exception Error of int * int * string

let regexp alpha = [ 'a' - 'z' 'A' - 'Z' ]
let regexp digit = [ '0' - '9' ]
let regexp blank = [ ' ' '\t' '\n' ]

let regexp blanks = blank+
let regexp num = digit+
let regexp ident = alpha (alpha | num)*
let regexp symbol = [^ 'a' - 'z' 'A' - 'Z' '0' - '9' ' ' '\t' '\n' ]
let regexp tex_token = '\\' alpha+
let regexp lparen = [ '(' '[' '{' ]
let regexp rparen = [ ')' ']' '}' ]
let regexp meta = '?' (alpha | num)+

let keywords = Hashtbl.create 17
let _ =
  List.iter (fun keyword -> Hashtbl.add keywords keyword ("", keyword))
    [ "Prop"; "Type"; "Set"; "let"; "rec"; "using"; "match"; "with" ]

let error lexbuf msg =
  raise (Error (Ulexing.lexeme_start lexbuf, Ulexing.lexeme_end lexbuf, msg))
let error_at_end lexbuf msg =
  raise (Error (Ulexing.lexeme_end lexbuf, Ulexing.lexeme_end lexbuf, msg))

let return lexbuf token = (token, Ulexing.loc lexbuf)

let rec token = lexer
| blanks -> token lexbuf
| ident ->
    let lexeme = Ulexing.utf8_lexeme lexbuf in
    (try
      return lexbuf (Hashtbl.find keywords lexeme)
    with Not_found ->
      return lexbuf ("IDENT", lexeme))
| num -> return lexbuf ("INT", Ulexing.utf8_lexeme lexbuf)
| lparen -> return lexbuf ("LPAREN", Ulexing.utf8_lexeme lexbuf)
| rparen -> return lexbuf ("RPAREN", Ulexing.utf8_lexeme lexbuf)
| meta -> return lexbuf ("META", Ulexing.utf8_lexeme lexbuf)
| symbol -> return lexbuf ("SYMBOL", Ulexing.utf8_lexeme lexbuf)
| tex_token ->
    let macro =
      Ulexing.utf8_sub_lexeme lexbuf 1 (Ulexing.lexeme_length lexbuf - 1)
    in
    (try
      return lexbuf ("SYMBOL", Macro.expand macro)
    with Macro.Macro_not_found _ ->
      return lexbuf ("SYMBOL", Ulexing.utf8_lexeme lexbuf))
| eof -> return lexbuf ("EOI", "")
| _ -> error lexbuf "Invalid character"

let tok_func stream =
  let lexbuf = Ulexing.from_utf8_stream stream in
  Token.make_stream_and_location
    (fun () ->
      try
	token lexbuf
      with
      | Ulexing.Error -> error_at_end lexbuf "Unexpected character"
      | Ulexing.InvalidCodepoint i -> error_at_end lexbuf "Invalid code point")

let lex =
  { 
    Token.tok_func = tok_func;
    Token.tok_using = (fun _ -> ());
    Token.tok_removing = (fun _ -> ()); 
    Token.tok_match = Token.default_match;
    Token.tok_text = Token.lexer_text;
    Token.tok_comm = None;
  }