(assert-eq? 6 (: 2 4 6))
(assert-eq? 9 (: 2 4 (: 3 0 9)))

(:
  ($ a 4)
  (assert-eq? 4 a)

  (:
    ($ a 7)
    (assert-eq? 7 a)
  )

  (assert-eq? 4 a)
)