Natural_deduction : FML_main.fml_of

let rec fml_of_string ?(print_tokens = false) (s:string): t_fml =
        let b : Lexing.lexbuf = Lexing.from_string s in
        try
                FML_parser.main (lexer print_tokens) b
        with
        |_ ->
                match print_tokens with
                |false -> 
                        let _ : unit = IO.print_to_stderr_red ("FML_parser failed; read the the following tokens:") in
                        fml_of_string ~print_tokens:true s
                |true -> raise (Parse_error s)