(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.