August 2017 - Haskell-Cafe

profiling of functions generated by LLVM
by Henning Thielemann 30 Aug '17

30 Aug '17

I use LLVM to create sub-routines for efficient inner loops. I like to profile them. However, it seems that GHC's profiler does not interact well with such generated functions. Say, I have a function that creates an efficient subroutine for filling a block of data. It looks like the following: generateFill :: IO (Word64 -> Ptr Float -> IO ()) generateFill = generateFunction (LLVM code for traversing block) main :: IO () main = do let n = 100*10^6 fill <- generateFill allocaArray n $ \ptr -> {-# SCC fill #-} fill (fromIntegral n) ptr I run this with profiling. The resulting .prof report says, that 'generateFunction' demands all the computation time and 'fill' inherits it. fill Main 1297 1 0.0 0.0 99.9 0.0 generateFill Main 1298 0 0.0 0.0 99.9 0.0 generateFunction Main 1299 0 99.9 0.0 99.9 0.0 I have a rough idea why GHC treats the generated functions the way it does. However, it is pretty counter-intuitive and difficult to understand in more complex programs.

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Munich Haskell Meeting, 2017-08-31 @ 19:30
by Christian Neukirchen 29 Aug '17

29 Aug '17

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, August 31 at Augustiner-Gaststätte Rumpler (Baumstraße 21) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html 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-aug-2017/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Haddock's Hackage page --- Bravo!
by Albert Y. C. Lai 28 Aug '17

28 Aug '17

https://hackage.haskell.org/package/haddock now puts the whole cheatsheet up front. Well done! Bravo! Whoever thought up this is a genius! Thanks!

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Does the streaming package need a new/additional maintainer?
by David Feuer 28 Aug '17

28 Aug '17

The streaming package has a couple old pull requests that have not been commented on. My recently reported issues and pull requests have also met with silence. It appears that the maintainer, Michael Thompson, was last active on GitHub and Reddit in April. I emailed him a few days ago, but have not yet received a response. I hope he is just on a short break, but if not, someone should probably take over the package. David

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Numerical / Data Special Interest Group at ICFP'17
by Marco Zocca 28 Aug '17

28 Aug '17

Dear all, thanks to the ICFP organisers and to D.Steinitz (https://idontgetoutmuch.wordpress.com/) we will have a late-minute workshop on the numerical and data-related Haskell at ICFP'17 (Oxford) on Saturday 9th September in the slot 12:30 - 14:00. Looking forward to meeting you all there; Best, Marco Zocca https://github.com/ocramz

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GHC 8.2's new ghci commands: `:type +d` and `:type +v`
by Takenobu Tani 28 Aug '17

28 Aug '17

Dear cafe, GHC 8.2 supports two new ghci commands. They are `:type +d` and `:type +v` [1]. 0. normal `:type` command: Prelude> :type length length :: Foldable t => t a -> Int Prelude> :type ($) ($) :: (a -> b) -> a -> b 1. new `:type +d` command for newcomers: Prelude> :type +d length length :: [a] -> Int 2. new `:type +v` command for detail information: Prelude> :type +v ($) ($) :: forall (r :: GHC.Types.RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b That's excellent :) [1]: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghci.html#g… Regards, Takenobu

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undefined reference to '__gxx_personality_v0'
by Henning Thielemann 28 Aug '17

28 Aug '17

I have trouble to compile my llvm-ffi package containing C++ binding code. I am on Ubuntu 16.04 and I have created a custom llvm.pc file: $ cat /usr/local/lib/pkgconfig/llvm-3.8.pc Name: LLVM Description: Low-level Virtual Machine compiler framework Version: 3.8.0 URL: http://www.llvm.org/ Requires: Conflicts: Libs: -L/usr/lib/llvm-3.8/lib -lLLVM-3.8.0 Cflags: -I/usr/lib/llvm-3.8/include -std=c++0x -std=c++11 /tmp$ cabal unpack llvm-ffi Unpacking to llvm-ffi-3.8.1/ /tmp$ cd llvm-ffi-3.8.1/ /tmp/llvm-ffi-3.8.1$ cabal configure -fbuildExamples --with-ghc=ghc-8.2.1 Resolving dependencies... Configuring llvm-ffi-3.8.1... /tmp/llvm-ffi-3.8.1$ cabal build Preprocessing library for llvm-ffi-3.8.1.. cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C cc1: warning: command line option ‘-std=c++11’ is valid for C++/ObjC++ but not for C Building library for llvm-ffi-3.8.1.. [ 1 of 22] Compiling LLVM.FFI.Core ( dist/build/LLVM/FFI/Core.hs, dist/build/LLVM/FFI/Core.o ) [ 2 of 22] Compiling LLVM.FFI.BitWriter ( src/LLVM/FFI/BitWriter.hs, dist/build/LLVM/FFI/BitWriter.o ) [ 3 of 22] Compiling LLVM.FFI.BitReader ( src/LLVM/FFI/BitReader.hs, dist/build/LLVM/FFI/BitReader.o ) [ 4 of 22] Compiling LLVM.FFI.Analysis ( src/LLVM/FFI/Analysis.hs, dist/build/LLVM/FFI/Analysis.o ) ... Preprocessing executable 'llvm-ffi-example' for llvm-ffi-3.8.1.. Building executable 'llvm-ffi-example' for llvm-ffi-3.8.1.. [1 of 1] Compiling Main ( example/JIT.hs, dist/build/llvm-ffi-example/llvm-ffi-example-tmp/Main.o ) Linking dist/build/llvm-ffi-example/llvm-ffi-example ... /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMGetHostFeatures: error: undefined reference to 'operator new(unsigned long)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMGetHostFeatures: error: undefined reference to 'operator delete(void*)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMCheckFeature(llvm::StringMap<bool, llvm::MallocAllocator>*, llvm::StringMapConstIterator<bool>*): error: undefined reference to 'operator delete(void*)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMGetFirstFeature: error: undefined reference to 'operator new(unsigned long)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMCreateExecutionEngineKindForModuleCPU: error: undefined reference to 'operator delete(void*)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMCreateExecutionEngineKindForModuleCPU: error: undefined reference to 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_replace(unsigned long, unsigned long, char const*, unsigned long)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:function LLVMCreateExecutionEngineKindForModuleCPU: error: undefined reference to 'operator delete(void*)' /tmp/llvm-ffi-3.8.1/dist/build/libHSllvm-ffi-3.8.1-KKUvbYcVYVe5ZjJKumuzkS.a(support.o):support.cpp:DW.ref.__gxx_personality_v0: error: undefined reference to '__gxx_personality_v0' collect2: error: ld returned 1 exit status `gcc' failed in phase `Linker'. (Exit code: 1) StackOverflow discussions on those linker errors suggest that it is important to link with g++, not gcc. Can I control how GHC links? How do other packages cope with C++ code? It seems that they most oftenly come with custom Setup modules that cause trouble with different Cabal versions. I hoped that I can prevent those difficulties using pkg-config. Unfortunately, pkg-config seems to be limited to C libraries. Thus the warnings about the -std=c++11 option in the beginning. Maybe it is cleaner to write a separate LLVM C package that interfaces to the C++ code and bind Haskell to C via pkg-config. However, it would mean that I have to maintain a C library for Linux, Mac and Windows with autoconf et.al.

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how would I do this properly in Haskell?
by Dennis Raddle 25 Aug '17

25 Aug '17

I have a problem which I can solve with OO organization, but I want to know how to do it properly in Haskell. I have a search optimization problem in which there are a lot of individual fitness functions which combine scores to give an overall fitness level. Each fitness function will be associated with data, both initial data to configure it, and a cache that it maintains. So I could have something like this: data Fitness = Fit1 SomeData1 | Fit2 SomeData2 | Fit3 SomeData3 -- this function would evaluate the fitness of a particular -- result of type 'S' (in my case, a partially-constructed -- musical composition) evaluate :: Fitness -> S -> (Fitness,Double) -- something like this would have to be written for -- every sub-type of "Fitness" evaluate (Fit1 d) s = (Fit1 d',v) where (d',v) = evaluate1 d s evaluate1 :: SomeData1 -> S -> (SomeData1,Double) Is there a better way to do this? D

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Announce: Haskell Platform 8.2.1
by Gershom B 24 Aug '17

24 Aug '17

On behalf of the Haskell Platform team, I'm happy to announce the release of Haskell Platform 8.2.1 Now available at https://www.haskell.org/platform/ This includes GHC 8.2.1, cabal-install 2.0.0.0, and stack 1.5.1, all with many bugfixes and improvements since the last platform release. A full list of contents is available at https://www.haskell.org/platform/contents.html Thanks to all the contributors to this release, thanks to all the package and tool maintainers and authors, and a big thanks to the GHC team for all their hard work. Due to GHC bug #14081 (https://ghc.haskell.org/trac/ghc/ticket/14081) we do not have Win32 builds in this release. We anticipate resuming support for Win32 once the current issues with GHC on Win32 are fixed in the next release. A list of new GHC changes is available at: https://ghc.haskell.org/trac/ghc/blog/ghc-8.2.11-released A list of cabal changes is available at: https://hackage.haskell.org/package/cabal-install-2.0.0.0/changelog (note the support for the Backpack module system, as described at: https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpa…) The cabal documentation page is at: https://cabal.readthedocs.io/en/latest/ A list of stack changes is at: https://docs.haskellstack.org/en/stable/ChangeLog/ The stack documentation page is at: https://docs.haskellstack.org/en/stable/README/ Happy Haskell Hacking all, Gershom (Note -- one feature we still have not implemented yet for the platform but would like to is a generic linux installer that allows one to set a custom location and does not require root. Anyone who would like to volunteer to help with this, please get in touch!)

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Haskell Platform
by Stuart A. Kurtz 24 Aug '17

24 Aug '17

Dear Colleagues, What's the status of the Haskell Platform? Is it still the/a preferred way to install a working Haskell system? What is the update status of the Platform? [I note that the platform is at 8.0.2, whereas GHC is at 8.2.1, so I'm really asking if there's a roadmap/timeline for updates.] I write because I teach an introductory class in Haskell, and we've long used the Platform as a way to get the system up and running on the student's systems. I'm at a quarter school, but I have to think this is a sharp question for anyone trying to teach a Haskell course at a semester school. Is the Platform still the best way to do this? Will cabal continue to be a reasonable choice as default package manager? Thank you for your consideration. Peace, Stu

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