Re: [Haskell-cafe] Instance deps (was: [announcement] filtrable: class of filtrable containers)

There are discussions once in a while: https://www.reddit.com/r/haskell/comments/2rajq1/is_there_anything_planned_t... https://www.reddit.com/r/haskell/comments/2rajq1/is_there_anything_planned_t... https://www.reddit.com/r/haskell/comments/1id0p7/backpack_retrofitting_haske... https://www.reddit.com/r/haskell/comments/1id0p7/backpack_retrofitting_haske... I’m not sure what’s the story with backpack, way or another it would need to solve instance problem. - Oleg

On 17 Feb 2016, at 20:34, amindfv@gmail.com wrote:

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El 17 feb 2016, a las 12:16, M Farkas-Dyck escribió:

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On 17/02/2016, Joachim Breitner wrote: You might want to add laws in the style of

If this is also a Foldable, then toList . mapMaybe f = mapMapybe f . toList toList . catMaybes = catMaybes . toList toList . filter f = filter f . toList

Shall do.

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Do you plan to add instances for all the other data structures in base that are filtrable?

Yes, if i missed any, please let me know which ☺

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On 17/02/2016, Oleg Grenrus wrote: - I’d also like to see instances for types in containers, unordered-containers, vector and semigroup.

I was hoping to have no deps but base... alas, Cabal and Hackage seem to have no good way to have instance deps, so the instances must be in either the package defining the class or the one defining the types which are instances of it.

Are there any existing proposals for a solution to this?

Tom

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If you don’t mind I can make a PR for the instances.

Feel free to do so for containers and vector at least. I may want this to not transitively depend on unordered-containers → hashable → text, but if enough potential users want these instances i'll include them (containers and vector come with GHC so it's not so bad). What types in semigroups would you add instances of?

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- The OtherLicense seems a bit scary (even the contents aren’t), is there a good reason why you don’t use more familiar MIT or BSD3?

Too verbose. I might use ISC if it weren't also an OtherLicense...

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The law:

filter f = mapMaybe (liftA2 (<$) id (guard ∘ f))

is very hard to understand.

Rewritten.

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On 17/02/2016, Simon Jakobi wrote: your package looks very similar to http://hackage.haskell.org/package/witherable!

Witherable has Traversable superclass, but some Filtrable types may not be Traversable. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

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