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

On 2014-12-30 23:41, Milan Straka wrote:

Hi all,

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

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

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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.

Well, there's an opposing point called "usability". If there are already "obvious" functions to use in other data structure modules then they should *probably* also be represented in the other data structure modules. (I don't claim that this is necessarily a "trump", but I think it bears consideration.) Regards,