partitions.clj

(defn partitions [sizes coll]
  (lazy-seq
   (when-let [n (first sizes)]
     (when-let [s (seq coll)]
       (cons (take n coll)
	     (partitions (next sizes) (drop n coll)))))))

(defn partitions [sizes coll]
  (second (reduce
	   (fn [[coll res] n]
	     [(drop n coll) (conj res (vec (take n coll)))])
	   [coll []] sizes)))

(defn partitions [sizes coll]
  (->> sizes
       (reductions (fn [[_ coll] part]
		     (split-at part coll))
		   [nil coll] ,)
       next
       (map first ,)
       (take-while seq ,))

(defn partitions [sizes coll]
  (unfold (fn [[[n & sizes] coll]]
	    [(take n coll) [sizes (drop n coll)]])
	  (partial not-any? seq)
	  [sizes coll]))

user> (partitions [1 2 3 2 1] [1 2 3 4 5 6 7 8 9])
((1) (2 3) (4 5 6) (7 8) (9))