($ a 32)

(! a 54)

(assert= 54 a)

(:
   ($ a 12)
   (! a 99)
   (assert= 99 a)
)

(assert= 54 a)

($ f (-> (x) (+ 2 x)))

(assert= 5 (f 3))

(! f (-> (x) (* x 4)))

(assert= 12 (f 3))