ref: fd1b8b6f31b7a8c2705c3ac01e46fd707c0d3c9e 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 }