gistfile1.clj

(defn toggled    
  "Add a toggle to an input channel.
  
  The ctrl channel accepts truthy, falsy or :toggle values. 
  The toggle value in the loop determines whether the input value is piped
  to the output channel or not.
            _____
  =[in]===>|     |
           | alt |=[out]=>
  =[ctrl]=>|     |
           '-----'  
  "
  ([in ctrl]
   (toggled in ctrl (chan)))
  
  ([in ctrl out]
   (go-loop [toggle true]            
            (alt! in ([v] (if (and v toggle) (>! out v))
                          (recur toggle))
                  ctrl ([v] (recur (if (= :toggle v) (not toggle) v)))))  
   out))