- Haskell-Cafe - Haskell.org

augmenting GHC package database
by Sylvester Hazel 28 Aug '20

28 Aug '20

Hi Haskellers, Cabal couldn't resolve dependencies for a generated package so I used Stack that used 2 different GHC versions to build library from this package. Stack stored the library as libHSclient-something.a , HSclient-something.o and helper ".hi" files The dependent libraries Stack stored and registered at C:\sr..\lib\ How to add this information to GHC or Cabal database to be able to use this new library? This is on Chocolatey managed Windows platform;-)

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writing wizards in Yesod
by Olaf Klinke 27 Aug '20

27 Aug '20

Dear Café, TL;DR: What is the canonical way to deal with state in Yesod? IORef? StateT? Routes? Subsites? The Yesod book [1,2] gives examples where state is encoded in an IORef inside the foundational type, like so: data AppState = ... data App = App {appState :: IORef AppState} All handlers would then first read the AppState via getsYesod appState >>= (liftIO . readIORef) and branch on the result. I wonder if there are other ways to deal with state that changes through user interaction. After all, we have instance MonadHandler m => MonadHandler (StateT s m) in Yesod.Core. What is this useful for? From [1]: "By just providing you with a readable environment, you’re able to recreate a StateT transformer by relying on mutable references." also: "In order to run these [monad transformer actions], we can use the standard [...] unwrap functions [...] to run the action and get back a normal Handler." I interpret quote 1 as "StateT is to be emulated (via IORef), not used literally" and quote 2 as "real StateT can not be used directly, but must be unwrapped to be used in a handler". Context for my question: I found that Kleisli maps model wizards nicely as a sequence of fragments, e.g. Program User f :: () -> m a g :: a -> m b h :: b -> m c i :: c -> m d j :: d -> m () wizard :: m () wizard = (f >=> g >=> h >=> i >=> j) () The intermediate types a, c are questions and b, d are answers, and all types together form the program states. If the user side of the wizard is to be provided by websites, we need to model these states explicitly somehow. My current approach is to use the union type AppState = Start | Answer1 b | Answer2 d that tells the handler what step to serve next. Olaf [1] https://www.yesodweb.com/book/yesods-monads#yesods-monads_adding_a_new_mona… [2] https://www.yesodweb.com/book/visitor-counter

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Munich Haskell Meeting, 2020-08-27 @ 19:30
by Leah Neukirchen 26 Aug '20

26 Aug '20

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, August 27 at Hirschgarten at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html Please add yourself here if you want to come so we know who to look out for: https://dudle.inf.tu-dresden.de/haskell-munich-aug-2020/ Unfortunately, I almost forgot about the meeting tomorrow, please excuse the short notice. I'm also at Hirschgarten for other reasons, so I may drop by only for a short time. Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Call for participation for IFL 2020: 32nd Symposium on Implementation and Application of Functional Languages
by Simon Thompson 26 Aug '20

26 Aug '20

[apologies for any multiple copies] ======================================================= IFL 2020 32nd Symposium on Implementation and Application of Functional Languages Call for Participation 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. ### Registration The symposium will be run via Zoom (zoom.us<http://zoom.us>). If you can use Zoom, then you can participate. Please register for free via Eventbrite on the symposium webpage: https://www.cs.kent.ac.uk/events/2020/ifl20/ ### Programme Day 1: Wednesday, 2 September 12:45 Welcome 13:00 Nico Naus and Johan Jeuring: End-user feedback in multi-user workflow systems 13:30 Mart Lubbers, Haye Böhm, Pieter Koopman and Rinus Plasmeijer: Asynchronous Shared Data Sources 14:00 Pieter Koopman, Steffen Michels and Rinus Plasmeijer: Dynamic Editors for Well-Typed Expressions 14:30 Bas Lijnse and Rinus Plasmeijer: Asymmetric Composable Web Editors in iTasks 15:00 Social break 15:30 Sven-Olof Nyström: A subtyping system for Erlang 16:00 Andrew Marmaduke, Christopher Jenkins and Aaron Stump: Generic Zero-Cost Constructor Subtyping 16:30 Joris Burgers, Jurriaan Hage and Alejandro Serrano: Heuristics-based Type Error Diagnosis for Haskell - The case of GADTs and local reasoning 17:00 Social break 17:30 Kavon Farvardin and John Reppy: A New Backend for Standard ML of New Jersey 18:00 Chaitanya Koparkar, Mike Rainey, Michael Vollmer, Milind Kulkarni and Ryan R. Newton: A Compiler Approach Reconciling Parallelism and Dense Representations for Irregular Trees 18:30 Hans-Nikolai Vießmann and Sven-Bodo Scholz: Effective Host-GPU Memory Mangement Through Code Generation 20:00 Virtual Pub Day 2: Thursday, 3 September 10:00 Virtual Breakfast 13:00 Michal Gajda: Less Arbitrary waiting time 13:30 Sólrún Halla Einarsdóttir and Nicholas Smallbone: Template-based Theory Exploration: Discovering Properties of Functional Programs by Testing 14:00 Péter Bereczky, Dániel Horpácsi, Judit Kőszegi, Soma Szeier and Simon Thompson: Validating Formal Semantics by Comparative Testing 14:30 Social break 15:00 Gergo Erdi: An Adventure in Symbolic Execution 15:30 Joshua M. Schappel, Sachin Mahashabde and Marco T. Morazan: Using OO Design Patterns in a Functional Programming Setting 16:00 Filipe Varjão: Functional Programming and Interval Arithmetic with High Accuracy 16:30 Social break 17:00 Laith Sakka, Chaitanya Koparkar, Michael Vollmer, Vidush Singhal, Sam Tobin-Hochstadt, Ryan R. Newton and Milind Kulkarni: General Deforestation Using Fusion, Tupling and Intensive Redundancy Analysis 17:30 Benjamin Mourad and Matteo Cimini: A Declarative Gradualizer with Lang-n-Change 18:00 Maheen Riaz Contractor and Matthew Fluet: Type- and Control-Flow Directed Defunctionalization 19:30 Virtual Pub Day 3: Friday, 4 September 10:00 Virtual Breakfast 13:00 Michal Gajda: Towards a more perfect union type 13:30 Folkert de Vries, Sjaak Smetsers and Sven-Bodo Scholz: Container Unification for Uniqueness Types 14:00 Alejandro Díaz-Caro, Pablo E. Martínez López and Cristian Sottile: Polymorphic System I 14:30 Social break 15:00 Michal Gajda: Schema-driven mutation of datatype with multiple representations 15:30 Alexandre Garcia de Oliveira, Mauro Jaskelioff and Ana Cristina Vieira de Melo: On Structuring Pure Functional Programs with Monoidal Profunctors 16:00 Sara Moreira, Pedro Vasconcelos and Mário Florido: Resource Analysis for Lazy Evaluation with Polynomial Potential 16:30 Social break 17:00 Neil Mitchell, Moritz Kiefer, Pepe Iborra, Luke Lau, Zubin Duggal, Hannes Siebenhandl, Matthew Pickering and Alan Zimmerman: Building an Integrated Development Environment (IDE) on top of a Build System 17:30 Evan Sitt, Xiaotian Su, Beka Grdzelishvili, Zurab Tsinadze, Zongpu Xie, Hossameldin Abdin, Giorgi Botkoveli, Nikola Cenikj, Tringa Sylaj and Viktoria Zsok: Functional Programming Application for Digital Synthesis Implementation 18:00 Jocelyn Serot: HoCL: High level specification of dataflow graphs 19:30 Virtual Pub All times are in British Summer Time (BST), the local time in Canterbury, UK. So please translate these into your own time zone, using a service such as time and date. Simon Thompson | Professor Emeritus of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk<mailto:s.j.thompson@kent.ac.uk> | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt<http://www.cs.kent.ac.uk/~sjt>

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First and Only Call for Participation for IFL 2020 (Implementation and Application of Functional Languages)
by Jurriaan Hage 26 Aug '20

26 Aug '20

Hello, Please, find below the first and final call for participation 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 Call for Participation 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. ### Registration The symposium will be run via Zoom (zoom.us). If you can use Zoom, then you can participate. Please register for free via Eventbrite on the symposium webpage: https://www.cs.kent.ac.uk/events/2020/ifl20/ ### Programme Day 1: Wednesday, 2 September 12:45 Welcome 13:00 Nico Naus and Johan Jeuring: End-user feedback in multi-user workflow systems 13:30 Mart Lubbers, Haye Böhm, Pieter Koopman and Rinus Plasmeijer: Asynchronous Shared Data Sources 14:00 Pieter Koopman, Steffen Michels and Rinus Plasmeijer: Dynamic Editors for Well-Typed Expressions 14:30 Bas Lijnse and Rinus Plasmeijer: Asymmetric Composable Web Editors in iTasks 15:00 Social break 15:30 Sven-Olof Nyström: A subtyping system for Erlang 16:00 Andrew Marmaduke, Christopher Jenkins and Aaron Stump: Generic Zero-Cost Constructor Subtyping 16:30 Joris Burgers, Jurriaan Hage and Alejandro Serrano: Heuristics-based Type Error Diagnosis for Haskell - The case of GADTs and local reasoning 17:00 Social break 17:30 Kavon Farvardin and John Reppy: A New Backend for Standard ML of New Jersey 18:00 Chaitanya Koparkar, Mike Rainey, Michael Vollmer, Milind Kulkarni and Ryan R. Newton: A Compiler Approach Reconciling Parallelism and Dense Representations for Irregular Trees 18:30 Hans-Nikolai Vießmann and Sven-Bodo Scholz: Effective Host-GPU Memory Mangement Through Code Generation 20:00 Virtual Pub Day 2: Thursday, 3 September 10:00 Virtual Breakfast 13:00 Michal Gajda: Less Arbitrary waiting time 13:30 Sólrún Halla Einarsdóttir and Nicholas Smallbone: Template-based Theory Exploration: Discovering Properties of Functional Programs by Testing 14:00 Péter Bereczky, Dániel Horpácsi, Judit Kőszegi, Soma Szeier and Simon Thompson: Validating Formal Semantics by Comparative Testing 14:30 Social break 15:00 Gergo Erdi: An Adventure in Symbolic Execution 15:30 Joshua M. Schappel, Sachin Mahashabde and Marco T. Morazan: Using OO Design Patterns in a Functional Programming Setting 16:00 Filipe Varjão: Functional Programming and Interval Arithmetic with High Accuracy 16:30 Social break 17:00 Laith Sakka, Chaitanya Koparkar, Michael Vollmer, Vidush Singhal, Sam Tobin-Hochstadt, Ryan R. Newton and Milind Kulkarni: General Deforestation Using Fusion, Tupling and Intensive Redundancy Analysis 17:30 Benjamin Mourad and Matteo Cimini: A Declarative Gradualizer with Lang-n-Change 18:00 Maheen Riaz Contractor and Matthew Fluet: Type- and Control-Flow Directed Defunctionalization 19:30 Virtual Pub Day 3: Friday, 4 September 10:00 Virtual Breakfast 13:00 Michal Gajda: Towards a more perfect union type 13:30 Folkert de Vries, Sjaak Smetsers and Sven-Bodo Scholz: Container Unification for Uniqueness Types 14:00 Alejandro Díaz-Caro, Pablo E. Martínez López and Cristian Sottile: Polymorphic System I 14:30 Social break 15:00 Michal Gajda: Schema-driven mutation of datatype with multiple representations 15:30 Alexandre Garcia de Oliveira, Mauro Jaskelioff and Ana Cristina Vieira de Melo: On Structuring Pure Functional Programs with Monoidal Profunctors 16:00 Sara Moreira, Pedro Vasconcelos and Mário Florido: Resource Analysis for Lazy Evaluation with Polynomial Potential 16:30 Social break 17:00 Neil Mitchell, Moritz Kiefer, Pepe Iborra, Luke Lau, Zubin Duggal, Hannes Siebenhandl, Matthew Pickering and Alan Zimmerman: Building an Integrated Development Environment (IDE) on top of a Build System 17:30 Evan Sitt, Xiaotian Su, Beka Grdzelishvili, Zurab Tsinadze, Zongpu Xie, Hossameldin Abdin, Giorgi Botkoveli, Nikola Cenikj, Tringa Sylaj and Viktoria Zsok: Functional Programming Application for Digital Synthesis Implementation 18:00 Jocelyn Serot: HoCL: High level specification of dataflow graphs 19:30 Virtual Pub All times are in British Summer Time (BST), the local time in Canterbury, UK. So please translate these into your own time zone, using a service such as time and date.

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doctest-extract
by Henning Thielemann 22 Aug '20

22 Aug '20

I have started an alternative implementation of 'doctest'. In contrast to the original one, doctest-extract extracts Haskell test-modules from doctest comments. This integrates better with Cabal and its package version resolution and the tests are compiled, not interpreted in GHCi. Disadvantage is that doctest-extract does not support all features of 'doctest', e.g. IO-tests. I uploaded a preview as package candidates to Hackage: $ cabal install $(for pkg in doctest-extract-0.0 doctest-lib-0.0 utility-ht-0.0.16 non-empty-0.3.3; do echo https://hackage.haskell.org/package/$pkg/candidate/$pkg.tar.gz; done) Extract test modules like so: $ doctest-extract -i src/ -o test/ --executable-main=Test/Main.hs --import-tested $$(cat test-module.list) There is still a problem: A failing QuickCheck test does not abort the whole test-suite. 'cabal test' will report success even if one QuickCheck property test fails. I wonder what is the proposed way to make a failing property fail the test-suite? I could use (QC.whenFail exitFailure). Is this the intended way?

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ICFP tutorial on hardware design using BH (Bluespec Haskell)
by Rishiyur Nikhil 20 Aug '20

20 Aug '20

REMINDER: My tutorial "Designing Hardware Systems and Accelerators with Open-Source BH (Bluespec Haskell)" on Aug 23 at #ICFP2020 (online). Please pre-install tools; instructions in tutorial repo README: https://tinyurl.com/y29zxrow . ICFP web page: https://icfp20.sigplan.org . #RISCV #Bluespec #BSV #BH.

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Dhall for Word8, Word16, Double, etc
by ☂Josh Chia (謝任中) 19 Aug '20

19 Aug '20

Hi, Let's say I have a record type: data Foo = Foo { v :: Word16 } I want to have a FromDhall instance for Foo. I know this is easy to do if v is Integer instead of Word16. But v is Word16. Does Dhall enable the user to cleanly express how to input a Word16 with the requisite range checks, or is the user expected to only use Integer and do his own conversion and range checks within Haskell after inputting the Integer from Dhall? I have a record with Word32, Word16, Word8 & Double fields instead of Integer & Scientific.

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Third Call for Participation: ICFP 2020
by Sam Tobin-Hochstadt 19 Aug '20

19 Aug '20

===================================================================== Third 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/ Pre-registration ends August 21! ==================================================================== 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. Watch our new video, and Don't Stop ICFP: https://www.youtube.com/watch?v=Fte5wwnwCws Pre-registration ends August 21st! https://icfp20.sigplan.org/attending/Registration This year, the conference will be a virtual event. All activities will take place online. There are training sessions for Clowdr, our new online platform, on August 20 and 21. https://icfp20.sigplan.org/track/icfp-2020-clowdr-training#program 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've written a blog post about how conference mirroring will work for ICFP: https://blog.sigplan.org/2020/08/04/come-to-virtual-icfp/ 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 * Full Schedule: https://icfp20.sigplan.org/program/program-icfp-2020 * 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/ * Student Research Competition: https://icfp20.sigplan.org/track/icfp-2020-Student-Research-Competition * Tutorials https://icfp20.sigplan.org/track/icfp-2020-tutorials#program * 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) As well as tutorials on 8/23, 8/27, and 8/28. ### 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] Counterintuitive ScopedTypeVariables behaviour
by Anthony Clayden 18 Aug '20

18 Aug '20

Well I'll go to 'foot of our stairs! > [Erik] the above feels very similar to writing something like: > add :: _ => a -> b -> _ > add x y = x + y > > But that doesn't type check, since the types `a` and `b` are not the same, > but `+` needs them to be. Replying to both Erik's and Tom's replies. I'm afraid Alexis' went completely over my head. As I mentioned, the `PatternSignatures` part of `ScopedTypeVariables` has been around a long time. So long that it's in Hugs 2006. The same? Not quite. If I try Tom's O.P. add (x :: aa) (y :: b) = x + y Hugs complains 'Type annotation uses distinct variables aa and b where a single variable was inferred'. So the short answer is: if that's how your intuitions go, use Hugs. My explanation was going to be (this now only applies for GHC): just as using `x, y` as the dummy arguments to `add` doesn't come with any guarantees they're distinct values; so using `aa, b` as the dummy variables doesn't come with any guarantees they're distinct types. Specifying distinct tyvars in a stand-alone signature is different: you're giving the most general type to which `add` must conform. And using distinct tyvars means `add` must cope with those being distinct types. (Which it's equation doesn't.) BTW GHC accepts: add (x :: aa) (y :: b) = (x + y :: aa) :: b which shows how happy it is to use distinct tyvars for the same type. AntC

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