July 2019 - Haskell-Cafe

[language-dart] Package takeover initiation
by Sergey Bushnyak 28 Jul '19

28 Jul '19

Hi all, I tried to contact the author via github issues and direct email with no response in couple weeks. This is my statement on desire to takeover package maintainership forhttps://hackage.haskell.org/package/language-dart <https://hackage.haskell.org/package/language-dart> -- Sergey Bushnyak

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Munich Haskell Meeting, 2019-07-31 @ 19:30
by Leah Neukirchen 28 Jul '19

28 Jul '19

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, July 31 at Augustiner-Gaststätte Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jul-2019/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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type variable is ambiguous in a non-injective type family
by Henry Laxen 28 Jul '19

28 Jul '19

Dear Cafe, I really don't understand what is going on here. I've searched, but I don't really understand the links that I found. The closest I've come is: https://sulzmann.blogspot.com/2013/01/non-injective-type-functions-and.html but I don't understand it enough to see my way to a solution. Here is a minimal example of what I'm trying to do: -------------------------------------------------------------------------------- {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE AllowAmbiguousTypes #-} module Ambiguous where class Ambi a where type SubAmbi a :: * toSubAmbi :: a -> SubAmbi a toBool :: SubAmbi a -> Bool whatsWrong :: Ambi a => a -> IO () whatsWrong a = do let s = toSubAmbi a b = toBool s if b then print "True" else print "False" {- src/Games/Ambiguous.hs:15:16: error: … • Couldn't match expected type ‘SubAmbi a0’ with actual type ‘SubAmbi a’ NB: ‘SubAmbi’ is a non-injective type family The type variable ‘a0’ is ambiguous • In the first argument of ‘toBool’, namely ‘s’ In the expression: toBool s In an equation for ‘b’: b = toBool s • Relevant bindings include s :: SubAmbi a (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:14:5) a :: a (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:12:12) whatsWrong :: a -> IO () (bound at /home/henry/nadineloveshenry/bin/nlh/src/Games/Ambiguous.hs:12:1) | Compilation failed. -} -------------------------------------------------------------------------------- Could any of you Haskell sages please explain how to do this? Best wishes, Henry Laxen -- Nadine and Henry Laxen The rest is silence Villa Alta #6 Calle Gaviota #10 Never try to teach a pig to sing Chapala It wastes your time +52 (376) 765-3181 And it annoys the pig

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Final call for draft papers for IFL 2019 (Implementation and Application of Functional Languages)
by Jurriaan Hage 26 Jul '19

26 Jul '19

Hello, Please, find below the final call for draft papers for IFL 2019. 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 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: June 15, 2019 Submission of draft papers: August 1, 2019 Regular papers notification: August 1, 2019 Regular draft papers notification: August 7, 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, Toho University - 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 31st IFL is organized by the National University of Singapore. Singapore is located in the heart of South-East Asia, and the city itself is extremely well connected by trains and taxis. 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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Re: [Haskell-cafe] What is the most modern associative list in types?
by Daniel Díaz 24 Jul '19

24 Jul '19

Hi Serguey, I don’t know what extra functionality you require but, for what is worth, my library red-black-record features a Symbol-to-Type map . It’s implemented as a type-level red-black-tree. https://hackage.haskell.org/package/red-black-record-2.0.2.2/docs/Data-RBR.… The map can be manipulated with the Insert, Delete and Value associated type families. Regards, Daniel Díaz > Hello cafe. > > I am trying to express some environment in types to constrain program > behavour. For this I need associative list of types, something along the > lines of [(Symbol, *)] so that I can lookup on "variable" name and get type > associated with it. > > I looked into HList library but it does not provide one most generally > useful way (albeit there are dozen or so of ways in there). > > So where can I get most modern HList-like library? Or what should I read > to get most modern HList myself?

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What is the most modern associative list in types?
by Serguey Zefirov 24 Jul '19

24 Jul '19

Hello cafe. I am trying to express some environment in types to constrain program behavour. For this I need associative list of types, something along the lines of [(Symbol, *)] so that I can lookup on "variable" name and get type associated with it. I looked into HList library but it does not provide one most generally useful way (albeit there are dozen or so of ways in there). So where can I get most modern HList-like library? Or what should I read to get most modern HList myself?

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[ANNOUNCE] GHC 8.8.1 release candidate 1 is now available
by Ben Gamari 22 Jul '19

22 Jul '19

Hello everyone, The GHC team is pleased to announce the release candidate for GHC 8.8.1. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/ghc/8.8.1-rc1 This release is the culmination of over 3000 commits by over one hundred contributors and has several new features and numerous bug fixes relative to GHC 8.6: * Profiling now works correctly on 64-bit Windows (although still may be problematic on 32-bit Windows due to platform limitations; see #15934) * A new code layout algorithm for amd64's native code generator * The introduction of a late lambda-lifting pass which may reduce allocations significantly for some programs. * Further work on Trees That Grow, enabling improved code re-use of the Haskell AST in tooling * More locations where users can write `forall` (GHC Proposal #0007) * A comprehensive audit of GHC's memory ordering barriers has been performed, resulting in a number of fixes that should significantly improve the reliability of programs on architectures with weakly-ordered memory models (e.g. PowerPC, many ARM and AArch64 implementations). * A long-standing linker limitation rendering GHCi unusable with projects with cyclic symbol dependencies has been fixed (#13786) * Further work on the Hadrian build system * Numerous bug-fixes As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.1-rc1/docs/html/users_guide/8.8.1-not…

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Translating a pre-image witness from agda to haskell
by Ruben Astudillo 22 Jul '19

22 Jul '19

Dear list I've been playing with agda lately, I've been following the tutorials on their homepage to get a grasp of dependent types. The exposition has been good and clear. Some techniques can be passed over to haskell by using GADTs and DataKinds. Some examples require singletons to have the same kind of quantification as in agda. Currently I am trying to write in haskell the following data type and function data Image {A B : Set} (f : A -> B) : B -> Set where im : (x : A) -> Image f (f x) inv : {A B : Set} (f : A -> B) (y : B) -> Image f y -> A inv f .(f x) (im x) = x The `Image` datatype correspond to the proposition that the function `f : A -> B` has a pre-image for certain element on `B`. This is witnessed only if the `im` data constructor exists. The `inv` function is there only to show how agda can know by the presence of the `im x` data constructor that the value of `y` cannot be other than `f x`, mind bending stuff. I've been trying to write this ADT on haskell. I haven't got luck in so far. The problem is that referring to a `type family` constructed from a term level function is not clear to me, even with singletons, as I cannot guarantee such type family is defined. Currently I got this data Image (f :: Type -> Type) Type where Im :: Proxy (Sing t1 -> Sing (f t1)) -> f t1 -> Image (Sing t1 -> Sing (f t1)) (f t1) Which isn't exactly what the agda version is. Does anyone has an idea on how to continue or has done this example before? I am perfectly OK with being told it's not possible yet or what should I read. -- -- Ruben -- PGP: 4EE9 28F7 932E F4AD

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Journeys in Computational Logic: Tributes to Roy Dyckhoff : CFP
by Ekaterina Komendantskaya 22 Jul '19

22 Jul '19

CALL FOR PARTICIPATION Journeys in Computational Logic: Tributes to Roy Dyckhoff at TABLEAUX 2019, the 28th International Conference on Automated Reasoning with Analytic Tableaux and Related Methods, Middlesex University, London https://tableaux2019.org/ Main conference: 3 September to 5 September 2019 Journeys in Computational Logic: 3 September 2019 Roy Dyckhoff (1948 - 2018) worked in logic and proof theory, having begun his career as a topologist and category theorist (for which one of his thesis advisors was Dana Scott). Much of his work concerned various aspects of intuitionistic logic, but he also contributed to work in programming languages, type theory, natural language processing, and model checking. The event will commemorate and celebrate Roy’s work, by speakers who have crossed paths with Roy, and/or whose work or scientific views have been influenced by him. The workshop will follow the Tableaux invited talks by Sara Negri and Stéphane Graham-Lengrand, also dedicated to Roy’s work and contribution to the field. The list of contributors is as follows: Marta Bilkova Alessio Guglielmi Jacob Howe Jael Kriener James McKinna Mehrnoosh Sadrzadeh Peter Schroeder-Heister Christian Urban SOCIAL EVENT The workshop will be followed by the Tableaux welcome reception. ORGANISERS If you have any questions, or wish to contribute a talk, please contact the organisers: Ekaterina Komendantskaya: http://www.macs.hw.ac.uk/~ek19/ Stephane Graham-Lengrand: http://www.csl.sri.com/users/sgl/ Mehrnoosh Sadrzadeh: https://msadrzadeh.com/

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ANNOUNCE: lens-family 2.0.0 anniversary edition!
by roconnor＠theorem.ca 20 Jul '19

20 Jul '19

In celebration of the 10th anniversary of Twan van Laarhoven's seminal blog post ``CPS based functional references''[1], I am releasing version 2.0 of lens-family[2] and lens-family-core[3] packages. This new release continues to explore the design of Van Laarhoven style optics with new support for adapters, grates, grids[4], and prisms. To bring support to these new optics necessarily means moving a little further away from syntactic compatibility with Kmett's lens library. In particular, lens-family's 'under' is unrelated to Kmett's lens library's 'under' combinator. Nonetheless the 'under' combinator plays a crucial role in lens-family as a dual to the 'over' combinator and this naming is hard to resist despite the conflict. This new version comes with some minor incompatibilities with the version 1.2 library that may require user updates. See <https://hackage.haskell.org/package/lens-family-2.0.0/changelog>. [1]<https://www.twanvl.nl/blog/haskell/cps-functional-references> [2]<https://hackage.haskell.org/package/lens-family-2.0.0> [3]<https://hackage.haskell.org/package/lens-family-core-2.0.0> [4]A grid is an optic that is both a grate and a traversal. -- Russell O'Connor <http://r6.ca/>

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