[4clojure #60] Write a function which behaves like reduce, but returns each intermediate value of the reduction. Your function must accept either two or three arguments, and the return sequence must be lazy.

step-reduce.clj

(fn step-reduce
  ([f coll]
     (step-reduce f (first coll) (rest coll)))
  ([f x coll]
     (if (seq coll)
       (let [next-coll (rest coll)
             next-x (f x (first coll))]
         (cons x (lazy-seq (step-reduce f next-x next-coll))))
       (cons x (lazy-seq '())))))