How many arguments does a function take?

Question

How can i get a lambda list specification of a some function parameters, or at least a number of arguments it takes?

For example:

(defun a (a b) )
(get-arg-list #'a) ;-> '(a b)

Answer 1

Common Lisp provides the function FUNCTION-LAMBDA-EXPRESSION which may be able to recover the source expression, which then includes the lambda list.

LispWorks has defined a function FUNCTION-LAMBDA-LIST which returns the arglist.

Many other implementations have some form of ARGLIST function in some internal package.

Many Common Lisp users use SLIME, a very clever editor extension for the GNU Emacs editor. It has a backend for Common Lisp called SWANK. The SWANK sources provide all kinds of interfaces to the various Common Lisp implementations, including getting the arglist of functions.

Answer 2

This is implementation specific, but this CLHS function might get you started - http://clhs.lisp.se/Body/f_descri.htm