ref: c634b3005ccd2ddfe903b1c1c7b7d61e2e8d6fb4 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 }