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Haskell 2010 report nit?
by Viktor Dukhovni 18 Dec '19

18 Dec '19

Not sure where to post about this, and it has likely been noted elsewhere already, but reading through the report I see in Section 3.17.2 > • Consider the following declarations: > > newtype N = N Bool > data D = D !Bool > > These examples illustrate the difference in pattern matching between types defined by data and newtype: > > (\ (N True) -> True) ⊥ ⇒ ⊥ > (\ (D True) -> True) ⊥ ⇒ ⊥ > (\ ~(D True) -> True) ⊥ ⇒ True > > Additional examples may be found in Section 4.2.3. But unlike the examples in 4.2.3, which do show differences between "newtype" and "data", the above does not seem to show any actual difference. For that the pattern after the constructor would I believe have to be irrefutable, which "True" is not. Thus, e.g. the below (which duplicates 4.2.3) would do the job: (\ (N _) -> True) ⊥ ⇒ True (\ (D _) -> True) ⊥ ⇒ ⊥ Perhaps I misunderstood something, but if not, and this has not been noted before, it may be worth fixing in the next revision. -- Viktor.

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Practical Aspects of Declarative Languages (PADL 2020) Call for Participation
by Ekaterina Komendantskaya 18 Dec '19

18 Dec '19

PADL 2020 Final Call for Participation: Please see many exciting talks and events at PADL 2020: The 22nd Symposium on Practical Aspects of Declarative Languages https://popl20.sigplan.org/home/PADL-2020 (Early registration by 12/18) Invited Talks Nikolaj Bjørner, Microsoft Research Logical Engines for Cloud Configurations Adnan Darwiche, UCLA Symbolic Reasoning About Machine Learning Systems Invited Experience and Direction Session Invited Talks Molham Aref, Relational AI Relational Artificial Intelligence Mayur Naik, University of Pennsylvania Learning Interpretable Rules from Structured Data Grant Passmore, Imandra Inc. and Cambridge University An Introduction to the Imandra Automated Reasoning System Philip Wadler, University of Edinburgh We Are All Poor Schmucks: On the Value of Gradual Types [image: Nikolaj Bjørner][image: Adnan Darwiche][image: Molham Aref][image: Grant Passmore][image: Mayur Naik][image: Phil Wadler] Complete Program https://popl20.sigplan.org/home/PADL-2020#program This includes also presentations of 10 full papers and 4 short papers; four discussion panels: (1) Programming with Logic for the Masses, (2) Memory and Real-Time Programming in Practice, (3) Reasoning for Machine Learning at Large, and (4) Experience and Direction; and a competitive programming experience session. Registration https://regmaster4.com/2020conf/POPL20/register.php Early rate closes on December 18th

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[ANNOUNCE] lzlib - lzma compression/decompression for Haskell
by Vanessa McHale 18 Dec '19

18 Dec '19

Hi all, I have written http://hackage.haskell.org/package/lzlib, a high-level interface to the lzlib library. Cheers, Vanessa McHale

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10 PhD studentships in Nottingham
by Graham Hutton 17 Dec '19

17 Dec '19

Dear all, The School of Computer Science at the University of Nottingham is seeking applications for 10 fully-funded international PhD studentships: https://tinyurl.com/10-phds-2020 Applicants in the area of the Functional Programming Laboratory (https://tinyurl.com/fp-notts) are strongly encouraged! If you are interested in applying, please contact a potential supervisor as soon as possible (the application deadline is 17th January): Thorsten Altenkirch - constructive logic, proof assistants, homotopy type theory, category theory, lambda calculus. Venanzio Capretta - type theory, mathemZZatical logic, corecursive structures, proof assistants, category theory, epistemic logic. Graham Hutton - not taking on any new students this year, but you may find these notes useful: https://tinyurl.com/scbkxkr Henrik Nilsson - functional reactive programming, domain- specific languages, generalised notions of computation. These positions are only open to international applicants. An advert for UK/EU applicants will be posted in January 2020. Best wishes, Graham +-----------------------------------------------------------+ 10 Fully-Funded International PhD Studentships School of Computer Science University of Nottingham, UK https://tinyurl.com/10-phds-2020 Applications are invited for 10 fully-funded international PhD studentships in the School of Computer Science at the University of Nottingham, starting on 1st October 2020. The topics for the studentships are open, but should relate to the interests of one of the School’s research groups: Agents Lab; Computational Optimisation and Learning Lab; Computer Vision Lab; Functional Programming; Intelligent Modelling and Analysis; Mixed Reality Lab; Data Driven Algorithms, Systems and Design and Uncertainty in Data and Decision Making The studentships are for three and a half years and include a stipend of £15,009 per year and tuition fees. Applicants are normally expected to have a first-class Masters or Bachelors degree in Computer Science or a related discipline, and must obtain the support of a potential supervisor in the School prior to submitting their application. Initial contact with supervisors should be made at least two weeks prior to the closing date for applications. Successful applicants are expected to apply for an International VC Scholarship. Informal enquiries may be addressed to Kathleen.Fennemore(a)nottingham.ac.uk. To apply, please submit the following items by email to: Marc.Williams(a)nottingham.ac.uk: (1) a copy of your CV, including your actual or expected degree class(es), and results of all University examinations; (2) an example of your technical writing, such as a project report or dissertation; (3) contact details for two academic referees. (4) a research proposal – max 2 x sides A4 You may also include a covering letter but this is optional. Closing date for applications: Friday 17 January 2020. +-----------------------------------------------------------+ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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[ANN] Call for Participation: BOB 2020 (February 28, Berlin)
by Stefan Wehr 16 Dec '19

16 Dec '19

================================================================================ BOB 2020 Conference “What happens if we simply use what’s best?” February 28, 2020, Berlin http://bobkonf.de/2020/ Program: http://bobkonf.de/2020/en/program.html Registration: http://bobkonf.de/2020/en/registration.html ================================================================================ BOB is the conference for developers, architects and decision-makers to explore technologies beyond the mainstream in software development, and to find the best tools available to software developers today. Our goal is for all participants of BOB to return home with new insights that enable them to improve their own software development experiences. The program features 14 talks and 8 tutorials on current topics: http://bobkonf.de/2020/en/program.html The subject range of talks includes functional programming, formal methods, architecture documentation, functional-reactive programming, and language design. The tutorials feature introductions to Idris, Haskell, F#, TLA+, ReasonML, and probabilistic programming. Heather Miller will give the keynote talk. Registration is open online: http://bobkonf.de/2020/en/registration.html NOTE: The early-bird rates expire on February 19, 2020! BOB cooperates with racketfest and :clojureD on the day before/after BOB: https://racketfest.com/ https://clojured.de/

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Why many .tix files are generated in Haskell Program Coverage
by F L 16 Dec '19

16 Dec '19

I am using Haskell Program Coverage (HPC) to collect coverage information for Pandoc (https://github.com/jgm/pandoc) However, after adding the -fhpc option to GHC and running the program, two .tix files are generated. One is test-pandoc.tix in the main directory and the other is pandoc.tix under the "test" directory (test/pandoc.tix). These two files have different contents and I just cannot see the meaning of them from their names. Moreover, I tried to execute "hpc show xxx.tix" for them and test/pandoc.tix gives "hpc: hash in tix file for module Main does not match hash in ./.hpc/Main.mix". So, I wonder the specific generation rules of HPC tix files (possibly including the number and location) and how I can get the correct coverage information. Thanks very much!

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[ANNOUNCE] GHC 8.8.2-rc1 is now available
by Ben Gamari 13 Dec '19

13 Dec '19

Hello everyone, The GHC team is proud to announce the first release candidate of GHC 8.8.2. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.8.2-rc1 Release notes are also available [1]. This release fixes a handful of issues affecting 8.8.1: - A bug (#17088) in the compacting garbage collector resulting in segmentations faults under specific circumstances. Note that this may affect user programs even if they did not explicitly request the compacting GC (using the -c RTS flag) since GHC may fallback to compacting collection during times of high memory pressure. - A code generation bug (#17334) resulting in GHC panics has been fixed. - A bug in the `process` library causing builds using `hsc2hs` to fail non-deterministically on Windows has been fixed (Trac #17480) - A typechecker bug (#12088) resulting in programs being unexpectedly rejected has been fixed. - A bug in the implementation of compact normal forms resulting in segmentation faults in some uses (#17044) has been fixed. - A bug causing GHC to incorrectly complain about incompatible LLVM versions when using LLVM 7.0.1 has been fixed (#16990). As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.2-rc1/docs/html/users_guide/8.8.2-not…

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"Deep" Coding Support in Haskell
by Dušan Kolář 12 Dec '19

12 Dec '19

Dear Café, let me allow quite naive question, is there any library/tool/plugin supporting rapid application development in Haskell? I mean something that supports code completion, hints, help, code refactoring etc. Similar to Java support in e.g. Eclipse or IntelliJ IDEA. So far, I've found support for Vim, Eclipse. Nevertheless, my question goes farther - for implicit GUI editor/application development environment like Eclipse. Several years ago, I was able to run something in Eclipse, but not with good results. These days it seems dead (since 2015). Similarly, for IntelliJ IDEA - installed community version, downloaded Haskell plugin, tried to install additional plugins inside IntelliJ IDE, but after that no support for Haskell project (I'm on Arch linux, IDE from AUR, plugin install inside failed, downloaded it from https://plugins.jetbrains.com/plugin/8258-intellij-haskell/ versions[1] and it worked, at least installation, other plugins installed inside IDE worked partially - some of them were disabled by GUI after error). I'm sorry if I'm asking natural question. I've not found any additional how-tos to make it work... Best regards, Dusan -------- [1] https://plugins.jetbrains.com/plugin/8258-intellij-haskell/versions

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stack install ghcide fails
by Dušan Kolář 11 Dec '19

11 Dec '19

Hello Café, Using stack, I've tried stack install ghcide, it reported to put the following into my global extra-deps: - haskell- lsp-0.17.0.0@sha256:ddfcc2798f04bcb1ec20fafc02c03faa197322192578e879cef5852 aba43ebcb,5264 - haskell-lsp- types-0.17.0.0@sha256:9078237412d0596a7d09d432389c8fa21d6f3e21ed2ed761b3 093a21607d6c28,2941 - hie- bios-0.2.1@sha256:5f98a3516ce65e0a3ffd88bf6fb416b04cc084371d0fbf0e1762780d e1d652ce,3219 - rope-utf16- splay-0.3.1.0@sha256:15a53c57f8413d193054bb5f045929edae3b2669def4c6af6319 7b30dc1d5003,2029 Nevertheless, the build failed anyway: stack install ghcide ghcide> configure ghcide> Configuring ghcide-0.0.4... ghcide> build ghcide> Preprocessing library for ghcide-0.0.4.. ghcide> Building library for ghcide-0.0.4.. ghcide> [ 1 of 33] Compiling Development.IDE.Core.Debouncer ghcide> [ 2 of 33] Compiling Development.IDE.Core.PositionMapping ghcide> [ 3 of 33] Compiling Development.IDE.GHC.Compat ghcide> [ 4 of 33] Compiling Development.IDE.GHC.CPP ghcide> [ 5 of 33] Compiling Development.IDE.Spans.Type ghcide> [ 6 of 33] Compiling Development.IDE.Types.Location ghcide> [ 7 of 33] Compiling Development.IDE.Types.Diagnostics ghcide> [ 8 of 33] Compiling Development.IDE.LSP.Protocol ghcide> [ 9 of 33] Compiling Development.IDE.GHC.Util ghcide> [10 of 33] Compiling Development.IDE.GHC.Orphans ghcide> [11 of 33] Compiling Development.IDE.Import.DependencyInformation ghcide> [12 of 33] Compiling Development.IDE.GHC.Error ghcide> [13 of 33] Compiling Development.IDE.Import.FindImports ghcide> [14 of 33] Compiling Development.IDE.GHC.Warnings ghcide> [15 of 33] Compiling Development.IDE.Core.Preprocessor ghcide> [16 of 33] Compiling Development.IDE.Core.RuleTypes ghcide> [17 of 33] Compiling Development.IDE.Types.Logger ghcide> [18 of 33] Compiling Development.IDE.Types.Options ghcide> [19 of 33] Compiling Development.IDE.Core.Shake ghcide> ghcide> /tmp/stack204611/ghcide-0.0.4/src/Development/IDE/Core/Shake.hs:106:5: error: ghcide> • No instance for (Control.Monad.Fail.MonadFail Rules) ghcide> arising from a do statement ghcide> with the failable pattern ‘Just x’ ghcide> • In a stmt of a 'do' block: ghcide> Just x <- getShakeExtraRules @ShakeExtras ghcide> In the expression: ghcide> do Just x <- getShakeExtraRules @ShakeExtras ghcide> return x ghcide> In an equation for ‘getShakeExtrasRules’: ghcide> getShakeExtrasRules ghcide> = do Just x <- getShakeExtraRules @ShakeExtras ghcide> return x ghcide> | ghcide> 106 | Just x <- getShakeExtraRules @ShakeExtras ghcide> | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ghcide> -- While building package ghcide-0.0.4 using: /home/kolar/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal- simple_mPHDZzAJ_2.4.0.1_ghc-8.6.3 --builddir=.stack-work/dist/x86_64-linux-tinfo6/ Cabal-2.4.0.1 build --ghc-options " -fdiagnostics-color=always" Process exited with code: ExitFailure 1 Does that mean the ghcide is broken? Or am I doing something wrong? Best regards, Dusan

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Request for Nominations to the GHC Steering Committee
by Joachim Breitner 11 Dec '19

11 Dec '19

Dear Haskell community, the GHC Steering committee is seeking nominations for one new member. The committee scrutinizes, nitpicks, improves, weights and eventually accepts or rejects proposals that extend or change the language supported by GHC and other (public-facing) aspects of GHC. Our processes are described at https://github.com/ghc-proposals/ghc-proposals which is also the GitHub repository where proposals are proposed. We are looking for a member who has the ability * to understand such language extension proposals, * to find holes and missing corner cases in the specifications, * foresee the interaction with other language features and specifications, * comment constructively and improve the proposals, * judge the cost/benefit ratio and * finally come to a justifiable conclusion. We look for committee members who have some of these properties: * have substantial experience in writing Haskell applications or libraries, which they can use to inform judgements about the utility or otherwise of proposed features, * have made active contributions to the Haskell community, for some time, * have expertise in language design and implementation, in either Haskell or related languages, which they can share with us. The committee’s work requires a small, but non-trivial amount of time, especially when you are assigned a proposal for shepherding. We estimate the workload to be around 2 hours per week, and our process works best if members usually respond to technical emails within 1-2 weeks (within days is even better). Please keep that in mind if your email inbox is already overflowing. The GHC developers themselves are already well represented already. We seek Haskell _users_ more than GHC hackers. There is no shortage of people who are eager to get fancy new features into the language, both in the committee and the wider community. But each new feature imposes a cost, to implement, to learn, (particularly) through its unexpected interaction with other features. We need to strike a balance, one that encourages innovation (as GHC always has) while still making Haskell attractive for real-world production use and for teaching. We therefore explicitly invite “conservative” members of the community to join the committee. To make a nomination, please send an email to me (as the committee secretary) at mail(a)joachim-breitner.de until January 2nd. I will distribute the nominations among the committee, and we will keep the nominations and our deliberations private. We explicitly encourage self-nominations. You can nominate others, but please obtain their explicit consent to do so. (We don’t want to choose someone who turns out to be unable to serve.) On behalf of the committee, Joachim Breitner -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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