- Haskell-Cafe - Haskell.org

Why Haskell?
by Clinton Mead 30 Mar '21

30 Mar '21

I’m looking for recommendations of videos/articles to show to a software development manager about why one should use Haskell, focused more from a benefits to business perspective. Naturally this may involve some code, this manager isn’t completely clueless when it comes to programming languages, but basically something that explains why I’m raving about this “Haskell” thing all the time and why it’s a good idea. Thanks, Clinton

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Arrays in base... (was: ... indexing lists)
by Viktor Dukhovni 29 Mar '21

29 Mar '21

On Mon, Mar 29, 2021 at 10:58:49AM +0200, Henning Thielemann wrote: > On Mon, 29 Mar 2021, Viktor Dukhovni wrote: > > > Thus I applaud Michael Snoyman's quest to address the absense of a basic > > array type in the `base` library. Perhaps more users would stop abusing > > lists (memoisable iterators) as an indexed store. > > Data.Array actually _was_ part of base-3. > > However, I think we should split 'base' in more smaller parts rather than > making it bigger. FWIW, I don't think that splitting base into multiple libraries would achieves much, it would likely raise the cost of coordinating versioning. I do however agree that perhaps separating base from GHC could be a good idea, if GHC could ship a smaller foundational library with primops, ... and `base` evolved somewhat independently. However that too has potential drawbacks, because packages would be more likely to have non-overlapping version bounds on a separately evolving base... Probably manageable, but something to keep in mind. -- Viktor.

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Munich Virtual Haskell Meeting, 2021-03-31 @ 19:30
by Leah Neukirchen 29 Mar '21

29 Mar '21

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Wednesday, March 31 on Google Meet at 19:30 CEST. **Due to meetup limitations in Bavaria, this meeting will take place online!** For details see here: https://muenchen.haskell.bayern/dates.html A Google Meet link to join the room is provided on the page. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Why does my module take so long to compile?
by Troels Henriksen 29 Mar '21

29 Mar '21

I have a program with about 220 modules. One of these modules takes _much_ longer to compile than the others (several minutes longer). I don't understand why. It compiled much faster with GHC 8.8.3, but got orders of magnitude slower when I changed to GHC 8.10.2. I don't understand why, since I don't think there is nothing special about the module - e.g. no type-level programming. Is there any good way to "profile" the stack or cabal compilation process to at least get an intuition for what takes so long? Note that the module is in the middle of the dependency tree of my program, so it is not viable to separate it out and compile it manually with GHC. It's slow even when I pass '--fast' to stack which should disable the optimiser, so I guess the type checker may be spending a lot of time on handling the admittedly large amount of typeclass constraints I have on some of my definitions. I'm mostly looking for techniques and tools I can also use next time this problem occurs, not the specific problem here, but if anyone's curious, the module in question is this one: https://github.com/diku-dk/futhark/blob/master/src/Futhark/Pass/ExtractKern… -- \ Troels /\ Henriksen

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Some questions about Fudgets library
by Antonio 28 Mar '21

28 Mar '21

I wonder why there is no Fudgets package in Hackage. I found this, but the fudgets link is broken: http://hackage.haskell.org/user/ThomasHallgren Nevertheless, there is a cabalized package in the Fudgets homepage, so it's strange it's not in Hackage. Also, is there an arrowized version of Fudgets? If not, why? Is there some fundamental reason that makes it impossible to port it to the arrows framework or simply nobody cared to port it? (Also, the license seems to not allow modifications.) I'm trying to write a bittorrent client in Haskell. I decided to use arrows for it and took a look at Fudgets and Yampa. I haven't decided yet which one to use. Fudgets seems more suitable and I like it more, but the fact that it doesn't use the arrow notation and classes is a bit annoying. I read that Fruit is more or less a mix of Fudgets and Yampa that uses arrows. Sadly, it's unmaintained, the web doesn't exist and it's not in Hackage. Is there any other Fudgets-like option? Greetings.

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Install on Ubuntu
by Galaxy Being 28 Mar '21

28 Mar '21

I've found a Haskell setup guide here, but after the stack setup it wants to install cabal curl -sSL https://get.haskellstack.org | sh then stack install cabal-install cabal update Why do I want to install cabal after stack? Any advice welcome on the "definitive setup." Just started a new machine with Ubuntu 20.10 on it. LB

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Does Haskell have this SML syntax?
by Galaxy Being 27 Mar '21

27 Mar '21

I saw this in *The Little MLer*, a book on SML datatype 'a list = Empty | Cons of 'a * 'a list fun subst_c (pred) = fn (n,Empty) => Empty | (n,Cons(e,t)) => if pred (e) then Cons (n,subst_c (pred) (n,t)) else Cons (e,subst_c (pred) (n,t)) The data type is just a homemade list, and the function subst_c takes a predicate ('a -> Bool) and determines whether an incoming list's elements pass or fail. What is interesting is the fn ... => ... part which takes in more parameters, namely an 'a and an 'a list. Technically this fn... is an anonymous, nameless function, and it seems bizarre to me that it's nested inside the named function but still taking in parameters as if it were at the top level. Here's a previous version showing all three parameters at the top level fun subst_c (pred) (n,Empty) = Empty ... The purpose of the first function was to demonstrate currying. IOW, what the second unnamed function is doing behind the scenes can be broken down to two-stages (currying) of the first with named, then unnamed functions. So my question is, is there anything like this in Haskell where a function inside a function -- named or anonymous -- can take incoming parameters as if it were top level? LB

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Query regarding GSOC
by Shubham Mittal 26 Mar '21

26 Mar '21

Hello I am Shubham from India currently pursuing BTech IT 2nd year. I would like to contribute to Haskell-Cafe as a part of GSOC. Can you please guide me how I can i do so? Thanks and Regards, Shubham Mittal

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IFL2021 First call for papers
by Pieter Koopman 24 Mar '21

24 Mar '21

================================================================================ IFL 2021 33rd Symposium on Implementation and Application of Functional Languages venue: online 1 - 3 September 2021 https://ifl21.cs.ru.nl <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> ================================================================================ Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2021 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Industrial track and topics of interest This year's edition of IFL explicitly solicits original work concerning *applications* of functional programming in industry and academia. These contributions will be reviewed by experts with an industrial background. Topics of interest to IFL include, but are not limited to: * language concepts * type systems, type checking, type inferencing * compilation techniques * staged compilation * run-time function specialisation * run-time code generation * partial evaluation * (abstract) interpretation * meta-programming * generic programming * automatic program generation * array processing * concurrent/parallel programming * concurrent/parallel program execution * embedded systems * web applications * (embedded) domain-specific languages * security * novel memory management techniques * run-time profiling performance measurements * debugging and tracing * testing and proofing * virtual/abstract machine architectures * validation, verification of functional programs * tools and programming techniques * applications of functional programming in the industry, including ** functional programming techniques for large applications ** successes of the application functional programming ** challenges for functional programming encountered ** any topic related to the application of functional programming that is interesting for the IFL community Post-symposium peer-review Following IFL tradition, IFL 2021 will use a post-symposium review process to produce the formal proceedings. Before the symposium authors submit draft papers. These draft papers will be screened by the program chairs to make sure that they are within the scope of IFL. The draft papers will be made available to all participants at the symposium. Each draft paper is presented by one of the authors at the symposium. After the symposium every presenter is invited to submit a full paper, incorporating feedback from discussions at the symposium. Work submitted to IFL may not be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected for the formal proceedings. We plan to publish these proceedings in the International Conference Proceedings Series of the ACM Digital Library, as in previous years. Moreover, the proceedings will also be made publicly available as open access. Important dates Submission deadline of draft papers: 17 August 2021 Notification of acceptance for presentation: 19 August 2021 Registration deadline: 30 August 2021 IFL Symposium: 1-3 September 2021 Submission of papers for proceedings: 6 December 2021 Notification of acceptance: 3 February 2022 Camera-ready version: 15 March 2022 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Organisation IFL 2021 Chairs: Pieter Koopman and Peter Achten, Radboud University, The Netherlands IFL Publicity chair: Pieter Koopman, Radboud University, The Netherlands PC (under construction): Peter Achten (co-chair) - Radboud University, Netherlands Thomas van Binsbergen - University of Amsterdam, Netherlands Edwin Brady - University of St. Andrews, Scotland Laura Castro - University of A Coruña, Spain Youyou Cong - Tokyo Institute of Technology, Japan Olaf Chitil - University of Kent, England Andy Gill - University of Kansas, USA Clemens Grelck - University of Amsterdam, Netherlands John Hughes - Chalmers University, Sweden Pieter Koopman (co-chair) - Radboud University, Netherlands Cynthia Kop - Radboud University, Netherlands Jay McCarthey - University of Massachussetts Lowell, USA Neil Mitchell - Facebook, England Jan De Muijnck-Hughes - Glasgow University, Scotland Keiko Nakata - SAP Innovation Center Potsdam, Germany Jurriën Stutterheim - Standard Chartered, Singapore Simon Thompson - University of Kent, England Melinda Tóth - Eötvos Loránd University, Hungary Phil Trinder - Glasgow University, Scotland Meng Wang - University of Bristol, England Viktória Zsók - Eötvos Loránd University, Hungary Virtual symposium Because of the Covid-19 pandemic, this year IFL 2021 will be an online event, consisting of paper presentations, discussions and virtual social gatherings. Registered participants can take part from anywhere in the world. Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organisers for their work, which is reused here. [image: beacon]

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ANN closed-intervals-0.1
by Olaf Klinke 24 Mar '21

24 Mar '21

Dear Cafe, I am pleased to announce the first release of closed-intervals [1], a package for querying and manipulating collections of closed intervals in totally ordered types. Other packages exist which either deal with a single interval type [2,4] or provide an interval type class [3]. Having both closed, open and half-open intervals makes the interface complicated, however. The focus of closed-intervals is on intervals including both end-points and is intended to be used on records with length or duration information. My use cases are mostly sequences of annotated time intervals [*], parsed from time-stamped data. Against these sequences overlap-, coverage- and intersection queries are run using single intervals as query. The package contains many doctests. Testing builds on Henning Thielemann's doctest-extract [5] and doctest-exitcode-io [6] packages. closed-intervals is, after provenience [7], the second package in an effort to open-source my employer's entire Haskell codebase. We will gradually publish from general to problem-specific. Cheers, Olaf [1] https://hackage.haskell.org/package/closed-intervals [2] https://hackage.haskell.org/package/data-interval [3] https://hackage.haskell.org/package/IntervalMap [4] https://hackage.haskell.org/package/intervals [5] https://hackage.haskell.org/package/doctest-extract [6] https://hackage.haskell.org/package/doctest-exitcode-io [7] https://hackage.haskell.org/package/provenience [*] Since time types are fine-grained and a time point is an idealized concept, the question of end-point inclusion is not that relevant for time intervals. We do distinguish between intersection in end-points and proper intersection, though.

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