fdefinition function-name → definition

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

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.

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.

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.

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

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.