How to use the coffee-script.tokens function in coffee-script

function findTokensForRangeIgnoringInvalidTrailingCharacters(source, start, end) {
  var candidateEnd = end;
  var error;

  while (start <= candidateEnd) {
    var slice = source.slice(start, candidateEnd);
    try {
      return {
        tokens: tokens(slice, { rewrite: false }),
        start: start,
        end: candidateEnd
      };
    } catch (ex) {
      if (!error) {
        error = ex;
      }
      candidateEnd--;
    }
  }

  throw error;
}