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Compact Region Short-Circuiting
by Andrew Martin 11 May '17

11 May '17

In the paper on compact regions (http://ezyang.com/papers/ezyang15-cnf.pdf) we find the following: > However, if we want to apply a functional update to this tree, we may > want to specify the already existing compact region so we can reuse any > already compacted shared data... appendCompact, like newCompact, fully > evaluates a; however, it copies the result into the same compact region > as Compact b. Additionally, it short-circuits the evaluation/copying > process if a subgraph is already in the target compact region. However, in the docs for both the compact library and the ghc-compact library (still only on phabricator), this short-circuiting behavior is not mentioned. Did this end up in the final implementation on was it dropped? If it is implemented, I think it's worth mentioning in the docs for `compactAdd`. -Andrew Martin

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ANNOUNCE: graphviz 2999.19.0.0
by Ivan Lazar Miljenovic 03 May '17

03 May '17

I've just released a new version of my Haskell bindings to the Graphviz graph visualisation toolkit. Note that the major version bump is solely because I had to remove what I thought was a useful feature (trying to allow you to do things like `"a" --> ["b", "c", "d"]` in Monadic graphs by automagically converting the "a" into ["a"]) turned out not to work in practice (as people will typically use this with literal values, but when combined with OverloadedStrings results in GHC getting confused as to what the type is). So unless you actually managed to use this functionality, then the API remains the same as 2999.18.* and you should just be able to bump your upper versions in your .cabal files (which you all do, right)? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Re: Civility notes (was "Traversable instances for (,,) a b")
by Theodore Lief Gannon 30 Apr '17

30 Apr '17

I'm also -1 to an explicit code of conduct. Sure, once in a while someone has to step in with Wheaton's Law or what I can't resist calling Simon Says; but all it takes is a gentle reminder. Nobody here is genuinely contemptuous toward anyone else. The barrier of entry is too high -- the trolls are happy enough on reddit. ;) On Apr 6, 2017 6:17 AM, "Andreas Abel" <andreas.abel(a)ifi.lmu.de> wrote: On 03.04.2017 10:42, Henning Thielemann wrote: > On Mon, 3 Apr 2017, Simon Peyton Jones via Libraries wrote: > > I’ve been talking to a couple of people about whether it would be >> useful to have an explicit Haskell Community Code of Conduct. Many >> online communities have one (e.g. Rust), and it might be helpful for >> everyone to have a concrete baseline rather than an unwritten >> standard. Any views on that? >> > > I think these Code of Conducts make things even worse because then some > people start to check every word against these codes. Instead I suggest > we make more use of humor. E.g. Carter Schonwald's comment about grumpy > people made me think about renaming my prelude-compat package to > grumpy-prelude. :-) > I agree with Henning. The discussion gets heated because people are passionate about Haskell; and the latter is a good thing. I rather stomach some insults on a mailing list than having a formal code of conduct. Severe violations of politeness can be pointed out without having such a formal code. We can apply common sense. -- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel(a)gu.se http://www.cse.chalmers.se/~abela/ _______________________________________________ Libraries mailing list Libraries(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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Re: Functor, Applicative, Monad, Foldable, Traversable instances for (, , ) a b
by Jonathon Delgado 27 Apr '17

27 Apr '17

Code please? An actual, concrete example?

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Functor, Applicative, Monad, Foldable, Traversable instances for (, , ) a b
by Fumiaki Kinoshita 26 Apr '17

26 Apr '17

It's surprising that they are missing (forgive me, I'm not here to make people grumpy).

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Add Arg{Min,Max} pattern synonyms to Data.Semigroup
by Baldur Blöndal 21 Apr '17

21 Apr '17

Add (explicitly-bidirectional record) pattern synonyms to Data.Semigroup: pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue) pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax {maxArg, maxValue} = Max (Arg maxArg maxValue) As described in https://ghc.haskell.org/trac/ghc/ticket/13572

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Is mkTrApp unsafe?
by Andrew Martin 15 Apr '17

15 Apr '17

I've been playing around with the GHC 8.2 release candidate. In Type.Reflection.Unsafe, there's a really handy function named mkTrApp. Everything else in that module is pretty evidently unsafe, but I'm not so sure about mkTrApp. I'm wondering if it should actually be exported by Type.Reflection instead or if I've missed some way it could be used to create an ill-kinded TypeRep. -Andrew Martin

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Banded Matrices
by Dominic Steinitz 13 Apr '17

13 Apr '17

Hi Henning, I just noticed https://hackage.haskell.org/package/hmatrix-banded. I have just made a PR to hmatrix to add a tridiagonal solver: https://github.com/albertoruiz/hmatrix/pull/224. I don’t think there is anything to do but I thought it worth sharing. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Re: Constraints on definition of `length` should be strengthened
by Anthony Clayden 10 Apr '17

10 Apr '17

[Errk, somehow posted this with no Subject. Trying again.] > On Sun Apr 9 19:24:12 UTC 2017, Sven Panne wrote: >> 2017-04-09 2:01 GMT+02:00 Ben Franksen : >>> Am 08.04.2017 um 04:03 schrieb Anthony Clayden: >>> [...] So to take your examples from an earlier thread, >>> what do you expect Haskell to do here?: >>> >>> maximum (True,2) => ? >>> minimum ((3, 4),5) => ? -- i.e. :: ((Int, Int), Int) >>> sum (7,3.14) => ? -- i.e. :: (Int, Double) >>> product (Left $ error "Errk") => ? -- i.e. :: >>> Either e Int >> >> I (and others) think these should be type errors. >> > Exactly. OK. Do y'all think there should be a `toList` method for them? Indeed, should there be a `toList` method available for any data type that doesn't implement `fromList`? Perhaps `toList` should not be a method of Foldable? > >>> Do you expect Foldable (a, a) to behave differently >>> vs Foldable (b, a) vs Foldable ((a, a), a) vs ...? >>> >> It would be nice if we could all agree on removing these >> instances. >> > Yep. :-) >> BTW, I find it remarkable that of those who defend these >> instances, few seem to be especially interested >> in clarifying the OP's question: what >> laws exactly do we expect for Foldable? [...] >> One of the Laws appears to be that `length` etc behave as `length . toList`. AntC

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None
by Anthony Clayden 10 Apr '17

10 Apr '17

> On Sun Apr 9 19:24:12 UTC 2017, Sven Panne wrote: >> 2017-04-09 2:01 GMT+02:00 Ben Franksen : >>> Am 08.04.2017 um 04:03 schrieb Anthony Clayden: >>> [...] So to take your examples from an earlier thread, >>> what do you expect Haskell to do here?: >>> >>> maximum (True,2) => ? >>> minimum ((3, 4),5) => ? -- i.e. :: ((Int, Int), Int) >>> sum (7,3.14) => ? -- i.e. :: (Int, Double) >>> product (Left $ error "Errk") => ? -- i.e. :: >>> Either e Int >> >> I (and others) think these should be type errors. >> > Exactly. OK. Do y'all think there should be a `toList` method for them? Indeed, should there be a `toList` method available for any data type that doesn't implement `fromList`? Perhaps `toList` should not be a method of Foldable? > >>> Do you expect Foldable (a, a) to behave differently >>> vs Foldable (b, a) vs Foldable ((a, a), a) vs ...? >>> >> It would be nice if we could all agree on removing these instances. >> > Yep. :-) >> BTW, I find it remarkable that of those who defend these instances, few >> seem to be especially interested in clarifying the OP's question: what >> laws exactly do we expect for Foldable? [...] >> One of the Laws appears to be that `length` etc behave as `length . toList`. AntC

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