X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypes%2FTyCon.lhs;h=befc4e6f938bfe3c0d7c3b27e002aa9bc3b23ad0;hp=dc7e2d3e327caff4534d6a10572fd045ebfe9a83;hb=da2e18b9ab29131bda1ac8e3962dc50b635589a5;hpb=eb6e1243d28a5acd967b981893a6cc96f145207f

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index dc7e2d3..befc4e6 100644
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -39,6 +39,7 @@ module TyCon(
         isCoercionTyCon, isCoercionTyCon_maybe,
         isForeignTyCon,
 
+	isInjectiveTyCon,
 	isDataTyCon, isProductTyCon, isEnumerationTyCon, 
 	isNewTyCon, isAbstractTyCon, isOpenTyCon,
         isUnLiftedTyCon,
@@ -815,6 +816,17 @@ isOpenTyCon (SynTyCon {synTcRhs = OpenSynTyCon {}}) = True
 isOpenTyCon (AlgTyCon {algTcRhs = OpenTyCon {}})    = True
 isOpenTyCon _					    = False
 
+-- | Injective 'TyCon's can be decomposed, so that
+--     T ty1 ~ T ty2  =>  ty1 ~ ty2
+isInjectiveTyCon :: TyCon -> Bool
+isInjectiveTyCon tc = not (isSynTyCon tc)
+	-- Ultimately we may have injective associated types
+        -- in which case this test will become more interesting
+	--
+	-- It'd be unusual to call isInjectiveTyCon on a regular H98
+	-- type synonym, because you should probably have expanded it first
+	-- But regardless, it's not injective!
+
 -- | Extract the mapping from 'TyVar' indexes to indexes in the corresponding family
 -- argument lists form an open 'TyCon' of any sort, if the given 'TyCon' is indeed
 -- such a beast and that information is available