pleat

pleat.clj

(defn screw-up-some-collections-1 [xs ys]
  (reduce
    (fn [acc1, x]
      (conj acc1
        (reduce
          (fn [acc2, y]
            (conj acc2 [x y]))
          []
          ys)))
    []
    xs))

(defn pleat
  "reduce with the syntax flipped, if you're into that sort of thing"
  ([coll f]
     (reduce f coll))
  ([coll init f]
     (reduce f init coll)))

;; look this is nicer:
(defn screw-up-some-collections-2 [xs ys]
  (pleat xs, [],
    (fn [acc1, x]
      (conj acc1
        (pleat ys, []
          (fn [acc2, y]
            (conj acc2 [x y])))))))

;; =>  (= (screw-up-some-collections-1 (range 5) (range 5))
;;       (screw-up-some-collections-2 (range 5) (range 5)))

;; true

;; => (pprint (screw-up-some-collections-2 (range 5) (range 5)))
 
;; [[[0 0] [0 1] [0 2] [0 3] [0 4]]
;;  [[1 0] [1 1] [1 2] [1 3] [1 4]]
;;  [[2 0] [2 1] [2 2] [2 3] [2 4]]
;;  [[3 0] [3 1] [3 2] [3 3] [3 4]]
;;  [[4 0] [4 1] [4 2] [4 3] [4 4]]]