open Lexing

type ('token, 'ast) historic_parser =
    (lexbuf -> 'token) -> lexbuf -> 'ast

type ('token, 'ast) revised_parser =
    (unit -> 'token) -> 'ast

let upgrade (p : ('token, 'ast) historic_parser) : ('token, 'ast) revised_parser =
  fun (next : unit -> 'token) ->
    let (* dummy *) lexbuf =
      Lexing.from_string ""
    and lexer lexbuf =
      next()
    in
    p lexer lexbuf

let downgrade (p : ('token, 'ast) revised_parser) : ('token, 'ast) historic_parser =
  fun (lexer : lexbuf -> 'token) lexbuf ->
    let next () =
      lexer lexbuf
    in
    p next