Re: Proposal: Export cycleN from Data.Sequence

Hi, I consent, and have no advice to offer :-) Greetings, Joachim Am Montag, den 25.04.2016, 23:50 -0400 schrieb David Feuer:

It's been quite a while, and I've had a single +1 on this with very little comment. Does anyone else have an opinion? Is anyone opposed? Does anyone think `cycleN n` should produce a *result* of length `n` instead of cycling `n` times? I seek advice and consent of anyone who cares.

On Wed, Mar 11, 2015 at 11:14 AM, David Feuer wrote:

...

Yesterday I rewrote `*>` for Data.Sequence (again), using an internal function

cycleN :: Int -> Seq a -> Seq a

The name of the function is based on that of Data.Sequence.iterateN. cycleN takes a sequence and cycles it as many times as requested:

cycleN 0 $ fromList [1,2] = [] cycleN 5 $ fromList [1,2] = [1,2,1,2,1,2,1,2,1,2]

The function is written to maximize sharing in the result sequence and to minimize construction time. Specifically, cycleN n xs should take something like O(|xs| + log n) space (of which all but O(log |xs| + log n) is shared with the structure of xs) and O(log |xs| + log n) time.

With current (on GitHub) Data.Sequence exports, the only way to get this functionality with these time and space bounds is to combine replicate with *> :

cycleN n xs = replicate n () *> xs

This strikes me as a bit unpleasant.

David

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