Rectangle

public defstruct Rectangle <: Shape :
  width: Double with: (ensure => non-negative!)
  height: Double with: (ensure => non-negative!)
  pose: Pose

public defn Rectangle (w:Double, h:Double) :
  Rectangle(w, h, loc(0.0, 0.0))

public defn Rectangle (anchor:Anchor, w:Double, h:Double) :
  val [vt, hr] = components(anchor)
  val dx = match(hr) :
    (hr:W) : w / 2.0
    (hr:C) : 0.0
    (hr:E) : w / -2.0
  val dy = match(vt) :
    (vt:S) : h / 2.0
    (vt:C) : 0.0
    (vt:N) : h / -2.0
  Rectangle(w, h, loc(dx, dy))

Rectangle(2.0, 3.0, loc(0.0, 0.0))
Rectangle(2.0, 3.0)
Rectangle(C, 2.0, 3.0)