def rtype_item
      skip_whitespace

      key = @input.scan(/[a-zA-Z0-9_]+/)
      return false unless key
      @out << key

      skip_whitespace
      if @input.scan(/:/)
        @out << ":"
        skip_whitespace
        return false unless null_type
        skip_whitespace
      end

      true
    end
def rtype_item
      skip_whitespace

      key = @input.scan(/[a-zA-Z0-9_]+/)
      return false unless key
      @out << key

      skip_whitespace
      if @input.scan(/:/)
        @out << ":"
        skip_whitespace
        return false unless null_type
        skip_whitespace
      end

      true
    end
<rtype-item> ::= <ident> ":" <null-type>
                    | <ident>