X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=compiler%2Ftypecheck%2FTcSimplify.lhs;h=47c92af1f39f61bb6ae4812d2713d7a41e821c54;hb=041c35e5d9f3aefab6908b4c776a3fd8242720ab;hp=708b8e4d7873c5b7c3abfe73e3d447b047bd0ca2;hpb=fd17403d85c172ba898bc9a4817bb4f9e175bf8f;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 708b8e4..47c92af 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -849,10 +849,11 @@ bindIrredsR loc qtvs co_vars reft givens irreds
 		-- The givens can include methods
 		-- See Note [Pruning the givens in an implication constraint]
 
-	   -- If there are no 'givens', then it's safe to 
+	   -- If there are no 'givens' *and* the refinement is empty
+	   -- (the refinement is like more givens), then it's safe to 
 	   -- partition the 'wanteds' by their qtvs, thereby trimming irreds
 	   -- See Note [Freeness and implications]
-	; irreds' <- if null givens'
+	; irreds' <- if null givens' && isEmptyRefinement reft
 	     	     then do
 	     	    	{ let qtv_set = mkVarSet qtvs
 	     	    	      (frees, real_irreds) = partition (isFreeWrtTyVars qtv_set) irreds
@@ -862,7 +863,8 @@ bindIrredsR loc qtvs co_vars reft givens irreds
 	
 	; let all_tvs = qtvs ++ co_vars	-- Abstract over all these
 	; (implics, bind) <- makeImplicationBind loc all_tvs reft givens' irreds'
-				-- This call does the real work
+			-- This call does the real work
+			-- If irreds' is empty, it does something sensible
 	; extendLIEs implics
 	; return bind } 
 
@@ -875,6 +877,8 @@ makeImplicationBind :: InstLoc -> [TcTyVar] -> Refinement
 -- The binding looks like
 --	(ir1, .., irn) = f qtvs givens
 -- where f is (evidence for) the new implication constraint
+--	f :: forall qtvs. {reft} givens => (ir1, .., irn)
+-- qtvs includes coercion variables
 --
 -- This binding must line up the 'rhs' in reduceImplication
 makeImplicationBind loc all_tvs reft
@@ -2190,9 +2194,8 @@ tc_simplify_top doc interactive wanteds
 	-- OK, so there are some errors
 	{	-- Use the defaulting rules to do extra unification
 		-- NB: irreds are already zonked
-	; extended_default <- if interactive then return True
-			      else doptM Opt_ExtendedDefaultRules
-	; disambiguate extended_default irreds1	-- Does unification
+	; dflags <- getDOpts
+	; disambiguate interactive dflags irreds1	-- Does unification
 	; (irreds2, binds2) <- topCheckLoop doc irreds1
 
 		-- Deal with implicit parameter
@@ -2240,10 +2243,10 @@ Since we're not using the result of @foo@, the result if (presumably)
 @void@.
 
 \begin{code}
-disambiguate :: Bool -> [Inst] -> TcM ()
+disambiguate :: Bool -> DynFlags -> [Inst] -> TcM ()
 	-- Just does unification to fix the default types
 	-- The Insts are assumed to be pre-zonked
-disambiguate extended_defaulting insts
+disambiguate interactive dflags insts
   | null defaultable_groups
   = do { traceTc (text "disambigutate" <+> vcat [ppr unaries, ppr bad_tvs, ppr defaultable_groups])
 	;     return () }
@@ -2256,10 +2259,17 @@ disambiguate extended_defaulting insts
 					-- use [Integer, Double]
 				do { integer_ty <- tcMetaTy integerTyConName
 				   ; checkWiredInTyCon doubleTyCon
-				   ; return [integer_ty, doubleTy] }
+				   ; string_ty <- tcMetaTy stringTyConName
+				   ; if ovl_strings 	-- Add String if -foverloaded-strings
+					then return [integer_ty,doubleTy,string_ty] 
+					else return [integer_ty,doubleTy] }
+
 	; traceTc (text "disambigutate" <+> vcat [ppr unaries, ppr bad_tvs, ppr defaultable_groups])
 	; mapM_ (disambigGroup default_tys) defaultable_groups  }
   where
+   extended_defaulting = interactive || dopt Opt_ExtendedDefaultRules dflags
+   ovl_strings = dopt Opt_OverloadedStrings dflags
+
    unaries :: [(Inst,Class, TcTyVar)]  -- (C tv) constraints
    bad_tvs :: TcTyVarSet	  -- Tyvars mentioned by *other* constraints
    (unaries, bad_tvs) = getDefaultableDicts insts
@@ -2271,21 +2281,26 @@ disambiguate extended_defaulting insts
 
    defaultable_group :: [(Inst,Class,TcTyVar)] -> Bool
    defaultable_group ds@((_,_,tv):_)
-	=  not (isImmutableTyVar tv)	-- Note [Avoiding spurious errors]
+	=  isTyConableTyVar tv	-- Note [Avoiding spurious errors]
 	&& not (tv `elemVarSet` bad_tvs)
 	&& defaultable_classes [c | (_,c,_) <- ds]
    defaultable_group [] = panic "defaultable_group"
 
    defaultable_classes clss 
 	| extended_defaulting = any isInteractiveClass clss
-	| otherwise = all isStandardClass clss && any isNumericClass clss
+	| otherwise 	      = all is_std_class clss && (any is_num_class clss)
 
  	-- In interactive mode, or with -fextended-default-rules,
 	-- we default Show a to Show () to avoid graututious errors on "show []"
    isInteractiveClass cls 
-	= isNumericClass cls
-	|| (classKey cls `elem` [showClassKey, eqClassKey, ordClassKey])
+	= is_num_class cls || (classKey cls `elem` [showClassKey, eqClassKey, ordClassKey])
+
+   is_num_class cls = isNumericClass cls || (ovl_strings && (cls `hasKey` isStringClassKey))
+	-- is_num_class adds IsString to the standard numeric classes, 
+	-- when -foverloaded-strings is enabled
 
+   is_std_class cls = isStandardClass cls || (ovl_strings && (cls `hasKey` isStringClassKey))
+	-- Similarly is_std_class
 
 disambigGroup :: [Type]			-- The default types
 	      -> [(Inst,Class,TcTyVar)]	-- All standard classes of form (C a)