Variadic Multi-Dispatch (or, M-D on certain invocants only)

[chromatic]

Hi there,

I have a spot in Pheme where I'd like to use multi-dispatch on only the first 
argument to a function.  The function itself is slurpy.  That is:

        .sub some_function :multi( Array )
                .param pmc args
                # ...
        .end

        .sub some_function :multi( string )
                .param string first_arg
                .param pmc    args :slurpy
                # ...
        .end

I can't seem to get this to work.  I'm ambivalent whether the right approach 
is to require a special "maybe variadic" marker in the multi param list or to 
say that any multi params are the only dispatchable invocants and let the 
remaining params, if any, go unchecked.

Another approach is fine too.

Now I probably *should* handle this elsewhere in the Pheme compiler, but it 
seems like an issue that may come up in other places.

-- c