machine.clj

(defmacro machine [sym args & body]
  (let [gosym (symbol (str sym (hash sym)))
        [state value] args
        pre (take-while (comp not {'-> 1} first) body)
        inputs (filter (comp {'-> 1} first) body)
        chans (cons '_kill_ (map (comp first rest) inputs))
        conds (map #(list '= 'c %) chans)
        outputs (cons nil (map (comp first format rest rest) inputs))]
    `(do
      ~@(map (fn [c] (concat ['def c] ['(chan (async/sliding-buffer 1))])) chans)
      (~'def ~gosym nil)
      (~'defn ~sym [initial#] 
        (try (~'close! ~gosym) ~'(catch js/Error e))
        (~'set! ~gosym 
          (~'go
            (loop [~state initial#]
                ~@pre
                (~'let [[~value ~'c] (~'alts! [~@chans])]
                  (when ~value 
                    (~'cond ~@(interleave conds outputs)))))))))))