(define (tasks)
  (make-plan `((foo ()
                    .
                    ,(lambda _ (print "foo called")))
               (bar (foo)
                    .
                    ,(lambda _ (print "bar called")))
               (baz ,((lambda () '(foo bar)))
                    . ,(lambda _
                         (print "baz called"))))))

(realize-plan (tasks) 'baz)
(print "================")
(realize-plan (tasks) 'bar)