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Wiki page for 3-Release-Policy is not found
by Takenobu Tani 04 Nov '20

04 Nov '20

Dear Libraries, Currently, a wiki page of `3-Release-Policy` is not found: * https://prime.haskell.org/wiki/Libraries/3-Release-Policy Does anyone have a plan to migrate those pages? Regards, Takenobu

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Stepping away
by Sean Chalmers 30 Oct '20

30 Oct '20

Hi all, For various reasons I'm not interested in maintaining my Haskell packages any more. If anyone has any interest in taking over then I am happy to hand them over: async-io-either classy-influxdb-simple haskell-time-range hoist-error reflex-dom-svg servant-waargonaut tasty-hedgehog-coverage tasty-wai waargonaut Been swell, swellings gone down. Cheers, Sean Chalmers

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[Proposal] Strict `sum` and `product`
by Hécate 27 Oct '20

27 Oct '20

My fellow Haskell developers, contributors and maintainers, I wish to present what is certainly a controversial proposal for the `base` library: Making the `sum` and `product` functions from the `base` library strict. This is not a new question, the debate is old, but I am personally convinced that the existence of those two lazy functions is something that should never have happened. One of the first goals that led to the creation of Haskell was to enable collaboration and research in the domain of lazy (or non-strict) programming languages and techniques. While it led to the discovery of new methods and ways to represent programs, we also realised that this paradigm has proven to produce sub-optimal implementations for these functions. And while maintaining backward compatibility *is* important when designing and maintaining a programming language, we have thankfully developed deprecation mechanisms that can be used to signal that bad, or sub-optimal decisions of the past can be corrected. To refresh our collective memory, here is the current state of things, regarding `sum`: ``` ❯ ghci +RTS -M1024m GHCi, version 8.10.1: https://www.haskell.org/ghc/ :? for help λ❯ sum [1..10^9] *** Exception: heap overflow ``` Whereas, with an alternative implementation, such as `foldl'`: ``` λ❯ foldl' (+) 0 [1..10^9] 500000000500000000 (31.35 secs, 88,000,076,288 bytes) ``` I do not think a heap overflow, and the underlying space leak occasioned by the laziness of `foldl`, are behaviours we should aim to preserve for the sake of backward compatibility. And actually, I think that moving these two functions to a strict, space leak-free implementation would benefit the lazy PL research domain by showing a good counter-example of why it is not necessarily suitable for every kind of computation. I also think, and this is rooted from experience, that we must strive to empower our users with the power of laziness. Not burden them with it. Standing on the shoulders of giants is what made Haskell so great, but this should not prevent us from spreading our wings to go higher. ——— Now, there have been Prelude replacements (such as Relude) and companion libraries (like `strict`) who have been shipping such alternative implementations for quite some time now. A point that can be raised is: Why should we bother? Isn't `strict` already enough? To this I answer: `strict` and Relude, ultimately, patches on an tire's inner tube. We may be able to roll with them for some distance, but their very existence is a response to an abnormal situation that we have grown to accept. However, any bicycle rider who has the means to change their tire should do so. I believe we have the means to do so. Another point that could be raised as well is the fact that this implementation change would deviate from the 2010 Haskell Report[0]. If we want to stay true to the spirit and letter of the Report, this is actually a non-issue. Indeed, it is noted that: > This report defines the syntax for Haskell programs and an informal abstract semantics for the meaning of such programs. We leave as implementation dependent the ways in which Haskell programs are to be manipulated, interpreted, compiled, etc. This includes such issues as the nature of programming environments and the error messages returned for undefined programs (i.e. programs that formally evaluate to⊥).[1] As well as in chapter 9: > In this chapter the entire Haskell Prelude is given. It constitutes a specification for the Prelude. Many of the definitions are written with clarity rather than efficiency in mind, and it is not required that the specification be implemented as shown here.[2] And finally, regarding the non-strict nature of Haskell, the Report references strict evaluation to avoid "unneeded laziness."[3] Thus it was expected that laziness would not be a silver bullet, and it could harm performance. ——— Regarding the implementation detail, `sum` and `product` would piggy-back on the already-present `foldMap'` function. Thank you very much for reading, I believe we can all go together towards improving the experience of Haskell developers, starting with this. [0]: Haskell 2010 Language Report, https://www.haskell.org/definition/haskell2010.pdf [1]: Haskell 2010 Language Report, page 3 [2]: Haskell 2010 Language Report, Chapter 9 Standard Prelude, page 105 [3]: Haskell 2010 Language Report, Section 6.2 Strict Evaluation, page 75 -- Hécate ✨ IRC: Uniaika WWW: https://glitchbra.in RUN: BSD

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Version bump in 'unix' and 'parsec'
by Vladislav Zavialov 12 Oct '20

12 Oct '20

Three weeks ago I sent 10 pull requests to GHC boot libraries, bumping the upper bound on ‘base’ to accept base-4.16, for the next GHC release. Most of these were merged, but two remain: 1. https://github.com/haskell/unix/pull/158 2. https://github.com/haskell/parsec/pull/118 Could somebody with the permissions hit the merge button? It’s just a version bump and I need it to unblock some other work. - Vlad

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Use of evaluate in Control.Concurrent.MVar
by David Feuer 12 Oct '20

12 Oct '20

Control.Concurrent.MVar uses `evaluate` in a couple places, and I don't understand why: modifyMVar :: MVar a -> (a -> IO (a,b)) -> IO b modifyMVar m io = mask $ \restore -> do a <- takeMVar m (a',b) <- restore (io a >>= evaluate) `onException` putMVar m a putMVar m a' return b modifyMVarMasked :: MVar a -> (a -> IO (a,b)) -> IO b modifyMVarMasked m io = mask_ $ do a <- takeMVar m (a',b) <- (io a >>= evaluate) `onException` putMVar m a putMVar m a' return b The general purpose is to make sure that the result of the IO action is forced to head normal form within the scope of the `catch` block created by `onException`. But in this context, I don't see why we need to use `evaluate` rather than just `seq`, or why that is desirable. Couldn't we just do this? modifyMVar m io = mask $ \restore -> do a <- takeMVar m (a',b) <- restore (io a >>= (pure $!)) `onException` putMVar m a putMVar m a' return b David

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llvm-hs version 10, and library maintainers
by Travis Whitaker 02 Oct '20

02 Oct '20

Hello fellow Haskellers, LLVM version 10 is out, and LLVM 11 is on the way. I'm curious if anyone has begun work on getting llvm-hs working with version 10. This is likely to be a bit more of a chore than usual, because of changes in the JIT API. Furthermore, activity on the llvm-hs GitHub repo seems to have slowed; I'm curious who the current maintainers are and whether or not they could use a hand? I make active use of the package and would be happy to contribute time to help out any way I can. Thanks, Travis Whitaker

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How the heck should we fix Ord for Array?
by David Feuer 02 Oct '20

02 Oct '20

At present, the Eq instance for Data.Array.Array is somewhat broken[1]. In particular, it ignores the array bounds for empty arrays (but not for other arrays), so its meaning is inconsistent, and the bounds function doesn't respect ==. The fix to that is tiny and obvious: pay attention to the bounds regardless. Eq and Ord instances are expected to be compatible: a == b <==> compare a b = EQ So when I started putting together a merge request to fix the Eq instance, I glanced over at the Ord instance to see what that was doing. That instance was 1. Incompatible with the current Eq instance. 2. Incompatible with the proposed Eq instance. Specifically, that instance compares the association lists of the two arrays, ignoring the bounds in all cases. It is not at all obvious to me what the Ord instance should actually be, except that it should be compatible with Eq. [1] https://gitlab.haskell.org/ghc/ghc/-/issues/18700

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Status of tasty-discover
by John Ky 28 Sep '20

28 Sep '20

Hello, Does anyone know what the status of tasty-discover <https://hackage.haskell.org/package/tasty-discover> is? The package links to http://git.coop/lwm/tasty-discover, which redirects to https://git.coop/decentral1se/tasty-discover, which says *Archived project! Repository and other project resources are read only*. I'd like to raise a ticket on the project, but haven't been able to. Cheers, -John

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Diagonalization/ dupe for monads and tuples?
by Carter Schonwald 26 Sep '20

26 Sep '20

It was pointed out to me in a private communication that the tuple function \x->(x,x) is actually a special case of a diagonalization for biapplicative and some related structures monadicially. Another example in the same flavor is pure impl for the applicative instance for sized lists. diag x = bipure x x So framed a litttle differently, there’s definitely an abstraction or common pattern lurking here. Perhaps folks can help Tease this out. One person I chatted with this morning alluded to it being relevant to computational flavors of adjunctions or some such ? It def matters in a different way when doing computation resource aware programming in a symmetric monoidal category. Let’s collect some ideas and patterns and get to the bottom of this!

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[ANN] bytestring-0.11.0.0
by Andrew Lelechenko 26 Sep '20

26 Sep '20

On behalf of the maintainers team I'm happy to announce that bytestring-0.11.0.0 (http://hackage.haskell.org/package/bytestring-0.11.0.0) is finally released. It is to be shipped with the upcoming GHC 9.0. Highlights from the changelog (https://github.com/haskell/bytestring/blob/0.11.0.0/Changelog.md) * Optimize internal representation of ByteString reducing allocations. * Rewrite rules for {take,drop}While, any, all, findInd{ex,ices} (an order of magnitude faster in certain cases). * Faster (up to 5%-30%) implementations of fold{l,r}, scan{l,r}, mapAccum{L,R}, any, all, filter. * Add indexMaybe and synonym (!?) for safe indexing. * Re-export Data.ByteString.Lazy.{from,to}Strict from Data.ByteString. * Remove deprecated modules and functions. Many people contributed their time and effort to make this release happen. Just to name a few in no particular order, mostly according to `git log`: * Alexandre Esteves * Andreas Klebinger * Andrew Martin * Ben Gamari * Cole Miller * Edward Kmett * Fintan Halpenny * Fumiaki Kinoshita * Hécate Kleidukos * Peter Duchovni * Sergey Vinokurov * Simon Jakobi * Sylvain Henry * Viktor Dukhovni * me Here is an incantation for `stack` folks: resolver: nightly-2020-09-23 packages: - . extra-deps: - bytestring-0.11.0.0 - github: haskell/cabal commit: 5139d6e72d391bffa3cf06f08884277799eb0b45 subdirs: - Cabal - binary-0.8.8.0 - directory-1.3.6.0 - text-1.2.3.2 - unix-2.7.2.2 - parsec-3.1.14.0 - process-1.6.9.0 allow-newer: true Best regards, Andrew

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