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ANN: toysolver 0.3.0 released
by Masahiro Sakai 02 Jun '15

02 Jun '15

Dear all, I'm announcing the release of the toysolver package. http://hackage.haskell.org/package/toysolver https://github.com/msakai/toysolver It provides solver implementations of various problems including SAT, Max-SAT, PBS (Pseudo Boolean Satisfaction), PBO (Pseudo Boolean Optimization), MILP (Mixed Integer Linear Programming) and non-linear real arithmetic. In particular it contains moderately-fast pure-Haskell SAT solver 'toysat'. It can also be used as a backend for ersatz and satchmo. http://hackage.haskell.org/package/ersatz-toysat http://hackage.haskell.org/package/satchmo-toysat Regards, -- Masahiro Sakai

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A Dockerfile to provision a build environment for an Android game written in Haskell
by Sean Seefried 01 Jun '15

01 Jun '15

Fellow Haskell users! For the last few months I've been working on a small game targeting Android devices. It's still in development and will probably change radically from what I've already done. However, in the process of developing this game I've managed to develop a Dockerfile that will provision a build environment to build the game, which I think is worth releasing to the Haskell community right away. I'd appreciate some assistance in validating that it, in fact, works. The repo containing the Dockerfile is hosted at: https://github.com/sseefried/docker-epidemic-build-env The repo containing the game is: https://github.com/sseefried/open-epidemic-game Please use the latest version of Docker when you attempt to build this, at least version 1.6. Be aware that this will take a long time to build. You will need to download an image from THe Docker Hub Registry that is about 1.1G and then pull down even more files when building all the C and Haskell libraries. Be patient and if you have any issues please let me know via GitHub. Oh, and if you want to see a demo of what you are building click here: https://goo.gl/FZFPsm (It's a very simple game at present. Don't expect too much.) Enjoy! Sean

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.a files not found
by Henk-Jan van Tuyl 31 May '15

31 May '15

L.S., I get messages about .a files not being found, when I try to install package data-default-instances-base, data-default-instances-containers, data-default-instances-dlist or data-default-instances-old-locale. How can I solve this? I am using GHC 7.10.1 on Windows. Sample output: C:\X\data-default-instances-old-locale-0.0.1> cabal install Resolving dependencies... Configuring data-default-instances-old-locale-0.0.1... Building data-default-instances-old-locale-0.0.1... Failed to install data-default-instances-old-locale-0.0.1 Build log ( C:\Users\X\AppData\Roaming\cabal\logs\data-default-instances-old-locale-0.0.1.log ): Building data-default-instances-old-locale-0.0.1... Preprocessing library data-default-instances-old-locale-0.0.1... [1 of 1] Compiling Data.Default.Instances.OldLocale ( Data\Default\Instances\OldLocale.hs, dist\build\Data\Default\Instances\OldLocale.o ) C:\Programs\Haskell\MinGHC-7.10.1\ghc-7.10.1\mingw\bin\ar.exe: dist\build\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a-2192\libHSdata-default-instances-old-locale-0.0.1-6jcjjaR25tK4x3nJhHHjFM.a: No such file or directory cabal: Error: some packages failed to install: data-default-instances-old-locale-0.0.1 failed during the building phase. The exception was: ExitFailure 1 Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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foldt fix proposal (HaskellWiki)
by Michael V. Antosha 31 May '15

31 May '15

hi ALL, I think I've found a mistake in foldt implementation on the Fold page[1] of the HaskellWiki. foldt :: (a -> a -> a) -> a -> [a] -> a foldt f z [] = z foldt f z [x] = x -- mistake? -- foldt f z [x] = f x z -- fix proposal foldt f z xs = foldt f z (pairs f xs) pairs :: (a -> a -> a) -> [a] -> [a] pairs f (x:y:t) = f x y : pairs f t pairs f t = t Without the fix, foldt just ignores z value in all cases except for the case of empty input list. (Which is an inconsistent behaviour I suppose.) The Examples page[2] also needs corresponding fix. Is this mail list a right place to ask for the HaskellWiki page fix? Thanks! Michael. [1] Tree-like folds @ Fold @ HaskellWiki https://wiki.haskell.org/Fold#Tree-like_folds [2] Examples @ Fold @ HaskellWiki https://wiki.haskell.org/Fold#Examples -- Michael V. Antosha http://mivael.in.ua xmpp:m@mivael.in.ua (Jabber ID)

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Why is vector sort slower than list sort?
by Holden Lee 30 May '15

30 May '15

>From places like http://programmers.stackexchange.com/questions/180417/fastest-haskell-libra… and http://stackoverflow.com/questions/3655329/how-does-one-sort-with-data-vect… I'm led to believe that sorting mutable vectors is faster than sorting lists. However, when running on my own computer, I'm seeing the opposite effect. What's wrong with what I'm doing, or am I misunderstanding something? What's the fastest way to sort? Here's the code: Sort0.hs (List version) import Control.Monad import System.Random import qualified Data.Vector as IV import qualified Data.Vector.Mutable as MV import qualified Data.Vector.Generic as V import qualified Data.Vector.Algorithms.Intro as VA import qualified Data.List as L randList :: IO [Int] randList = sequence $ replicate 1000000 (randomIO :: IO Int) main = do v <- randList print $ L.sort v Here's Sort1.hs import Control.Monad import System.Random import qualified Data.Vector as IV import qualified Data.Vector.Mutable as MV import qualified Data.Vector.Generic as V import qualified Data.Vector.Algorithms.Intro as VA randVector :: IO (MV.IOVector Int) randVector = do v <- MV.new 1000000 forM [0..999999] $ \x -> do r <- randomIO :: IO Int MV.write v x r return v main = do v <- randVector VA.sort v iv <- V.unsafeFreeze v :: IO (IV.Vector Int) print . V.toList $ iv I'm compiling and running as follows: ghc -prof -fprof-auto -rtsopts -o Sort0 Sort0.hs ./Sort0 +RTS -p -sstderr -K99999999 -RTS Here are the traces; the first one is Sort0.hs (list version) and takes ~11s while the other takes ~17s: Sat May 30 05:06 2015 Time and Allocation Profiling Report (Final) Sort0.exe +RTS -p -sstderr -K99999999 -RTS total time = *11.43 secs* (11434 ticks @ 1000 us, 1 processor) total alloc = 1,966,669,596 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc main Main 61.4 49.4 randList Main 38.6 50.6 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 41 0 0.0 0.0 100.0 100.0 CAF GHC.IO.Encoding.CodePage 69 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding 67 0 0.0 0.0 0.0 0.0 CAF System.CPUTime 59 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Handle.FD 58 0 0.0 0.0 0.0 0.0 CAF Data.Fixed 54 0 0.0 0.0 0.0 0.0 CAF Data.Time.Clock.POSIX 50 0 0.0 0.0 0.0 0.0 CAF System.Random 49 0 0.0 0.0 0.0 0.0 CAF Main 48 0 0.0 0.0 100.0 100.0 randList Main 83 1 1.7 3.1 1.7 3.1 main Main 82 1 61.4 49.4 98.3 96.9 randList Main 84 0 36.9 47.6 36.9 47.6 Sat May 30 04:59 2015 Time and Allocation Profiling Report (Final) Sort1.exe +RTS -p -sstderr -K99999999 -RTS total time = * 17.07 secs* (17066 ticks @ 1000 us, 1 processor) total alloc = 5,783,472,528 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc main Main 71.9 81.5 randVector.\ Main 25.0 16.5 randVector Main 3.1 2.0 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 60 0 0.0 0.0 100.0 100.0 CAF GHC.IO.Encoding.CodePage 108 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding 106 0 0.0 0.0 0.0 0.0 CAF System.CPUTime 98 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Handle.FD 95 0 0.0 0.0 0.0 0.0 CAF Data.Fixed 87 0 0.0 0.0 0.0 0.0 CAF Data.Time.Clock.POSIX 82 0 0.0 0.0 0.0 0.0 CAF System.Random 81 0 0.0 0.0 0.0 0.0 CAF Main 67 0 0.0 0.0 100.0 100.0 randVector Main 121 1 0.0 0.0 0.0 0.0 main Main 120 1 71.9 81.5 100.0 100.0 randVector Main 122 0 3.1 2.0 28.1 18.5 randVector.\ Main 123 1000000 25.0 16.5 25.0 16.5 Thanks, Holden

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Threads and critical sections (threadWaitRead)
by Lars Petersen 30 May '15

30 May '15

Hello cafe, I'm currently trying to understand Haskell's threading model and GHC's implementation of it. Specifically I wondered about the safety of file IO. Consider this piece of code: > newtype Socket = Socket (MVar Fd) > > read :: Socket -> IO ByteString > read (Socket mfd) = do > fd <- readMVar mfd > -- (1) > threadWaitRead fd > -- (2) > withMVar mfd $ \fd'-> do > -- (3) the actual read... Context: - The socket is configured non-blocking. - No other operation will hold the MVar over a blocking call (because this would make it impossible to close it while it's blocking). - My close operation will fill the MVar with -1 after it's closed and will hold the MVar during the close operation. Questions: - Is it theoretically possible that my thread gets paused at (1) or within threadWaitRead, another thread closes the socket (or even worse opens another file with the same fd) _and_ my thread is resumed afterwards (I'm not asking about async exceptions)? - What constructs contain safepoints and which are guaranteed to be executed without interruption? Considerations (so far): - It is unlikely that (1) is a safepoint as no memory allocations occur, but is it guaranteed? - If the socket were closed during (1), threadWaitRead throws an exception complaining about a bad file descriptor which is unexpected but not harmful. - I found this thread (https://mail.haskell.org/pipermail/haskell-cafe/2014-September/115841.html) which is somewhat related, but I couldn't extract a clear answer from it. Best, Lars

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Disambiguating a Num/RealFrac instance
by amindfv＠gmail.com 30 May '15

30 May '15

Given: data GPA = F Float | Excuse String class ToGPA a where giveGPA :: a -> GPA Is there any way (without IncoherentInstances or Rebindablesyntax) that I can let the user write e.g. "giveGPA 4.0" (and "giveGPA 4") and get back "F 4" without getting type errors that "4.0"'s type is ambiguous? I can guarantee there won't be any additional instances to "ToGPA" (For my uses, I really (actually!) don't want to make the user write e.g. "F 4.0") I've gotten this working, once with IncoherentInstances and once with RebindableSyntax, but both of those flags feel pretty dirty. Thanks, Tom

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GHC + musl = easier static linking
by Marios Titas 30 May '15

30 May '15

TL;DR: I made some GHC binaries for linux that rely on musl instead of glibc for easier static linking. Scroll down for the link. Dear *, As most of you know, musl is a linux only C standard library that is optimized for static linking. Statically linked binaries can simplify distribution and deployment. If you have tried to statically link a program with glibc, you will probably know that this does not always work as expected: for example, in many cases the resulting binary will require to be executed in a system that has the exact same version of glibc as the one that was used to compiled it. In essence, static binaries linked with glibc are oftentimes *less* portable than dynamic ones. I decided to see if I could use GHC with musl. The problem was that while I could find some references online, I could not find a precompiled version of GHC that uses musl. So I decided to try and a build one myself. I was able to successfully bootstrap GHC under musl and I am posting it today in case someone else finds it usefull: https://drive.google.com/folderview?id=0B0zktggRQYRkbGJkbmU0UFFSYUE#list I posting this on google drive, I have no better place to host this, hopefully google will not disable my account :-) This is a fully bootstrapped (i.e. stage 2) GHC and *not* a cross compiler. So this will *not* work in a typical glibc based linux distribution. You need a complete musl based environment to use it (see bellow for that). Also, the binaries produced by this GHC will all depend on musl and not work on most glibc based distros. On the other hand, statically compiled binaries should be very portable and will not depend on any particular C standard library. I have done some minimal testing and it seems to work rather well; everything I tried to compile from hackage just worked. Additionally it can compile GHC itself which is always a good test. The size of the resulting static binaries is acceptable. In my 64 bit system, a simple hello world has the following sizes (stripped): 800K glibc dynanic, 1648K glibc static, and 1012K musl static. Why not use a cross-compiler? I have found that in practice it is easier to have a separete environment for producing static binaries. A cross-compiler requires that you also cross-compile all the C libraries that you use. Additionally, cabal has still problems (e.g. [1]) with cross-compiling and will not work out of the box. Note that musl is not 100% compatible with glibc, so some things might work slightly differently. If you do not like using a GHC precompiled by someone else, you can use my binaries to compile GHC under musl yourself; it would be easier than cross-compiling GHC from scratch. So how do you use this? You need a complete musl based environment. There a few musl based distros [2], albeit most of them are geared towards embedded applications. I personally use the experimental musl based gentoo image [3] which feels more like a regular distro. You can use it with chroot, lxc, or systemd-nspawn. For the sake of completeness, I have included at the end of this message some quick and dirty instructions on how to do this. [1] https://github.com/haskell/cabal/issues/1493 [2] http://wiki.musl-libc.org/wiki/Projects_using_musl [3] http://distfiles.gentoo.org/experimental/amd64/musl/ 8<------------------------------------- # gentoo stage3 image instructions CHROOT_PATH=/var/tmp/gentoo-musl cd /var/tmp wget http://distfiles.gentoo.org/experimental/amd64/musl/stage3-amd64-musl-vanil… mkdir "$CHROOT_PATH" tar xjf stage3-amd64-musl-vanilla-20150405.tar.bz2 -C "$CHROOT_PATH" for x in dev proc sys; do mount --bind /$x "$CHROOT_PATH/$x"; done cp -L /etc/resolv.conf "$CHROOT_PATH/etc" chroot "$CHROOT_PATH" /bin/bash -l PS1="(chroot) $PS1" # fetch the gentoo package db for the first time (slow): emerge-webrsync # enable static libraries (*.a), which are disabled by default: sed -ie 's/USE="/USE="static-libs /' /etc/portage/make.conf # reinstall/recompile gmp so that we have its static libs: emerge --oneshot dev-libs/gmp # install ghc: tar xJf /path/to/ghc-7.10.1-x86_64-unknown-linux-musl.tar.xz -C /tmp cd /tmp/ghc-7.10.1; ./configure --prefix=/opt/ghc-7.10.1; make install # compile a hello world: cd /tmp echo 'main = putStrLn "Hello world"' > test.hs /opt/ghc-7.10.1/bin/ghc --make -O -optl-static test.hs ./test file ./test # Of course, using chroot this way is insecure, don't use to install packages from hackage.

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Annoucing Eddie 1.0.0
by Mike Meyer 30 May '15

30 May '15

Eddie is a tool to let you use Haskell code in shell scripts, in a manner similar to the way awk and other scripting languages can be used. The jump to 1.0.0 isn't because it's finished, but because this is a rewrite from the ground up to incorporate more modern Haskell features (the old version was my first non-trivial Haskell program), resulting in changes to various behaviors as well as some option tweaks. Most notably, it no longer uses [Char] for everything. In text mode, it uses Text, with options to specify both input and output encodings. In binary mode, it uses ByteString, with an option to set the output back to Text so you can generate summaries as opposed to simply filter. To make using Text and ByteString sane, it also uses ClassyPrelude instead of Prelude + Data.Char & Data.List so your Haskell list habits work - at least mostly. See CHANGES.md in the source or ChangeLog in the wiki for detailed changes. Otherwise, the manual page is available on the web site.

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ANNOUNCE: Haskell Communities and Activities Report (28th ed., May 2015)
by Mihai Maruseac 30 May '15

30 May '15

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (28th edition, May 2014) is now available, in PDF and HTML formats: http://haskell.org/communities/05-2015/report.pdf http://haskell.org/communities/05-2015/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of September 2015: target deadline for contributions to the November 2015 edition of the HC&A Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in October (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Mihai Maruseac and Alejandro Serrano Mena <hcar at haskell.org> -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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