GADTs and scoped type variables don't work right

In this program, which is also in the testsuite as gadt/scoped.hs, all three definitions of g should work

{-# OPTIONS_GHC -XGADTs -XScopedTypeVariables -XPatternSignatures #-}

module GADT where

data C x y where
     C :: a -> C a a

data D x y where
     D :: C b c -> D a c

-------  All these should be ok

-- Rejected!
g1 :: forall x y . C x y -> ()
-- C (..) :: C x y
-- Inside match on C, x=y
g1 (C (p :: y)) = ()

-- OK!
g2 :: forall x y . C x y -> ()
-- C (..) :: C x y
-- Inside match on C, x=y
g2 (C (p :: x)) = ()

-- Rejected!
g3 :: forall x y . D x y -> ()
-- D (..)  :: D x y
-- C (..)  :: C sk y
--	sk = y
-- p :: sk
g3 (D (C (p :: y))) = ()

But they don't. The reason is that the "refinement" is applied to the environment only after checking an entire pattern; but the refinement is needed during checking the pattern if scoped type variables are to work right.

I don't propose to fix this, because it'll come out in the wash when we get rid of type refinements in favour of equality constraints.

Trac metadata

Trac field	Value
Version	6.8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ganesh@earth.li
Operating system	Unknown
Architecture	Unknown