- Haskell-Cafe - Haskell.org

[ANN] Haskell Beginners WT.Social Community: "Haskell: The Haskell-Beginners Community"
by Benjamin L. Russell 18 Apr '20

18 Apr '20

Twenty-eight days ago (on March 23, 2020 JST), I created a new Haskell beginners WT.Social community, "Haskell: The Haskell-Beginners Community" (see https://pashpost.com/group/haskell-the-haskell-beginners-community) and migrated a substantial portion of the posts originally from my former corresponding pashPOST (since renamed to "theTUNDRA") community of the same name thereto (sansposts with missing links or irrelevant content). Feel free to join and contribute! -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Computer Science Document Translator/Editor "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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GHC Dockerimage
by Alexander Ben Nasrallah 18 Apr '20

18 Apr '20

Hi fellow Haskellers, since I was missing a Dockerimage for GHC built with musl and integer-simple for static linking, which is kept up to date, I created my own. I use it to test compatibility with different GHC versions and provide a full statically linked binary for download with GitLab CI/CD. Maybe someone will find it useful, too. Or maybe there already is another more sophisticated project someone can point me to. https://registry.hub.docker.com/r/neosimsim/ghc

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Attoparsec: match many, skipping rest
by amindfv＠gmail.com 17 Apr '20

17 Apr '20

Say I've got an Attoparsec parser like: p = string "prio:" *> digit And some text, e.g. s = "this is just a prio:5 example, I'd prio:6 very much like to prio:4 parse" What's the most idiomatic way to apply p to s so that I get out a list ['5', '6', '4']? Thanks, Tom

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streaming package: How to demux a stream properly?
by ☂Josh Chia (謝任中) 15 Apr '20

15 Apr '20

I have a streaming package question. Suppose I have a: Stream (Of (Int, a)) m () I would like to demultiplex it into Vector (Stream (Of a) m ()) using the Int as the index of an item into the Vector of output streams. How can I do this efficiently (constant memory and linear time)? Does the following work? import qualified Streaming.Prelude as SP import qualified Data.Vector as V type StreamOf a m r = Stream (Of a) m r demuxStream :: forall a m. MonadIO m => Int -> StreamOf (Int, a) m () -> m (Vector (StreamOf a m ())) demuxStream numSyms stream = let emptyStreams = V.replicate numSyms (pure ()) processItem v (iD, x) = V.modify (\vm -> VM.modify vm (>> SP.yield x) iD) v in SP.fold_ processItem emptyStreams id stream My guess is that it takes more than constant memory as it goes through the entire input stream before returning. Josh

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Haskell Symposium 2020 -- Call for Papers: Regular track & demos
by Tom Schrijvers 14 Apr '20

14 Apr '20

================================================================================ ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2020 New Jersey, United States 27--28 August, 2020 http://www.haskell.org/haskell-symposium/2020/ ================================================================================ The ACM SIGPLAN Haskell Symposium 2020 will be co-located with the 2020 International Conference on Functional Programming (ICFP). Like last year, we will be using a lightweight double-blind reviewing process. See further information below. The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative programming. Topics of interest include: * Language design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts; * System Demonstrations, based on running software rather than novel research results. Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. Experience reports and functional pearls need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementers, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. System demonstrations should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. Submission Details ================== Early and Regular Track ----------------------- The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Strong papers submitted to the early track are accepted outright, and the others will be given their reviews and invited to resubmit to the regular track. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Formatting ---------- Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. Authors should use the `acmart` format, with the `sigplan` sub-format for ACM proceedings. For details, see: http://www.sigplan.org/Resources/Author/#acmart-format It is recommended to use the `review` option when submitting a paper; this option enables line numbers for easy reference in reviews. Functional pearls, experience reports, and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2020 will use a lightweight double-blind reviewing process. To facilitate this, submitted papers must adhere to two rules: 1. Author names and institutions must be omitted, and 2. References to authors’ own related work should be in the third person (e.g., not “We build on our previous work …” but rather “We build on the work of …”). The purpose of this process is to help the reviewers come to an initial judgment about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. A reviewer will learn the identity of the author(s) of a paper after a review is submitted. Page Limits ----------- The length of submissions should not exceed the following limits: Regular paper: 12 pages Functional pearl: 12 pages Experience report: 6 pages Demo proposal: 2 pages There is no requirement that all pages are used. For example, a functional pearl may be much shorter than 12 pages. In all cases, the list of references is not counted against these page limits. Deadlines --------- Early track: Submission deadline: 20 March 2020 (Fri) Notification: 24 April 2020 (Fri) Regular track and demos: Submission deadline: 15 May 2020 (Fri) Notification: 26 June 2020 (Fri) Deadlines are valid anywhere on Earth. Submission ---------- Submissions must adhere to SIGPLAN's republication policy (http://sigplan.org/Resources/Policies/Republication/) and authors should be aware of ACM's policies on plagiarism (https://www.acm.org/publications/policies/plagiarism) Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers should be submitted through HotCRP at: https://haskell20.hotcrp.com/ Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Supplementary material: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. This supplementary material should not be submitted as part of the main document; instead, it should be uploaded as a separate PDF document or tarball. Supplementary material should be uploaded at submission time, not by providing a URL in the paper that points to an external repository. Authors are free to upload both anonymized and non-anonymized supplementary material. Anonymized supplementary material will be visible to reviewers immediately; non-anonymized supplementary material will be revealed to reviewers only after they have submitted their review of the paper and learned the identity of the author(s). Resubmitted Papers: Authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the principal editor will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. Travel Support ============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC program, see its web page (http://pac.sigplan.org) Proceedings =========== Accepted papers will be included in the ACM Digital Library. Their authors will be required to choose one of the following options: - Author retains copyright of the work and grants ACM a non-exclusive permission-to-publish license (and, optionally, licenses the work with a Creative Commons license); - Author retains copyright of the work and grants ACM an exclusive permssion-to-publish license; - Author transfers copyright of the work to ACM. For more information, please see ACM Copyright Policy (http://www.acm.org/publications/policies/copyright-policy) and ACM Author Rights (http://authors.acm.org/main.html) Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Artifacts ========= Authors of accepted papers are encouraged to make auxiliary material (artifacts like source code, test data, etc.) available with their paper. They can opt to have these artifacts published alongside their paper in the ACM Digital Library (copyright of artifacts remains with the authors). If an accepted paper's artifacts are made permanently available for retrieval in a publicly accessible archival repository like the ACM Digital Library, that paper qualifies for an Artifacts Available badge (https://www.acm.org/publications/policies/artifact-review-badging#available ). Applications for such a badge can be made after paper acceptance and will be reviewed by the PC chair. Program Committee ================= Arthur Azevedo de Amorim Carnegie Mellon University Manuel Chakravarty Tweag I/O / IOHK Jan Christiansen Flensburg University of Applied Sciences Youyou Cong Tokyo Institute of Technology Pierre-Evariste Dagand CNRS Anton Ekblad Chalmers University of Technology Jurriaan Hage Universiteit Utrecht Graham Hutton University of Nottingham José Pedro Magalhães Standard Chartered Clare Martin Oxford Brookes University Andrey Mokhov Jane Street Shin-Cheng Mu Academia Sinica Nikolaos Papaspyrou National Technical University of Athens Simon Peyton Jones Microsoft Research Cambridge Norman Ramsey Tufts University Exequiel Rivas INRIA Tom Schrijvers (chair) KU Leuven Martin Sulzmann Karlsruhe University of Applied Sciences If you have questions, please contact the chair at: tom.schrijvers(a)kuleuven.be ================================================================================

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Re: [Haskell-cafe] Eff verbose/ambiguous/type safety
by Anthony Clayden 14 Apr '20

14 Apr '20

Hi Daneel, welcome > Recently I discovered for my self an alternative for monad > transformers - extensible effects. > > http://okmij.org/ftp/Haskell/extensible/ > So straight away a word of warning: the 'ok' there is Oleg Kiselyov, who has produced many wonderful demonstrations of the power of Haskell's type system. (HList is anoher inspiration.) Many would say he has warped the type system beyond what it could reasonably be expected to achieve. So we measure the brain power needed to understand type signatures and messages in milli-Olegs. > Overall it is really cool and Eff1.hs started working right away, > but I noticed a problem with mixing several effects in 1 function. > Type checker requires pretty verbose type signature, which looks > unreasonable plus the error reported to a beginner developer > is not intuitive. Extensible effects/all of Oleg's work is not aimed at beginners. I advise beginners to stay well clear. You can expect enormous, inscrutable type errors. I agree with Georgi you should give type signatures everywhere you can. And your code should be used only by type experts. AntC

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Eff verbose/ambiguous/type safety
by Daneel Yaitskov 13 Apr '20

13 Apr '20

Hello Group, Recently I discovered for my self an alternative for monad transformers - extensible effects. http://okmij.org/ftp/Haskell/extensible/ Overall it is really cool and Eff1.hs started working right away, but I noticed a problem with mixing several effects in 1 function. Type checker requires pretty verbose type signature, which looks unreasonable plus the error reported to a beginner developer is not intuitive. So my questions are: - why it happens? - what could I do to get more friendly error message? - is there a workaround enforcing GHC make an extra mile and work without these "extra hints"? - any more maintainable Eff implementations? Here it an example I wish should working. $ stack gchi Eff1.hs *Eff1 > doLift = lift (putStrLn "EFF!") *Eff1 > doWrite = tell "HELLO" *Eff1 > doLiftAndWrite = doLift >> doWrite *Eff1 > runLift (runWriter doLiftAndWrite) <interactive>:82:20: error: * Couldn't match type `Writer [Char]' with `Lift IO' arising from a use of `doLiftAndWrite' * In the first argument of `runWriter', namely `doLiftAndWrite' In the first argument of `runLift', namely `(runWriter doLiftAndWrite)' In the expression: runLift (runWriter doLiftAndWrite) The error message looks unclear, because documentation makes me think that Writer and Lift are members of same Eff monad and they are composable and doLiftAndWrite has been evaluated successfully. And my workaround: *Eff1 > runLift $ do { x :: ((), [String]) <- runWriter doLiftAndWrite; return x; } EFF! ((),["HELLO"]) Plus GHCi swallows a type error: *Eff1 > badCast = do { x :: ((), [Int]) <- runWriter doLiftAndWrite; return x; } *Eff1 > :t badCast badCast :: (MemberU2 Lift (Lift IO) r, OpenUnion52.FindElem (Writer [Char]) r) => Eff r ((), [Int]) Definitely Extensible Effects are more flexible that MTL, but compile type safety looks jeopardized. Type verbosity overhead is kind of acceptable, but having possibility of run-time errors is too big price for flexibility. -- Daneel S. Yaitskov

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Targeting old Windows versions
by Andreas Klebinger 08 Apr '20

08 Apr '20

Hello devs, GHC is planning to use the Large Address Space mode of allocation for future releases on windows. See https://gitlab.haskell.org/ghc/ghc/issues/12576 This is a significant optimization for the GC and well tested as we use it on Linux already. However it will regress memory useage on versions of windows *older* than Windows 8.1/Sever 2012. Please let us know if you are targeting older versions than that either by responding to the mailing list, commenting on the ticket or contacting me directly if you have privacy concerns. Depending on how many people are affected by this change we might consider measures to reduce the impact. Cheers, Andreas

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Uppercase OverloadedLabels
by Alejandro Serrano Mena 07 Apr '20

07 Apr '20

Dear Haskell-Café / GHC devs, Is there any reason why the `OverloadedHaskell` extension does not work with labels starting with an uppercase letter? Kind regards, Alejandro

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New stack.yaml.lock file to master source repo?
by David Banas 06 Apr '20

06 Apr '20

What’s the general consensus on whether or not the new stack.yaml.lock file should be stored in the master source repo.? Thanks, -db

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Looking for a library for DerivingVia idioms
by Jack Kelly 06 Apr '20

06 Apr '20

Hello Cafe, Here is a problem a friend (CC'd - please include him in replies) and I wanted to solve using DerivingVia. We have a solution (below). I'm wondering whether a library for these newtypes exists, and if not, whether it should. This email is Literate Haskell. The problem: given two types `Foo` and `Bar`, and an injection `foo2bar :: Foo -> Bar`, use DerivingVia to derive instances for `Foo` in terms of `Bar`. > {-# LANGUAGE DerivingVia, MultiParamTypeClasses #-} > {-# LANGUAGE ScopedTypeVariables, TypeOperators #-} > > import Data.Function (on) > import Data.Coerce (coerce) > > data Foo = Foo deriving Eq via (Foo `InjectedInto` Bar) > data Bar = Bar deriving Eq > > foo2bar :: Foo -> Bar > foo2bar Foo = Bar Section 4.3 of the DerivingVia paper[1] shows how to use a newtype wrapper to derive instances for one type in terms of another, so long as their generic representation is the same. We can use the same technique. We need a newtype that's representationally equal to `a`, to pass to DerivingVia: > newtype InjectedInto a b = InjectedInto a We also need a class, so that we can find our injection given the type: > class Injective a b where > -- Law: to x = to y => x = y > to :: a -> b > > instance Injective Foo Bar where > to = foo2bar We need an instance that uses the InjectedInto newtype: > instance (Eq b, Injective a b) => Eq (a `InjectedInto` b) where > (==) = (==) `on` (to :: a -> b) . coerce The `deriving Eq via (Foo `InjectedInto` Bar)` above compiled successfully, so everything seems to work well. I'm wondering: 1. Is a library collecting useful DerivingVia wrappers? 2. If not, suppose I wanted to stand up such a library. Is there a canonical library providing classes like `Injection`? I found the `type-iso` package, which provides an `Injective` typeclass[2], but it has few revdeps and a dubious instance Default a => Injective (Maybe b) (Either a b). 3. What about DerivingVia for types not of kind `Type`? It might be possible to repeat this structure one level up for `Eq1` &c. Is it worth supporting `Eq1` etc in a world with QuantifiedConstraints? 4. Is there a better name than `InjectedInto`? It doesn't scan well. A type operator, perhaps? Thanks for reading. I look foward to your responses. -- Jack [1]: https://www.kosmikus.org/DerivingVia/deriving-via-paper.pdf [2]: https://hackage.haskell.org/package/type-iso-1.0.1.0/docs/Data-Types-Inject…

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Two PhD positions in Utrecht
by Wouter Swierstra 06 Apr '20

06 Apr '20

============================================================== Two PhD positions in functional programming ============================================================== The Department of Information and Computing Sciences at Utrecht University is currently advertising two PhD positions in Functional Programming. The candidates will join the Intelligent Systems group, working with Johan Jeuring, Gabriele Keller, and Wouter Swierstra. Besides research, the successful candidate will be expected to help supervise MSc students and assist in the teaching of courses. The positions should be filled by September 2020, although the exact starting date is negotiable. --------------------------------- Research topics --------------------------------- These two positions are tied to two specific topics. * Programming tutors for Functional Languages (Johan Jeuring) The focus of the position is on designing new technologies to support students working in an intelligent tutoring system for functional programming. We expect to use techniques from dependently typed programming, refinement types, program synthesis, automated theorem proving, and more to analyse student programs, and to help students in taking the next step when developing a program. The candidate will investigate the design and use of multiple technologies for this purpose, add them to Ask-Elle, our intelligent tutoring system, perform experiments with the system, and improve the technologies based on the outcome of the experiments. * Compiler verification for a smart contract language (Wouter Swierstra & Gabriele Keller) This project aims to develop a certifying compiler for Plutus Tx, a subset of the purely functional language Haskell that is used to implement smart contracts for the Cardano blockchain. The Plutus smart contract framework is being developed by IOHK for Cardano and the present project is a joint effort of IOHK and Utrecht University. The Plutus Tx compiler is based on the GHC Haskell compiler and adds a translation step from GHC Core to a minimal lambda calculus. Programs in this lambda calculus are executed during transaction validation in a sandboxed execution environment in a manner that is crucial to the security of the blockchain. This project aims to formalise the semantics of the languages involved, to reason about the transformation and optimisation steps that the compiler performs, and finally, to generate a proof object certifying the correctness of the generated code together with that code. --------------------------------- What we are looking for --------------------------------- The ideal candidates should have a degree in Computer Science, be highly motivated, speak and write English well, and be proficient in producing scientific reports. Furthermore, candidates should be able to demonstrate experience with functional programming languages, such as Haskell, OCaml, ML, Agda, Idris, or Coq. --------------------------------- What we offer --------------------------------- The candidates are offered a full-time position for four or five years, depending on the teaching load. The gross salary ranges between €2,325 in the first year and €2,972 in the fourth year per month for full-time employment. A part-time position of at least 0.8 fte may also be possible. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 8.3% per year. The position also includes a generous allocation of fully-paid vacation days. In addition we offer: a pension scheme, partially paid parental leave, and flexible employment conditions. Conditions are based on the Collective Labour Agreement Dutch Universities. The research group will provide the candidate with necessary support on all aspects of the project. More information is available on the website: Terms and employment: http://bit.ly/1elqpM7 Utrecht is consistently ranked as one of the best places in the world to live. --------------------------------- How to apply --------------------------------- To apply please attach a letter of motivation, a curriculum vitae, and (email) addresses of two referees. Make sure to also include a transcript of the courses you have followed (at bachelor and master level), with the grades you obtained, and to include a sample of your scientific writing, such as your MSc or BSc thesis. It is possible to apply for this position if you are close to obtaining your undergraduate degree. In that case include a letter of your supervisor with an estimate of your progress, and do not forget to include at least a sample of your technical writing skills. The application deadline for the first position closes on April 29th. You can apply through the University's website: https://www.uu.nl/en/organisation/working-at-utrecht-university/jobs/5-year… The application for the second position is not yet open -- but feel free to contact me directly if you're interested. If you're still unsure about the topic, feel free to apply using the link above; we're happy to discuss which topic fits your interests best during the application process.

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Call for participation: Utrecht AFP Summer School
by Wouter Swierstra 06 Apr '20

06 Apr '20

SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Utrecht, the Netherlands, 06-10 July 2020 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. We have decided to advertise the Summer School and accept new registrations for the moment, but we are monitoring the situation with COVID-19 carefully. All the Utrecht Summer Schools offer participants a full refund of their registration fee if they decide to cancel their registration. The lectures will cover several more advanced topics regarding the theory and practice of Haskell programming, including topics such as: * lambda calculus; * monads and monad transformers; * lazy evaluation; * generalized algebraic data types; * type families and type-level programming; * concurrency and parallelism. The summer school consists of a mix of lectures, labs, and a busy social program. ## 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 July, 2020 School: 06-10 July, 2020 ## Costs 1700 euro - Housing and registration 1500 euro - Registration only We offer a 1000 discount for students and staff members affiliated with a university or other non-profit organization. ## Scholarships If you're struggling to finance your trip to Utrecht, please let us know. We have a very limited number of scholarships or discounts available for students that would not be able to attend otherwise, especially for women and under-represented minorities. ## Further information Further information, including instructions on how to register, is available on our website: http://www.afp.school

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Efficiency of passing function arguments
by KS 04 Apr '20

04 Apr '20

Hello everyone, I was coming from a C++ background and I always wondered if there is a distinction between pass-by-value and pass-by-reference in Haskell (or pass-by-thunk? since an argument might be partially evaluated due to laziness in Haskell). Is there a way to guarantee that an function argument is passed in an efficient manner? For example, if we have a data type data Document = Document { title :: Text , author :: Name , content :: Text -- and potentially many more } doc = Document {..} -- omitted and we want to pass doc to a function, we should ideally hope that doc is not getting duplicated when passing it as an argument. Another example might be the Reader monad, where we are passing possibly the same environment to multiple functions. In C++, we could either pass by a pointer or a reference, but I'm not sure what the best practices are in Haskell. The most relevant construct in Haskell seems to be IORef, though I'm not sure if this is the correct way to use it. For exmaple, if I want to pre-load a template document on disk as Text or ByteString into the memory when the program starts, should I put it in a IORef and pass it into (more than one) functions or should I pass it into the function directly? Should I worry about this at all? This question might be related to the implementation of the ghc compiler. It would be better if anyone could shed some lights on the implementation details. Thank you, Kram

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How to safely and fast write repa array to a file?
by cyberfined 04 Apr '20

04 Apr '20

Hello, all. I decide to write parallel ray tracer on haskell with repa. Now, to save repa array to file I use dirty trick casting repa array ptr to bytestring with fromForeignPtr and then writing it to file with hPut. It looks something like that: import qualified Data.Array.Repa as R import qualified Data.Array.Repa.Repr.ForeignPtr as RF import qualified Data.ByteString as B import qualified Data.ByteString.Char8 as BC import qualified Data.ByteString.Internal as BI type Image = Array F DIM2 Pixel writeImage :: FilePath -> Image -> IO () writeImage path img = bracket (openFile path WriteMode) (hClose) $ \hdl -> B.hPut hdl header >> B.hPut hdl body where Z :. h :. w = R.extent img header = BC.pack $ "P6\n" ++ show w ++ ' ':show h ++ "\n255\n" body = BI.fromForeignPtr(castForeignPtr $ RF.toForeignPtr img) 0 (w*h*3) My question is: how to write repa array to file safely and fast?

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ML Family Workshop 2020: Call for presentations
by Leo White 04 Apr '20

04 Apr '20

We are happy to invite submissions to the ML Family Workshop 2020, to be held during the ICFP conference week on Thursday, August 27th. 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. Currently, the workshop is still scheduled to go ahead as planned in Jersey City, however it is likely that the ML workshop will end up being a virtual workshop this year. Either way provisions will be made to allow speakers to present their work remotely. See our detailed CFP online on the ICFP website: https://icfp20.sigplan.org/home/mlfamilyworkshop-2020 Important dates --------------- - Friday 15th May (any time zone): Abstract submission deadline - Friday 26th June: Author notification - Thursday 27th August: ML Family Workshop Program committee ----------------- - Youyou Cong (Tokyo Institute of Technology) - Gowtham Kaki (Purdue University) - Neel Krishnaswami (University of Cambridge) - Daan Leijen (Microsoft Research) - Koko Muroya (Kyoto University) - Atsushi Ohori (Tohoku University) - Jonathan Protzenko (Microsoft Research) - Gabriel Radanne (INRIA) - Claudio Russo (Dfinity) - Leo White (Jane Street) (Chair) - Jeremy Yallop (University of Cambridge) Submission details ------------------ See the online CFP for the details on the expected submission format. Submissions must be uploaded to the workshop submission website https://ml2020.hotcrp.com/ before the submission deadline.

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ANN: stack-2.3.0.1 release candidate
by Emanuel Borsboom 03 Apr '20

03 Apr '20

### First release candidate for v2.3 **Changes since v2.1.3** Release notes: Major changes: * `setup-info-locations` yaml configuration now allows overwriting the default locations of `stack-setup-2.yaml`. [#5031](https://github.com/commercialhaskell/stack/pull/5031) [#2983](https://github.com/commercialhaskell/stack/issues/2983) [#2913](https://github.com/commercialhaskell/stack/issues/2913) * The `setup-info` configuration key now allows overwriting parts of the default `setup-info` * The `--setup-info-yaml` command line flag now may be used in all stack commands such as `stack build`, and not only in `stack setup` * The `--setup-info-yaml` may specify multiple locations for `stack-setup.yaml` files. * The `stack upload` can read first reads environment Variable `$HACKAGE_USERNAME` and `$HACKAGE_PASSWORD` if they are missing only then asks for `username` or `password` * Fully remove GHCJS support. * Remove the `freeze` command. It has been replaced by lock files. Behavior changes: * Remove the deprecated `--stack-setup-yaml` command line argument in favor of `--setup-info-yaml` [#2647](https://github.com/commercialhaskell/stack/issues/2647) * We now recommend checking in generated cabal files for repos. When generating lock files for extra-deps that only include `package.yaml` files, a deprecation warning will be generated. Also, those packages will no longer be included in the generated lock files. See [#5210](https://github.com/commercialhaskell/stack/issues/5210). Other enhancements: * Add `build-output-timestamps` flag in yaml. Setting it to true prefixes each build log output line with a timestamp. * Show warning about `local-programs-path` with spaces on windows when running scripts. See [#5013](https://github.com/commercialhaskell/stack/pull/5013) * Add `ls dependencies json` which will print dependencies as JSON. `ls dependencies --tree` is now `ls dependencies tree`. See [#4424](https://github.com/commercialhaskell/stack/pull/4424) * Remove warning for using Stack with GHC 8.8 and Cabal 3.0. * Allow relative paths in `--setup-info-yaml` and tool paths [#3394](https://github.com/commercialhaskell/stack/issues/3394) Bug fixes: * Upgrade `pantry`: module mapping insertions into the database are now atomic. Previously, if you SIGTERMed at the wrong time while running a script, you could end up with an inconsistent database state. * `--resolver global` doesn't retrieve snapshots list from the internet beause doesn't need it. See [#5103](https://github.com/commercialhaskell/stack/issues/5103) * Fix using relative links in haddocks output. See [#4971](https://github.com/commercialhaskell/stack/issues/4971). * Do not include generated cabal file information in lock files. See [#5045](https://github.com/commercialhaskell/stack/issues/5045). * Use proper Hoogle executable path when installed automatically. See [#4905](https://github.com/commercialhaskell/stack/issues/4905) * Fix GHC version for batched package unregistration. See [#4951](https://github.com/commercialhaskell/stack/issues/4951) * Use Hoogle from the snapshot used and not the latest version. See [#4905](https://github.com/commercialhaskell/stack/issues/4905) * Resolve "'stty' is not recognized". See [#4901](https://github.com/commercialhaskell/stack/issues/4901) * Fix missing reconfigure check causing errors when a package gets used in multiple projects. See [#5147](https://github.com/commercialhaskell/stack/issues/5147)

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[ANN] acme-dont-1.2 - a "don't" construct
by Jack Kelly 02 Apr '20

02 Apr '20

Hello all, I have taken over the maintainership of acme-dont, and am pleased to announce a new acme-dont release on Hackage[1]. acme-dont provides a `don't` function, which does not execute its argument. For example, the following code will not print anything: import Acme.Dont (don't) quiet :: IO () quiet = don't $ putStrLn "You'll never see this on stdout" New in this release: * `don't` has been generalised from `Monad` to `Applicative`. If you have been waiting since GHC 8.0.1's release in 2016[2] to use `don't` with `-XApplicativeDo`, wait no longer. * A test suite, to ensure that `don't` does not do anything. Previous versions could have been defined as `don't = void` for all we knew. Also, the acme-dont community now has a new home on sourcehut. On there, you can find the following invaluable resources: * A source repository[3], to track further developement and new ways of not doing things, with a commit history reconstructed from the release tarballs uploaded to Hackage. * A mailing list[4] for the acme-dont community to discuss the best ways of not doing things. * A bug tracker[5] to handle reports, in case someone observes acme-dont doing something. * Continuous integration[6], to ensure that acme-dont continues to not do things across multiple versions of GHC. I would like to thank Gracjan Polak for uploading the initial releases of `acme-dont`, and for maintaining the package these past eleven years. I do not intend to betray the responsibility he has assigned me in handing over this critical package. Best, -- Jack [1]: https://hackage.haskell.org/package/acme-dont-1.2 [2]: https://www.haskell.org/ghc/download_ghc_8_0_1 [3]: https://git.sr.ht/~jack/acme-dont [4]: https://lists.sr.ht/~jack/acme-dont-discuss [5]: https://todo.sr.ht/~jack/acme-dont [6]: https://builds.sr.ht/~jack/acme-dont

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Using State monad with lens
by Michael Hull 02 Apr '20

02 Apr '20

Hi, I use the State monad in a lot of places, but when I use it with the lens library, I find myself writing code like: myFunc :: StateT MyState ([ResultType]) myFunc = do st <- get case st ^. some_property of True -> do my_value .= "Hello" True -> do my_value .= "Goodbye" I want to do something based on a 'state-variable', but I have to write 'get' -- is there a pattern that allows me to avoid the intermediate 'st' variable? I want to write something like: myFunc = do case (get ^. some_property) of True -> do my_value .= "Hello" True -> do my_value .= "Goodbye" but that won't compile. Best wishes, Mike

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Re: [Haskell-cafe] [ANN] acme-dont-1.2 - a "don't" construct
by Jack Kelly 01 Apr '20

01 Apr '20

Dear Henk-Jan, You can view the preprint yourself with the following commands: $ true > dont.txt $ less dont.txt You'll then start seeing it everywhere you look, and I'm not sure that wider distribution is possible. -- Jack "Henk-Jan van Tuyl" <b.vantuyl1(a)upcmail.nl> writes: > Thanks, > > The `don't` function is a big step forward in computering; it will > surely prevent many bugs from occurring, with little effort to > software developers. > > Is it published in a scientific magazine yet? > > Regards, > Henk-Jan van Tuyl > > > On Wed, 01 Apr 2020 10:38:08 +0200, Jack Kelly <jack(a)jackkelly.name> wrote: > >> Hello all, >> >> I have taken over the maintainership of acme-dont, and am pleased to >> announce a new acme-dont release on Hackage[1]. >> >> >> acme-dont provides a `don't` function, which does not execute its >> argument. For example, the following code will not print anything: >> >> import Acme.Dont (don't) >> >> quiet :: IO () >> quiet = don't $ putStrLn "You'll never see this on stdout" >> >> >> New in this release: >> >> * `don't` has been generalised from `Monad` to `Applicative`. If you >> have been waiting since GHC 8.0.1's release in 2016[2] to use >> `don't` with >> `-XApplicativeDo`, wait no longer. >> >> * A test suite, to ensure that `don't` does not do anything. Previous >> versions could have been defined as `don't = void` for all we knew. >> >> >> Also, the acme-dont community now has a new home on sourcehut. On there, >> you can find the following invaluable resources: >> >> * A source repository[3], to track further developement and new ways of >> not doing things, with a commit history reconstructed from the release >> tarballs uploaded to Hackage. >> >> * A mailing list[4] for the acme-dont community to discuss the best ways >> of not doing things. >> >> * A bug tracker[5] to handle reports, in case someone observes acme-dont >> doing something. >> >> * Continuous integration[6], to ensure that acme-dont continues to not >> do things across multiple versions of GHC. >> >> >> I would like to thank Gracjan Polak for uploading the initial releases >> of `acme-dont`, and for maintaining the package these past eleven >> years. I do not intend to betray the responsibility he has assigned me >> in handing over this critical package. >> >> Best, >> >> -- Jack >> >> [1]: https://hackage.haskell.org/package/acme-dont-1.2 >> [2]: https://www.haskell.org/ghc/download_ghc_8_0_1 >> [3]: https://git.sr.ht/~jack/acme-dont >> [4]: https://lists.sr.ht/~jack/acme-dont-discuss >> [5]: https://todo.sr.ht/~jack/acme-dont >> [6]: https://builds.sr.ht/~jack/acme-dont >> _______________________________________________ >> 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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mmap Failure in: 24:Counters should be zero
by YueCompl 01 Apr '20

01 Apr '20

Hi mmap maintainers, Today I found the last test case out of 25 failed like: ```bash $ cabal v2-run -f mmaptest mmaptest Resolving dependencies... Build profile: -w ghc-8.6.5 -O1 In order, the following will be built (use -v for more details): - mmap-0.5.9 (exe:mmaptest) (configuration changed) Configuring mmap-0.5.9... Preprocessing executable 'mmaptest' for mmap-0.5.9.. Building executable 'mmaptest' for mmap-0.5.9.. <no location info>: warning: [-Wmissing-home-modules] These modules are needed for compilation but not listed in your .cabal file's other-modules: System.IO.MMap <no location info>: warning: [-Wmissing-home-modules] These modules are needed for compilation but not listed in your .cabal file's other-modules: System.IO.MMap ### Failure in: 24:Counters should be zero tests/mmaptest.hs:256 expected: 0 but got: 4 Cases: 25 Tried: 25 Errors: 0 Failures: 1 ``` And the test code is: ```haskell test_counters_zero = do System.Mem.performGC threadDelay 1000 counters <- c_system_io_counters return (counters @?= 0) ``` I see it is to make sure no resource held open after 1 millisecond after garbage collection is triggered. I tried extending the threadDelay to 10 second and still got 4 thus failing the test, maybe newer machinery of GC with GHC 8.6 should be leveraged to prevent such leakage? I CC haskell-cafe list to seek for broader community help, maybe some one can confirm that I can just live with this specific failure without worries? Thanks & best regards, Compl

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How to make a Hashable instance for (Finite n)?
by David Banas 31 Mar '20

31 Mar '20

What is the most expedient way to get around this error? Could not deduce (Hashable (Finite n)) Thanks, -db

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Research Assistant/Associate Position (Postdoc) at Imperial College London
by David Castro 30 Mar '20

30 Mar '20

Hello, We are looking for candidates for this position at Imperial College London. The official text of the advertisement follows: Department of Computing, Imperial College London Research Assistant/Associate Position (Full Time) 35,477 GBP to 47,579 GBP per annum Reference: ENG01270 Fixed-term: 2 years (with a possible 24 month extension) Starting date: as soon as possible (no later than 1st October 2020) Closing Date: 26th April 2020 The Research Assistant will work under the EPSRC Established Career Fellowship Project, POST: Protocols, Observabilities and Session Types. Imperial College London provides a flexible arrangement to be able to start and work remotely until we re-open the campus (this depends on your nationality and current living address). Please contact with Nobuko Yoshida (n.yoshida(a)imperial.ac.uk) Imperial College London if you would like to apply to the position to have informal discussions. The application deadline is also extendable. ------------------------------------------------------------ The project has particular emphasis on putting theory into practice, by embedding session types in a range of programming languages and applying them to case studies; or developing the links between session types and other areas of theoretical computer science. The research programme includes collaboration with several companies and organisations. Candidates for the post-doc position will need to have expertise in either: 1. programming language design and implementation; or 2. formal semantics, type theory and concurrency theory Different positions will be suitable for different points on the theory/practice spectrum. We are especially interested in candidates with a combination of theoretical and practical skills. For more details, see http://mrg.doc.ic.ac.uk. The focus of Imperial College London Group is theories and applications of (Multiparty) Session Types (JACM,POPL'08) which include: -- Go (POPL'19,ICSE'18,POPL'17,CC'16), Scala (PLDI'19,ECOOP'17,ECOOP'16), F# (CC'18), Erlang (CC'17), Haskell (CC'20,POPL'16), OCaml (SOC), Java (FASE'16,FASE'17), MPI-C (FPL'16,OOPSLA'15,CC'15) and Python (FOAC,LMCS,FMSD); -- session types theories (ESOP'20,POPL'19,ESOP'19,ESOP'16,CONCUR'15), automata theories (CAV'19,CONCUR'19,FoSSaCs'17,TACAS'16,CONCUR'15,POPL'15), game semantics (POPL'19,FoSSaCs'19), Implicit Complexity (LICS'18) and linear logic (ESOP'18,FoSSaCs'18,CONCUR'15); or -- mechanisation of session types meta-theory (Coq, Isabelle, Agda, etc) (TACAS 20) -- other applications such as blockchains (FSE'19) and robotics (ECOOP'19) The contact person is Professor Nobuko Yoshida, Imperial College London (n.yoshida(a)imperial.ac.uk) The candidate is welcome to contact her. Details: https://www.imperial.ac.uk/jobs/description/ENG01270/research-assistant-res…

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[ANN] esqueleto-3.3.3.0: Support for UNION, safer joins, and subquery joins!
by Christian Charukiewicz 30 Mar '20

30 Mar '20

Hi all, My friend Ben Levy and I spent a while writing and documenting Database.Esqueleto.Experimental, a new module in the esqueleto package which adds support for UNION, subqueries, and improves the safety of outer JOINs. We've done a lot of use/testing of this implementation, but it is currently in the Experimental module in order to allow for gathering feedback. It is now live on Hackage as esqueleto-3.3.3.0. The module docs give examples of the new functionality. Feel free to take a take a look here: https://hackage.haskell.org/package/esqueleto-3.3.3.0/docs/Database-Esquele… Thanks, Christian

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gitlab.haskell.org down?
by Ivan Perez 29 Mar '20

29 Mar '20

Hi, Is the Haskell gitlab down or has anything changed? https://downforeveryoneorjustme.com/gitlab.haskell.org Cheers, Ivan

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Re: [Haskell-cafe] Strange error when cabal installing.
by David Banas 28 Mar '20

28 Mar '20

Okay, I was able to get the _Haskell Platform_ approach to work, by doing the following: - Uninstall Haskell Platform. - Reinstall Haskell Platform, overriding the default suggested installation path with something _not containing spaces_. - Change my `~\AppData\Roaming\cabal\config` file from this: ``` extra-prog-path: C:\HaskellPlatform\8.6.5\msys\usr\bin, C:\Users\capnf\AppData\Roaming\cabal\bin ``` to this: ``` extra-prog-path: C:\HaskellPlatform\8.6.5\msys\usr\bin extra-prog-path: C:\Users\capnf\AppData\Roaming\cabal\bin ``` -db

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Why does the Haskell Platform Windows installer suggest a path with spaces?!
by David Banas 28 Mar '20

28 Mar '20

Why does the Haskell Platform Windows installer suggest a default installation path that contains spaces?! This breaks builds: configure:2365: checking build system type configure:2379: result: x86_64-pc-msys configure:2399: checking host system type configure:2412: result: x86_64-pc-msys configure:2487: checking for gcc configure:2514: result: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe configure:2743: checking for C compiler version configure:2752: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe --version >&5 C:\/Users/capnf/Documents/GitHub/gitit/network-3.1.1.1/configure: line 2754: C:\PROGRA~1\Haskell: No such file or directory configure:2763: $? = 127 configure:2752: C:\PROGRA~1\Haskell Platform\8.6.5\lib\../mingw/bin\gcc.exe -v >&5 C:\/Users/capnf/Documents/GitHub/gitit/network-3.1.1.1/configure: line 2754: C:\PROGRA~1\Haskell: No such file or directory -db

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Which option causes 'cabal install' to leave temp. build dirs. in place?
by David Banas 28 Mar '20

28 Mar '20

Hi all, Which option to a 'cabal install' command will cause the temporary build directories to be left in place, so that I can inspect, for instance, the 'config.log' file of a failed dependency build? Thanks, -db

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ANN: latex-svg
by Oleg Grenrus 27 Mar '20

27 Mar '20

I occasionally write blog posts with some math. So far I have been using latex-formulae family of packages. This week Andres Löh asked whether LaTeX can be rendered as SVGs. The answer turns out to be yes, it wasn't few years ago. The preview CTAN package, and the dvisvgm tool make it very easy. I forked latex-formulae into latex-svg to use above mentioned tools. There are three packages on Hackage now: - latex-svg-image: render LaTeX formulae to SVG images - latex-svg-pandoc: render LaTeX formulae in pandoc documents - latex-svg-hakyll: render LaTeX formulae in hakyll pages To mention some differences between latex-formulae and latex-svg: - latex-svg-image uses only latex and dvisvgm, ImageMagick is not required. You don't need to tweak policy.xml to allow rasterization of PostScript. (See this StackOverflow question). - latex-svg-image supports global cache (off by default), which speedups hakyll site builds. My blog builds in 20 seconds instead of three minutes with empty cache. I wouldn't worry about space usage too much, the cache contents take 15M after building my blog. which is way less than the size of site executable. - latex-svg-hakyll has initFormulaCompilerSVGPure variant, which doesn't need IO to be created. You don't need to thread renderFormulae function through. Together with global cache, the perfomance penalty is small. - One drawback is that result pages become bigger (and slower). For example a formula-heavy https://oleg.fi/gists/posts/2018-12-12-find-correct-laws.html is - 576k in size with latex-formulae - 2819k in size with latex-svg (almost 5 times larger). Rendering SVG images is also more CPU expensive. Otherwise the API and module names are the same. If you are already a user of latex-formulae you can easily migrate to latex-svg. See the announcement blog post how some examples look like: https://oleg.fi/gists/posts/2020-03-06-latex-svg.html <http://oleg.fi/gists/posts/2020-03-06-latex-svg.html> <http://oleg.fi/gists/posts/2020-03-06-latex-svg.html> Crisp math-blogging to everyone - Oleg Grenrus <http://oleg.fi/gists/posts/2020-03-06-latex-svg.html>

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2nd Workshop on Formal Methods for Blockchains (FMBC) 2020 - First Call
by Bruno Bernardo 26 Mar '20

26 Mar '20

[ Please distribute, apologies for multiple postings. ] ======================================================================== 2nd Workshop on Formal Methods for Blockchains (FMBC) 2020 - First Call https://fmbc.gitlab.io/2020 July 19, 2020, Los Angeles, USA Co-located with the 32nd International Conference on Computer-Aided Verification (CAV 2020) http://i-cav.org/2020/ ------------------------------------------------------------- IMPORTANT DATES -------------------------------- Abstract submission: April 21, 2020 Full paper submission: April 28, 2020 Notification: June 9, 2020 Camera-ready: July 7, 2020 Conference: July 19, 2020 -------------------------------- -------------------------------- TOPICS OF INTEREST -------------------------------- Blockchains are decentralized transactional ledgers that rely on cryptographic hash functions for guaranteeing the integrity of the stored data. Participants on the network reach agreement on what valid transactions are through consensus algorithms. Blockchains may also provide support for Smart Contracts. Smart Contracts are scripts of an ad-hoc programming language that are stored in the Blockchain and that run on the network. They can interact with the ledger’s data and update its state. These scripts can express the logic of possibly complex contracts between users of the Blockchain. Thus, Smart Contracts can facilitate the economic activity of Blockchain participants. With the emergence and increasing popularity of cryptocurrencies such as Bitcoin and Ethereum, it is now of utmost importance to have strong guarantees of the behavior of Blockchain software. These guarantees can be brought by using Formal Methods. Indeed, Blockchain software encompasses many topics of computer science where using Formal Methods techniques and tools are relevant: consensus algorithms to ensure the liveness and the security of the data on the chain, programming languages specifically designed to write Smart Contracts, cryptographic protocols, such as zero-knowledge proofs, used to ensure privacy, etc. This 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 -------------------------------- -------------------------------- SUBMISSION -------------------------------- Submit original manuscripts (not published or considered elsewhere) with a maximum of twelve pages (full papers), six pages (short papers), and two pages (extended abstract) describing new and emerging ideas or summarizing existing work). Each paper should include a title and the name and affiliation of each author. Authors of selected extended-abstracts are invited to give a short lightning talk. At least one author of an accepted paper is expected to present the paper at the workshop as a registered participant. Submission link: https://easychair.org/conferences/?conf=fmbc2020 -------------------------------- -------------------------------- PROCEEDINGS -------------------------------- All submissions will be peer-reviewed by at least three members of the program committee for quality and relevance. Accepted regular papers (full and short papers) will be included in the workshop proceedings. -------------------------------- -------------------------------- INVITED SPEAKER -------------------------------- Grigore Rosu, Professor at University of Illinois at Urbana-Champaign, USA and Founder of Runtime Verification http://fsl.cs.illinois.edu/index.php/Grigore_Rosu https://runtimeverification.com/ -------------------------------- -------------------------------- PROGRAM COMMITTEE -------------------------------- PC CO-CHAIRS * Bruno Bernardo (Nomadic Labs, France) (bruno(a)nomadic-labs.com) * Diego Marmsoler (University of Exeter, UK) (D.Marmsoler(a)exeter.ac.uk) PC MEMBERS * Wolfgang Ahrendt (Chalmers University of Technology, Sweden) * Lacramioara Astefanoei (Nomadic Labs, France) * Massimo Bartoletti (University of Cagliari, Italy) * Bernhard Beckert (Karlsruhe Institute of Technology, Germany) * Achim Brucker (University of Exeter, UK) * Silvia Crafa (Universita di Padova, Italy) * Zaynah Dargaye (Nomadic Labs, France) * Jérémie Decouchant (University of Luxembourg, Luxembourg) * Ansgar Fehnker (University of Twente, Netherlands) * Georges Gonthier (Inria, France) * Florian Kammueller (Middlesex University London, UK) * Maurice Herlihy (Brown University, USA) * Igor Konnov (Informal, Austria) * Andreas Lochbihler (Digital Asset, Switzerland) * Anastasia Mavridou (NASA Ames, USA) * Simão Melo de Sousa (Universidade da Beira Interior, Portugal) * Karl Palmskog (KTH, Sweden) * Vincent Rahli (University of Birmingham, UK) * Andreas Rossberg (Dfinity Foundation, Germany) * Claudio Russo (Dfinity Foundation, USA) * César Sanchez (Imdea, Spain) * Clara Schneidewind (TU Wien, Austria) * Ilya Sergey (Yale-NUS College/NUS, Singapore) * Bas Spitters (Aarhus University/Concordium, Denmark) * Mark Staples (CSIRO Data61, Australia) * Meng Sun (Peking University, China) * Simon Thompson (University of Kent, UK) * Philip Wadler (University of Edinburgh / IOHK, UK) (Note: Additional PC members may be added in the coming weeks.)

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GSoC 2020
by Guillem Bartrina Moreno 25 Mar '20

25 Mar '20

Hello everybody! My name is Guillem and I'm a 3rd year computer science student from Spain. This semester I'm taking Functional Programming, where we use Haskell as base language, and Compilers courses. I really love Haskell and the functional programming paradigm in general, so when I saw it in the GSoC list I got really excited. The idea that caught my attention, that is related to both Haskell and Compilers, is: - Update stylish-haskell to use ghc-lib-parser I have a medium understanding of Haskell and I would like to know if this idea is suitable for me. I've tried to start reading the source code and I have understood the most part. I will proceed to write my proposal in the next few days if all goes well. All thoughts are welcome! Thanks for your attention, -- Guillem Bartrina Moreno

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Munich Virtual Haskell Meeting, 2020-03-25 @ 19:30
by Leah Neukirchen 23 Mar '20

23 Mar '20

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Wednesday, March 25. **Due to curfew 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 Wednesday. 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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Strange error when cabal installing.
by David Banas 23 Mar '20

23 Mar '20

After installing the *Haskell Platform* on my Windows 10 machine, I attempted to cabal install something and got: cabal.exe: The package has a './configure' script. If you are on Windows, This requires a Unix compatibility toolchain such as MinGW+MSYS or Cygwin. If you are not on Windows, ensure that an 'sh' command is discoverable in your path. I've confirmed that the following line is in my cabal config file: extra-prog-path: C:\Program Files\Haskell Platform\8.6.5\msys\usr\bin, C:\Users\capnf\AppData\Roaming\cabal\bin and that there *is* a *sh.exe* file in the "C:\Program Files\Haskell Platform\8.6.5\msys\usr\bin" directory. What am I missing? Thanks, -db

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Multiple Research Positions (3 Doctoral, 5 Post-doctoral) on AI Verification
by Ekaterina Komendantskaya 21 Mar '20

21 Mar '20

AI Secure and Explainable by Construction: Multiple Research Positions (3 Doctoral, 5 Post-doctoral) available at Heriot-Watt, Edinburgh and Strathclyde Universities, Scotland, UK. Start date: 1 September 2020; End date: 30 August 2023 Postdoctoral Salary Scale: £31,866 to £40,322 per annum PhD funding: covering PhD fees and stipend for 3.5 years Closing date for Postdoctoral applications: 1 June 2020 We encourage interested applicants to contact us informally ASAP. The project has sufficient flexibility to mitigate the effect of COVID-19, i.e. by accommodating later start date and remote working. The project spans several subjects: type theory, automated and interactive theorem proving, security, AI and machine learning, autonomous systems, natural language processing and generation, legal aspects of AI. It will cover two main application areas: autonomous cars and chatbots, drawing from expertise and infrastructure provided by industrial partners working in these two areas. The project has a significant international span, with 12 partners from Academia and Industry in Europe (France, Germany, Israel, the Netherlands, Norway) and the US. Researchers joining this project will have excellent opportunities to travel to international conferences, organise scientific events, spend time with industrial partners, collaborate with academic leaders in the field, develop their own research profiles as well as gain experience in other AI and CS disciplines. For further information, and instructions how to apply, please visit: http://laiv.uk/index.php/vacancies/ Ekaterina Komendantskaya: http://www.macs.hw.ac.uk/~ek19/ Robert Atkey: https://bentnib.org/ David Aspinall: https://homepages.inf.ed.ac.uk/da/ Burkard Schafer: https://www.law.ed.ac.uk/people/professor-burkhard-schafer Verena Rieser: https://sites.google.com/site/verenateresarieser/

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2 PhD Positions in the Safety and Security of Advanced Systems Group (University of Exeter, UK Deadline 2020-05-01)
by Achim D. Brucker 21 Mar '20

21 Mar '20

Two fully funded PhD scholarships for EU/UK applicants are available in the Security and Trust of Advanced Systems Group [1] (Prof. Achim Brucker [2] and Dr. Diego Marmsoler [3]) at the Department of Computer Science of the University of Exeter, UK [4]. We are looking for enthusiastic and outstanding Computer Science or Mathematics students with a strong background in some of the following topics: - safety or security of (software) systems, - formal modelling or formal reasoning/verification, - program analysis or program verification, - language-based security - semantics of programming languages, - theorem proving, model checking, - cryptographic protocols, - distributed systems (e.g., blockchain), - specification-based testing, and - design and implementation of security architectures. This award provides annual funding to cover UK/EU tuition fees and a tax-free stipend. For students who pay UK/EU tuition fees the award will cover the tuition fees in full, plus at least £15,009 per year tax-free stipend. The studentship will be awarded on the basis of merit for 3.5 years of full-time study. For more details, please consult the official advertisement: http://www.exeter.ac.uk/studying/funding/award/?id=3887 The closing date for applications is midnight on 1 May 2020. Project-specific queries should be directed to the supervisors, Prof Achim Brucker (A.Brucker(a)exeter.ac.uk) or Dr Diego Marmsoler (D.Marmsoler(a)exeter.ac.uk) Best, Achim and Diego [1] http://emps.exeter.ac.uk/computer-science/research/cyber-security/ [2] https://www.brucker.uk/ [3] https://marmsoler.com/ [4] http://emps.exeter.ac.uk/computer-science/ -- Prof. Achim Brucker | https://www.brucker.ch | https://logicalhacking.com/blog *We are hiring:* * Lecturer (Assistant Professor) - Deadline 2020-04-08: https://www.jobs.ac.uk/job/BZH668/lecturer-in-computer-science-education-an… * Two PhD Studentships (EU/UK Tuition Fees) - Deadline 2020-05-01: http://www.exeter.ac.uk/studying/funding/award/?id=3887

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Open Position: Lecturer in Computer Science (Exeter, Deadline 2020-04-08)
by Achim D. Brucker 21 Mar '20

21 Mar '20

Open Position: Lecturer in Computer Science (Exeter, Deadline 2020-04-08) As part of the expansion of the Department of Computer Science at the University of Exeter [1], we are recruiting for a Lecturer in Cybersecurity. The lecturer will be part of the newly formed Security and Trust of Advanced Systems Group [2]. We are looking for a candidate with an outstanding research record in any area related to cyber security (information security) such as (but not limited to): - access control - usable security - software/application security - formal methods for security - language-based security/privacy - secure programming - information flow - security protocols - network security - security of distributes systems - human aspects of security - hardware security - security economics - security-by-design - applied cryptography - privacy-enhancing technologies - threat hunting, security analytics - threat modelling - forensics, reverse engineering - trustworthy AI/ML - security/penetration testing You will have a PhD or equivalent in Cybersecurity, Computer Science, Mathematics, Engineering or a related area. Please refer to the job description for full details. We understand **security and safety entangled concepts**: in most modern systems one cannot be achieved without the other. Hence, we encourage also candidates working in related domains such as **safety, dependability, resilience, or reliability** to apply. Please apply by 8th of April 2020! See the full announcement and application details at https://jobs.exeter.ac.uk/hrpr_webrecruitment/wrd/run/ETREC107GF.open?VACAN… We are happy to do online/remote interviews. Feel free to contact me for informal inquiries about the post. Best, Achim [1] https://www.exeter.ac.uk/computer-science/ [2] https://emps.exeter.ac.uk/computer-science/research/cyber-security/ -- Prof. Achim Brucker | https://www.brucker.ch | https://logicalhacking.com/blog *We are hiring:* * Lecturer (Assistant Professor) - Deadline 2020-04-08: https://www.jobs.ac.uk/job/BZH668/lecturer-in-computer-science-education-an… * Two PhD Studentships (EU/UK Tuition Fees) - Deadline 2020-05-01: http://www.exeter.ac.uk/studying/funding/award/?id=3887

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Help with async library and killing child processes
by Michael Hull 20 Mar '20

20 Mar '20

Hi, I am currently learning Haskell, and really enjoying it, thankyou to the community for this well considered language. I have started using the async library, and I can't quite figure out some of the documentation, and I wonder if someone could help. https://hackage.haskell.org/package/async-2.2.2/docs/Control-Concurrent-Asy… Makes the comment that: "This is a useful variant of async <https://hackage.haskell.org/package/async-2.2.2/docs/Control-Concurrent-Asy…> that ensures an Async is never left running unintentionally." However, I can't see how I would use this. To make the example more concrete, I have a function that looks like this: runNodeHwBridgeUdp :: NodeHwInterface -> NodeHwUdpConfig-> IO() runNodeHwBridgeUdp (NodeHwInterface l0up l0down) config = do putStrLn "Starting Node bridge" -- Launch all the subprocesses: t0 <- async $ (runMsgUpReader hwBridgeSharedData l0up) t1 <- async $ (evalStateT (runUDPWriter hwBridgeSharedData) (initialUdpDispatchData timeUs) ) t2 <- async $ (runUDPReader hwBridgeSharedData l0down) putStrLn "Created child processes. Waiting...." (a, is_exception) <- waitAnyCatchCancel [t0, t1, t2] case is_exception of Right _ -> do error "SHOULD NOT GET HERE" Left exception -> do case (fromException exception) of Just (ex :: HwDestroyException) -> do putStrLn $ "BRIDGE ENDING: >>>> GOOD: SHUTDOWN: " ++ show exception Nothing -> do throwIO exception return () This process launches 3 child processes, and then waits on them. I launch this function as an async-process, and it would be really helpful if when I "cancel"ed it, it would also also cancelled the children, but I don't understand how I would structure that... t0 <- withAsync $ (runMsgUpReader hwBridgeSharedData l0up) $ \async -> do ???? t1 <- withAsync $ (evalStateT (runUDPWriter hwBridgeSharedData) (initialUdpDispatchData timeUs) ) $ \async -> do ???? t2 <- async $ (runUDPReader hwBridgeSharedData l0down) $ \async -> do ???? I feel like I must be missing something here. I'd appreciate any input; many thanks for your time, Mike

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Re: [Haskell-cafe] Adding Content-Addressable Storage to GHC
by Michal J Gajda 19 Mar '20

19 Mar '20

Great idea! We already have syntax for package imports: ``` import "bytestring" Data.ByteString ``` Source plugin could probably pull and build package by CAS: ``` import "CAS_6ffeacff768590" Data.ByteString ``` That would reuse existing syntax without confusion. And without inconvenience of having to import expressions one by one. Or declaring their types. One could even add CAS hashes to Hackage db. Probably the source plugin can add `-package` parameters with GHC_OPTIONS? On the expression side, it seems easy to use Generics to derive hashable for `Exp`, given a *particular compiler version*. Warning is, that one needs to be more careful when the `Exp`ression type changes. -- Cheers Michal

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Adding Content-Addressable Storage to GHC
by Chris Done 19 Mar '20

19 Mar '20

Hi all, Is there any effort or designs ongoing to add CAS (content-addressable storage) to GHC, as in Unison? < https://www.unisonweb.org/docs/tour/> == The idea == The summary of the idea is simply that top-level declarations can be addressed by a hash of their contents. Recursive definitions are transformed into the worker/wrapper to eliminate the self-referencing issue of hashing. == Why I want this == There are lots of advantages to this, but the one that excites me the most is that we can move to running tests, especially property tests, at compile-time. The main downside to running tests at compile-time, as seen done with template-haskell is that you will re-run tests every time the module is recompiled, making your dev cycle slower. However, if your tests are keyed upon CAS hashes, then those hashes are only invalidated when individual declarations actually change. This means the re-running of tests becomes granular at the declaration-level. When a single test completes, either successfully or not, you can cache the result and lookup the result next time, using e.g. the SHA512 of the expression evaluated. Therefore you could change a single function in a library and it would only re-run the tests that are actually affected, rather than running all the tests in the whole module, and rather than the more typical approach which is running ALL tests in a test suite just because one thing changed. If you can couple tests with code then you can avoid the decoupling of code from the tests. == Implementation approaches == There are various ways to implement this with varying degrees of satisfaction: 1. Use TH: reify declarations, inspect the AST, and produce a SHA512. Use ambient values such as the GHC version, instances in scope, extensions, ghc options, etc. With TH, I'm confident that you can only achieve an imperfect hash because I doubt that all information is available to TH. Names that come from external packages could be treated as CAS'd at the scope of the package's installed hash. Ideally, you could have granularity into other packages. But it's not a necessity if you just want caching for your current development package. 2. Use a source plugin. A source plugin is already capable of accessing all GHC context information, so this might lead to more of a perfect hash. 3. Add it to GHC directly. Exposing a `expressionSHA512 :: Exp -> ByteString` could be one imaginary way to access this information. With such a function you could implement caching of fine-grained tests. A related discussion is the deterministic builds: https://gitlab.haskell.org/ghc/ghc/wikis/deterministic-builds Anyone else exploring this? Cheers, Chris

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 199, Issue 15
by Michal J Gajda 18 Mar '20

18 Mar '20

Great idea! We already have syntax for package imports: ``` import "bytestring" Data.ByteString ``` Source plugin could probably pull and build package by CAS: ``` import "CAS_6ffeacff768590" Data.ByteString ``` That would reuse existing syntax without confusion. And without inconvenience of having to import expressions one by one. Or declaring their types. One could even add CAS hashes to Hackage db. Wonder if source plugin can add `-package` parameters? On Wed, Mar 18, 2020, 13:01 <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. Re: Help with async library and killing child processes (YueCompl) > 2. Adding Content-Addressable Storage to GHC (Chris Done) > > > > ---------- Forwarded message ---------- > From: YueCompl <compl.yue(a)icloud.com> > To: Branimir Maksimovic <branimir.maksimovic(a)gmail.com> > Cc: haskell-cafe(a)haskell.org > Bcc: > Date: Wed, 18 Mar 2020 18:42:56 +0800 > Subject: Re: [Haskell-cafe] Help with async library and killing child > processes > Um, event processing applications by procedural programmers (part data > analyst personnels for some) is a thing in my org, so I'm baking an DSL > doing it. > > On 2020-03-18, at 18:18, Branimir Maksimovic < > branimir.maksimovic(a)gmail.com> wrote: > > That's just library, not built into language. You can do it with forkIO as > I do it per specifics > > of application. > > Greets, > Branimir. > On 3/18/20 11:06 AM, YueCompl wrote: > > No, not to cancel a thread, but the business task on that thread's way > ahead. That's what Go's Context is designed for. > > > - About Go context from: https://blog.golang.org/context > > At Google, we require that Go programmers pass a Context parameter as the > first argument to every function on the call path between incoming and > outgoing requests. This allows Go code developed by many different teams to > interoperate well. It provides simple control over timeouts and cancelation > and ensures that critical values like security credentials transit Go > programs properly. > Server frameworks that want to build on Context should provide > implementations of Context to bridge between their packages and those that > expect a Context parameter. Their client libraries would then accept a > Context from the calling code. By establishing a common interface for > request-scoped data and cancelation, Context makes it easier for package > developers to share code for creating scalable services. > > I (and seems Windows api too) strongly agree that cancelling a thread is > problematic: > > > https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-pro… > > TerminateThread is a dangerous function that should only be used in the > most extreme cases. You should call TerminateThread only if you know > exactly what the target thread is doing, and you control all of the code > that the target thread could possibly be running at the time of the > termination. For example, TerminateThread can result in the following > problems: > > - If the target thread owns a critical section, the critical section > will not be released. > - If the target thread is allocating memory from the heap, the heap > lock will not be released. > - If the target thread is executing certain kernel32 calls when it is > terminated, the kernel32 state for the thread's process could be > inconsistent. > - If the target thread is manipulating the global state of a shared > DLL, the state of the DLL could be destroyed, affecting other users of the > DLL. > > > On 2020-03-18, at 17:16, Branimir Maksimovic < > branimir.maksimovic(a)gmail.com> wrote: > > I'm pretty sure you can't cancel goroutine. Actually I have > > very bad experience with thread cancelation. Therefore flags > > passed via channels/mvars or shared flags are used to stop > > threads. > > Greets, > Branimir. > On 3/18/20 10:10 AM, YueCompl wrote: > > Idiomatic resource leakage prevention in short. > > An app wants to be as responsive to its users as practically feasible, it > would try multiple paths to load-balanced resources, and use the first > response that come back, then cancel other paths. Cancellation can help > reducing vain computation in such architectures, sometimes largely enough. > > On 2020-03-18, at 16:58, Branimir Maksimovic < > branimir.maksimovic(a)gmail.com> wrote: > > What's wrong with forkIO? > > Greets, > Branimir. > On 3/18/20 9:37 AM, YueCompl via Haskell-Cafe wrote: > > If not for tight loops or other CPU intensive tasks, you may be interested > in Edh, which introduces Go's goroutine to GHC runtime. But Edh threads add > much higher overhead on top of GHC threads, so there's a price to pay for > simplicity of end programmer's job. > > It's briefly described at > https://github.com/e-wrks/edh/tree/master/Tour#program--threading-model . > This is very new and I'm right now actively working on it for PoC of an STM > powered in-memory graph database implementation. > > Best regards, > Compl > > On 2020-03-18, at 11:15, Niklas Hambüchen <mail(a)nh2.me> wrote: > > I've you're new to async, also check out my recent rework of the docs that > talk about this topic specifically: > > https://github.com/simonmar/async/pull/105/files > > (To be available in the next release of async.) > _______________________________________________ > 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. > > > > _______________________________________________ > 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. > > _______________________________________________ > 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. > > > > > > > > ---------- Forwarded message ---------- > From: Chris Done <haskell-cafe(a)chrisdone.com> > To: haskell-cafe(a)haskell.org > Cc: > Bcc: > Date: Wed, 18 Mar 2020 11:21:29 +0000 > Subject: [Haskell-cafe] Adding Content-Addressable Storage to GHC > Hi all, > > Is there any effort or designs ongoing to add CAS (content-addressable > storage) to GHC, as in Unison? < > https://www.unisonweb.org/docs/tour/> > > == The idea == > > The summary of the idea is simply that top-level declarations can be > addressed by a hash of their contents. Recursive definitions are > transformed into the worker/wrapper to eliminate the self-referencing issue > of hashing. > > == Why I want this == > > There are lots of advantages to this, but the one that excites me the most > is that we can move to running tests, especially property tests, at > compile-time. > > The main downside to running tests at compile-time, as seen done with > template-haskell is that you will re-run tests every time the module is > recompiled, making your dev cycle slower. However, if your tests are keyed > upon CAS hashes, then those hashes are only invalidated when individual > declarations actually change. This means the re-running of tests becomes > granular at the declaration-level. When a single test completes, either > successfully or not, you can cache the result and lookup the result next > time, using e.g. the SHA512 of the expression evaluated. > > Therefore you could change a single function in a library and it would > only re-run the tests that are actually affected, rather than running all > the tests in the whole module, and rather than the more typical approach > which is running ALL tests in a test suite just because one thing changed. > > If you can couple tests with code then you can avoid the decoupling of > code from the tests. > > == Implementation approaches == > > There are various ways to implement this with varying degrees of > satisfaction: > > 1. Use TH: reify declarations, inspect the AST, and produce a SHA512. Use > ambient values such as the GHC version, instances in scope, extensions, ghc > options, etc. With TH, I'm confident that you can only achieve an imperfect > hash because I doubt that all information is available to TH. > > Names that come from external packages could be treated as CAS'd at the > scope of the package's installed hash. Ideally, you could have granularity > into other packages. But it's not a necessity if you just want caching for > your current development package. > > 2. Use a source plugin. A source plugin is already capable of accessing > all GHC context information, so this might lead to more of a perfect hash. > > 3. Add it to GHC directly. Exposing a `expressionSHA512 :: Exp -> > ByteString` could be one imaginary way to access this information. With > such a function you could implement caching of fine-grained tests. > > A related discussion is the deterministic builds: > https://gitlab.haskell.org/ghc/ghc/wikis/deterministic-builds > > Anyone else exploring this? > > Cheers, > > Chris > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >

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[HiW'20] Call for Talks
by Ben Gamari 16 Mar '20

16 Mar '20

Hello everyone, Haskell Implementors Workshop is calling for talk proposals. Co-located with ICFP, HiW is an ideal place to describe a Haskell library, a Haskell extension, compiler, works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. The deadline for submissions is July 2nd 2020. Call for Talks ============== The 12th Haskell Implementors’ Workshop is to be held alongside ICFP 2020 this year in New Jersey. 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 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 2020. 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, optimization 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 can be made via HotCRP at https://icfp-hiw20.hotcrp.com/ until July 2nd (anywhere on earth). 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 --------- We recognize the on-going threat that COVID-19 poses to our participants' safety. While August is nearly half a year away, we must account for the possibility that the virus continues to pose a significant threat into the summer. For this reason, we are investigating options that would allow remote presentations this year. In light of this, we urge potential presenters not to be discouraged from submitting and encourage participants to keep time open in their calendars, regardless of the on-going COVID situation. Rest assured that the conference organizers are working to ensure that the Implementors Workshop can be held safely and productively, regardless of how the COVID-19 situation evolves. Program Committee ----------------- - Andrey Mokhov (Newcastle University) - Ben Gamari (Well-Typed LLP) - Christian Baaij (QBayLogic) - George Karachalias (Tweag I/O) - Klara Marntirosian (KU Leuven) - Matthew Pickering (Univeristy of Bristol) - Ryan Scott (Indiana University Bloomington) Best wishes, Ben

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Re: [Haskell-cafe] Data.Map - visiting tree nodes withi a given key range ?
by Olaf Klinke 16 Mar '20

16 Mar '20

You can roll your own indexKeyRange using the Data.Map.Internal module which exposes the (currently used) Map implementation. Also note that if the list of values in range is to be consumed immediately, you might want to go for a fold-based function: foldlWithRange :: (a -> k -> b -> a) -> (a,a) -> b -> Map k a -> b Olaf

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Data.Map - visiting tree nodes within a given key range ?
by Compl Yue 15 Mar '20

15 Mar '20

Hello, I have a question regarding 'Data.Map' api, filed an issue https://github.com/haskell/containers/issues/708 And may be I can ask here at the same time? I'm not sure why|Data.Map|doesn't have a key range based visiting API, I figured out I can do it this way: |indexKeyRange :: IndexKey -> IndexKey -> Map IndexKey Object -> [(IndexKey, Object)] indexKeyRange !minKey !maxKey = toList . takeWhileAntitone (<= maxKey) . dropWhileAntitone (< minKey) | But wouldn't it save the computation needed to re-balance the intermediate tree generated ? Or that re-balancing can be optimized out actually ? I am creating an in-memory graph database, using|Data.Map.Strict.Map|as business object indices with specified object attributes. The typical scenario will be querying a small number of entries by key range, out of possibly all business objects of a certain class globally, so the implementation above would work, but not reasonable by far as it seems. I think a lazy list returned by mere node visiting (i.e. no new node creation) would satisfy my needs, or I missed something ? Thanks, Compl

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Calling a State Monad recursively from within a let-block, via runState?
by David Banas 14 Mar '20

14 Mar '20

Can I call a State Monad recursively from within a let-block, via `runState`, or is that going way out of bounds? -db

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ANNOUNCE: Save the date! Compose Conference 2020 colocated with ICFP
by MightyByte 13 Mar '20

13 Mar '20

We are excited to announce that the Compose Conference will be colocated with ICFP this year. Compose will be Thursday and Friday August 20 and 21 at the NJCU School of Business, a short subway / bus ride from Manhattan. The Compose Unconference will be Saturday and Sunday August 22 and 23 at Microsoft in Times Square. Regarding COVID-19, the Compose Team is closely monitoring the situation and are prepared to make responsible decisions if it comes to that. That being said, the situation will undoubtedly evolve a lot between now and August. We have been very excited about the collaboration between Compose and ICFP and wanted to get an announcement out so that if the conferences do happen as planned everyone is aware. A more detailed announcement will be coming when we have more confirmed details, but if you are already planning to attend ICFP, consider extending your trip by a few days and coming to Compose as well. To get a sense of Compose, you can check out the great talks from past conferences and the Compose Conference website: https://www.youtube.com/channel/UC0pEknZxL7Q1j0Ok8qImWdQ http://www.composeconference.org/ We look forward to seeing you! The Compose Conference Team Sent via Superhuman ( https://sprh.mn/?vip=mightybyte@gmail.com )

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Using GHC option '-optl-static' causes segfault
by Nutr1t07 11 Mar '20

11 Mar '20

Hi, I added '-optl-static' in GHC option to make my program compiled statically. When I compiled the following code using 'stack build': -- Main.hs {-# LANGUAGE OverloadedStrings #-} module Main where import Web.Scotty as Scotty import Network.Wreq as Wreq import Control.Monad.IO.Class main :: IO () main = scotty 8443 $ do Scotty.get (literal "/") $ do _ <- liftIO $ Wreq.get "https://www.google.com/" html "Could not see this" -- Ran the compiled program and accessing "http://localhost:8443" would raise a segmentation fault. Here are what in my 'ghc-option': ghc-options: - -optl-static - -threaded - -rtsopts - -with-rtsopts=-N Then I removed the '-optl-static', compiled it, and the program ran well. It seems that it something has to do with glibc. What can I do with this problem? Regards PS. I'm using GHC 8.8.2, stack 2.1.3

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[ANN] ghc-tag-plugin
by Marcin Szamotulski 09 Mar '20

09 Mar '20

Hi, I wrote a GHC plugin which writes tags files. I've been proof testing it on a large code base where parts of it is using various type extensions, or formats (literate haskell, haskell, hsc files) - it works very well. Here's a blog post about it: https://coot.me/posts/ghc-tags-plugin.html And here's a very fresh hackage version 0.1.3.0: https://hackage.haskell.org/package/ghc-tags-plugin Best regards, Marcin Szamotulski

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WST 2020 - 2nd Call for Papers
by Samir Genaim 05 Mar '20

05 Mar '20

========================================================================== WST 2020 - Call for Papers 17th International Workshop on Termination http://costa.fdi.ucm.es/wst2020 June 29-30, 2020, Paris, France co-located with IJCAR and FSCD 2020. ========================================================================== The Workshop on Termination (WST) traditionally brings together, in an informal setting, researchers interested in all aspects of termination, whether this interest be practical or theoretical, primary or derived. The workshop also provides a ground for cross-fertilization of ideas from the different communities interested in termination (e.g., working on computational mechanisms, programming languages, software engineering, constraint solving, etc.). The friendly atmosphere enables fruitful exchanges leading to joint research and subsequent publications. The workshop is part of "Paris Nord Summer of LoVe 2020", a joint event on LOgic and VErification at Université Paris 13, made of Petri Nets 2020, IJCAR 2020, FSCD 2020, and over 20 satellite events. https://lipn.univ-paris13.fr/summer-of-love-2020/ IMPORTANT DATES: * submission deadline: April 12, 2020 * notification: May 10, 2020 * final version due: May 31, 2020 * workshop: June 29-30, 2020 TOPICS: The 17th International Workshop on Termination welcomes contributions on all aspects of termination. In particular, papers investigating applications of termination (for example in complexity analysis, program analysis and transformation, theorem proving, program correctness, modeling computational systems, etc.) are very welcome. Topics of interest include (but are not limited to): * abstraction methods in termination analysis * certification of termination and complexity proofs * challenging termination problems * comparison and classification of termination methods * complexity analysis in any domain * implementation of termination methods * non-termination analysis and loop detection * normalization and infinitary normalization * operational termination of logic-based systems * ordinal notation and subrecursive hierarchies * SAT, SMT, and constraint solving for (non-)termination analysis * scalability and modularity of termination methods * termination analysis in any domain (lambda calculus, declarative programming, rewriting, transition systems, etc.) * well-founded relations and well-quasi-orders COMPETITION: Since 2003, the catalytic effect of WST to stimulate new research on termination has been enhanced by the celebration of the Termination Competition and its continuously developing problem databases containing thousands of programs as challenges for termination analysis in different categories, see http://termination-portal.org/wiki/Termination_Competition In 2020, the Termination Competition will run shortly before WST and the main venues (IJCAR-FSCD), and the results will be presented at IJCAR or FSCD. PROGRAM COMMITTEE: Martin Avanzini - INRIA Sophia, Antipolis Florian Frohn - Max-Planck-Institut für Informatik, Saarbrücken Carsten Fuhs - Birkbeck, U. of London Samir Genaim (chair) - U. Complutense de Madrid Jürgen Giesl - RWTH Aachen Matthias Heizmann - U. of Freiburg Cynthia Kop - Radboud U. Nijmegen Salvador Lucas - U. Politècnica de València Étienne Payet - U. de La Réunion Albert Rubio - U. Complutense de Madrid René Thiemann - U. of Innsbruck Johannes Waldmann - HTWK Leipzig INVITED SPEAKERS: tba SUBMISSION: Submissions are short papers/extended abstracts which should not exceed 5 pages. There will be no formal reviewing. In particular, we welcome short versions of recently published articles and papers submitted elsewhere. The program committee checks relevance and provides additional feedback for each submission. The accepted papers will be made available electronically before the workshop. Papers should be submitted electronically via the submission page: https://easychair.org/conferences/?conf=wst2020 Please, use LaTeX and the LIPIcs style file http://drops.dagstuhl.de/styles/lipics/lipics-authors.tgz to prepare your submission.

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LF: senior Haskeller to be GSoC mentor
by Jason Chau 03 Mar '20

03 Mar '20

Hi, I am looking for a someone who has a lot of Haskell, OS, networking, and databases experience and knowledge to be a mentor for Google Summer of Code. I need advise on best practises. The project URL is https://github.com/jasonsychau/graphql-w-persistent. Jason Sent from my iPhone

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lib for drawing with mouse
by mechvel＠scico.botik.ru 03 Mar '20

03 Mar '20

Please, does there exist a tool (library) in Haskell that supports doing the following with graphics? (1) To draw a curve by mouse on a screen and save this picture in a file (many different curves to be input this way). (2) To save in data.txt the coordinates of the points of this curve, say, 800 pairs of numbers (floating point or rational ...). (3) Reversely: to draw a curve on a screen by inputting from such data.txt. The main is (1)&(2). Because currently I set a curve by putting many times the '*' character and `space' to a text file, and this takes long. Thanks, ------ Sergei

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