calc-slice-count.clj

(defn calc-slice-count [thing]
  "Calculates the number of possible slices using the formula:
	(n + r - 1)!
	------------
	r!(n - 1)!
   where n is (count thing) and r is 2"
  (let [! #(reduce * (take % (iterate inc 1)))
	n (count thing)
	r 2]
    (/ (! (- (+ n r) 1))
       (* (! r) (! (- n 1))))))

(extend-type String
	      Sliceable
	      (slice [this s e] (.substring this s (inc e)))
	      (sliceCount [this] (calc-slice-count this)))
(slice "abc" 0 1)