Slight refactoring for overloaded strings

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 29938ee..1278662 100644 (file)
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -2257,14 +2257,14 @@ 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