August 2015 - Haskell-Cafe

Compilation time
by Corentin Dupont 25 Aug '15

25 Aug '15

Hi guys, I have an application with around 7K loc in 4 packages. It takes 1min30 to compile with stack. Is it a normal compilation time? My computer is fairly recent with Intel i7... I run some music in background :). Is there some statistics about compilation time somewhere? Thanks. Corentin

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[ANN] frpnow-0.12
by Atze van der Ploeg 25 Aug '15

25 Aug '15

Dear Cafe, We have released the (nearly) first version of FRPNow, the functional reactive programming library based on the ICFP 2015 paper "Principled Practical FRP: Forget the Past, Change the Future, FRPNow!" ( https://www.reddit.com/r/haskell/comments/3ai7hl/principled_practical_frp_f… ) The main package: http://hackage.haskell.org/package/frpnow Examples: https://github.com/atzeus/FRPNow/tree/master/Examples Gloss interoperability: http://hackage.haskell.org/package/frpnow-gloss GTK interoperability: http://hackage.haskell.org/package/frpnow-gtk (hackage doesn't like the newer GTK docs, so you can read the docs at http://www.cse.chalmers.se/~atze/frpnow-gtk/ ) Cheers, Atze

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New Functional Programming Job Opportunities
by Functional Jobs 24 Aug '15

24 Aug '15

Here are some functional programming job opportunities that were posted recently: Haskell Engineer at Wagon http://functionaljobs.com/jobs/8857-haskell-engineer-at-wagon Cheers, Sean Murphy FunctionalJobs.com

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Alternative to newtypes or orphan instances
by Clinton Mead 24 Aug '15

24 Aug '15

Lets say there's a type `T` I've imported from a package I don't control. I can easily write new functions to work on `T`. For example, I could write: f :: T -> T -> T f x y = ... I've extended T's functionality. No need for newtypes. This makes sense. Whilst a newtype in the following case: newtype Time = Time Int because in this case `Time` is conceptually different to `Int`. For example, you shouldn't multiply two `Time`s So in summary, we've just extended T's functionality appropriately, without introducing a newtype. But this could be dangerous. Lets say another module writer writes a similar function "f". Then if someone imports their module and ours, there will be a clash. Fortunately the compiler tells about this when it happens, and we can then use qualified imports to workaround the clash. This I'll get back to later. Now lets say I want to extend T's functionality some more, but this time by making it an instance of class C. Class C already exists in a package I don't control. Now it would be unreasonable for every class writer to write instances for every possible data type that is appropriate for their class. As you can see, it's an O(n^2) problem, so there will undoubtably be situations where one needs to write instances for data types and classes in separate packages. One recommended approach here is to newtype T, like the following: newtype MyT = MyT T however I find this incredibly ugly. Conceptually, there is no "newtype", and now there's different types of Ts bashing around which really are the same thing. Not only that, they're incompatible, for no good reason. Instead of these different Ts being different types because they're conceptually different things that shouldn't be mixed, the type of these objects depends solely on what operations I want to apply to them. Imagine a rule where: f :: T -> T -> T was only legal in the module T was defined. If you wanted to define T anywhere else, you'd have to do: f :: MyT -> MyT -> MyT That's how messy the newtype solution is, it wouldn't be accepted for ordinary functions, and I don't think it's reasonable to apply that messiness to class functions. A second approach is an orphan instance. The recommendation here is to put the orphan instances in their own module, so the user can choose to import them. This may works ok if your user is writing an executable. But what if your user is writing a library themselves. But once, you, or your user, directly uses one of the instances, they need to import it, and they pollute the global instance namespace for anyone that uses their package. This is okay if you're the only person doing it, but I think it's reasonable to say that if your practices would be bad if someone else was doing them also, then they're a bad practice. Indeed, if someone else writes their own instances and they clash with yours, people simply can't use your package and their package in the same program. This is bad. In the simple "function" case. We deal with the clash of two functions named "f" using qualified imports. We can't do that instances, nor can we even hide one of the instances. So to recap here we've tried: (1) Copying the data type. We've decided this has lots of problems. (2) Just making an orphan instance. This has serious problems too. I want to suggest a third option: (3) Copying the class. What would this involve: a) Making a new class (say C1), with the same class methods as the existing one (say C). b) Making an instance of the class like so: instance (C x) => C1 x where f = ModuleC.f ... which forwards all the calls to C. c) Add your new instances to C1 (these will overlap with the above but they will be more specific so with overlapping instances this is allowed). Now if your users want to use your instances, they import C1. They can still use the data type T as usual on the old instances, or on any existing functions defined on T directly. The big question is, what if someone else does this, and creates C2? Then they'll be a clash. But in this case, classes, unlike instances, can be explicitly imported and qualified. Your packages won't be impossible to use together, just the user will have to import one of them qualified. That's acceptable, we understand we have to do this sometimes with clashing function names too. So I guess my questions are: What do you think of my analysis? Are there parts that are incorrect? What do you think of my solution? Is there reasons why it is not as good as the "newtype" or "orphan instances" approach? Is there a way to make my solution easier to implement, i.e. less typing?

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getNumCapabilities always returns 1 with GHC 7.10.2 on OS X
by Geraldus 24 Aug '15

24 Aug '15

I have OS X Yosemite 10.10.4. There are two bundles of GHC (from ghcformacosx.github.io): 7.10.1 and 7.10.2. The latter always shows me one core when running `getNumCapabilities` action: *GHC 7.10.2* > stack ghci +RTS -N8 Using resolver: lts-3.0 from global config file: /Users/arthurfayzrakhmanov/.stack/global/stack.yaml Configuring GHCi with the following packages: GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help Prelude> :m +Control.Concurrent Prelude Control.Concurrent> getNumCapabilities 1 *GHC 7.10.1* > /Applications/ghc-7.10.1.app/Contents/bin/ghci +RTS -N8 GHCi, version 7.10.1: http://www.haskell.org/ghc/ :? for help Prelude> :m +Control.Concurrent Prelude Control.Concurrent> getNumCapabilities 8 It looks like a 7.10.2 bug, can some one confirm that?

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ANN: MicrosoftTranslator-0.1.0.1
by Ernesto Rodriguez 23 Aug '15

23 Aug '15

Dear Cafe, I needed to translate text in my Haskell code and Microsoft Translator[2] seems to be the easiest and cheapest (free 2M chars/month) way to do it. I wrapped my code in this package[1]. I tried to make it easy to use. If you plan to use Microsoft Translator in Haskell but don't want to use my package, I still recommend you look at my source code since the documentation in Microsoft's page appears to be incorrect (I had to see the source code of the Python package to get it to work). In any case, it is very easy to use: > translate "clientId" "clientSecret" "hello" English German Right "hallo" It is in an early stage and I haven't added most of the languages supported by Microsoft Translator. Pull requests are welcome :) Best Regards, Ernesto Rodriguez [1] http://hackage.haskell.org/package/MicrosoftTranslator-0.1.0.1 [2] https://www.microsoft.com/en-us/translator/default.aspx -- Ernesto Rodriguez Masters Student Computer Science Utrecht University www.netowork.me github.com/netogallo

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Re: [Haskell-cafe] octree implementation - followup to "How to model outer space for a MUD"
by Michal J Gajda 23 Aug '15

23 Aug '15

Hi, And if you search for Octree on Hackage, you would have also found my Octree implementation. It does not do re-balancing, but in this type of application you talk about it may not be needed. http://hackage.haskell.org/package/Octree Funny part, is that implementation may be easier to read than algo description I read first time: http://hackage.haskell.org/package/Octree-0.5.4.2/docs/src/Data-Octree-Inte… . It worked perfectly for my use cases (checking for collisions of 1000-100000 objects), but (just in case) the initial creation from list structure make the octree balanced. Note that balanced octree is supposed to be much faster than KD-tree, and may be also faster than R-tree in memory, since it is very shallow structure - log_8 between 10k and 1m changes only from below 5 to below 7! I was also very happy with its cache behaviour, although in theory R-tree could be better. I am also extremely interested in making sure that Haskell has a good choice of multidimensional metric data structures, so I am closely following maintenance of kd-tree, Ashley´s, and Gloss´ quadtrees. And if you really want to have re-balancing, please contact me on my email. -- Best regards Michal

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HAL-10 (preliminary announcement)
by Johannes Waldmann 22 Aug '15

22 Aug '15

Dear all, > ... this year's Haskell in Leipzig I have been busy with many other things, so there are no concrete plans right now. But I think we should do it, and I am willing to host it at my institution. So - how about December 4/5 (Friday noon - Saturday noon)? (it is easier to get lecture rooms on the week-end) If you have comments or suggestions for HAL this year, then please email me, or stammtisch at haskell.iba-cg.de , or someone could set up a wiki page somewhere. Let's say we start collecting opinions now, and make a decision and a formal announcement end of September. http://www.imn.htwk-leipzig.de/~waldmann/HAL2015/ - Johannes Waldmann.

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Haskell Weekly News
by Kim-Ee Yeoh 21 Aug '15

21 Aug '15

*Top picks:* - Gabriel Gonzalez evaluates Haskell <https://github.com/Gabriel439/post-rfc/blob/master/sotu.md> in the style of a State-of-the-Union address. He rates Haskell from Immature to Mature to Best-in-class under 28 headings, the first four being *Compilers,* *Server-side web programming,* *Scripting / Command-line applications,* and *Numerical programming.* He also recommends libraries and tutorials under each heading. Reverberations on Hacker News <https://news.ycombinator.com/item?id=10071535> and /r/haskell <https://www.reddit.com/r/haskell/comments/3haulk/state_of_the_haskell_ecosy…> . - Challenged over claims of FP productivity improvement, Douglas M. Auclair rattles off success stories from his previous work <http://logicaltypes.blogspot.com/2015/08/pure-functional-programming-claims…> at various subsidiaries of the US Federal Gov fending for the taxpayer to the tune of billions of dollars. Nibbles of interest on Hacker News <https://news.ycombinator.com/item?id=10057661>. - Aaron Wolf goes from zero programming directly to Haskell and writes of his experience. <https://snowdrift.coop/p/snowdrift/blog/technical-history> His favorite learning resource is the Haskell Wikibook <https://en.wikibooks.org/wiki/Haskell>, which he can improve as he reads. He is co-founder of Snowdrift.coop, a crowdfunding platform for freely-licensed works <https://snowdrift.coop/p/snowdrift/w/en/about>. The Haskell Reddit <https://www.reddit.com/r/haskell/comments/3hbrom/learning_haskell_from_noth…> finds Aaron's testimony a change from the "Haskell is too hard for me" meme. - The season of introspection continues. On the heels of Hu, Hughes, and Wang on "How Functional Programming Mattered" (see previous HWN <http://haskell.1045720.n5.nabble.com/Fwd-Haskell-Weekly-News-tp5815292.html>); Michael Green, Kathleen Fisher, and David Walker <http://tmpl.weaselhat.com/> track the ebb and flow of research topics in the conference proceedings of the Big Four: Principles of PL (POPL), PL Design and Implementation (PLDI), International Conference on FP (ICFP); and OOP, Systems, Languages, Apps (OOPSLA). No mention of Haskell but if you're looking for a brief history of PL research -- the slides are even more succinct <http://www.cs.ox.ac.uk/ralf.hinze/WG2.8/33/slides/Kathleen.pdf> -- this is the only data-driven survey you'll find. - Doug Beardsley <http://softwaresimply.blogspot.com/2015/08/why-version-bounds-cannot-be-inf…> reminds us that date-based version inference cannot replace the role of explicit version upper bounds. The reason? The package developer might not be using the latest version of its dependencies on the day they publish the work. Also, among the 72 comments of the /r/haskell convo <https://www.reddit.com/r/haskell/comments/3h83jl/why_version_bounds_cannot_…>, Doug observes that Stackage over-conservatively locks to a single version, whereas community-wide adherence to the Package Versioning Policy (PVP) of original hackage <https://wiki.haskell.org/Package_versioning_policy> yields seamless delivery of bugfixes and improvements. - In less than a week, Xmonad will lose its issue tracking system. On Aug 24, Google Code goes read-only <http://google-opensource.blogspot.sg/2015/03/farewell-to-google-code.html>. Community heroes Brandon Allbery and Daniel Wagner <http://haskell.1045720.n5.nabble.com/google-code-issues-td5815183.html> work at grabbing a backup of the issues. Still no consensus over what and where to migrate to. - Mark Dominus <http://blog.plover.com/aliens/dd/> delves into the bits and bytes of the 1999 Cosmic Call <http://en.wikipedia.org/wiki/Cosmic_Call> attempt by astrophysicists to contact aliens. He shows the visual bitmaps transmitted into space. Brent Yorgey <http://mathlesstraveled.com/2015/08/19/cosmic-call-at-the-universe-of-disco…> writes to say he enjoys the 23-part series interspersed with little puzzles. *Quotes of the Week:* - Doug McIlroy <http://ircbrowse.net/browse/haskell?id=20962286&timestamp=1435683815#t14356…>: Conditional compilation is admitting defeat. - /u/kamatsu <https://www.reddit.com/r/haskell/comments/3h5og6/i_now_tend_to_think_that_t…>: I feel like the reason people find Haskell an eye-opening experience is because their CS education was deficient. - @wfaler <https://twitter.com/wfaler/status/631815511949615104>: Is there a club to join when you silently sob at having to give your Monad Transformers Monad Transformers? Sounds a lot like #EnterpriseFP -- Kim-Ee

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Re: [Haskell-cafe] List of nitpicks
by Johannes Waldmann 21 Aug '15

21 Aug '15

> Should there be a similar place for tooling and libraries? a Gargantuan task > QuickCheck fails by letting all tests pass > when you mistakenly provide polymorphic type signatures. No! Prelude Test.QuickCheck> quickCheck $ ( (\ x -> 1 > 9) :: a -> Bool) *** Failed! Falsifiable (after 1 test): () I think you mean "defaults everything to () and thus runs polymorphic tests at unexpected types" Prelude Test.QuickCheck> quickCheck $ ( (\ xs -> xs == reverse xs ) :: Eq a => [a] -> Bool) +++ OK, passed 100 tests. - J.W.

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