April 2025 - Haskell-Cafe

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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type-class and subclasses
by lloyd allison 10 Apr '25

10 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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Is there a way to make this code compose generic ?
by PICCA Frederic-Emmanuel 09 Apr '25

09 Apr '25

Hello, I have this data DataSourceShape = DataSourceShape ([HSize], [Maybe HSize]) | DataSourceShape'Range !DIM1 !DIM1 a function which combine 2 DataSourceShape and produce an new one (monoid operation ?) combine'Shape ∷ DataSourceShape → DataSourceShape → DataSourceShape I use this in this class with familly types. class DataSource a where data DataSourcePath a ∷ Type data DataSourceAcq a ∷ Type ds'Shape ∷ MonadSafe m ⇒ DataSourceAcq a → m DataSourceShape withDataSourceP ∷ (Location l, MonadSafe m) ⇒ ScanFile l → DataSourcePath a → (DataSourceAcq a → m r) → m r and here an instance for one of my type DataFrameQCustom (I have plenty of them). they are all constructed the same way. data DataSourceAcq DataFrameQCustom = DataSourceAcq'DataFrameQCustom (DataSourceAcq Attenuation) (DataSourceAcq Geometry) (DataSourceAcq Image) (DataSourceAcq Mask) (DataSourceAcq Timestamp) (DataSourceAcq Timescan0) (DataSourceAcq Scannumber) ds'Shape(DataSourceAcq'DataFrameQCustom a g i m idx t0 s) = do sa ← ds'Shape a sg ← ds'Shape g si ← ds'Shape i sm ← ds'Shape m sidx ← ds'Shape idx st0 ← ds'Shape t0 ss ← ds'Shape s pure $ foldl1 combine'Shape [sa, sg, si, sm, sidx, st0, ss] withDataSourceP f (DataSourcePath'DataFrameQCustom a g i m idx t0 s) gg = withDataSourceP f a $ λa' → withDataSourceP f g $ λg' → withDataSourceP f i $ λi' → withDataSourceP f m $ λm' → withDataSourceP f idx $ λidx' → withDataSourceP f s $ λs' → withDataSourceP f t0 $ λt0' → gg (DataSourceAcq'DataFrameQCustom a' g' i' m' idx' t0' s') My question is, how should avoid writting by hand all these ds'Shape / withDatasourceP implementations, which seems quite mechanical. thanks for your help Frederic

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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 06 Apr '25

06 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 06 Apr '25

06 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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