Started with unions.

src/GF/Source/AbsGF.hs

@@ -41,6 +41,7 @@ data ModBody =
    MBody Extend Opens [TopDef]
  | MWith Ident [Open]
  | MReuse Ident
+ | MUnion [Included]
   deriving (Eq,Ord,Show)
 
 data Extend =
@@ -70,6 +71,11 @@ data QualOpen =
  | QOInterface
   deriving (Eq,Ord,Show)
 
+data Included =
+   IAll Ident
+ | ISome Ident [Ident]
+  deriving (Eq,Ord,Show)
+
 data Def =
    DDecl [Ident] Exp
  | DDef [Ident] Exp