prev_macro.cr

  def prev(offset)
    @points.prev offset
  end

  macro prev_value(offset, source)
    @points.prev({{offset}}).{{source}}
  end

  def weighted_average(source, value=nil)
    [ 4.0 * (value || prev_value(0, source)),
      3.0 * prev_value(1, source),
      2.0 * prev_value(2, source),
            prev_value(3, source),
    ].sum / 10.0
  end