Hi,
there is an example in programming clojure (Chapter 2.6, Where is my
for loop? on page 52)
that I don't really get.
(defn index-filter [pred coll]
(when pred
(for [[idx elt] (indexed coll) :when (pred elt)] idx)))
The explanation in the book explains the for/:when but not the
when. ;) What I do not understand is
why there is the outer (when) .
If I remove the (when):
(defn index-filter-2 [pred coll]
(for [[idx elt] (indexed coll) :when (pred elt)] idx))
it seems to do the same as the first version. So what's the reason for
the (when) ?
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