threader.clj

(ns psykotic.threader
  (:use clojure.walk))

(defmacro >> [& xs]
  (reduce (fn [x1 x2]
            (let [x1- (gensym)]
              `(let [~x1- ~x1]
                 ~(postwalk (fn [x] (if (= x '%) x1- x)) x2))))
          (macroexpand-all xs)))

(println (>> 42 (+ 8 %) (/ % 2))) ; Vary threading position per expression
(println (>> 42 (+ 8 %) (* % %))) ; Refer multiple times to previous result, without reevaluation