(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)
)