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])

Should probably be (if as), no? Won't matter for ints, but is a more general pattern for if the coll can have nil/false elements.

And isn't ((fn [h] (h h)) f) identical to (f f)?

Oh, you're right about (f f), I can't believe I missed that. :)

(if as ..) would terminate too early afaik.

you're right about the issues though, this is better:

(ns ycomb-simpler)

(defn sum-gen [h](fn [[a0 & as :as a]]
%28if %28seq a%29
%28+ a0 %28%28h h%29 as%29%29
0%29))

Yeah, you're right about as. Silly me.

try to paste this code again:

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

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!