Re: Add instance Monad ZipList

Agreed, that would be a great addition. On Thu, Jun 4, 2020, 8:31 AM Simon Jakobi wrote:

This sounds worth documenting though.

Dannyu, would you be interested in updating the ZipList docs to say why it doesn't have a Monad instance?

Cheers, Simon

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David is right. This can't happen, unfortunately

On Thu, Jun 4, 2020, 12:48 AM David Feuer wrote:

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I don't remember why right now, but it's moderately well-known that

Am Do., 4. Juni 2020 um 17:21 Uhr schrieb chessai . https://stackoverflow.com/questions/6463058/help-on-writing-the-colist-monad... by pigworker (Conor McBride) and C. A. McCann.

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On Thu, Jun 4, 2020, 2:53 AM Dannyu NDos wrote:

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instance Monad ZipList where ZipList [] >>= _ = ZipList [] ZipList (x:xs) >>= f = ZipList $ do let ZipList y' = f x guard (not (null y')) let ZipList ys = ZipList xs >>= ZipList . join . maybeToList .

fmap snd . uncons . getZipList . f

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head y' : ys

instance MonadFail ZipList where fail _ = empty

instance MonadPlus ZipList _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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