gistfile1.clj

(defn conj-entry [trails entry transform]
  (let [all-trails (sort-by #(trail-proximity % entry) trails)]
    (if (empty? all-trails)
      [(make-trail entry)]
      (loop [[trail & trails] all-trails
	     results (transient [])]
	(cond	       
	 ;; no matches found after scanning all trails
	 (nil? trail)
	 (do
	   (when *debug* (print "!"))
	   (conj (persistent! results) (make-trail entry)))

	 ;; trail matches 
	 (trail-matches? trail (transform-entry transform entry))
	 (let [new-trail (add-entry trail entry)]
	   (when *debug* (print "+"))
	   (apply conj (persistent! results) new-trail trails))

	 :else ;; try the next trail
	 (recur trails
		(conj! results trail)))))))

(defn propagate-iterative [entries transform relevant-trails other-trails]
  (loop [entries entries
	 trails relevant-trails]
      (if (empty? entries)
    	(do (when *debug* (println))
    	    (if (empty? other-trails)
	      trails
    	      (apply conj trails other-trails)))
    	(let [entry (first entries)]
    	  (recur (rest entries)
    		 (conj-entry trails entry transform))))))