We want to write a function that generates accumulators-- a function that takes a number n, and returns a function that takes another number i and returns n incremented by i. See the article Revenge of the Nerds http://www.paulgraham.com/icad.html This Clojure solution comes from http://rosettacode.org/wiki/Accumulator_factory#Clojure

Accumulator.clj

(defn accum [n]
  (let [acc (atom n)]
    (fn [m] (swap! acc + m))))