gr :: AST -> Gr
gr ast =
    let (start, rules, nonT) = (gr' ast)
    in (start, rules)

gr' :: AST -> (String, [(String, String)], [String])
gr' (Star x) =
    let (start, rules, nonT) = gr' (x)
    in (start, [(a, "") | a <- nonT] ++ rules, nonT)
gr' (C x) =
    ("A", [("A", x)], ["A"])
gr' (Seq x y) =
    (xstart, , xnonT ++ ynonT)
        where (xstart, xrules, xnonT) = gr' x
              (ystart, yrules, ynonT) = gr' y