X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcSimplify.lhs;h=95250f8c6d81fb67d5fafaf1e4a08062c9339392;hb=ddf73c04de77994ad138771a7492007d794faf5e;hp=29938ee52c03e65072f7a04ab7b32eb720e569a5;hpb=90dc9026b091be5cca5da4c6cbd3713ecc493361;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 29938ee..95250f8 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -863,7 +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 } 
 
@@ -876,6 +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
@@ -2257,14 +2260,14 @@ disambiguate extended_defaulting insts
 					-- use [Integer, Double]
 				do { integer_ty <- tcMetaTy integerTyConName
 				   ; checkWiredInTyCon doubleTyCon
-				   ; return [integer_ty, doubleTy] }
-        ; string_ty <- tcMetaTy stringTyConName
-	; ovlStr <- doptM Opt_OverloadedStrings
-	-- XXX This should not be added unconditionally, but the default declaration stuff
-	-- is too wired to Num for me to understand.  /LA
-        ; let default_str_tys = default_tys ++ if ovlStr then [string_ty] else []
+				   ; string_ty <- tcMetaTy stringTyConName
+				   ; ovl_str <- doptM Opt_OverloadedStrings
+				   ; if ovl_str 	-- 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_str_tys) defaultable_groups  }
+	; mapM_ (disambigGroup default_tys) defaultable_groups  }
   where
    unaries :: [(Inst,Class, TcTyVar)]  -- (C tv) constraints
    bad_tvs :: TcTyVarSet	  -- Tyvars mentioned by *other* constraints