(alias
 (name runtest)
 (deps (:workspace_root foo))
 (action (echo "%{workspace_root}\n")))

(alias
 (name   runtest)
 (deps   (:read x))
 (action (progn
          (echo %{read})
          (echo %{read:y}))))

(rule (with-stdout-to x (echo "a\n")))
(rule (with-stdout-to y (echo "b\n")))