- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] [ANNOUNCE] GHC 8.8.4 is now available
by Gregory Guthrie 19 Jul '20

19 Jul '20

I don't see any windows binaries listed; are they there, elsewhere? Lots of Linux (=0.7% desktop market share) versions, but Windows (=78%) only source?. ---------------------------------------------------------------- -----Original Message----- From: Haskell-Cafe <haskell-cafe-bounces(a)haskell.org> On Behalf Of haskell-cafe- On Wed, Jul 15, 2020 at 07:38:31PM -0400, Ben Gamari wrote: > The GHC team is proud to announce the release of GHC 8.8.4. The source > distribution, binary distributions, and documentation are available at > > https://downloads.haskell.org/~ghc/8.8.4

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What causes this "Ambiguous type variable" message (involving an existential type)?
by James Cook 18 Jul '20

18 Jul '20

Hi haskell-cafe, I've run into a strange error. It's easy for me to work around, but I still would like to know what causes it. Here's a minimal example. {-# LANGUAGE Rank2Types #-} module Example where data T = T (forall n . (Show n) => n) d :: a -> Int d = undefined f :: T -> Int f (T t) = d t when I try to compile it (ghc Example.hs) I see the following error: Example.hs:11:13: error: • Ambiguous type variable ‘a0’ arising from a use of ‘t’ prevents the constraint ‘(Show a0)’ from being solved. Probable fix: use a type annotation to specify what ‘a0’ should be. These potential instances exist: instance Show Ordering -- Defined in ‘GHC.Show’ instance Show Integer -- Defined in ‘GHC.Show’ instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’ ...plus 22 others ...plus 12 instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the first argument of ‘d’, namely ‘t’ In the expression: d t In an equation for ‘f’: f (T t) = d t | 11 | f (T t) = d t | ^ My question: what causes this error? This seems backward to me. The way I see it, I've told the compiler that any value of type T is guaranteed to contain a value of a type implementing Show, so there should be no question about solving a constraint involving Show. Moreover, the function "d" doesn't even require its input to implement Show. I'm guessing there's some basic rule about existential types that I'm violating here, but I'm not sure where to look if I want to read about that. I've skimmed https://wiki.haskell.org/Existential_type and didn't find anything, but maybe I skimmed too quickly. (Note: if I use Num or Fractional instead of Show, I don't get the error. I guess it's because of defaulting rules for numeric type classes.) If you're interested in how I ran into this, here's a summary. I have this type Scene g with two record fields. Notice the gl_camera_info field doesn't mention the type parameter g. data Scene g where Scene :: RandomGenD g => { part_ :: Part g , gl_camera_info :: GLCameraInfo } -> Scene g Then later I have an existentially quantified scene passed to the VScene constructor here... data BaseVal = VIint Int | VS String | VScene (forall g . (RandomGenD g) => Scene g) | VIO (ShellState -> IO ShellState) | VError String data Val = Val { val_f :: Val -> Val , val_base :: BaseVal } and later (somewhere inside a "where" clause): f (Val _ (VScene scene)) = base_val (VIO (fork_render (gl_camera_info scene) (RLS.muts scene 5e-2 1e-1))) (I don't think the definitions of base_val or RLS.muts matter here.) The use of gl_camera_info seems to cause the problem in this case. I see Shell.hs:137:79: error: • Ambiguous type variable ‘g0’ arising from a use of ‘scene’ prevents the constraint ‘(RandomGenD g0)’ from being solved. Probable fix: use a type annotation to specify what ‘g0’ should be. These potential instances exist: instance [safe] RandomGenD g => RandomGenD (RList g) -- Defined in ‘RList’ instance [safe] RandomGenD StdGen -- Defined in ‘Rand’ • In the first argument of ‘gl_camera_info’, namely ‘scene’ In the first argument of ‘fork_render’, namely ‘(gl_camera_info scene)’ In the first argument of ‘VIO’, namely ‘(fork_render (gl_camera_info scene) (RLS.muts scene 5e-2 1e-1))’ | 137 | f (Val _ (VScene scene)) = base_val (VIO (fork_render (gl_camera_info scene) (RLS.muts scene 5e-2 1e-1))) | ^^^^^ My planned solution is simply to not use an existential type here. I can just make g a parameter of the BaseVal type. But I'm still curious to understand what went wrong. -- James

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[ANNOUNCE] GHC 8.8.4 is now available
by Ben Gamari 17 Jul '20

17 Jul '20

Hello everyone, The GHC team is proud to announce the release of GHC 8.8.4. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.8.4 Release notes are also available [1]. This release fixes a handful of issues affecting 8.8.3: - Fixes a bug in process creation on Windows (#17926). Due to this fix we strongly encourage all Windows users to upgrade immediately. - Works around a Linux kernel bug in the implementation of timerfd (#18033) - Fixes a few linking issues affecting ARM - Fixes "missing interface file" error triggered by some uses of Data.Ord.Ordering (#18185) - Fixes an integer overflow in the compact-normal-form import implementation (#16992) - `configure` now accepts a `--enable-numa` flag to enable/disable `numactl` support on Linux. - Fixes potentially lost sharing due to the desugaring of left operator sections (#18151). - Fixes a build-system bug resulting in potential miscompilation by unregisteised compilers (#18024) As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.4/docs/html/users_guide/8.8.4-notes.h…

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Final Call for Tutorials, Discussions, and Social Events: ICFP 2020
by Sam Tobin-Hochstadt 16 Jul '20

16 Jul '20

FINAL CALL FOR TUTORIAL, DISCUSSION, AND SOCIAL EVENT PROPOSALS ICFP 2020 25th ACM SIGPLAN International Conference on Functional Programming August 23 - 28, 2020 Virtual https://icfp20.sigplan.org/ The 25th ACM SIGPLAN International Conference on Functional Programming will be held virtually on August 23-28, 2020. 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". To increase social interaction on the first ICFP virtual conference, this year we invite proposals for social events on topics of broader interest to the PL community. Such events can be panels and discussions (in the lines of the successful #ShutDownPL event), focused discussions (e.g., problem identifications, retrospective analysis, technical demos), social activities (e.g., treasure hunt, bingo, problem solving, artistic challenges). The typical duration of such events ranges from 30 minutes to one hour, but can be of any length. Tutorials may occur before or after ICFP, co-located with the associated workshops, on August 23 or August 27-28. Social events may be scheduled throughout the week. ---------------------------------------------------------------------- Submission details Deadline for submission: July 17th, 2020 Notification of acceptance: July 22nd, 2020 Prospective organizers of tutorials are invited to submit a completed tutorial proposal form in plain text format to the ICFP 2020 workshop co-chairs (Jennifer Hackett and Leonidas Lampropoulos), via email to icfp-workshops-2020(a)googlegroups.com by July 17th, 2020. Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by July 22nd, 2020. The proposal form is available at: http://www.icfpconference.org/icfp2020-files/icfp20-panel-form.txt http://www.icfpconference.org/icfp2020-files/icfp20-tutorials-form.txt ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2020 organizing committee. Tutorials Co-Chair: Jennifer Hackett (University of Nottingham) Tutorials Co-Chair: Leonidas Lampropoulos (University of Maryland) General Chair: Stephanie Weirich (University of Pennsylvania) Program Chair: Adam Chlipala (MIT) ---------------------------------------------------------------------- Further information Any queries should be addressed to the tutorial co-chairs (Jennifer Hackett and Leonidas Lampropoulos), via email to icfp-workshops-2020(a)googlegroups.com

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How does the RTS "know" about ExitCode
by Georgi Lyubenov 15 Jul '20

15 Jul '20

Hi! I'm wondering how values stored in ExitCode "get to" the RTS (i.e. actually make the program exit with the given number). As far as I can tell ExitCode is used as an everyday normal-looking exception (which are defined entirely in "library code", by using the raise#/catch# primitives), without any direct link to the RTS. What am I missing? ====== Georgi

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setting ISO-8859-1 encoding on Raspbian for GHC
by Henning Thielemann 15 Jul '20

15 Jul '20

On Raspbian Buster I get: pi@raspberrypi:~ $ LANG=de_DE ghc -e 'print System.IO.localeEncoding' UTF-8 pi@raspberrypi:~ $ LANG=de_DE.iso88591 ghc -e 'print System.IO.localeEncoding' UTF-8 pi@raspberrypi:~ $ LANG=de_DE@euro ghc -e 'print System.IO.localeEncoding' UTF-8 Which is not, what I want. On Debian Buster it is correct: $ LANG=de_DE ghc -e 'print System.IO.localeEncoding' ISO-8859-1 How can I check whether this is a GHC problem and has anyone an idea how to fix it?

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Second call for draft papers for IFL 2020 (Implementation and Application of Functional Languages)
by Jurriaan Hage 15 Jul '20

15 Jul '20

Hello, Please, find below the second call for draft papers for IFL 2020. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL ================================================================================ IFL 2020 32nd Symposium on Implementation and Application of Functional Languages venue: online 2nd - 4th September 2020 https://www.cs.kent.ac.uk/events/2020/ifl20/ ================================================================================ ### 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 2020 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 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 - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Post-symposium peer-review Following IFL tradition, IFL 2020 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 chair 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. ### Important dates Submission deadline of draft papers: 17 August 2020 Notification of acceptance for presentation: 19 August 2020 Registration deadline: 31 August 2020 IFL Symposium: 2-4 September 2020 Submission of papers for proceedings: 7 December 2020 Notification of acceptance: 3 February 2021 Camera-ready version: 15 March 2021 ### 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 ### 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. ### Programme committee Kenichi Asai, Ochanomizu University, Japan Olaf Chitil, University of Kent, United Kingdom (chair) Martin Erwig, Oregon State University,United States Daniel Horpacsi, Eotvos Lorand University, Hungary Zhenjiang Hu, Peking University, China Hans-Wolfgang Loidl, Heriot-Watt University, United Kingdom Neil Mitchell, Facebook, UK Marco T. Morazan, Seton Hall University, United States Rinus Plasmeijer, Radboud University, Netherlands Colin Runciman, University of York, United Kingdom Mary Sheeran, Chalmers University of Technology, Sweden Josep Silva, Universitat Politecnica de Valencia, Spain Jurrien Stutterheim, Standard Chartered, Singapore Josef Svenningsson, Facebook, UK Peter Thiemann, University of Freiburg, Germany Kanae Tsushima, National Institute of Informatics, Japan. Marcos Viera, Universidad de la Republica, Montevideo, Uruguay Janis Voigtlander, University of Duisburg-Essen, Germany ### Virtual symposium Because of the Covid-19 pandemic, this year IFL 2020 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.

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containers-0.6.3.1
by David Feuer 14 Jul '20

14 Jul '20

At long last, we have released containers-0.6.3.1. The most important changes in this release are bug fixes for IntMap traversals: * Fix traverse and traverseWithKey for IntMap, which would previously produce invalid IntMaps when the input contained negative keys (Thanks, Felix Paulusma). * Fix the traversal order of various functions for Data.IntMap: traverseWithKey, traverseMaybeWithKey, filterWithKeyA, minimum, maximum, mapAccum, mapAccumWithKey, mapAccumL, mapAccumRWithKey, mergeA (Thanks, Felix Paulusma, Simon Jakobi). These now traverse in key order; previously they would traverse non-negative keys before negative keys. If you traverse any IntMaps, please take note of these changes. We also have several additions to the API: * Add compose for Map and IntMap (Thanks, Alexandre Esteves). * Add alterF for Set and IntSet (Thanks, Simon Jakobi). * Add Data.IntSet.mapMonotonic (Thanks, Javran Cheng). * Add instance Bifoldable Map (Thanks, Joseph C. Sible). Performance improvements of note: * Make (<*) for Data.Sequence incrementally asymptotically optimal (Thanks, David Feuer). This finally completes the task, begun in December 2014, of making all the Applicative methods for sequences asymptotically optimal even when their results are consumed incrementally. Many thanks to Li-Yao Xia and Bertram Felgenhauer for helping to clean up and begin to document this rather tricky code. * Speed up fromList and related functions in Data.IntSet, Data.IntMap and Data.IntMap.Strict (Thanks, Bertram Felgenhauer). * Use count{Leading,Trailing}Zeros in Data.IntSet internals (Thanks, Alex Biehl). There are also numerous documentation improvements and packaging updates. Please see the changelog for full details. Thanks to all the contributors, The containers team

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Call for Participation: ICFP 2020
by Sam Tobin-Hochstadt 14 Jul '20

14 Jul '20

===================================================================== Call for Participation ICFP 2020 25th ACM SIGPLAN International Conference on Functional Programming and affiliated events August 23 - August 28, 2020 Online http://icfp20.sigplan.org/ Early Registration until August 8! The ICFP Programming Contest starts on July 17! ===================================================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. This year, the conference will be a virtual event. All activities will take place online. The ICFP Programming competition will be July 17th through 20th, 2020! The main conference will take place from August 24-26, 2020 during two time bands. The first band will be 9AM-5:30PM New York, and will include both technical and social activities. The second band will repeat (with some variation) the technical program and social activities 12 hours later, 9AM-5:30PM Beijing, the following day. We’re excited to announce our two invited speakers for 2020: Evan Czaplicki, covering the Elm programming language and hard lessons learned on driving adoption of new programming languages; and Audrey Tang, Haskeller and Taiwan’s Digital Minister, on how software developers can contribute to fighting the pandemic. ICFP has officially accepted 37 exciting papers, and (as a fresh experiment this year) there will also be presentations of 8 papers accepted recently to the Journal of Functional Programming. Co-located symposia and workshops will take place the day before and two days immediately after the main conference. Registration is now open. The early registration deadline is August 8th, 2020. Registration is not free, but is significantly lower than usual. Students who are ACM or SIGPLAN members may register for FREE before the early deadline. https://regmaster.com/2020conf/ICFP20/register.php New this year: Attendees will be able to sign-up for the ICFP Mentoring Program (either to be a mentor, receive mentorship or both). * Overview and affiliated events: http://icfp20.sigplan.org/home * Accepted papers: http://icfp20.sigplan.org/track/icfp-2020-papers#event-overview * JFP Talks: https://icfp20.sigplan.org/track/icfp-2020-jfp-talks#event-overview * Registration is available via: https://regmaster.com/2020conf/ICFP20/register.php Early registration ends 8 August, 2020. * Programming contest: https://icfpcontest2020.github.io/ The Programming Contest begins July 17th! * Student Research Competition: https://icfp20.sigplan.org/track/icfp-2020-Student-Research-Competition * Follow us on Twitter for the latest news: http://twitter.com/icfp_conference This year, there are 10 events co-located with ICFP: * Erlang Workshop (8/23) * Haskell Implementors' Workshop (8/28) * Haskell Symposium (8/27-8/28) * Higher-Order Programming with Effects (8/23) * miniKanren Workshop (8/27) * ML Family Workshop (8/27) * OCaml Workshop (8/28) * Programming Languages Mentoring Workshop (8/23) * Scheme Workshop (8/28) * Type-Driven Development (8/23) ### ICFP Organizers General Chair: Stephanie Weirich (University of Pennsylvania, USA) Program Chair: Adam Chlipala (MIT, USA) Artifact Evaluation Co-Chairs: Brent Yorgey (Hendrix College, USA) Ben Lippmeier (Ghost Locomotion, Australia) Industrial Relations Chair: Alan Jeffrey (Mozilla Research, USA) Programming Contest Organizer: Igor Lukanin (Kontur, Russia) Publicity and Web Chair: Sam Tobin-Hochstadt (Indiana University, USA) Student Research Competition Chair: Youyou Cong (Tokyo Institute of Technology, Japan) Workshops Co-Chair: Jennifer Hackett (University of Nottingham, UK) Leonidas Lampropoulos (University of Pennsylvania, USA) Video Chair: Leif Andersen (Northeastern University, USA) Student Volunteer Co-Chair: Hanneli Tavante (McGill University, Canada) Victor Lanvin (IRIF, Université Paris Diderot, France)

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Re: [Haskell-cafe] Caching functions compiled with llvm-hs
by Tom Westerhout 12 Jul '20

12 Jul '20

On 11/07/2020, Georgi Lyubenov <godzbanebane(a)gmail.com> wrote: > Is there something wrong with your idea? (other than ideological issues > with unsafePerformIO - I guess then the standard approach would be to use > some State holding your compiled functions or a Reader over an MVar holding > your compiled functions) The part that feels wrong here is that one has to create a new Module for every single function. I always thought of LLVM Modules as kind of compilation units. Or is this an okay-ish approach? > > The only thing you should make sure to do is add a NOINLINE to wherever the > unsafePerformIO is, so that it doesn't get inlined and executed more than > once. Oh I totally forgot! Thank you for reminding! Cheers, Tom

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