- Haskell-Cafe - Haskell.org

"Magical Haskell" book is finally finished and available :)
by Anton Antich 22 Apr '25

22 Apr '25

Dear all, I have started working on this book almost 10 years ago, wrote about a third and then took a big pause until last year, when I got approached by Springer and finished the book in another 6 months, dedicating the 2nd part to Agentic AI and now it's finally out and available and I would really love to get the community's feedback :) I tried to introduce Haskell from the first mathematical principles, but very gently, so that it is accessible to a much wider audience as we all know the learning curve can be a bit steep. Here is a sample free chapter on medium: https://medium.com/superstringtheory/functor-bifunctor-trifunctor-c1424f962… The book itself is available on Springer: https://link.springer.com/book/10.1007/979-8-8688-1282-8 And there is a 20% discount with the code APAUT - or just scan the QR code below. I put a lot of effort into this book, being passionate about the language we all love and do hope it will help more people to become proficient and fluent in Haskell! Best wishes, Anton Antich, CPO and founder, Integrail.ai [image: image.png]

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Release: webdriver-precore
by John Walker 21 Apr '25

21 Apr '25

Hi All, We are happy to announce the release of [webdriver-precore]( https://hackage.haskell.org/package/webdriver-precore) ~ *A typed wrapper for [W3C WebDriver](https://www.w3.org/TR/2025/WD-webdriver2-20250306/) protocol* This library is intended to be used as a base for other libraries that provide a WebDriver client implementation and higher level functions for browser automation. More details can be found in the [project README]( https://github.com/pyrethrum/webdriver) John & Adrian

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type-class and subclasses
by lloyd allison 16 Apr '25

16 Apr '25

I have a general question: I would like to have a type-class C in which types that are instances of C have some type parameters and then a subclass S of C where some of the type parameters of an instance of S are more constrained in some way -- perhaps by being equal and/or being instances of some other class. I have an entirely artificial example (att.) that illustrates this situation and struggled (it's a while since I wrote much Haskell) to get it past the ghc type checker until stumbling across GADTs which do seem to do the trick, so I could leave it at that but... ...I am very far from sure that this is the correct way to look at the problem and am hoping for some illumination. regards Lloyd. -- No AI was used in composing this message.

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TyDe 2025 - Call for Papers & Extended Abstracts
by Andras Kovacs 11 Apr '25

11 Apr '25

========================================================================= The Tenth International Workshop on TYPE-DRIVEN DEVELOPMENT Call for papers and extended abstracts Singapore, 12 October 2025 https://icfp25.sigplan.org/home/tyde-2025 ========================================================================= The Workshop on Type-Driven Development (TyDe) aims to show how static type information may be used effectively in the development of computer programs. Co-located with ICFP and SPLASH, this workshop brings together leading researchers and practitioners who are using or exploring types as a means of program development. We welcome all contributions, both theoretical and practical, on a range of topics including: * dependently typed programming; * generic programming; * design and implementation of programming languages, exploiting types in novel ways; * exploiting typed data, data dependent data, or type providers; * static and dynamic analyses of typed programs; * tools, IDEs, or testing tools exploiting type information; * pearls, being elegant, instructive examples of types used in the derivation, calculation, or construction of programs. ### Important dates ### * Mon 9 Jun 2025 (AoE): Submission deadline for papers and extended abstracts * Wed 16 Jul 2025: Notification of acceptance * Wed 30 Jul 2025: Submission of camera-ready papers to ACM * Sun 12 Oct 2025: Workshop ### Proceedings and Copyright ### We will have formal proceedings for full-length papers, published by the ACM. Accepted papers will be included in the ACM Digital Library. Authors must grant ACM publication rights upon acceptance, but may retain copyright if they wish. Authors are encouraged to publish auxiliary material with their paper (source code, test data, and so forth). The proceedings will be freely available for download from the ACM Digital Library from one week before the start of the conference until two weeks after the conference. The official publication date is the date the papers are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. ### Submission Details ### Submissions should fall into one of two categories: * regular research papers (12 pages); * extended abstracts (3 pages). The bibliography will not be counted against the page limits for either category. Regular research papers are expected to present novel and interesting research results, and will be included in the formal proceedings. Extended abstracts should report work in progress that the authors would like to present at the workshop. Extended abstracts will be distributed to workshop attendees but will not be published in the formal proceedings. We welcome submissions from PC members (with the exception of the two co-chairs), but these submissions will be held to a higher standard. Submission is handled through HotCRP: > https://tyde25.hotcrp.com All submissions should be in portable document format (PDF) and formatted using the ACM SIGPLAN style guidelines: > https://www.sigplan.org/Resources/Author/ Note that submissions should use the new ‘acmart’ format and the two-column ‘sigplan’ subformat (not to be confused with the one-column ‘acmsmall’ subformat). Extended abstracts must be submitted with the label ‘Extended Abstract’ clearly in the title. ### Presentations ### We expect that each accepted submission is presented at the workshop. Presentations are around 20 minutes plus questions. Remote presentation is possible. ### Participant Support ### Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover participation-related expenses. PAC also offers other support, such as for child-care expenses during the meeting or for accommodations for members with physical disabilities. For details on the PAC program, see its web page: > https://www.sigplan.org/PAC/

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Extended deadline - CFP - Haskell Implementors' Workshop 2025
by Andreas Herrmann 07 Apr '25

07 Apr '25

Extended deadline to April 18, 2025 Call for proposals for the Haskell Implementors' Workshop https://haskell.foundation/events/2025-haskell-implementors-workshop.html June 6, 2025 Organized by the Haskell Community Co-located with ZuriHac 2025 and Haskell Ecosystem Workshop 2025 Hosted by the Haskell Foundation at Eastern Switzerland University of Applied Sciences (OST) https://www.ost.ch/en/university-of-applied-sciences/campus/rapperswil-jona… ## Overview * Extended Deadline: April 18, 2025 * Notification: May 5, 2025 * Workshop: June 6, 2025 The 17th Haskell Implementors' Workshop is to be held alongside ZuriHac 2025 this year near Zurich. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure to share their work and to discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos, and lightning talks. In the past the Haskell Implementors’ Workshop was co-located with ICFP (International Conference on Functional Programming). However, in recent years it has become more and more challenging to attract a large enough audience and sufficiently many speakers for an appealing program. ZuriHac and the Haskell Ecosystem Workshop have become an important annual gathering of a large part of the Haskell community. This year the Haskell Implementors’ Workshop will be co-located with these events to be accessible to a broader audience. ## Scope and Target Audience The Haskell Implementors' Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community are encouraged to attend the workshop - we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are especially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimization and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment ## Talks We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Submissions can be made via the form linked below until April 18, 2025 (anywhere on earth). https://docs.google.com/forms/d/e/1FAIpQLSdczGbxJYGc4eusvPrxwBbZl561PnKeYno… We will also have a lightning talks session. Lightning talks should be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. ## Program Committee * Luite Stegeman * Jaro Reinders * Emily Pillmore * Rodrigo Mesquita * Ian-Woo Kim * Andreas Herrmann (chair) ## Contact * Andreas Herrmann

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Re: [Haskell-cafe] type level function with different return kinds
by Barak A. Pearlmutter 07 Apr '25

07 Apr '25

Can a type level function have different return kinds depending on its arguments? I think this question is best answered by quoting https://aphyr.com/posts/342-typing-the-technical-interview “Haskell is a dynamically-typed, interpreted language.”

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type level function with different return kinds
by Zoran Bošnjak 07 Apr '25

07 Apr '25

Dear haskellers, is it possible to write a type/kind level function that returns types of different kinds for different inputs. Either by using open/closed type families, a typeclass, extensions or any other type level magic. Something like this: {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeFamilies #-} import GHC.TypeLits data A = A1 | A2 data B = B1 | B2 type family F (n :: Nat) where F 0 = 'A1 F 1 = 'A2 F 2 = 'B1 F 3 = 'B2 The problem with this approach is that (F 0) and (F 1) are ok, but not in combination with (F 2). The error says: • Expected kind ‘A’, but ‘'B1’ has kind ‘B’ If I instead write: type family F (n :: Nat) :: k where ... I get compile error already on the (F 0) line • Expected kind ‘k’, but ‘'A1’ has kind ‘A’ Any ideas how to remove the "same kind" restriction or how to workaround it? I am using ghc 9.6.6. regards, Zoran

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dumping ByteArray#
by Kazu Yamamoto 29 Mar '25

29 Mar '25

Hello, For debugging, I need to dump the inside of `ByteArray#`. Are there any utility functions for this purpose? --Kazu

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implementing a class using superclasses?
by Mark McConnell 29 Mar '25

29 Mar '25

Here is a simplified, self-contained version of some code I'm working on. I have a Ord type Foo that I want to be ordered primarily by comp1, and, in case of ties, secondarily by comp2. It is important to my users to know that the primary sorting will always be by comp1. Therefore, I am trying to use to the type system to articulate that Foo must be ordered in a two-fold lexicographic way. My code is module Lex2Test where class Ord a => Primary a where comp1 :: a -> a -> Ordering comp1 = compare class Ord a => Secondary a where comp2 :: a -> a -> Ordering comp2 = compare class (Primary a, Secondary a) => Lex2 a instance Lex2 a => Ord a where compare x y = comp1 x y <> comp2 x y However, when I load the code into ghci, I get Lex2Test.hs:13:10: error: • The constraint ‘Lex2 a’ is no smaller than the instance head ‘Ord a’ (Use UndecidableInstances to permit this) • In the instance declaration for ‘Ord a’ |13 | instance Lex2 a => Ord a where | ^^^^^^^^^^^^^^^ I feel I must be missing something. UndecidableInstances seems too extreme for what I am trying to do. (I have never said that I want to go backwards in class inference from Ord to Lex2.) If this were C++, I would be just trying to implement some virtual functions in terms of other virtual functions. Any comments would be appreciated.

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Call for Nominations: SLE 2025 - Artifact Evaluation Committee, Nominations Wanted
by Andrei Chis 28 Mar '25

28 Mar '25

18th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2025) 12-13 June 2025 Koblenz, Germany https://conf.researchr.org/home/sle-2025 https://www.sleconf.org/2025/ https://x.com/sleconf ------------------------------------------------------------------------ The SLE 2025 Artifact Evaluation Committee (AEC) is looking for nominations and self-nominations for committee members. If you are a PhD student, postdoctoral researcher, associate, or professor working in software language engineering, we encourage you to apply. Serving on the AEC is an excellent opportunity to contribute to the community and gain valuable experience in artifact evaluation. -------------------------------------- Important Dates (All deadlines are AoE) -------------------------------------- Artifact submission deadline: April 23, 2025 Artifact bidding: April 24–26, 2025 Camera-ready deadline for SLE papers: May 1, 2025 Kick-the-tires review deadline & rebuttal phase: May 2, 2025 Final review deadline: May 24, 2025 Artifact discussion: May 25–31, 2025 Artifact notification: June 1, 2025 ------------------------------------------------------------------------ To nominate yourself or someone else, please complete the following form by April 6, 2025 Form: https://docs.google.com/forms/d/15Q-9i1tCwHzrtdtRqfJbWqZs4hV7DnJfwBSZuop75b… For any questions, please do not hesitate to contact us. SLE 2025 Artifact Evaluation Co-Chairs, Idriss Riouak and Jeff Smits Idriss Riouak: idriss.riouak(a)cs.lth.se Jeff Smits: j.smits-1(a)tudelft.nl

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