{
  open Funparse
  exception EndInput

  let rec unescape s =
    let strpop  s = s.[0], String.sub s 1 (String.length s - 1)
    and chr2str c = Printf.sprintf "%c" c in

    match String.length s with
    | 0   -> ""
    | 1   -> s
    | len -> let c1,s = strpop s in
        if c1 = '\\' then
          let c2,s = strpop s in
            if      c2 = 'n' then "\n" ^ (unescape s)
            else if c2 = 't' then "\t" ^ (unescape s)
            else (chr2str c2) ^ (unescape s)
        else (chr2str c1) ^ (unescape s)
}

(* You can assign names to commonly-used regular expressions in this part
   of the code, to save the trouble of re-typing them each time they are used *)

let numeric = ['0' - '9']

let letter =['a' - 'z' 'A' - 'Z' '_']

rule mytoken = parse
  | [' ' '\t' '\n'] { mytoken lexbuf }  (* skip over whitespace *)

  (*YOUR CODE GOES HERE...*)

  | eof     { raise EndInput } 

(*YOU CAN DEFINE NEW rules HERE*)


(* do not modify this function: *)
{ 
  let lextest s =
    let rec lbuf = Lexing.from_string s 
    and lextest_aux () =
      try
        let res = mytoken lbuf
        in
          res :: lextest_aux ()
      with EndInput ->
        []
    in
      lextest_aux ()
 }