- Libraries - Haskell.org

Generalise type of deleteBy
by Matthew Pickering 01 Oct '16

01 Oct '16

The type of `deleteBy` in `Data.List` could easily be generalised in a useful way. ``` deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a] ``` to ``` deleteBy :: (a -> b -> Bool) -> a -> [b] -> [b] ``` There is this closed ticket but no reasons for not generalising. https://ghc.haskell.org/trac/ghc/ticket/3399 Discussion Period: 1 week. Matt

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Proposal: add Monoid1 and Semigroup1 classes
by David Feuer 01 Oct '16

01 Oct '16

I've been playing around with the idea of writing Haskell 2010 type classes for finite sequences and non-empty sequences, somewhat similar to Michael Snoyman's Sequence class in mono-traversable. These are naturally based on Monoid1 and Semigroup1, which I think belong in base. class Semigroup1 f where (<<>>) :: f a -> f a -> f a class Semigroup1 f => Monoid1 f where mempty1 :: f a Then I can write class (Monoid1 t, Traversable t) => Sequence t where singleton :: a -> t a -- and other less-critical methods class (Semigroup1 t, Traversable1 t) => NESequence where singleton1 :: a -> t a -- etc. I can, of course, just write my own, but I don't think I'm the only one using such.

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Bug in Eq/Ord typeclass documentation?
by Grant Wu 26 Sep '16

26 Sep '16

Neither Eq nor Ord have the types/summary of the methods that are part of the minimal complete definition listed. See http://hackage.haskell.org/package/base-4.9.0.0/docs/Prelude.html#t:Eq. Hopefully this is the right place to email. If not, apologies in advance. Thanks, Grant Wu grantwwu(a)gmail.com

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Numeric read seems too strict
by David Feuer 12 Sep '16

12 Sep '16

I noticed the other day that readMaybe (fix ('a':)) :: Maybe Double is an infinite loop. The problem is that the lexer doesn't know that it's expected to lex a number. It just keeps scanning and scanning to get to the end of the endless token. Shall we fix this?

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Discussion: name for reversing fromList in Data.Sequence
by David Feuer 05 Sep '16

05 Sep '16

I'd like to add a function fromListReversing :: [a] -> Seq a to Data.Sequence, with fromListReversing = reverse . fromList = fromList . reverse I don't know just what to call this function, however.

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Modules for new map merge functions may be renamed
by David Feuer 02 Sep '16

02 Sep '16

We hope to make one more, fairly small, major release for containers for inclusion in GHC 8.2. I am considering renaming the new modules Data.Map.Merge.Lazy and Data.Map.Merge.Strict instead of Data.Map.Strict.Merge and Data.Map.Lazy.Merge. That seems more consistent with the module scheme for the rest of the package, and leaves open the option of adding extra merge-related modules in the future. I'm sorry about the potential wobble, but I think taking care of this now will lead to much less trouble than waiting till later.

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Re: Discussion: name for reversing fromList in Data.Sequence
by David Feuer 01 Sep '16

01 Sep '16

My concern is for what happens when such rules don't fire. If someone converts a large list to a sequence only to reverse it, then the badly-ordered sequence will end up being evacuated by the garbage collector unnecessarily, pushing up the next major collection. In contrast, I've used rewrite rules to fuse map with reverse; the worst case there is some extra churn in the nursery. That said, if others don't consider it important enough, or have enough faith that rules will fire in this case (which may very well be), I can go the rules route. On Sep 1, 2016 3:51 PM, "John Wiegley" <johnw(a)newartisans.com> wrote: >>>>> "DF" == David Feuer <david.feuer(a)gmail.com> writes: FD> I'd like to add a function DF> fromListReversing :: [a] -> Seq a Hi David, Perhaps rather than proliferating the libraries with fused compositions that are faster than their composites via (.), we could defer things like this to REWRITE rules. -- John Wiegley GPG fingerprint = 4710 CF98 AF9B 327B B80F http://newartisans.com 60E1 46C4 BD1A 7AC1 4BA2

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Proposal: Add <&> to Data.Functor
by David Feuer 01 Sep '16

01 Sep '16

The <&> operator is rather popular: (<&>) :: Functor f => f a -> (a -> b) -> f b (<&>) = flip fmap Now that we have (&) in Data.Function, I think we should have (<&>) in Data.Functor.

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Announcing containers 0.5.8.1
by David Feuer 31 Aug '16

31 Aug '16

There's a lot to see in this one. There are plenty of brand-new functions in Data.Map, Data.Set, and Data.Sequence, including a highly-optimized lens-inspired map alteration function and a brand-new API for merging maps efficiently. Several key map, set, and sequence functions have sped up considerably. The full change log is below. I have tried to give appropriate credit to all the non-maintainers who contributed to this release, some of whom made very major contributions indeed. If I missed anyone, please give a shout. General package changes: Remove all attempts to support nhc98 and any versions of GHC before 7.0. Integrate benchmarks with Cabal. (Thanks, Gabriel Gonzalez!) Make Cabal report required extensions properly, and stop using default extensions. Note that we do not report extensions conditionally enabled based on GHC version, as doing so would lead to a maintenance nightmare with no obvious benefits. Use BangPatterns throughout to reduce noise. This extension is now required to compile containers. Improve QuickCheck properties taking arbitrary functions by using Test.QuickCheck.Function.Fun instead of evil Show instances for functions. Expose several internal modules through Cabal (as requested by Edward Kmett). These remain completely unsupported. New exports and instances: Add alterF, restrictKeys, and withoutKeys to Data.Map and Data.IntMap. Add take, drop, splitAt, takeWhileAntitone, dropWhileAntitone, and spanAntitone for Data.Map and Data.Set. Thanks to Cale Gibbard for suggesting these. Add merge, mergeA, and associated merge tactics for Data.Map. Many thanks to Cale Gibbard, Ryan Trinkle, and Dan Doel for inspiring the merge idea and helping refine the interface. Add fromDescList, fromDescListWith, fromDescListWithKey, and fromDistinctDescList to Data.Map. Add fromDescList and fromDistinctDescList to Data.Set. Add Empty, :<|, and :|> pattern synonyms for Data.Sequence, as originally envisioned in the finger tree paper by Paterson and Hinze. Add adjust', (!?), lookup, chunksOf, cycleTaking, insertAt, deleteAt, intersperse, foldMapWithIndex, and traverseWithIndex for Data.Sequence. Derive Generic and Generic1 for Data.Tree.Tree, Data.Sequence.ViewL, and Data.Sequence.ViewR. Add foldTree for Data.Tree. (Thanks, Daniel Wagner!) Semantic changes: Make Data.Sequence.splitAt strict in its arguments. Previously, it returned a lazy pair. Fix completely erroneous definition of length for Data.Sequence.ViewR. Make Data.Map.Strict.traverseWithKey force result values before installing them in the new map. Make Data.Tree.drawTree handle newlines better. (Thanks, recursion-ninja!) Deprecations: All functions in Data.Map proper that have been documented as deprecated since version 0.5 or before now have DEPRECATED pragmas and will actually be removed after another cycle or two. Tree printing functions in Data.Map intended for library debugging are now deprecated. They will continue to be available for the foreseeable future in an internal module. Performance changes: Substantially speed up splitAt, zipWith, take, drop, fromList, partition, foldl', and foldr' for Data.Sequence. Special thanks to Lennart Spitzner for digging into the performance problems with previous versions of fromList and finding a way to make it really fast. Slightly optimize replicateA. Stop traverse from performing many unnecessary fmap operations. Most operations in Data.Sequence advertised as taking logarithmic time (including >< and adjust) now use their full allotted time to avoid potentially building up chains of thunks in the tree. In general, the only remaining operations that avoid doing more than they really need are the particular bulk creation and transformation functions that really benefit from the extra laziness. There are some situations where this change may slow programs down, but I think having more predictable and usually better performance more than makes up for that. Add rewrite rules to fuse fmap with reverse for Data.Sequence. Switch from hedge algorithms to divide-and-conquer algorithms for union, intersection, difference, and merge in both Data.Map and Data.Set. These algorithms are simpler, are known to be asymptotically optimal, and are faster according to our benchmarks. Speed up adjust for Data.Map. Allow map to inline, and define a custom (<$). This considerably improves mapping with a constant function. Remove non-essential laziness throughout the Data.Map.Lazy implementation. Slightly speed up deletion and alteration functions for Data.IntMap.

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Proposal: Add `restriction` to Data.Map and Data.IntMap
by David Feuer 25 Aug '16

25 Aug '16

Cale Gibbard proposes the following: Data.IntMap.restriction :: IntSet -> IntMap a -> IntMap a Data.Map.restriction :: Ord k => Set k -> Map k a -> Map k a In each case, the map is filtered to contain only the keys that are also found in the set. This can be implemented efficiently using a slightly stripped-down version of Data.Map.intersection. David Feuer

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