Portable way to get a function's arg list (ala Control-Shift-A)?

[hall@aplcen.apl.jhu.edu (Marty Hall)]

Is there a portable way to get the parameter list to a function?
Ie I want a way to be able to tell the user that function Foo
has two required args named xxx and yyy and one &optional arg
named zzz with a default value of aaa, just as Symbolics does
with control-shift-A (and elsewhere).  I tried to see how Symbolics did
it, but I couldn't find anything portable, especially as I'm not
allowed to assume anything about the structure of the object "function"
or "symbol-function" returns (right?). IS there a way?

I assume the answer is "no", but I wanted to confirm this with the
wizards.
					- Marty
(setf (need-p 'disclaimer) NIL)