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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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Fwd: Fwd: Compatibility etiquette for apps, with cabal sandboxes and `stack`
by Paolo Giarrusso 30 Nov '15

30 Nov '15

On 29 November 2015 at 20:12, Michael Orlitzky <michael(a)orlitzky.com> wrote: > On 11/29/2015 01:37 PM, Omari Norman wrote: >> >> Distribution packagers are savvy enough to use stack. > > Ignoring the question of *how* that might work, most distributions > forbid bundled dependencies because it creates a maintenance nightmare > and fills our users' machines with untraceable security vulnerabilities. But doesn't Haskell do static linking (usually) and cross-module inlining? Or are you fine with static linking as long as it's somehow tracked by the package manager, so that upgrading some-vuln-lib from 1.0 to 1.1 forces upgrading all client programs (looks quite doable at least with Debian packages)? -- Paolo G. Giarrusso - Ph.D. Student, Tübingen University http://ps.informatik.uni-tuebingen.de/team/giarrusso/ -- Paolo G. Giarrusso - Ph.D. Student, Tübingen University http://ps.informatik.uni-tuebingen.de/team/giarrusso/

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Fwd: Fwd: Compatibility etiquette for apps, with cabal sandboxes and `stack`
by Sven Panne 30 Nov '15

30 Nov '15

[... and now to the whole list, I hate gmail's defaults... :-] ---------- Forwarded message ---------- From: Sven Panne <svenpanne(a)gmail.com> Date: 2015-11-29 21:12 GMT+01:00 Subject: Re: [Haskell-cafe] Fwd: Compatibility etiquette for apps, with cabal sandboxes and `stack` To: Imants Cekusins <imantc(a)gmail.com> 2015-11-29 20:52 GMT+01:00 Imants Cekusins <imantc(a)gmail.com>: > [...] What if the top package (in namespace) contained major version? > > E.g. Cabal_1_22 > > below packages might use minor versions - basically, whenever api changes, > change the version part of the affected package. [...] > As a developer, what should I import if my program/library works with e.g. the version range [1.20 .. 1.23]? It definitely can't be import Cabal_1_23.Foo.Bar because if it later still works with e.g. 1.24, I would have to rename all my imports. And always using the lower bound is probably too restrictive, unless I'm mistaken... In general I think it's a bad idea to spread build dependencies all over the code. Cheers, S.

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make a server & connect to it - strange behavior
by Patrick Redmond 30 Nov '15

30 Nov '15

Hi Haskell Cafe, When I start a web server (http-server:Network.HTTP.Server.serverWith) on a separate thread (async:Control.Concurrent.Async.withAsync) and then try to retrieve a response from the server (HTTP:Network.Browser.*) on a threaded runtime, I see either - connection refusals or - deadlock. Before I sink time into reading the source of the packages in question, does anybody see what's wrong with the code below? Increasing the timeout to wait for the server to initialize doesn't solve the problem. Using a bound thread doesn't solve the problem. I'm compiling with options "-threaded -rtsopts -with-rtsopts=-N". Thank you for taking a look. --Patrick This test project is on github. <https://github.com/plredmond/http-server-test-hs/blob/master/src/Lib.hs> module Lib ( someFunc ) where import Control.Monad.IO.Class (liftIO) import qualified Control.Concurrent as Concurrent import qualified Control.Concurrent.Async as Async import qualified Control.Exception as Exception import qualified Data.Maybe as Maybe import qualified Network.Browser as Browser import qualified Network.HTTP as HTTP import qualified Network.HTTP.Server as Server import qualified Network.HTTP.Server.Logger as ServerL import qualified Network.HTTP.Server.Response as ServerR import qualified Network.URI as URI someFunc :: IO (Either Exception.SomeException (URI.URI, HTTP.Response String)) someFunc = do Async.withAsync (Server.serverWith config handler) $ \_ -> do Concurrent.threadDelay . round $ 2e6 Exception.try . Browser.browse . Browser.request . Browser.defaultGETRequest $ uri where uri = Maybe.fromJust . URI.parseURI $ "http://localhost:8080/" config = Server.Config ServerL.stdLogger "localhost" 8080 handler _ url req = return (ServerR.respond ServerR.OK :: Server.Response String)

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Fwd: Compatibility etiquette for apps, with cabal sandboxes and `stack`
by Omari Norman 30 Nov '15

30 Nov '15

On Sun, Nov 29, 2015 at 6:54 AM, Paolo Giarrusso <p.giarrusso(a)gmail.com> wrote: > Hi all, > > IIUC, people used to spend nontrivial effort making their Haskell tools > work across a range of dependencies, and be careful about dropping support > for older ones. > Given the tools we had, this was not easy. I was never aware of any tool that substantially helped with making sure that a package remained compatible with the range of packages that was theoretically allowed by the package's .cabal file. > Do cabal sandboxes or Stack reduce that need, at least for applications?* > Or conversely, how bad is it to restrict support to users having them? I > guess I am asking about common policies, but this probably depends on > adoption of those tools. > > IMO there is really no one right answer to this question. It depends on how nice you are, or whether someone is paying you. Obviously if someone is paying you, do as she says or do what she needs. If no one is paying you, then how nice do you want to be by expending the work? Honestly I'm not very nice. I keep stuff working in the current Stackage Nightly but that's it. Maintaining compatibility with huge dependency matrices is just an enormous amount of work. In my view, someone installing an application can just use stack and Stackage.

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Semi-closed handles and I/O errors: misleading documentation?
by Daniel Díaz 30 Nov '15

30 Nov '15

In the documentation for System.IO <http://hackage.haskell.org/package/base-4.8.1.0/docs/System-IO.html>, we find the following assertion: Any I/O errors encountered while a handle is semi-closed are simply discarded. also this other one: Encoding and decoding errors are always detected and reported, except during lazy I/O (hGetContents, getContents, and readFile), where a decoding error merely results in termination of the character stream, as with other I/O errors. Is this really correct, though? This SO question <http://stackoverflow.com/questions/16257037/detecting-i-o-exceptions-in-a-l…> says that exceptions found during lazy I/O are thrown from pure code, and a small experiment <http://stackoverflow.com/a/33985047/1364288> seems to confirm it. I personally prefer that behaviour, by the way. Perhaps the documentation should be updated?

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Re: [Haskell-cafe] Compatibility etiquette for apps, with cabal sandboxes and `stack`
by Paolo Giarrusso 30 Nov '15

30 Nov '15

On Sunday, November 29, 2015 at 1:23:58 PM UTC+1, Michael Snoyman wrote: > > For your particular example, you can use the transformers-compat package. > Thanks, that's useful! But to answer your general question: for applications, I strongly advocate > supporting just a single set of package version combos for dependencies. > Stack does do this by default, but cabal freeze files can get you most of > the way there too (barring some corner cases with different OSes and > OS-specific packages). > > I'm sure others will disagree with this recommendation, but I see no > reason to absorb a large amount of compatibility work just so that two > installations of the same application may end up behaving differently at > runtime because of differences in the behavior of a dependency. > Personally, I switched all the way to stack. I added mention of cabal sandboxes to address anybody who didn't switch yet or who prefers to stick to cabal.

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Compatibility etiquette for apps, with cabal sandboxes and `stack`
by Paolo Giarrusso 29 Nov '15

29 Nov '15

Hi all, IIUC, people used to spend nontrivial effort making their Haskell tools work across a range of dependencies, and be careful about dropping support for older ones. Do cabal sandboxes or Stack reduce that need, at least for applications?* Or conversely, how bad is it to restrict support to users having them? I guess I am asking about common policies, but this probably depends on adoption of those tools. As in: a) without sandboxes or Stack, packages need to build with whatever environment is there. b) with either of sandboxes or Stack, you can just specify the environment and get it. With Stack, you can even specify whichever (supported) GHC you want, without impacting the environment. Concretely, Control.Monad.Trans.Error is deprecated in transformers-0.4.3.0, but the replacement Control.Monad.Trans.Except does not exist in transformers-0.3.x, thus in the one-but-last Haskell Platform (2014.2.0.0). Hence, fixing the deprecation would make this application hard to install** for some users, including past me (around two months ago).*** Would you apply such a patch? Would you keep it out? Or would you even use CPP (something I'd really like to avoid)? Cheers, Paolo * I take for granted libraries are a different matter — composing libraries means intersecting their supported versions. ** I'll omit detailing "hard to install", because that's a matter of opinion; I considered `constraint: transformers installed` necessary in my cabal config (https://www.vex.net/~trebla/haskell/cabal-cabal.xhtml) and I've read that's becoming the default in the HP, so I think users are entitled to this opinion. *** This particular app has a tiny userbase, so my question is a curiosity.

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How to create a Wiki account?
by Jeffrey Brown 29 Nov '15

29 Nov '15

This [1] is as close as I can seem to get. I noticed [2] had obsolete information; it says Either is not by default a Monad. [1] https://wiki.haskell.org/HaskellWiki:New_accounts [2] https://wiki.haskell.org/Failure -- Jeffrey Benjamin Brown

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