Massive patch for the first months work adding System FC to GHC #35

[ghc-hetmet.git] / compiler / types / InstEnv.lhs

diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs
index 70e6166..7aaf6dd 100644 (file)
--- a/compiler/types/InstEnv.lhs
+++ b/compiler/types/InstEnv.lhs
@@ -33,8 +33,10 @@ import TcType                ( Type, PredType, tcEqType,
                          tyClsNamesOfType, tcSplitTyConApp_maybe
                        )
 import TyCon           ( tyConName )
-import Unify           ( tcMatchTys, tcUnifyTys, BindFlag(..) )
+import TcGadt          ( tcUnifyTys, BindFlag(..) )
+import Unify           ( tcMatchTys )
 import Outputable
+import BasicTypes      ( OverlapFlag(..) )
 import UniqFM          ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM )
 import Id              ( idType, idName )
 import SrcLoc          ( pprDefnLoc )
@@ -61,7 +63,8 @@ data Instance
             , is_tys  :: [Type]        -- Full arg types
 
             , is_dfun :: DFunId
-            , is_flag :: OverlapFlag
+            , is_flag :: OverlapFlag   -- See detailed comments with
+                                       -- the decl of BasicTypes.OverlapFlag
 
             , is_orph :: Maybe OccName }
 
@@ -213,39 +216,6 @@ instanceCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
 -- False is non-committal
 instanceCantMatch (Just t : ts) (Just a : as) = t/=a || instanceCantMatch ts as
 instanceCantMatch ts           as            =  False  -- Safe
-
----------------------------------------------------
-data OverlapFlag
-  = NoOverlap  -- This instance must not overlap another
-
-  | OverlapOk  -- Silently ignore this instance if you find a 
-               -- more specific one that matches the constraint
-               -- you are trying to resolve
-               --
-               -- Example: constraint (Foo [Int])
-               --          instances  (Foo [Int])
-               --                     (Foo [a])        OverlapOk
-               -- Since the second instance has the OverlapOk flag,
-               -- the first instance will be chosen (otherwise 
-               -- its ambiguous which to choose)
-
-  | Incoherent -- Like OverlapOk, but also ignore this instance 
-               -- if it doesn't match the constraint you are
-               -- trying to resolve, but could match if the type variables
-               -- in the constraint were instantiated
-               --
-               -- Example: constraint (Foo [b])
-               --          instances  (Foo [Int])      Incoherent
-               --                     (Foo [a])
-               -- Without the Incoherent flag, we'd complain that
-               -- instantiating 'b' would change which instance 
-               -- was chosen
-  deriving( Eq )
-
-instance Outputable OverlapFlag where
-   ppr NoOverlap  = empty
-   ppr OverlapOk  = ptext SLIT("[overlap ok]")
-   ppr Incoherent = ptext SLIT("[incoherent]")
 \end{code}