- Haskell-Cafe - Haskell.org

when does ghc(i) expand type synonyms?
by Johannes Waldmann 25 Oct '23

25 Oct '23

Dear cafe, my students were asking: why are types printed differently here? ghci> :set +t ghci> "foo" "foo" it :: String ghci> reverse "foo" "oof" it :: [Char] ... and I add ghci> fst ("foo", 42) "foo" it :: String compiler docs do not really explain the difference https://downloads.haskell.org/ghc/latest/docs/users_guide/ghci.html#ghci-cm… (it says "display the type of .." while technically it is "display some representation of the type of ..."?) I found this explanation of a somewhat related issue https://gitlab.haskell.org/ghc/ghc/-/issues/9183#note_83743 While playing around with this, I noticed: ghci> let x = "foo" in (x <> reverse x) "foooof" it :: String ghci> let x = "foo" in (x ++ reverse x) "foooof" it :: [Char] Well, it's just optics: when I extract the type programmatically, the synonym necessarily does get expanded ghci> import Data.Data ghci> typeOf (let x = "foo" in (x <> reverse x)) [Char] it :: TypeRep - Johannes

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Hackage not building package
by Ivan Perez 23 Oct '23

23 Oct '23

Hi, I recently uploaded a package ( https://hackage.haskell.org/package/dunai-0.12.0) and hackage is not building it. I don't see info anywhere and I cannot re-trigger a build: attempting to do so shows the message "Report not found -Build report does not exist" Is everything ok with hackage? Thanks Ivan

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Where did pem-0.2.4 come from? a.k.a. is anyone compelled to take-over this project?
by Noon van der Silk 19 Oct '23

19 Oct '23

Glancing at hackage, I happened to noticed that pem is at 0.2.4 - https://hackage.haskell.org/package/pem-0.2.4 Glancing at the repo, I notice that pem is at 0.2.3 - https://github.com/vincenthz/hs-pem It seems there _is_ a tag for 0.2.4, but `master` has not been updated <https://github.com/vincenthz/hs-pem/compare/master..pem-v0.2.4>. Is there anyone out there that feels compelled or excited to fix this? And perhaps relatedly, given vincent has archived all these repos; perhaps there could be a kind of "global takeover" by the HF cryptography working group of these projects? -- Noon van der Silk, ن http://silky.github.io/ "My programming language is kindness."

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Request for take over: graphviz
by Daniel Casanueva 18 Oct '23

18 Oct '23

Hello, graphviz [1] maintenance has been inactive for a long time now. Revisions have been published, but the maintainer seems unresponsive. Last year, Bodigrim suggested the package needs a new maintainer in a GitHub thread [2] that one month ago I found while looking if someone had already done the fix I needed. I'm happy to help keeping the package alive so, about a month ago, I emailed Ivan (graphviz's author) to the e-mail address from his GitHub profile, offering my assistance with graphviz. I haven't gotten any answer yet, so I thought I should be making my offer public, as indicated by the "Taking over a package" wikipage [3]. I don't have big change plans for graphviz. Most likely I will just be patching it to keep it working with future GHC releases and reviewing/accepting PRs. Thank you, Daniel [1] https://hackage.haskell.org/package/graphviz [2] https://github.com/ivan-m/graphviz/pull/53#issuecomment-1261496914 [3] https://wiki.haskell.org/Taking_over_a_package

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Assistant Prof at Barnard College, Columbia U
by Mark Santolucito 17 Oct '23

17 Oct '23

Hi all, Barnard College, Columbia University has an opening for an Assistant Professor: https://cs.barnard.edu/assistant-professor-computer-science-2024 The deadline is Oct 27 for full consideration. Barnard is the women's college of Columbia and has a 2-2 teaching load (typically with additional reductions). If you are interested, please feel free to reach out to me directly to discuss more. This is a unique place that I have really enjoyed the past few years! Mark https://www.marksantolucito.com/

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CFP: Workshop on Hardware Acceleration of Functional and Declarative Languages
by Rob Stewart 17 Oct '23

17 Oct '23

Hi haskell-cafe, Call for participation: HAFDAL 2024 The 1st Workshop on Hardware Acceleration of Functional and Declarative Languages (HAFDAL) will be co-located with HPCA, Edinburgh on March 2nd or 3rd 2024. This workshop will bring together computer architects and programming language implementers to explore software/hardware co-designs of high level execution models. We invite two forms of participation: (1) full paper submissions for 30 minute talks, (2) 5-10 minute lightning talks about related projects and early results. For full papers, we are looking for submissions that cover the motivation, design, or real-world application of hardware technology for functional/declarative languages, their compilers and runtime systems. Submission deadline: 20 November 2023. The call for participation and all key dates are here: https://haflang.github.io/images/hafdal24_cfp.pdf The workshop's website is: https://haflang.github.io/workshops/hafdal24.html Best wishes, Rob Stewart Associate Professor Mathematical and Computer Sciences Heriot-Watt University

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Release: stan, supporting GHCs 8.8-9.4
by Tom Ellis 15 Oct '23

15 Oct '23

I'm pleased to announce a new release of `stan`, a static analysis tool for Haskell. `stan` now supports GHCs in the range 8.8-9.4[1]. ### About `stan` Stan is a command-line tool for analysing Haskell projects. It discovers which parts of the code can potentially be improved, and offers suggestions on how to do so. Read more about `stan` in its [`README`](https://github.com/kowainik/stan/#what-this-tool-is-about). ### Installation I recommend obtaining `stan` from Hackage by following [the installation instructions in the README](https://github.com/kowainik/stan/#hackage). https://hackage.haskell.org/package/stan-0.1.0.0 ### Help wanted `stan` lacks active maintainers and is currently in essential maintainance only mode. I am helping out to make sure `stan` can continue to build with newer GHCs. I would welcome assistance, particularly on the following issues: * Supporting GHC 9.6 * Supporting GHC 9.8 * Prospective support for GHC 9.10 * Fixing caching on Github Actions If you would like to contribute to Stan please [create an issue](https://github.com/kowainik/stan/issues) on the Github repository. ### Credits Thanks to the Kowainik team for creating `stan` in the first place. Thanks to Veronika Romashkina for accepting me as a new maintainer for the project. ---- [1] Some point releases are excluded because the GHC API doesn't seem to provide enough type information, notably the later releases in the 9.2 series.

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CFP: Workshop on the Implementation of Type Systems (WITS) '24
by Richard Eisenberg 13 Oct '23

13 Oct '23

---------------------------------------------------------------------- CALL FOR CONTRIBUTIONS 3rd Workshop on the Implementation of Type Systems WITS 2024 January 20, 2024 London, United Kingdom https://popl24.sigplan.org/home/wits-2024 <https://popl24.sigplan.org/home/wits-2024> ---------------------------------------------------------------------- WITS 2024 is the third Workshop on the Implementation of Type Systems. The workshop will be held on January 20, 2024, in London, United Kingdom, co-located with POPL. The goal of this workshop is to bring together the implementors of a variety of languages with advanced type systems. The main focus is on the practical issues that come up in the implementation of these systems, rather than the theoretical frameworks that underlie them. In particular, we want to encourage exchanging ideas between the communities around specific systems that would otherwise be accessible to only a very select group. The workshop will have a mix of invited and contributed talks, organized discussion times, and informal collaboration time. *Scope* We invite participants to share their experiences, study differences among the implementations, and generalize lessons from those. We also want to promote the creation of a shared vocabulary and set of best practices for implementing type systems. Here are a few examples of topics we are interested to discuss: * syntax with binders and substitution * conversion modulo beta and eta * implicit arguments and metavariables * unification and constraint solving * metaprogramming and tactic languages * editor integration and automation * discoverability of language features * pretty printing and error messages This list is not exhaustive, so please contact the PC chairs in case you are unsure if a topic falls within the scope of the workshop. *Submissions* WITS solicits two kinds of submissions: * Contributed talks on the basis of an abstract. This can be on recently published or submitted work, work in progress, or a project that is still in the idea phase. * Proposals for roundtable discussions. This can be on any topic within the scope of the workshop, but should have a broader scope than a contributed talk. If accepted, you will be in charge of leading a discussion of 45 minutes around the proposed topic together with other interested attendees. Both kinds of proposals should be accompanied by an abstract of max. 1 page (exclusive of references), formatted according to the guidelines for SIGPLAN conferences: use the `sigplan` option to the `acmart` LaTeX document class. WITS will have no published proceedings, so submitting to WITS does not interfere with submission (before, after, or simultaneously) with other venues. Submissions are handled via https://wits24.hotcrp.com/ <https://wits24.hotcrp.com/>. *Important Dates* - Abstract submission deadline: 10 November, 2023 (AoE) - Notification: 1 December, 2023 - Workshop in London: 20 January, 2024 *Attendance and registration* WITS 2024 is colocated with POPL 2024 in London, UK. Information on registration and attendance will be posted on the POPL website at https://popl24.sigplan.org/ <https://popl24.sigplan.org/>. *Program Committee* Lennart Augustsson Epic Games, Sweden Edwin Brady St. Andrews, UK Jesper Cockx TU Delft, Netherlands co-chair Richard Eisenberg Jane Street, USA co-chair Jacques-Henri Jourdan CRNS, France Matthieu Sozeau INRIA, France Ningning Xie U. of Toronto, Canada

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[ANNOUNCE] GHC 9.8.1 is now available
by Ben Gamari 12 Oct '23

12 Oct '23

The GHC developers are very pleased to announce the availability of the final release of GHC 9.8.1. Binary distributions, source distributions, and documentation are available at downloads.haskell.org: https://downloads.haskell.org/ghc/9.8.1 GHC 9.8 brings a number of new features and improvements, including: * Preliminary support the `TypeAbstractions` language extension, allowing types to be bound in type declarations [TypeAbstractions]. * Support for the `ExtendedLiterals` extension, providing syntax for non-word-sized numeric literals in the surface language [extended-literals] * Improved rewrite rule matching behavior, allowing limited matching of higher-order patterns * Better support for user-defined warnings by way of the `WARNING` pragma [warnings] * The introduction of the new `GHC.TypeError.Unsatisfiable` constraint, allowing more predictable user-defined type errors [unsatisfiable] * Implementation of the export deprecation proposal, allowing module exports to be marked with `DEPRECATE` pragmas [deprecated-exports] * The addition of build semaphore support for parallel compilation; with coming support in `cabal-install` this will allow better use of parallelism in multi-package builds [jsem] * More efficient representation of info table provenance information, reducing binary sizes by over 50% in some cases when `-finfo-table-map` is in use A full accounting of changes can be found in the [release notes][]. Plans for GHC's future releases can be found on the [GHC Wiki][status]. We would like to thank GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. Happy compiling, ~ Ben [TypeAbstractions]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0425-d… [extended-literals]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0451-s… [unsatisfiable]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0433-u… [warnings]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0541-w… [deprecated-exports]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0134-d… [jsem]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0540-j… [release notes]: https://downloads.haskell.org/ghc/9.8.1/docs/users_guide/9.8.1-notes.html [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status

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ambiguous type variable question
by Zoran Bošnjak 11 Oct '23

11 Oct '23

Hi all, I want to convert a type level structure to the value level structure of the same shape. This is the simplified example: {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE UndecidableInstances #-} module Test where import GHC.TypeLits import Data.Kind import Data.Proxy -- This data structure serves both for 'type level' and 'value level'. data Content n s b = ContentRaw | ContentTable [(n, s)] | ContentBool b deriving instance (Show n, Show s, Show b) => Show (Content n s b) -- Convert from types to values. class IsSchema s where type SchemaVal s :: Type schema :: SchemaVal s instance IsSchema 'ContentRaw where type (SchemaVal 'ContentRaw) = Content Integer String Bool schema = ContentRaw instance IsSchema ('ContentTable '[]) where type (SchemaVal ('ContentTable '[])) = Content Integer String Bool schema = ContentTable [] instance ( IsSchema ('ContentTable ts) , t ~ '(n, s), KnownNat n, KnownSymbol s , SchemaVal ('ContentTable ts) ~ Content Integer String Bool ) => IsSchema ('ContentTable (t ': ts)) where type SchemaVal ('ContentTable (t ': ts)) = Content Integer String Bool schema = case schema @('ContentTable ts) of ContentTable lst -> let n = natVal (Proxy @n) s = symbolVal (Proxy @s) in ContentTable ((n,s) : lst) _ -> error "internal error" If I remove the type parameter 'b', 'ContentBool b' and coresponding 'Bool' from the sample, the conversion works as expected. >>> schema @'ContentRaw ContentRaw >>> schema @('ContentTable ( '(1,"test1") ': '(2,"test2") ': '[])) ContentTable [(1,"test1"),(2,"test2")] But for some reason, as soon as I extend the example with 'b' and 'Bool' as shown above, it results in the following error: * Could not deduce (SchemaVal ('ContentTable ts) ~ Content Integer String b0) from the context: (IsSchema ('ContentTable ts), t ~ '(n, s), KnownNat n, KnownSymbol s, SchemaVal ('ContentTable ts) ~ Content Integer String Bool) bound by the instance declaration at test2.hs:(34,5)-(37,43) The type variable `b1' is ambiguous How do I fix it or how do I rewrite it to get the intended result? regards, Zoran

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