ref: 8a8f41b17cb8c2f51b26e3e3a541e7b0a876ec3c 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 }