ref: 1c61d05cba15d7e93d3207d4f3ab3c6043d63b77 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 }