[m-dev.] subtyping proposal (repost)

[Ralph Becket]

This all looks like good stuff to me.  The second syntax suggestion
gets my vote on aesthetic grounds (can't think of anything straight
away to otherwise differentiate between them).  Anything that makes
the mode system less hassle to use is a Good Thing, IMHO.

> 	One problem with this proposal as it stands is that using the
> 	mode system for subtypes doesn't work well with polymorphic
> 	predicates or containers.
> 
> 	We could fix these problems by adding support for polymorphic
> 	modes, with the inst variables required to name ground insts.
> 	This restriction would make polymorphic modes relatively easy
> 	to implement.  For polymorphically typed predicates, we could
> 	propagate type information into the modes so that all
polymorphically
> 	typed predicates also become polymorphically moded.

Would this mode propagation render the now polymorphic mode
declarations redundant, then?

Ralph
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