Union

public defstruct Union <: Shape  :
  shapes: Tuple<Shape>
with:
  constructor => #Union

public defn Union (ss:Seqable<Shape|Seqable>) :
  val ss* = generate<Shape> :
    let loop (s:Shape|Seqable = ss) :
      match(s) :
        (s:Union) : do(yield, shapes(s))
        (s:Shape) : yield(s)
        (s:Seqable) : do(loop, s)
  if empty?(ss*) :
    fatal("Cannot form union from no shapes.")
  else :
    val s0 = next(ss*)
    if empty?(ss*) : s0
    else : #Union(to-tuple(cat([s0], ss*)))

Union([Circle(1.0), Rectangle(4.0, 0.5)])