Tom Ellis
I can't bind unlifted values at the top level:
foo = (##)
Top-level bindings for unlifted types aren't allowed: foo = (##)
I can understand why I shouldn't be able to bind unlifted *expressions* at the top level
foo = complicatedExpression
Perhaps complicatedExpression doesn't terminate! But why can't I bind _values_, i.e. things that are already evaluated? Given that (##) and proxy# already exist at the top-level it seems reasonable that I should be allowed to define my own!
There are a few things going on here. The case you give here is not just unlifted but also unboxed (namely, being an unboxed tuple). It's hard to see how top-level binding of unboxed values would work operationally (e.g. how is the garbage collector to know how to trace this object, given that unboxed objects have no object header?). However, I suspect you do have a point when it comes to unlifted data constructors. I think it would be fine to allow an application of a data constructor of an unlifted type on the top-level: type UMaybe :: Type -> UnliftedType data UMaybe a = UNothing | UJust a x :: UMaybe Int x = UJust 42 Perhaps you could open a ticket for this? Cheers, - Ben