X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcSimplify.lhs;h=8632895b10893c194b036a2ab034c8f7490d6d0c;hb=2f223e8f4a4e2fb22a8bb0638cd48256e9f2f0e2;hp=cd3da492bf6016d7ad0431e33387013c621c6990;hpb=296058a1cafa80dec0b3f998348bce7c65f668b0;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index cd3da49..8632895 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -45,7 +45,6 @@ import Class
 import FunDeps
 import PrelInfo
 import PrelNames
-import Type
 import TysWiredIn
 import ErrUtils
 import BasicTypes
@@ -54,7 +53,6 @@ import VarEnv
 import FiniteMap
 import Bag
 import Outputable
-import Maybes
 import ListSetOps
 import Util
 import SrcLoc
@@ -1589,13 +1587,23 @@ Simpler, maybe, but alas not simple (see Trac #2494)
 tcSimplifyRuleLhs :: [Inst] -> TcM ([Inst], TcDictBinds)
 tcSimplifyRuleLhs wanteds
   = do	{ wanteds' <- zonkInsts wanteds
-	; (irreds, binds) <- go [] emptyBag wanteds'
+    	
+		-- Simplify equalities  
+		-- It's important to do this: Trac #3346 for example
+        ; (_, wanteds'', tybinds, binds1) <- tcReduceEqs [] wanteds'
+        ; execTcTyVarBinds tybinds
+
+	  	-- Simplify other constraints
+	; (irreds, binds2) <- go [] emptyBag wanteds''
+
+	  	-- Report anything that is left
 	; let (dicts, bad_irreds) = partition isDict irreds
 	; traceTc (text "tcSimplifyrulelhs" <+> pprInsts bad_irreds)
 	; addNoInstanceErrs (nub bad_irreds)
 		-- The nub removes duplicates, which has
 		-- not happened otherwise (see notes above)
-	; return (dicts, binds) }
+
+	; return (dicts, binds1 `unionBags` binds2) }
   where
     go :: [Inst] -> TcDictBinds -> [Inst] -> TcM ([Inst], TcDictBinds)
     go irreds binds []
@@ -1637,7 +1645,7 @@ this bracket again at its usage site.
 \begin{code}
 tcSimplifyBracket :: [Inst] -> TcM ()
 tcSimplifyBracket wanteds
-  = do	{ tryHardCheckLoop doc wanteds
+  = do	{ _ <- tryHardCheckLoop doc wanteds
 	; return () }
   where
     doc = text "tcSimplifyBracket"
@@ -2856,6 +2864,7 @@ disambiguate doc interactive dflags insts
 
   where
    extended_defaulting = interactive || dopt Opt_ExtendedDefaultRules dflags
+   		       -- See also Trac #1974
    ovl_strings = dopt Opt_OverloadedStrings dflags
 
    unaries :: [(Inst, Class, TcTyVar)]  -- (C tv) constraints
@@ -2902,12 +2911,16 @@ disambigGroup :: [Type]			-- The default types
 	      -> TcM ()	-- Just does unification, to fix the default types
 
 disambigGroup default_tys dicts
-  = try_default default_tys
+  = do { mb_chosen_ty <- try_default default_tys
+       ; case mb_chosen_ty of
+            Nothing        -> return ()
+            Just chosen_ty -> do { _ <- unifyType chosen_ty (mkTyVarTy tyvar) 
+	    	 	         ; warnDefault dicts chosen_ty } }
   where
     (_,_,tyvar) = ASSERT(not (null dicts)) head dicts	-- Should be non-empty
     classes = [c | (_,c,_) <- dicts]
 
-    try_default [] = return ()
+    try_default [] = return Nothing
     try_default (default_ty : default_tys)
       = tryTcLIE_ (try_default default_tys) $
     	do { tcSimplifyDefault [mkClassPred clas [default_ty] | clas <- classes]
@@ -2917,10 +2930,7 @@ disambigGroup default_tys dicts
 		-- For example, if Real a is reqd, but the only type in the
 		-- default list is Int.
 
-		-- After this we can't fail
-	   ; warnDefault dicts default_ty
-	   ; unifyType default_ty (mkTyVarTy tyvar) 
-	   ; return () -- TOMDO: do something with the coercion
+	   ; return (Just default_ty) -- TOMDO: do something with the coercion
 	   }