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[ANN] acme-dont-1.2 - a "don't" construct
by Jack Kelly 02 Apr '20

02 Apr '20

Hello all, I have taken over the maintainership of acme-dont, and am pleased to announce a new acme-dont release on Hackage[1]. acme-dont provides a `don't` function, which does not execute its argument. For example, the following code will not print anything: import Acme.Dont (don't) quiet :: IO () quiet = don't $ putStrLn "You'll never see this on stdout" New in this release: * `don't` has been generalised from `Monad` to `Applicative`. If you have been waiting since GHC 8.0.1's release in 2016[2] to use `don't` with `-XApplicativeDo`, wait no longer. * A test suite, to ensure that `don't` does not do anything. Previous versions could have been defined as `don't = void` for all we knew. Also, the acme-dont community now has a new home on sourcehut. On there, you can find the following invaluable resources: * A source repository[3], to track further developement and new ways of not doing things, with a commit history reconstructed from the release tarballs uploaded to Hackage. * A mailing list[4] for the acme-dont community to discuss the best ways of not doing things. * A bug tracker[5] to handle reports, in case someone observes acme-dont doing something. * Continuous integration[6], to ensure that acme-dont continues to not do things across multiple versions of GHC. I would like to thank Gracjan Polak for uploading the initial releases of `acme-dont`, and for maintaining the package these past eleven years. I do not intend to betray the responsibility he has assigned me in handing over this critical package. Best, -- Jack [1]: https://hackage.haskell.org/package/acme-dont-1.2 [2]: https://www.haskell.org/ghc/download_ghc_8_0_1 [3]: https://git.sr.ht/~jack/acme-dont [4]: https://lists.sr.ht/~jack/acme-dont-discuss [5]: https://todo.sr.ht/~jack/acme-dont [6]: https://builds.sr.ht/~jack/acme-dont

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Using State monad with lens
by Michael Hull 02 Apr '20

02 Apr '20

Hi, I use the State monad in a lot of places, but when I use it with the lens library, I find myself writing code like: myFunc :: StateT MyState ([ResultType]) myFunc = do st <- get case st ^. some_property of True -> do my_value .= "Hello" True -> do my_value .= "Goodbye" I want to do something based on a 'state-variable', but I have to write 'get' -- is there a pattern that allows me to avoid the intermediate 'st' variable? I want to write something like: myFunc = do case (get ^. some_property) of True -> do my_value .= "Hello" True -> do my_value .= "Goodbye" but that won't compile. Best wishes, Mike

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Re: [Haskell-cafe] [ANN] acme-dont-1.2 - a "don't" construct
by Jack Kelly 02 Apr '20

02 Apr '20

Dear Henk-Jan, You can view the preprint yourself with the following commands: $ true > dont.txt $ less dont.txt You'll then start seeing it everywhere you look, and I'm not sure that wider distribution is possible. -- Jack "Henk-Jan van Tuyl" <b.vantuyl1(a)upcmail.nl> writes: > Thanks, > > The `don't` function is a big step forward in computering; it will > surely prevent many bugs from occurring, with little effort to > software developers. > > Is it published in a scientific magazine yet? > > Regards, > Henk-Jan van Tuyl > > > On Wed, 01 Apr 2020 10:38:08 +0200, Jack Kelly <jack(a)jackkelly.name> wrote: > >> Hello all, >> >> I have taken over the maintainership of acme-dont, and am pleased to >> announce a new acme-dont release on Hackage[1]. >> >> >> acme-dont provides a `don't` function, which does not execute its >> argument. For example, the following code will not print anything: >> >> import Acme.Dont (don't) >> >> quiet :: IO () >> quiet = don't $ putStrLn "You'll never see this on stdout" >> >> >> New in this release: >> >> * `don't` has been generalised from `Monad` to `Applicative`. If you >> have been waiting since GHC 8.0.1's release in 2016[2] to use >> `don't` with >> `-XApplicativeDo`, wait no longer. >> >> * A test suite, to ensure that `don't` does not do anything. Previous >> versions could have been defined as `don't = void` for all we knew. >> >> >> Also, the acme-dont community now has a new home on sourcehut. On there, >> you can find the following invaluable resources: >> >> * A source repository[3], to track further developement and new ways of >> not doing things, with a commit history reconstructed from the release >> tarballs uploaded to Hackage. >> >> * A mailing list[4] for the acme-dont community to discuss the best ways >> of not doing things. >> >> * A bug tracker[5] to handle reports, in case someone observes acme-dont >> doing something. >> >> * Continuous integration[6], to ensure that acme-dont continues to not >> do things across multiple versions of GHC. >> >> >> I would like to thank Gracjan Polak for uploading the initial releases >> of `acme-dont`, and for maintaining the package these past eleven >> years. I do not intend to betray the responsibility he has assigned me >> in handing over this critical package. >> >> Best, >> >> -- Jack >> >> [1]: https://hackage.haskell.org/package/acme-dont-1.2 >> [2]: https://www.haskell.org/ghc/download_ghc_8_0_1 >> [3]: https://git.sr.ht/~jack/acme-dont >> [4]: https://lists.sr.ht/~jack/acme-dont-discuss >> [5]: https://todo.sr.ht/~jack/acme-dont >> [6]: https://builds.sr.ht/~jack/acme-dont >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post.

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mmap Failure in: 24:Counters should be zero
by YueCompl 01 Apr '20

01 Apr '20

Hi mmap maintainers, Today I found the last test case out of 25 failed like: ```bash $ cabal v2-run -f mmaptest mmaptest Resolving dependencies... Build profile: -w ghc-8.6.5 -O1 In order, the following will be built (use -v for more details): - mmap-0.5.9 (exe:mmaptest) (configuration changed) Configuring mmap-0.5.9... Preprocessing executable 'mmaptest' for mmap-0.5.9.. Building executable 'mmaptest' for mmap-0.5.9.. <no location info>: warning: [-Wmissing-home-modules] These modules are needed for compilation but not listed in your .cabal file's other-modules: System.IO.MMap <no location info>: warning: [-Wmissing-home-modules] These modules are needed for compilation but not listed in your .cabal file's other-modules: System.IO.MMap ### Failure in: 24:Counters should be zero tests/mmaptest.hs:256 expected: 0 but got: 4 Cases: 25 Tried: 25 Errors: 0 Failures: 1 ``` And the test code is: ```haskell test_counters_zero = do System.Mem.performGC threadDelay 1000 counters <- c_system_io_counters return (counters @?= 0) ``` I see it is to make sure no resource held open after 1 millisecond after garbage collection is triggered. I tried extending the threadDelay to 10 second and still got 4 thus failing the test, maybe newer machinery of GC with GHC 8.6 should be leveraged to prevent such leakage? I CC haskell-cafe list to seek for broader community help, maybe some one can confirm that I can just live with this specific failure without worries? Thanks & best regards, Compl

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How to make a Hashable instance for (Finite n)?
by David Banas 01 Apr '20

01 Apr '20

What is the most expedient way to get around this error? Could not deduce (Hashable (Finite n)) Thanks, -db

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Research Assistant/Associate Position (Postdoc) at Imperial College London
by David Castro 30 Mar '20

30 Mar '20

Hello, We are looking for candidates for this position at Imperial College London. The official text of the advertisement follows: Department of Computing, Imperial College London Research Assistant/Associate Position (Full Time) 35,477 GBP to 47,579 GBP per annum Reference: ENG01270 Fixed-term: 2 years (with a possible 24 month extension) Starting date: as soon as possible (no later than 1st October 2020) Closing Date: 26th April 2020 The Research Assistant will work under the EPSRC Established Career Fellowship Project, POST: Protocols, Observabilities and Session Types. Imperial College London provides a flexible arrangement to be able to start and work remotely until we re-open the campus (this depends on your nationality and current living address). Please contact with Nobuko Yoshida (n.yoshida(a)imperial.ac.uk) Imperial College London if you would like to apply to the position to have informal discussions. The application deadline is also extendable. ------------------------------------------------------------ The project has particular emphasis on putting theory into practice, by embedding session types in a range of programming languages and applying them to case studies; or developing the links between session types and other areas of theoretical computer science. The research programme includes collaboration with several companies and organisations. Candidates for the post-doc position will need to have expertise in either: 1. programming language design and implementation; or 2. formal semantics, type theory and concurrency theory Different positions will be suitable for different points on the theory/practice spectrum. We are especially interested in candidates with a combination of theoretical and practical skills. For more details, see http://mrg.doc.ic.ac.uk. The focus of Imperial College London Group is theories and applications of (Multiparty) Session Types (JACM,POPL'08) which include: -- Go (POPL'19,ICSE'18,POPL'17,CC'16), Scala (PLDI'19,ECOOP'17,ECOOP'16), F# (CC'18), Erlang (CC'17), Haskell (CC'20,POPL'16), OCaml (SOC), Java (FASE'16,FASE'17), MPI-C (FPL'16,OOPSLA'15,CC'15) and Python (FOAC,LMCS,FMSD); -- session types theories (ESOP'20,POPL'19,ESOP'19,ESOP'16,CONCUR'15), automata theories (CAV'19,CONCUR'19,FoSSaCs'17,TACAS'16,CONCUR'15,POPL'15), game semantics (POPL'19,FoSSaCs'19), Implicit Complexity (LICS'18) and linear logic (ESOP'18,FoSSaCs'18,CONCUR'15); or -- mechanisation of session types meta-theory (Coq, Isabelle, Agda, etc) (TACAS 20) -- other applications such as blockchains (FSE'19) and robotics (ECOOP'19) The contact person is Professor Nobuko Yoshida, Imperial College London (n.yoshida(a)imperial.ac.uk) The candidate is welcome to contact her. Details: https://www.imperial.ac.uk/jobs/description/ENG01270/research-assistant-res…

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[ANN] esqueleto-3.3.3.0: Support for UNION, safer joins, and subquery joins!
by Christian Charukiewicz 30 Mar '20

30 Mar '20

Hi all, My friend Ben Levy and I spent a while writing and documenting Database.Esqueleto.Experimental, a new module in the esqueleto package which adds support for UNION, subqueries, and improves the safety of outer JOINs. We've done a lot of use/testing of this implementation, but it is currently in the Experimental module in order to allow for gathering feedback. It is now live on Hackage as esqueleto-3.3.3.0. The module docs give examples of the new functionality. Feel free to take a take a look here: https://hackage.haskell.org/package/esqueleto-3.3.3.0/docs/Database-Esquele… Thanks, Christian

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gitlab.haskell.org down?
by Ivan Perez 29 Mar '20

29 Mar '20

Hi, Is the Haskell gitlab down or has anything changed? https://downforeveryoneorjustme.com/gitlab.haskell.org Cheers, Ivan

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Re: [Haskell-cafe] Strange error when cabal installing.
by David Banas 28 Mar '20

28 Mar '20

Okay, I was able to get the _Haskell Platform_ approach to work, by doing the following: - Uninstall Haskell Platform. - Reinstall Haskell Platform, overriding the default suggested installation path with something _not containing spaces_. - Change my `~\AppData\Roaming\cabal\config` file from this: ``` extra-prog-path: C:\HaskellPlatform\8.6.5\msys\usr\bin, C:\Users\capnf\AppData\Roaming\cabal\bin ``` to this: ``` extra-prog-path: C:\HaskellPlatform\8.6.5\msys\usr\bin extra-prog-path: C:\Users\capnf\AppData\Roaming\cabal\bin ``` -db

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Why does the Haskell Platform Windows installer suggest a path with spaces?!
by David Banas 28 Mar '20

28 Mar '20

Why does the Haskell Platform Windows installer suggest a default installation path that contains spaces?! This breaks builds: configure:2365: checking build system type configure:2379: result: x86_64-pc-msys configure:2399: checking host system type configure:2412: result: x86_64-pc-msys configure:2487: checking for gcc configure:2514: result: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe configure:2743: checking for C compiler version configure:2752: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe --version >&5 C:\/Users/capnf/Documents/GitHub/gitit/network-3.1.1.1/configure: line 2754: C:\PROGRA~1\Haskell: No such file or directory configure:2763: $? = 127 configure:2752: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe -v >&5 C:\/Users/capnf/Documents/GitHub/gitit/network-3.1.1.1/configure: line 2754: C:\PROGRA~1\Haskell: No such file or directory -db

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