On 20 March 2006 12:26, Bulat Ziganshin wrote:
2) to allow "changing" of strictness inside existing ADTs, i propose to "copy" strictness annotations on type arguments to the type declaration bodies:
data List a = Nil | Cons (List a) a type StrictElements a = List !a
is equal to the:
data StrictElements a = Nil | Cons (List a) !a
So, in fact StrictElements is not compatible with the List type at all (that is, you can't pass a value of type (StrictElements Int) to a function expecting (List Int)). I can envisage that this might be a sound extension, and imlementable, but is it what you mean? I don't think so. I imagine you want a lot of automatic conversion back and forth bewteen strict and lazy types. This is where it gets a *lot* trickier, starting with the type system.
i.e. it's the same list but each element is strict. using strictness annotation on type constructor itself should mean strictifying of all other (non-type-variable) fields:
type StrictList a = !List a => data StrictList a = !Nil | !Cons !(List a) a
I don't know what !Nil or !Cons mean.
of course, i don't mean introducing new incompatible types - that is a compiler responsibility (sorry, Simon :)
Well, you haven't told me what type system I need to implement, so it's not just an implementation issue. And it seems to me that you *are* introducing incompatible types. Cheers, Simon