Proposal: Export cycleN from Data.Sequence

[Joachim Breitner]

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 <david.feuer at gmail.com>
> 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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-- 
Joachim “nomeata” Breitner
  mail at joachim-breitner.de • https://www.joachim-breitner.de/
  XMPP: nomeata at joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F
  Debian Developer: nomeata at debian.org

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