Because the fn is wrapped in a lazy sequence, the effects won't run if you
ask for the same value again--
For instance:
(def a (iterate (fn [cnt]
(prn cnt)
;; save data to csv
(inc cnt)) 0))
(nth a 5) ... all the effects are fired.
(nth a 5) ... simply returns 5-- no effects are fired because the lazy
sequence has already been realized up to this point. This may not be what
you expect.
Also, you shouldn't in general trust effects to be run the 'correct' amount
of times. For instance, if we were operating on a chunked-sequence, if you
asked for the 3rd element, you would get the side effects for the next 32
elements, which may not be what you'd expect. That doesn't happen to be the
case here but it's something to keep in mind as well.
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