X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FInstEnv.lhs;h=7aaf6ddbb711972dcfc4938720532dd4f9e69154;hb=67ee8a93fc96a38c3f73468cb86d8421a11d2911;hp=d4a7b771b7de4b9c7d46c968929e30a4236b319b;hpb=0065d5ab628975892cea1ec7303f968c3338cbe1;p=ghc-hetmet.git diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs index d4a7b77..7aaf6dd 100644 --- 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 } @@ -108,7 +111,7 @@ data Instance -- This is used for versioning; the instance decl is -- considered part of the defn of n when computing versions -- --- Nothing The head mentions nothing defined in this modle +-- Nothing The head mentions nothing defined in this module -- -- If a module contains any orphans, then its interface file is read -- regardless, so that its instances are not missed. @@ -213,38 +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 - -instance Outputable OverlapFlag where - ppr NoOverlap = empty - ppr OverlapOk = ptext SLIT("[overlap ok]") - ppr Incoherent = ptext SLIT("[incoherent]") \end{code}