- Haskell-Cafe - Haskell.org

Spurious memory leak example from the wiki
by Christopher Allen 06 Jan '16

06 Jan '16

I can't get the two examples (sum/product) in: https://wiki.haskell.org/Memory_leak#Holding_a_reference_for_a_too_long_time to behave differently under O2 or O0. Same profile report each time. Have changes to prelude (FTP? Rewrite rules/build stuff for folds?) made these do the same thing? The foldl/foldl' examples behave the same as you might expect. (216mb vs. 1mb of heap) --- Chris Allen

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Compose Conference Call for Participation [NYC, Feb 4-5]
by Gershom B 05 Jan '16

05 Jan '16

=============================================== Call for Participation Compose Conference 2016 February 4-5, 2016 New York, NY http://www.composeconference.org/ =============================================== The practice and craft of functional programming :: Conference Compose is a conference for typed functional programmers, focused specifically on Haskell, OCaml, F#, SML, and related technologies. Typed 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. It will feature a keynote by Eugenia Cheng on her work popularizing mathematics, two days of great talks, and plans are underway for a weekend hackathon/unconference. * Invited Talks: Eugenia Cheng: How to Bake 'How to Bake Pi': reflections on making abstract mathematics palatable * Local Information (venue): http://www.composeconference.org/2016/ * Accepted Talks and Tutorials Aditya Siram: FLTKHS - Easy Native GUIs in Haskell, Today! Austin Seipp: Cryptography and Verification with Cryptol Kenneth Foner: 'There and Back Again' and What Happened After Krzysztof Cieslak: Ionide and state of F# open source environment Leonid Rozenberg: The Intersection of Machine Learning, Types and Testing Luite Stegeman: Fun with GHCJSi Markus Mottl: AD-OCaml - Parallel Algorithmic Differentiation for OCaml Mindy Preston: Composing Network Operating Systems Niki Vazou: Liquid Types for Haskell Paulmichael Blasucci: (Nearly) Everything You Ever Wanted to Know About F# Active Patterns but were Afraid to Ask Rachel Reese: Chaos Testing at Jet Riccardo Terrell: Functional Reactive Programming for Natural User Interface Stephen Compall: Add a type parameter! One 'simple' design change, a panoply of outcomes Stephanie Weirich: Dynamic Typing in GHC Tikhon Jelvis: Analyzing Programs with Z3 Zvonimir Pavlinovic, Tim King and Thomas Wies: Improving Type Error Localization for Languages with Type Inference * Full abstracts: http://www.composeconference.org/2016/speakers/ * Registration: http://composeconference.eventbrite.com * Follow @composeconf on twitter for news: https://twitter.com/composeconf * On freenode irc, chat will fellow attendees at #composeconference * Corporate sponsorships are welcome. Current sponsors list forthcoming. * Policies (diversity and anti-harassment): http://www.composeconference.org/conduct * Email us with any questions at info(a)composeconference.org * Please forward this announcement to interested parties and lists.

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Haskell popularity
by Henk-Jan van Tuyl 04 Jan '16

04 Jan '16

L.S., Haskell scores quite high on GitHub and Stack Overflow, see: http://redmonk.com/sogrady/2015/07/01/language-rankings-6-15/ Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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wxHaskell + GHCi
by Henk-Jan van Tuyl 03 Jan '16

03 Jan '16

L.S., For people who gave up on wxHaskell in the past, because wxHaskell didn't run (properly) in GHCi: I just found out, that wxHaskell programs run properly in GHCi on Windows, if you use the newest wxHaskell plus GHC 7.10.3 (both the 32 bit and the 64 bit version). Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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For one cabal'ised library: running specific benchmarks & tests, and obtaining multiple Travis reports
by Rob Stewart 03 Jan '16

03 Jan '16

Hi, Three questions: 1) running specific criterion benchmark groups, 2) running specific test-framework test groups, and 3) getting multiple Travis CI reports for one cabal'ised library. 1. Running specific criterion benchmark groups Given this benchmark harness: main = defaultMain [ bgroup "fib" [ bench "1" $ whnf fib 1 , bench "5" $ whnf fib 5 , bench "9" $ whnf fib 9 , bench "11" $ whnf fib 11 ] ] How do I run one specific group benchmar, or a specific benchmark in a specific group? Can I run: $ cabal bench "fib" or $ cabal bench "fib/1" 2. Running specific test-framework test groups Given this test harness with test-framework: main = defaultMain tests tests = [ testGroup "Sorting-Group-1" [ testProperty "sort1" prop_sort1, testProperty "sort2" prop_sort2, testProperty "sort3" prop_sort3 ], testGroup "Sorting-Group-2" [ testProperty "sort4" prop_sort4, testProperty "sort5" prop_sort5, testProperty "sort6" prop_sort6, testCase "sort7" test_sort7, testCase "sort8" test_sort8 ] ] Can I run: $ cabal test "Sorting-Group-1" or $ cabal test "Sorting-Group-1/sort3" 3. Separating cabal'ised project to separate Travis CI badges For my current project, I get one Travis CI report for all of HUnit and QuikCheck tests I write for a cabal'ised library expressed with test-framework. For example, if 108 tests fail I get one Travis CI report saying #108 failing tests, and I get one Travis CI badge of the form: https://travis-ci.org/<my_username>/<library_name>.png?branch=master What I'd really like is to retrieve multiple Travis CI reports and multiple Travis CI badges for one Haskell libray. E.g. API tests: passing (with a URL for a green badge). Parser tests: #108 failing (with a URL for a red badge). Messaging tests: #16 failing (with a URL for a red badge). How could I refactor my test groups so that Travis CI will provide me multiple reports for one cabal'ised project? Thanks! -- Rob Stewart

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Month in haskell-ide-engine December 2015
by Alan & Kim Zimmerman 02 Jan '16

02 Jan '16

Welcome Haskell IDE Engine (future) users, [also available online at https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2015-…] Haskell IDE Engine progress report for December 2015. What is Haskell IDE Engine? Not an IDE, still no release, it is a work in progress. It is a common point to join together the effort of integrating tools into an IDE and the effort of writing tools for an IDE, by providing an API in the middle that each of these parties can work from and to. Important developments This month has been mostly about turning ideas into practice, and dealing with the details that come out when things become concrete. The more concrete things we have are: 1. Auto-generated API documentation (@cocreature) One of the principles of HIE is that each plugin/command provides a PluginDescriptor documenting the commands it provides, parameters they take and return types. Moritz Kiefer has created a module[1] to take this information and generate API documentation[2]. The information is present, but help with styling / presentation will be gladly accepted. [1] https://github.com/haskell/haskell-ide-engine/tree/master/hie-docs-generator [2] https://haskell.github.io/haskell-ide-engine/ 2. Leksah context menu (@jpmoresmau) JP Moresmau has extended the Leksah integration[3][4] to now provide a context-specific menu providing available HIE commands. This includes the ability to invoke HaRe to do refactorings. To enable this we now have a specific hie-base[5] module with just the basic types which can be included in the IDE side if it is fortunate enough to use haskell. [3] https://github.com/JPMoresmau/leksah/tree/hie_integration [4] https://github.com/JPMoresmau/leksah-server/tree/hie_integration [5] https://github.com/haskell/haskell-ide-engine/tree/master/hie-base 3. Deeper Emacs integration (@cocreature) The Emacs integration uses the PluginDescriptor to generate a set of elisp functions corresponding to each plugin command. The macro generating these has been extended to populate the docstrings for these. It also handles the HieDiff return type which means it can apply the changes from a HaRe refactoring, or any other plugin generating a diff. It prompts interactively for any additional parameters required. 4. New plugins applyrefact is a wrapper around Matthew Pickering's library to apply hlint changes to source code. egasync is an example wrapper showing how a plugin can launch its own process in the server and stream output from it back to the IDE, if the transport used supports this. Otherwise the transport will batch it up when a request is received for the output. Current project focus The current project focus is still on getting our collective heads straight on what actually needs to be done, and providing working integrations to at least 2 IDEs to get a better feel for what is needed. Both of these are well in hand, and if anyone would like to join in the discussion happens via the github issue tracker and docs section of the project, as well as IRC at #haskell-ide-engine on freenode. Issues closed in December Decide on matching an existing IDE protocol or designing a new one #2 Representation of arbitrary types for a plugin #14 Plugin function definition #16 Add QuickCheck tests for FromJSON / ToJSON instances #48 Check PluginDescriptor on loading #52 Add a signal handler to flush logs on exit #58 Plugin startup / private data #83 Create a diff type #95 Replace logging package #112 Split between haskell-ide-engine and haskell-plugin-api #118 Document existance of module-management package and ghc-vis #124 Provide ghc-modi transport? #125 Sort out ghc-mod session management #127 Git integration #128 apply-refact plugin #131 emacs: how to run hie with arguments / logging #134 Change HieDiff to represent a standard patch format #138 Pull requests merged in December Detect plugin param name collisions #115 Bring in a diff type, and introduce semantic types #116 New logger #120 Rework api split #122 (elisp) Add log of hie process input / output #123 Ghc mod session #130 Apply refact plugin #133 Ghc mod find #135 Plugin state #137 Change HieDiff to use a patch format #139 Hare context #141 Initial example async process plugin #143 Base split #144 Support more commands #145 Add tests for hie-create-command #146 Add integration test for hie-hare-rename #147 Move to a plugin/command url scheme #148 Documentation generator #149 Contributors active in December Alan Zimmerman, Daniel Gröber, JP Moresmau, Michael Sloan, Moritz Kiefer, Tobias G. Waaler Contributing Haskell IDE Engine needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-ide-engine Also drop by our IRC channel: #haskell-ide-engine at irc.freenode.net. Thanks!

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Month in Haskell Mode December 2015
by Gracjan Polak 01 Jan '16

01 Jan '16

Welcome Haskell Mode users, Haskell Mode progress report for December 2015. For previous issue see November 2015 <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-November…> . Reddit discussion <https://www.reddit.com/r/haskell/comments/3z063t/month_in_haskell_mode_dece…> . <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>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 constantly looking for contributions. For more information see https://github.com/haskell/haskell-mode. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>Important developments Font locking now knows how to use language specific syntax coloring for quasi quotes. {-# LANGUAGE QuasiQuotes #-} query conn [sql| SELECT column_a, column_b FROM table1 NATURAL JOIN table2 WHERE ? <= time AND time < ? AND name LIKE ? ORDER BY size DESC LIMIT 100 |] (beginTime,endTime,string) Indentation learned how to indent multiline strings with continuation escapes, for example: main = putStrLn "Multiline\n\ \Hello\n\ \World!\n" <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>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-December…>Issues closed in December - Flymake produce temp file without cleaning it up #130 <https://github.com/haskell/haskell-mode/issues/130> - haskell-indentation's behaviour is slightly different from haskell-indent #208 <https://github.com/haskell/haskell-mode/issues/208> - Support shallow indentation #366 <https://github.com/haskell/haskell-mode/issues/366> - flymake-init uses nil haskell-saved-check-command #384 <https://github.com/haskell/haskell-mode/issues/384> - haskell-mode prompts for a new session every emacs session #407 <https://github.com/haskell/haskell-mode/issues/407> - On opening a file, haskell-doc opens several files defined in import section #742 <https://github.com/haskell/haskell-mode/issues/742> - haskell-indentation-indent-region and smartparens interact poorly #796 <https://github.com/haskell/haskell-mode/issues/796> - Is it possible to use ghci-ng with "stack-ghci" haskell-process-type? #889 <https://github.com/haskell/haskell-mode/issues/889> - Use caching docker TravisCI infrastructure #910 <https://github.com/haskell/haskell-mode/issues/910> - Makefile doesn't work in a shell under emacs #972 <https://github.com/haskell/haskell-mode/issues/972> - Emacs hangs when typing behind whitespace #980 <https://github.com/haskell/haskell-mode/issues/980> - Make haskell-indentation-phrase-rest non-recursive #998 <https://github.com/haskell/haskell-mode/issues/998> - Case indentation error #1000 <https://github.com/haskell/haskell-mode/issues/1000> - Stray ^H characters appear in haskell-process-log #1009 <https://github.com/haskell/haskell-mode/issues/1009> - Broken indentation in Emacs 24.5 #1013 <https://github.com/haskell/haskell-mode/issues/1013> - Haskell indentation weirdly re-indents lines after sp-kill-sexp #1031 <https://github.com/haskell/haskell-mode/issues/1031> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>Pull requests merged in December - Remove horizontal whitespace based smart indentation mode haskell-simple-indent #958 <https://github.com/haskell/haskell-mode/pull/958> - Remove haskell-bot.el #960 <https://github.com/haskell/haskell-mode/pull/960> - Bump version to 13.17-git #1007 <https://github.com/haskell/haskell-mode/pull/1007> - Guard stack overflow, introduce a test #1008 <https://github.com/haskell/haskell-mode/pull/1008> - Failing testcase for bug #981: M-j to continue a comment on the next lines indents the next line #1010 <https://github.com/haskell/haskell-mode/pull/1010> - Non-recursive haskell-indentation-phrase-rest #1011 <https://github.com/haskell/haskell-mode/pull/1011> - Add test for a case expression with multiple paths on their own lines. #1016 <https://github.com/haskell/haskell-mode/pull/1016> - Check indentation per line #1017 <https://github.com/haskell/haskell-mode/pull/1017> - Show expected result first in haskell indentation tests #1018 <https://github.com/haskell/haskell-mode/pull/1018> - Support shallow indentation #1019 <https://github.com/haskell/haskell-mode/pull/1019> - Use vanilla buffer file name for hlint command #1020 <https://github.com/haskell/haskell-mode/pull/1020> - Use Trusty platform for TravisCI #1021 <https://github.com/haskell/haskell-mode/pull/1021> - Find Emacs once #1023 <https://github.com/haskell/haskell-mode/pull/1023> - Case expression indentation fix #1024 <https://github.com/haskell/haskell-mode/pull/1024> - Simpler apt-get #1025 <https://github.com/haskell/haskell-mode/pull/1025> - Fix align imports for modules named "Instance" #1028 <https://github.com/haskell/haskell-mode/pull/1028> - Add some common extensions to haskell-rgrep #1029 <https://github.com/haskell/haskell-mode/pull/1029> - Remove haskell-indentation-dyn-first-position #1030 <https://github.com/haskell/haskell-mode/pull/1030> - Cleanup tests with with-temp-switch-to-buffer #1033 <https://github.com/haskell/haskell-mode/pull/1033> - Indent multiline strings #1035 <https://github.com/haskell/haskell-mode/pull/1035> - Implement font-lock for quasi quoted XML, HTML and JavaScript #1036 <https://github.com/haskell/haskell-mode/pull/1036> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…>Contributors active in December Emmanuel Touzery, Gracjan Polak, Sergey Vinokurov, Wayne Lewis, vwyu <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-December…> 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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Question on nested fmaps.
by David Banas 31 Dec '15

31 Dec '15

Is this true, in general?: fmap h (fmap g f) == fmap (h . g) f Is there a simple proof? Thanks, -db

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Naming inner elements
by amindfv＠gmail.com 31 Dec '15

31 Dec '15

I've looked all around but haven't found a nice syntax for this -- anyone have suggestions?: What I'd like to do is assign toplevel variable names to inner elements of a structure. Pseudocode for what I'd like to do is: things = [ foo@"thing1" , bar@"thing2" ] The major difference from just `foo = "thing1" ; things = [foo, ...` is that it's much more visually clear which values are in `things` (imagine I create a `baz` but forget to add it to `things`). The best I've found (which is not at all ideal) is to say e.g.: things@ [ foo , bar , baz ] = ["thing1", "thing2", "thing3"] But of course, for starters, I run off the page very quickly. I don't see anything in the usual places (e.g. the Haskell Report), but has anyone come across this and found an elegant solution? Thanks! Tom

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costate
by Peter Padawitz 31 Dec '15

31 Dec '15

When is cobinding in the costate/funarg/incontext comonad (c -> a,c) (see papers by Kieburtz, Uustalu, Vene, Orchard, Mycroft, …) preferable to (better-known) currying? f <<= (g,x) is equivalent to (curry f g,x) ! HNY, Peter

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