Add support for overloaded string literals.

[ghc-hetmet.git] / compiler / typecheck / TcSimplify.lhs

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 7b9f1f1..29938ee 100644 (file)
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -2258,8 +2258,13 @@ disambiguate extended_defaulting insts
                                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 []
        ; traceTc (text "disambigutate" <+> vcat [ppr unaries, ppr bad_tvs, ppr defaultable_groups])
-       ; mapM_ (disambigGroup default_tys) defaultable_groups  }
+       ; mapM_ (disambigGroup default_str_tys) defaultable_groups  }
   where
    unaries :: [(Inst,Class, TcTyVar)]  -- (C tv) constraints
    bad_tvs :: TcTyVarSet         -- Tyvars mentioned by *other* constraints
@@ -2279,13 +2284,13 @@ disambiguate extended_defaulting insts
 
    defaultable_classes clss 
        | extended_defaulting = any isInteractiveClass clss
-       | otherwise = all isStandardClass clss && any isNumericClass clss
+       | otherwise = all isStandardClass clss && (any isNumericClass clss || any ((== isStringClassKey) . classKey) 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])
+       || (classKey cls `elem` [showClassKey, eqClassKey, ordClassKey, isStringClassKey])
 
 
 disambigGroup :: [Type]                        -- The default types