Friends

I propose that we support the GHC proposal “Declare Constraint is not apart from Type”

Currently GHC operates an uneasy compromise:

• Constraint and Type are treated as distinct in the type checker (e.g. do not unify)
• But they are treated as the same in Core

I have spent ages in discussion with Richard and others for how to fix this wart.  Really, they should be either

• completely different (like Int and Bool), or
• completely the same (like [Char] and String).

But both these stances have problems, and nothing satisfying has emerged.  So this proposal simply fixes the worst aspect (unsoundness) of the current setup.

So I regard it as a way to stay explicitly non-committal, leaving the main question open.

There are a couple of clarifications I’d like which I’ve put on the discussion thread.

Simon