ref: eadf2bcb3c9dbe20b8bef1cf7e6059703f1e5ac6 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 }