gistfile1.clj

(defn Y [f]
  (f f))

((Y (fn [coll]
      (if-let [[a0 & as] (seq coll)]
        (+ a0 ((h h) as))
        0))) 
    [1 2 3 4 5])

Anyways, now the ycombinator is laughably simple.

The more complex version is just to get prettier anonymous function declarations, such as:

(defn sum-gen [h]
  (fn [[a0 & as :as a]]
    (if (seq a)
      (+ a0 (h as))
      0)))

instead of (h h)

(fn [coll]
  (if-let [[a & as] (seq coll)]
    ...))

Perfect!