ref: 14d4a8e93c6804eb049eec51a5102c9d8b10c1c5 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 }