{
  open Lexing
  open Oflan

  exception SyntaxError of string

  let next_line lexbuf =
    let pos = lexbuf.lex_curr_p in
    lexbuf.lex_curr_p <-
      { pos with pos_bol = lexbuf.lex_curr_pos;
                pos_lnum = pos.pos_lnum + 1
      }
}

let digit = ['0'-'9']
let digits =  digit*
let alpha = ['a'-'z' 'A'-'Z']
let ident = (alpha) (alpha|digit|'_')* (* regex for identifier *)
let whitespace = [' ' '\t']+
let newline = '\r' | '\n' | "\r\n"

let int = digits

rule read =
  parse
  | whitespace { read lexbuf }
  | newline { next_line lexbuf; read lexbuf }
  | int { Int (int_of_string (Lexing.lexeme lexbuf))}
  | "let" { Let }
  | ident { Ident (Lexing.lexeme lexbuf) }
  | '=' { Equal }
  | '(' { LParen }
  | 'R' { RParen }
  | eof { Eof }
  | _ { raise (SyntaxError ("Unexpected char: " ^ Lexing.lexeme lexbuf)) }