X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=02b0a2ab0522f31a1ef251eee576acdee7e803f3;hb=0ae16401a0c73548ba4c08f588174f618c363a73;hp=786afa19640166a878d5e97eb44e16a18e0a9001;hpb=17b297d97d327620ed6bfab942f8992b2446f1bf;p=ghc-hetmet.git

diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs
index 786afa1..02b0a2a 100644
--- a/compiler/types/FunDeps.lhs
+++ b/compiler/types/FunDeps.lhs
@@ -8,16 +8,9 @@ FunDeps - functional dependencies
 It's better to read it as: "if we know these, then we're going to know these"
 
 \begin{code}
-{-# OPTIONS_GHC -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/WorkingConventions#Warnings
--- for details
-
 module FunDeps (
  	Equation, pprEquation,
-	oclose, grow, improveOne,
+	oclose, improveOne,
 	checkInstCoverage, checkFunDeps,
 	pprFundeps
     ) where
@@ -27,13 +20,16 @@ module FunDeps (
 import Name
 import Var
 import Class
-import TcGadt
 import TcType
+import Unify
 import InstEnv
 import VarSet
 import VarEnv
 import Outputable
 import Util
+import FastString
+
+import Data.List	( nubBy )
 import Data.Maybe	( isJust )
 \end{code}
 
@@ -136,44 +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 = 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 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}
     
 %************************************************************************
 %*									*
@@ -204,9 +162,10 @@ type Equation = (TyVarSet, [(Type, Type)])
 -- We usually act on an equation by instantiating the quantified type varaibles
 -- to fresh type variables, and then calling the standard unifier.
 
+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])]
+  = vcat [ptext (sLit "forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)),
+	  nest 2 (vcat [ ppr t1 <+> ptext (sLit "~") <+> ppr t2 | (t1,t2) <- pairs])]
 \end{code}
 
 Given a bunch of predicates that must hold, such as
@@ -250,7 +209,7 @@ improveOne :: (Class -> [Instance])		-- Gives instances for given class
 						-- combined (for error messages)
 -- Just do improvement triggered by a single, distinguised predicate
 
-improveOne inst_env pred@(IParam ip ty, _) preds
+improveOne _inst_env pred@(IParam ip ty, _) preds
   = [ ((emptyVarSet, [(ty,ty2)]), pred, p2) 
     | p2@(IParam ip2 ty2, _) <- preds
     , ip==ip2
@@ -297,11 +256,12 @@ 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 inst_env eq_pred preds
+improveOne _ _ _
   = []
 
 
@@ -323,7 +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
@@ -473,7 +433,8 @@ badFunDeps :: [Instance] -> Class
 	   -> TyVarSet -> [Type]	-- Proposed new instance type
 	   -> [Instance]
 badFunDeps cls_insts clas ins_tv_set ins_tys 
-  = [ ispec | fd <- fds,	-- fds is often empty
+  = nubBy eq_inst $
+    [ ispec | fd <- fds,	-- fds is often empty, so do this first!
 	      let trimmed_tcs = trimRoughMatchTcs clas_tvs fd rough_tcs,
 	      ispec@(Instance { is_tcs = inst_tcs, is_tvs = tvs, 
 				is_tys = tys }) <- cls_insts,
@@ -486,19 +447,26 @@ badFunDeps cls_insts clas ins_tv_set ins_tys
   where
     (clas_tvs, fds) = classTvsFds clas
     rough_tcs = roughMatchTcs ins_tys
+    eq_inst i1 i2 = instanceDFunId i1 == instanceDFunId i2
+	-- An single instance may appear twice in the un-nubbed conflict list
+	-- because it may conflict with more than one fundep.  E.g.
+	--	class C a b c | a -> b, a -> c
+	--	instance C Int Bool Bool
+	--	instance C Int Char Char
+	-- The second instance conflicts with the first by *both* fundeps
 
 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}