{
  open Parser
  exception LexingError of string

  let create_hashtable size init =
    let tbl = Hashtbl.create size in
    List.iter (fun (key, data) -> Hashtbl.add tbl key data) init;
    tbl

  let keyword_table =
    let mapping = [
      ("main", MAIN);
      ("skip", SKIP);
      ("if", IF);
      ("else", ELSE);
      ("while", WHILE);
      ("for", FOR);
      ("do", DO);
      ("true", BOOL(true));
      ("false", BOOL(false));
      ("not", BNOT);
      ("rand", RAND);
      ("powmod", POWERMOD);
    ]
    in create_hashtable (List.length mapping) mapping
}

let digit   = ['0'-'9']
let alpha   = ['a'-'z' 'A'-'Z']
let white   = [' ' '\t']+ | '\r' | '\n' | "\r\n"

let integer = (digit)(digit*)
let var     = (alpha|'_') (alpha|digit|'_')*

let symbols = ['!'-'/' ':'-'?' '[' ']' '^' '{'-'}' '~']

(* lexing rules *)
rule read = parse
  | white           {read lexbuf}
  | var as v        {
      match Hashtbl.find_opt keyword_table v with
      | Some keyword -> keyword
      | None -> VARIABLE(v)
    }
  | ";"             {SEQUENCE}
  | ","             {COMMA}
  | "{"             {LEFTGPAR}
  | "}"             {RIGHTGPAR}
  | "("             {LEFTPAR}
  | ")"             {RIGHTPAR}
  | "<"             {BCMPLESS}
  | ">"             {BCMPGREATER}
  | "+"             {PLUS}
  | "-"             {MINUS}
  | "*"             {TIMES}
  | "/"             {DIVISION}
  | "%"             {MODULO}
  | "^"             {POWER}
  | ":="            {ASSIGNMENT}
  | "&&"            {BAND}
  | "||"            {BOR}
  | "=="            {BCMP}
  | "<="            {BCMPLESSEQ}
  | ">="            {BCMPGREATEREQ}
  | integer as i    {INT(int_of_string i)}
  | "(*"            {comments 0 lexbuf}
  | eof             {EOF}
  | _               {
      raise
        (LexingError
           (Printf.sprintf
              "Error scanning %s on line %d at char %d"
              (Lexing.lexeme lexbuf)
              (lexbuf.Lexing.lex_curr_p.Lexing.pos_lnum)
              (lexbuf.Lexing.lex_curr_p.Lexing.pos_lnum)
           ))}
and comments level = parse
  | "*)"    {if level = 0
             then read lexbuf
             else comments (level-1) lexbuf}
  | "(*"    {comments (level+1) lexbuf}
  | _       {comments level lexbuf}
  | eof     {raise (LexingError ("Comment is not closed"))}


{
  let lex = read
}