Commit 428bee9c authored by Simon Peyton Jones's avatar Simon Peyton Jones Committed by pcapriotti
Browse files

Don't assume that coercion variables have (~) types

The constraint solver doesn't zonk the types of coercion variables
so we can't assume that a coercion variable will have a (~) type.

Fixes Trac #7090.

MERGED from commit d6918e90
parent 4709d3e1
......@@ -36,7 +36,7 @@ import Var
import PprCore () -- Instance OutputableBndr TyVar
import TypeRep -- Knows type representation
import TcType
import Type( tyConAppArgN, getEqPredTys_maybe, tyConAppTyCon_maybe, getEqPredTys )
import Type( tyConAppArgN, tyConAppTyCon_maybe, getEqPredTys )
import TysPrim( funTyCon )
import TyCon
import PrelNames
......@@ -114,7 +114,7 @@ isEqVar v = case tyConAppTyCon_maybe (varType v) of
isTcReflCo_maybe :: TcCoercion -> Maybe TcType
isTcReflCo_maybe (TcRefl ty) = Just ty
isTcReflCo_maybe _ = Nothing
isTcReflCo_maybe _ = Nothing
isTcReflCo :: TcCoercion -> Bool
isTcReflCo (TcRefl {}) = True
......@@ -185,13 +185,12 @@ mkTcInstCos co tys = foldl TcInstCo co tys
mkTcCoVarCo :: EqVar -> TcCoercion
-- ipv :: s ~ t (the boxed equality type)
mkTcCoVarCo ipv
| ty1 `eqType` ty2 = TcRefl ty1
| otherwise = TcCoVarCo ipv
(ty1, ty2) = case getEqPredTys_maybe (varType ipv) of
Nothing -> pprPanic "mkCoVarLCo" (ppr ipv)
Just tys -> tys
mkTcCoVarCo ipv = TcCoVarCo ipv
-- Previously I checked for (ty ~ ty) and generated Refl,
-- but in fact ipv may not even (visibly) have a (t1 ~ t2) type, because
-- the constraint solver does not substitute in the types of
-- evidence variables as it goes. In any case, the optimisation
-- will be done in the later zonking phase
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