class Sass::SCSS::StaticParser

def a_n_plus_b
  if (parity = tok(/even|odd/i))
    return parity
  end
  if tok(/[+-]?[0-9]+/)
    ss
    return true unless tok(/n/)
  else
    return unless tok(/[+-]?n/i)
  end
  ss
  return true unless tok(/[+-]/)
  ss
  @expected = "number"
  tok!(/[0-9]+/)
  true
end