- Haskell-Cafe - Haskell.org

PhD position on the formalization of logical calculi in Saarbrücken
by Andrei Popescu 26 May '21

26 May '21

A PhD position is open at the MPI for Informatics in Saarbrücken, supervised by Christoph Weidenbach, Jasmin Blanchette and Sophie Tourret. The project is about using Isabelle/HOL to formalize logical calculi. See https://www.cs.vu.nl/~jbe248/sb_job.html for more information.

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(Online) Utrecht Summer School on Advanced functional programming
by Swierstra, W.S. (Wouter) 25 May '21

25 May '21

SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Online - 05-9 July 2021 http://www.afp.school # Call for Participation ## About The Advanced Functional Programming summer school has been running for more than ten years. We aim to educate aspiring Haskell programmers beyond the basic material covered by many textbooks. This year the course will be offered *online only*. A typical day will consist a 2-3 hours of lectures, sandwiched between supervised lab sessions. Lectures will be held in the (European) afternoon, but recordings will be made available if attending live is problematic. The lectures will cover several more advanced topics regarding programming with types in Haskell, including topics such as: * monads and applicative functors; * lambda calculus; * generalized algebraic datatypes; * datatype generic programming * type families and type-level programming; ## Lecturers Utrecht staff: * Gabriele Keller * Trevor McDonell * Wouter Swierstra ## Prerequisites We expect students to have a basic familiarity with Haskell already. You should be able to write recursive functions over algebraic data types, such as lists and trees. There is a great deal of material readily available that covers this material. If you've already started learning Haskell and are looking to take your functional programming skills to the next level, this is the course for you. Soft registration deadline: 1 June, 2021 School: 05-09 July, 2021 ## Costs 50 euro - Registration fee We ask ask participants to pay a small registration fee to cover some of our organizational expenses. If this is problematic for you *for whatever reason*, please let us know and we can waive your registration fee. ## Further information Further information, including instructions on how to register, is available on our website: http://www.afp.school

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Package takeover: int-cast
by Mikolaj Konarski 24 May '21

24 May '21

To whom it may concern, I'd like to take over package https://hackage.haskell.org/package/int-cast (I'd maintain it privately, though I'm subscribed to this mailing list from a company address). People have trouble compiling the roguelike game I maintain, because int-cast is not updated to GHC 9.0.1: https://github.com/LambdaHack/LambdaHack/issues/250 Also the test suite QuickCheck dependency is outdated. I've tried contacting the author, but without success. I'm fine giving the package back once the maintainer re-appears, but I'd also be honoured to maintain it indefinitely --- it's a splendid package. I'd also love to share the maintenance burden, mostly to raise the bus factor, so if anybody would like to get the Hackage permissions together with me, please let me know. Cheers, Mikolaj

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Using field accessors both ways in the same block of code?
by David Banas 23 May '21

23 May '21

Is it possible to use record field accessors both in their “normal” way and as values, via RecordWildCards and MyData{..}, in the same block of code?

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Trouble compiling Data.PriorityQueue?
by David Banas 22 May '21

22 May '21

Has anyone else bumped into this compilation error when trying to use Data.PriorityQueue? Building library for priority-queue-0.2.1.. [1 of 1] Compiling Data.PriorityQueue ( src/Data/PriorityQueue.hs, dist/build/Data/PriorityQueue.o ) src/Data/PriorityQueue.hs:120:50-54: error: Ambiguous occurrence ‘unzip’ It could refer to either ‘List.unzip’, imported from ‘Data.List’ at src/Data/PriorityQueue.hs:55:1-24 (and originally defined in ‘GHC.List’) or ‘Seq.unzip’, imported from ‘Data.Sequence’ at src/Data/PriorityQueue.hs:54:1-27 (and originally defined in ‘Data.Sequence.Internal’) | 120 | batches = map ((head *** fromList) . unzip) grouped | ^^^^^ cabal: Failed to build priority-queue-0.2.1 (which is required by exe:ex1 from haskarch-0.1.0.0). See the build log above for details. -db

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[ANN] Darcs 2.16.4 release
by Ben Franksen 21 May '21

21 May '21

On behalf of the Darcs team, I would like to announce the release of Darcs 2.16.4 [1]. Quoting from the release notes [2]: This release is mostly to fix http://bugs.darcs.net/issue2674 which can lead to repository corruption. This is not quite as bad as it sounds, since the broken changes that you could have recorded were consistently ignored when applying the patch. This bug has been in darcs for a very long time and even our own repos contain (ancient) patches with broken move changes, and so far it hasn't caused us any trouble. That said, there are certain patch commutations that will erroneously (and unexpectedly) fail when such a patch is involved. We therefore recommend to upgrade. You may also (after upgrading) run 'darcs check' on your repositories to see if you are affected, and 'darcs repair' them if that is the case. Fortunately, the broken move changes can be safely eliminated from existing patches, and the improved repair command now does exactly that. Thanks to Henning Thielemann for bringing this bug to our attention. [1] https://hackage.haskell.org/package/darcs-2.16.3 [2] https://hackage.haskell.org/package/darcs-2.16.3/changelog Cheers Ben -- I would rather have questions that cannot be answered, than answers that cannot be questioned. -- Richard Feynman

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ML Family Workshop 2021: final call for short abstracts and presentations
by Jonathan Protzenko 21 May '21

21 May '21

(tl;dr) The ML family workshop is back, and the deadline is in a week. The workshop does not have proceedings, making it the perfect venue to run some ideas with the community or present some work in progress within a friendly environment. The PC has a broad expertise and submissions are 3 pages long: when in doubt, just submit! (long version) We are happy to announce that the ML Family Workshop is back for its 2021 edition, which we will be held online on Thursday August 26th, in conjunction with ICFP 2021. The ML family workshop warmly welcomes submission touching on the programming languages traditionally seen as part of the "ML family" (Standard ML, OCaml, F#, CakeML, SML#, Manticore, MetaOCaml, etc.). The scope of the workshop includes all aspects of the design, semantics, theory, application, implementation, and teaching of the members of the ML family. We also encourage presentations from related languages (such as Haskell, Scala, Rust, Nemerle, Links, Koka, F*, Eff, ATS, etc), to exchange experience of further developing ML ideas. ## Submission details Submissions must be at most three pages long; see the full call for papers <https://icfp21.sigplan.org/home/mlfamilyworkshop-2021#Call-for-Presentations> for details. Submission site: https://ml21.hotcrp.com/ ## Important dates Thu, May 27th 2021 (AoE): submission deadline Thu, Jun 17th 2021 (AoE): author notification Thu, Aug 26th: workshop (time slots TBD) ## Program committee Danel Ahman (University of Ljubljana) Robert Atkey (University of Strathclyde) Frédéric Bour (Tarides) Ezgi Çiçek (Facebook London) Youyou Cong (Tokyo Institute of Technology) Richard A. Eisenberg (Tweag I/O) Martin Elsman (University of Copenhagen, Denmark) Ohad Kammar (University of Edinburgh) Naoki Kobayashi (University of Tokyo, Japan) Benoît Montagu (Inria) Jonathan Protzenko (Microsoft Research) (Chair) Kristina Sojakova (INRIA Paris) Don Syme (Microsoft) Matías Toro (University of Chile) Katsuhiro Ueno (Tohoku University)

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faster faster faster but not uglier (how to make nice code AND nice core)?
by Johannes Waldmann 20 May '21

20 May '21

Dear Cafe, * how to un-uglify the following program? * and is it even ugly enough? The following is some artificial example but I think it illustrates some general questions - for which I don't have answers. Do you? I wanted a really fast implementation of a vector addition system where the "vector" contains small numbers only. and I want it packed into a machine word (and finally put these into Data.IntSet). I can write this in low-level Haskell (I did), and I could even use some low-level language (I also did) but I was hoping that I don't need to. https://gitlab.imn.htwk-leipzig.de/waldmann/tf/-/blob/master/TF4.hs#L108 * this is too low-level: This is for vectors of one fixed size - but I want the code to be more generic, and have the compiler do the specialization/unrolling. * and not low-level enough: How do I tell GHC to pack (coerce?) `data Pos` into `Word64`? (It's not https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/pragmas.html#unpack… ?) And would it help? Or is it even needed? If I have the data spread over several words, it could still be fine - as long as it's kept in registers? How can I then check that "it's fine"? Yes I know, just look at the core. (That seems to be the ultima ratio of https://ghc.gitlab.haskell.org/ghc/doc/users_guide/hints.html#faster-produc…) But is there/could there be some higher-level mechanism? Perhaps a (type?) annotation that guarantees or checks that core (locally) looks "good"? (does not allocate, ...) NB: For the concrete application (evaluation of positions in some game): 1. graph size is exponential, so a linear speed-up won't really help. 2. brute-force gameplay should be replaced by some symbolic evaluation and simplification. That is in fact my goal. But - as long as we don't have this, the program may be useful for generating conjectures. - J.

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ICFP 2021: First Call for Students Volunteers
by Jaemin Hong 20 May '21

20 May '21

Please don't hesitate to share this information with your students, classmates or colleagues! ICFP'21 FIRST 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 The permanent link to this form can be found on the official conference website. https://icfp21.sigplan.org/track/icfp-2021-student-volunteers There are two rounds of calls with the following deadlines: * deadline for first round: June 11th, 2021 AoE (notification: June 15th) * deadline for second round: July 16th, 2021 AoE (notification: July 20th)

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Default implementation of Floating (**)
by Fabrício Olivetti de França 19 May '21

19 May '21

Hi, I was using Numeric.Interval in my code and found an issue with the (**) operator, if the interval contains negative values, it will return a wrong result (as reported in this open issue https://github.com/ekmett/intervals/issues/50) Investigating the source of this problem, I found that it uses the default implementation of (**) from base defined as x ** y = exp (log x * y). So I was wondering, is there any reason to have this (potentially dangerous) default implementation on base? Best, Fabricio Olivetti de França

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