def drawGrid(draw: Shape => Unit) {
    var y_spacing = 0
    var x_spacing = 0

    val numLines = G_SIZE / G_INTERVAL

    def makeLn(axis: Char) {
      val aLine = axis match {
        case 'y' =>
          y_spacing += G_INTERVAL
          makeLine(y_spacing, 0, y_spacing, G_SIZE)
        case 'x' =>
          x_spacing += G_INTERVAL
          makeLine(0,x_spacing, G_SIZE, x_spacing)
      }
      draw(aLine)
    }
    (1 to numLines).foreach(_ => makeLn('y'))
    (1 to numLines).foreach(_ => makeLn('x'))
  }