(rule (copy %{read:x} a))
(rule (copy %{read:y} b))

(rule (progn (run true) (with-stdout-to x (echo b))))
(rule (progn (run true) (with-stdout-to y (echo a))))

(rule (progn
       (write-file result1 "")
       (copy input result2)))

(rule (copy result2 input))