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 )
, 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 }
-- 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}