RE: Unlifted primop types

Simon Peyton Jones writes:

| Huh! It looks like what we currently do for some primops is just use a | totally bogus kind. For example, mkWeak# will happily accept an Int# as | its first argument.

Well, I see primop MkWeakOp "mkWeak#" GenPrimOp o -> b -> (State# RealWorld -> (# State# RealWorld, c #))

and I believe (from Ben's message) that the "o" means "open type variable", which is the old terminology for what we now call levity-polymorphic.

Right; currently (largely for historical reasons) we use `o` to accommodate cases that accept both lifted and unlifted pointers. Cheers, - Ben