X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=b8b97b11e2d3a2835c89cba9840cd995c42d4b5f;hp=cad292b1207230ed1c3ed784538a270c5ac107ec;hb=2e9952b703341351298739b5d4f869fbdfc8490e;hpb=dfcbc18e016540cb136ec3298a07a4a55b488db0

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index cad292b..b8b97b1 100644
--- a/compiler/types/FunDeps.lhs
+++ b/compiler/types/FunDeps.lhs
@@ -21,8 +21,6 @@ import Name
 import Var
 import Class
 import TcGadt
-import Type
-import Coercion
 import TcType
 import InstEnv
 import VarSet
@@ -125,24 +123,43 @@ 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
--- See Note [Ambiguity] in TcSimplify
 grow preds fixed_tvs 
-  | null preds = fixed_tvs
-  | otherwise  = loop fixed_tvs
+  | null preds = real_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 pred_sets
+	  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
 
-    pred_sets = [tyVarsOfPred pred | pred <- preds]
+    (ip_tvs, non_ip_tvs) = partitionWith get_ip preds
+    get_ip (IParam _ ty) = Left (tyVarsOfType ty)
+    get_ip other         = Right (tyVarsOfPred other)
 \end{code}
     
 %************************************************************************
@@ -276,7 +293,7 @@ improveOne inst_env pred@(ClassP cls tys, _) preds
 	, let rough_fd_tcs = trimRoughMatchTcs cls_tvs fd rough_tcs
 	, ispec@(Instance { is_tvs = qtvs, is_tys = tys_inst, 
 		 	    is_tcs = mb_tcs_inst }) <- instances
-	, not (instanceCantMatch mb_tcs_inst rough_tcs)
+	, not (instanceCantMatch mb_tcs_inst rough_fd_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")