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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 25 Aug '17

25 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 25 Aug '17

25 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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GHC fails to fuse [1 .. 30000000 :: Double] but fuses fromIntegral <$> [1 :: Int .. 30000000]?
by Mateusz Kowalczyk 25 Aug '17

25 Aug '17

Hi, I had few minutes timeout waiting for CI today and I stumbled upon [1]. This is a many years old question and the optimal solution given there was using Vector. I thought that for such a problem it should not be necessary at all. Indeed I wrote `mean :: [Int] -> Int` and got a much faster solution. However the original signature was `mean :: [Double] -> Int`. After trivial changes (change couple of places to Double and add a single fromIntegral) I expected the same result: after all, code is nearly exactly the same. However to my disappointment, the code in question was much slower than the vector solution: how could this be? Looking in Core, I saw that GHC was not getting rid of [Double] like it was with [Int]. I was able to convince GHC to go back to fusing the list into the worker with a `map fromIntegral` but I am unhappy: why is this needed? I don't understand why GHC would not decide to fuse the initial attempt. Honestly it seems like a bug to me. What are your thoughts? For reference here is the core with fromIntegral: as expected, GHC fuses the list and inserts int2Double# as it's generating it: ``` Main.$wgo = \ (w_s5xT :: GHC.Prim.Int#) (ww_s5xX :: GHC.Prim.Int#) (ww1_s5xY :: GHC.Prim.Double#) -> case w_s5xT of wild_Xz { __DEFAULT -> Main.$wgo (GHC.Prim.+# wild_Xz 1#) (GHC.Prim.+# ww_s5xX 1#) (GHC.Prim.+## ww1_s5xY (GHC.Prim.int2Double# wild_Xz)); 30000000# -> (# GHC.Prim.+# ww_s5xX 1#, GHC.Prim.+## ww1_s5xY 3.0e7## #) } ``` Contrast this with version that's commented out in [2]: ``` Main.$wgo = \ (w_s5vE :: [Double]) (ww_s5vI :: GHC.Prim.Int#) (ww1_s5vJ :: GHC.Prim.Double#) -> case w_s5vE of _ [Occ=Dead] { [] -> (# ww_s5vI, ww1_s5vJ #); : y_a3dU ys_a3dV -> case y_a3dU of _ [Occ=Dead] { GHC.Types.D# y1_a3dG -> Main.$wgo ys_a3dV (GHC.Prim.+# ww_s5vI 1#) (GHC.Prim.+## ww1_s5vJ y1_a3dG) } } … case Main.$wgo Main.main3 0# 0.0## … Main.main3 = GHC.Real.numericEnumFromTo @ Double GHC.Classes.$fOrdDouble GHC.Float.$fFractionalDouble Main.main5 Main.main4 … Main.main4 = GHC.Types.D# 3.0e7## … Main.main5 = GHC.Types.D# 1.0## ``` Why? There should be nothing stopping it from doing ``` Main.$wgo = \ (w_s5xT :: GHC.Prim.Double#) (ww_s5xX :: GHC.Prim.Int#) (ww1_s5xY :: GHC.Prim.Double#) -> case w_s5xT of wild_Xz { __DEFAULT -> Main.$wgo (GHC.Prim.+# wild_Xz 1#) (GHC.Prim.+# ww_s5xX 1#) (GHC.Prim.+## ww1_s5xY wild_Xz); 3.0e7## -> (# GHC.Prim.+# ww_s5xX 1#, GHC.Prim.+## ww1_s5xY 3.0e7## #) ``` Perhaps it's afraid to make the pattern match on a floating point number? Insights welcome. [1]: https://stackoverflow.com/questions/3300995/computing-the-mean-of-a-list-ef… [2]: https://stackoverflow.com/a/45840148/1432740 -- Mateusz K.

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Managing a sum type with a lot of constructors
by Adam Flott 24 Aug '17

24 Aug '17

I have a sum type with a lot of constructors and I'm not sure how to represent the type with maintainability in mind. For example, data A = A1 | A2 Int | A3 Text Int32 Bool | ... | A100 Bool Every inner type is concrete. There are 100+ constructors with no sign of ever getting reduced. What technique would you recommend to keep the sum type approach but not having to define them all in one spot? I'm thinking 1 inner type + 1 function to construct per file (if that's possible).

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[ANN] HSvm: Haskell bindings to libsvm library
by Pavel Ryzhov 24 Aug '17

24 Aug '17

Hi all, I am happy to announce the new version of HSvm package: http://hackage.haskell.org/package/HSvm The changelog is: 1. Upgraded to libsvm 3.22. 2. Compatibility with GHC 8.0.2 and GHC 8.2.1. 3. Fixed few bugs in marshaling of C structures. 4. Code cleanup. 5. Documentation is improved. HSvm sources are now available on GitHub: https://github.com/paulrzcz/HSvm The package is also available at Stackage Nightly from 2017-08-17: https://www.stackage.org/nightly-2017-08-17/package/HSvm-0.1.0.3.22 Thanks to Paolo Losi for package and cooperation! Cheers, Pavel

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ANN: Compose :: Melbourne Conference and Unconference [Melbourne, Australia - August 28 & 29]
by Lyndon Maydwell 24 Aug '17

24 Aug '17

Since I don't believe I've updated Haskell Cafe since this year's CFP, on behalf of the Melbourne Committee I'm sending a last-minute reminder that Compose :: Conference Melbourne is running this Monday and Tuesday the 28th and 29th! All information is available online at http://www.composeconference.org/ Tickets are on sale for Day-One on Eventbrite: https://www. eventbrite.com/e/compose-melbourne-2017-tickets-34612742645 Programme: http://www.composeconference.org/2017-melbourne/day-one-program/ The second day (unconference) is free for all and will feature workshops, talks, and many other organised and disorganised activities! Unconference Information: http://www.composeconference.org/2017- melbourne/unconference/ Follow the Melbourne event on Twitter: https://twitter.com/ComposeMelb About Compose and Compose :: Melbourne Compose is a conference for functional programmers, focused on technologies such as Haskell, Scala, Clojure, OCaml, F#, SML and others. Functional programming has been taken up widely, by industry and hobbyists alike. For many of us it has renewed our belief that code should be beautiful, and that programming can be as enjoyable as it is practical. Compose is about bringing together functional programmers of all levels of skill and experience — from technical leads to novices, and from long-time hackers to students just getting started. Our experiences have shown that the theoretical can be put into practice with great success, and that topics once considered “advanced” can be made understandable and spread widely. For example, type systems, often considered complex, can simplify our lives by teaching compilers to do some of our reasoning for us. Compose Conference began in New York in 2015. Warm Regards, - Lyndon

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[ANN] tasty-hedgehog: Adds support for the hedgehog property-based testing library to the tasty testing framework
by David Laing 24 Aug '17

24 Aug '17

Hi, I'm happy to announce tasty-hedgehog: https://hackage.haskell.org/package/tasty-hedgehog They are two great flavours that (now) work together, so I hope it's useful to many of you. There's an example of usage in the README on the GitHub page: https://github.com/qfpl/tasty-hedgehog Cheers, Dave

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How to split (or not split) modules
by Clinton Mead 24 Aug '17

24 Aug '17

Given that one can write modules that just do reexports to control namespaces, it seems to me you've got a lot of flexibility about how you organise your actual code into modules. As long as mutually recursive functions are in the same module and instances are not orphan, you can go from the one extreme of placing all the code on one module to the other extreme of placing each function in a separate module. I believe any performance concerns regarding inlining can be addressed with explicit inline annotations. I can see the point of not having non exported functions in their own module, because to do so would mean producing extra interface code which is never directly used by clients. But other than the concerns mentioned above, I can't really work out whether to have all my code for a package in one module and split it with re-export modules, or have it in lots of little modules and combine it with re-export modules. Any guidance with the pros/cons of both approaches would be appreciated.

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