ref: caa2cd99e469f598d19a03f2ba4d3c23c6e9d6f5 dir: /lib/std/swap.myr/
pkg std = generic swap : (a : @a#, b : @a# -> void) ;; generic swap = {a : @a#, b : @a# var t t = a# a# = b# b# = t }