code: public RubyEnumerator<String> eachLine() {
      if (mode.isReadable() == false)
        throw new IllegalStateException("IOError: not opened for reading");
  
      return Ruby.Enumerator.of(new EachLineIterable(file));
    }
docs: Returns a {@link RubyEnumerator} of lines in the file.
  
  @return {@link RubyEnumerator}
  @throws IllegalStateException
  if file is not readable