May 2014 - Haskell-Cafe

porting Haskell to Mageia
by Roelof Wobben 22 May '14

22 May '14

Hello, I like to port Haskell to mageia linux. Now I found out that someone has already made a bootstrap package. Now my question is how can I use that one so I can make the full package like fedora has. So a lot of small packages instead of one big package. Roelof

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llvm is generating invalid instructions (problem with autovectorization?)
by Mike Izbicki 22 May '14

22 May '14

I have some code* that is causing llvm to throw a fit. In particular, I get (compiling with GHC 7.8 and llvm 3.4): /tmp/ghc1685_0/ghc1685_5.bc:150324:0: Error: no such instruction: `sarxq %rax,%rbx,%r14' Similar errors get repeated several thousand times, and it's always a sarxq instruction. Now, my code doesn't use any of the simd primops, so the sarxq must be coming from llvm's autovectorization. Is it possible that somehow GHC's output bytecode could be responsible, or is the problem more likely with llvm proper? Is there any way I can force GHC to pass flags to llvm so I can experiment with different settings? Another clue that the cause might be in llvm's autovectorization is that when I compile with llvm 3.0 (which does not support autovectorization), there are no error messages. * I suspect my code is far too complicated for it to shed any light on this question, but it's available at: https://github.com/mikeizbicki/HLearn/tree/dev-7.8/src/examples/hlearn-allk… If need be, I can create a minimal sample of code that causes the error, but I don't want to go through the trouble if it's not needed.

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Re: [Haskell-cafe] Default implementation of type class member function not working as expected.
by David Banas 21 May '14

21 May '14

That worked, Brandon; thanks! Gurus, I’d still love to understand exactly what I broke, trying to do it the other way. Any thoughts? Thanks, -db On May 21, 2014, at 12:14 AM, haskell-cafe-request(a)haskell.org wrote: > if there's only one definition, then define it > *outside* the typeclass. > >> I have a typeclass, which defines the following two member functions: >> (t is a Rose Tree.) >> >> getCompNodes :: t -> [CompNode a] >> >> getAllCompNodes :: t -> [CompNode a] >> getAllCompNodes t = getCompNodes t >> ++ (concatMap getAllCompNodes (subForest t)) >> The first one must be defined uniquely by each instance, but the second >> never needs a unique definition. >> So, I provided its implementation in the typeclass definition, as shown. >>

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ghc-mod version 4.1.0
by Kazu Yamamoto 21 May '14

21 May '14

Hello guys, I have released ghc-mod version 4.1.0. In this version, ghc-modi provides "info" and "type" commands. This means that you can display types and information of expressions very quickly on Emacs. http://hackage.haskell.org/package/ghc-mod Thanks to GHC's -fdefer-type-errors, "type" and "info" can work even if the file contains type errors. Yay! Of course, you can make use of GHC's hole. For more information, please read the "Types" subsection of the following page: http://mew.org/~kazu/proj/ghc-mod/en/emacs.html Enjoy! --Kazu

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One PhD position is available at the University of Dundee, Scotland
by Ekaterina Komendantskaya 21 May '14

21 May '14

One PhD position is available at the University of Dundee, Scotland. Contact ——————————— Katya Komendantskaya - katya(a)computing.dundee.ac.uk Profile ——————————— The subject of the studentship is programming language semantics and implementation. The specific topic for the studentship will depend on the interests and expertise of the potential candidate. Possible topics are: computational logic, interactive or automated theorem proving, verification, type systems, type inference, logics and applications, program analysis tools. Conditions ——————————— The studentship covers 3 years with a standard stipend of about £13-14k a year plus some eligible travel and consumables. Requirements ——————————— The ideal candidate must show a solid Mathematical or Computer Science background and interest in theoretical and/or practical aspects of declarative programming languages. Previous experience in one or more of the areas described in the profile will be considered a plus. How to apply ——————————— The position is available immediately. Candidates please contact Katya Komendantskaya - katya(a)computing.dundee.ac.uk Dundee and the university ——————————— Dundee is the fourth-largest city in Scotland and it is well connected with Edinburgh, Glasgow and Aberdeen. Dundee is promoted as 'One City, Many Discoveries' in honor of Dundee's history of scientific activities and of the RRS Discovery exploration vessel, which is berthed in the city harbor. Biomedical, technological and video game industries have been important for the development of the city in the last 20 years. The University of Dundee counts about 18.000 students and is situated in the city center. The university is ranked in the World's Top 250 Universities and has been voted one of the best universities in the UK for student experience. http://en.wikipedia.org/wiki/Dundee http://www.dundee.ac.uk The Theory of Computation group ——————————— The Theory of Computation group focuses on research into different areas covering functional programming, program analysis, computational logic, theorem proving, machine learning, constraint programming, graph theory, algorithms and applications like privacy, security, complexity, optimisation, and artificial intelligence. ************************ Ekaterina Komendantskaya Senior Lecturer, Head of PhD Studies Room 1.04, Queen Mother Building School of Computing, University of Dundee Scotland, DD14HN Tel: (+44) 01382384820

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TemplateHaskell forces manual declaration ordering?
by Michael Alan Dorman 21 May '14

21 May '14

Hey, all, While refactoring some code, I moved a newtype declaration, and suddenly the compiler (up-to-date ghc-7.6.3 on Debian) started complaining that it wasn't in scope when I attempted to use it in an ADT. I'm still new to Haskell, so I assumed it was my misunderstanding, and looked for documentation of declaration ordering constraints and couldn't find any. So then I went to make a toy case to demonstrate the problem, and it worked: data Baz = Baz { foo :: Foo, bar :: !(Maybe Bar) } newtype Foo = Foo String newtype Bar = Bar String So I started looking at the differences between that and my real code, and the only thing that seemed at all signficant was that I was using TH to generate some lenses. And sure enough, adding that caused it to fail: {-# LANGUAGE TemplateHaskell #-} import Control.Lens data Baz = Baz { foo :: Foo, bar :: !(Maybe Bar) } makeLenses ''Baz newtype Foo = Foo String newtype Bar = Bar String If you feed this to ghci, you now get: test.hs:3:25: Not in scope: type constructor or class `Foo' test.hs:3:45: Not in scope: type constructor or class `Bar' Perhaps you meant `Baz' (line 3) Wondering if lens was somehow doing something so exotic it was breaking things, I tried aeson's TH support instead: {-# LANGUAGE TemplateHaskell #-} import Data.Aeson data Baz = Baz { foo :: Foo, bar :: !(Maybe Bar) } deriveJSON defaultOptions ''Baz newtype Foo = Foo String newtype Bar = Bar String Exact same error. That said, if I move the splices to the end of the file, everything works: {-# LANGUAGE TemplateHaskell #-} import Data.Aeson data Baz = Baz { foo :: Foo, bar :: !(Maybe Bar) } newtype Foo = Foo String newtype Bar = Bar String deriveJSON defaultOptions ''Baz I looked at the GHC docs on TH, and read the wiki page, and didn't see anything suggesting that this was a known limitation, nor did I see a bug in the known bug list that seemed pertinent. So, I'm wondering if I've found an actual bug, or a known limitation whose documentation should be made more prominent (since it seems to me that it has pretty dramatic implications for program structure), or what? And is there any way around it other than moving all the splices to the end of the source file? Mike.

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Manually control linker options in Cabal build system
by Oleg Durandin 21 May '14

21 May '14

Hi all! Not long ago, I faced with problem building library with Cabal. I'm trying to build simple Haskell project as a shared library for use in MS Visual Studio (yes, I use FFI for this). And I created simple test project: / {-# LANGUAGE ForeignFunctionInterface #-} module GrepWrap where import Foreign import Foreign.C.String import Data.Char printCString :: CString -> IO () printCString s = do ss <- peekCString s putStrLn ss getCStringFromKey :: IO CString getCStringFromKey = do guess <- getLine newCString guess hello :: IO() hello = do putStrLn "Hi there!" foreign export stdcall В В В В hello :: IO () foreign export stdcallВ В printCString :: CString -> IO () foreign export stdcallВ В getCStringFromKey :: IO CString/ Also, I created file for safe initialization with wrappers for hs_init() and hs_exit() calls: /// StartEnd.c #include <Rts.h> extern void __stginit_GrepWrap(void); void HsStart() { int argc = 1; char* argv[] = {"ghcDll", NULL}; // argv must end with NULL // Initialize Haskell runtime char** args = argv; hs_init(&argc, &args); } void HsEnd() { hs_exit(); }/ I compile these files with the next commands: /*> ghc -c GrepWrap.c*//* *//*> ghc -c StartEnd.c*//* *//*> ghc -shared -o grepWrap.dll grepWrap.hs StartEnd.o*/ /Linking grepWrap.dll ...// //Creating library file: grepWrap.dll.a// /// After it, I've got grepWrap.dll and grepWrap.dll.a files. I successfully linked that library with my simple C++ test app, that uses these functions. And I was able to use my Haskell functions in my simple C++ app. Further, I'd like to use Cabal build system for building the same Haskell library filles. My cabal file looks like this: /*name: GrepWrap version: 1.0 synopsis: example shared library for C use build-type: Simple cabal-version: >=1.10 library default-language: Haskell2010 exposed-modules: GrepWrap extra-libraries: HSbase-4.6.0.1, wsock32, user32, shell32, HSinteger-gmp-0.5.0.0, HSghc-prim-0.3.0.0, HSrts, gdi32, winmm c-sources: StartEnd.c extensions: ForeignFunctionInterface build-depends: base >= 4 --ghc-options: "-v"*/ After build, in directory dist/build I got a set of files and among them there are: _/libHSGrepWrap-1.0-ghc7.6.3.dll/_ , ___/libHSGrepWrap-1.0-ghc7.6.3.dll.a/_ and /_GrepWrap_stub.h_/ . I use these files in the same Visual Studio project (of course, I changed names of dependent libraries in dependencies configuration in Visual Studio). Application successfully builds, but after run this app, I've got the next exception: Unhandled exception at 0x6D7905FB (libHSrts-ghc7.6.3.dll) in GrepWrapCabalUseDll.exe: 0xC0000005: Access violation reading location 0x00000000 It occurs, when I call functions from library (but when HsStart() already called). When I use "-v" flag with compilation (using ghc) I saw such linker message log: /*** Linker:// //"C:\Program Files (x86)\Haskell Platform\2013.2.0.0\lib/../mingw/bin/gcc.exe" "-fno-stack-protector" "-Wl,--hash-size=31" "-Wl,--reduce-memory-overheads" "-o" "grepWrap.dll" "-shared" "-Wl,--out-implib=grepWrap.dll.a" "grepWrap.o" "-Wl,--enable-auto-import" "StartEnd.o" "-LC:\Program Files (x86)\Haskell Platform\2013.2.0.0\lib\base-4.6.0.1" "-LC:\Program Files (x86)\Haskell Platform\2013.2.0.0\lib\integer-gmp-0.5.0.0" "-LC:\Program Files (x86)\Haskell Platform\2013.2.0.0\lib\ghc-prim-0.3.0.0" "-LC:\Program Files (x86)\Haskell Platform\2013.2.0.0\lib" "-lHSbase-4.6.0.1" "-lwsock32" "-luser32" "-lshell32" "-lHSinteger-gmp-0.5.0.0" "-lHSghc-prim-0.3.0.0" "-lHSrts" "-lm" "-lwsock32" "-lgdi32" "-lwinmm" "-u" "_ghczmprim_GHCziTypes_Izh_static_info" "-u" "_ghczmprim_GHCziTypes_Czh_static_info" "-u" "_ghczmprim_GHCziTypes_Fzh_static_info" "-u" "_ghczmprim_GHCziTypes_Dzh_static_info" "-u" "_base_GHCziPtr_Ptr_static_info" "-u" "_ghczmprim_GHCziTypes_Wzh_static_info" "-u" "_base_GHCziInt_I8zh_static_info" "-u" "_base_GHCziInt_I16zh_static_info" "-u" "_base_GHCziInt_I32zh_static_info" "-u" "_base_GHCziInt_I64zh_static_info" "-u" "_base_GHCziWord_W8zh_static_info" "-u" "_base_GHCziWord_W16zh_static_info" "-u" "_base_GHCziWord_W32zh_static_info" "-u" "_base_GHCziWord_W64zh_static_info" "-u" "_base_GHCziStable_StablePtr_static_info" "-u" "_ghczmprim_GHCziTypes_Izh_con_info" "-u" "_ghczmprim_GHCziTypes_Czh_con_info" "-u" "_ghczmprim_GHCziTypes_Fzh_con_info" "-u" "_ghczmprim_GHCziTypes_Dzh_con_info" "-u" "_base_GHCziPtr_Ptr_con_info" "-u" "_base_GHCziPtr_FunPtr_con_info" "-u" "_base_GHCziStable_StablePtr_con_info" "-u" "_ghczmprim_GHCziTypes_False_closure" "-u" "_ghczmprim_GHCziTypes_True_closure" "-u" "_base_GHCziPack_unpackCString_closure" "-u" "_base_GHCziIOziException_stackOverflow_closure" "-u" "_base_GHCziIOziException_heapOverflow_closure" "-u" "_base_ControlziExceptionziBase_nonTermination_closure" "-u" "_base_GHCziIOziException_blockedIndefinitelyOnMVar_closure" "-u" "_base_GHCziIOziException_blockedIndefinitelyOnSTM_closure" "-u" "_base_ControlziExceptionziBase_nestedAtomically_closure" "-u" "_base_GHCziWeak_runFinalizzerBatch_closure" "-u" "_base_GHCziTopHandler_flushStdHandles_closure" "-u" "_base_GHCziTopHandler_runIO_closure" "-u" "_base_GHCziTopHandler_runNonIO_closure" "-u" "_base_GHCziConcziIO_ensureIOManagerIsRunning_closure" "-u" "_base_GHCziConcziSync_runSparks_closure" "-u" "_base_GHCziConcziSignal_runHandlers_closure"// //Creating library file: grepWrap.dll.a// //link: done/ But, when I call cabal build with "-v2" option to get build log, I get the following: /> cabal build -v2 I've got the next log: creating dist\build creating dist\build\autogen Building GrepWrap-1.0... Preprocessing library GrepWrap-1.0... Building library... creating dist\build C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe --make -fbuilding-cabal-package -O -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 GrepWrap-1.0 -hide-all-packages -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 -XHaskell2010 -XForeignFunctionInterface GrepWrap [1 of 1] Compiling GrepWrap ( GrepWrap.hs, dist\build\GrepWrap.o ) C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe --make -fbuilding-cabal-package -O -prof -osuf p_o -hisuf p_hi -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 GrepWrap-1.0 -hide-all-packages -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 -XHaskell2010 -XForeignFunctionInterface GrepWrap [1 of 1] Compiling GrepWrap ( GrepWrap.hs, dist\build\GrepWrap.p_o ) C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe --make -fbuilding-cabal-package -O -dynamic -fPIC -osuf dyn_o -hisuf dyn_hi -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 GrepWrap-1.0 -hide-all-packages -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 -XHaskell2010 -XForeignFunctionInterface GrepWrap [1 of 1] Compiling GrepWrap ( GrepWrap.hs, dist\build\GrepWrap.dyn_o ) Building C Sources... creating dist\build C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe -c -prof -odir dist\build -Idist\build -optc-O2 -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 StartEnd.c C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe -c -prof -dynamic -fPIC -osuf dyn_o -odir dist\build -Idist\build -optc-O2 -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 StartEnd.c Linking... C:\Program Files (x86)\Haskell Platform\2013.2.0.0\mingw\bin\ar.exe -r dist\build\libHSGrepWrap-1.0.a dist\build\GrepWrap.o dist\build\StartEnd.o C:\Program Files (x86)\Haskell Platform\2013.2.0.0\mingw\bin\ar.exe: creating dist\build\libHSGrepWrap-1.0.a C:\Program Files (x86)\Haskell Platform\2013.2.0.0\mingw\bin\ar.exe -r dist\build\libHSGrepWrap-1.0_p.a dist\build\GrepWrap.p_o dist\build\StartEnd.o C:\Program Files (x86)\Haskell Platform\2013.2.0.0\mingw\bin\ar.exe: creating dist\build\libHSGrepWrap-1.0_p.a C:\Program Files (x86)\Haskell Platform\2013.2.0.0\mingw\bin\ld.exe -x --hash-size=31 --reduce-memory-overheads -r -o dist\build\HSGrepWrap-1.0.o dist\build\GrepWrap.o dist\build\StartEnd.o C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc.exe -shared -dynamic -lHSbase-4.6.0.1 -lwsock32 -luser32 -lshell32 -lHSinteger-gmp-0.5.0.0 -lHSghc-prim-0.3.0.0 -lHSrts -lgdi32 -lwinmm -package-name GrepWrap-1.0 -no-auto-link-packages -package-db dist\package.conf.inplace -package-id base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 dist\build\GrepWrap.dyn_o dist\build\StartEnd.dyn_o -o dist\build\libHSGrepWrap-1.0-ghc7.6.3.dll Creating library file: dist\build\libHSGrepWrap-1.0-ghc7.6.3.dll.a In-place registering GrepWrap-1.0... C:\Program Files (x86)\Haskell Platform\2013.2.0.0\bin\ghc-pkg.exe update - --global --user --package-db=dist\package.conf.inplace/ I'm confused.. Cabal uses a batch of options, it adds multiple options that I can't control. I'd like to control this options. How can I build my Haskell library with Cabal build system as same as building it with simple ghc? I can call ghc manually, but it will be a hard task, when I'll compile library for multiple files. Best regards, Oleg Durandin

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Fwd: extending Do notation
by Miguel Mitrofanov 21 May '14

21 May '14

Forgot to reply the list -------- Пересылаемое сообщение -------- 20.05.2014, 18:26, "Miguel Mitrofanov" <miguelimo38(a)yandex.ru>: 20.05.2014, 18:14, "Kim-Ee Yeoh" <ky3(a)atamo.com>: >> 2) you can't use >>= in an if condition > Could you give an example of the if condition you want an >>= in? Actually, something like do ... if <- checkCondition then doReportSuccess else doReportFailure as well as do ... case <- generateResult of Nothing -> ... Just r -> ... instead of do ... b <- checkCondition if b ... and do ... r <- generateResult case r of ... would be very nice. -------- Завершение пересылаемого сообщения --------

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Default implementation of type class member function not working as expected.
by David Banas 20 May '14

20 May '14

Hi all, I have a typeclass, which defines the following two member functions: (t is a Rose Tree.) getCompNodes :: t -> [CompNode a] getAllCompNodes :: t -> [CompNode a] getAllCompNodes t = getCompNodes t ++ (concatMap getAllCompNodes (subForest t)) The first one must be defined uniquely by each instance, but the second never needs a unique definition. So, I provided its implementation in the typeclass definition, as shown. However, I don’t get the expected behavior! If I copy and paste the code, above, for getAllCompNodes into my instance definition, then I get the expected results. Does anyone know why this is happening? Thanks, -db

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Hackage Down?
by Alexander Solla 20 May '14

20 May '14

I can get to the Hackage website, but I'm having problems doing things with cabal. I have plenty of disk space. I deleted my package cache, since it was complaining about a truncated tar archive for a specific package. Now I'm trying: $ cabal update Downloading the latest package list from hackage.haskell.org cabal: truncated tar archive

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