Python-style Generators in Arc

(= fail (uniq))

(def make-gen (f)
  (withs (next   nil
          exit   nil
          yield  (fn (val)
                   (ccc (fn (c)
                          (= next c)
                          (exit val)))))
    (fn args
      (ccc (fn (c)
        (if next (next args)
                 (do (= exit c)
                     (f yield)
                     fail)))))))

(mac gen body
  `(make-gen (fn (yield) ,@body)))