some-via-reduce.clj

;;Implemented some using reduce, based on a challenge in Daniel Higginbotham's "Clojure for the Brave and True
;;This doesn't really work right; it breaks on lists, and it keeps running through the sequence even after it finds 
;;a value that passes the predicate... 
(defn my-some
  "If the predicate is true for some value, returns that value (implemented with reduce)"
  [pred sequence]
  (reduce (fn
            [x y]
            (if (pred x) x y)) (conj sequence nil)))
          
(my-some #(and (< 30 %) %) [1 2 3 4 5 6 7]) ;;returns nil as expected
(my-some #(and (< 3 %) %) [1 2 3 4 5 6 7]) ;;returns 4 as expected
(my-some #(and (< 3 %) %) '(1 2 3 4 5 6 7)) ;; Uh oh, NPE...

;;EDIT: found a function called "reduced" that will terminate/short-circuit a reduce. Awesome, but how does it work!?
(defn my-some
  "If the predicate is true for some value, returns that value (implemented with reduce)"
  [pred sequence]
  (reduce (fn
            [x y]
            (if (pred x) (reduced x) y)) sequence))