- Haskell-Cafe - Haskell.org

ANN: psqueues
by Jasper Van der Jeugt 26 Jun '14

26 Jun '14

Here at Better, we have just a released a package which implements faster priority search queues for Haskell. We hope it proves to be useful to the community! More information can be found in this blogpost: http://medium.com/@bttr/announcing-psqueues-8a0fe9fe939 Grab it from Hackage or GitHub: http://hackage.haskell.org/package/psqueues https://github.com/bttr/psqueues On behalf of the engineering team at Better, Jasper Van der Jeugt

3 2

Quantification in Instance Contexts
by Julian K. Arni 26 Jun '14

26 Jun '14

Hi Cafe, I'm playing around with simple logic-programming at the type level. For instance, encoding trees: >> {-# LANGUAGE MultiParamTypeClasses >> , FunctionalDependencies >> , FlexibleInstances >> , UndecidableInstances >> , FlexibleContexts >> , OverlappingInstances #-} >> {-# OPTIONS_GHC -fcontext-stack=100 #-} >> >> >> -- *A >> -- / \ >> -- B* *C >> -- | >> -- D* >> >> >> data A >> data B >> data C >> data D >> class Child a b bool | a b -> bool >> instance Child A B TrueT >> instance Child B D TrueT >> instance Child B C TrueT >> class Path a b bool | a b -> bool Now the following obviously doesn't work (never mind for now that 'Path' needs a recursive definition, and that this is really just 'Grandchild'): >> instance (Child a b TrueT, Child b c TrueT) => Path a c TrueT Because 'b' is ambiguous. Fair enough. But I can't directly use a fundep, because 'b' *is* in fact ambiguous. What I want to tell the compiler is that it's really okay, since the RHS side (and any possible 'where' expressions) doesn't depend on what is instantiated for 'b'. I know I could switch to a class 'Children a bs bool' and encode all children of as a type-level list, and then have a fundep between 'a' and 'bs'. That's not a *bad* solution: it does give a good sense of the intention. But it's not very extensible; really I'd rather be using something like 'forall' - something, I would guess, along the lines of: >> instance forall a c. (forall b. (Child a b TrueT, Child b c TrueT)) => Path >> a c TrueT That, however, fails with: Malformed instance head: (forall b. (Child a b TrueT, Child b c TrueT)) -> Path a c TrueT In the instance declaration for ‘Path a c TrueT’ So: is there a way (presumably with 'forall') of telling the compiler that the ambiguous type 'b' actually won't "leak through" to the RHS, so stop bugging me about ambiguity? Thanks, Julian

4 7

direct-fastcgi and logging
by Denis Shevchenko 26 Jun '14

26 Jun '14

Hi all! I write a FastCGI-server based on excellent package 'direct-fastcgi' (http://hackage.haskell.org/package/direct-fastcgi) It works perfectly, but I want to inject a logging facility into a handler of requests. For example: import Control.Concurrent (forkIO) import Network.FastCGI main :: IO () main = acceptLoop forkIO handleRequest handleRequest :: FastCGI () handleRequest = do -- >>> In this place I want to log a message <<< setResponseStatus 400 setResponseHeader HttpContentType "application/json" fPutStr "{ "my": "problem_description" }" Yes, I know about this function in 'Network.FastCGI': fLog :: MonadFastCGI m => String -> m () but it "logs a message using the web server's logging facility", and I want to log into _my_own_ file. So which solution I can use here? I'd be very grateful for any help. ---------- Sincerely, Denis Shevchenko haskell(a)dshevchenko.biz

2 1

BNFC-meta being maintained? Is there public src repo?
by Ki Yung Ahn 26 Jun '14

26 Jun '14

Dear BNFC-meta developers and users, I've been using BNFC-meta for the parser of my experimental language Nax language implementation ( https://github.com/kyagrd/mininax ). It's very cool 'cause you don't need to write makefile or cabal entries to call the command line tools (bnfc, alex, happy), and you get quasiquoters for free, which really makes the early development pleasant. But due to the bug fixed in recent versions of BNFC, probably after latest BNFC-meta release, I'll have to switch back to using plain BNFC at some point. (FYI,the bug is that block comments arn't working). If there is a source repository that has ported more recent versions of BNFC into BNFC-meta, it'll be helpful for people like me. Or, if the source repository has open access and easy to participate (e.g., putting on github or something like that), we can draw community support maintaining BNFC-meta to keep up with the recent BNFC (and also happy and alex) versions. -- Ki Yung Ahn

2 1

determine hoolge database directory
by Tobias Pflug 25 Jun '14

25 Jun '14

Hi haskellers, i'm new to haskell and am currently working on some tool that is supposed to fiddle with hoogle database files. Now I'm looking for a sane way to determine the directory where hoogle stores its database directories (when you perform `hoogle data`). In my case this is: .cabal/share/x86_64-linux-ghc-7.8.2/hoogle-4.2.33/databases So this is [home directory]/.cabal/[ghc-version]/[hoogle-version]/databases Could someone suggest me a sane way how I can determine this path at runtime ? Maybe there is a way to extract this from somewhere ? I'm out of ideas on this. I could of course take the easy way out and let users declare the path as config parameter but it would be nice if there was a way ... thanks in advance. regards, Tobi

2 1

accessing a ByteArray from FFI
by Mihaly Barasz 25 Jun '14

25 Jun '14

Hello, I want to access the contents of a Data.Vector.Primitive from FFI. I came up with the following so far: {-# LANGUAGE ForeignFunctionInterface #-} module FFIExample (exampleFn) where import Control.Monad.Primitive (touch) import Control.Monad.ST (runST) import Data.Primitive.Addr (Addr(..)) import Data.Primitive.ByteArray (mutableByteArrayContents) import qualified Data.Vector.Primitive as P import qualified Data.Vector.Primitive.Mutable as PM import GHC.Ptr (Ptr(..), plusPtr) import Data.Word (Word64) foreign import ccall unsafe "my_external_fn" myExternalFn :: Ptr Word64 -> Int -> Int exampleFn :: P.Vector Word64 -> Int exampleFn v = runST $ do PM.MVector off len mba <- P.unsafeThaw v let ptr = case mutableByteArrayContents mba of Addr addr -> Ptr addr `plusPtr` off result = myExternalFn ptr len result `seq` touch mba return result This seems to work, but I have questions that I haven't been able to find the answers to on my own: 1. Is this actually OK to do? I guess that this wouldn't be OK if the foreign import were "safe", as then the GC could move the contents of the byte array while the foreign function is running. But is it safe like this? 2. If the answer to the previous question is no, then is there a way to do it properly? Or there is just no way to pass an unpinned byte array to a foreign call? What about foreign import prim? 3. If the answer to Q1 is no, then would it be OK if the underlying byte array were pinned? 4. Any other simplifications? Pointers to resources on these topics would be more than welcome! But, I haven't been able to find any. Thanks, Mihaly

2 4

Fwd: 自动回复：Re: ANN: hmatrix-0.16
by Dominic Steinitz 25 Jun '14

25 Jun '14

Hello Cafe, Everytime I post something via gmane I get what I assume is spam - see below. Is this a gmane feature or a haskell-cafe feature? Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com Begin forwarded message: > From: <zhangliu529(a)sina.com> > Subject: 自动回复：Re: [Haskell-cafe] ANN: hmatrix-0.16 > Date: 22 June 2014 11:37:49 BST > To: <dominic(a)steinitz.org> > > 您发的邮件我已收到，我将尽快给您答复。

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ANN: hmatrix-0.16
by Alberto Ruiz 24 Jun '14

24 Jun '14

Hi! I am happy to announce the release of hmatrix-0.16, a Haskell package for matrix computations and numeric linear algebra. New features: - BSD3 license. The modules depending on GSL have been moved to a new package hmatrix-gsl (GPL). Now hmatrix depends only on BLAS/LAPACK. - Simpler reexport modules with improved documentation and usage examples. There are a few API changes but the traditional modules are also exposed for backwards compatibility. - Alternative interface using type-level literals for static dimension checking and inference (work in progress). - Initial support for sparse linear systems. - Minor improvements and bug fixes (see the changelog for details). http://hackage.haskell.org/package/hmatrix https://github.com/albertoruiz/hmatrix Some examples: http://dis.um.es/~alberto/hmatrix/hmatrix.html Suggestions, contributions, and bug reports are welcome. Thanks! Alberto

4 4

ANN: Graphics.OpenSCAD
by Mike Meyer 24 Jun '14

24 Jun '14

Graphics.OpenSCAD provides an algebraic data type for creating OpenSCAD 3d models, as well a a function to generate an OpenSCAD program from a data structure. OpenSCAD is a "programmers" CAD tool. It provides a declarative language for 3d models with a primitive functional language for doing computation. The Graphics.OpenSCAD module tries to preserve the declarative parts by providing tools for building data structures that match the OpenSCAD declarative models, then embedding that in a powerful, modern functional language. The critical problem with OpenSCAD is the error handling. At it's best, it will say "syntax error" and provide sufficient location information to easily find the error. At times, the location information points outside the file. Errors in dealing with variables may have no error messages, or messages that are easy to overlook, resulting in models that are radically different from what was expected with no way to determine the problem except searching the complete program text. Graphics.OpenSCAD attempts to solve that by leveraging Haskell's type system as far as possible. While not every run-time OpenSCAD error can be detected in Haskell, as many as possible are. Hackage page with pointers to source and documentation: http://hackage.haskell.org/package/OpenSCAD

1 0

how to upgrade to a new version of Haskell?
by Johan Larson 24 Jun '14

24 Jun '14

I am currently running an old installation of the Haskell environment from 2012, and I would like to upgrade. Can I just grab the installer from https://www.haskell.org/platform/windows.html and run it? This is on Windows. -- Johan Larson -- Toronto, Canada

4 4

New Assistant Professorship in Nottingham
by Graham Hutton 23 Jun '14

23 Jun '14

Dear all, The School of Computer Science at the University of Nottingham in the UK is seeking to appoint a new Assistant Professor: http://www.nottingham.ac.uk/jobs/currentvacancies/ref/SCI181514 Applications in the area of the Functional Programming (FP) lab would be most welcome. The FP lab is keen to receive applications from candidates with an excellent publication record, experience in combining theory with practice, and the ability to secure external funding to support their research. Further information about the FP lab is available from: http://fp.cs.nott.ac.uk The deadline for applications is Friday 22nd August 2014. The advert mentions computer vision, but the position is open to applicants from any area of Computer Science. Best wishes, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

hayoo doesn't find the Kleisli arrow?
by Erik Rantapaa 23 Jun '14

23 Jun '14

I just happen to notice that this query comes back empty in Hayoo: (a -> m b) -> (b -> m c) -> (a -> m c) Hoogle is able to find (>=>), and I'm wondering if its a bug or...?

2 1

Pathological overloaded function
by Simon Yarde 23 Jun '14

23 Jun '14

Could anyone chip in with examples of a pathological overloaded functions in relation to the GHC Guide 6.2: > Overloaded functions are not your friend: > Haskell's overloading (using type classes) is elegant, neat, etc., etc., but it is death to performance if left to linger in an inner loop. How can you squash it? > > Give explicit type signatures: > Signatures are the basic trick; putting them on exported, top-level functions is good software-engineering practice, anyway. (Tip: using -fwarn-missing-signatures can help enforce good signature-practice). http://lambda.haskell.org/platform/doc/current/ghc-doc/users_guide/faster.h… Best Regards, Simon

1 0

cabal-install failure
by Magicloud Magiclouds 23 Jun '14

23 Jun '14

Hi, This is a box that used to work well. But today, I found that I could not install anything by cabal. I removed ~/.ghc and ~/.cabal to start all userspace thing from the beginning. I used Setup.hs to install Cabal, and bootstrap.sh to install cabal-install. All succeeded. Then I tried to install data-default-class, I got following. Notice the ld fail near the end. Versions: OS: Ubuntu Precise; ghc 7.8.2; Cabal/cabal-install: latest from github. % cabal install -v3 data-default-class Searching for ghc in path. Found ghc at /usr/local/bin/ghc ("/usr/local/bin/ghc",["--numeric-version"]) /usr/local/bin/ghc is version 7.8.2 looking for tool ghc-pkg near compiler in /usr/local/bin found ghc-pkg in /usr/local/bin/ghc-pkg ("/usr/local/bin/ghc-pkg",["--version"]) /usr/local/bin/ghc-pkg is version 7.8.2 ("/usr/local/bin/ghc",["--supported-languages"]) ("/usr/local/bin/ghc",["--info"]) Reading installed packages... ("/usr/local/bin/ghc-pkg",["dump","--global","-v0"]) ("/usr/local/bin/ghc-pkg",["dump","--user","-v0"]) ("/usr/local/bin/ghc",["--print-libdir"]) Reading available packages... Warning: The package list for the local repo '/home/local/ANT/shida/.cabal/packages/cabal-src/' is missing. The repo is invalid. Resolving dependencies... targets: data-default-class constraints: base installed ghc-prim installed integer-gmp installed stanzas data-default-class preferences: strategy: PreferAllLatest [__0] trying: data-default-class-0.0.1 (user goal) [__1] trying: base-4.7.0.0/installed-018... (dependency of data-default-class-0.0.1) [__2] trying: rts-1.0/installedbuil... (dependency of base-4.7.0.0/installed-018...) [__3] trying: integer-gmp-0.5.1.0/installed-dc4... (dependency of base-4.7.0.0/installed-018...) [__4] next goal: ghc-prim (dependency of base-4.7.0.0/installed-018...) [__4] trying: ghc-prim-0.3.1.0/installed-948... [__5] done Ready to install data-default-class-0.0.1 Waiting for install task to finish... Extracting /home/local/ANT/shida/.cabal/packages/ hackage.haskell.org/data-default-class/0.0.1/data-default-class-0.0.1.tar.gz to /tmp/data-default-class-0.0.1-19534... Updating data-default-class.cabal with the latest revision from the index. Using internal setup method with build-type Simple and args: ["configure","--verbose=3","--ghc","--prefix=/home/local/ANT/shida/.cabal","--bindir=/home/local/ANT/shida/.cabal/bin","--libdir=/home/local/ANT/shida/.cabal/lib","--libsubdir=x86_64-linux-ghc-7.8.2/data-default-class-0.0.1","--libexecdir=/home/local/ANT/shida/.cabal/libexec","--datadir=/home/local/ANT/shida/.cabal/share","--datasubdir=x86_64-linux-ghc-7.8.2/data-default-class-0.0.1","--docdir=/home/local/ANT/shida/.cabal/share/doc/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1","--htmldir=/home/local/ANT/shida/.cabal/share/doc/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1/html","--haddockdir=/home/local/ANT/shida/.cabal/share/doc/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1/html","--sysconfdir=/home/local/ANT/shida/.cabal/etc","--enable-split-objs","--user","--dependency=base=base-4.7.0.0-018311399e3b6350d5be3a16b144df9b","--disable-tests","--exact-configuration","--disable-benchmarks"] Configuring data-default-class-0.0.1... creating dist Searching for ghc in path. Found ghc at /usr/local/bin/ghc ("/usr/local/bin/ghc",["--numeric-version"]) /usr/local/bin/ghc is version 7.8.2 looking for tool ghc-pkg near compiler in /usr/local/bin found ghc-pkg in /usr/local/bin/ghc-pkg ("/usr/local/bin/ghc-pkg",["--version"]) /usr/local/bin/ghc-pkg is version 7.8.2 ("/usr/local/bin/ghc",["--supported-languages"]) ("/usr/local/bin/ghc",["--info"]) Reading installed packages... ("/usr/local/bin/ghc-pkg",["dump","--global","-v0"]) ("/usr/local/bin/ghc-pkg",["dump","--user","-v0"]) ("/usr/local/bin/ghc",["--print-libdir"]) Dependency base ==4.7.0.0: using base-4.7.0.0 Searching for alex in path. Cannot find alex on the path Searching for ar in path. Found ar at /usr/bin/ar Searching for c2hs in path. Cannot find c2hs on the path Searching for cpphs in path. Cannot find cpphs on the path Searching for ffihugs in path. Cannot find ffihugs on the path Searching for gcc in path. Found gcc at /usr/bin/gcc ("/usr/bin/gcc",["-dumpversion"]) /usr/bin/gcc is version 4.6 Searching for greencard in path. Cannot find greencard on the path Searching for haddock in path. Found haddock at /usr/local/bin/haddock ("/usr/local/bin/haddock",["--version"]) /usr/local/bin/haddock is version 2.14.2 Searching for happy in path. Cannot find happy on the path Searching for hmake in path. Cannot find hmake on the path Searching for hpc in path. Found hpc at /usr/local/bin/hpc ("/usr/local/bin/hpc",["version"]) /usr/local/bin/hpc is version 0.67 looking for tool hsc2hs near compiler in /usr/local/bin found hsc2hs in /usr/local/bin/hsc2hs ("/usr/local/bin/hsc2hs",["--version"]) /usr/local/bin/hsc2hs is version 0.67 Searching for HsColour in path. Cannot find HsColour on the path Searching for hugs in path. Cannot find hugs on the path Searching for jhc in path. Cannot find jhc on the path Searching for ld in path. Found ld at /usr/bin/ld Environment: [("COLORFGBG","12;default;8"),("COLORTERM","rxvt-xpm"),("DBUS_SESSION_BUS_ADDRESS","unix:abstract=/tmp/dbus-5El0U8sCi8,guid=09290436e309789f9814dffc00000406"),("DEFAULTS_PATH","/usr/share/gconf/xmonad.default.path"),("DESKTOP_SESSION","xmonad"),("DISPLAY"," 10.69.208.185:0"),("EDITOR","vim"),("GDMSESSION","xmonad"),("GPG_AGENT_INFO","/tmp/gpg-KKH3WT/S.gpg-agent:5467:1"),("GREP_COLOR","1;32"),("GREP_OPTIONS","--color=auto --exclude-dir=.cvs --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn"),("GTK_IM_MODULE","xim"),("HOME","/home/local/ANT/shida"),("LANG","C.UTF-8"),("LC_ALL","C.UTF-8"),("LC_CTYPE","C.UTF-8"),("LESS","-R"),("LOGNAME","shida"),("LSCOLORS","Gxfxcxdxbxegedabagacad"),("MANDATORY_PATH","/usr/share/gconf/xmonad.mandatory.path"),("NODE_PATH","/usr/lib/nodejs:/usr/lib/node_modules:/usr/share/javascript"),("OLDPWD","/home/local/ANT/shida/src/git/cabal/cabal-install"),("PAGER","less"),("PATH","/usr/local/heroku/bin:.:/home/local/ANT/shida/.cabal/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/lib/lightdm/lightdm:/usr/local/bin:/usr/bin:/bin"),("PULSE_SERVER","10.69.208.185"),("PWD","/home/local/ANT/shida"),("QT_IM_MODULE","xim"),("SHELL","/usr/bin/zsh"),("SHLVL","1"),("SSH_AGENT_PID","14748"),("SSH_AUTH_SOCK","/tmp/ssh-NeRVrYb14746/agent.14746"),("TERM","rxvt-unicode-256color"),("UBUNTU_MENUPROXY","libappmenu.so"),("USER","shida"),("VISUAL","vim"),("WINDOWID","14683293"),("XAUTHORITY","/home/local/ANT/shida/.Xauthority"),("XDG_CONFIG_DIRS","/etc/xdg/xdg-xmonad:/etc/xdg"),("XDG_DATA_DIRS","/usr/share/xmonad:/usr/local/share/:/usr/share/"),("XDG_SEAT_PATH","/org/freedesktop/DisplayManager/Seat1"),("XDG_SESSION_COOKIE","05ca21f0ee7e6a10e18260ac00001d83-1402975930.974487-843139146"),("XDG_SESSION_PATH","/org/freedesktop/DisplayManager/Session0"),("XMODIFIERS","@im=ibus"),("ZSH","/home/local/ANT/shida/.oh-my-zsh"),("_","/home/local/ANT/shida/.cabal/bin/cabal")] ("/usr/local/bin/ghc",["-c","/tmp/19534.c","-o","/tmp/19534.o"]) ("/usr/bin/ld",["-x","-r","/tmp/19534.o","-o","/tmp/19535.o"]) Searching for lhc in path. Cannot find lhc on the path Searching for lhc-pkg in path. Cannot find lhc-pkg on the path Searching for nhc98 in path. Cannot find nhc98 on the path Searching for pkg-config in path. Found pkg-config at /usr/bin/pkg-config ("/usr/bin/pkg-config",["--version"]) /usr/bin/pkg-config is version 0.26 Searching for strip in path. Found strip at /usr/bin/strip Searching for tar in path. Found tar at /bin/tar Searching for uhc in path. Cannot find uhc on the path Using Cabal-1.21.0.0 compiled by ghc-7.8 Using compiler: ghc-7.8.2 Using install prefix: /home/local/ANT/shida/.cabal Binaries installed in: /home/local/ANT/shida/.cabal/bin Libraries installed in: /home/local/ANT/shida/.cabal/lib/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1 Private binaries installed in: /home/local/ANT/shida/.cabal/libexec Data files installed in: /home/local/ANT/shida/.cabal/share/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1 Documentation installed in: /home/local/ANT/shida/.cabal/share/doc/x86_64-linux-ghc-7.8.2/data-default-class-0.0.1 Configuration files installed in: /home/local/ANT/shida/.cabal/etc No alex found Using ar found on system at: /usr/bin/ar No c2hs found No cpphs found No ffihugs found Using gcc version 4.6 found on system at: /usr/bin/gcc Using ghc version 7.8.2 found on system at: /usr/local/bin/ghc Using ghc-pkg version 7.8.2 found on system at: /usr/local/bin/ghc-pkg No greencard found Using haddock version 2.14.2 found on system at: /usr/local/bin/haddock No happy found Using haskell-suite found on system at: haskell-suite-dummy-location Using haskell-suite-pkg found on system at: haskell-suite-pkg-dummy-location No hmake found Using hpc version 0.67 found on system at: /usr/local/bin/hpc Using hsc2hs version 0.67 found on system at: /usr/local/bin/hsc2hs No hscolour found No hugs found No jhc found Using ld found on system at: /usr/bin/ld No lhc found No lhc-pkg found No nhc98 found Using pkg-config version 0.26 found on system at: /usr/bin/pkg-config Using strip found on system at: /usr/bin/strip Using tar found on system at: /bin/tar No uhc found ("/usr/bin/gcc",["/tmp/19534.c","-o","/tmp/19534","-D__GLASGOW_HASKELL__=708","-Dlinux_BUILD_OS=1","-Dx86_64_BUILD_ARCH=1","-Dlinux_HOST_OS=1","-Dx86_64_HOST_ARCH=1","-Idist/build/autogen","-I.","-I/usr/local/lib/ghc-7.8.2/base-4.7.0.0/include","-I/usr/local/lib/ghc-7.8.2/integer-gmp-0.5.1.0/include","-I/usr/local/lib/ghc-7.8.2/include","-L/usr/local/lib/ghc-7.8.2/base-4.7.0.0","-L/usr/local/lib/ghc-7.8.2/integer-gmp-0.5.1.0","-L/usr/local/lib/ghc-7.8.2/ghc-prim-0.3.1.0","-L/usr/local/lib/ghc-7.8.2/rts-1.0"]) Using internal setup method with build-type Simple and args: ["build","--verbose=3"] Component build order: library creating dist/build creating dist/build/autogen Building data-default-class-0.0.1... Preprocessing library data-default-class-0.0.1... Building library... creating dist/build Environment: [("COLORFGBG","12;default;8"),("COLORTERM","rxvt-xpm"),("DBUS_SESSION_BUS_ADDRESS","unix:abstract=/tmp/dbus-5El0U8sCi8,guid=09290436e309789f9814dffc00000406"),("DEFAULTS_PATH","/usr/share/gconf/xmonad.default.path"),("DESKTOP_SESSION","xmonad"),("DISPLAY"," 10.69.208.185:0"),("EDITOR","vim"),("GDMSESSION","xmonad"),("GPG_AGENT_INFO","/tmp/gpg-KKH3WT/S.gpg-agent:5467:1"),("GREP_COLOR","1;32"),("GREP_OPTIONS","--color=auto --exclude-dir=.cvs --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn"),("GTK_IM_MODULE","xim"),("HOME","/home/local/ANT/shida"),("LANG","C.UTF-8"),("LC_ALL","C.UTF-8"),("LC_CTYPE","C.UTF-8"),("LESS","-R"),("LOGNAME","shida"),("LSCOLORS","Gxfxcxdxbxegedabagacad"),("MANDATORY_PATH","/usr/share/gconf/xmonad.mandatory.path"),("NODE_PATH","/usr/lib/nodejs:/usr/lib/node_modules:/usr/share/javascript"),("OLDPWD","/home/local/ANT/shida/src/git/cabal/cabal-install"),("PAGER","less"),("PATH","/usr/local/heroku/bin:.:/home/local/ANT/shida/.cabal/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/lib/lightdm/lightdm:/usr/local/bin:/usr/bin:/bin"),("PULSE_SERVER","10.69.208.185"),("PWD","/home/local/ANT/shida"),("QT_IM_MODULE","xim"),("SHELL","/usr/bin/zsh"),("SHLVL","1"),("SSH_AGENT_PID","14748"),("SSH_AUTH_SOCK","/tmp/ssh-NeRVrYb14746/agent.14746"),("TERM","rxvt-unicode-256color"),("UBUNTU_MENUPROXY","libappmenu.so"),("USER","shida"),("VISUAL","vim"),("WINDOWID","14683293"),("XAUTHORITY","/home/local/ANT/shida/.Xauthority"),("XDG_CONFIG_DIRS","/etc/xdg/xdg-xmonad:/etc/xdg"),("XDG_DATA_DIRS","/usr/share/xmonad:/usr/local/share/:/usr/share/"),("XDG_SEAT_PATH","/org/freedesktop/DisplayManager/Seat1"),("XDG_SESSION_COOKIE","05ca21f0ee7e6a10e18260ac00001d83-1402975930.974487-843139146"),("XDG_SESSION_PATH","/org/freedesktop/DisplayManager/Session0"),("XMODIFIERS","@im=ibus"),("ZSH","/home/local/ANT/shida/.oh-my-zsh"),("_","/home/local/ANT/shida/.cabal/bin/cabal")] ("/usr/local/bin/ghc",["--make","-v","-fbuilding-cabal-package","-O","-split-objs","-static","-dynamic-too","-dynosuf","dyn_o","-dynhisuf","dyn_hi","-outputdir","dist/build","-odir","dist/build","-hidir","dist/build","-stubdir","dist/build","-i","-idist/build","-i.","-idist/build/autogen","-Idist/build/autogen","-Idist/build","-optP-include","-optPdist/build/autogen/cabal_macros.h","-package-name","data-default-class-0.0.1","-hide-all-packages","-package-db","dist/package.conf.inplace","-package-id","base-4.7.0.0-018311399e3b6350d5be3a16b144df9b","-XHaskell98","Data.Default.Class"]) Glasgow Haskell Compiler, Version 7.8.2, stage 2 booted by GHC version 7.8.1 Using binary package database: /usr/local/lib/ghc-7.8.2/package.conf.d/package.cache Using binary package database: /home/local/ANT/shida/.ghc/x86_64-linux-7.8.2/package.conf.d/package.cache Using package config file: dist/package.conf.inplace wired-in package ghc-prim mapped to ghc-prim-0.3.1.0-948744e1f99cc8bcc7c7d3ba60c7c2d8 wired-in package integer-gmp mapped to integer-gmp-0.5.1.0-dc47f6b546fc171f67a7f7d311684a99 wired-in package base mapped to base-4.7.0.0-018311399e3b6350d5be3a16b144df9b wired-in package rts mapped to builtin_rts wired-in package template-haskell mapped to template-haskell-2.9.0.0-dcc8c210fb02937e104bc1784d7b0f06 wired-in package dph-seq not found. wired-in package dph-par not found. Hsc static flags: wired-in package ghc-prim mapped to ghc-prim-0.3.1.0-948744e1f99cc8bcc7c7d3ba60c7c2d8 wired-in package integer-gmp mapped to integer-gmp-0.5.1.0-dc47f6b546fc171f67a7f7d311684a99 wired-in package base mapped to base-4.7.0.0-018311399e3b6350d5be3a16b144df9b wired-in package rts mapped to builtin_rts wired-in package template-haskell mapped to template-haskell-2.9.0.0-dcc8c210fb02937e104bc1784d7b0f06 wired-in package dph-seq not found. wired-in package dph-par not found. *** Chasing dependencies: Chasing modules from: *Data.Default.Class Stable obj: [] Stable BCO: [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2014-06-23 03:29:30.794067064 UTC ms_mod = data-default-class-0.0.1:Data.Default.Class, ms_textual_imps = [import (implicit) Prelude] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file ./Data/Default/Class.hs Created temporary directory: /tmp/ghc19596_0 *** Checking old interface for data-default-class-0.0.1:Data.Default.Class: [1 of 1] Compiling Data.Default.Class ( Data/Default/Class.hs, dist/build/Data/Default/Class.o ) *** Parser: *** Renamer/typechecker: *** Desugar: Result size of Desugar (after optimization) = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Specialise: Result size of Specialise = {terms: 0, types: 0, coercions: 0} *** Float out(FOS {Lam = Just 0, Consts = True, PAPs = False}): Result size of Float out(FOS {Lam = Just 0, Consts = True, PAPs = False}) = {terms: 0, types: 0, coercions: 0} *** Float inwards: Result size of Float inwards = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Demand analysis: Result size of Demand analysis = {terms: 0, types: 0, coercions: 0} *** Worker Wrapper binds: Result size of Worker Wrapper binds = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Float out(FOS {Lam = Just 0, Consts = True, PAPs = True}): Result size of Float out(FOS {Lam = Just 0, Consts = True, PAPs = True}) = {terms: 0, types: 0, coercions: 0} *** Common sub-expression: Result size of Common sub-expression = {terms: 0, types: 0, coercions: 0} *** Float inwards: Result size of Float inwards = {terms: 0, types: 0, coercions: 0} *** Simplifier: Result size of Simplifier = {terms: 0, types: 0, coercions: 0} *** Tidy Core: Result size of Tidy Core = {terms: 4, types: 7, coercions: 2} writeBinIface: 2 Names writeBinIface: 16 dict entries writeBinIface: 2 Names writeBinIface: 16 dict entries *** CorePrep: Result size of CorePrep = {terms: 4, types: 7, coercions: 2} *** Stg2Stg: *** CodeOutput: *** New CodeGen: *** CPSZ: *** CPSZ: *** Splitter: /usr/local/lib/ghc-7.8.2/ghc-split /tmp/ghc19596_0/ghc19596_2.split_s /tmp/ghc19596_0/ghc19596_4.split /tmp/ghc19596_0/ghc19596_4.split *** Assembler: /usr/bin/gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE -c -o dist/build/Data/Default/Class_o_split/Class__1.o /tmp/ghc19596_0/ghc19596_4.split__1.s *** Assembler: /usr/bin/gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE -c -o dist/build/Data/Default/Class_o_split/Class__2.o /tmp/ghc19596_0/ghc19596_4.split__2.s *** Linker: /usr/bin/gcc -fno-stack-protector -DTABLES_NEXT_TO_CODE -nostdlib -Wl,-r -nodefaultlibs '-Wl,--build-id=none' -o dist/build/Data/Default/Class.o /tmp/ghc19596_0/ghc19596_5.ldscript /usr/bin/ld: error: cannot find dist/build/Data/Default/Class_o_split/Class__1.o /usr/bin/ld: error: cannot find dist/build/Data/Default/Class_o_split/.o::Class(void) collect2: ld returned 1 exit status *** Deleting temp files: Deleting: /tmp/ghc19596_0/ghc19596_5.ldscript /tmp/ghc19596_0/ghc19596_4.split__1.s /tmp/ghc19596_0/ghc19596_4.split__2.s /tmp/ghc19596_0/ghc19596_4.split /tmp/ghc19596_0/ghc19596_3.c /tmp/ghc19596_0/ghc19596_2.split_s /tmp/ghc19596_0/ghc19596_1.split_s Warning: deleting non-existent /tmp/ghc19596_0/ghc19596_3.c Warning: deleting non-existent /tmp/ghc19596_0/ghc19596_1.split_s *** Deleting temp dirs: Deleting: /tmp/ghc19596_0 /usr/local/bin/ghc returned ExitFailure 1 Failed to install data-default-class-0.0.1 Updating world file... cabal: Error: some packages failed to install: data-default-class-0.0.1 failed during the building phase. The exception was: ExitFailure 1 -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

1 1

Problems with Parallel N Queens using Control.Parallel.Strategy
by bruce li 23 Jun '14

23 Jun '14

Hello, Cafe, I'm currently reading Parallel and Concurrent Programming in Haskell. I tried to implement an n-queens problem as an exercise, but a little bit overwhelmed by the strategy mystery. The code is listed at http://pastebin.com/ySgc3VSR. I implemented the higher order skeleton of search and try to add parallelism. My original idea was spawning a few threads while the search tree was small and each thread handles the following expansion of the tree. Hence, I gave a "maxDepth" variable to restrict the parallelism. But this did not go very well if I set the maxDepth to very small value, say, 2, 3, 4 etc. The speed up was very small. Viewing in threadscope, it seems there was very small amount of parallelism. Then I tried to let it go, which means I set the tree depth to a value larger than the maximum possible depth, say 20. Then it speeds up about 1.4 times on 2-cores. Viewing in threadscope, it seems the 2 cores are fully utilized. But the report is a bit annoying: SPARKS: 4686728 (100456 converted, 3461 overflowed, 0 dud, 4540817 GC'd, 41994 fizzled) with no restrictions on the parallelism, a lot of sparks are not converted and are GC'd. I wonder if there is some way to further improve the results, reducing un-convereted sparks and achieving better speed-up ratio. Thanks.

1 0

Re: [Haskell-cafe] ANN: set-cover solves Sudoku, Soma cube, 8 Queens etc.
by Johannes Waldmann 22 Jun '14

22 Jun '14

Henning Thielemann <lemming <at> henning-thielemann.de> writes: > .. package set-cover for solving exact set cover problems. > http://hackage.haskell.org/package/set-cover It's hard to evaluate whether one could use the library because there's essentially no visible documentation. E.g., what does Math.SetCover.Exact.search do? Its type refers to "State" which seems implementation-dependent, and hides the connection to the specification of the set cover problem. Putting some text and examples into the haddocks might help. But of course putting the specification there would be even better. Also, care to explain what algorithm your solver uses, and give some performance data (e.g., N-queens for N=10,20,40,..)? - J.W.

2 1

Re: [Haskell-cafe] diagrams
by Dominic Steinitz 22 Jun '14

22 Jun '14

> Message: 3 > Date: Fri, 20 Jun 2014 13:30:29 -0700 > From: Joachim Breitner <mail(a)joachim-breitner.de> > To: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] diagrams > Message-ID: <1403296229.16156.3.camel@kirk> > Content-Type: text/plain; charset="utf-8" > > Hi, > > Am Mittwoch, den 18.06.2014, 23:44 -0400 schrieb Anthony Cowley: > >>> I have no doubt that diagrams can make the diagrams themselves. What >>> I wonder about is the animation capabilities---ability to have >>> elements move or cross-fade (dissolve), in particular. > > I very recently created this animation with diagrams, which does move > and fade stuff: > http://joachim-breitner.de/publications/haskell_bytes_portland_2014-06-13.w… > > But the ride was not as smooth as it should have been. See > https://gist.github.com/nomeata/cde96a2e693a23cca8ee for the code. The > function positionSpec contains a ?script?, i.e. a sequence of animated > modifications to the image, using lenses to position the change. > > I guess with the right combinators, this can be greatly simplified, but > it is hard to come up with the right combinators. Especially as our code > is one-dimensional, and we want to compose in three dimensions (x, y and > time). It’s still a nice example though - thanks for posting it. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

1 0

diagrams
by Dennis Raddle 21 Jun '14

21 Jun '14

I'm a math tutor and I want to create videos to explain certain math concepts, and I'm wondering if the diagrams library would help me. There are two questions--first, whether it has the capability to do what I want, and second how hard it would to integrate the animations into YouTube videos with voice-over. To describe the capability, I'm looking first to typeset equations. Then, second, to represent manipulation of equations by having elements of equations move locations or cross-fade. Also "elements" could mean pictures or non-mathematical notation. I have no doubt that diagrams can make the diagrams themselves. What I wonder about is the animation capabilities---ability to have elements move or cross-fade (dissolve), in particular. As far as the ability to integrate these into YouTube videos, that is probably beyond the scope of this list, but maybe someone happens to have done this and knows the answer. Mike

3 2

Do you recognize this type?
by Corentin Dupont 20 Jun '14

20 Jun '14

Hi guys, I am making a DSL for event composition (inspired from digestive-functor & reactive-banana) and I find myself wanting a primitive like that: -- given a list of events, evaluate the function on those that have already fired. -- returns an event yelding the result when ready. ListEvent :: [Event a] -> ([a] -> Maybe b) -> Event b Does this type tell you something? Is there a better abstraction that can encompass it? My DSL is like that: -- | Composable events data Event a where SumEvent :: Event a -> Event a -> Event a -- The first event to fire will be returned AppEvent :: Event (a -> b) -> Event a -> Event b -- Both events should fire, and then the result is returned PureEvent :: a -> Event a -- Create a fake event. The result is useable with no delay. EmptyEvent :: Event a -- An event that is never fired. BaseEvent :: (Typeable a) => Field a -> Event a -- Embed a base event It's easy to define instances for Applicative and Alternative. But then I have a use case that I cannot solve: In the case of votations (which use this DSL), sometime you can end prematuraly the voting, even if not everybody voted yet: for example if the majority is already reached. In this case no need to wait for everybody, we can end the vote. This does not seem to be possible with Applicative or Monad interfaces: things have to be sequenced in a monad, they cannot be evaluated in parralel. For example: do v1 <- getVote1 v2 <- getVote2 v3 <- getVote3 evalMajority(v1, v2, v3) In this example I have to wait for all 3 votes to be completed, but in fact only two would suffice to achieve majority. That's why I added "ListEvent" to the DSL above which allow to achieve that but I'm wondering if there is a better/bigger abstraction to put it in. Thanks!! Corentin

4 6

How to represent a board?
by Rafael Almeida 20 Jun '14

20 Jun '14

Hello, There are many examples of games which use boards: chess, checkers, go, etc. Many people starting out at programming and/or game programming are very much tempted to code a board game. It looks like such a game would be easy to build at first sight. Even more sophisticated games sometimes use a grid system, which looks a lot like boards as well. In a grid system the movements of a given agent are bound do discrete positions. Although the user may not see the board underneath pretty graphics, it is a board game. Having in mind the sort of operations such games have to make on boards, I ask: what are the best representations for a board in Haskell? In many languages a NxN array seems like a good pick. In Haskell, most would translate that into lists of lists. I know I have. However, traversing those lists to get a position, calculate where a piece or agent could go, etc., feels awkward and unefficient. Beside the point already made, we have no type safe guarantee that our 64x64 won't become a 63x63 + 65x1 board due to some misbehaving function. It strikes me that list of lists is not a great board representation. I think STArrays are a better pick; from the perspective of translating an NxN array into Haskell, at least. However, maybe there is an even more elegant way to deal with a board in Haskell. I hope you can help me out figuring it out. []'s Rafael

8 8

Fwd: Do you recognize this type?
by Corentin Dupont 20 Jun '14

20 Jun '14

Yes it looks like, but I don't think it is: the argument function in ListEvent is taking a list itself, so that's not a fold. It's a sort of interruptible computation (since as soon as the argument function returns Just, we remove all remaining events). But I'm sure there is a better way to write it. ListEvent :: [Event a] -> ([a] -> Maybe b) -> Event b On Fri, Jun 20, 2014 at 4:31 PM, Kyle Marek-Spartz < kyle.marek.spartz(a)gmail.com> wrote: > Isn’t this a fold? > > – > Kyle Marek-Spartz > > > > On Jun 20, 2014, 7:59:41 AM, Corentin Dupont <corentin.dupont(a)gmail.com> > wrote: > ------------------------------ > Nobody on that? > What I really want is: a computation that can be interrupted if enough > result is already there. > I would be surprise if that concept doesn't exist already somewhere :) > > > On Thu, Jun 19, 2014 at 5:17 PM, Corentin Dupont < > corentin.dupont(a)gmail.com> wrote: > >> Hi guys, >> I am making a DSL for event composition (inspired from >> digestive-functor & reactive-banana) and I find myself wanting a primitive >> like that: >> >> -- given a list of events, evaluate the function on those that have >> already fired. >> -- returns an event yelding the result when ready. >> ListEvent :: [Event a] -> ([a] -> Maybe b) -> Event b >> >> Does this type tell you something? Is there a better abstraction that >> can encompass it? >> My DSL is like that: >> >> -- | Composable events >> data Event a where >> SumEvent :: Event a -> Event a -> Event a -- The first event >> to fire will be returned >> AppEvent :: Event (a -> b) -> Event a -> Event b -- Both events >> should fire, and then the result is returned >> PureEvent :: a -> Event a -- Create a fake >> event. The result is useable with no delay. >> EmptyEvent :: Event a -- An event that is >> never fired. >> BaseEvent :: (Typeable a) => Field a -> Event a -- Embed a base >> event >> >> It's easy to define instances for Applicative and Alternative. >> But then I have a use case that I cannot solve: >> In the case of votations (which use this DSL), sometime you can end >> prematuraly the voting, even if not everybody voted yet: for example if the >> majority is already reached. >> In this case no need to wait for everybody, we can end the vote. >> >> This does not seem to be possible with Applicative or Monad interfaces: >> things have to be sequenced in a monad, they cannot be evaluated in >> parralel. >> For example: >> >> do >> v1 <- getVote1 >> v2 <- getVote2 >> v3 <- getVote3 >> evalMajority(v1, v2, v3) >> >> In this example I have to wait for all 3 votes to be completed, but in >> fact only two would suffice to achieve majority. >> That's why I added "ListEvent" to the DSL above which allow to achieve >> that but I'm wondering if there is a better/bigger abstraction to put it >> in. >> >> Thanks!! >> Corentin >> >> > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

1 0

Relations between Functor typeclass and kind
by Gautier DI FOLCO 19 Jun '14

19 Jun '14

Hi all, Some days ago, I was talking with someone about Kinds and GADTs. At some point he mention that types with this Kind: (* -> *) are called Functors. So, is there any relations between Functor typeclass and Functor kind? Is it considered as a "pattern"? if so, are there some other ones? If you have any link on this, I'll take them. Thanks in advance for your help.

2 2

dead links on mailing list page
by Yomna Nasser 19 Jun '14

19 Jun '14

I was trying to look at some mailing list archives, and encountered several dead links in section 1.3 on this page: http://www.haskell.org/haskellwiki/Mailing_lists - 3rd paragraph, link to http://www.cse.unsw.edu.au/~dons/haskell-1990-2006/threads.html (a 403 is returned), where the link is under the text "hosted here" - 4th paragraph, link to the Google Coop Haskell Search Engine (a 404 is returned) I wasn't sure where else to report this.

2 1

Haskell Weekly News: Issue 297
by Daniel Santa Cruz 19 Jun '14

19 Jun '14

Welcome to issue 297 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from June 8 to 14, 2014 Quotes of the Week * dpwright: this afternoon I've literally taken an entire (portrait) screen's worth of code and reduced it to about three lines and a few lens operators * tommd: Haskell is a great language. I needed to test a program under high CPU load, so to burn some cycles I cabal-installed lens. Is there anything Haskell can't do? * bernalex: I imagine hell as a place where spj & edwardk are holding talks at the same time and I have to choose. Top Reddit Stories * Haxl on Github Domain: github.com, Score: 124, Comments: 25 Original: [1] http://goo.gl/zw8Y8q On Reddit: [2] http://goo.gl/FoV1zw * www.dohaskell.com Domain: dohaskell.com, Score: 92, Comments: 23 Original: [3] http://goo.gl/uxmtUy On Reddit: [4] http://goo.gl/xkGJUb * cloud-haskell is on hackage now Domain: hackage.haskell.org, Score: 87, Comments: 7 Original: [5] http://goo.gl/eCHMgO On Reddit: [6] http://goo.gl/h9j7H1 * Facebook releases Haxl, a library for async data access Domain: code.facebook.com, Score: 65, Comments: 0 Original: [7] http://goo.gl/D6xEnM On Reddit: [8] http://goo.gl/GCqeEt * The problem with mtl Domain: ro-che.info, Score: 61, Comments: 58 Original: [9] http://goo.gl/hDncB8 On Reddit: [10] http://goo.gl/2uRfm2 * Why programmers can’t make any money: dimensionality and the Eternal Haskell Tax Domain: michaelochurch.wordpress.com, Score: 56, Comments: 37 Original: [11] http://goo.gl/Ums4cZ On Reddit: [12] http://goo.gl/ytLSN2 * A Year of Functional Programming Domain: japgolly.blogspot.com.au, Score: 52, Comments: 17 Original: [13] http://goo.gl/torrXD On Reddit: [14] http://goo.gl/XTSVed * Haskell for all: Spreadsheet-like programming in Haskell Domain: haskellforall.com, Score: 52, Comments: 26 Original: [15] http://goo.gl/eaaeHa On Reddit: [16] http://goo.gl/biUwQf * GHC bug squashing at ZuriHac 2014 Domain: joachim-breitner.de, Score: 50, Comments: 0 Original: [17] http://goo.gl/zgd6qV On Reddit: [18] http://goo.gl/HDp0Wt * There is no Fork—our ICFP 2014 paper about Haxl Domain: community.haskell.org, Score: 47, Comments: 4 Original: [19] http://goo.gl/yvbvAH On Reddit: [20] http://goo.gl/pwcBxO * EclipseFP 2.6.0 released Domain: jpmoresmau.blogspot.fr, Score: 46, Comments: 18 Original: [21] http://goo.gl/fohXYx On Reddit: [22] http://goo.gl/duJMir * Haskell Development Workflow Demo, first video I've made, wanted to see if any found it useful Domain: youtube.com, Score: 44, Comments: 11 Original: [23] http://goo.gl/O1REsS On Reddit: [24] http://goo.gl/KTK1kk * Announcement: Bang, a drum machine DSL for Haskell Domain: self.haskell, Score: 42, Comments: 17 Original: [25] http://goo.gl/QVlj3E On Reddit: [26] http://goo.gl/QVlj3E * How do you learn to write systems in Haskell? (and a story) Domain: self.haskell, Score: 42, Comments: 66 Original: [27] http://goo.gl/PXiZUD On Reddit: [28] http://goo.gl/PXiZUD * The Haskell Cast #7 - Chris Done on Compiling to JavaScript and SQL Domain: haskellcast.com, Score: 41, Comments: 15 Original: [29] http://goo.gl/747Kpj On Reddit: [30] http://goo.gl/n0nlLJ * ICFP 2014 accepted papers Domain: github.com, Score: 40, Comments: 3 Original: [31] http://goo.gl/XZ962N On Reddit: [32] http://goo.gl/VnuyDW * cabal - the simple guide Domain: katychuang.com, Score: 40, Comments: 16 Original: [33] http://goo.gl/svwYE1 On Reddit: [34] http://goo.gl/oGidxo * Two failed attempts at extensible effects Domain: ro-che.info, Score: 37, Comments: 12 Original: [35] http://goo.gl/DD7WX9 On Reddit: [36] http://goo.gl/wh8fWW * Follow up blog post: "Understanding the RealWorld": the Haskell heap, function calls, and primitive types. Domain: well-typed.com, Score: 34, Comments: 12 Original: [37] http://goo.gl/9OMjWu On Reddit: [38] http://goo.gl/N0B4cJ * "Why Haskell?" Elevator Pitch Domain: self.haskell, Score: 33, Comments: 70 Original: [39] http://goo.gl/xsIOqw On Reddit: [40] http://goo.gl/xsIOqw Top StackOverflow Questions * Why should Applicative be a superclass of Monad? votes: 21, answers: 3 Read on SO: [41] http://goo.gl/Z1Q6uo * What do you call the data wrapped inside a monad? votes: 15, answers: 2 Read on SO: [42] http://goo.gl/iNtQAX * What algorithm is used in Haskell (GHC) for deriving types of recursive expressions? votes: 14, answers: 1 Read on SO: [43] http://goo.gl/7QvfqM * What container really mimics std::vector in Haskell? votes: 14, answers: 4 Read on SO: [44] http://goo.gl/k0vk2n * Why the cycle function cannot work with empty list? votes: 14, answers: 2 Read on SO: [45] http://goo.gl/B5Na0a Until next time, [46]+Daniel Santa Cruz References 1. https://github.com/facebook/Haxl 2. http://www.reddit.com/r/haskell/comments/27sv88/haxl_on_github/ 3. http://www.dohaskell.com/ 4. http://www.reddit.com/r/haskell/comments/27wjwk/wwwdohaskellcom/ 5. http://hackage.haskell.org/package/cloud-haskell-0.0.1.0 6. http://www.reddit.com/r/haskell/comments/281sbp/cloudhaskell_is_on_hackage_… 7. https://code.facebook.com/projects/854888367872565/haxl/ 8. http://www.reddit.com/r/haskell/comments/27syj2/facebook_releases_haxl_a_li… 9. http://ro-che.info/articles/2014-06-11-problem-with-mtl.html 10. http://www.reddit.com/r/haskell/comments/27vhd1/the_problem_with_mtl/ 11. http://michaelochurch.wordpress.com/2014/06/06/why-programmers-cant-make-an… 12. http://www.reddit.com/r/haskell/comments/27onwq/why_programmers_cant_make_a… 13. http://japgolly.blogspot.com.au/2014/06/a-year-of-functional-programming.ht… 14. http://www.reddit.com/r/haskell/comments/27oxr4/a_year_of_functional_progra… 15. http://www.haskellforall.com/2014/06/spreadsheet-like-programming-in-haskel… 16. http://www.reddit.com/r/haskell/comments/284enc/haskell_for_all_spreadsheet… 17. http://www.joachim-breitner.de/blog/archives/651-ZuriHac-2014.html 18. http://www.reddit.com/r/haskell/comments/27p2nc/ghc_bug_squashing_at_zuriha… 19. http://community.haskell.org/~simonmar/papers/haxl-icfp14.pdf 20. http://www.reddit.com/r/haskell/comments/27tjpj/there_is_no_forkour_icfp_20… 21. http://jpmoresmau.blogspot.fr/2014/06/eclipsefp-260-released.html 22. http://www.reddit.com/r/haskell/comments/27utrw/eclipsefp_260_released/ 23. https://www.youtube.com/watch?v=Li6oaO8x2VY 24. http://www.reddit.com/r/haskell/comments/27lcz3/haskell_development_workflo… 25. http://www.reddit.com/r/haskell/comments/27s6py/announcement_bang_a_drum_ma… 26. http://www.reddit.com/r/haskell/comments/27s6py/announcement_bang_a_drum_ma… 27. http://www.reddit.com/r/haskell/comments/28575l/how_do_you_learn_to_write_s… 28. http://www.reddit.com/r/haskell/comments/28575l/how_do_you_learn_to_write_s… 29. http://www.haskellcast.com/episode/007-chris-done-on-compiling-to-javascrip… 30. http://www.reddit.com/r/haskell/comments/27sh2d/the_haskell_cast_7_chris_do… 31. https://github.com/yallop/icfp2014-papers/blob/master/README.md 32. http://www.reddit.com/r/haskell/comments/27p8xo/icfp_2014_accepted_papers/ 33. http://katychuang.com/cabal-guide/ 34. http://www.reddit.com/r/haskell/comments/280h9h/cabal_the_simple_guide/ 35. http://ro-che.info/articles/2014-06-14-extensible-effects-failed.html 36. http://www.reddit.com/r/haskell/comments/285prk/two_failed_attempts_at_exte… 37. http://www.well-typed.com/blog/95/ 38. http://www.reddit.com/r/haskell/comments/27yg67/follow_up_blog_post_underst… 39. http://www.reddit.com/r/haskell/comments/282yky/why_haskell_elevator_pitch/ 40. http://www.reddit.com/r/haskell/comments/282yky/why_haskell_elevator_pitch/ 41. http://stackoverflow.com/questions/24112786/why-should-applicative-be-a-sup… 42. http://stackoverflow.com/questions/24127190/what-do-you-call-the-data-wrapp… 43. http://stackoverflow.com/questions/24105812/what-algorithm-is-used-in-haske… 44. http://stackoverflow.com/questions/24123967/what-container-really-mimics-st… 45. http://stackoverflow.com/questions/24223201/why-the-cycle-function-cannot-w… 46. https://plus.google.com/105107667630152149014/about

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Hackage "500 Internal Server Error"
by Conal Elliott 18 Jun '14

18 Jun '14

Is hackage uploading broken? I'm trying to upload a new version of vector-space and am getting "500 Internal Server Error". -- Conal

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ANNOUNCE: haste-perch
by Alberto G. Corona 18 Jun '14

18 Jun '14

Hi, haste-perch defines builder elements (perchs) for Haste.DOM elements that are appendable, so that dynamic HTML can be created in the client in a natural way, like textual HTML, but programmatically and with the advantage of static type checking. It can be ported to other haskell-js compilers. http://hackage.haskell.org/package/haste-perch This program, when compiled with haste: main= do withElem "idelem" $ build $ do div $ do div $ do p "hello" p ! atr "style" "color:red" $ "world" return () Creates these element: <div id= "idelem"> <-- was already in the HTML <div> <div> <p> hello </p> <p style= "color:red"> world </p> </div> </div> </div> Since the creation is in the browser, that permit quite dynamic pages for data presentation, and interctive textual (a.k.a "serious") applications and, in general the development of client-side web frameworks using haskell with the haste compiler. See the README in the git repository: https://github.com/agocorona/haste-perch -- Alberto.

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What are the problems with instances for polymorphic types?
by Gábor Lehel 18 Jun '14

18 Jun '14

In other words instances for forall-types, such as: instance Foo (forall a. [a]) where ... It feels obvious to me that there *would* be problems with this, but I'm curious about what, exactly, they are. Could someone familiar with the matter either elaborate on them, or refer me to an existing explanation, a previous discussion, or something of the sort? I *don't* have any kind of use case in mind, I'm merely seeking a better understanding of the type-system issues involved. (I attempted Google, but didn't have much success.) Thanks in advance.

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Building static libraries with -fPIC
by Nikolay Amiantov 18 Jun '14

18 Jun '14

Hello all, I'm trying to build a shared (.so) library written in Haskell with "foreign export"s, which is statically linked with all needed dependencies. To do this, as far as I understood, I need to build all my dependencies (I use Cabal) with -fPIC flag, and also somehow get RTS static library built with -fPIC. Two questions regarding to this: 1) How can I add a build flag which will be added while building all my dependencies in Cabal. 2) How can I get needed RTS library. 3) How can I deal with "base"? Can I just build it with Cabal, so this question reduces to (1)? Thanks, Nikolay.

1 0

Warnings with OverloadedLists
by Nikolay Amiantov 18 Jun '14

18 Jun '14

Hello, I've bumped into strange GHC behaviour with OverloadedLists and pattern matching. Consider this example: {-# LANGUAGE OverloadedLists #-} len :: [a] -> Int len [] = 0 len (_:t) = 1 + len t If I load this with "ghci -Wall", I get a warning: Test.hs:4:1: Warning: Pattern match(es) are non-exhaustive In an equation for ‘len’: Patterns not matched: [] If I disable OverloadedLists extension, warning goes away. Can someone clear this behaviour out for me? It looks like a bug, but I'm not sure. Thanks for help, Nikolay.

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Support of multi-constructor types by UNPACK pragma
by Nikita Volkov 18 Jun '14

18 Jun '14

Currently the pragma only supports single-constructor types. So in the following example it will simply be ignored: data A = A1 Char | A2 {-# UNPACK #-} !B data B = B1 Int | B2 Bool However it seems to be easily solvable by changing the type A to something like the following during unpacking: data A = A1 Char | A2_1 Int | -- from B1 A2_2 Bool -- from B2 Am I missing something? Why is it not implemented?

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ANN: haddock-library 1.0.0
by Mateusz Kowalczyk 18 Jun '14

18 Jun '14

Hi, haddock-library is a package aiming to provide bits of Haddock to the rest of the Haskell world without imposing the GHC dependency that we have on the ‘haddock’ package itself. Please note that this does not deprecate the ‘haddock’ package which aims to expose other bits of Haddock, including those talking with GHC. Specifically, 1.0.0 exposes the types used by the comment parser and the parser itself. This allows you to supply the Haddock parser with String and get a Haddock ADT back out to play with. This means that if in the past you were processing Haddock strings with your own solution (or copy + pasted Alex parser we had) then you should now switch to this package instead. The API is subject to change so upper version bound is advised. Tested on 7.6.3, 7.8.x and current HEAD. The parser exposed is what is used in Haddock itself which now internally depends on this package. There are plans to move more parts into this package, exposing as much useful functionality as possible without the GHC dependency. New releases are independent of the GHC release cycle, unlike Haddock itself. To file issues for this package, use the Haddock issue tracker that's now on GitHub. Thanks -- Mateusz K.

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return with mutable object
by Baojun Wang 18 Jun '14

18 Jun '14

Hi List, Per my understanding, return x would make a new copy of the object. What if the returned object is mutable? Will this make a new (mutable) object? My concern is if I created a very large mutable object, does return mutable make a full copy of the original mutable data, or just copy a reference (pointer?)? Thanks baojun

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"Spinless Tagless G-Machine" erratum?
by Tom Ellis 18 Jun '14

18 Jun '14

I am reading SPJ's seminal work "Implementing lazy functional languages on stock hardware: the Spinless Tagless G-machine" (1992) and I am confused by something which may be a minor notational error, or may be a key detail I am misunderstanding. The paper is available here http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.3729 On page 26 we have aList = {} \n Cons {thing,nil} nil = {} \n Nil {} but I have not seen this use of the notation elsewhere in the paper. It strikes me that this should be aList = {} \n {} -> Cons {thing,nil} nil = {} \n {} -> Nil {} Is my intuition correct, or am I missing a key detail? Thanks, Tom

1 0

Package Maintenance: hfuse
by Montez Fitzpatrick 17 Jun '14

17 Jun '14

I would like to take over maintenance of the following package: "hfuse." I have attempted to e-mail the original package author and maintainer with no response.

1 0

Fwd: testing platform
by Roelof Wobben 17 Jun '14

17 Jun '14

Hello, IM learning Haskell by this book : Programming Haskell. Which test platform can I also learn the best or can I better first learn Haskell and later the test platforms ? Roelof

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1 = 0?
by Alexey Muranov 17 Jun '14

17 Jun '14

Is this the expected behavior that 1 = 0 does not raise any error? What does this mean? Thanks. Alexey.

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data/newtype vs. class
by martin 17 Jun '14

17 Jun '14

Hello all, I find myself trying to define a class, where a newtype would suffice. E.g. once I was pondering over "named" things and my initial thought was "well that's a class, which asks for a function 'getName'". But then here http://www.haskell.org/pipermail/haskell-cafe/2010-June/078803.html someone showed me a solution without any classes. Recently I was pondering over "timed things" (things which change at specific ponts in time) and again my initial thought was "that's a class, which asks for a method 'at'". Then I remembered things like State, i.e. data types which wrap around functions. State is not a class, which asks for a function 'nextState', it is all defined with data. Can someone give me some guidance, when to use classes and when to use data? Are the two concepts interchangeable in some scenarios? Martin

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Re: [Haskell-cafe] Uploading to hackage fails: bad file names in tarball
by Niklas Larsson 16 Jun '14

16 Jun '14

Hi! For extremely ancient and cludgy reasons AUX isn't a valid filename on windows, it's a DOS device. The other similarly reserved name are CON, PRN and NUL. Niklas ----- Ursprungligt meddelande ----- Från: "Arie Peterson" <ariep(a)xs4all.nl> Skickat: ‎2014-‎06-‎16 10:45 Till: "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Ämne: [Haskell-cafe] Uploading to hackage fails: bad file names in tarball Since some time, I have been unable to upload packages to Hackage, via either the 'cabal upload' command, or using the web form. The error message it gives is this: ==== ✂ ==== Hackage username: AriePeterson Hackage password: Uploading dist/np-linear-0.1.1.1.tar.gz... Error: dist/np-linear-0.1.1.1.tar.gz: 400 Bad Request Error: Invalid package Invalid windows file name in tar archive: "np-linear-0.1.1.1\\src\\Aux.hs". For portability, hackage requires that file names be valid on both Unix and Windows systems, and not refer outside of the tarball. ==== ✂ ==== The tarball is created by 'cabal sdist': cabal-install version 1.18.0.2 using version 1.18.1.1 of the Cabal library. I also installed the newest cabal-install, on another machine, but this did not help (same error). I also tried to create a tarball by hand, using 'tar --format=ustar', but this again resulted in the same error message. By the way, I'm on linux, not Windows, so it is not clear how the backslashes get in the file names. What could be going on? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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What is GHC 7.8.2 doing here (typed holes, data+poly kinds, type families etc.)
by Dominic Mulligan 16 Jun '14

16 Jun '14

Hi, I've come across some behaviour in GHC 7.8.2 which seems strange, and may be a bug, but I wish to check before reporting it. Consider the minimum example pasted at the bottom of this message. At the line plusComm (SS m') n' = _ GHC tells me that I have a single hole in the file with type 'S (m1 :+: n) :~: (n :+: 'S m1) which is straightforward to provide, by rewriting with the inductive hypothesis (a recursive call of plusComm) and then some fiddling. However, replacing this line with the refinement plusComm (SS m') n' = substR (plusComm m' n') _ GHC tells me that the remaining hole now has type 'S (m1 :+: n) :~: (m1 :+: n) which seems completely incorrect to me. Shouldn't this hole have type 'S (n :+: m1) :~: (n :+: S m1) ? Can anybody give any clues as to what is happening? Thanks, Dominic {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} module MinimumExample where data (:~:) (a :: k) (b :: k) where Refl :: a :~: a substR :: a :~: b -> f a -> f b substR Refl x = x substL :: a :~: b -> f b -> f a substL Refl x = x cong :: a :~: b -> f a :~: f b cong Refl = Refl data Nat where Z :: Nat S :: Nat -> Nat data NatS (m :: Nat) where ZS :: NatS Z SS :: NatS m -> NatS (S m) type family (:+:) (m :: Nat) (n :: Nat) :: Nat where Z :+: n = n (S m) :+: n = S (m :+: n) plusZRightNeutral :: NatS m -> (m :+: Z) :~: m plusZRightNeutral ZS = Refl plusZRightNeutral (SS m') = cong (plusZRightNeutral m') plusComm :: NatS m -> NatS n -> (m :+: n) :~: (n :+: m) plusComm ZS n' = substL (plusZRightNeutral n') Refl -- everything seems correct here plusComm (SS m') n = _ -- but things look completely incorrect, here -- plusComm (SS m') n' = substR (plusComm m' n') _

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Re: [Haskell-cafe] Uploading to hackage fails: bad file names intarball
by Niklas Larsson 16 Jun '14

16 Jun '14

The extension wasn't really part of the filename in those days. So aux.c and aux.hs is interpreted as aux. The funny thing is that Microsoft soon recognized how bad it was and added a flag to make it unix-like (\dev\nul etc) and free the names in dos 2.0, but the default stayed as it was. Niklas ----- Ursprungligt meddelande ----- Från: "Frerich Raabe" <raabe(a)froglogic.com> Skickat: ‎2014-‎06-‎16 13:15 Till: "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> Ämne: Re: [Haskell-cafe] Uploading to hackage fails: bad file names intarball Hi, There are a couple more special files, most (all?) of which are documented at http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).a… That page also says "Also avoid these names followed immediately by an extension; for example, NUL.txt is not recommended." and I suspect that it may be this recommendation based on which the error is raised. "NUL.txt" as well as "Aux.hs" are valid file names though. There is no file named 'AUX' though, and "Aux.hs" is a valid filename. On 2014-06-16 11:45, Niklas Larsson wrote: > Hi! > > For extremely ancient and cludgy reasons AUX isn't a valid filename on > windows, it's a DOS device. The other similarly reserved name are CON, > PRN and NUL. > > Niklas > > ----- Ursprungligt meddelande ----- > Från: "Arie Peterson" <ariep(a)xs4all.nl> > Skickat: ‎2014-‎06-‎16 10:45 > Till: "haskell-cafe(a)haskell.org" <haskell-cafe(a)haskell.org> > Ämne: [Haskell-cafe] Uploading to hackage fails: bad file names in tarball > > Since some time, I have been unable to upload packages to Hackage, via > either > the 'cabal upload' command, or using the web form. > > The error message it gives is this: > > ==== ✂ ==== > Hackage username: AriePeterson > Hackage password: > Uploading dist/np-linear-0.1.1.1.tar.gz... > Error: dist/np-linear-0.1.1.1.tar.gz: 400 Bad Request > Error: Invalid package > > Invalid windows file name in tar archive: > "np-linear-0.1.1.1\\src\\Aux.hs". > For portability, hackage requires that file names be valid on both Unix > and > Windows systems, and not refer outside of the tarball. > ==== ✂ ==== > > The tarball is created by 'cabal sdist': > cabal-install version 1.18.0.2 > using version 1.18.1.1 of the Cabal library. > > I also installed the newest cabal-install, on another machine, but this > did > not help (same error). > > I also tried to create a tarball by hand, using 'tar --format=ustar', but > this > again resulted in the same error message. > > By the way, I'm on linux, not Windows, so it is not clear how the > backslashes > get in the file names. > > > What could be going on? > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe -- Frerich Raabe - raabe(a)froglogic.com www.froglogic.com - Multi-Platform GUI Testing _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Fwd: Problem with loading unix-compat in GHCi on Windows: is suggested solution acceptable?
by German Zhivotnikov 16 Jun '14

16 Jun '14

Hi all, There is a minor problem with unix-compat module on Windows: when one tries to load it (or the module that depends on it) into GHCi, i.e. in REPL mode, - GHCi refuses to load unix-compat with a message like that: ghc.exe: (skipped).cabal-sandbox\x86_64-windows-ghc-7.8.2\unix-compat-0.4.1.1\HSunix-compat-0.4.1.1.o: unknown symbol 'snprintf' ghc.exe: unable to load package 'unix-compat-0.4.1.1' Note that it only concerns REPL mode: when GHC is building a binary that uses unix-compat, - it produces correct executable that works fine. My hypothese is that this is because in typical Win32 build environment snprintf resides in libmingwex.a, which is static library, which GHCi is incapable of loading. Please correct me if I'm wrong. There is a solution - to make unix-compat depend on MSVCRT.DLL (instead of static mingwex.a) and replace 'snprintf' with Microsoft's '_snprintf' (and there's also stat/_stat to be replaced). However this introduces at least new dependency on MSVCRT.DLL, and maybe something else, which might be unexpected. Therefore, before accepting the solution into official codebase, it would be great to have an input - if anyone can foresee possible unintended side effects from suggested solution for code that depends on unix-compat module. Corresponding pull request resides at https://github.com/jystic/unix-compat/pull/12/files - could you possibly take a look if you've got something to say on that issue. Thank you in advance.

1 0

Uploading to hackage fails: bad file names in tarball
by Arie Peterson 16 Jun '14

16 Jun '14

Since some time, I have been unable to upload packages to Hackage, via either the 'cabal upload' command, or using the web form. The error message it gives is this: ==== ✂ ==== Hackage username: AriePeterson Hackage password: Uploading dist/np-linear-0.1.1.1.tar.gz... Error: dist/np-linear-0.1.1.1.tar.gz: 400 Bad Request Error: Invalid package Invalid windows file name in tar archive: "np-linear-0.1.1.1\\src\\Aux.hs". For portability, hackage requires that file names be valid on both Unix and Windows systems, and not refer outside of the tarball. ==== ✂ ==== The tarball is created by 'cabal sdist': cabal-install version 1.18.0.2 using version 1.18.1.1 of the Cabal library. I also installed the newest cabal-install, on another machine, but this did not help (same error). I also tried to create a tarball by hand, using 'tar --format=ustar', but this again resulted in the same error message. By the way, I'm on linux, not Windows, so it is not clear how the backslashes get in the file names. What could be going on?

3 3

improved jhc manual
by John Meacham 16 Jun '14

16 Jun '14

Hi all, I just wanted to show off the new jhc manual http://repetae.net/computer/jhc/manual.html If anyone has any feedback, that would be great, even better would be patches of course :) Manual writing is not my strong point. The entire manual is in the darcs repo as markdown formatted files or as literate code embedded in the source files. Something I need to figure out is how to get haddock to not barf on jhc's input files. A problem with haddock is that it tries to replicate ghc's module chasing algorithm and falls down when anything is slightly off, jhc's ability to handle recursive modules throws it for a loop. Now I can easily get jhc to spit out fully resolved module names, it does so with the --annotate-source option, but need some sort of hook into haddock saying "don't try to resolve module names, here they all are." Even haddock just having a 'keep going' option would be great to get something out there. Or even improving haddock to handle recursive module imports. John -- John Meacham - http://notanumber.net/

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type families and type classes
by Gautier DI FOLCO 16 Jun '14

16 Jun '14

Hi all, I have a bunch of data types which are "divided" in other data types as following: type FileName = String data FileWish = File FileName deriving (Show, Eq) data FileFact = FileExist | FileDontExist deriving (Show, Eq) data FileAction = FileCreate deriving (Show, Eq) observe :: FileWish -> [FileFact] observe :: undefined plan :: FileWish -> FileFact -> [FileAction] plan (File _) FileDontExist = [FileCreate] plan (File _) FileExist = [] perform :: FileWish -> [FileAction] -> IO () perform :: undefined I want to have a model as extensible as possible, even if I'm new to Haskell, I think that it's preferable to base parts of system on behavior (type classes) rather than data types. So I have File that give a Wish, a Fact (via observe) and a Action (via plan). I want to put observe, plan and perform in different type classes (let's say Observable, Plannable and Performable). When I create a new thing (like File) I want, for example, that : observe :: Wish e -> [Fact e] where e is File. But I want (Fact e) be an instance of Plannable. And so on. At first glance, I think I have to use this: https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/t… But it is coupled to data type and one type class. If you have any hints for me. Maybe I don't take the right way to solve my problem. Thanks in advance.

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Taking a number to a power and taking its mod
by Rafael Almeida 15 Jun '14

15 Jun '14

Hello, I've been trying to do a problem from SPOJ which requires me to find prime numbers in a range. I've been battling with several possibility, so far I have had no luck. I remember primality tests from college. So I looked up the one I knew: fermat's little theorem. It requires me to do this check: a^(p-1) `mod` p == 1 However, taking a number to a large power is very slow. So it was even worse than the solution I was already trying. I'm not here for your guys to give me the solution. But I'm here to understand how can I do that operation quickly. This wiki entry implements powMod http://www.haskell.org/haskellwiki/Testing_primality Calling that funcion with powMod 999999527 2 (999999527-1) is very fast. What's going on? Can someone shed me some light? []'s Rafael

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Splitting HList
by Gautier DI FOLCO 15 Jun '14

15 Jun '14

Hello, I want to know if it is possible to split a HList? I want to have a function like this: splitV :: HList (s ++ s') -> (HList s, HList s') splitV = _ So I have begun by something which I thought simple: type family HSplit (ts :: [k]) (xs :: [k]) :: ([k], [k]) type instance HSplit ts xs = ([xs], SndHSplit ts xs) type family SndHSplit (ts :: [k]) (xs :: [k]) :: [k] type instance SndHSplit ts '[] = ts type instance SndHSplit (t ': ts) (x ': xs) = SndHSplit ts xs But I get the following error: H.hs:133:50: The second argument of ‘SndHSplit’ should have kind ‘[k0]’, but ‘xs’ has kind ‘*’ In the type ‘([xs], SndHSplit ts xs)’ In the type instance declaration for ‘HSplit’ I don't understand why because xs and the first element of the tuple have the same kind ([k]). Thanks by advance for your help/explanations.

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RFC: Unicode primes and super/subscript characters in GHC
by Mikhail Vorozhtsov 15 Jun '14

15 Jun '14

Hello lists, As some of you may know, GHC's support for Unicode characters in lexemes is rather crude and hence prone to inconsistencies in their handling versus the ASCII counterparts. For example, APOSTROPHE is treated differently from PRIME: λ> data a +' b = Plus a b <interactive>:3:9: Unexpected type ‘b’ In the data declaration for ‘+’ A data declaration should have form data + a b c = ... λ> data a +′ b = Plus a b λ> let a' = 1 λ> let a′ = 1 <interactive>:10:8: parse error on input ‘=’ Also some rather bizarre looking things are accepted: λ> let ᵤxᵤy = 1 In the spirit of improving things little by little I would like to propose: 1. Handle single/double/triple/quadruple Unicode PRIMEs the same way as APOSTROPHE, meaning the following alterations to the lexer: primes -> U+2032 | U+2033 | U+2034 | U+2057 symbol -> ascSymbol | uniSymbol (EXCEPT special | _ | " | ' | primes) graphic -> small | large | symbol | digit | special | " | ' | primes varid -> (small { small | large | digit | ' | primes }) (EXCEPT reservedid) conid -> large { small | large | digit | ' | primes } 2. Introduce a new lexer nonterminal "subsup" that would include the Unicode sub/superscript[1] versions of numbers, "-", "+", "=", "(", ")", Latin and Greek letters. And allow these characters to be used in names and operators: symbol -> ascSymbol | uniSymbol (EXCEPT special | _ | " | ' | primes | subsup ) digit -> ascDigit | uniDigit (EXCEPT subsup) small -> ascSmall | uniSmall (EXCEPT subsup) | _ large -> ascLarge | uniLarge (EXCEPT subsup) graphic -> small | large | symbol | digit | special | " | ' | primes | subsup varid -> (small { small | large | digit | ' | primes | subsup }) (EXCEPT reservedid) conid -> large { small | large | digit | ' | primes | subsup } varsym -> (symbol (EXCEPT :) {symbol | subsup}) (EXCEPT reservedop | dashes) consym -> (: {symbol | subsup}) (EXCEPT reservedop) If this proposal is received favorably, I'll write a patch for GHC based on my previous stab at the problem[2]. P.S. I'm CC-ing Cafe for extra attention, but please keep the discussion to the GHC users list. [1] https://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts [2] https://ghc.haskell.org/trac/ghc/ticket/5108

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Second Call for Papers: OCL 2014
by Achim D. Brucker 13 Jun '14

13 Jun '14

(Apologies for duplicates) CALL FOR PAPERS 14th International Workshop on OCL and Textual Modeling Applications and Case Studies (OCL 2014) Co-located with ACM/IEEE 17th International Conference on Model Driven Engineering Languages and Systems (MODELS 2014) September 28-30 (tbc), 2014, VALENCIA, SPAIN http://www.software.imdea.org/OCL2014/ Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but some of their features are difficult to formalize and lack the level of precision required to create complete and unambiguous specifications. Limitations of the graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. Topics of interest include (but are not limited to) =================================================== - Mappings between textual modeling languages and other languages/formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for -- validation, verification, and testing, -- model transformation and code generation, -- metamodeling and DSLs, and -- query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports -- usage of textual modeling languages and tools in complex domains, -- usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing applications and case studies of textual modeling as well as test suites and benchmark collections for evaluating textual modeling tools. Venue ===== The workshop will be organized as a part of MODELS 2014 Conference in Valencia, Spain. It continues the series of OCL workshops held at UML/MODELS conferences: York (2000), Toronto (2001), San Francisco (2003), Lisbon (2004), Montego Bay (2005), Genova (2006), Nashville (2007), Toulouse (2008), Denver (2009), Oslo (2010), Zurich (2011, at the TOOLs conference), 2012 in Innsbruck, and 2013 in Miami. Similar to its predecessors, the workshop addresses both people from academia and industry. The aim is to provide a forum for addressing integration of OCL and other textual modeling languages, as well as tools for textual modeling, and for disseminating good practice and discussing the new requirements for textual modeling. Workshop Format =============== The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. Submissions =========== Two types of papers will be considered: * short papers (6 pages) and * full papers (10 pages) in LNCS format. Submissions should be uploaded to EasyChair (https://www.easychair.org/conferences/?conf=ocl2014) The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a pre-conference edition of CEUR (http://www.ceur-ws.org) Authors of selected papers will be invited to submit an extended version of their workshop paper to a special issue of the Electronic Communications of the EASST (http://journal.ub.tu-berlin.de/eceasst) Important Dates =============== Submission of papers: July 11, 2014 Notification: August 8, 2014 Workshop date: one day during September 28-30, 2014 Organizers ========== Achim D. Brucker, SAP AG, Germany Carolina Dania, IMDEA Software Institute, Madrid, Spain Geri Georg, Colorado State University, Fort Collins, Colorado, USA Martin Gogolla, University of Bremen, Germany Programme Committee (partly confirmation pending) =================== Michael Altenhofen, SAP AG, Germany Thomas Baar, University of Applied Sciences Berlin, Germany Mira Balaban, Ben-Gurion University of the Negev, Israel Tricia Balfe, Nomos Software, Ireland Fabian Buettner, Ecole des Mines de Nantes, France Achim D. Brucker, SAP AG, Germany Jordi Cabot, INRIA-Ecole des Mines de Nantes, France Yoonsik Cheon, University of Texas, USA Dan Chiorean, Babes-Bolyai University, Romania Robert Clariso, Universitat Oberta de Catalunya, Spain Tony Clark, Middlesex University, UK Manuel Clavel, IMDEA Software Institute, Madrid, Spain Carolina Dania, IMDEA Software Institute, Madrid, Spain Birgit Demuth, Technische Universitat Dresden, Germany Marina Egea, Atos Research, Madrid, Spain Geri Georg, Colorado State University, Fort Collins, Colorado, USA Martin Gogolla, University of Bremen, Germany Pieter Van Gorp, Eindhoven University of Technology, The Netherlands Heinrich Hussmann, LMU Munchen, Germany Tihamer Levendovszky, Vanderbilt University, USA Shahar Maoz, Tel Aviv University, Israel Istvan Rath, Budapest University of Technology and Economics, Hungary Bernhard Rumpe, RWTH Aachen, Germany Shane Sendall, Snowie Research SA, Switzerland Michael Wahler, ABB Switzerland Ltd Corporate Research, Switzerland Claas Wilke, Technische Universitat Dresden, Germany Edward Willink, Willink Transformations Ltd., UK Burkhart Wolff, Univ Paris-Sud, France Steffen Zschaler, King’s College, London, UK -- Dr. Achim D. Brucker, SAP AG, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, http://www.brucker.ch/

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Re: [Haskell-cafe] ANN: io-memoize 1.1
by Peter Simons 13 Jun '14

13 Jun '14

Hi Dan, > 1. Create an empty cache with newCache > 2. fetch repeatedly from the cache, each time providing a fallback in > case it is empty. > > Fetching from a Cache is thread safe: only one "fallback" will execute > at a time, and after the first successful fallback, the cached value > will be set and no other fallbacks will be called. I'm not sure whether I get this correctly. If multiple threads fetch values from one cache, will only one of those threads run at a time? Or will those that fetch pairwise different values still run concurrently? In other words, does the cache have a global lock or is there a lock per value? Best regards, Peter

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Not in scope
by Julian K. Arni 13 Jun '14

13 Jun '14

I have a lot of boilerplate code that th-desugar has made significantly more manageable (thanks Richard!). Somewhere in the midst of it, I have: >> type_equal (DContT n1) (DContT n2) = {...} Which, when I compile with cabal, gives me: src/Language/Haskell/TH/Alpha.hs:180:13: Not in scope: data constructor ‘DContT’ Perhaps you meant one of these: ‘DConT’ (imported from Language.Haskell.TH.Desugar), ‘DConE’ (imported from Language.Haskell.TH.Desugar), ‘DConPa’ (imported from Language.Haskell.TH.Desugar) src/Language/Haskell/TH/Alpha.hs:180:25: Not in scope: data constructor ‘DContT’ Perhaps you meant one of these: ‘DConT’ (imported from Language.Haskell.TH.Desugar), ‘DConE’ (imported from Language.Haskell.TH.Desugar), ‘DConPa’ (imported from Language.Haskell.TH.Desugar) Huh? Of course 'DConT' is what I meant - that's exactly what I wrote! What in the world is going on? GHC is happy with all the other constructors! I tried rewriting, just to be sure I didn't *somehow* get a tricky unicode character in there...

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