment.

CL-USER> (setf (fdefinition 'foo) (lambda (x) (+ x 1)))
#<FUNCTION (LAMBDA (X)) {5436EE0B}>
CL-USER> (foo 3)
4 (3 bits, #x4, #o4, #b100)

This can be useful when wanting to bind a function returned from another function to a global name.

Notice that fdefinition is a function, so that its arguments are evaluated. Thus, if it is desirable to use a literal function name, it must be quoted.

If the name argument is not quoted, it will be taken to be the name of a variable, and if that variable does not have a value, an error will be signaled:

CL-USER> (setf (fdefinition bar) (lambda (x) (+ x 1)))
; in: SETF (FDEFINITION BAR)
;     (#:BAR2176 BAR)
; 
; caught WARNING:
;   undefined variable: COMMON-LISP-USER::BAR
; 
; compilation unit finished
;   Undefined variable:
;     BAR
;   caught 1 WARNING condition
; Debugger entered on #<UNBOUND-VARIABLE BAR {1005485F93}>

The variable BAR is unbound.
   [Condition of type UNBOUND-VARIABLE]