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Re: [Haskell-cafe] Announce: Haskell Platform 8.6.5 (Gershom B)
by Pierre_van_der_Laar (Functional Account) 21 May '19

21 May '19

Dear Gershom / GHC development team, The provided windows version of GHC contains lib-gmp. Hence, this version enforces a LGPL license on my code (see e.g. https://gitlab.haskell.org/ghc/ghc/wikis/replacing-gmp-notes for more info) . Unfortunately, this license is unacceptable for me. For me this raises the question: What is the strategy of GHC with respect to licensing? In particularly, * Why considers GHC a LGPL license for all the code developed by their users acceptable? * Is GHC considering to allow their user to standardly develop their code under a license of their own choice? * Are there plans to offer the GHC users an opportunity to choose the license in the near future? e.g. by distributing GHC binary distributions with integer-gmp and integer-simple. Thanks in advance for your answers, Pierre van de Laar --------------------------------------------------------------------- Date: Wed, 8 May 2019 16:28:21 -0400 From: Gershom B <gershomb(a)gmail.com> To: haskell-cafe <haskell-cafe(a)haskell.org>, haskell(a)haskell.org Subject: [Haskell-cafe] Announce: Haskell Platform 8.6.5 Message-ID: <CAM8RHpGB=mhYLJ_qDd__Td8vcJYBvZ66h0fErTU98H9DnWawmQ(a)mail.gmail.com> Content-Type: text/plain; charset="UTF-8" On behalf of the Haskell Platform team, I'm happy to announce the release of Haskell Platform 8.6.5 Now available at https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.haske… This includes GHC 8.6.5, cabal-install 2.4.1.0, and stack 1.9.3. It is an incremental release over 8.6.3 intended mainly to make available bugfixes for windows in subsequent revisions in the 8.6 series and otherwise leave everything the same. These windows fixes are important, and it is recommended all windows users upgrade to 8.6.5 whether through the platform installer or some other mechanism. For detail on these changes and fixes see https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.haske… https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.haske… As with the 8.6.3 release, we are only providing core builds. Further, in 8.6.3 we moved from generic linux installers to recommending users install ghc through ghcup. As discussed in the last announcement, we have now moved to recommending os x users also use ghcup rather than a dedicated binary installer. For more details, please see the 8.6.3 announcement at https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.hask… Happy Haskell Hacking all, Gershom ________________________________ The information contained in this message may be confidential and legally protected under applicable law. The message is intended solely for the addressee(s). If you are not the intended recipient, you are hereby notified that any use, forwarding, dissemination, or reproduction of this message is strictly prohibited and may be unlawful. If you are not the intended recipient, please contact the sender by return e-mail and destroy all copies of the original message.

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Second Call for Tutorial Proposals: ICFP 2019
by Sam Tobin-Hochstadt 20 May '19

20 May '19

*EXTENDED DEADLINE* - CALL FOR TUTORIAL PROPOSALS ICFP 2019 24th ACM SIGPLAN International Conference on Functional Programming August 18 - 23, 2019 Berlin, Germany https://icfp19.sigplan.org/ The 24th ACM SIGPLAN International Conference on Functional Programming will be held in Berlin, Germany on August 18-23, 2019. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for tutorials, lasting approximately 3 hours each, to be presented during ICFP and its co-located workshops and other events. These tutorials are the successor to the CUFP tutorials from previous years, but we also welcome tutorials whose primary audience is researchers rather than practitioners. Tutorials may focus either on a concrete technology or on a theoretical or mathematical tool. Ideally, tutorials will have a concrete result, such as "Learn to do X with Y" rather than "Learn language Y". Tutorials may occur after ICFP co-located with the associated workshops, from August 22 till August 23. ---------------------------------------------------------------------- Submission details Deadline for submission: June 3rd, 2019 Notification of acceptance: June 10th, 2019 Prospective organizers of tutorials are invited to submit a completed tutorial proposal form in plain text format to the ICFP 2018 workshop co-chairs (Jennifer Hackett and Christophe Scholliers), via email to icfp-workshops-2019(a)googlegroups.com by June 3rd, 2019. Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by June 10th, 2019. The proposal form is available at: http://www.icfpconference.org/icfp2019-files/icfp19-tutorials-form.txt ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2019 organizing committee. Tutorials Co-Chair: Jennifer Hackett (University of Nottingham) Tutorials Co-Chair: Christophe Scholliers (University of Ghent) General Chair: Derek Dreyer (MPI-SWS) Program Chair: François Pottier ( Inria, France) ---------------------------------------------------------------------- Further information Any queries should be addressed to the tutorial co-chairs (Jennifer Hackett and Christophe Scholliers), via email to icfp-workshops-2019(a)googlegroups.com

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How to dynamic plan in Haskell?
by Magicloud Magiclouds 20 May '19

20 May '19

Hi, I solved the question. But I could not figure out a FP style solution. Question: 1 - 9, nine numbers. Show all the possible combinations that sum up to 10. Different orders are counted as the same. For example, [1, 4, 5].

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zstd package. Proposal to take over maintenance
by Luis Pedro Coelho 20 May '19

20 May '19

Hi everyone, The zstd package contains important bugs (it produces malformed output in some cases) and seems unmaintained. I would like to take over maintenance of it. I have actually forked the package and fixed the bugs, releasing it as hs-zstd: https://github.com/luispedro/hs-zstd http://hackage.haskell.org/package/hs-zstd I was advised to consider taking over maintenance of zstd as an earlier attempt to contact the maintainers of zstd was not answered. I would still prefer not to have this responsibility, but I would also like to use zstd in my work. * The zstd issues are not obvious because 99% of the time it works well, so we actually used it in a release of ngless, but after 3 days in the wild, we had to release a "bugfix". This is because most code paths work well, but there is one which produces a broken file. http://ngless.embl.de/whatsnew.html#version-0-11 Thanks, Luis Luis Pedro Coelho | Fudan University | http://luispedro.org https://orcid.org/0000-0002-9280-7885

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First Call for Papers for IFL 2019 (Implementation and Application of Functional Languages)
by J. Stutterheim 19 May '19

19 May '19

Dear all, Please, find below the first call for papers for IFL 2019. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. Best regards, Jurriën Stutterheim --- ================================================================================ IFL 2019 31st Symposium on Implementation and Application of Functional Languages National University of Singapore September 25th-27th, 2019 http://2019.iflconference.org ================================================================================ ### 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 2019 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. 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 specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - 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 - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Keynote Speaker * Olivier Danvy, Yale-NUS College ### Submissions and peer-review Differently from previous editions of IFL, IFL 2019 solicits two kinds of submissions: * Regular papers (12 pages including references) * Draft papers for presentations ('weak' limit between 8 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. A set of regular papers will be conditionally accepted for publication. Authors of conditionally accepted papers will be provided with committee reviews along with a set of mandatory revisions. Regular papers not accepted for publication will be considered as draft papers, at the request of the author. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. Prior to the symposium: Authors of conditionally accepted papers and accepted presentations will submit a pre-proceedings version of their work that will appear in the draft proceedings distributed at the symposium. The draft proceedings does not constitute a formal publication. We require that at least one of the authors present the work at IFL 2019. After the symposium: Authors of conditionally accepted papers will submit a revised versions of their paper for the formal post-proceedings. The program committee will assess whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. Our interest is to ultimately accept all conditionally accepted papers. If you are an author of a conditionally accepted paper, please make sure that you address all the concerns of the reviewers. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings. 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. ### Publication The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication ### Important dates Submission of regular papers: May 31, 2019 Submission of draft papers: July 15, 2019 Regular and draft papers notification: August 1, 2019 Deadline for early registration: August 15, 2019 Submission of pre-proceedings version: September 15, 2019 IFL Symposium: September 25-27, 2019 Submission of papers for post-proceedings: November 30, 2019 Notification of acceptance: January 31, 2020 Camera-ready version: February 29, 2020 ### 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 Authors submit through EasyChair: https://easychair.org/conferences/?conf=ifl2019 ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored 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. ### Organization and Program committee Chairs: Jurrien Stutterheim (Standard Chartered Bank Singapore), Wei Ngan Chin (National University of Singapore) Program Committee: - Olaf Chitil, University of Kent - Clemens Grelck, University of Amsterdam - Daisuke Kimura, The University of Tokyo - Pieter Koopman, Radboud University - Tamás Kozsik, Eötvös Loránd University - Roman Leschinskiy, Facebook - Ben Lippmeier, The University of New South Wales - Marco T. Morazan, Seton Hall University - Sven-Bodo Scholz, Heriot-Watt University - Tom Schrijvers, Katholieke Universiteit Leuven - Alejandro Serrano, Utrecht University - Tony Sloane, Macquarie University - Simon Thompson, University of Kent - Marcos Viera, Universidad de la República - Wei Ngan Chin, NUS - Jurriën Stutterheim, Standard Chartered Bank ### Venue The 30th IFL is organized by the University of Massachusetts Lowell. The City of Lowell is located at the heart of the Merrimack Valley just 30 miles northwest of Boston. Lowell can be easily reached by train or taxi. See the website for more information on the venue. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organizers for their work, which is reused here. A part of IFL 2019 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

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Mocking out external services
by Francesco Ariis 19 May '19

19 May '19

(literate Haskell follows) Hello -cafe, I recently read "Three Layer Haskell Cake" [1] and decided to give it a go. I am stuck on a simple problem and feel like I am missing something easy. One of the first examples is a mocking of an `IO UTCTime` function. > > {-# Language FlexibleInstances #-} > > data UTCTime = UTCTime Int > > class MonadTime m where > getCurrentTime :: m UTCTime > > instance MonadTime ((->) UTCTime) where > getCurrentTime = id > > -- instance IO omitted > Everything is clear. I decided to write another function, mocking a stream-of-Char input. > > class MonadKeys m where > getKeys :: m [Char] > > instance MonadKeys ((->) [Char]) where > getKeys = id > > -- instance IO omitted > Again, fine. But now, if I want to write a function which combines the two external services, like: > > someFun :: (MonadTime m, MonadKeys m) => m () > someFun = undefined > there is no non-IO instance satisfying the two constraints. I could of course write a type > > data Env = Env UTCTime [Char] > and make it instance of MonadTime and MonadKeys, but then I am passing non-relevant arguments to a mocked function like getCurrentTime, which would only need UTCTime. What am I doing incorrectly? -F [1] https://www.parsonsmatt.org/2018/03/22/three_layer_haskell_cake.html

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Identity operator for types
by Juan Miguel Vilar 17 May '19

17 May '19

Hi, Café: I am not sure how to make the question, but the idea is to have a type operator that returns the same type. Let me show what I need. I have some type like this: data Example f t = Example (f t) So if I want a type variable that contains a list of integers, I can use Example [] Int and then treat the content like a list: f :: Example [] Int -> Int f (Example l) = length l Now, the problem is what can I do to have a type that contains a single Int? Is there a sort of id for types so that I can write f :: Example ?? Int -> Int f (Example i) = 2 * i ? Thanks in advance Juan Miguel Vilar -- Juan Miguel Vilar Torres Profesor titular de universidad Departamento de Lenguajes y Sistemas Informáticos Escuela Superior de Tecnología y Ciencias Experimentales Universitat Jaume I Av. de Vicent Sos Baynat s/n 12071 Castelló de la Plana (Spain) Tel: +34 964 72 8365 Fax: +34 964 72 8435 jvilar(a)uji.es

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How to express a logic matrix clearly?
by Magicloud Magiclouds 17 May '19

17 May '19

Hi, I have trouble describing this clearly. Let me show code directly. data Rule1 = A1 | A2 | A3 data Rule2 = B1 | B2 | B3 foo a b = if a == A1 then if b == B1 then fun1 else if b == B2 then fun2 else if b == B3 then fun3 else fun4 ... Basically, Rule1 and Rule2 compose a matrix, for each case of Rule1 and Rule2, I need to do different things. Above is already long and not quite clear, and it is far from complete. So my question is, is there a way/lib that I can make this clear to read/understand?

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Re: [Haskell-cafe] Dispatching user code at runtime, injecting appropriate typeclass instances into user code scope
by Evgeny Permyakov 16 May '19

16 May '19

Hi. reflection is about selecting a type instance of a typeclass that is known to exist over type. Completely different thing. Monads ... I guess, using monadic context in some way is an option, but not exactly what I have in mind. Still, worth looking into. On Thu, 16 May 2019 at 10:20, Georgi Lyubenov <godzbanebane(a)gmail.com> wrote: > Hi, > > It seems like the "extensible" parts you want is something similar to most > extensible effects stuff. Perhaps check out the "Member stuff" from the > "Freer Monads, More Extensible Effects" paper and some EE libraries > (freer-simple, fused-effects, polysemy)? Also, if you want runtime > typeclasses reflection <http://hackage.haskell.org/package/reflection> can > help. > > ======= > Georgi >

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Dispatching user code at runtime, injecting appropriate typeclass instances into user code scope
by Evgeny Permyakov 16 May '19

16 May '19

Let's suppose that at runtime I create a hardware context and test it for a set of supported operation and want to adapt the way I work with it based on the set of operations available. (RL example: OpenGL extension discovery and use) Naturally, I can create a function that checks hardware and then, based on the result, returns different dictionaries of functions over the context, maybe as closures. This is verbose and crude, even if it shall work. However, I want to work with the context using a typeclass interface. It isn't hard when number of options is low. I suppose, we can use something like typeclass Context a where > { dispatch :: MonadIO m => forall k . Context a -> (forall a . Testable1 > a -> a -> m k) -> (forall a. Testable2 a -> a -> m k ) -> a -> m k } > Here, Context typeclass defines a function that selects appropriate handler from the set of user-provided functions and each instance takes the function it likes. Fine. The problems are twofold: - This is not extensible, the set of possible cases is defined on the definition of Context typeclass - This approach is hardly appropriate if we have a lot of cases, For example, if context may support ten optional operation sets in addtion to basic one, the number of possible cases *dispatch* needs to support A more modular approach is needed, something like (pseudocode) dispatch :: typeclassSet Defined, -- collection of defined typeclasses typeClass Tested, -- what we test for Dispatchable a, Defined a -- what we test =>forall b. (forall a . Defined a => a -> b) -- 'fallback' function -> (forall a . Defined a, Tested a => a -> b) -- this is called if A supports Tested interface. -> b This way one can gradually inject typeclass instances into scope. But how I can do it? PS. Naturally, I don't want to expose internals of the type I dispatch over, it is an abstract type.

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