- Haskell-Cafe - Haskell.org

Generators? Iterators?
by Christopher Howard 23 Apr '16

23 Apr '16

Hi. I'm more in the shallow end of the Haskell pool right now, so forgive me if this is really basic... In Haskell, what is the class for things that can provide an infinite sequence? I mean, things that produce a value as well as function for producing the next value? Clearly RandomGen does this, but what is the next level of abstraction above RandomGen (i.e., RandomGen minus the randomness aspect). -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

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Documenting extensions
by Doug McIlroy 23 Apr '16

23 Apr '16

I'd like to believe the Haskell report is a bible. I learned H98 using the Prelude as a source of examples and Hugs as a testbed. That was a comfortable and rewarding combination. Later I discovered that by default GHC rejected almost all my report-conforming (H98 and H2010) code. Ironically, its website at the time asserted, "Haskell is a standard language." In fact, far from reflecting biblical authority, the de facto Haskell discussed in this cafe comes in some 2^99 flavors -- enough to use a different language for every run of the compiler for the life of the universe. Witness: ghc --supported-languages | grep -v '^No[A-Z]' | wc -l (99 is the answer for GHC 7.8.4. In fact not all combinations of -X options are legal, but you get the point.) Unfortunately there is no coherent discussion of all those Haskells. The extensions section of the GHC User Guide gives no formal syntax, often teaches semantics only by example, and is replete with sales pitches, partial analogies, inconsistent terminology, and (helpful) appeals to outside sources. Definitely not a bible. I understand that many GHC extensions are probationary. Nevertheless, in the interest of facilitating their full and correct use, I would plead that a report-grade description accompany each language feature incorporated in official releases. This seems like a small amount of effort beyond the hard work of conception and implementation. Are there cogent reasons for doing otherwise? Doug

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Haskell in Leipzig 2016: Call for Papers
by Joachim Breitner 22 Apr '16

22 Apr '16

Haskell in Leipzig September 14-15, 2016 HTKW Leipzig, Germany http://hal2016.haskell.org/ == About HaL == The workshop series “Haskell in Leipzig”, now in its 11th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts and Haskell beginners to listen to talks, take part in tutorials, and join in interesting conversations. Everything related to Haskell is on topic, whether it is about current research, practical applications, interesting ideas off the beaten track, education, or art, and topics may extend to functional programming in general and its connections to other programming paradigms as well. This year, HaL is colocated with two related conferences, * the Workshop on Functional and (Constraint) Logic Programming (WFLP) and * the Workshop on (Constraint) Logic Programming (WLP), to form the Leipzig Week of Declarative Programming (L-DEC): http://nfa.imn.htwk-leipzig.de/LDEC2016/ In order to accommodate and welcome a more international audience, this year’s HaL will be held in English. == Submissions == Contributions can take the form of * talks (about 30 minutes), * tutorials (about 90 minutes), * demonstrations, artistic performances, or other extraordinary things. Please submit an abstract that describes the content and form of your presentation, the intended audience, and required previous knowledge. We recommend a length of 2 pages, so that the PC and the audience get a good idea of your submission, but this is not a hard requirement. You can submit your abstract, as an PDF document, at https://easychair.org/conferences/?conf=hal2016 until Friday, July 1, 2016. You will be notified by July 15, 2016. == Program committee == * Andreas Abel, Chalmers and Gothenburg University, Sweden * Heinrich Apfelmus, Leipzig, Germany * Joachim Breitner, Karlsruhe Institute of Technology, Germany (Chair) * Matthias Fischmann, Zerobuzz, Germany * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Institute of Cybernetics at Tallinn University of Technology, Estonia * Andres Löh, Well-Typed LLP, Germany * Alejandro Serrano Mena, Universiteit Utrecht, Netherlands * Neil Mitchell, Standard Chartered Bank, UK * Katie Ots, Facebook, UK * Peter Stadler, University of Leipzig, Germany * Henning Thielemann, Freelancer, Germany * Niki Vazou, University of California, San Diego, USA If you have any questions, please don’t hesitate to contact Joachim Breitner <breitner(a)kit.edu>. -- Dipl.-Math. Dipl.-Inform. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.ipd.kit.edu/~breitner

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I have a question about Haskell
by Eunsu Kim 22 Apr '16

22 Apr '16

Hi i have a problem in my code! here is my code: here is error message: in very bottom function (polyEvaluate), why is not working “result <- map (\(a,b) -> a+b) powers” ??? in Prelude, it is working Thanks!

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I've wanted a Haskell shirt for awhile
by Stegosaurus Armatus 21 Apr '16

21 Apr '16

Does anyone know where I can get one? Failing that, I made one to celebrate today. https://teespring.com/haskell-stay-lifted Disclaimer: I don't intend to be spammy, but I totally understand and respect if some people don't like this. I was just happy and wanted to share. Please don't hate.

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Generics changes in GHC 8 break containers
by David Feuer 21 Apr '16

21 Apr '16

containers does not currently build with GHC 8 because of changes to Generics. I only have a shallow understanding of GHC.Generics. Could someone give me a hand figuring out what I need to change? Thanks, David Feuer

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ANN: New Haskell.org committee members
by John Wiegley 21 Apr '16

21 Apr '16

The Haskell.org committee has selected its new member following the March self-nomination period. The new (returning) member is: * Gershom Bazerman Thank you to everyone who submitted a self-nomination. Note that if you have self-nominated in the past, but not been picked, please self-nominate again in the future. -- John Wiegley GPG fingerprint = 4710 CF98 AF9B 327B B80F http://newartisans.com 60E1 46C4 BD1A 7AC1 4BA2

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ghc-mod errors in Emacs
by Đorđe Grbić 21 Apr '16

21 Apr '16

Greetings dear Haskell community, I'm trying to use Spacemacs for Haskell development but as soon as I open a .hs file ghc-mod dumps errors: ghc-mod: <command line>: cannot satisfy -package-id base-4.6.0.1-8aa5d403c45ea59dcd2c39f123e27d57 (use -v for more information) <command line>: cannot satisfy -package-id base-4.6.0.1-8aa5d403c45ea59dcd2c39f123e27d57 (use -v for more information) <command line>: cannot satisfy -package-id base-4.6.0.1-8aa5d403c45ea59dcd2c39f123e27d57 (use -v for more information) I have ghc-mod version: 5.5.0.0 compiled by GHC 7.8.4. GHC version : 7.8.4 Emacs: 24.5.1 Spacemacs: 0.105.18 OS: Ubuntu 14.04.4 LTS Any help is appreciated, Djordje Grbic

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Re: [Haskell-cafe] Documenting extensions
by Doug McIlroy 21 Apr '16

21 Apr '16

>>> Later I discovered >>> that by default GHC rejected almost all my report-conforming (H98 >>> and H2010) code. >> >> Do you mean that GHC can't compile Haskell2010 conformant code? >> Can you please post (or point to) some examples? > > This page [1] lists the ways in which GHC diverges from the standard. > > Erik > > [1] https://downloads.haskell.org/~ghc/master/users-guide/bugs.html The main problem was that my code relied on constraint (Num a) implying (Eq a) per the standard. I also had context clauses in data declarations. Thus I had to make pervasive, albeit trivial, changes to get past GHC's nonconformance. (Presumably option -XHaskell2010 would have papered over the trouble, but I prefer to maximize code portability.) Doug McIlroy

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Hugs
by David Feuer 21 Apr '16

21 Apr '16

Apparently, Eric Meijer is now teaching a large class using Hugs, which leads to many of his students asking questions about it on StackOverflow. I therefore suggest that we change the status of Hugs on the website from "is no longer in development" to "has been maintained by Eric Meijer since 2015". I think we should also include on the website a statement to the effect that people seeking help using Hugs should contact Eric Meijer directly, and provide his email address to facilitate that. Obviously, he'll need full write access to the Hugs source repo to fulfill his duties as maintainer. Yes, this is all a bit tongue-in-cheek, but I really do think that pointing students to an unmaintained language implementation (regardless of the pedagogical reasons) has negative consequences for the functional programming community as a whole.

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