a vector is a function of its indices
a map is a function of its keys
a set is a function of its elements

does this help at all?

Jim



On 03/02/14 15:29, action wrote:
(defn index-filter [pred coll]
  (when pred
    (for [[idx elt] (indexed coll) :when (pred elt)] idx)))

(index-filter #{\a \b} "abcdef")
-> (0 1)

but I don't know why use "when pred" in the code,
and why "(index-filter {\a \b} "abcdef")" doesn't work?
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