Re: Proposal: Add filterM or filterA to Data.Sequence

Hi all,

-----Original message----- From: David Feuer Sent: 30 Dec 2014, 13:15

On Tue, Dec 30, 2014 at 12:05 PM, Johan Tibell wrote:

...

We should check that `filterM . toList` isn't as fast. That was the case for bytestring and we rejected adding filterM there for that reason.

Let me expand that definition to what it really looks like:

filterMSeq f = fmap fromList . filterM f . toList

Yes, you can do this. Yes, it's probably even pretty efficient. But it's a bit painful to have to expand things out like this just to switch a bit of code from lists to sequences.

the problem with this is that there are really many functions that "would be useful", but we do not really want to add them all. A general rule I have been using is "can this be implemented straightforwardly using existing methods without hurting performance much"? So I would like to see the numbers, please. Also, filterM is not yet settled in base, so we should wait some time until it is. Cheers, Milan PS: It is a shame we cannot reuse Foldable and/or Traversable for filtering. Maybe we should add a new Filterable class?