tree.ml1 2 3 4 5 6 7 8 9(** Type definition of Regular Expression Abstract Syntax Tree *) type re = | Literal of string (* a ∈ Σ *) | Epsilon (* ε *) | Empty (* ∅ *) | Union of re * re (* E + R *) | Concat of re * re (* E·R *) | Star of re (* E* *)