src/Diagram.hs

@@ -34,6 +34,11 @@ data Diagram vtx = Diagram
   }
   deriving (Show, Read)
 
+data Direction
+  = Up
+  | Down
+  deriving (Eq, Ord, Read, Show)
+
 data InsertError vtx
   = InsertError_DuplicateVertex
   | InsertError_UnknownDownVertex vtx