ref: 4aa0e6c6b8a1a23b144b0382d6156aaa55b2c7fd 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 }