X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcUnify.lhs;h=21578c0d747a62558c3be9096124073401d984a4;hb=25f84fa7e4b84c3db5ba745a7881c009b778e0b1;hp=c9def341360c63c00ddcf8ab0501744fd8e77fc2;hpb=5822cb8d13aa3c05d2b46b4510c13d94b902eb21;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs
index c9def34..21578c0 100644
--- a/compiler/typecheck/TcUnify.lhs
+++ b/compiler/typecheck/TcUnify.lhs
@@ -6,6 +6,13 @@
 Type subsumption and unification
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module TcUnify (
 	-- Full-blown subsumption
   tcSubExp, tcFunResTy, tcGen, 
@@ -1362,9 +1369,15 @@ involves the unfication x = y. It is deferred until we bring into account the
 context x ~ y to establish that it holds.
 
 If available, we defer original types (rather than those where closed type
-synonyms have already been expanded via tcCoreView).  This is as usual, to
+synonyms have already been expanded via tcCoreView).  This is, as usual, to
 improve error messages.
 
+We need to both 'unBox' and zonk deferred types.  We need to unBox as
+functions, such as TcExpr.tcMonoExpr promise to fill boxes in the expected
+type.  We need to zonk as the types go into the kind of the coercion variable
+`cotv' and those are not zonked in Inst.zonkInst.  (Maybe it would be better
+to zonk in zonInst instead.  Would that be sufficient?)
+
 \begin{code}
 defer_unification :: Bool               -- pop innermost context?
                   -> SwapFlag
@@ -1374,8 +1387,8 @@ defer_unification :: Bool               -- pop innermost context?
 defer_unification outer True ty1 ty2
   = defer_unification outer False ty2 ty1
 defer_unification outer False ty1 ty2
-  = do	{ ty1' <- zonkTcType ty1
- 	; ty2' <- zonkTcType ty2
+  = do	{ ty1' <- unBox ty1 >>= zonkTcType      -- unbox *and* zonk..
+ 	; ty2' <- unBox ty2 >>= zonkTcType      -- ..see preceding note
         ; traceTc $ text "deferring:" <+> ppr ty1 <+> text "~" <+> ppr ty2
 	; cotv <- newMetaTyVar TauTv (mkCoKind ty1' ty2')
 		-- put ty1 ~ ty2 in LIE