{
type first_line =
  { lang    : Loc.t * string
  ; version : Loc.t * string
  }

let make_loc lexbuf : Loc.t =
  { start = Lexing.lexeme_start_p lexbuf
  ; stop  = Lexing.lexeme_end_p   lexbuf
  }

let invalid_lang_line start lexbuf =
  lexbuf.Lexing.lex_start_p <- start;
  Loc.fail_lex lexbuf
    "Invalid first line, expected: (lang <lang> <version>)"
}

let newline   = '\r'? '\n'
let blank     = [' ' '\t']
let atom_char = [^';' '(' ')' '"' '#' '|' '\000'-'\032']

rule is_script = parse
  | "(* -*- tuareg -*- *)" { true }
  | ""                     { false }

and first_line = parse
  | '(' blank* "lang"
    { let start = Lexing.lexeme_start_p lexbuf in
      let lang    = atom start lexbuf in
      let version = atom start lexbuf in
      first_line_end start lexbuf;
      { lang; version }
    }
  | ""
    { let start = Lexing.lexeme_start_p lexbuf in
      to_eol lexbuf;
      invalid_lang_line start lexbuf
    }

and atom start = parse
  | blank+
    { atom start lexbuf
    }
  | atom_char+ as s
    { (make_loc lexbuf, s)
    }
  | _ | eof
    { to_eol lexbuf;
      invalid_lang_line start lexbuf
    }

and first_line_end start = parse
  | blank* ')' blank* (newline | eof)
    { ()
    }
  | ""
    { to_eol lexbuf;
      invalid_lang_line start lexbuf
    }

and to_eol = parse
  | [^'\r' '\n']*
    { ()
    }