X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=b8b97b11e2d3a2835c89cba9840cd995c42d4b5f;hb=c8732b3c99e93c36ad28e23d2b901b794e89542a;hp=06248b7b3cd4a79ee1ee6f534fb050be078e2b89;hpb=ab22f4e6456820c1b5169d75f5975a94e61f54ce;p=ghc-hetmet.git

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 06248b7..b8b97b1 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, improve, 
+	oclose, grow, improve, improveOne,
 	checkInstCoverage, checkFunDeps,
 	pprFundeps
     ) where
@@ -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}
     
 %************************************************************************
@@ -229,6 +246,63 @@ improve inst_env preds
 	-- In any case, improvement *generates*, rather than
 	-- *consumes*, equality constraints
 
+improveOne :: (Class -> [Instance])
+	   -> Pred_Loc
+	   -> [Pred_Loc]
+	   -> [(Equation,Pred_Loc,Pred_Loc)]
+
+-- Just do improvement triggered by a single, distinguised predicate
+
+improveOne inst_env pred@(IParam ip ty, _) preds
+  = [ ((emptyVarSet, [(ty,ty2)]), pred, p2) 
+    | p2@(IParam ip2 ty2, _) <- preds
+    , ip==ip2
+    , not (ty `tcEqType` ty2)]
+
+improveOne inst_env pred@(ClassP cls tys, _) preds
+  | tys `lengthAtLeast` 2
+  = instance_eqns ++ pairwise_eqns
+	-- NB: we put the instance equations first.   This biases the 
+	-- order so that we first improve individual constraints against the
+	-- instances (which are perhaps in a library and less likely to be
+	-- wrong; and THEN perform the pairwise checks.
+	-- The other way round, it's possible for the pairwise check to succeed
+	-- and cause a subsequent, misleading failure of one of the pair with an
+	-- instance declaration.  See tcfail143.hs for an example
+  where
+    (cls_tvs, cls_fds) = classTvsFds cls
+    instances	       = inst_env cls
+    rough_tcs 	       = roughMatchTcs tys
+
+	-- NOTE that we iterate over the fds first; they are typically
+	-- empty, which aborts the rest of the loop.
+    pairwise_eqns :: [(Equation,Pred_Loc,Pred_Loc)]
+    pairwise_eqns	-- This group comes from pairwise comparison
+      = [ (eqn, pred, p2)
+	| fd <- cls_fds
+	, p2@(ClassP cls2 tys2, _) <- preds
+	, cls == cls2
+	, eqn <- checkClsFD emptyVarSet fd cls_tvs tys tys2
+	]
+
+    instance_eqns :: [(Equation,Pred_Loc,Pred_Loc)]
+    instance_eqns	-- This group comes from comparing with instance decls
+      = [ (eqn, p_inst, pred)
+	| fd <- cls_fds		-- Iterate through the fundeps first, 
+				-- because there often are none!
+	, 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_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")
+			<+> ppr (getSrcLoc ispec))
+	]
+
+improveOne inst_env eq_pred preds
+  = []
+
 ----------
 checkGroup :: (Class -> [Instance])
 	   -> [Pred_Loc]