(assert= 6 (: 2 4 6))
(assert= 9 (: 2 4 (: 3 0 9)))

(:
  ($ a 4)
  (assert= 4 a)
  (set! a 42)
  (assert= 42 a)

  (:
    ($ a 7)
    (assert= 7 a)
    (set! a 32)
    (assert= 32 a)
  )

  (assert= 42 a)
)