added parser and eval stub

src/BC/Types.hs

@@ -0,0 +1,13 @@
+module BC.Types where
+
+data Value = BInt Integer
+           | BOp String
+           | BErr String
+instance Show Value where
+  show (BInt i) = show i
+  show (BOp  o) = o
+  show (BErr e) = "error: " ++ e
+
+isErr :: Value -> Bool
+isErr (BErr _) = True
+isErr _        = False