(defmacro doseq2
  [seq-exprs & body]
  (let [forms (loop [[[binding seq-expr] & seq-exprs] (partition 2 seq-exprs)
                     forms []]
                (if (and binding seq-expr)
                  (let [[mods seq-exprs] (split-with (comp keyword? first) seq-exprs)]
                    (recur seq-exprs
                           (conj forms {:seq-expr seq-expr
                                        :mods mods
                                        :binding binding})))
                  forms))

        emit-mod (fn [form [k expr]]
                    (case k
                      :while `(if ~expr
                                (do ~form)
                                (reduced nil))
                      :when `(when ~expr
                               ~form)
                      :let `(let ~expr
                              ~form)))

        step (fn step
               [[e & exprs]]
               (let [inner-expr (if exprs (step exprs) `(do ~@body nil))
                     rfnbody (reduce emit-mod inner-expr (reverse (:mods e)))]
                 `(reduce (fn [_# ~(:binding e)]
                                                      ~rfnbody)
                         
                     nil     ~(:seq-expr e))))]
    (step forms)))

(def hund (into [] (range 100)))
(def ten (into [] (range 10)))
(def arr (int-array 100))
(def s "superduper")

(println ";; big range, few bindings:")

(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a (range 100000000)])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a (range 100000000)])))

(println ";; med range, few bindings:")

(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a (range 500000)])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a (range 500000)])))


(println ";; small range, few bindings:")

(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a (range 500)])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a (range 500)])))

(println ";; small unchunked reducible, few bindings:")
(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a s b s c s])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a s b s c s])))

(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a arr b arr c arr])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a arr b arr c arr])))

(println ";; small chunked reducible, few bindings:")
(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a hund b hund c hund])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a hund b hund c hund])))

(println ";; more bindings:")
(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a ten b ten c ten d ten ])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a ten b ten c ten d ten ])))

(println "core/doseq")
(dotimes [_ 5]
  (time (doseq [a ten b ten c ten d ten e ten])))

(println "doseq2")
(dotimes [_ 5]
  (time (doseq2 [a ten b ten c ten d ten e ten])))