- Haskell-Cafe - Haskell.org

Melbourne Haskell Meetup, 2015-10-29 @ 18:30
by Lyndon Maydwell 26 Oct '15

26 Oct '15

Hi All, This week, the monthly Melbourne Haskell Meetup will take place on Thursday, October 29 at the Silverpond offices on Hardware Lane. For details see here: http://www.meetup.com/Melbourne-Haskell-Users-Group/events/225596759/ There will be a talk on Constraint Programming in Haskell by David Overton, as well as the usual free discussion about all things Haskell. Please come along if this interests you :-) - Lyndon ( Thanks to Christian Neukirchen's Munich Haskell announcement for reminding me to tell the Café about our meetup from time to time. )

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Munich Haskell Meeting, 2015-10-29 @ 19:30
by Christian Neukirchen 26 Oct '15

26 Oct '15

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, October 29 at Cafe Puck at 19h30. For details see here: http://chneukirchen.github.io/haskell-munich.de/dates (http://www.haskell-munich.de/ is currently out of order, but will be restored soon! I hope...) If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-oct-2015/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Hackage feature request: show types of names listed in index page
by Ömer Sinan Ağacan 26 Oct '15

26 Oct '15

I pretty much said all I wanted to say in the title, but just to rephrase, I think it'd be super helpful if Hackage listed types of names listed in index pages. The reason is because most of the time I'm using index pages for searching things, but if I wanted to list all functions that somehow use a type, for example, index pages don't help. With type information in the index pages I can just search for a type and my browser would highlight all functions that somehow use the type.

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Five more days: Call for Contributions: BOB 2016 - Berlin, Feb 19, 2016
by Matthias Fischmann 26 Oct '15

26 Oct '15

The submission deadline for is five days away. We are happy with the submissions so far, but you can always have more. So if you always wanted to look into some library that everybody is fussing about and then tell people what you learned, or if you have this trick or you wrote that piece of code that you are fond of, please take a minute to check out our submission guidelines this week. http://bobkonf.de/2016/cfp (We have speaker grants for under-represented groups.) cheers, m.

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mashup of Haskell News and hdiff
by Erik Rantapaa 26 Oct '15

26 Oct '15

Hi all, For Haskell News junkies I created a simple mashup of haskellnews.org and Luite Stegeman's hdiff site. It adds a "hdiff" link to all Hackage upload news items so you can conveniently see what changed in the new version. It consists of just an html file and .js file and is available at: https://github.com/erantapaa/haskellnews-hdiff ER

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Glib-0.13.2.1 build failure: multiple definition of `__debugbreak' (ghc-7.11.20151024)
by Burkhard Groh 25 Oct '15

25 Oct '15

In my latest attempt to finally build the gtk3 package with ghc-head 'ghc-master' (7.11.20151024) for a current project under windows x64 using the latest msys2-version and its supplied gtk3 libraries (mingw64/mingw-w64-x86_64-gtk3 3.18.2-1) I encountered this cryptical (linking) error. (See complete log for command './Setup build -v3' attached) I should add that I'm rather a beginner with regards to the Haskell language and its package distribution system cabal. Thus all thoughts, ideas and suggestions how to fix this problem are welcome. Best regards Burkhard complete building response in msys2-shell using the mingw64 script: $ ./Setup build -v3 Component build order: library creating dist\build creating dist\build\autogen Building glib-0.13.2.1... Environment: [("","C:=C:\\Windows\\System32"),("ACLOCAL_PATH","C:\\MSYS2\\mingw64\\share\\aclocal;C:\\MSYS2\\usr\\share\\aclocal"),("ALLUSERSPROFILE","C:\\ProgramData"),("APPDATA","C:\\Users\\PC-08\\AppData\\Roaming"),("CHECKDEF","C:\\Applications\\wingx\\bin"),("COMMONPROGRAMFILES","C:\\Program Files\\Common Files"),("COMMONPROGRAMFILES(X86)","C:\\Program Files (x86)\\Common Files"),("COMMONPROGRAMW6432","C:\\Program Files\\Common Files"),("COMPUTERNAME","PC-08"),("COMSPEC","C:\\Windows\\system32\\cmd.exe"),("FP_NO_HOST_CHECK","NO"),("HOME","C:\\MSYS2\\home\\Ms PC-08"),("HOMEDRIVE","C:"),("HOMEPATH","\\Users\\PC-08"),("HOSTNAME","PC-08"),("INFOPATH","C:\\MSYS2\\usr\\local\\info;C:\\MSYS2\\usr\\share\\info;C:\\MSYS2\\usr\\info;C:\\MSYS2\\share\\info"),("LANG","de_DE.UTF-8"),("LOCALAPPDATA","C:\\Users\\PC-08\\AppData\\Local"),("LOGONSERVER","\\\\PC-08"),("MANPATH","C:\\MSYS2\\mingw64\\share\\man;C:\\MSYS2\\usr\\local\\man;C:\\MSYS2\\usr\\share\\man;C:\\MSYS2\\usr\\man;C:\\MSYS2\\share\\man"),("MSYSCON","mintty.exe"),("MSYSTEM","MINGW64"),("NUMBER_OF_PROCESSORS","4"),("OLDPWD","C:/MSYS2/home/Ms PC-08/cabal"),("ORTEPDIR","C:\\Applications\\ortep3"),("OS","Windows_NT"),("PATH","C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin;C:\\Haskell\\ghc-7.11.20151024\\bin;C:\\Haskell\\ghc-7.11.20151024\\mingw\\bin;C:\\MSYS2\\mingw64\\bin;C:\\MSYS2\\usr\\local\\bin;C:\\MSYS2\\usr\\bin;C:\\MSYS2\\usr\\bin;C:\\Program Files (x86)\\CambridgeSoft\\ChemOffice2015\\ChemScript\\Lib;C:\\Windows\\system32;C:\\Windows;C:\\Windows\\System32\\Wbem;C:\\Windows\\System32\\WindowsPowerShell\\v1.0;C:\\Program Files (x86)\\ATI Technologies\\ATI.ACE\\Core-Static;C:\\Program Files\\Intel\\WiFi\\bin;C:\\Program Files\\Common Files\\Intel\\WirelessCommon;C:\\Applications\\LinksPortable;C:\\Program Files\\Intel\\WiFi\\bin;C:\\Program Files\\Common Files\\Intel\\WirelessCommon;C:\\Program Files\\Miktex\\miktex\\bin\\x64;C:\\MSYS2\\usr\\bin\\site_perl;C:\\MSYS2\\usr\\bin\\vendor_perl;C:\\MSYS2\\usr\\bin\\core_perl;C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin;C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin"),("PATHEXT",".COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC"),("PGFONT","C:\\Applications\\wingx\\files\\grfont.dat"),("PKG_CONFIG_PATH","C:\\MSYS2\\mingw64\\lib\\pkgconfig;C:\\MSYS2\\mingw64\\share\\pkgconfig"),("PRINTER","Brother HL-5270DN"),("PROCESSOR_ARCHITECTURE","AMD64"),("PROCESSOR_IDENTIFIER","Intel64 Family 6 Model 69 Stepping 1, GenuineIntel"),("PROCESSOR_LEVEL","6"),("PROCESSOR_REVISION","4501"),("PROGRAMDATA","C:\\ProgramData"),("PROGRAMFILES","C:\\Program Files"),("PROGRAMFILES(X86)","C:\\Program Files (x86)"),("PROGRAMW6432","C:\\Program Files"),("PROMPT","$P$G"),("PS1","\\[\\e]0;\\w\\a\\]\\n\\[\\e[32m\\]\\u@\\h \\[\\e[35m\\]$MSYSTEM\\[\\e[0m\\] \\[\\e[33m\\]\\w\\[\\e[0m\\]\\n\\$ "),("PSMODULEPATH","C:\\Windows\\system32\\WindowsPowerShell\\v1.0\\Modules\\"),("PUBLIC","C:\\Users\\Public"),("PWD","C:/Haskell/gtk2hs-master/glib"),("PYTHONPATH","C:\\Program Files (x86)\\CambridgeSoft\\ChemOffice2015\\ChemScript\\Lib"),("RASMOLPATH","C:\\Program Files (x86)\\RasWin"),("SESSIONNAME","Console"),("SHELL","C:/MSYS2/usr/bin/bash"),("SHLVL","1"),("SYSTEMDRIVE","C:"),("SYSTEMROOT","C:\\Windows"),("TEMP","C:\\Users\\PC-08\\AppData\\Local\\Temp"),("TERM","xterm-256color"),("TMP","C:\\Users\\PC-08\\AppData\\Local\\Temp"),("UOIPME_REG_PATH","C:\\Program Files\\Intel Corporation\\USB over IP"),("USER","Ms PC-08"),("USERDOMAIN","PC-08"),("USERNAME","Ms PC-08"),("USERPROFILE","C:\\Users\\PC-08"),("VS110COMNTOOLS","C:\\Program Files (x86)\\Microsoft Visual Studio 11.0\\Common7\\Tools\\"),("VS120COMNTOOLS","C:\\Program Files (x86)\\Microsoft Visual Studio 12.0\\Common7\\Tools\\"),("WD","C:\\MSYS2\\usr\\bin\\"),("WINDIR","C:\\Windows"),("WINGXDIR","C:\\Applications\\wingx"),("XML_CATALOG_FILES","C:/MSYS2/etc/xml/docbook-xml /etc/xml/catalog"),("_","./Setup")] ("C:\\Haskell\\ghc-7.11.20151024\\bin\\ghc-pkg.exe",["init","dist\\package.conf.inplace","-v2"]) writing cache dist\package.conf.inplace\package.cache Preprocessing library glib-0.13.2.1... creating dist\build\System\Glib Environment: [("","C:=C:\\Windows\\System32"),("ACLOCAL_PATH","C:\\MSYS2\\mingw64\\share\\aclocal;C:\\MSYS2\\usr\\share\\aclocal"),("ALLUSERSPROFILE","C:\\ProgramData"),("APPDATA","C:\\Users\\PC-08\\AppData\\Roaming"),("CHECKDEF","C:\\Applications\\wingx\\bin"),("COMMONPROGRAMFILES","C:\\Program Files\\Common Files"),("COMMONPROGRAMFILES(X86)","C:\\Program Files (x86)\\Common Files"),("COMMONPROGRAMW6432","C:\\Program Files\\Common Files"),("COMPUTERNAME","PC-08"),("COMSPEC","C:\\Windows\\system32\\cmd.exe"),("FP_NO_HOST_CHECK","NO"),("HOME","C:\\MSYS2\\home\\Ms PC-08"),("HOMEDRIVE","C:"),("HOMEPATH","\\Users\\PC-08"),("HOSTNAME","PC-08"),("INFOPATH","C:\\MSYS2\\usr\\local\\info;C:\\MSYS2\\usr\\share\\info;C:\\MSYS2\\usr\\info;C:\\MSYS2\\share\\info"),("LANG","de_DE.UTF-8"),("LOCALAPPDATA","C:\\Users\\PC-08\\AppData\\Local"),("LOGONSERVER","\\\\PC-08"),("MANPATH","C:\\MSYS2\\mingw64\\share\\man;C:\\MSYS2\\usr\\local\\man;C:\\MSYS2\\usr\\share\\man;C:\\MSYS2\\usr\\man;C:\\MSYS2\\share\\man"),("MSYSCON","mintty.exe"),("MSYSTEM","MINGW64"),("NUMBER_OF_PROCESSORS","4"),("OLDPWD","C:/MSYS2/home/Ms PC-08/cabal"),("OS","Windows_NT"),("PATH","C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin;C:\\Haskell\\ghc-7.11.20151024\\bin;C:\\Haskell\\ghc-7.11.20151024\\mingw\\bin;C:\\MSYS2\\mingw64\\bin;C:\\MSYS2\\usr\\local\\bin;C:\\MSYS2\\usr\\bin;C:\\MSYS2\\usr\\bin;C:\\Windows\\system32;C:\\Windows;C:\\Windows\\System32\\Wbem;C:\\Windows\\System32\\WindowsPowerShell\\v1.0;C:\\Program Files (x86)\\ATI Technologies\\ATI.ACE\\Core-Static;C:\\Program Files\\Intel\\WiFi\\bin;C:\\Program Files\\Common Files\\Intel\\WirelessCommon;C:\\Program Files\\Intel\\WiFi\\bin;C:\\Program Files\\Common Files\\Intel\\WirelessCommon;C:\\Program Files\\Miktex\\miktex\\bin\\x64;C:\\MSYS2\\usr\\bin\\site_perl;C:\\MSYS2\\usr\\bin\\vendor_perl;C:\\MSYS2\\usr\\bin\\core_perl;C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin;C:\\Users\\PC-08\\AppData\\Roaming\\cabal\\bin"),("PATHEXT",".COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC"),("PGFONT","C:\\Applications\\wingx\\files\\grfont.dat"),("PKG_CONFIG_PATH","C:\\MSYS2\\mingw64\\lib\\pkgconfig;C:\\MSYS2\\mingw64\\share\\pkgconfig"),("PRINTER",""),("PROCESSOR_ARCHITECTURE","AMD64"),("PROCESSOR_IDENTIFIER","Intel64 Family 6 Model 69 Stepping 1, GenuineIntel"),("PROCESSOR_LEVEL","6"),("PROCESSOR_REVISION","4501"),("PROGRAMDATA","C:\\ProgramData"),("PROGRAMFILES","C:\\Program Files"),("PROGRAMFILES(X86)","C:\\Program Files (x86)"),("PROGRAMW6432","C:\\Program Files"),("PROMPT","$P$G"),("PS1","\\[\\e]0;\\w\\a\\]\\n\\[\\e[32m\\]\\u@\\h \\[\\e[35m\\]$MSYSTEM\\[\\e[0m\\] \\[\\e[33m\\]\\w\\[\\e[0m\\]\\n\\$ "),("PSMODULEPATH","C:\\Windows\\system32\\WindowsPowerShell\\v1.0\\Modules\\"),("PUBLIC","C:\\Users\\Public"),("PWD","C:/Haskell/gtk2hs-master/glib"),("PYTHONPATH","C:\\Program Files (x86)\\CambridgeSoft\\ChemOffice2015\\ChemScript\\Lib"),("RASMOLPATH","C:\\Program Files (x86)\\RasWin"),("SESSIONNAME","Console"),("SHELL","C:/MSYS2/usr/bin/bash"),("SHLVL","1"),("SYSTEMDRIVE","C:"),("SYSTEMROOT","C:\\Windows"),("TEMP","C:\\Users\\PC-08\\AppData\\Local\\Temp"),("TERM","xterm-256color"),("TMP","C:\\Users\\PC-08\\AppData\\Local\\Temp"),("UOIPME_REG_PATH","C:\\Program Files\\Intel Corporation\\USB over IP"),("USER","Ms PC-08"),("USERDOMAIN","PC-08"),("USERNAME","Ms PC-08"),("USERPROFILE","C:\\Users\\PC-08"),("VS110COMNTOOLS","C:\\Program Files (x86)\\Microsoft Visual Studio 11.0\\Common7\\Tools\\"),("VS120COMNTOOLS","C:\\Program Files (x86)\\Microsoft Visual Studio 12.0\\Common7\\Tools\\"),("WD","C:\\MSYS2\\usr\\bin\\"),("WINDIR","C:\\Windows"),("WINGXDIR","C:\\Applications\\wingx"),("XML_CATALOG_FILES","C:/MSYS2/etc/xml/docbook-xml /etc/xml/catalog"),("_","./Setup")] ("C:\\Haskell\\ghc-7.11.20151024\\bin\\hsc2hs.exe",["--cc=C:\\Haskell\\ghc-7.11.20151024\\mingw\\bin\\gcc.exe","--ld=C:\\Haskell\\ghc-7.11.20151024\\mingw\\bin\\gcc.exe","--cflag=-fno-stack-protector","--lflag=-fno-stack-protector","--cflag=-D__GLASGOW_HASKELL__=711","--cflag=-Dmingw32_BUILD_OS=1","--cflag=-Dx86_64_BUILD_ARCH=1","--cflag=-Dmingw32_HOST_OS=1","--cflag=-Dx86_64_HOST_ARCH=1","--cflag=-Idist\\build\\autogen","--cflag=-Idist\\build","--cflag=-ISystem/Glib","--cflag=-IC:/MSYS2/mingw64/include/glib-2.0","--cflag=-IC:/MSYS2/mingw64/lib/glib-2.0/include","--cflag=-mms-bitfields","--cflag=-U__BLOCKS__","--cflag=-D__attribute__(A)=","--cflag=-DUSE_GCLOSURE_SIGNALS_IMPL","--cflag=-Idist\\build\\autogen","--cflag=-include","--cflag=dist\\build\\autogen\\cabal_macros.h","--lflag=-LC:/MSYS2/mingw64/lib","--lflag=-lgobject-2.0","--lflag=-lglib-2.0","--lflag=-lintl","--cflag=-IC:\\Haskell\\ghc-7.11.20151024\\lib\\bytestring-0.10.6.0\\include","--cflag=-IC:\\Haskell\\ghc-7.11.20151024\\lib\\base-4.8.2.0\\include","--cflag=-IC:\\Haskell\\ghc-7.11.20151024\\lib\\integer-gmp-1.0.0.0\\include","--cflag=-IC:\\Haskell\\ghc-7.11.20151024\\lib/include","--lflag=-LC:\\Users\\PC-08\\AppData\\Roaming\\cabal\\x86_64-windows-ghc-7.11.20151024\\utf8s_LAIfwUZWplI3JK3b6W44Yv","--lflag=-LC:\\Users\\PC-08\\AppData\\Roaming\\cabal\\x86_64-windows-ghc-7.11.20151024\\text_IqwR9CiNGjxJyQdu3bLbNv","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\binary-0.7.5.0","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\containers-0.5.6.2","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\bytestring-0.10.6.0","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\deepseq-1.4.1.1","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\array-0.5.1.0","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\base-4.8.2.0","--lflag=-lwsock32","--lflag=-luser32","--lflag=-lshell32","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\integer-gmp-1.0.0.0","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib\\ghc-prim-0.4.0.0","--lflag=-LC:\\Haskell\\ghc-7.11.20151024\\lib/rts","--lflag=-lm","--lflag=-lwsock32","--lflag=-lgdi32","--lflag=-lwinmm","-o","dist\\build\\System\\Glib\\StoreValue.hs","System\\Glib\\StoreValue.hsc"]) dist\build\System\Glib\StoreValue_hsc_utils.o:StoreValue_hsc_utils.c:(.text+0x0): multiple definition of `__debugbreak' dist\build\System\Glib\StoreValue_hsc_make.o:StoreValue_hsc_make.c:(.text+0x0): first defined here collect2.exe: error: ld returned 1 exit status linking dist\build\System\Glib\StoreValue_hsc_make.o failed (exit code 1) command was: C:\Haskell\ghc-7.11.20151024\mingw\bin\gcc.exe dist\build\System\Glib\StoreValue_hsc_make.o dist\build\System\Glib\StoreValue_hsc_utils.o -o dist\build\System\Glib\StoreValue_hsc_make.exe -fno-stack-protector -LC:/MSYS2/mingw64/lib -lgobject-2.0 -lglib-2.0 -lintl -LC:\Users\PC-08\AppData\Roaming\cabal\x86_64-windows-ghc-7.11.20151024\utf8s_LAIfwUZWplI3JK3b6W44Yv -LC:\Users\PC-08\AppData\Roaming\cabal\x86_64-windows-ghc-7.11.20151024\text_IqwR9CiNGjxJyQdu3bLbNv -LC:\Haskell\ghc-7.11.20151024\lib\binary-0.7.5.0 -LC:\Haskell\ghc-7.11.20151024\lib\containers-0.5.6.2 -LC:\Haskell\ghc-7.11.20151024\lib\bytestring-0.10.6.0 -LC:\Haskell\ghc-7.11.20151024\lib\deepseq-1.4.1.1 -LC:\Haskell\ghc-7.11.20151024\lib\array-0.5.1.0 -LC:\Haskell\ghc-7.11.20151024\lib\base-4.8.2.0 -lwsock32 -luser32 -lshell32 -LC:\Haskell\ghc-7.11.20151024\lib\integer-gmp-1.0.0.0 -LC:\Haskell\ghc-7.11.20151024\lib\ghc-prim-0.4.0.0 -LC:\Haskell\ghc-7.11.20151024\lib/rts -lm -lwsock32 -lgdi32 -lwinmm C:\Haskell\ghc-7.11.20151024\bin\hsc2hs.exe returned ExitFailure 1

2 2

Avoiding Dependency loops
by martin 25 Oct '15

25 Oct '15

Hello all, I just split up a program I'm working on into several source files and ran into the following difficulty: module Process implements Process which has a field Runner. Runner is a basically a function which alters a 'System' state. So Process needs Runner, Runner needs System and thus Process needs System. module System implements among others a collection of Processes (because Processes can alter their states). So System needs Process. Eh voila, I have a loop. What I did was to leave the type of the Runner unspecified in Process, i.e. I now have (Process r) where r is the type of the Runner. Thus Process no longer needs to know about System. This does work, but it feels strange and I'm a bit worried that this is an indication for a design flaw, but I cannot see it.

2 4

Projectional editing: Separating a program's AST from its presentation
by Jeffrey Brown 25 Oct '15

25 Oct '15

These ideas were touched on in a previous thread [1]. Our work would be easier if, as data, we separated a program's AST from its layout. If, for instance, the order in which a library's functions are presented on the page were stored as a "projection", separate from the AST that defined those functions, then one could reorder the functions without obscuring the history of changes to anything that was "moved". I assume I am not alone in making a lot of edits aimed solely at allowing me to read or traverse the code faster? Those within-function changes of presentation, like across-function changes of order, obscure the record of functional (as opposed to cosmetic) changes. They don't have to. Moreover, if projections and the AST were separate data, one could use contradictory hierarchiies|projections|layouts for the same data. One projection might group functions by their common purpose (an "is-tree"), while another grouped them by priority to the reader-rewriter (a "do-tree"). Given current technology, text folding does allow us to impose a hierarchy on a text document (even a Haskell document! you just need to indent the code relative to the comments that define the hierarchy). However, if the code is stored as text, then only one hierarchy is possible. In particular one is presently forced to choose between an "is-tree" and a "do-tree". https://groups.google.com/forum/#!msg/haskell-cafe/d8h8J8VxZxo/BNlKUjWeAgAJ -- Jeffrey Benjamin Brown

1 0

Google Cloud API
by Tomas Carnecky 24 Oct '15

24 Oct '15

I recently migrated some infrastructure from AWS to Google Cloud and needed a way to upload a file to a storage bucket. For AWS there's an awesome Haskell library (aws), but I couldn't find anything comparable for interacting with the Google Cloud APIs. While it wouldn't be difficult to write a standalone function for that simple task, I decided to package it up in a library. Currently implemented is uploading a ByteString to a bucket and some metadata server queries. That's all I need currently, but I may add a few more selected APIs in the near future (mostly around managing compute instances). Adding support for new APIs should be relatively easy, even without having to change the library itself. All the internals are exposed to users of the library. There is nothing private or hidden. The library gives you access to convenience functions to send HTTP requests. That, coupled with a bit of JSON/aeson parsing, should cover most use cases. http://hackage.haskell.org/package/google-cloud https://github.com/wereHamster/google-cloud#readme

4 5

wxHaskell on Windows compilation problems
by Michael Jones 24 Oct '15

24 Oct '15

I’m trying to compile an established wxHaskell application (Ubuntu) on Windows 7 and after a day of frustration, I wanted to see if anyone had some clues. The problem is getting wxc to compile against wxWidgets, where wxWidgets was compiled with MinGHC (GHC 7.8.4). Following are my steps up to trouble: - On 64 bit Win 7, install MinGHC, which ends up in the AppData path. - Grab wxWidgets with git and using MSYS shell compile like: mingw32-make -f makefile.gcc SHARED=1 UNICODE=1 BUILD=release clean mingw32-make -f makefile.gcc SHARED=1 UNICODE=1 BUILD=release with the goal of compiler compatibility. - Setup some environment variables like: C_INCLUDE_PATH == C:\PCRE\include CPLUS_INCLUDE_PATH == C:\Libs\wxWidgets\3.0.2\include LIBRARY_PATH == C:\PCRE\lib;C:\Libs\wxHaskell\3.0.2\\lib\gcc_lib MSYSTEM == MINGW64 WXCFG == gcc_dll\mswu WXWIN == C:\Libs\wxWidgets\3.0.2 PATH = C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\git-2.4.5.1\cmd;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\git-2.4.5.1\usr\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\bin;C:\Users\michaeljones\AppData\Roaming\cabal\bin; - Tweak wxUSE_GRAPHICS_CONTEXT - Create sandbox for my project with pointer to a local copy of wxHaskell - Apply a few patches to enable some new table support (stable stuff) - Configure with cabal and compile The first problem is it can’t run wx-config because it looks for a script, so I tweaked the Setup.hs to use the exe and it continues to compile. It gets this error: Building wxc C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin\gcc.exe -Isrc/include -IC:/Users/michaeljones /Documents/linti/libs/wxHaskell/wxc -IC:/Users/michaeljones/Documents/linti/libs/wxHaskell/wxc -DWXUSINGDLL -D_UNICODE -D__WXDEBUG __ -D__WXMSW__ -DHAVE_W32API_H -DwxcREFUSE_MEDIACTRL -DBUILD_DLL -c src\cpp\apppath.cpp -o dist\dist-sandbox-95204306\build\src/cp p/apppath.o In file included from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20:0, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:22: fatal error: wx/setup.h: No such file or directory compilation terminated. So, I copy the wxWidgets setup.h file from include/msvc/wx to include/wx and compile to a new error: Build log ( C:\Users\michaeljones\Documents\linti\linti-beagle\.cabal-sandbox\logs\wxc-0.92.0.0.log ): Building wxc C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin\gcc.exe -Isrc/include -IC:/Users/michaeljones /Documents/linti/libs/wxHaskell/wxc -IC:/Users/michaeljones/Documents/linti/libs/wxHaskell/wxc -DWXUSINGDLL -D_UNICODE -D__WXDEBUG __ -D__WXMSW__ -DHAVE_W32API_H -DwxcREFUSE_MEDIACTRL -DBUILD_DLL -c src\cpp\apppath.cpp -o dist\dist-sandbox-95204306\build\src/cp p/apppath.o In file included from C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:0, from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:12:6: error: #error "This file should only be included when using Microsoft Visual C++" In file included from C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:0, from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "/" and "vc_x64_dll" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "vc_x64_dll" and "/" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "/" and "msw" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "mswu" and "/" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:27: fatal error: ../../../lib/vc_x64_dll /mswu /wx/setup.h: No such file or directo I assume the problem is that the wxWidget compilation that comes with makefile.gcc is somehow bypassing some linux based compilation method and not leaving the tree in the proper state for wxHaskell. The Wiki page is based on platform, not MinGHC. I used MinGHC because it got me over problems compiling regex-pcre against libpcre where I failed with cygwin. From reading is appeared MinGHC was a good general path. Note, I had the TDM compiler on the machine, but it was taken out, so there is no accidentally use of the wrong compiler or anything going on. Does anyone have any clues how to make wxHaskell and MinGHC work together? Mike

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ICFP 2016 Call for Workshop and Co-located Event Proposals
by Lindsey Kuper 23 Oct '15

23 Oct '15

         CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS                             ICFP 2016  21st ACM SIGPLAN International Conference on Functional Programming                      September 18-24, 2016                           Nara, Japan                http://icfpconference.org/icfp2016/ The 21st ACM SIGPLAN International Conference on Functional Programming will be held in Nara, Japan on September 18-24, 2016. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as tutorials) to be affiliated with ICFP 2016 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on September 18 (the day before ICFP) and September 22-24 (the three days after ICFP). ---------------------------------------------------------------------- Submission details  Deadline for submission:     November 21, 2015  Notification of acceptance:  December 20, 2015 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2016 workshop co-chairs (Andres Loeh and Nicolas Wu), via email to     icfp2016-workshops(a)googlegroups.com by November 21, 2015. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by December 20, 2015, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2016-files/icfp16-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://www.sigplan.org/Resources/Proposals/Sponsored/ ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2016 organizing committee, together with the members of the SIGPLAN executive committee.  Workshop Co-Chair: Andres Loeh                        (Well-Typed LLP)  Workshop Co-Chair: Nicolas Wu                  (University of Bristol)  General Co-Chair : Jacques Garrigue                (Nagoya University)  General Co-Chair : Gabriele Keller     (University of New South Wales)  Program Chair:     Eijiro Sumii                    (Tohoku University) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Andres Loeh and Nicolas Wu), via email to icfp2016-workshops(a)googlegroups.com

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[ANN] haskell-ide project
by Alan & Kim Zimmerman 23 Oct '15

23 Oct '15

The ongoing effort to save us as a community from separately implementing the same functionality over and over around IDEs[1] has found a home in the haskell-ide project on github [2]. This mail serves as a call to collaborate for all parties interested in this space. It is still at a very early stage, but the intent is to pool resources so that we can have really good support for IDEs that can extend through the entire tool chain from changes to GHC to better support tooling through the build environment and community information management. This should mean that people who are familiar with a particular part of the chain can focus their efforts there, knowing that the other parts will be covered too. This is a deliberately broad and vague scope, the reality is likely to be much more limited initially, but the sooner we can get started the sooner we will have something concrete to criticise and improve. For those wishing to get involved the following resources currently exist * the haskell-ide mailing list [3] * the github project page [1] * The #haskell-ide channel on IRC Freenode. This is not aimed at some small inner circle of people, anyone who wants to will be added to the project on github, adress your request to me or @hvr. Regards Alan [1] IDE is a loose term for anything that enables a user to interact with the code. [2] https://github.com/haskell/haskell-ide [3] https://groups.google.com/forum/#!forum/haskell-ide

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New STM Data Structures Collection
by Алексей Семин 23 Oct '15

23 Oct '15

Hi everyone! I want to present a couple of STM data structures which were implemented by me and Ryan Yates this summer (during GSOC 2015). I decided to create only a candidate package [1]. I would be glad if anyone can take a look and/or comment on topic. Since Hackage does not provide the easy way to `cabal install` candidate packages I have written a script [2] which should do all the work for you. It create a directory in /tmp and initialized sandbox along with cloning the library from github [3]. After that it will download Haskell program with an example of data structure usage. Thank you for your attention. [1] https://hackage.haskell.org/package/stm-data-collection-0.1.0.0/candidate [2] https://gist.github.com/Alllex/445f3d74e872fe032596 [3] https://github.com/Alllex/stm-data-collection -- Regards, Alex Semin

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how to create a pipes producer from websockets?
by Dimitri DeFigueiredo 22 Oct '15

22 Oct '15

Hello All, I am trying to use both the websockets library and the pipes library. They seem like a natural fit. However, I wanted to use the websockets library to build a pipes 'Producer' and that does not seem possible without some heavy lifting. The websockets library does not give me a connection I can read from and write to. Instead, I need to supply an IO action (called a clientApp). And execute it using something like: --runClient :: String -- ^ Host -- -> Int -- ^ Port -- -> String -- ^ Path -- -> ClientApp a -- ^ Client application -- type ClientApp a = Connection -> IO a -- -> IO a main :: IO () main = withSocketsDo $ runClient "echo.websocket.org" 80 "/" app The problem happens when you couple this restriction with the requirement that ClientApps have type 'Connection -> IO a'. Pipes producers are Monad transformer stacks. For example, I would like to build something like: messageProducer :: Producer' WebsocketMessage IO () But this does not run in the IO monad and at the same time I cannot get a 'Connection' object unless I use runClient. So, it seems I have a catch22 situation. Or have I overlooked something? I'd rather not have to do "un-lifting" on the monad transformer stack. Has anyone done this before? Any suggestions on how to go about it? Thanks, Dimitri

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Re: [Haskell-cafe] Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`
by Simon Thompson 21 Oct '15

21 Oct '15

Hello all. I write this to be a little provocative, but … It’s really interesting to have this discussion, which pulls in all sorts of well-made points about orthogonality, teaching, the evolution of the language and so on, but it simply goes to show that the process of evolving Haskell is profoundly broken. Other languages do evolve, but in a managed and reflective way. Simply throwing in changes that would have a profound impact on systems that are commercially and potentially safety critical in an à la carte, offhand, way seems like a breakdown of the collective responsibility of the Haskell community to its users and, indirectly, to its future. If we make claims - I believe rightly - that Haskell is hitting the mainstream, then we need to think about all changes in terms of the costs and benefits of each of them in the widest possible sense. There’s an old fashioned maxim that sums this up in a pithy way: “if it ain’t broke, don’t fix it”. Simon Thompson > On 5 Oct 2015, at 10:47, Michał J Gajda <mjgajda(a)gmail.com> wrote: > > Hi, > > As a person who used Haskell in all three capacities (for scientific research, for commercial purpose, and to introduce others to benefits of pure and strongly typed programming), I must voice an supportive voice for this change: > 1. Orthogonal type classes are easier to explain. > 2. Gradual improvements helps us to generalize further, and this in turn makes education easier. > 3. Gradual change that break only a little help to prevent either stagnation (FORTRAN) and big breakage (py3k). That keeps us excited. > > That would also call to split TCs into their orthogonal elements: return, ap, bind having the basic TC on their own. > > So: > +1, but only if it is possible to have compatibilty mode. I believe that rebindable syntax should allow us to otherwise make our own prelude, if we want such a split. Then we could test it well before it is used by the base library. > > That said, I would appreciate Haskell2010 option just like Haskell98 wad, so that we can compile old programs without changes. Even by using some Compat version of standard library. Would that satisfy need for stability? > > PS And since all experts were beginners some time ago, I beg that we do not call them "peripheral". > -- > Best regards > Michał > > On Monday, 5 October 2015, Malcolm Wallace <malcolm.wallace(a)me.com <mailto:malcolm.wallace@me.com>> wrote: > On other social media forums, I am seeing educators who use Haskell as a vehicle for their main work, but would not consider themselves Haskell researchers, and certainly do not have the time to follow Haskell mailing lists, who are beginning to say that these kinds of annoying breakages to the language, affecting their research and teaching materials, are beginning to disincline them to continue using Haskell. They are feeling like they would be > (...) > > > -- > Pozdrawiam > Michał > _______________________________________________ > Haskell-prime mailing list > Haskell-prime(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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[ANN] codex 0.4
by Alois Cochard 21 Oct '15

21 Oct '15

Hello Café, I have released a new version of `codex`[1] (a ctags file generator for cabal/stack projects and their dependencies). This release include some fixes but more important it *include support for `stack`* projects. As `stack` is multi-platform and so is `codex`, it should work seamlessly on any OS but I have only done testing on unix. Cheers [1] https://github.com/ <https://github.com/aloiscochard/codex>aloiscochard/ codex <https://github.com/aloiscochard/codex> -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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Hac Phi: Haskell Exchange in Philadelphia, Nov 6-8
by Richard Eisenberg 21 Oct '15

21 Oct '15

Hi café, Hac Phi, a yearly weekend of Haskell in Philadelphia, will take place Nov. 6-8, hosted at the University of Pennsylvania. Hac Phi is a gathering of hackers and Haskell enthusiasts. Come bring a project you're working on or offer to help someone else on a project of theirs. Come give a talk if you've got something to share. Come to learn something new. Though the event has the same structure as in previous years, it has been renamed from a Haskell Hackathon to a Haskell Exchange (not to be confused with The Haskell eXchange, a different event.) The organizers felt that the title "hackathon" has been given to events too unlike Hac Phi, events where participants code under pressure or over long times in competition. Those are fun affairs, indeed... but they're not like Hac Phi. So, we now say that Hac Phi is a yearly Haskell Exchange, where academics, professionals, and hobbyists can all meet, mingle, hack on each others' projects, and generally have a good time. All the details are on the wiki page: https://wiki.haskell.org/Hac_Phi I hope to see you there! Richard

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Callstack Implicit Param for Unsafe Prelude Functions
by aditya siram 20 Oct '15

20 Oct '15

Since the latest base now has a way of getting generating stack traces via the `CallStack` implicit param, is there any reason not to add that param to the error messages of unsafe functions in the Prelude ( and even commonly used modules like Data.Maybe/Data.List)? The type signature will change but for most users it should be a drop-in replacement and a great aid to debugging. Thanks! -deech

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Job opportunities at Kaspersky Lab (Moscow)
by Dmitry Kulagin 20 Oct '15

20 Oct '15

Here at Kaspersky Lab, we are developing a secure platform&framework. We have two job opportunities right now. Both opportunities assume good command of Haskell, since we use Haskell extensively. These are full time positions, available at our Moscow (Russia) office. If you are interested, please apply on the corporate site or send your CV to me directly at dmitry.kulagin(a)kaspersky.com Descriptions: Software Engineer: Responsibilities: * Development of core of the security system * Tools development (such as compilers/DSL) Skills/experience: * Strong experience developing with Haskell * C/C++ development experience * Good knowledge of basic algorithms and data structures * Compilers/DSLs development experience (desirable) * System programming experience (desirable) * Understanding of OS internals (desirable) * Experience in development of embedded and/or real-time applications (desirable) URL: * http://www.kaspersky.ru/job?vac=283264 Researcher (formal methods/computer security): Responsibilities: * Development of approaches to express and verify security and safety properties of systems Skills/experience: * Masters degree in CS or equivalent. PhD in CS (or related field) is desirable * Strong interest in computer security * Experience in formal verification * Good writing and presentation skills * Haskell programming experience is highly desirable * C-programming experience (desirable) * Prolog programming experience (desirable) URL: * http://www.kaspersky.ru/job?vac=283263

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Displaying specializations in :info or separately?
by David Kraeutmann 20 Oct '15

20 Oct '15

Hi, I'm working on a GHC feature [1] that allows users to view specializations of functions like in (name subject to change) ---- > :binfo find find :: Foldable t => (a -> Bool) -> t a -> Maybe a Specialisations: t ~ [] => find :: (a -> Bool) -> [a] -> Maybe a > :binfo first first :: Arrow a => a b c -> a (b, d) (c, d) Specialisations: a ~ (->) => first :: (b -> c) -> (b, d) -> (c, d) ---- Now there are two things left to decide on: * What command should the specializations be visible under? We can either put it under :info or make a special command :sinfo or :binfo that displays only the expression's type and specialisations like in the example above? * What specializations do we want to display? goldfire suggested using the default list, which has the added benefit of being customizable by e.g. instructors, so adding a default Maybe (in conjunction with [2]) gives the desired behavior and not too many specializations. Thanks for your time! David ---- Links: [1] : https://ghc.haskell.org/trac/ghc/ticket/10972 [2] : https://ghc.haskell.org/trac/ghc/ticket/10971

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Problems with Stack on Gentoo Linux
by Nicola Gigante 20 Oct '15

20 Oct '15

Hi all I’m sorry if this is not the right list to ask, I was unsure. I’m having problems compiling a project with stack on a Gentoo machine. I only have shell access to the machine, so I don’t have too much info about it, but the admin assured me that everything is up to date. I’ve upgraded to the latest stack, but the problem was also present with 0.1.4. While doing stack build on my project with resolver lts 3.10 I get the following strange error: ---------------------------------------------------------------------------------------------- -- While building package transformers-base-0.4.4 using: /home/gigabytes/.stack/setup-exe-cache/setup-Simple-Cabal-1.22.4.0-x86_64-linux-ghc-7.10.2 --builddir=.stack-work/dist/x86_64-linux/Cabal-1.22.4.0/ build --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 Logs have been written to: /home/gigabytes/gigabytes.it/.stack-work/logs/transformers-base-0.4.4.log Configuring transformers-base-0.4.4... Building transformers-base-0.4.4... Preprocessing library transformers-base-0.4.4... [1 of 1] Compiling Control.Monad.Base ( src/Control/Monad/Base.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.4.0/build/Control/Monad/Base.o ) src/Control/Monad/Base.hs:22:1: Warning: The import of `Data.Monoid' is redundant except perhaps to import instances from `Data.Monoid' To import instances alone, use: import Data.Monoid() src/Control/Monad/Base.hs:24:1: Warning: The import of `Control.Applicative' is redundant except perhaps to import instances from `Control.Applicative' To import instances alone, use: import Control.Applicative() .stack-work/dist/x86_64-linux/Cabal-1.22.4.0/build/src/Control/Monad/Base.dump-hi: commitBuffer: invalid argument (invalid character) ---------------------------------------------------------------------------------------------- Note that the warnings are not stopping the compile process themselves, but they somehow trigger the last error which kills the compiler. Stack is using the system-installed GHC here, which is version 7.10.2 (of course, otherwise stack wouldn’t have selected it). Maybe the system-wide compiler wasn’t installed properly (I doubt it, since the admin told me he uses a Gentoo package manager which is written in haskell and everything works well). So I’ve tried installing a stack-local GHC version, but I get a sanity check error: ---------------------------------------------------------------------------------------------- The GHC located at /home/gigabytes/.stack/programs/x86_64-linux/ghc-7.10.2/bin/ghc failed to compile a sanity check. Please see: https://github.com/commercialhaskell/stack/blob/release/doc/install_and_upg… for more information. Exception was: Running /home/gigabytes/.stack/programs/x86_64-linux/ghc-7.10.2/bin/ghc /tmp/stack-sanity-check22752/Main.hs -no-user-package-db exited with ExitFailure 1 [1 of 1] Compiling Main ( /tmp/stack-sanity-check22752/Main.hs, /tmp/stack-sanity-check22752/Main.o ) Linking /tmp/stack-sanity-check22752/Main ... /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/../../../../x86_64-pc-linux-gnu/bin/ld: /tmp/stack-sanity-check22752/Main.o: relocation R_X86_64_32S against `stg_bh_upd_frame_info' can not be used when making a shared object; recompile with -fPIC /tmp/stack-sanity-check22752/Main.o: error adding symbols: Bad value collect2: error: ld returned 1 exit status ---------------------------------------------------------------------------------------------- So to recap: - The system-wide ghc crashes compiling transformers-base-0.4.4 - The stack-local ghc does not pass a sanity check On an OS X machine, the project compiles and work very well with the same stack and ghc versions and the same LTS, so I suppose this has to do with Gentoo. Any ideas? Thank you, Nicola

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A GC'd heap using weak pointers
by Thomas Koster 20 Oct '15

20 Oct '15

Good afternoon list, I am implementing a simple, interpreted language that needs a garbage- collected heap for storage. Like most discussions on memory management, I use the term "heap" by analogy - the actual data structure is not necessarily a true heap. My Heap type is basically a map of "addresses" (Int) to values. Values may themselves contain addresses, perhaps recursively to each other (like letrec). The extra field in Heap stores the next unused address, used to allocate fresh slots, as you can see in "heapAlloc". > type Address = Int > data Value = ...things with Addresses... > data Heap = Heap !Address (Map Address Value) > > heapAlloc :: Heap -> (Address, Heap) > heapAlloc (Heap nextFreeAddr binds) = > (nextFreeAddr, Heap (succ nextFreeAddr) binds) There is also a stack of roots and an expression under evaluation. > type Stack = [...things with Addresses...] > data Expr = ...things with Addresses... The function I need to write is: > heapGC :: [Address] -> Heap -> Heap > heapGC roots heap = ...collect unreachable values from heap... Rather than re-invent this particularly complex wheel, I am wondering if I could use GHC weak pointers and have the GHC runtime collect values in my heap for me. Something like this: > type Address = Int > data Reference = Reference Address > data Value = ...things with References... > data Heap = Heap !Address (Map Address (Weak Value)) > > heapAlloc :: Heap -> (Reference, Heap) > heapAlloc (Heap nextFreeAddr binds) = > (Reference nextFreeAddr, Heap (succ nextFreeAddr) binds) > > heapStore :: Reference -> Value -> Heap -> IO Heap > heapStore ref@(Reference addr) val (Heap nextFreeAddr binds) = do > weakVal <- mkWeak ref val Nothing > return $ Heap nextFreeAddr (Map.insert addr weakVal binds) Note the new type, Reference. This replaces Address everywhere except in the heap's internal structure, which continues to use Address. Reference values are opaque, unique and obtained from the heap using heapAlloc. The idea is that only two things should cause Values to stay alive: 1. reachable holders of Reference (by GHC's definition of "reachable"), 2. ordinary Haskell closures arising from stepping the interpreter. "Being in the Heap" should not be enough to keep a Value alive. Then, my heapGC function should only have to prune dead addresses from the map. I am having trouble getting a proof-of-concept working (I am unable to observe any finalizers running, ever), but before I get into that, is this idea sound? Has somebody else implemented this in a library already? Thanks, Thomas Koster

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Global fixity (our status quo) vs. local fixity
by Jeffrey Brown 20 Oct '15

20 Oct '15

In Haskell, fixity is global. There are ten levels. You can't stick something between two levels, and you can't subvert the order of the levels. If you want something that binds before >>= but after the logical operators && and ||, you're out of luck -- unless you're willing to define synonyms for && and || that bind faster. (Tidal, a music DSL written in Haskell (it's on Hackage), exemplifies that problem with its |+| operator.) Conceptually, by contrast, fixity is local. The arithmetic operators (* + - / and **), for instance, have a certain fixity defined relative to each other, and that order does not, I believe, in the mind of most users extend beyond arithmetic. Does anybody else think it would be nice if a library's author had only to decide its operators' precedence relative to each other, and could let users decide for themselves how fast its operators should bind relative to operators from another library? -- Jeffrey Benjamin Brown

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hoogte db for the ghc api?
by Erik Rantapaa 19 Oct '15

19 Oct '15

Hi all, Is there a hoogle database for modules which come with GHC? - i.e. the modules on this page: http://downloads.haskell.org/~ghc/7.10.2/docs/html/libraries/ghc-7.10.2/ind… The text files would be preferable to a .hoo file, but I'll take either. Thanks! ER

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Future of FPComplete Haskell Center (IDE)
by Thomas Bereknyei 19 Oct '15

19 Oct '15

FPComplete is deprecating Haskell Center and removing support for their hosted IDE at the end of the year. I enjoy using the IDE in many situations and would like to have a similar capability available to the community. I know several people have expressed interest in helping maintain a version that can go on. Michael Snoyman has stated that there are some issues with the existing codebase and that there are many things that can/should be improved. There are some limitations due to NDA, but I believe FPComplete would be willing to hand over much of the codebase. I intend this thread to bring together those people interested in helping with this effort in any way. Personally, I would be willing to provide limited hosting and some development support. My goals would be to upgrade support to 8.x GHC, latest Stackage - LTS and create a path for people to self-host the IDE. -Tom Bereknyei

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[NL-FP 2016] Announcement: Dutch Functional Programming Day 2016
by Atze Dijkstra 19 Oct '15

19 Oct '15

[My apologies for multiple received copies of the same message] Dear all, The next Dutch Functional Programming day (NL-FP 2016) will be held on Friday, January 8, 2016 at the Utrecht University, The Netherlands. You are invited to participate and to give a presentation. At the end of the day we will have a joint dinner. On the web page http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome <http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome> for the day you’ll find preliminary information which will be further filled in due time. Registration is by letting me know via email (with a subject header that begins with [NL-FP 2016]) whether you want to (1) participate, (2) join dinner, (3) give a presentation (please include title + abstract), also see the webpage for additional details. If you intend to participate, please let me know as soon as possible because we like to know how many people we can expect. Hope to meet you all in Utrecht at the next FP Day! Best regards, - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)uu.nl ............... / |___\

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Building 32-bit binaries on a 64-bit system?
by Mike Meyer 19 Oct '15

19 Oct '15

I've got someone who wants to run one of my haskell apps on a 32-bit Windows 10 box. I've pretty much moved to 64-bit everywhere, so don't have such a system to build on. Is it possible to get stack/cabal/ghc to build a 32-bit Windows binary on a 64-bit Windows box? Google found a bunch of things about building 64 bit applications, and the ghc manual doesn't seem to have such an option. So do I need to get a 32-bit system for this?

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STM and garbage collector
by Tomas Carnecky 18 Oct '15

18 Oct '15

If a thread is blocking indefinitely in an STM transaction (reading from a queue to which nobody else has a reference and thus can not write into), is the runtime smart enough to GC the thread? Or do I have to kill the thread manually?

3 3

make an PrimMonad-wrapped FFI call
by Alexey Egorov 18 Oct '15

18 Oct '15

Hello haskellers, I'm writing FFI bindings to C library which uses some allocations across functions call, for example: int *alloc_buf(void); void free_buf(int *); So I need to use newForeignPtr to make sure buffer will be free'd when all pointers to it get collected. But what if I want to do this in PrimMonad (say, ST) and not IO (returned by newForeignPtr)? Thanks.

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How to specialize a type
by martin 17 Oct '15

17 Oct '15

Hello all, Suppose I have a type "Process" which stands either for a Train or a moving Belt. In both cases there is a place of departure and a place of arrival. However the other parameters which describe a Process differ. A Train has departure and arrival times, but a Belt has a speed. I tried the following: type PlaceDep = Int type PlaceArr = Int data Process = Train PlaceDep PlaceArr TP | MovingBelt PlaceDep PlaceArr BP deriving (Eq, Show) data TP = TP Int deriving (Eq, Show) data BP = BP Int deriving (Eq, Show) prc1 = Train 10 11 (TP 1) prc2 = MovingBelt 12 13 (BP 2) What I don't like about this is that the fact that all Processes have PlaceDep and PlaceArr appears somewhat "coincidental". This in contrast, captures the common parts more clearly: type PlaceDep = Int type PlaceArr = Int data ProcessParams = DepartureTime Int | Speed Int deriving (Eq, Show) data Process = Process PlaceDep PlaceArr ProcessParams deriving (Eq, Show) prc1 = Process 10 11 (DepartureTime 1) prc2 = Process 12 13 (Speed 2) Is this the classic way of specializing a type or are there better options See also: http://stackoverflow.com/questions/33156656/subclassing-a-type-in-haskell/3…

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Trying to write an Embedded DSL that threads a monad?
by Oleg 17 Oct '15

17 Oct '15

> Ian Bloom wrote: > I've been hoping to design a domain specific embedded language in > Haskell that would let me pipe a commutative monad throughout an expression > written in the language. Special terms within the language will eventually > have access to this monad. Is there a reason tagless-final approach does not work for you? You can easily thread any monad, even if you don't make any provision for it initially. For example, http://okmij.org/ftp/tagless-final/index.html#call-by-any http://okmij.org/ftp/tagless-final/course/CBAny.hs uses monad to print out traces of the expression and then later to implement lazy evaluation for EDLS (which needs mutable cells).

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Three open positions at Beautiful Destinations
by Tom Nielsen 16 Oct '15

16 Oct '15

The Data Science team at Beautiful Destinations is looking for three full-time developers and researchers with strong quantitative and programming skills. Beautiful Destinations ( http://www.beautifuldestinations.com/) is the world's largest travel influencer with a highly engaged audience of over 7 million followers across Instagram, Facebook and Snapchat. Beautiful Destinations distributes beautiful travel photography to its followers and helps clients to grow their social media channels. Our in-house photographers use drones and still photography to create content for our own accounts and our clients. The data science team has three aims: to predict and enhance the engagement of photographs on specific accounts; to measure influence on social media; and to determine the factors that contribute to the growth of social media accounts. Our internal API and core infrastructure are written in Haskell (using PostgreSQL), our Bayesian statistical time-series models use Stan ( http://mc-stan.org/) as well as some statistical models in Haskell. For image processing we use convolutional neural networks (in Python) and SIFT (C++/CUDA/Haskell). We are open to people bringing their preferred tools and maintain a polyglot environment. We are looking for developers who can fill the gap between data science and software engineering. We are at this stage only looking for full-time employees who can work in our London office. We welcome recent graduates and applicants with non-traditional backgrounds who show strong programming skills and capacity for independent learning. Please email contact(a)beautifuldestinations.com with any questions or with a CV if you are interested in this opportunity. -- <https://instagram.com/beautifuldestinations/>

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Talk at tonight's Haskell Meetup at the Hacker Dojo.
by David Banas 16 Oct '15

16 Oct '15

Hi all, I plan to give a short talk, at tonight’s Haskell Meetup at the Hacker Dojo in Mountain View, CA, on using Conal’s Circat and Lambda-CCC machinery to implement the Fast Fourier Transform (FFT). Hope to see you there, -db

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Specializing argument to forM_, mapM_ & foldM_ in base-4.8
by Amit Aryeh Levy 15 Oct '15

15 Oct '15

I've been running into a relatively small but frequent annoyance with base >= 4.8 (GHC 7.10). `Control.Monad.foldM_`, `Control.Monad.mapM_` and `Control.Monad.forM_` are generalized traverse over any `Foldable a` rather than just arrays (`[a]`). This is great, except I'm finding that, for a lot of my code that works well in previous versions, I need to specialize the argument to `[a]` now. If other people are encoutering a similar patter, I wonder what are your best practices for doing this: ScopedTypeVariables? Deconstruct the reconstruct the array? ... The most common example is when I deserialize a JSON array with aeson and want to traverse over that array (say, to store the objects to a DB): ``` let objArray = eitherDecode myjson case objArray of Left err -> ... Right (objs :: [MyObjType]) -> forM_ objs $ \obj -> saveToDb obj ``` The above fix requires `ScopedTypeVariables` (which is probably OK). Another option is to deconstruct and reconstruct the list: ``` Right (o:objs) -> forM_ (o:objs) $ \obj -> saveToDb obj ``` Does this get optimized away? Penny for your thoughts? Cheers! Amit

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Trying to write an Embedded DSL that threads a monad?
by Ian Bloom 15 Oct '15

15 Oct '15

I've been wrestling with this for a while and I decided eventually to look for help. I've been hoping to design a domain specific embedded language in Haskell that would let me pipe a commutative monad throughout an expression written in the language. Special terms within the language will eventually have access to this monad. I've created a simplified version here to represent the main issues. Here is what I'd like from the language: * To use haskell syntax for substitution and pattern matching rather than implementing this myself. * To be able to express lambdas in my language. * To be able to embed any haskell terms including functions into the language. * I'd like the Haskell type checker to tell me about bad terms. * I'd like to thread a monad through the entire expression. So here is the first implementation that I tried of this (full source here: http://lpaste.net/142959) data Exp m x where Val :: m x -> Exp m x Lam1 :: m (a -> Exp m b) -> Exp m (a -> b) Lam2 :: m (a -> Exp m (b -> c)) -> Exp m (a -> b -> c) a function liftE allows me to lift a haskell term into an expression: liftE x = Val $ return x Application is a function <@> so: (<@>) :: forall m a b. Monad m => Exp m (a -> b) -> Exp m a -> Exp m b (<@>) (Val f) (Val x) = Val $ f `ap` x (<@>) (Lam2 f) (Val x) = Lam1 $ f >>= \f' -> x >>= \x' -> unLam1 $ f' x' (<@>) (Lam1 f) (Val x) = Val $ f >>= \f' -> x >>= \x' -> unVal $ f' x' Seems like it might work! In fact it does typecheck. So the first test expressions I'd like to try are these: mapE :: Monad m => Exp m ((a -> b) -> [a] -> [b]) mapE = Lam2 $ return $ \ f -> Lam1 $ return $ \ xxs -> case xxs of [] -> liftE [] (x:xs) -> liftE (:) <@> liftE (f x) <@> (mapE <@> liftE f <@> liftE xs) testExpression :: Monad m => Exp m [Int] testExpression = mapE <@> liftE (+10) <@> liftE [1,2,3,4] and just to justify doing any of this I'll create a Monad called BindCounter that counts the number of times bind is called: newtype BindCounter a = BC (Int -> (Int, a)) runBC (BC f) = f 0 instance Functor (BindCounter) where fmap f (BC x) = BC $ \t -> let (t', x') = x t in (t', f x') instance Applicative (BindCounter) where pure x = BC (\t -> (t,x)) f <*> x = f >>= \f' -> x >>= \x' -> return $ f' x' instance Monad (BindCounter) where return = pure BC f >>= g = BC $ \old -> let (new, val) = f (old + 1) BC f' = g val in f' new now I can try a test test = let (count, result) = runBC (unVal testExpression) in putStrLn $ "Count: " ++ show count ++ " Result: " ++ show result The result in ghci is: Count: 36 Result: [11,12,13,14] Ok so that's a lot. I was surprised I got this working. You can see from the code that my main gripe with this is I haven't found a way to remove the need to specify the number of embedded lambdas using Lam1 and Lam2 (we could easily add more) and I haven't found a way to apply a Lam to another Lam. I'm also curious if I am reinventing the wheel, I hadn't found a library yet that let's me do something similar.

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Re: [Haskell-cafe] Talk at tonight's Haskell Meetup at the Hacker Dojo.
by David Banas 15 Oct '15

15 Oct '15

Yes, you may attend without being a member of the Hacker Dojo. -db On Thu, Oct 15, 2015 at 10:27 AM, Andrew Gibiansky < andrew.gibiansky(a)gmail.com> wrote: > Can I come if I'm not a member of Hacker Dojo? The website is unclear. > > -- Andrew > > On Thu, Oct 15, 2015 at 7:33 AM, David Banas <capn.freako(a)gmail.com> > wrote: > >> Hi all, >> >> I plan to give a short talk, at tonight’s Haskell Meetup at the Hacker >> Dojo in Mountain View, CA, on using Conal’s Circat and Lambda-CCC machinery >> to implement the Fast Fourier Transform (FFT). >> >> Hope to see you there, >> -db >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> > >

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ANN: stack-0.1.6.0
by Emanuel Borsboom 15 Oct '15

15 Oct '15

New version released of Stack, a build tool. See README <https://github.com/commercialhaskell/stack/tree/release#how-to-install> for installation and upgrade instructions. Major changes: - “stack setup” now supports building and booting GHCJS from source tarball. - On Windows, build directories no longer display “pretty” information (like x86_64-windows/Cabal-1.22.4.0), but rather a hash of that content. The reason is to avoid the 260 character path limitation on Windows. See #1027 <https://github.com/commercialhaskell/stack/pull/1027> - Rename config files and clarify their purposes #969 <https://github.com/commercialhaskell/stack/issues/969> - ~/.stack/stack.yaml → ~/.stack/config.yaml - ~/.stack/global → ~/.stack/global-project - /etc/stack/config → /etc/stack/config.yaml - Old locations still supported, with deprecation warnings - New command “stack eval CODE”, which evaluates to “stack exec ghc — -e CODE”. Other enhancements: - No longer install git on Windows #1046 <https://github.com/commercialhaskell/stack/issues/1046>. You can still get this behavior by running the following yourself: stack exec -- pacman -Sy --noconfirm git. - Typing enter during —file-watch triggers a rebuild #1023 <https://github.com/commercialhaskell/stack/pull/1023> - Use Haddock’s --hyperlinked-source (crosslinked source), if available #1070 <https://github.com/commercialhaskell/stack/pull/1070> - Use Stack-installed GHCs for stack init --solver #1072 <https://github.com/commercialhaskell/stack/issues/1072> - New experimental stack query command #1087 <https://github.com/commercialhaskell/stack/issues/1087> - By default, stack no longer rebuilds a package due to GHC options changes. This behavior can be tweaked with the rebuild-ghc-options setting. #1089 <https://github.com/commercialhaskell/stack/issues/1089> - By default, ghc-options are applied to all local packages, not just targets. This behavior can be tweaked with the apply-ghc-options setting. #1089 <https://github.com/commercialhaskell/stack/issues/1089> - Docker: download or override location of stack executable to re-run in container #974 <https://github.com/commercialhaskell/stack/issues/974> - Docker: when Docker Engine is remote, don’t run containerized processes as host’s UID/GID #194 <https://github.com/commercialhaskell/stack/issues/194> - Docker: set-user option to enable/disable running containerized processes as host’s UID/GID #194 <https://github.com/commercialhaskell/stack/issues/194> - Custom Setup.hs files are now precompiled instead of interpreted. This should be a major performance win for certain edge cases (biggest example: building Cabal itself <https://github.com/commercialhaskell/stack/issues/1041>) while being either neutral or a minor slowdown for more common cases. - stack test --coverage now also generates a unified coverage report for multiple test-suites / packages. In the unified report, test-suites can contribute to the coverage of other packages. Bug fixes: - Ignore stack-built executables named ghc #1052 <https://github.com/commercialhaskell/stack/issues/1052> - Fix quoting of output failed command line arguments - Mark executable-only packages as installed when copied from cache #1043 <https://github.com/commercialhaskell/stack/pull/1043> - Canonicalize temporary directory paths #1047 <https://github.com/commercialhaskell/stack/pull/1047> - Put code page fix inside the build function itself #1066 <https://github.com/commercialhaskell/stack/issues/1066> - Add explicit-setup-deps option #1110 <https://github.com/commercialhaskell/stack/issues/1110>, and change the default to the old behavior of using any package in the global and snapshot database #1025 <https://github.com/commercialhaskell/stack/issues/1025> - Precompiled cache checks full package IDs on Cabal < 1.22 #1103 <https://github.com/commercialhaskell/stack/issues/1103> - Pass -package-id to ghci #867 <https://github.com/commercialhaskell/stack/issues/867> - Ignore global packages when copying precompiled packages #1146 <https://github.com/commercialhaskell/stack/issues/1146>

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Haskell developer job offer
by Vagif Verdi 14 Oct '15

14 Oct '15

https://home2.eease.adp.com/recruit2/?id=19008792&t=1 Email me if interested.

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ghc-mod and IDE / plugin integration
by Alan & Kim Zimmerman 14 Oct '15

14 Oct '15

Historically ghc-mod provided (and still does) support for emacs and vim as part of its distribution. It is also used by a number of other IDE backends to provide a way of getting information about a project without worrying too much about the details of how the project is organised on the file system. There is currently a discussion between various interested parties about adjusting the way ghc-mod communicates with the IDE, to make it simpler to provide this support for other environments. This should end up with a definition of a protocol that ghc-mod can expose, which should also allow tools (such as HaRe) to be plugged into it, so that IDE integration can be handled by the various IDE integrators in a clean, common way. This is all just hand waving at the moment, so if anyone would like to get involved I am proposing that we revive the "Haskell IDE implementation"[1] google group/mailing list to host the discussion. The new design is/will be captured here [2] Regards Alan [1] https://groups.google.com/forum/#!forum/haskell-ide [2] https://github.com/kazu-yamamoto/ghc-mod/wiki/Library-API-Redesign

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Re: [Haskell-cafe] MRP, 3-year-support-window, and the non-requirement of CPP
by Herbert Valerio Riedel 14 Oct '15

14 Oct '15

On 2015-10-06 at 10:10:01 +0200, Johan Tibell wrote: [...] >> You say that you stick to the 3-major-ghc-release support-window >> convention for your libraries. This is good, because then you don't need >> any CPP at all! Here's why: >> >> [...] >> > > So what do I have to write today to have my Monad instances be: > > * Warning free - Warnings are useful. Turning them off or having spurious > warnings both contribute to bugs. Depends on the warnings. Some warnings are more of an advisory kind (hlint-ish). I wouldn't consider redundant imports a source of bugs. Leaving off a top-level signature shouldn't be a source of correctness bugs either. Also, warnings about upcoming changes (i.e. deprecation warnings) also are not necessarily a bug, but rather a way to raise awareness of API changes. At the other end of the spectrum are more serious warnings I'd almost consider errors, such as failing to define a non-defaulting method or violating a MINIMAL pragma specification, as that can lead to bottoms either in the form of runtime errors or even worse, hanging computations (in case of cyclic definitions). IMO, GHC should classify its warnings into severities/categories or introduce some compromise between -Wall and not-Wall. > * Use imports that either are qualified or have explicit import lists - > Unqualified imports makes code more likely to break when dependencies add > exports. > * Don't use CPP. That being said, as how to write your Monad instances today with GHC 7.10 w/o CPP, while supporting at least GHC 7.4/7.6/7.8/7.10: This *does* work (admittedly for an easy example, but this can be generalised): --8<---------------cut here---------------start------------->8--- module MyMaybe where import Control.Applicative (Applicative(..)) import Prelude (Functor(..), Monad(..), (.)) -- or alternatively: `import qualified Prelude as P` data Maybe' a = Nothing' | Just' a instance Functor Maybe' where fmap f (Just' v) = Just' (f v) fmap _ Nothing' = Nothing' instance Applicative Maybe' where pure = Just' f1 <*> f2 = f1 >>= \v1 -> f2 >>= (pure . v1) instance Monad Maybe' where Nothing' >>= _ = Nothing' Just' x >>= f = f x return = pure -- "deprecated" since GHC 7.10 --8<---------------cut here---------------end--------------->8--- This example above compiles -Wall-clean and satisfies all your 3 stated requirements afaics. I do admit this probably not what you had in mind. But to be consistent, if you want to avoid unqualified imports at all costs in order to have full control of what gets imported into your namespace, you shouldn't tolerate an implicit unqualified wildcard `Prelude` import either. As `Prelude` can, even if seldom, gain new exports as well (or even loose them -- `interact` *could* be a candidate for removal at some point). > Neither AMP or MRP includes a recipe for this in their proposal. That's because -Wall-hygiene (w/o opting out of harmless) warnings across multiple GHC versions is not considered a show-stopper. In the specific case of MRP, I can offer you a Wall-perfect transition scheme by either using `ghc-options: -fno-mrp-warnings` in your cabal-file, or if that doesn't satisfy you, we can delay phase1 (i.e. redundant return-def warnings) to GHC 8.2: Now you can continue to write `return = pure` w/o GHC warning bothering you until GHC 8.2, at which point the 3-year-window will reach to GHC 7.10. Then starting with GHC 8.2 you can drop the `return` definition, and keep your More generally though, we need more language-features and/or modifications to the way GHC triggers warnings to make such refactorings/changes to the libraries -Wall-perfect as well. Beyond what Ben already suggested in another post, there was also the more general suggestion to implicitly suppress warnings when you explicitly name an import. E.g. import Control.Applicative (Applicative(..)) would suppress the redundant-import warning for Applicative via Prelude, because we specifically requested Applicative, so we don't mind that Prelude re-exports the same symbol. > AMP got one post-facto on the Wiki. It turns out that the workaround > there didn't work (we tried it in Cabal and it conflicted with one of > the above requirements.) Yes, that unqualified `import Prelude`-last trick mentioned on the Wiki breaks down for more complex imports with (redundant) explicit import lists. However, the Maybe-example above works at the cost of a wordy Prelude-import, but it's more robust, as you pin down exactly which symbol you expect to get from each module. > The problem by discussions is that they are done between two groups with > quite a difference in experience. On one hand you have people like Bryan, > who have considerable contributions to the Haskell ecosystem and much > experience in large scale software development (e.g. from Facebook). On the > other hand you have people who don't. That's okay. We've all been at the > latter group at some point of our career. [...] At the risk of stating the obvious: I don't think it matters from which group a given argument comes from as its validity doesn't depend on the messenger. Neither does it matter whether an argument is repeated several times or stated only once. Also, every argument deserves to be considered regardless of its origin or frequency. -- hvr

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https://hackage.haskell.org/package/hoq build problems
by Vasili I. Galchin 14 Oct '15

14 Oct '15

Hello, I stumbled across hoq and it sounds very interesting to me. However, it has build problems now enumerated in the official build reports. I was thinking to investigate and possibly fix these build problems. However, when I run "cabal configure", I already ran into a problem: "unrecognized option `--extra-prog-path=/home/vasili/.cabal/bin'" I have been trying to track this down. Not sure how to fix this. Any help?? Regards, Vasily

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[Announce] haskintex-0.6.0.0
by Daniel Díaz Casanueva 13 Oct '15

13 Oct '15

Dear Haskell users, I just released a new version of haskintex, the program that runs Haskell code inside LaTeX documents. http://hackage.haskell.org/package/haskintex # More about haskintex For those who don't know the program yet, _haskintex_ is a tool that executes Haskell code inside LaTeX documents, creating a new LaTeX document where each Haskell expression has been replaced by its result. Furthermore, since haskintex has a special command for using the HaTeX library, you will be able to write Haskell code that generates LaTeX code. Find more details in the haskintex documentation page: http://daniel-diaz.github.io/projects/haskintex # What's new? One of the main issues when evaluating Haskell code with haskintex was that haskintex was not aware of sandbox environments, so it had to rely on user or global package databases. From version 0.6.0.0, haskintex can now detect and use sandbox package databases, with no additional effort required from you. The -nosandbox flag has been added in case you still want the old behavior. Another addition is the -autotexy flag. Without the flag, every expression contained in a \hatex command is required to have type LaTeX. When the flag is enabled, this restriction is relaxed to any type that is an instance of the Texy typeclass. This typeclass contains instances for types that can be rendered to LaTeX syntax. Could be some text, numbers, or even matrices. You can create your own instances too. Suggestions, bugs, questions? Head to the haskintex issue tracker: https://github.com/Daniel-Diaz/haskintex/issues Happy texing, Daniel Díaz.

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CFP: Workshop on Real World Domain Specific Languages, March 2016
by Simon Thompson 12 Oct '15

12 Oct '15

CALL FOR PAPERS ================================= Workshop on Real World Domain Specific Languages https://sites.google.com/site/realworlddsl In conjunction with The International Symposium on Code Generation and Optimisation 2016. http://cgo.org/cgo2016 Barcelona, 12-13 March, 2016 ================================= As the use of computers proliferates, the complexity and variety of systems continues to grow. As a result, it is becoming increasingly inflexible to "hard wire” behaviours into software. Software developers can enable more control over their software configurations by exploiting Domain Specific Languages (DSLs). Such DSLs provide a systematic way to structure the underlying computational components: to coin a phrase, a DSL is a library with syntax. There is an enormous variety of DSLs for a very wide range of domains. Most DSLs are highly idiosyncratic, reflecting both the specific natures of their application domains and their designers’ own preferences. This workshop will bring together constructors of DSLs for “real world” domains; that is, DSLs intended primarily to aid in building software to solve real world problems rather than to explore the more theoretical aspects of language design and implementation. We are looking for submissions that present the motivation, design, implementation, use and evaluation of such DSLs. ================================= Key Dates: ---------------- Paper submission deadline: 10 January 2016. Author notification: 2 February 2016. Final manuscript due: 21 February 2016. Workshop: 12-13 March 2016. ---------------- Submission Instructions: The EasyChair submission page for this workshop is https://easychair.org/conferences/?conf=rwdsl16 Accepted submissions will be published in the ACM Digital Library within its International Conference Proceedings Series. Submissions should be 8-10 in ACM double-column format. Authors should follow the information for formatting ACM SIGPLAN conference papers, which can be found at http://www.sigplan.org/Resources/Author. We will provide more details of the submissions format and process at the beginning of November. ================================= Program Chairs Rob Stewart, Heriot-Watt University Greg Michaelson, Heriot-Watt University PC Members Jost Berthold, Commonwealth Bank of Australia Andy Gill, University of Kansas Kevin Hammond, University of St Andrews Rita Loogen, Philipps Universitat Marburg Patrick Maier, University of Glasgow Josef Svenningsson, Chalmers University Simon Thompson, University of Kent Phil Trinder, University of Glasgow Contact Please email inquiries concerning the workshop to: R.Stewart(a)hw.ac.uk Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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GHC 7.10.2 Stage 1 compiler
by Alexey Raga 12 Oct '15

12 Oct '15

Hello, On the "Download" page (https://www.haskell.org/ghc/download_ghc_7_10_2) I see the archive with the binaries for ARM. Unfortunately this archive doesn't seem to include stage 1 compiler (which would be a cross-compiler from x86 or x64 to ARM as far as I understand). I am trying to build one myself, but unfortunately no luck so far. Is it possible to know the detailed instructions on how the existing ARM package has been built? A script or a dockerfile would be ideal. I could tune that build and make a docker container that could cross-compile x64 -> ARM... Regards, Alexey.

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ANNOUNCE: mezzolens 0.0.0 & a puzzle
by roconnor＠theorem.ca 11 Oct '15

11 Oct '15

This is a pre-release of mezzolens, a library of first-order functional references based purely on profunctors. I wrote it because https://www.reddit.com/user/Faucelme asked for one. You can find it at https://hackage.haskell.org/package/mezzolens The main purpose of this pre-release is to provide background for framing the following question: In a pure profunctor lens libray, how do you write choosing and beside in such a way that it supports all the following types? choosing :: Lens ta tb a b -> Lens sa sb a b -> Lens (Either ta sa) (Either sa sb) a b choosing :: Traversal ta tb a b -> Travesal sa sb a b -> Traversal (Either ta sa) (Either sa sb) a b choosing :: SEC ta tb a b -> SEC sa sb a b -> SEC (Either ta sa) (Either sa sb) a b beside :: Traversal ta tb a b -> Travesal sa sb a b -> Traversal (Either ta sa) (Either sa sb) a b beside :: SEC ta tb a b -> SEC sa sb a b -> SEC (Either ta sa) (Either sa sb) a b One sufficent solution for choosing would be to write a single function that combines lensVL :: (forall f. Functor f => (a -> f b) -> ta -> f tb) -> Lens ta tb a b traversal :: (forall f. Applicative f => (a -> f b) -> ta -> f tb) -> Traversal ta tb a b into one. The obvious approach is to write an suitable adaptor that transforms any (strong) profunctor into a functor, and if the profunctor is wandering, it produces an applicative functor. But I haven't been able to devise such a suitable adaptor. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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Final Call for Haskell Prime language committee Nominations!
by Herbert Valerio Riedel 11 Oct '15

11 Oct '15

The submission deadline (Wed, Oct 14 23:59:59 UTC 2015) for Haskell Prime self-nominations (see also original CfN at [1]) is near! If you have already submitted a self-nomination, please make sure (if it was sent to the haskell-prime list) that it shows up in the mailing list archives at - https://mail.haskell.org/pipermail/haskell-prime/2015-September/ or - https://mail.haskell.org/pipermail/haskell-prime/2015-October/ or (if you have only sent it to me directly) that I acknowledged receiving your submission by an email reply. Regards, Herbert Valerio Riedel [1]: https://mail.haskell.org/pipermail/haskell-prime/2015-September/003936.html

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Monads for Drummers! Yet another monad tutorial with pictures!
by Anton Kholomiov 10 Oct '15

10 Oct '15

Yes! It's another monad tutorial. I've tried hard not to do it but finally it came out. I wrote a book on Haskell in Russian. It's a translation of the chapter that is dedicated to monads. I was convinced by friends to publish it. The monads are explained with pictures and Kleisli categories. Hope this can help to someone to grasp the monad concept. ------------------------------------- ps: pictures were made with diagrams Thank you for being kind with my awkward English!

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ANNOUNCE: unordered-graphs
by Ivan Lazar Miljenovic 10 Oct '15

10 Oct '15

I have a relatively hacked-together graph library that uses unordered-containers as a backend available if anyone finds it interesting/useful: http://hackage.haskell.org/package/unordered-graphs It's primarily developed just for my own needs and thus I'm not sure how much future work I'll be doing on it, but I'm willing to accept pull requests. This library was semi-experimental in that I also tried a few things out with it: * Polymorphic node type * Fixed auto-generated edge type: this is because (node,node, label) triples (ala fgl) do not provide sufficient information to be able to distinguish between multiple edges, etc. * Type parameter to determine whether the graph is directed or undirected. * Typeclass to allow you to determine the type/output of a a match (I didn't end up actually using this, as the one time I needed to do a match I found the extra polymorphism caused problems; it also isn't comprehensive as I didn't write all that many instances.) -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Interfacing with the GHC runtime from a library
by Nicola Gigante 10 Oct '15

10 Oct '15

Hi everybody, suppose to have an Haskell library which is in part implemented in C for whatever reason. Can the C part talk with the runtime, in particular the scheduler? In other words, does the runtime expose the functionality needed to implement, for example, the STM library from outside the GHC runtime itself? Thank you, Nicola

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Vote/comment on usability survey feedback
by Rick Dzekman 09 Oct '15

09 Oct '15

*Responses* Over 100 people responded to the Hackage usability survey. For a qualitative survey this was far more than expected so thank you all for contributing. I'm still going through the responses and will post a csv of the combined web, email and reddit responses soon. *Vote and comment* In the meantime I went through and collated all of the gripes and suggestions people made into two Trello boards: Suggestions board: https://trello.com/b/WJRNDtkD/hackage-usability-suggestions Issues & bugs board: https://trello.com/b/8YSJ5XYV/hackage-usability-issues If you have a Trello account (it's free to register) you can comment and vote on issues. *Please vote on the issues/suggestions you think are the best or most important*. Feel free to make any relevant comments on the cards as well. To vote simply open the card, look in the "Actions" section and select vote. That's it. If reading through the suggestions/issues makes you think of something new simply comment on the very top card and I can add your new suggestion to the list. *What happens next?* There are two things that I want to achieve: 1. Come up with a list of simple, easy to implement changes that can be done on Hackage/Haddocks 2. Come up with wireframes for a potential future state of Hackage that the community can comment on / contribute to, which encompasses everything learned from the survey Not every suggestion is going to be feasible regardless of how popular it is. Additionally, any suggestions which are feasible have to be implemented by someone. The more enthusiasm there is behind an idea (or issue) the more likely we are to see progress.

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