Type specification of &optional arguments.

[Gregor.pa@Xerox.ARPA]

The main problem with specialization by number of arguments is that it
adds complexity to the method-lookup rules. We shied away from more
complicated method-lookup rules in the kernel because we weren't sure
what it would be like to program with them.  In particular,  we haven't
actually programmed with type specification of &optional arguments so we
can't say how hard it is (for the programmer) to figure out which
methods get inherited and how.

There are no problems implementing type specification of &optional
arguments.  Once we have a little more experience programming with type
specification of &optional arguments and can say what its like with more
assurance I think we will suggest that the kernel be extended to include
it.