Type families: bug fixes

[ghc-hetmet.git] / compiler / typecheck / Inst.lhs

diff --git a/compiler/typecheck/Inst.lhs b/compiler/typecheck/Inst.lhs
index 1a8efe2..c009ebe 100644 (file)
--- a/compiler/typecheck/Inst.lhs
+++ b/compiler/typecheck/Inst.lhs
@@ -45,7 +45,8 @@ module Inst (
         mkIdEqInstCo, mkSymEqInstCo, mkLeftTransEqInstCo,
         mkRightTransEqInstCo, mkAppEqInstCo,
         isValidWantedEqInst,
-       eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst, finalizeEqInst, 
+       eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst,
+        wantedToLocalEqInst, finalizeEqInst, 
        eqInstType, updateEqInstCoercion,
        eqInstCoercion, eqInstTys
     ) where
@@ -1095,6 +1096,15 @@ mkWantedEqInst pred@(EqPred ty1 ty2)
        }
 mkWantedEqInst pred = pprPanic "mkWantedEqInst" (ppr pred)
 
+-- Turn a wanted equality into a local that propagates the uninstantiated
+-- coercion variable as witness.  We need this to propagate wanted irreds into
+-- attempts to solve implication constraints.
+--
+wantedToLocalEqInst :: Inst -> Inst
+wantedToLocalEqInst eq@(EqInst {tci_co = Left cotv})
+  = eq {tci_co = Right (mkTyVarTy cotv)}
+wantedToLocalEqInst eq = eq
+
 -- Turn a wanted into a local EqInst (needed during type inference for
 -- signatures) 
 --