December 2015 - Haskell-Cafe

[ANN] clang-pure-0.1.0.0: Pure C++ code analysis
by Patrick Chilton 01 Dec '15

01 Dec '15

Hi everyone, I've been working on a pure binding to libclang that lets you easily analyze any code that the Clang compiler understands. Github: https://github.com/chpatrick/clang-pure Hackage: http://hackage.haskell.org/package/clang-pure Haddock: http://chpatrick.github.io/clang-pure/ libclang documentation: http://clang.llvm.org/doxygen/group__CINDEX.html A short example that prints out the type of every function in a header file (very useful for binding generation): main = do idx <- createIndex tu <- parseTranslationUnit idx "foo.h" [] let root = translationUnitCursor tu funDecs = root ^.. cosmosOf cursorChildrenF . filtered (\c -> cursorKind c == FunctionDecl) . folding (\c -> fmap (\t -> ( cursorSpelling c, typeSpelling t )) (cursorType c)) for_ funDecs $ \(f, t) -> putStrLn $ BS.unpack f ++ " :: " ++ BS.unpack t Or to find the number of gotos: gotoCount = lengthOf (cosmosOf cursorChildrenF . filtered (\c -> cursorKind c == GotoStmt)) root (This uses lens, but the library itself only has one optional lens-style function). Please refer to libclang's good documentation for an explanation of the functions. The only thing to keep in mind is that functions clang_foo are renamed to just foo, functions clang_getBar are renamed to just bar, and types CXBaz are renamed to just Baz in the Haskell bindings. Under the hood, a reference counting system ensures that the C objects are freed at the right time and in the right order, which allows the public API to be simple and pure. The bindings are not yet complete, so if you find something missing please make an issue or better yet send a pull request. :) Patrick

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Month in Haskell Mode November 2015
by Gracjan Polak 01 Dec '15

01 Dec '15

Welcome Haskell Mode users, Haskell Mode progress report for November 2015 (online version <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…> ). For previous issue see October 2015 <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…> . Go to Reddit discussion <https://www.reddit.com/r/haskell/comments/3uz7jl/month_in_haskell_mode_nove…> . <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>What is Haskell Mode? Haskell Mode is an umbrella project for multiple Emacs tools for efficient Haskell development. Haskell Mode is an open source project developed by a group of volunteers. For more information see https://github.com/haskell/haskell-mode. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Important developments The bug that everybody was waiting for <https://github.com/haskell/haskell-mode/issues/962> was fixed! No more 'Illegal token' in indentation. Rejoice! <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Coming release In the beginning of December we plan to tag new stable release of haskell-mode with current state of the repo (plus possible bugfixes). <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Competitive projects Haskell editor landscape is growing and there are compelling propositions all over the place: - Atom IDE-Haskell <https://atom.io/packages/ide-haskell> - Haskell Vim IDE <https://github.com/begriffs/haskell-vim-now> - Leksah - Haskell IDE in Haskell <http://leksah.org/> - Haskell for Mac <http://haskellformac.com/> There is an idea turning into reality that there should be a common infrastructure powering all of the above. It is brewing in Haskell IDE Engine <https://github.com/haskell/haskell-ide-engine> repo. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Cruft removal, reminder Last month we declared that we plan to remove some cruft. Note that SCC functions got salvaged and now they are fully functional part of haskell-mode! Killing list for December: - Remove haskell-bot.el <https://github.com/haskell/haskell-mode/pull/960> - Remove horizontal whitespace based smart indentation mode haskell-simple-indent <https://github.com/haskell/haskell-mode/pull/958> - Remove Unicode input method <https://github.com/haskell/haskell-mode/pull/939> - Remove haskell-checkers.el <https://github.com/haskell/haskell-mode/pull/959> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Current project focus Current project focus is to lower entry barrier for newcomers by defining bite-sized tasks. Get 50 'well-defined-tasks' done as by the metric: https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de… A 'well-defined-task' is a category of tasks that have the field cleared for them, questions already sorted out and detailed information how to get them done. So you can just sit, search for 'well-defined-task' label and enjoy the coding! The point is to lower the entry barrier for new users, new issue reporters and advanced programmers but Emacs lisp beginners to contribute to the project. Current status: 14 well-defined-tasks closed <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> plus 13 more open <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> . If only you can help with reaching our targets please do so! <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Issues closed in November - Repl hanging #447 <https://github.com/haskell/haskell-mode/issues/447> - On opening a file, haskell-doc opens several files defined in import section #742 <https://github.com/haskell/haskell-mode/issues/742> - Indentation has been spoiled #782 <https://github.com/haskell/haskell-mode/issues/782> - Refactor load-or-reload #807 <https://github.com/haskell/haskell-mode/issues/807> - Make import sorting/aligning optional #914 <https://github.com/haskell/haskell-mode/issues/914> - Remove possibility of 'Illegal token' from haskell-indentation #962 <https://github.com/haskell/haskell-mode/issues/962> - Can't edit a buffer while resolving merge conflict because Invalid Token error. #969 <https://github.com/haskell/haskell-mode/issues/969> - C pragma and Illegal token: else #970 <https://github.com/haskell/haskell-mode/issues/970> - Please do not make haskell-mode non-useful without ghc-mod #974 <https://github.com/haskell/haskell-mode/issues/974> - haskell-process-load-file: cabal test-suite wants to inject deps into library #979 <https://github.com/haskell/haskell-mode/issues/979> - Parsing failure with type-level lists #982 <https://github.com/haskell/haskell-mode/issues/982> - Stop blocking me from typing my code #985 <https://github.com/haskell/haskell-mode/issues/985> - haskell-process-do-type truncates types too aggressively #988 <https://github.com/haskell/haskell-mode/issues/988> - Code duplication between haskell-process-do-type, haskell-process-insert-type #989 <https://github.com/haskell/haskell-mode/issues/989> - Issues trying to use local version of a package in a layer #993 <https://github.com/haskell/haskell-mode/issues/993> - Emacs haskell-mode: how to send PART of file to repl? #1002 <https://github.com/haskell/haskell-mode/issues/1002> - haskell-process-load-file error (wrong-type-argument number-or-marker-p nil) when code has an error #1004 <https://github.com/haskell/haskell-mode/issues/1004> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Pull requests merged in November - Add haskell-font-lock-tests.el. #957 <https://github.com/haskell/haskell-mode/pull/957> - [Doc] Add stack related configuration for compilation #971 <https://github.com/haskell/haskell-mode/pull/971> - Extract hoogle/hayoo code into haskell-hoogle.el and tidy up #973 <https://github.com/haskell/haskell-mode/pull/973> - Move some docs from wiki to manual #976 <https://github.com/haskell/haskell-mode/pull/976> - Don't spuriously modify tags-table-list's global value #978 <https://github.com/haskell/haskell-mode/pull/978> - Add an additional trigger for pragma suggestions #983 <https://github.com/haskell/haskell-mode/pull/983> - Add hayoo choice as part of hoogle url. #984 <https://github.com/haskell/haskell-mode/pull/984> - Clean up SCC code #986 <https://github.com/haskell/haskell-mode/pull/986> - Truncate multi-line messages less aggressively #990 <https://github.com/haskell/haskell-mode/pull/990> - Spelling #991 <https://github.com/haskell/haskell-mode/pull/991> - Use haskell-process-load-file, not -load-or-reload #992 <https://github.com/haskell/haskell-mode/pull/992> - Add RET, TAB and BACKTAB tests #994 <https://github.com/haskell/haskell-mode/pull/994> - Add case for haskell-debug-parse-module regex to parse #995 <https://github.com/haskell/haskell-mode/pull/995> - Remove duplicate filename in Makefile #996 <https://github.com/haskell/haskell-mode/pull/996> - Remove haskell-indentation-parse-error #997 <https://github.com/haskell/haskell-mode/pull/997> - Fix markup typo in README.md #999 <https://github.com/haskell/haskell-mode/pull/999> - Remove haskell-indentation-parse-error, fixup #1001 <https://github.com/haskell/haskell-mode/pull/1001> - Do not sort imports twice #1003 <https://github.com/haskell/haskell-mode/pull/1003> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…>Contributors active in November Cody Goodman, Daniel Bergey, Gabor Greif, Gracjan Polak, Moritz Kiefer, Sibi Prabakaran, Steve Purcell, Thien-Thi Nguyen <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…> Contributing Haskell Mode needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-mode/wiki Also drop by our IRC channel: #haskell-emacs at irc.freenode.net. Thanks!

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[ANN] dejafu-0.2.0.0: Overloadable primitives for testable, potentially non-deterministic, concurrency.
by Michael Walker 01 Dec '15

01 Dec '15

Hi cafe, I am happy to announce a new release of Déjà Fu, my library for testing concurrent Haskell programs! Things have advanced significantly since the paper I presented at the Haskell Symposium this year, both in terms of performance and functionality. Git: https://github.com/barrucadu/dejafu Hackage: https://hackage.haskell.org/package/dejafu-0.2.0.0 ## What is it? Déjà Fu is a library for developing and testing concurrent Haskell programs, it provides a typeclass-abstraction over GHC's regular concurrency API, allowing the concrete implementation to be swapped out. Why do we need this? Well, concurrency is really hard to get right. Empirical studies have found that many real-world concurrency bugs can be exhibited with small test cases using as few as two threads: so it’s not just big concurrent programs that are hard, small ones are too. We as programmers just don’t seem to have a very good intuition for traditional threads-and-shared-memory-style concurrency. The typical approach to testing concurrent programs is to just run them lots of times, but that doesn’t provide any hard coverage guarantees, and then we need to wonder: how many runs do we need? Fortunately, there has been a lot of research into testing concurrency in the past several years. Systematic concurrency testing is an approach where the source of nondeterminism, the actual scheduler, is swapped out for one under the control of the testing framework. This allows possible schedules to be systematically explored, giving real coverage guarantees for our tests. This is a library implementing systematic concurrency testing. It provides two typeclasses, MonadConc to abstract over much of Control.Concurrent and related modules, and MonadSTM, to similarly abstract over Control.Monad.STM. For examples, see the test suite and the async-dejafu source: - https://github.com/barrucadu/dejafu/tree/master/dejafu-tests - https://github.com/barrucadu/dejafu/tree/master/async-dejafu If you want to read more: - Recent technical report: http://misc.barrucadu.co.uk/pub/dejafu-techreport.pdf - Haskell Symposium paper about version 0.1.0.0: http://www.barrucadu.co.uk/publications/dejafu-hs15.pdf - A slew of things on my blog: http://www.barrucadu.co.uk/posts.html ## Changelog New stuff: - Relaxed memory: CRefs now behave just like IORefs, and testing can use one of three different memory models: sequential consistency, total store order (the default), and partial store order. - Support for 'yield'. - Integration with HUnit and tasty: https://hackage.haskell.org/package/hunit-dejafu https://hackage.haskell.org/package/tasty-dejafu - Version of the async library reimplemented to use MonadConc: https://hackage.haskell.org/package/async-dejafu - Fair bounding: which allows yield-based constructs like spinlocks to be tested without causing infinitely-long executions. - Length bounding: which allows for potentially non-terminating computations to be tested. Improvements: - Now uses partial-order reduction to cut down on the number of schedules to try, which is a *huge* improvement over just pre-emption bounding, which is what 0.1.0.0 did. - The 'autocheck' function has prettier output. ## How to use it: If you’re not making use of any IO in your code other than for concurrency, the transition to using MonadConc and MonadSTM will probably just be a textual substitution: - IO is replaced with MonadConc m => m - STM with MonadSTM m => m - *IORef with *CRef - *MVar with *CVar - *TVar with *CTVar - Most other things have the same name, and so can be replaced by just swapping imports around. If you are using other IO, you will need a gentle sprinkling of MonadIO and liftIO in your code as well. ## Is this really just a drop-in replacement for IO/STM? That’s the idea, yes. More specifically, the IO instance of MonadConc and the STM instance of MonadSTM just use the regular IO and STM functions, and so should have no noticeable change in behaviour. There are some differences which can lead to incorrect results when testing, but which should not affect code when used in an IO or STM context. Specifically: Control.Monad.Conc.Class.getNumCapabilities can lie to encourage more concurrency when testing; and Control.Exception.catch can catch exceptions from pure code, but Control.Monad.Conc.Class.catch can’t (except for the IO instance). -- Michael Walker (http://www.barrucadu.co.uk)

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