- Libraries - Haskell.org

Re: [GHC DevOps Group] Making GHC's fast release cadence work
by Boespflug, Mathieu 02 Jul '19

02 Jul '19

A related discussion came up previously: https://mail.haskell.org/pipermail/ghc-devops-group/2017-December/thread.ht…. >From the moment that GHC accepts unreleased dependencies on its release branch, GHC developers lose full control over their own release timeline. Because a new GHC release can only ship when the dependencies have been released, the release process could block on upstream for indefinite periods of time, like is currently happening with at least one GHC dependency that has been blocked on the maintainer for at least 27 days (and counting). It was suggested then that GHC should only use release versions of its dependencies on the master or release branch, and that if this isn't practical due to co-dependency, then that suggests said dependencies should have the same release cycle as GHC (i.e. same people can cut releases of both) or even be merged in GHC itself. -- Mathieu Boespflug Founder at http://tweag.io. On Mon, 1 Jul 2019 at 21:03, David Feuer <david.feuer(a)gmail.com> wrote: > I realize that my response came off as rather unfriendly. I'm sorry about > that. Thinking a bit more about it, I think GHC HQ can help Core Library > maintainers in several unintrusive ways. Here are a couple I would > appreciate myself; others may disagree. > > 1. Work with Herbert, Ryan, etc., to make it easy to use -Werror in Travis > scripts. See https://github.com/haskell/containers/pull/645 > > 2. Give us a nudge when you have a release timeframe in mind. "We're > hoping to have the core libraries ready for release by December 5" (several > weeks beforehand, repeated a couple times thereafter with appropriate > adjustments) is much less stressful than "We're basically ready for release > but we're waiting on core libraries." > > On Mon, Jul 1, 2019, 1:30 PM David Feuer <david.feuer(a)gmail.com> wrote: > >> I think it would be nice to start by letting the core library maintainers >> know your preferred release deadlines. >> >> On Mon, Jul 1, 2019, 1:22 PM Ben Gamari <ben(a)well-typed.com> wrote: >> >>> Hi everyone, >>> >>> GHC's core libraries are a critical part of the Haskell ecosystem. I >>> want to thank you for overseeing the maintenance of this infrastructure. >>> >>> However, for the last three weeks the release candidate for GHC 8.8.1 >>> has been ready aside from releases of a couple of our core libraries. >>> >>> Naturally, delays like this make it hard for GHC to maintain its faster >>> release cycle. At the same time, we do not want this cadence to impose >>> an undue burden on our core library maintainers. >>> >>> How do you think we might speed up this process? >>> >>> For instance, perhaps the GHC release manager could pick up >>> some of the "boring parts" of core library maintenance limited to: >>> >>> * Version bound bumps >>> >>> * Changes of CPP conditionals to accommodate changes in the >>> compiler and other core libraries >>> >>> * Changelog entries to describe these releases >>> >>> * Uploading these releases or revisions to Hackage >>> >>> Of course, this would merely be an offer to maintainers; this would be >>> GHC's way of carrying some of the burden that our release process >>> imposes. >>> >>> In general, I am interested in a discussion on how to make this faster >>> release pace work. Ideas? >>> >>> Cheers, >>> >>> - Ben >>> >>> _______________________________________________ > Ghc-devops-group mailing list > Ghc-devops-group(a)haskell.org > https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devops-group >

2 2

(no subject)
by Andrew Martin 01 Jul '19

01 Jul '19

To get GHC to raise an exception from an inline primop, I presume that I'd need to jump to stg_raisezh. None of the existing inline primops do anything quite like this. I see things like emitMemcmpCall and emitMemsetCall, but these ultimately just wrap emitForeignCall, which wraps mkUnsafeCall, which wraps the data constructor CmmUnsafeForeignCall. I think I want CmmCall instead, which is described by the comments as being used for "a native call or tail call". Hmm... emitRtsCall might be what I want. I'll try pursuing this route further. -- -Andrew Thaddeus Martin

2 1

Making Int{Map,Set} polymorphic over the key type
by Georg Rudoy 29 Jun '19

29 Jun '19

Hi folks, What do you think about making IntMap and IntSet polymorphic over the keys as long as the key type k is Coercible to Int? The motivation is that oftentimes one needs to have a collection of newtype wrappers around Int, and then they have to either unpack/repack it around the relevant containers (which is not nice), or just use HashMap/HashSet (which is perhaps suboptimal). If this is a direction the community might deem reasonable, I'd be happy to work on this and make a PR to the containers repo (perhaps after discussing the specific details about naming, etc). -- Georg Rudoy

4 7

Fwd: lazier writer monad
by Tristan Wibberley 26 Jun '19

26 Jun '19

Dear Haskell Libraries mailing list members, I've submitted a merge request for an increase in the laziness of the writer monad: https://gitlab.haskell.org/ghc/ghc/merge_requests/1262 and it requires discussion via this mailing list. The link above includes an example of the motivation for this change and I hope you can all extrapolate to see the importance of this change, sufficient to not only accept this but to be moved to add a language flag, available within the content of a module's source file, to match unique constructors lazily throughout a module that uses it, lifting _|_ to the next least-defined value. The core problem is that for the most handy and practical library interfaces, we need function results to be as well-defined as possible before a strict pattern match is required to choose between two constructors/values. There are several parts to providing that but one important part is that elements of patterns that cannot be unmatched should be lazily matched so the function's definition can be used without evaluating the function's arguments first. This avoids having to train users to always avoid patterns except after a let binding which would otherwise be necessary to establish a standard habit to lazily pattern match so the user base encourages each other to make their functions maximally useful. -- Tristan

3 2

transformers mirroring to GitHub
by chessai . 25 Jun '19

25 Jun '19

Could we mirror transformers from darcshub to GitHub? This would make browsing the current source easier for those of us who do not frequent darcshub. It would also help with the uniformity of having core libs on GitHub. Of course this would just be a mirror, and users would be advised to not open PRs there. Not sure how easy mirroring from DarcsHub to GitHub is. Thoughts? Thanks

2 2

Re: Data.Graph transitive closure
by Johannes Waldmann 24 Jun '19

24 Jun '19

> ... reasonably efficient transitive closure for Data.Graph ... well, since we have type Graph = Array Vertex [Vertex] efficiency is already questionable? We cannot quickly check whether an edge is present, we cannot quickly get all predecessors of a vertex. But perhaps we don't need to. The underlying assumptions (cost of elementary operations) of http://www.cs.hut.fi/~enu/thesis.html are not immediately clear. The cited Agda library has newtype Graph n e = Graph (Map n (Map n e)) Another option is to store back edges as well, as in https://github.com/haskell-works/relation/blob/master/src/Data/Relation/Int… FGL fuses these two maps type GraphRep a b = IntMap (Context' a b) type Context' a b = (IntMap [b], a, IntMap [b]) https://hackage.haskell.org/package/fgl-5.7.0.1/docs/src/Data.Graph.Inducti… this saves some look-ups (if you need successors and predecessors of the very same node) but this can't be used for relations, where start and end of an edge have different types. But for transitive closure, these types would agree anyway. What to make of this? Perhaps Data.Graph should be moved out of containers. The design space is just too large to single out one specific point? If we keep it, it would be very nice to document the complexity of algorithms. Section 7 of the King/Launchbury paper (cited in the API docs) claims "DFS in O(V+E)", backed up by experiments. This seems to be the main motivation for this library (DFS, with application: SCC). It's not clear whether the underlying design should be recommended for a general graph library. - Johannes

6 12

Re: Data.Graph transitive closure
by Johannes Waldmann 22 Jun '19

22 Jun '19

> .. I would use it. what is your use case? Can you extract test cases that could be used to validate correctness and complexity of an implementation? Specific question: assume the implementation gives you S = transitive-closure-of(R). Then what do you do with S (in your application)? Does Data.Graph (i.e., array of lists of successors) have the right structure? E.g., it is inefficient to test for membership in these lists. But lists are fine if you need to handle all successors anyway. Evaluation of (recursive) Datalog queries is another application area of transitive closure algorithms. (e.g., https://doi.org/10.1007/BF01264013 ) - J.

1 0

Re: Data.Graph transitive closure
by Alan Isaac 21 Jun '19

21 Jun '19

Feedback from an occasional Haskell user: I would use it. I've noticed that computational implementations of "transitive closure" often deviate from my (user-level) understanding of the standard mathematical definition. Specifically, self loops are often discarded. I assume/hope the math def will be used in haskell. A prominent example is Mathematica's TransitiveClosureGraph command. E.g., `TransitiveClosureGraph[{a -> b, b -> c, c -> a}]` has no self loops, even though `a` is clearly reachable from `a`, and TransitiveClosureGraph[{a -> a, b -> b, c -> c}]` is empty!) In the past networkx also had this flaw (although they indicated a plan to fix this; I'd have to recheck the current status). Cheers, Alan Isaac PS My apologies if I misread your post; I understood it to request user feedback, not just developer assessment. On 6/20/2019 8:00 AM, David wrote: > I just noticed that Data.Graph doesn't offer a transitive closure > operation. Looking into implementing one, I discovered that doing so > efficiently has been the subject of non-trivial research [*]. So if there's > any demand, we should try to implement a reasonably efficient version in > containers. Anybody want one?

1 0

Data.Graph transitive closure
by David Feuer 20 Jun '19

20 Jun '19

I just noticed that Data.Graph doesn't offer a transitive closure operation. Looking into implementing one, I discovered that doing so efficiently has been the subject of non-trivial research [*]. So if there's any demand, we should try to implement a reasonably efficient version in containers. Anybody want one? [*] http://www.cs.hut.fi/~enu/thesis.html

4 3

Add instance Bounded (Ratio a)
by Dannyu NDos 16 Jun '19

16 Jun '19

instance (Integral a, Bounded a) => Bounded (Ratio a) where minBound = minBound % 1 maxBound = maxBound % 1

4 4