December 2022 - Haskell-Cafe

Best way to implement "scoped exceptions"?
by Tom Ellis 16 Jun '23

16 Jun '23

I'd like to implement "scoped exceptions"[1], that is, a combinator of type withScopedException :: ((forall a. e -> IO a) -> IO r) -> IO (Either e r) so I can use exceptions in a convenient way, without having to set up fragile "action at a distance" based on the type of the thing I'm throwing and catching, for example: scopedExceptionExample :: IO (Either String (Either Int Void)) scopedExceptionExample = do withScopedException $ \throw1 -> withScopedException $ \throw2 -> if (1 :: Int) < 0 then throw1 "Hello" else throw2 1234 -- ghci> scopedExceptionExample -- Right (Left 1234) Here's a hacky way of doing it, based on tagging each exception with a unique value, and then filtering when handling: data MyException where MyException :: e -> Data.Unique.Unique -> MyException instance Show MyException where show _ = "<MyException>" instance Exception MyException withScopedException :: ((forall a. e -> IO a) -> IO r) -> IO (Either e r) wiathScopedException f = do fresh <- Data.Unique.newUnique flip tryJust (f (\e -> throwIO (MyException e fresh))) $ \case MyException e tag -> -- unsafeCoerce is very unpleasant if tag == fresh then Just (unsafeCoerce e) else Nothing This is the approach taken by the effectful library[2]. But is there a better way? Can I persuade GHC's RTS to work like this directly? Tom [1] I don't know if these already have a name [2] https://hackage.haskell.org/package/effectful-core-2.2.1.0/docs/src/Effectf…

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Special holiday Munich Haskell Meeting, 2023-01-04 @ 19:30
by Leah Neukirchen 30 Dec '22

30 Dec '22

Dear all, Next week, our special holiday Munich Haskell Meeting will take place on Wednesday, January 4 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 nuudel so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://nuudel.digitalcourage.de/cs8eLiDLkwZEd5hO Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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[Haskell] [ANNOUNCE] Haskell Language Server 1.9.0.0 released
by Zubin Duggal 26 Dec '22

26 Dec '22

Binaries for this release are available at https://downloads.haskell.org/~hls/haskell-language-server-1.9.0.0/ The prebuilt binaries in this release support the following GHC versions: - 8.10.7 - 9.0.2 - 9.2.5 - 9.4.3 - 9.4.4 These binaries can be installed using [GHCup](https://www.haskell.org/ghcup/) or version [2.0.0 and above](https://github.com/haskell/vscode-haskell/releases) of the VSCode extension. ## Changelog - Binaries for GHC 9.4.3, GHC 9.4.4 and GHC 9.2.5. - Dropped support for GHC 8.8 and GHC 8.10. - New plugins including: - Expanding record wild cards using hls-explicit-record-fields-plugin (#3304). - Formatting cabal fields using cabal-fmt via hls-cabal-fmt-plugin (#2047). - Warnings and errors for cabal files using hls-cabal-plugin (#2954). - Folding ranges using hls-code-range-plugin (#3058). - Support for many plugins like the refactor, splice, retrie, gadt, hlint, fourmolu and class plugins. - Completion for record dot fields (#3080). - Performance and memory usage improvements. - And many more bug fixes and improvements! For the full release notes, see https://github.com/haskell/haskell-language-server/releases/tag/1.9.0.0

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[ANNOUNCE] GHC 9.4.4 is now available
by Ben Gamari 24 Dec '22

24 Dec '22

The GHC developers are happy to announce the availability of GHC 9.4.4. Binary distributions, source distributions, and documentation are available at downloads.haskell.org [1]. This release is primarily a bugfix release. Bugs fixed include: * An issue where the wrong labels were used in the eventlog for events emitted when using info table profiling which was broken in 9.4.3 (#22452) * Fix a long standing bug where invalid eventlogs would be produced with long command-lines (#20221) * Fix a regression in eta-expansion which resulted in serious performance regressions in 9.4.3 (#22424) * Fix the `-fdefer-diagnostics` flag (#22391) * Fixes to several subtle compiler panics (#22491, #22416, #22549, #22475, #22039) * Add necessary write barriers to `IORef` operations, avoiding potential soundness issues on architectures with weakly-ordered memory models (#22468) Note that, as GHC 9.4 is the first release series where the release artifacts are all generated by our new Hadrian build system, it is possible that there will be packaging issues. If you enounter trouble while using a binary distribution, please open a [ticket]. Likewise, if you are a downstream packager, do consider migrating to [Hadrian] to run your build; the Hadrian build system can be built using `cabal-install`, `stack`, or the in-tree [bootstrap script]. See the accompanying [blog post] for details on migrating packaging to Hadrian. We would also like to emphasize that GHC 9.4 must be used in conjunction with Cabal-3.8 or later. This is particularly important for Windows users due to changes in GHC's Windows toolchain. We would like to thank Microsoft Azure, GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, 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. As always, do give this release a try and open a [ticket] if you see anything amiss. Happy Haskelling, - Ben [1]: https://downloads.haskell.org/ghc/9.4.4 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [bootstrap script]: https://gitlab.haskell.org/ghc/ghc/-/blob/e2520df3fffa0cf22fb19c5fb872832d1… [Hadrian]: https://gitlab.haskell.org/ghc/ghc/-/blob/e2520df3fffa0cf22fb19c5fb872832d1… [blog post]: https://www.haskell.org/ghc/blog/20220805-make-to-hadrian.html

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Meetup in Bay area
by Ivan Perez 23 Dec '22

23 Dec '22

Hi, Is there a Haskell or FP meetup in the Bay area? Cheers, Ivan

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lens and Maybe value
by PICCA Frederic-Emmanuel 20 Dec '22

20 Dec '22

Hello, I have a data whcih contain a Maybe value data A = A (_a = Maybe a) I would like to use a lens in order to merge two values with this log replace the value only if it is a (Just a) So My question is is there something more elegant than let myA' = case ma of Nothing -> conf (Just na) -> (a .~ na) myA Thanks for your help Frederic

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 232, Issue 6
by Douglas McIlroy 19 Dec '22

19 Dec '22

This note is to suggest an approach to introducing Haskell. It is not a pitch for a gig to do so. A big selling point for Haskell is how clean and simple some kinds of Haskell code are. My personal hobby horse of this type is stream processing. Lazy evaluation makes for dramatic simplification, as can be seen in a couple of offerings on my website. I have given talks based on this theme to (mathematically inclined) audiences who have absolutely no Haskell nous. For folks who know freshman calculus, power series computations in Haskell are an eye-opener--no fussing with storage allocation and no subscripts at all! Only rudimentary Haskell ideas need to be discussed to make these functions intelligible. https://www.cs.dartmouth.edu/~doug/powser.html. Another Haskell example, a basic prime-number sieve, reduces a page of C code, or a half-page of shell script to two elegant lines of code. https://www.cs.dartmouth.edu/~doug/sieve/sieve.pdf Doug McIlroy On Mon, Dec 19, 2022 at 7:19 AM <haskell-cafe-request(a)haskell.org> wrote: > > Send Haskell-Cafe mailing list submissions to > haskell-cafe(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > or, via email, send a message with subject or body 'help' to > haskell-cafe-request(a)haskell.org > > You can reach the person managing the list at > haskell-cafe-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Haskell-Cafe digest..." > > > Today's Topics: > > 1. Request for a presentation on Haskell (Jonathan Drews) > 2. Re: Request for a presentation on Haskell (Ivan Perez) > 3. Re: Request for a presentation on Haskell (Jonathan Drews) > 4. Re: Request for a presentation on Haskell (Ivan Perez) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sun, 18 Dec 2022 18:13:02 -0700 > From: Jonathan Drews <jondrews(a)fastmail.com> > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Request for a presentation on Haskell > Message-ID: <Y5+6ntGmiRUZ4xd1(a)leo.my.domain> > Content-Type: text/plain; charset=us-ascii > > Hi Folks: > > I would like to know if anyone from the Haskell organization would > like to give a presentation on Haskell to our BSD User Group (BSD = > Berkeley Software Development). We are the South Eastern Michigan BSD > User Group (http://www.semibug.org/) Myself and several other members > are very intereested in Haskell and would like to learn more about > this language. > > You would make the presentation online, by means of Jitsi. The date I > am hoping for is January 17th, 2023. I can move that date if need be. > The talks are usually given in the evenings. Contact me off list for > more details. > > Thanks in advance. > > -- > Kind regards, > Jonathan > > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > ~ > > > > ------------------------------ > > Message: 2 > Date: Sun, 18 Dec 2022 20:02:35 -0800 > From: Ivan Perez <ivanperezdominguez(a)gmail.com> > To: Jonathan Drews <jondrews(a)fastmail.com>, Haskell Cafe > <haskell-cafe(a)haskell.org> > Subject: Re: [Haskell-cafe] Request for a presentation on Haskell > Message-ID: > <CACZKWELYiL7qUP_qJ733PhZHHRcve0-OYO6iV8PZdMt5Lj5sSA(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Jonathan, > > I might be available, if you are interested. Most of my work is > Haskell-centric. I've made commercial games and apps (mobile, desktop, > web). In the last 5y I've focused on runtime monitoring and language > transformation (very broadly speaking). > > See https://ivanperez.io/ for details. > > If you are interested, we can continue the discussion off-list. > > Thanks, > > Ivan > > On Sun, 18 Dec 2022 at 17:13, Jonathan Drews <jondrews(a)fastmail.com> wrote: > > > Hi Folks: > > > > I would like to know if anyone from the Haskell organization would > > like to give a presentation on Haskell to our BSD User Group (BSD = > > Berkeley Software Development). We are the South Eastern Michigan BSD > > User Group (http://www.semibug.org/) Myself and several other members > > are very intereested in Haskell and would like to learn more about > > this language. > > > > You would make the presentation online, by means of Jitsi. The date I > > am hoping for is January 17th, 2023. I can move that date if need be. > > The talks are usually given in the evenings. Contact me off list for > > more details. > > > > Thanks in advance. > > > > -- > > Kind regards, > > Jonathan > > > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > ~ > > > > _______________________________________________ > > Haskell-Cafe mailing list > > To (un)subscribe, modify options or view archives go to: > > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > > Only members subscribed via the mailman list are allowed to post. >

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Request for a presentation on Haskell
by Jonathan Drews 19 Dec '22

19 Dec '22

Hi Folks: I would like to know if anyone from the Haskell organization would like to give a presentation on Haskell to our BSD User Group (BSD = Berkeley Software Development). We are the South Eastern Michigan BSD User Group (http://www.semibug.org/) Myself and several other members are very intereested in Haskell and would like to learn more about this language. You would make the presentation online, by means of Jitsi. The date I am hoping for is January 17th, 2023. I can move that date if need be. The talks are usually given in the evenings. Contact me off list for more details. Thanks in advance. -- Kind regards, Jonathan ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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Maintenance takeover: cached-io
by Luke Worth 14 Dec '22

14 Dec '22

Hello, We’ve recently started using https://hackage.haskell.org/package/cached-io, but the listed maintainer’s email address is bouncing, and the GitHub repo doesn’t exist any more. It appears that the original repository is https://github.com/glasserc/haskell-cached-io, but I cannot find any way to contact the owner. The fork https://github.com/Arguggi/haskell-cached-io has many useful contributions which ought to be incorporated into the Hackage release, but even the fork has been inactive since 2016. If nobody speaks up by Wednesday 2022-12-21, I’ll submit a takeover request to Hackage admins. Luke Worth | Senior Software Engineer ——————————— E luke.worth(a)bellroy.com W bellroy.com

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Interactive book/tutorial platform
by Todd Wilson 14 Dec '22

14 Dec '22

Hi Cafe, I've taught university Computer Science for 20+ years, many of those using Haskell to both illustrate and have students explore the concepts they learn, and now I'm looking to organize my course materials as interactive books or long-form tutorials for non-commercial release to a larger audience, and I am trying to find an appropriate platform. I've looked at a few possibilities already, such as org-mode, IHaskell notebooks, and some blogging platforms, but all would seem to involve significant configuration before they would be suitable for what I'm trying to achieve. And so I'm inquiring here to see if there are some choices that I hadn't considered, or ready-made configurations for some that I have, which I could look into further and adapt. Ideally, I would like to be able to: - use LaTeX or equivalent for high-quality typesetting (most of my current non-interactive materials are LaTeX documents), - organize content hierarchically, with varying visibility of subsections, so that readers could go into as much detail as needed (extra explanations, examples, diagrams, etc., that could be viewed if desired or easily skipped if not), using cookies to remember each reader's current visibility choices starting from an initial default, - provide code snippets that are executable in place with results incorporated into the document and perhaps modifiable for experimentation, - export to PDF. Suggestions or templates for the above would be very welcome. Thanks, Todd Wilson California State University, Fresno

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