testing arity

[Jon Wilson]

Hi,
Is there a good way to determine the number of arguments that a given 
procedure will take?  I suppose I can look at
(source proc)
and extract the list of formals, and write a procedure which does this 
automatically, but I'd hate to reinvent the wheel.  Also, I'm not sure how 
well using source will work when we have optional or keyword arguments.

Also, on an unrelated note, is it possible to define values (as in (lambda 
() (values 1 2)) ) in terms of McCarthy's original seven lisp primitives? 
Or would this question be better asked somewhere else (like c.l.scheme)?
Regards,
Jon