ref: 3360bf0e88b086b0c7f7957eeb4a6f0b4eaeebc7 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 }