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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 ,
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.