- Haskell-Cafe - Haskell.org

Why can't I seem to use environment variables in my cabal file?
by David Banas 26 Jun '21

26 Jun '21

I’m trying to make use of an environment variable in my cabal file: ${ENV_VAR}, but I don’t think its value is getting used correctly. Is this a known issue? Workaround?

2 1

Cabal v misses changes to cxx-files: files?
by David Banas 25 Jun '21

25 Jun '21

Using Cabal v3.2.0.0 and with the following stanza in my *.cabal file: executable ex9 import: shared-properties main-is: src/ex/ex9.hs cxx-sources: src/ex/ex9.cpp {snip} if I edit the file: `src/ex/ex9.cpp`, and then execute: `cabal build`, I'm told: $ cabal build Up to date Is this a known issue? Is there a workaround? Thanks, -db

3 2

ICFP 2021: Second Call for Students Volunteers
by Jaemin Hong 24 Jun '21

24 Jun '21

Please don't hesitate to share this information with your students, classmates or colleagues! ICFP'21 SECOND CALL FOR STUDENT VOLUNTEERS ========================================= ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. In order to smoothly run the conference, associated workshops, and tutorials, we need student volunteers to help out on the practical aspect of the organization. All the events associated with ICFP'21 will take place **virtually** from Sun 22 - Fri 27 August 2021. Even though the event will be virtual, we will more than ever need the help of student volunteers to make sure everything runs smoothly. In return, as an ICFP 2021 student volunteer, you will get more visibility and be able to interact closely with researchers, academics and practitioners from various disciplines and discuss with other students from around the world. While the exact structure of the conference is still being discussed, job assignments for student volunteers will probably include: 1- Assisting with technical sessions, workshops, tutorials, Q&A sessions, social activities, and panels. 2- Helping to get authors' videos prepped and ready for broadcast. 3- Managing channels on a virtual event platform. To be considered as a student volunteer for ICFP, please fill in the following application form. https://forms.gle/cEXE4GfXzm24f6mF6 <https://forms.gle/cEXE4GfXzm24f6mF6> The permanent link to this form can be found on the official conference website. https://icfp21.sigplan.org/track/icfp-2021-student-volunteers <https://icfp21.sigplan.org/track/icfp-2021-student-volunteers> There is one remaining round of a call with the following deadline: * deadline for second round: July 16th, 2021 AoE (notification: July 20th)

1 0

Fwd: Is anyone running regular virtual Haskell hacking events?
by Chris Smith 24 Jun '21

24 Jun '21

Forwarding as I forgot to include the mailing list in my reply. ---------- Forwarded message --------- From: Chris Smith <cdsmith(a)gmail.com> Date: Wed, Jun 23, 2021 at 9:21 PM Subject: Re: [Haskell-cafe] Is anyone running regular virtual Haskell hacking events? To: Jeffrey Brown <jeffbrown.the(a)gmail.com> Jeffrey Brown <jeffbrown.the(a)gmail.com> wrote: > I think it's a great idea. What would helping you organize involve? > Great question. I think what I need most is: 1. Well before the event: a second brain to look at the plan and help think of things that can go wrong for some attendees, and what we might do to mitigate these factors, or anything else that should be done differently from what's in my head. 2. Shortly before the event: advertise! Make sure people know about it and are excited to come. 3. During the event: someone to play host a bit and help people find something to do, and generally be helpful to anyone who is lost or confused. That's not a role that I'm very good at, and I think it's more than a one-person job anyway. >

2 1

How to debug HSC to HS conversion failure?
by David Banas 23 Jun '21

23 Jun '21

I’m getting the following error in response to `cabal build`: running {pros_dir}/dist-newstyle/build/x86_64-osx/ghc-8.8.4/haskarchpriv-0.1.0.0/build/HaskArch/TLM2_hsc_make failed (exit code -11) rsp file was: “{proj_dir}/dist-newstyle/build/x86_64-osx/ghc-8.8.4/haskarchpriv-0.1.0.0/build/HaskArch/hsc2hscall86171-3.rsp" My project contains one *.hsc file, which is the target of the error above. How can I debug the cause of this? The “rsp” file is nowhere to be found; what is(was) it? And, is it a helpful debugging aid? If so, is there an option I can give, to preserve it? Thanks! -db

2 1

Is anyone running regular virtual Haskell hacking events?
by Chris Smith 23 Jun '21

23 Jun '21

I'm thinking of ideas, and wondering if anyone's beat me to this one. Before COVID-19, I organized a "co-hack" with the New York Haskell User Group one Saturday per month, where people would get together and write or discuss Haskell for several hours. I always had a great time, but... then COVID-19. Does something like this exist online? If not, I was just looking at Zoom, and realized they have breakout rooms where people can divide up and separately talk in groups. I was thinking of setting up an event something like this: Start: 9am Pacific / 12pm Eastern / 4pm GMT / 6pm CET - 15 minute intro and logistics - 30 minute Small group intros. Divide people up randomly into small groups to introduce themselves and talk about their Haskell stories and what they are working on. About 4-5 people per group (because 2 people feels too small, but too many people means shy people are afraid to speak up.) - 30 minute lightning talks and project pitches: Maybe 5 minutes / 3 slides max, sign up in advance or jump in and do a talk impulsively - 2.5 hours project time. Use for working together on projects, pair programming, teach and learn Haskell, etc. Use Zoom breakout groups and let people hop from room to room as desired. Pre-create some rooms for common activities (like "Beginner Questions", "Project Euler", etc.) Create some generic rooms people can jump in as they like for short collaborations. Create persistent project-specific rooms on demand. - 15 minute wrap-up. Finish: 1pm Pacific / 4pm Eastern / 8pm GMT / 10pm CET What does everyone think? I don't see any reason this couldn't go really well. The Cohack in New York was really fun, and I'd like to give it a shot. Anyone else motivated to help run this? If I can get at least one co-facilitator, I'll jump in and make it happen. I'll spring for the Zoom account. Probably use Meetup to take signups and manage scheduling, unless someone has another preference. Thanks, Chris Smith

3 3

Final Call for Talks: Haskell Implementors' Workshop @ ICFP'21
by Ningning Xie 23 Jun '21

23 Jun '21

Final Call for Talks ACM SIGPLAN Haskell Implementors' Workshop https://icfp21.sigplan.org/home/hiw-2021 Virtual, 22 Aug, 2021 Co-located with ICFP 2021 https://icfp21.sigplan.org/ New: Invited Speaker -------------------- Title: Haskell reinterpreted – large-scale real-world experience with the Mu compiler in Financial Markets Speaker: Bengt Marten Agren, Standard Chartered Bank Important dates --------------- Deadline: Wednesday, 30 June, 2021 (AoE) Notification: Wednesday, 14 July, 2021 Workshop: Sunday, 22 August, 2021 The 13th Haskell Implementors' Workshop is to be held alongside ICFP 2021 this year virtually. 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 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 short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2021. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. The 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 encouraged to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are specially 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, optimisation 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. Please submit a talk title and abstract of no more than 300 words. Submissions should be made via HotCRP. The website is: https://icfp-hiw21.hotcrp.com/ We will also have lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks 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. Logistics --------- Due to the on-going COVID-19 situation, ICFP (and, consequently, HIW) will be held remotely this year. However, the organizers are still working hard to provide for a great workshop experience. While we are sad that this year will lack the robust hallway track that is often the highlight of HIW, we believe that this remote workshop presents a unique opportunity to include more of the Haskell community in our discussion and explore new modes of communicating with our colleagues. We hope that you will join us in making this HIW as vibrant as any other. Program Committee ----------------- * Dominique Devriese (Vrije Universiteit Brussel) * Daan Leijen (Microsoft Research) * Andres Löh (Well-Typed LLP) * Julie Moronuki (Typeclass Consulting) * John Wiegley (DFINITY) * Ningning Xie (the University of Hong Kong) * Edward Z. Yang (Facebook AI Research) Contact ------- * Ningning Xie <xnning at hku.hk>

1 0

Re: [Haskell-cafe] Tips for debugging seg. faults?
by David Banas 22 Jun '21

22 Jun '21

Thank you, Viktor! Wrt/ `withForeignPtr`, you are suggesting that I use it, not that I avoid it; correct? Wrt/ “pinned memory”, could you give me a little more explanation? Thanks, -db :) > On Jun 20, 2021, at 5:00 AM, haskell-cafe-request(a)haskell.org wrote: > > Thus functions like `withForeignPtr` which try to make sure the the > referenced memory is not released too early. > > Buffer pointers should be to pinned memory, ...

4 3

Re: [Haskell-cafe] Pearl! I just proved theorem about impossibility of monad transformer for parsing with (1) unbiased choice and (2) ambiguity checking before running embedded monadic action (also, I THREAT I will create another parsing lib)
by Askar Safin 22 Jun '21

22 Jun '21

Hi. Thanks for answer! I already wrote arrow parsing lib. I will publish it when I was done. Also, you forgot to add haskell-cafe(a)haskell.org to CC. Понедельник, 21 июня 2021, 21:53 +03:00 от "Olaf Klinke" <olf(a)aatal-apotheke.de>: > Dear Askar, > > your theorem is convincing. While a counterexample is sufficient for a > rigorous proof, I'll try to add some mathematical theory to this. Many > monad transformers are of the form FooT m a = g (m (f a)) where (f,g) > is an adjoint pair of functors. The Kleisli lifting operation (=<<) for > such a composite monad uses the Kleisli lifting of m. For your > application that means that you can not use monadic actions of your > monad transformer without executing the monadic actions of the > transformed monad m. I conjecture that any transformer FooT with the > property that FooT m is a monad provided m is a monad necessarily runs > m-actions. > > A transformer that does not require m to be a monad is the continuation > transformer ContT m r a = (a -> m r) -> m r. However, for this > transformer the lift operation is interdefinable with an operation m (m > r) -> m r so it seems that at least lift will run m-actions. > > As Chris Smith pointed out, this does not rule out that Applicative- > style parsing code may be able to prevent executing the m-actions. > > Olaf > == Askar Safin http://safinaskar.com https://sr.ht/~safinaskar https://github.com/safinaskar

1 0

Is `MonadBaseControl` dead?
by YueCompl 21 Jun '21

21 Jun '21

Greetings! This is also posted at https://www.reddit.com/r/haskell/comments/o4sggi/is_monadbasecontrol_dead/ <https://www.reddit.com/r/haskell/comments/o4sggi/is_monadbasecontrol_dead/> but I'd like to also seek wider help here. (Background issue I'm facing: https://github.com/snapframework/snap-core/issues/309) I think the functionality of [MonadUnliftIO](https://hackage.haskell.org/package/unliftio-core-0.2.0.1/do… is exactly what I want, but unfortunately [Snap](https://hackage.haskell.org/package/snap-core-1.0.4.2/docs/Snap-Core.… appears not eligible for: > the intuition is that a monad must have no monadic state, but may have monadic context. This essentially limits MonadUnliftIO to ReaderT and IdentityT transformers on top of IO. Then I found `Snap` [has a MonadBaseControl instance](https://hackage.haskell.org/package/snap-core-1.0.4.2/docs/src/Sn…, and thought it should work for me. But sadly to find it [losing states](https://github.com/snapframework/snap-core/issues/309). Also I failed to find a user side example of `MonadBaseControl` on Github ([as there're only instance impl. hits](https://github.com/search?l=Haskell&q=org%3Asnapframework+liftBaseWit…) so I have not way to verify whether that's due to my incorrect usage. Any way quoting u/snoyberg : https://github.com/fpco/unliftio/issues/17#issuecomment-363655106 > Continuation-based monads cannot have instances of MonadUnliftIO, the same as MonadBaseControl and MonadMask. Then I'm not sure `Snap`'s `MonadBaseControl` instance shall really work. Also seems there had been debates I'm not aware of with clue at: https://github.com/fpco/unliftio/tree/master/unliftio#monad-control > > The main contention until now is that unlifting in a transformer like > `StateT` is unsafe. This is not universally true: if only one action > is being unlifted, no ambiguity exists. So, for example, `try :: IO a > -> IO (Either e a)` can safely be unlifted in `StateT`, while `finally > :: IO a -> IO b -> IO a` cannot. > > `monad-control` allows us to unlift both styles. In theory, we could > write a variant of `lifted-base` that never does state discards, and > let `try` be more general than `finally`. In other words, this is an > advantage of `monad-control` over `MonadUnliftIO`. We've avoided > providing any such extra typeclass in this package though, for two > reasons: > > * `MonadUnliftIO` is a simple typeclass, easy to explain. We don't > want to complicated matters (`MonadBaseControl` is a notoriously > difficult to understand typeclass). This simplicity > is captured by the laws for `MonadUnliftIO`, which make the > behavior of the run functions close to that of the already familiar > `lift` and `liftIO`. > * Having this kind of split would be confusing in user code, when > suddenly `finally` is not available to us. We would rather encourage > [good practices](https://www.fpcomplete.com/blog/2017/06/readert-design-pattern) > from the beginning. > > Another distinction is that `monad-control` uses the `MonadBase` > style, allowing unlifting to arbitrary base monads. In this package, > we've elected to go with `MonadIO` style. This limits what we can do > (e.g., no unlifting to `STM`), but we went this way because: > > * In practice, we've found that the vast majority of cases are dealing > with `IO` > * The split in the ecosystem between constraints like `MonadBase IO` > and `MonadIO` leads to significant confusion, and `MonadIO` is by > far the more common constraints (with the typeclass existing in > `base`) > So is `MonadBaseControl` dead or alive? Any user side example for it?

1 0