- Haskell-Cafe - Haskell.org

Linking + zstd on FreeBSD
by Vanessa McHale 10 Jul '20

10 Jul '20

I tried linking against zstd within a Vagrant simulating FreeBSD. I get the following: ld: error: duplicate symbol: XXH64 >>> defined at xxhash.c >>> xxhash.o:(XXH64) in archive /home/vagrant/.cabal/store/ghc-8.8.3/zstd-0.1.2.0-c8ee757c8e8a7307779ab3cfbc91f3445940e16bbf8f9916f4c90432a0ac499e/lib/libHSzstd-0.1.2.0-c8ee757c8e8a7307779ab3cfbc91f3445940e16bbf8f9916f4c90432a0ac499e.a >>> defined at xxhash.c:693 (/wrkdirs/usr/ports/lang/ghc/work/ghc-8.8.3/rts/xxhash.c:693) >>> RTS.o:(.text.XXH64+0x0) in archive /usr/local/lib/ghc-8.8.3/rts/libHSrts.a ... I am using GHC version 8.8.3_1 and cabal-install 3.0 installed by 'sudo pkg install ...' (I was trying to run cabal install language-dickinson) Cheers, Vanessa McHale

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Re: [Haskell-cafe] Test on identity?
by Olaf Klinke 09 Jul '20

09 Jul '20

> Dear Café, > > I'm trying to build a DAG from a binary tree. I don't think there's a > big trouble. > Nevertheless, I do even some transformations. Thus, I would like to > know it is still a > DAG, not adding, accidentally, a node. > > Is there any way, if I have data like > > data Ex > = Val Int > | Add Ex Ex > > so that I can test that some value Val i === Val i ? I mean, the > pointers go to the > same data box? I could do that via some IORefs, AFAIK, but I don't > think it is > feasible. Maybe to tune the algorithm... > > Best regards, > > Dusan So the binary tree is a value e :: Ex, right? And the DAG (directed acyclic graph) is an explicit representation of the internal pointer structure in e? Did I understand you right? This sounds like you should represent Ex as a fixed point and then invoke some fixed point magic like catamorphisms. Your transformation might have to be re-written as a cata/ana/hylomorphism, too. Below is a recipe to turn any element of any fixed point type into a graph, that is, into a list of nodes and edges. Of course this will loop if your data was not a finite DAG, e.g. due to self-reference. -- make type recursion for your type Ex explicit data ExF x = Val Int | Add x x deriving (Show) instance Functor ExF where fmap f (Val i) = Val i fmap f (Add x y) = Add (f x) (f y) instance Foldable ExF where foldMap _ (Val _) = mempty foldMap f (Add x y) = f x <> f y instance Traversable ExF where traverse f (Val i) = pure (Val i) traverse f (Add x y) = Add <$> (f x) <*> (f y) -- represent Ex via the general -- Fix :: (* -> *) -> * -- See e.g. package data-fix or recursion-schemes -- cataM below taken from the data-fix package type Ex = Fix ExF -- = Fix {unFix :: ExF (Fix ExF)} -- Add () () tells you the node is internal type ExNode = ExF () data GraphElem f = Node Int (f ()) | Edge Int Int instance Show (GraphElem ExF) where show (Node n (Val i)) = show n ++ ":Val " ++ show i show (Node n (Add _ _)) = show n ++ ":Add" show (Edge i j) = show i ++ " -> " ++ show j type Graph = [GraphElem ExF] type GraphM = StateT Int (Writer Graph) structure :: (Traversable f, MonadState Int m, MonadWriter [GraphElem f] m) => f Int -> m Int structure fi = do this <- get tell [Node this (void fi)] traverse (\child -> tell [Edge this child]) fi put (this+1) return this -- depth-first traversal. More generally dag has type -- (Traversable f) => Fix f -> [GraphElem f] -- and the Traversable instance determines the order -- of the traversal. dag :: Ex -> Graph dag = snd . runWriter . flip evalStateT 0 . cataM structure -- Cheers, Olaf

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Test on identity?
by Dušan Kolář 09 Jul '20

09 Jul '20

Dear Café, I'm trying to build a DAG from a binary tree. I don't think there's a big trouble. Nevertheless, I do even some transformations. Thus, I would like to know it is still a DAG, not adding, accidentally, a node. Is there any way, if I have data like data Ex = Val Int | Add Ex Ex so that I can test that some value Val i === Val i ? I mean, the pointers go to the same data box? I could do that via some IORefs, AFAIK, but I don't think it is feasible. Maybe to tune the algorithm... Best regards, Dusan

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FMBC 2020 - Call for Participation
by Bruno Bernardo 08 Jul '20

08 Jul '20

[ Please distribute, apologies for multiple postings. ] ======================================================================== 2nd Workshop on Formal Methods for Blockchains (FMBC) 2020 - Call for Participation https://fmbc.gitlab.io/2020 July 20 and 21, 2020, Online, 6AM-8AM PDT Co-located with the 32nd International Conference on Computer-Aided Verification (CAV 2020) http://i-cav.org/2020/ --------------------------------------------------------- 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 accecpted papers is available on the FMBC 2020 website: https://fmbc.gitlab.io/2020/program.html There will be one keynote by Grigore Rosu, Professor at University of Illinois at Urbana-Champaign, USA and Founder of Runtime Verification. Registration Registration to FMBC 2020 is free but required. It is done through the CAV 2020 registration form: http://i-cav.org/2020/attending/ Please register before *July 10, 2020*.

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ekg-core/RTS : bogus GC stats when running on Google Cloud Run
by Marco Zocca 05 Jul '20

05 Jul '20

Hi all, I have two services deployed on Google cloud infrastructure; Service 1 runs on Compute Engine and Service 2 on Cloud Run and I'd like to log their memory usage via the `ekg-core` library (https://hackage.haskell.org/package/ekg-core-0.1.1.7/docs/System-Metrics.ht…) (which is just a thin wrapper around GHC.Stats ). The logging bracket is basically this : mems <- newStore registerGcMetrics mems void $ concurrently io (loop mems) where loop ms = do m <- sampleAll ms ... (lookup the gauges from m and log their values) threadDelay dt loop ms I'm very puzzled by this: both rts.gc.current_bytes_used and rts.gc.max_bytes_used gauges return constant 0 in the case of Service 2 (the Cloud Run one), even though I'm using the same sampling/logging functionality and build options for both services. This is about where my knowledge ends; could this behaviour be due to the Google Cloud Run hypervisor ("gRun") implementing certain syscalls in a non-standard way (gRun syscall guide : https://gvisor.dev/docs/user_guide/compatibility/linux/amd64/) ? Thank you for any pointers to guides/manuals/computer wisdom. Details : Both are built with these options : -optl-pthread -optc-Os -threaded -rtsopts -with-rtsopts=-N -with-rtsopts=-T the only difference is that Service 2 has an additional flag -with-rtsopts=-M2G since Cloud Run services must work with 2 GB of memory at most. The container OS in both cases is Debian 10.4 ("Buster").

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Is there a handy refl or refl generator for converting GADT types?
by chris done 02 Jul '20

02 Jul '20

Hi all, I have stages in my compiler that convert e.g. Global Renamed -> Global Generated, etc. where certain constructors are available in certain stages. data GlobalRef s where FromIntegerGlobal :: GlobalRef s FromDecimalGlobal :: GlobalRef s InstanceGlobal :: !InstanceName -> GlobalRef Resolved E.g. after type class resolution is done, the InstanceGlobal constructor is available. But instances can't appear in the AST at other stages. In three stages, I've had to copy/paste this code: + refl = + case name of + FromIntegerGlobal -> FromIntegerGlobal + FromDecimalGlobal -> FromDecimalGlobal Because if I just put `name` then GHC will complain that the types are different, which is correct. But a straight-forward pattern match gives GHC the proof that they can be converted. Is there a handy way already implemented that could derive either this code or this proof for me? Cheers, Chris

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ICFP 2020: Second Call for Student Volunteers
by Victor Lanvin 29 Jun '20

29 Jun '20

Please don't hesitate to share this information with your students, classmates or colleagues! ICFP'20 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'20 will take place **virtually** from Sun 23 - Fri 28 August 2020. 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 2020 Student Volunteer, you will interact closely with researchers, academics and practitioners from various disciplines and meet other students from around the world. While the exact structure of the conference is still being worked on, job assignments for student volunteers will include but will not be restriced to: 1- Assisting with technical sessions, workshops, tutorials and panels. 2- Helping to get speakers prepped and ready for broadcast. 3- Managing the various slack channels and social activities. To be considered as a Student Volunteer for ICFP, please fill in the following application form. https://forms.gle/YPsgEb4qiqnuHteB7 The permanent link to this form can be found on the official conference website. https://icfp20.sigplan.org/track/icfp-2020-student-volunteering The deadline for the second round of applications is July 19th, 2020 AoE. The notification will be on July 21st. Positive notifications given in the first round are firm and the second round is only for spots not filled by the first round. If your application was not accepted in the first round, it will automatically be included in the 2nd round.

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PEP622
by Olaf Klinke 29 Jun '20

29 Jun '20

An excerpt from PEP622 [1]: > Let us start from some anecdotal evidence: isinstance() is one of the > most called functions in large scale Python code-bases (by static > call count). In particular, when analyzing some multi-million line > production code base, it was discovered that isinstance() is the > second most called builtin function (after len()). Even taking into > account builtin classes, it is still in the top ten. Most of such > calls are followed by specific attribute access. > > There are two possible conclusions that can be drawn from this > information: > > * Handling of heterogeneous data (i.e. situations where a variable > can take values of multiple types) is common in real world code. > * Python doesn't have expressive ways of destructuring object data > (i.e. separating the content of an object into multiple variables). > I just want to say a big thank you to the Haskell creators for giving us a tool to efficiently write real world code (as it is called above). [1] https://www.python.org/dev/peps/pep-0622/#rationale-and-goals

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Munich Virtual Haskell Meeting, 2020-06-30 @ 19:30
by Leah Neukirchen 29 Jun '20

29 Jun '20

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, June 30 at 19:30. **Due to meetup limitations in Bavaria, this meeting will take place online!** For details see here: http://muenchen.haskell.bayern/dates.html A Google Meet link to join the room will be provided on Tuesday. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Second Call for Papers: Reactive and Event-Based Languages and Systems (REBLS 2020)
by Ivan Perez 26 Jun '20

26 Jun '20

SECOND CALL FOR PAPERS 7th Workshop on Reactive and Event-based Languages and Systems (REBLS 2020) co-located with the SPLASH Conference Chicago, Illinois, USA Sun 15 - Fri 20 November 2020 Website: https://2020.splashcon.org/home/rebls-2020 IMPORTANT DATES Submission Deadline: 24 Jul 2020 Author Notification: 24 Aug 2020 Camera Ready Deadline: 25 Sep 2020 INTRODUCTION Reactive programming and event-based programming are two closely related programming styles that are becoming more important with the ever increasing requirement for applications to run on the web or on mobile devices, and the advent of advanced High-Performance Computing (HPC) technology. A number of publications on middleware and language design -- so-called reactive and event-based languages and systems (REBLS) -- have already seen the light, but the field still raises several questions. For example, the interaction with mainstream language concepts is poorly understood, implementation technology is still lacking, and modularity mechanisms remain largely unexplored. Moreover, large applications are still to be developed, and, consequently, patterns and tools for developing large reactive applications are still in their infancy. This workshop will gather researchers in reactive and event-based languages and systems. The goal of the workshop is to exchange new technical research results and to better define the field by developing taxonomies and discussing overviews of the existing work. We welcome all submissions on reactive programming, functional reactive programming, and event- and aspect- oriented systems, including but not limited to: * Language design, implementation, runtime systems, program analysis, software metrics, patterns and benchmarks. * Formal models for reactive and event-based programming. * Study of the paradigm: interaction of reactive and event-based programming with existing language features such as object-oriented programming, pure functional programming, mutable state, concurrency. * Modularity and abstraction mechanisms in large systems. * Advanced event systems, event quantification, event composition, aspect-oriented programming for reactive applications. * Functional Reactive Programming (FRP), self-adjusting computation and incremental computing. * Synchronous languages, modeling real-time systems, safety-critical reactive and embedded systems. * Applications, case studies that show the efficacy of reactive programming. * Empirical studies that motivate further research in the field. * Patterns and best-practices. * Related fields, such as complex event processing, reactive data structures, view maintenance, constraint-based languages, and their integration with reactive programming. * Implementation technology, language runtimes, virtual machine support, compilers. * IDEs, Tools. The format of the workshop is that of a mini-conference. Participants can present their work in slots of 30 mins with Q&A included. Because of the declarative nature of reactive programs, it is often hard to understand their semantics just by looking at the code. We therefore also encourage authors to use their slots for presenting their work based on live demos. SUBMISSIONS REBLS encourages submissions of two types of papers: * Full papers: papers that describe complete research results. These papers will be published in the ACM digital library. * In-progress papers: papers that have the potential of triggering an interesting discussion at the workshop or present new ideas that require further systematic investigation. These papers will not be published in the ACM digital library. Format: * Submissions should use the ACM SIGPLAN Conference acmart Format with the two-column, sigplan Subformat, 10 point font, using Biolinum as sans-serif font and Libertine as serif font. All submissions should be in PDF format. If you use LaTeX or Word, please use the ACM SIGPLAN acmart Templates. The page http://www.sigplan.org/Resources/Author/#acmart-format contains instructions for authors, and a package that includes an example file acmart-sigplan.tex. * Authors are required to explicitly specify the type of paper in the submission (i.e., full paper, in-progress paper). * Full papers can be *up to* 12 pages in length, excluding references. In-progress papers can be *up to* 6 pages, excluding references. Papers do not need to make use of all pages, but they will be summarily rejected if they exceed the page limits. Instructions for the Authors: * Papers should be submitted through: https://rebls20.hotcrp.com/ * For fairness reasons, all submitted papers should conform to the formatting instructions. Submissions that violate these instructions will be summarily rejected. * Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. * Papers must describe unpublished work that is not currently submitted for publication elsewhere as described by SIGPLAN’s Republication Policy (http://www.sigplan.org/Resources/Policies/Republication) Submitters should also be aware of ACM’s Policy and Procedures on Plagiarism. * All submissions are expected to comply with the ACM Policies for Authorship detailed at https://www.acm.org/publications/authors/information-for-authors. PROGRAM COMMITTEE Ivan Perez (PC Chair; NIA) Alan Jeffrey, Mozilla Research. Christiaan Baaij, QBayLogic. César Sánchez, IMDEA Software. Daniel Winograd-Cort, Target Corp. Edward Amsden, Black River Software, LLC. Guerric Chupin, University of Nottingham. Heinrich Apfelmus. Jonathan Thaler, University of Applied Sciences Vorarlberg. Louis Mandel, IBM Research. Manuel Bärenz, sonnen eServices GmbH. Marc Pouzet, Université Pierre et Marie Curie. Mark Santolucito, University of Yale. Neil Sculthorpe, University of Nottingham Trent. Noemi Rodrigues, Pontifícia Universidade Católica do Rio de Janeiro Oleksandra Bulgakova, Sukhomlynsky Mykolaiv National University Patrick Bahr, University of Copenhagen Takuo Watanabe, Tokyo Institute of Technology Tetsuo Kamina, Oita University Tom Van Cutsem, Nokia Bell Labs Yoshiki Ohshima, HARC / Y Combinator Research ORGANIZING COMMITTEE Guido Salvaneschi, TU Darmstadt, Germany Wolfgang De Meuter, Vrije Universiteit Brussel, Belgium Patrick Eugster, Universita della Svizzera Italiana, Switzerland Francisco Sant'Anna, Rio de Janeiro State University, Brazil Lukasz Ziarek, SUNY Buffalo, United States For any questions, please use the form on the website or contact the Chair at ivan.perezdominguez(a)nasa.gov

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