index-of-any - Programming Clojure "2. Exploring Clojure" p71

index-of-any.clj

;; Programming Clojure "2. Exploring Clojure" p71
;; 

; NOTE: The ``indexed`` function already exists as part of
; clojure-contrib (coljure.contrib.seq/indexed).
(defn indexed
  "Returns a lazy sequence of [index, item] pairs, where items
  come from 'coll' and indexes count up from zero."
  [coll]
  (map vector (iterate inc 0) coll))

(defn index-filter
  "Returns the indexes of the matches."
  [pred coll]
  (when pred
    (for [[idx, elt] (indexed coll) :when (pred elt)] idx)))

(defn index-of-any [pred col]
  (first (index-filter pred col)))