fboundp

fboundp name → generalized-boolean

[ ef bau̇ndpē ]

name — a function name.

generalized-boolean — a generalized boolean.

Returns true if name is fbound; otherwise, returns false.

 (fboundp 'car) → true 
 (fboundp 'nth-value) → false 
 (fboundp 'with-open-file) → true 
 (fboundp 'unwind-protect) → true 
 (defun my-function (x) x) → MY-FUNCTION 
 (fboundp 'my-function) → true 
 (let ((saved-definition (symbol-function 'my-function))) 
   (unwind-protect (progn (fmakunbound 'my-function) 
                          (fboundp 'my-function)) 
     (setf (symbol-function 'my-function) saved-definition))) 
→ false 
 (fboundp 'my-function) → true 
 (defmacro my-macro (x) `',x) → MY-MACRO 
 (fboundp 'my-macro) → true 
 (fmakunbound 'my-function) → MY-FUNCTION 
 (fboundp 'my-function) → false 
 (flet ((my-function (x) x)) 
   (fboundp 'my-function)) → false

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

symbol-function, fmakunbound, fdefinition

It is permissible to call symbol-function on any symbol that is fbound.

fboundp is sometimes used to “guard” an access to the function cell, as in:

(if (fboundp x) (symbol-function x))

Defining a setf expander F does not cause the setf function (setf F) to become defined.