How to get a collection of return values from a function with side effects?

Question

Looking for a way to generate a collection of return values from a function with side effects, so that I could feed it to take-while.

(defn function-with-side-effects [n]
  (if (> n 10) false (do (perform-io n) true)))

(defn call-function-with-side-effects []
  (take-while true (? (iterate inc 0) ?)))

UPDATE

Here is what I have after Jan's answer:

(defn function-with-side-effects [n]
  (if (> n 10) false (do (println n) true)))

(defn call-function-with-side-effects []
  (take-while true? (map function-with-side-effects (iterate inc 0))))

(deftest test-function-with-side-effects
  (call-function-with-side-effects))

Running the test doesn't print anything. Using doall results in out of memory exception.

score 5 · Accepted Answer · edited May 23 '17 at 11:56

5

Shouldn't a map solve the problem?

(defn call-function-with-side-effects []
  (take-while true? (map function-with-side-effects (iterate inc 0))))

If you want all side effects to take effect use doall. Related: How to convert lazy sequence to non-lazy in Clojure.

(defn call-function-with-side-effects []
  (doall (take-while true? (map function-with-side-effects (iterate inc 0)))))

Mind that I replaced the true in the second line with true? assuming that this was what you meant.

edited May 23 '17 at 11:56

Community

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answered Jan 03 '13 at 15:36

Jan

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Jan, I would appreciate a comment on the updated section of the question. Thanks! – Yuriy Zubarev Jan 03 '13 at 16:17
Yuriy, good point, I should have explicitly state where the `doall` should go. I've revised the answer. Does it work now? – Jan Jan 03 '13 at 16:23
Got it, great! Thank you for helping a Clojure noob! – Yuriy Zubarev Jan 03 '13 at 16:26
More than happy to help, mate. – Jan Jan 03 '13 at 16:27

How to get a collection of return values from a function with side effects?

1 Answers1