- Haskell-Cafe - Haskell.org

Help understanding John Hughes' "The Design of a Pretty-printing Library"
by Galaxy Being 09 Jul '21

09 Jul '21

Getting stuck in *Real World Haskell*'s chapter on pretty printing (chap 5), I decided to take a look at one of the suggested sources, i.e., John Hughes' *The Design of a Pretty-printing Library <https://www.researchgate.net/publication/226525714_The_Design_of_a_Pretty-p…>*. Not that I fully got the first three section, still, let me skip ahead to section 4, *Designing a Sequence Type *where we're designing a supposedly generic sequence type, I'm guessing in the same universal, fundamental way that Peano's Axioms give a generic underpinning of the natural numbers. Good. I get it. This is why Haskell is unique. So he says we take the following *signature* as our starting point nil :: Seq a unit :: a -> Seq a cat :: Seq a -> Seq a -> Seq a list :: Seq a -> [a] where nil , unit , and cat give us ways to build sequences, and list is an *observation *[explained before]. The correspondence with the usual list operations is nil = [] unit x = [x] cat = (++) These operations are to satisfy the following laws: xs `cat` ( ys `cat` zs ) = ( xs `cat` ys ) `cat` zs nil `cat` xs = xs xs `cat` nil = xs list nil = [] list ( unit x `cat` xs ) = x : list xs My first question is why must we satisfy these laws? Where did these laws come from? Is this a universal truth thing? I've heard the word *monoid *and *semigroup* tossed around. Is this germane here? Next in *4.1 Term Representation* I'm immediately lost with the concept of *term. *On a hunch, I borrowed a book *Term Rewriting and All That *from Baader and Nipkow which I'm sure goes very deep into the concept of terms, but I'm not there yet. What is meant by *term*? As 4.1 continues, confusing is this passage The most direct way to represent values of [the?] sequence type is just as terms of the algebra [huh?], for example using data Seq a = Nil j Unit a j Seq a `Cat` Seq a But this trivial representation does not exploit the algebraic laws that we know to hold [huh?], and moreover the list observation will be a little tricky to de ne (ideally we would like to implement observations by very simple, non-recursive functions: the real work should be done in the implementations of the Seq operators themselves). Instead, we may choose a restricted subset of terms -- call them simplified forms -- into which every term can be put using the algebraic laws. Then we can represent sequences using a datatype that represents the syntax of simplified forms. In this case, there is an obvious candidate for simplified forms: terms of the form nil and unit x `cat` xs , where xs is also in simplified form. Simplified forms can be represented using the type data Seq a = Nil j a `UnitCat` Seq a with the interpretation Nil = nil x `UnitCat` xs = unit x `cat` xs All of this presupposes much math lore that I'm hereby asking someone on this mailing list to point me towards. I threw in a few [huh?] as specific points, but in general, I'm not there yet. Any explanations appreciated. ⨽ Lawrence Bottorff Grand Marais, MN, USA borgauf(a)gmail.com

3 2

IFL'21 Third call for papers
by Pieter Koopman 09 Jul '21

09 Jul '21

================================================================================ IFL 2021 33rd Symposium on Implementation and Application of Functional Languages venue: online 1 - 3 September 2021 https://ifl21.cs.ru.nl <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> ================================================================================ News - Paper submission details. - Registration information added Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2021 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Industrial track and topics of interest This year's edition of IFL explicitly solicits original work concerning *applications* of functional programming in industry and academia. These contributions will be reviewed by experts with an industrial background. Topics of interest to IFL include, but are not limited to: * language concepts * type systems, type checking, type inferencing * compilation techniques * staged compilation * run-time function specialisation * run-time code generation * partial evaluation * (abstract) interpretation * meta-programming * generic programming * automatic program generation * array processing * concurrent/parallel programming * concurrent/parallel program execution * embedded systems * web applications * (embedded) domain-specific languages * security * novel memory management techniques * run-time profiling performance measurements * debugging and tracing * testing and proofing * virtual/abstract machine architectures * validation, verification of functional programs * tools and programming techniques * applications of functional programming in the industry, including ** functional programming techniques for large applications ** successes of the application functional programming ** challenges for functional programming encountered ** any topic related to the application of functional programming that is interesting for the IFL community Post-symposium peer-review Following IFL tradition, IFL 2021 will use a post-symposium review process to produce the formal proceedings. Before the symposium authors submit draft papers. These draft papers will be screened by the program chairs to make sure that they are within the scope of IFL. The draft papers will be made available to all participants at the symposium. Each draft paper is presented by one of the authors at the symposium. After the symposium every presenter is invited to submit a full paper, incorporating feedback from discussions at the symposium. Work submitted to IFL may not be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected for the formal proceedings. We plan to publish these proceedings in the International Conference Proceedings Series of the ACM Digital Library, as in previous years. Moreover, the proceedings will also be made publicly available as open access. Important dates Submission deadline of draft papers: 17 August 2021 Notification of acceptance for presentation: 19 August 2021 Registration deadline: 30 August 2021 IFL Symposium: 1-3 September 2021 Submission of papers for proceedings: 6 December 2021 Notification of acceptance: 3 February 2022 Camera-ready version: 15 March 2022 Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> . (For LaTeX users, start your document with \documentclass[format=sigconf]{acmart}.) Note that this format has a rather long but limited list of packages that can be used. Please make sure that your document adheres to this list. The submission Web page for IFL21 is https://easychair.org/conferences/?conf=ifl21 <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> . Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Organisation IFL 2021 Chairs: Pieter Koopman and Peter Achten, Radboud University, The Netherlands IFL Publicity chair: Pieter Koopman, Radboud University, The Netherlands PC: Peter Achten (co-chair) - Radboud University, Netherlands Thomas van Binsbergen - University of Amsterdam, Netherlands Edwin Brady - University of St. Andrews, Scotland Laura Castro - University of A Coruña, Spain Youyou Cong - Tokyo Institute of Technology, Japan Olaf Chitil - University of Kent, England Andy Gill - University of Kansas, USA Clemens Grelck - University of Amsterdam, Netherlands John Hughes - Chalmers University, Sweden Pieter Koopman (co-chair) - Radboud University, Netherlands Cynthia Kop - Radboud University, Netherlands Jay McCarthey - University of Massachussetts Lowell, USA Neil Mitchell - Facebook, England Jan De Muijnck-Hughes - Glasgow University, Scotland Keiko Nakata - SAP Innovation Center Potsdam, Germany Jurriën Stutterheim - Standard Chartered, Singapore Simon Thompson - University of Kent, England Melinda Tóth - Eötvos Loránd University, Hungary Phil Trinder - Glasgow University, Scotland Meng Wang - University of Bristol, England Viktória Zsók - Eötvos Loránd University, Hungary Virtual symposium Because of the Covid-19 pandemic, this year IFL 2021 will be an online event, consisting of paper presentations, discussions and virtual social gatherings. Registered participants can take part from anywhere in the world. Registration Please use the below link to register for IFL 2021: https://docs.google.com/forms/d/e/1FAIpQLSdMFjo-GumKjk4i7szs7n4DhWqKt96t8of… <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> Thanks to the sponsors and the support of the Radboud university registration is free of charge. [image: beacon]

1 0

Re: [Haskell-cafe] Where have the discussions moved to?
by Anthony Clayden 09 Jul '21

09 Jul '21

Yes I miss the free-and-easy atmosphere of the cafe. As of 9/10 years ago, we thought we'd nearly figured out how to fix the bogusness with FunDeps. And there were several ideas for better records. But no, GHC's FunDeps are just as bad as 2006; records have got a bit of lipstick. My take is that GHC has got so loaded with features, it's almost impossible to engineer in any 'tweaks'. So there has to be a bloated bureaucratic proposals process to make sure nothing gets broken. No free-wheeling what-if kind of discussion. Reddit I find almost impossible to follow. The Discourse site seems to be too much cut-and-dried. If you want to peek at what code people are cutting, StackOverflow gets some surprising material. But yeah. Haskell is different these days. In a way I don't like. It doesn't feel like 'popularity and community has expanded'. AntC

1 0

Re: [Haskell-cafe] Prolog-style list syntax?
by Anthony Clayden 09 Jul '21

09 Jul '21

Ok thank you for the feedback, I get the message not to re-purpose currently valid syntax. For that reason, this won't fly: I see no technical issues in allowing > something like `[ x, y || ys]` `||` is already an operator in the Prelude. > [x, y ,: ys ] -- ? not currently valid We could make list syntax work harder > [x, y ,:+ ys ] Means desugar the commas by applying constructor `:+` instead of `:`. That could be in general any constructor starting `:`. Or indeed could be a pattern synonym starting `:`, which is a 'smart constructor' to build the list maintaining some invariant.

3 4

FMCAD Student Forum CFP (Deadline Sat July 10)
by Mark Santolucito 09 Jul '21

09 Jul '21

# Student Forum Continuing the tradition of the previous years, FMCAD 2021 is hosting a Student Forum that provides a platform for students at any career stage (undergraduate or graduate) to introduce their research to the wider Formal Methods community, and solicit feedback. The Student Forum will be held in a hybrid format, online via video conferencing. ## Submissions Submissions must be short reports describing research ideas or ongoing work that the student is currently pursuing. Joint submissions from two students are allowed, provided the students contributed equally to the work - however, joint submissions must be presented by a single student. The topic of the reports must be within the scope of the FMCAD conference. These reports will NOT be published, thus we welcome reports based on already submitted/published papers. However, the novel aspects to be addressed in future work must be clearly described. Submissions should follow the same formatting guidelines as those for regular FMCAD conference submissions, except that the length is limited to 2 pages IEEE format, including all figures and references. ## Important Dates - Student forum submission: July 10, 2021 - Student forum notification: Aug 6, 2021 These deadlines are 11:59 pm AoE (Anywhere on Earth) More info here: https://fmcad.org/FMCAD21/student_forum/ ## Main Activities ### Student Forum Talks. Each student will give a lightning talk. In the case that a student is attending FMCAD physically, the talk will be given in-person at the conference. In the case that a student is attending FMCAD remotely, the talk will be given over Zoom. ### Discussion Groups. Students will have the opportunity to explain and discuss their work in small groups. More details to come on the logistics of discussion for remote participants. Submissions for the event must be short reports describing research ideas or ongoing work that the student is currently pursuing, and must be within the scope of FMCAD. Work, part of which has been previously published, will be considered; the novel aspect to be addressed in future work must be clearly described in such cases. All submissions will be reviewed by a subgroup of FMCAD committee members. ## Format The event will consist of short presentations by the student authors of each accepted submission, and of a virtual poster session. All participants of the conference are encouraged to attend the talks, ask questions and discuss with their fellow students in the virtual post sessions. Instructions for the preparation of the talks and poster sessions will be announced on notification of acceptance. ## Visibility Accepted submissions will be listed, with title and author name, in the event description in the conference proceedings. The authors will also have the option to upload their slide deck/poster/presentation to the FMCAD website. The report itself will not appear in the FMCAD proceedings; thus, the presentation at FMCAD should not interfere with potential future submissions of this research (to FMCAD or elsewhere). The best contributions (determined by public vote by attendees) will be given public recognition and a certificate at the event. ***Forum Chair*** Mark Santolucito (msantolu(a)barnard.edu) chairs the Student Forum. Feel free to send an email if you have questions about the event.

1 0

Hyrum's law (Was: [RFC] Support Unicode characters in instance Show String)
by Henning Thielemann 08 Jul '21

08 Jul '21

moving to Haskell Cafe On Thu, 8 Jul 2021, Bardur Arantsson wrote: > On 08/07/2021 17.53, Oleg Grenrus wrote: > > [--snip--] > >> >> 78 out of 2819 tests failed (35.88s) >> > > The use of Show in 'golden' test suites is interesting because Show > doesn't really guarantee any real form of stability in its output. > > I guess Hyrum's Law applies here too. > > Anyway... just an idle observation. Obviously, breaking loads of test > suites is going to be hard to swallow. I found this explanation: https://www.hyrumslaw.com/ Nice to have a name for this observation. I think the problem can be relaxed if there are multiple implementations for the same interface. But then you often find, that the implementations do not even adhere to the interface, thus people start guessing what the interface actually means. I hope that in the future we can describe interfaces more formally, such that a user knows what he can rely on.

3 2

Where have the discussions moved to?
by Carette, Jacques 08 Jul '21

08 Jul '21

Haskell Café used to be quite active. But in the last 2 years, at least, there have been much less traffic. In the same time frame, Haskell's popularity and community has expanded greatly. The logical conclusion is that discussions have moved elsewhere. I know that, for example, there are at times a large amount of discussion happening via github on the proposals [1] (in fact, so much so that I unsubscribed). I am aware that the community page [2] does mention quite a few places - too many. Is there one of those places where the kinds of discussions that used to happen here have moved to? Jacques [1] https://github.com/ghc-proposals/ghc-proposals [2] https://www.haskell.org/community/

3 2

[ANN] Copilot 3.4 - hard realtime C runtime verification
by Frank Dedden 08 Jul '21

08 Jul '21

Dear all, We are pleased to announce the release of Copilot 3.4, a stream-based DSL for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms. Among others, Copilot has been used at the Safety Critical Avionics Systems Branch of NASA Langley Research Center for monitoring test flights of drones. This release introduces a number of bug fixes and deprecates functions that have been superseded. The newest release is available on hackage [1]. For more information, including documentation, examples and links to the source code, please visit the webpage [2]. Current emphasis is on facilitating the use with other systems, and improving the codebase in terms of stability and test coverage. Users are encouraged to participate by opening issues and asking questions via our github repo [3]. Kind regards, The Copilot developers: - Frank Dedden - Alwyn Goodloe - Ivan Perez [1] https://hackage.haskell.org/package/copilot [2] https://copilot-language.github.io [3] https://github.com/Copilot-Language/copilot

1 0

How to debug SQL disconnect error
by Olaf Klinke 07 Jul '21

07 Jul '21

Dear Café, How can I go about examining an SQL error [1] when using persistent- odbc to access an MS SQL database? Set up a pristine MS SQL server 2012. Installed the driver on Debian using apt-get install msodbcsql17. Upon running either of persitent's printMigration or runMigration, the disconnect produces an error: *** Exception: SqlError {seState = "["25000"]", seNativeError = -1, seErrorMsg = "freeDbcIfNotAlready/SQLDisconnect: ["0: [Microsoft][ODBC Driver 17 for SQL Server]Invalid transaction state"]"} Running the printed SQL statements with isql executes allright, so it is not the particular migration at fault here. Presently I don't even know whether persistent or persistent-odbc or any false assumptions about the connection configuration is the cause. Thanks in advance Olaf [1] https://github.com/gbwey/persistent-odbc/issues/26

1 0

FMBC 2021 - Call for Participation
by Bruno Bernardo 05 Jul '21

05 Jul '21

[ Please distribute, apologies for multiple postings. ] ======================================================================== 3rd International Workshop on Formal Methods for Blockchains (FMBC) 2021 - Call for Participation https://fmbc.gitlab.io/2021 July 18 and 19, 2021, Online, 8AM-10AM PDT Co-located with the 33rd International Conference on Computer-Aided Verification (CAV 2021) http://i-cav.org/2021/ --------------------------------------------------------- The FMBC workshop is a forum to identify theoretical and practical approaches of formal methods for Blockchain technology. Topics include, but are not limited to: * Formal models of Blockchain applications or concepts * Formal methods for consensus protocols * Formal methods for Blockchain-specific cryptographic primitives or protocols * Design and implementation of Smart Contract languages * Verification of Smart Contracts The list of lightning talks and conditionally accepted papers is available on the FMBC 2021 website: https://fmbc.gitlab.io/2021/program.html There will be one keynote by David Dill, Lead Researcher on Blockchain at Novi/Facebook and professor emeritus at Stanford University, USA. Registration Registration to FMBC 2021 is done through the CAV 2021 registration form: http://i-cav.org/2021/attending/ (*Early bird deadline is July 9.*)

1 0