X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=02b0a2ab0522f31a1ef251eee576acdee7e803f3;hb=59fa6266f00b6edcfc20c491c8de9a1b215dfa22;hp=69533dc5100ccba85c8a93d3e84f041e88c2ca43;hpb=4d7ac0e3227c408de20af4ef7898028863327492;p=ghc-hetmet.git

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 69533dc..02b0a2a 100644
--- a/compiler/types/FunDeps.lhs
+++ b/compiler/types/FunDeps.lhs
@@ -10,7 +10,7 @@ It's better to read it as: "if we know these, then we're going to know these"
 \begin{code}
 module FunDeps (
  	Equation, pprEquation,
-	oclose, grow, improveOne,
+	oclose, improveOne,
 	checkInstCoverage, checkFunDeps,
 	pprFundeps
     ) where
@@ -132,44 +132,6 @@ oclose preds fixed_tvs
 	      ]
 \end{code}
 
-Note [Growing the tau-tvs using constraints]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-(grow preds tvs) is the result of extend the set of tyvars tvs
-		 using all conceivable links from pred
-
-E.g. tvs = {a}, preds = {H [a] b, K (b,Int) c, Eq e}
-Then grow precs tvs = {a,b,c}
-
-All the type variables from an implicit parameter are added, whether or
-not they are mentioned in tvs; see Note [Implicit parameters and ambiguity] 
-in TcSimplify.
-
-See also Note [Ambiguity] in TcSimplify
-
-\begin{code}
-grow :: [PredType] -> TyVarSet -> TyVarSet
-grow preds fixed_tvs 
-  | null preds = fixed_tvs
-  | otherwise  = loop real_fixed_tvs
-  where
-	-- Add the implicit parameters; 
-	-- see Note [Implicit parameters and ambiguity] in TcSimplify
-    real_fixed_tvs = foldr unionVarSet fixed_tvs ip_tvs
- 
-    loop fixed_tvs
-	| new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs
-	| otherwise		  	      = loop new_fixed_tvs
-	where
-	  new_fixed_tvs = foldl extend fixed_tvs non_ip_tvs
-
-    extend fixed_tvs pred_tvs 
-	| fixed_tvs `intersectsVarSet` pred_tvs = fixed_tvs `unionVarSet` pred_tvs
-	| otherwise			        = fixed_tvs
-
-    (ip_tvs, non_ip_tvs) = partitionWith get_ip preds
-    get_ip (IParam _ ty) = Left (tyVarsOfType ty)
-    get_ip other         = Right (tyVarsOfPred other)
-\end{code}
     
 %************************************************************************
 %*									*
@@ -203,7 +165,7 @@ type Equation = (TyVarSet, [(Type, Type)])
 pprEquation :: Equation -> SDoc
 pprEquation (qtvs, pairs) 
   = vcat [ptext (sLit "forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)),
-	  nest 2 (vcat [ ppr t1 <+> ptext (sLit ":=:") <+> ppr t2 | (t1,t2) <- pairs])]
+	  nest 2 (vcat [ ppr t1 <+> ptext (sLit "~") <+> ppr t2 | (t1,t2) <- pairs])]
 \end{code}
 
 Given a bunch of predicates that must hold, such as
@@ -294,8 +256,9 @@ improveOne inst_env pred@(ClassP cls tys, _) preds
 	, not (instanceCantMatch inst_tcs trimmed_tcs)
 	, eqn <- checkClsFD qtvs fd cls_tvs tys_inst tys
 	, let p_inst = (mkClassPred cls tys_inst, 
-		        ptext (sLit "arising from the instance declaration at")
-			<+> ppr (getSrcLoc ispec))
+		        sep [ ptext (sLit "arising from the dependency") <+> quotes (pprFunDep fd)
+			    , ptext (sLit "in the instance declaration at") 
+			          <+> ppr (getSrcLoc ispec)])
 	]
 
 improveOne _ _ _
@@ -320,7 +283,7 @@ checkClsFD qtvs fd clas_tvs tys1 tys2
 --		    tys2 = [Maybe t1, t2]
 --
 -- We can instantiate x to t1, and then we want to force
--- 	(Tree x) [t1/x]  :=:   t2
+-- 	(Tree x) [t1/x]  ~   t2
 --
 -- This function is also used when matching two Insts (rather than an Inst
 -- against an instance decl. In that case, qtvs is empty, and we are doing
@@ -494,16 +457,16 @@ badFunDeps cls_insts clas ins_tv_set ins_tys
 
 trimRoughMatchTcs :: [TyVar] -> FunDep TyVar -> [Maybe Name] -> [Maybe Name]
 -- Computing rough_tcs for a particular fundep
---	class C a b c | a -> b where ... 
+--     class C a b c | a -> b where ...
 -- For each instance .... => C ta tb tc
--- we want to match only on the types ta, tc; so our
+-- we want to match only on the type ta; so our
 -- rough-match thing must similarly be filtered.  
--- Hence, we Nothing-ise the tb type right here
-trimRoughMatchTcs clas_tvs (_,rtvs) mb_tcs
+-- Hence, we Nothing-ise the tb and tc types right here
+trimRoughMatchTcs clas_tvs (ltvs, _) mb_tcs
   = zipWith select clas_tvs mb_tcs
   where
-    select clas_tv mb_tc | clas_tv `elem` rtvs = Nothing
-			 | otherwise	       = mb_tc
+    select clas_tv mb_tc | clas_tv `elem` ltvs = mb_tc
+                         | otherwise           = Nothing
 \end{code}