X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FInst.lhs;h=1496ec5e172e08ee3de520f1f9b232084a25c59e;hb=820ddd55446773b33c797267bcad9e09a621ab2b;hp=cee4b8955fac71db268e649abdce19897328727f;hpb=6c5637803d14fd1035c38235123b4c112d1c2b00;p=ghc-hetmet.git

diff --git a/compiler/typecheck/Inst.lhs b/compiler/typecheck/Inst.lhs
index cee4b89..1496ec5 100644
--- a/compiler/typecheck/Inst.lhs
+++ b/compiler/typecheck/Inst.lhs
@@ -37,7 +37,6 @@ import HsSyn
 import TcHsSyn
 import TcRnMonad
 import TcEnv
-import TcRnTypes
 import InstEnv
 import FunDeps
 import TcMType
@@ -89,7 +88,7 @@ newMethodFromName :: CtOrigin -> Name -> TcRhoType -> TcM (HsExpr TcId)
 newMethodFromName origin name inst_ty
   = do { id <- tcLookupId name
  	      -- Use tcLookupId not tcLookupGlobalId; the method is almost
-	      -- always a class op, but with -XNoImplicitPrelude GHC is
+	      -- always a class op, but with -XRebindableSyntax GHC is
 	      -- meant to find whatever thing is in scope, and that may
 	      -- be an ordinary function. 
 
@@ -295,7 +294,7 @@ mkOverLit (HsIsString s) = return (HsString s)
 %*									*
 %************************************************************************
 
-Suppose we are doing the -XNoImplicitPrelude thing, and we encounter
+Suppose we are doing the -XRebindableSyntax thing, and we encounter
 a do-expression.  We have to find (>>) in the current environment, which is
 done by the rename. Then we have to check that it has the same type as
 Control.Monad.(>>).  Or, more precisely, a compatible type. One 'customer' had
@@ -372,8 +371,8 @@ syntaxNameCtxt name orig ty tidy_env = do
 getOverlapFlag :: TcM OverlapFlag
 getOverlapFlag 
   = do 	{ dflags <- getDOpts
-	; let overlap_ok    = dopt Opt_OverlappingInstances dflags
-	      incoherent_ok = dopt Opt_IncoherentInstances  dflags
+	; let overlap_ok    = xopt Opt_OverlappingInstances dflags
+	      incoherent_ok = xopt Opt_IncoherentInstances  dflags
 	      overlap_flag | incoherent_ok = Incoherent
 			   | overlap_ok    = OverlapOk
 			   | otherwise     = NoOverlap
@@ -405,10 +404,18 @@ addLocalInst home_ie ispec
 		-- This is important because the template variables must
 		-- not overlap with anything in the things being looked up
 		-- (since we do unification).  
-		-- We use tcInstSkolType because we don't want to allocate fresh
-		--  *meta* type variables.  
+                --
+                -- We use tcInstSkolType because we don't want to allocate fresh
+                --  *meta* type variables.
+                --
+                -- We use UnkSkol --- and *not* InstSkol or PatSkol --- because
+                -- these variables must be bindable by tcUnifyTys.  See
+                -- the call to tcUnifyTys in InstEnv, and the special
+                -- treatment that instanceBindFun gives to isOverlappableTyVar
+                -- This is absurdly delicate.
+
 	  let dfun = instanceDFunId ispec
-	; (tvs', theta', tau') <- tcInstSkolType InstSkol (idType dfun)
+        ; (tvs', theta', tau') <- tcInstSkolType UnkSkol (idType dfun)
 	; let	(cls, tys') = tcSplitDFunHead tau'
 		dfun' 	    = setIdType dfun (mkSigmaTy tvs' theta' tau')	    
 	  	ispec'      = setInstanceDFunId ispec dfun'
@@ -474,11 +481,9 @@ hasEqualities :: [EvVar] -> Bool
 -- Has a bunch of canonical constraints (all givens) got any equalities in it?
 hasEqualities givens = any (has_eq . evVarPred) givens
   where
-    has_eq (EqPred {}) 	    = True
-    has_eq (IParam {}) 	    = False
-    has_eq (ClassP cls tys) = any has_eq (substTheta subst (classSCTheta cls))
-      where
-        subst = zipOpenTvSubst (classTyVars cls) tys
+    has_eq (EqPred {}) 	     = True
+    has_eq (IParam {}) 	     = False
+    has_eq (ClassP cls _tys) = any has_eq (classSCTheta cls)
 
 ----------------
 tyVarsOfWanteds :: WantedConstraints -> TyVarSet