- Haskell-Cafe - Haskell.org

Announcing containers 0.5.8.1
by David Feuer 01 Sep '16

01 Sep '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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Which tab width do you prefer for Haskell code?
by Christopher Done 01 Sep '16

01 Sep '16

Hi everyone, I'm trying to get a feel for the modern Haskell community's opinion on default tab-width for HIndent. Here is a link to the online poll: http://doodle.com/poll/82xf854t9mmuv22h#table Quote: > For the HIndent tool we'd like to choose the standard tab width. > For now, it is 4, the width set by the Johan Tibell style guide. > A survey of 1000 top-downloaded packages on Hackage reveals about 50-50 either way:https://gist.github.com/chrisdone/e3d1796d8f5df717b91db54aae36c440 > HIndent is meant as a "community standard" tool; it should reflect the community's actual practice. If there's a clear preference for 2, we'll switch to that. Otherwise, we remain with 4. Cheers!

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Cache miss performance costs for Haskell programs?
by Rob Stewart 31 Aug '16

31 Aug '16

Hi, Any Haskell profiling and performance tuning blog or tutorial will advise the use of memory space and runtime profiling, using GHC tooling. Far less is said about the impact of increased cache miss rates as program size increases. The paper "Secrets of the Glasgow Haskell Compiler inliner", in the Journal of Functional Programming, July 2002, talks a lot about the benefits of inlining, i.e. it's part of GHCs simplifier as it enables many other optimisations, some that ultimately reduce program size. Not much is said about detrimental effect that bad inlining choices has to runtime. The paper says: "Bloated programs are bad (increased compilation time, lower cache hit rates)" in Section 2.2. I'd really like to see how badly Haskell runtimes are affected as cache hit rates decrease. Is anyone aware of any empirical studies, or papers, or blog posts, that show examples where: For the same Haskell program, increasing inlining causes lower cache hit rates, which slows down runtime due to costly cycles to fetch from main memory more often. Thanks, -- Rob

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Re: [Haskell-cafe] [Haskell] I repeat my Question becaue I not really sure to do it right
by Ivan Lazar Miljenovic 29 Aug '16

29 Aug '16

On 28 August 2016 at 23:15, <CCUTM(a)web.de> wrote: > Hello it is possible that this is the solution. > But I don't know how I can istall it. See the Ubuntu section here: http://www.leksah.org/download.html > > Gesendet: Sonntag, 28. August 2016 um 15:07 Uhr > Von: "Ivan Lazar Miljenovic" <ivan.miljenovic(a)gmail.com> > An: CCUTM(a)web.de > Betreff: Re: Re: [Haskell] I repeat my Question becaue I not really sure to > do it right > Do you have the -dev libraries installed for gtk, glib, etc.? > > Or is there a gtk2hs package available for Ubuntu? > > On Sun, 28 Aug 2016, 11:05 PM <CCUTM(a)web.de> wrote: >> >> I'm seem rubish, >> but exactly that have I do >> And I have at first install cabal. >> But this is comming: >> >> Resolving dependencies... >> Configuring glib-0.13.4.0... >> Building glib-0.13.4.0... >> Failed to install glib-0.13.4.0 >> Build log ( /home/thomas/.cabal/logs/glib-0.13.4.0.log ): >> [1 of 1] Compiling Main ( >> /tmp/cabal-tmp-4585/glib-0.13.4.0/dist/setup/setup.hs, >> /tmp/cabal-tmp-4585/glib-0.13.4.0/dist/setup/Main.o ) >> Linking /tmp/cabal-tmp-4585/glib-0.13.4.0/dist/setup/setup ... >> Configuring glib-0.13.4.0... >> Building glib-0.13.4.0... >> Preprocessing library glib-0.13.4.0... >> /usr/bin/ld: dist/build/System/Glib/StoreValue_hsc_make.o: Die Umlagerung >> von >> dist/build/System/Glib/StoreValue_hsc_make.o: error adding symbols: >> Ungültiger Wert >> collect2: error: ld returned 1 exit status >> linking dist/build/System/Glib/StoreValue_hsc_make.o failed (exit code 1) >> command was: /usr/bin/gcc dist/build/System/Glib/StoreValue_hsc_make.o >> dist/build/System/Glib/StoreValue_hsc_utils.o -o >> dist/build/System/Glib/StoreValue_hsc_make -fno-PIE -fno-stack-protector >> -lgobject-2.0 -lglib-2.0 >> -L/home/thomas/.cabal/lib/x86_64-linux-ghc-7.10.3/utf8-string-1.0.1.1-L8eKHa7Iv9q7FVKUYW6u4b >> -Wl,-R,/home/thomas/.cabal/lib/x86_64-linux-ghc-7.10.3/utf8-string-1.0.1.1-L8eKHa7Iv9q7FVKUYW6u4b >> -L/home/thomas/.cabal/lib/x86_64-linux-ghc-7.10.3/text-1.2.2.1-HmqVQnZSpjaC156ABqPhne >> -Wl,-R,/home/thomas/.cabal/lib/x86_64-linux-ghc-7.10.3/text-1.2.2.1-HmqVQnZSpjaC156ABqPhne >> -L/usr/lib/ghc/binar_3uXFWMoAGBg0xKP9MHKRwi >> -Wl,-R,/usr/lib/ghc/binar_3uXFWMoAGBg0xKP9MHKRwi >> -L/usr/lib/ghc/conta_2C3ZI8RgPO2LBMidXKTvIU >> -Wl,-R,/usr/lib/ghc/conta_2C3ZI8RgPO2LBMidXKTvIU >> -L/usr/lib/ghc/bytes_6VWy06pWzJq9evDvK2d4w6 >> -Wl,-R,/usr/lib/ghc/bytes_6VWy06pWzJq9evDvK2d4w6 >> -L/usr/lib/ghc/deeps_6vMKxt5sPFR0XsbRWvvq59 >> -Wl,-R,/usr/lib/ghc/deeps_6vMKxt5sPFR0XsbRWvvq59 >> -L/usr/lib/ghc/array_67iodizgJQIIxYVTp4emlA >> -Wl,-R,/usr/lib/ghc/array_67iodizgJQIIxYVTp4emlA >> -L/usr/lib/ghc/base_HQfYBxpPvuw8OunzQu6JGM >> -Wl,-R,/usr/lib/ghc/base_HQfYBxpPvuw8OunzQu6JGM >> -L/usr/lib/ghc/integ_2aU3IZNMF9a7mQ0OzsZ0dS >> -Wl,-R,/usr/lib/ghc/integ_2aU3IZNMF9a7mQ0OzsZ0dS -lgmp >> -L/usr/lib/ghc/ghcpr_8TmvWUcS1U1IKHT0levwg3 >> -Wl,-R,/usr/lib/ghc/ghcpr_8TmvWUcS1U1IKHT0levwg3 -L/usr/lib/ghc/rts >> -Wl,-R,/usr/lib/ghc/rts -lm -lrt -ldl -lffi >> cabal: Error: some packages failed to install: >> ghcjs-dom-0.2.4.0 depends on glib-0.13.4.0 which failed to install. >> gio-0.13.3.0 depends on glib-0.13.4.0 which failed to install. >> glib-0.13.4.0 failed during the building phase. The exception was: >> ExitFailure 1 >> gtk3-0.14.5 depends on glib-0.13.4.0 which failed to install. >> gtksourceview3-0.13.3.0 depends on glib-0.13.4.0 which failed to install. >> jsaddle-0.3.0.3 depends on glib-0.13.4.0 which failed to install. >> leksah-0.15.2.0 depends on glib-0.13.4.0 which failed to install. >> leksah-server-0.15.2.0 depends on glib-0.13.4.0 which failed to install. >> ltk-0.15.0.5 depends on glib-0.13.4.0 which failed to install. >> pango-0.13.3.0 depends on glib-0.13.4.0 which failed to install. >> vcsgui-0.1.3.0 depends on glib-0.13.4.0 which failed to install. >> webkitgtk3-0.14.2.0 depends on glib-0.13.4.0 which failed to install. >> webkitgtk3-javascriptcore-0.13.2.0 depends on glib-0.13.4.0 which failed >> to >> install. >> >> Please can you help me!!? >> >> >> Gesendet: Sonntag, 28. August 2016 um 14:50 Uhr >> >> Von: "Ivan Lazar Miljenovic" <ivan.miljenovic(a)gmail.com> >> An: CCUTM(a)web.de >> Cc: "Haskell List" <haskell(a)haskell.org> >> Betreff: Re: [Haskell] I repeat my Question becaue I not really sure to do >> it right >> On 28 August 2016 at 22:40, <CCUTM(a)web.de> wrote: >> > This is Leksah http://leksah.org/ >> > Please excuse my false name for it >> > And the Question is why can I install it. >> >> What error messages do you have when you try? >> >> From here, this is what you need to do: >> https://github.com/leksah/leksah/wiki/download >> >> > cabal install gtk2hs-buildtools >> >> > cabal install leksah >> >> >> >> > >> > excuse me. >> > Mungo1981 >> > >> > Gesendet: Sonntag, 28. August 2016 um 13:49 Uhr >> > Von: "Ivan Lazar Miljenovic" <ivan.miljenovic(a)gmail.com> >> > An: CCUTM(a)web.de >> > Cc: "Haskell List" <haskell(a)haskell.org> >> > Betreff: Re: [Haskell] I repeat my Question becaue I not really sure to >> > do >> > it right >> > On 28 August 2016 at 20:43, <CCUTM(a)web.de> wrote: >> >> Ok Haskell is good. >> >> Ok Laska is great. >> >> And my Ubuntu Studio ist rubish >> >> So I try to install Laska on Ubuntu Studio >> >> But when I do this, i will get a long list of dependecies >> >> which could not reallise >> >> So I not know what should I do >> > >> > Which question? >> > >> > What is Laska that you're having trouble installing it? >> > >> >> >> >> Mungo1981 >> >> >> >> _______________________________________________ >> >> Haskell mailing list >> >> Haskell(a)haskell.org >> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell >> >> >> > >> > >> > >> > -- >> > Ivan Lazar Miljenovic >> > Ivan.Miljenovic(a)gmail.com >> > http://IvanMiljenovic.wordpress.com >> > >> > _______________________________________________ >> > Haskell mailing list >> > Haskell(a)haskell.org >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell >> > >> >> >> >> -- >> Ivan Lazar Miljenovic >> Ivan.Miljenovic(a)gmail.com >> http://IvanMiljenovic.wordpress.com -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell Tutorials to Spread the Word
by Will Tennien Murphy 29 Aug '16

29 Aug '16

Hey, I'm looking for people to help spread the word about Haskell by translating or writing tutorials. I'm a contributor to py-app.com . Py is an app that teaches programming concepts "on the go"—that is, with a mobile focus. Do you... 1. Want to help spread the word about Haskell? 2. Like helping other people learn? 3. Speak another natural language and can translate existing content? 4. Know a tutorial you'd like to make more mobile-friendly? If you meet ANY of these conditions—especially if you are proficient another language—drop me a line at wtmurp(a)gmail.com. I'm very intent on making things as easy as possible for writers so you can write in whatever you find most convenient[1] and I'll figure out how to get it into the app. [1] except PDF

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managing embedded structs
by Henning Thielemann 29 Aug '16

29 Aug '16

I want to write a Haskell interface to a C library that provides two data structures A and B, where B is contained in A. That is, if A is freed, then B is automatically freed, too. There are two ways to obtain a Ptr B. Either construct it separately or as part of A, i.e. b0 :: Ptr B b0 <- createB b1 :: Ptr B b1 <- getBofA =<< createA Now I want to let the garbage collector manage the resources for B in a ForeignPtr. The first case is easy: fb0 :: ForeignPtr B fb0 <- newForeignPtr deleteB =<< createB But how to create an fb1? fa1 :: ForeignPtr A fa1 <- newForeignPtr deleteA =<< createA fb1 :: ForeignPtr B fb1 <- newForeignPtr ??? =<< withForeignPtr fa1 getBofA Obviously, there is nothing I can insert for ???. fb1 must not have its own finalizer, because fa1 already has one. But I have to make sure that fa1 lives at least as long as fb1. How to do that?

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Is anybody interested in taking over maintaining hasktags?
by Marc Weber 29 Aug '16

29 Aug '16

There is not much to be done - patch requests come in once or twice a year. Current task would be uploading a new version to hackage fixing compilation bug. The patch is already on github Marc Weber

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Re: [Haskell-cafe] [Haskell] I repeat my Question becaue I not really sure to do it right
by Francesco Ariis 28 Aug '16

28 Aug '16

haskell(a)haskell.org is low traffic, for announcements only, I am replying to haskell-cafe(a)haskell.org , where this question is better suited (and most people willing to help are). On Sun, Aug 28, 2016 at 10:50:50PM +1000, Ivan Lazar Miljenovic wrote: > On 28 August 2016 at 22:40, <CCUTM(a)web.de> wrote: > > This is Leksah http://leksah.org/ > > Please excuse my false name for it > > And the Question is why can I install it. > > What error messages do you have when you try? > > From here, this is what you need to do: > https://github.com/leksah/leksah/wiki/download > > > cabal install gtk2hs-buildtools > > > cabal install leksah > > > > > > > excuse me. > > Mungo1981 > > > > Gesendet: Sonntag, 28. August 2016 um 13:49 Uhr > > Von: "Ivan Lazar Miljenovic" <ivan.miljenovic(a)gmail.com> > > An: CCUTM(a)web.de > > Cc: "Haskell List" <haskell(a)haskell.org> > > Betreff: Re: [Haskell] I repeat my Question becaue I not really sure to do > > it right > > On 28 August 2016 at 20:43, <CCUTM(a)web.de> wrote: > >> Ok Haskell is good. > >> Ok Laska is great. > >> And my Ubuntu Studio ist rubish > >> So I try to install Laska on Ubuntu Studio > >> But when I do this, i will get a long list of dependecies > >> which could not reallise > >> So I not know what should I do > > > > Which question? > > > > What is Laska that you're having trouble installing it? > > > >> > >> Mungo1981 > >> > >> _______________________________________________ > >> Haskell mailing list > >> Haskell(a)haskell.org > >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell > >> > > > > > > > > -- > > Ivan Lazar Miljenovic > > Ivan.Miljenovic(a)gmail.com > > http://IvanMiljenovic.wordpress.com > > > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell > > > > > > -- > Ivan Lazar Miljenovic > Ivan.Miljenovic(a)gmail.com > http://IvanMiljenovic.wordpress.com > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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Re: [Haskell-cafe] [Haskell-community] haskell.org download page
by Marco Zocca 28 Aug '16

28 Aug '16

-1 to making HP the first method Stack is easier to get started with and makes tinkering easier. In this sense, it's a more natural choice for beginners. Also, the Minimal option is kind of dead for Mac users since GHCForMacOSX is not maintained anymore. (NB: I speak out of personal experience and have no conflicting interests)

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Using MonadRandom with QuickCheck
by Magnus Grindal Bakken 27 Aug '16

27 Aug '16

Is there some easy way to use the Gen type from QuickCheck with the MonadRandom class? Links to the packages in question: https://hackage.haskell.org/package/MonadRandom https://hackage.haskell.org/package/QuickCheck Some background in case there's an easier way to solve the problem: I'm toying around with an API for a simple turn-based board game. The main type in my API is called GameState, and I'm trying to define an Arbitrary instance for it so I can set up invariants with QuickCheck. The Arbitrary instance should produce game states that are the result of playing a random number of random moves. At certain points in the gameplay the game itself needs to invoke some randomness. I've designed the public game API to have basically just two functions: playAction :: ActionData -> GameState -> GameState evaluateGameState :: MonadRandom m => GameState -> m GameState The usage is supposed to be that the client first calls playAction with an ActionData value that depends on the current move, and afterwards calls evaluateGameState to evaluate whatever random events need to happen at that point (e.g. reshuffling a deck of cards). That way my main "action" logic doesn't need to concern itself with any form of randomness. I'm using MonadRandom from Control.Monad.Random because it seems like a much nicer way to generate random numbers than using RandomGen directly. However I can't figure out how to make it play nice with QuickCheck. I can easily set up my Arbitrary instance to call playAction an arbitrary number of times, but I can't call evaluateGameState since it lives in the other monad. It would work if Gen were an instance of MonadRandom, but I can't quite work out how to write that instance since most functions on Gen only work if the output type is an instance of Arbitrary, while MonadRandom needs to work with any types that are part of the Random class. This part works: instance MonadRandom Gen where getRandomR = choose But I don't know how to define the other functions on MonadRandom for Gen. I think I might also be able to use the PropertyM monad transformer: https://hackage.haskell.org/package/QuickCheck-2.9.1/docs/Test-QuickCheck-M…, but monad transformers always confuse me so I haven't been able to figure out how to do that yet either. I've thought about rewriting the API to use the Gen type instead of MonadRandom, but it feels kind of iffy to have the API depend on a testing library. Has anyone tried to use these libraries together before?

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