Re more powerful constant creation: There's already a VTABLE method for constructing PMCs from STRINGs, e.g:
=item C<PMC new_from_string(STRING *rep, INTVAL flags)> Class method to construct an array from the string representation C<rep>, which is a string I<"(el0, el1, ...)">. used for creating param/args signature arrays inside src/pmc/fixedintegerarray.pmc.
