- Haskell-Cafe - Haskell.org

ANN: LeanCheck v0.9.0 -- enumerative property testing
by Rudy Matela 18 Jan '19

18 Jan '19

Hello Haskell Café, A new version of LeanCheck is out (v0.9.0). LeanCheck is a property testing library (like QuickCheck) that tests values enumeratively. _Example._ Here's a simple example of LeanCheck in action showing that sorting is idempotent and list union is not commutative: > import Test.LeanCheck > import Data.List (sort, union) > check $ \xs -> sort (sort xs) == sort (xs::[Int]) +++ OK, passed 200 tests. > check $ \xs ys -> xs `union` ys == ys `union` (xs::[Int]) *** Failed! Falsifiable (after 4 tests): [] [0,0] LeanCheck works on all types that are instances of the Listable typeclass and is able to derive instances automatically using either Template Haskell or GHC.Generics. See [LeanCheck's Haddock documentation] for more details. _Whats new?_ Version 0.9.0 marks the addition of Listable typeclass instances for most standard Haskell types defined in the Haskell 2010 Language Report. This means you'll be able to test more functions without needing to define Listable instances yourself. [LeanCheck's changelog] provides more details. A separate package [leancheck-instances] provides instances for other types in the Haskell Platform. _Installing._ You can find LeanCheck on [Hackage] or [GitHub]. It is also tracked on [Stackage]. As usual, you can install it with: $ cabal install leancheck -- Rudy [Hackage]: https://hackage.haskell.org/package/leancheck [GitHub]: https://github.com/rudymatela/leancheck [Stackage]: https://www.stackage.org/package/leancheck [LeanCheck's changelog]: https://hackage.haskell.org/package/leancheck/changelog [LeanCheck's Haddock documentation]: https://hackage.haskell.org/package/leancheck/docs/Test-LeanCheck.html

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determine a type by universal property
by Olaf Klinke 17 Jan '19

17 Jan '19

Dear cafe, We know how to derive free theorems from a type [1]. But there exist also examples where the existence of a certain function determines the type. I suppose this is a special case of a free theorem? For example, every functor that is right adjoint to another functor in Hask is representable in the sense of [2], that is, isomorphic to (r->) for some type r. [see * below] I have two type signatures where I conjecture the only functors satisfying these are the Identity functor and functors of the form (,)s. Can anyone give hints as how to tackle a proof? Signature 1: What functors t admit a function forall f. Functor f => t (f a) -> f (t a) Signature 2: What functors t admit a function t (t a -> b) -> a -> b Signature 1 is like Data.Traversable.sequence, only the Applicative constraint is weakened to Functor. It is somewhat dual to Distributive [3]. Signature 2 can, with some currying, for t = (,)s be transformed into Data.Function.flip. I am unable to comprehend the free theorem for signature 2. For signature 1, the Rank-2 type seems to cause trouble with free-theorems? Thanks, Olaf [1] https://hackage.haskell.org/package/free-theorems [2] https://hackage.haskell.org/package/adjunctions [3] https://hackage.haskell.org/package/distributive [*] The argument goes like this: (1) bottoms aside, every type x is isomorphic to () -> x. (2) f and g are adjoint if and only if (f a -> b) is isomorphic to (a -> g b). (3) g b is isomorphic to () -> g b by (1) with x = g b (4) () -> g b is isomorphic to f () -> b by (2) with a = (). (5) By (3) and (4), g b is isomorphic to f () -> b. We have found g = (r->) with r = f ().

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Taking over maintainership of bitvec
by Andrew Lelechenko 17 Jan '19

17 Jan '19

I would like to take over `bitvec` package (https://hackage.haskell.org/package/bitvec) Unfortunately, the source code has not been updated for years and the test suite does not build nowadays. There are also known issues. I have prepared patches and tried to reach its maintainer James Cook (cced) by email, but have not heard back. There was a takeover of another James' package in October 2018 (https://mail.haskell.org/pipermail/libraries/2018-October/029062.html) In that case James appeared to be out of reach. -- Best regards, Andrew

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HDBC database: error on accent table name
by Damien Mattei 16 Jan '19

16 Jan '19

Hi, i have this error: *** Exception: SqlError {seState = "", seNativeError = 1064, seErrorMsg = "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'es where Nom = 'A 20'' at line 1"} when doing this : rows_coordonnees <- quickQuery' conn "select * from sidonie.Coordonnées where Nom = 'A 20'" [] it seems tha the tabel name: Coordonnées that contain an accent is causing serious problem to the parser at some point, if i use a table name without accent it works fine. i'm at the point to rename the table which have great impact on all the project build with many other languages (Scheme) that deal correctly the table name with accent. any idea? to make accent works with haskell. Regards, Damien -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

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[Job] Soostone is hiring Haskell developers (NYC or remote)
by Ozgun Ataman 16 Jan '19

16 Jan '19

Dear Haskell Cafe, Soostone (http://www.soostone.com) is looking to hire for engineering positions in our Haskell development and operations team. At Soostone, you will be crafting and deploying products with various AI and optimization elements dealing with large quantities of data at their core to transform the way our clients tackle opportunities in consumer intelligence, marketing and pricing. We aim to develop high quality, reliable software while moving fast, being pragmatic and constantly improving our capabilities. Haskell usually makes this a little easier and we're big fans. We are located in New York City, but these are remote-friendly positions with little to no travel requirements. We will prefer candidates in North America, but will also consider qualified applications from elsewhere as long as the legal realities can be aligned. We are flexible in the work arrangement; depending on your jurisdiction and circumstances, these will either be direct hire or full-time contractor positions. Day-to-day, you will be interacting with technologies/components/libraries such as: - A relatively large Haskell codebase (500+ modules) spanning multiple applications and several reusable in-house libraries/packages - 200+ libraries from the Haskell ecosystem - Databases: PostgreSQL, Redis, DynamoDB - Analytics: Google BigQuery, tailor-made SQL EDSL/automation - A large suite of AWS and Google cloud solutions - APIs responding to millions of requests per day - Datasets spanning billions of rows …and typical activities will include: - Collaborative architecting and software design around new features - End-to-end implementation of entire components, from first line of code to the test suite - Interfacing with other languages, API services, foreign interfaces/functions as needed - Opportunities to work on all aspects of our platform, including both backend and frontend - Design/implementation of DSLs/EDSLs that supercharge tedious elements in the ecosystem - Abstract functionality into libraries and other reusable tools that ease the pain for other developers - Be on the lookout for opportunities to contribute back to the community through OSS work - Occasional trips to the land of Python, Typescript/JavaScript and Purescript for mission-specific needs Candidates of all skill/experience levels are invited to apply and will receive consideration, although these positions are likely not ideal for Haskell beginners or entry level developers without any experience. If you're interested, we encourage you to submit an application even if we've previously had conversations. If you have OSS contributions or a listing/linking of previous projects, please let us know as that's tremendously helpful to us in getting to know you. Please see the link below for more detail on the position and to submit an application. You can also reach out to us at jobs(a)soostone.com for any questions or ask here and we'll do our best to answer. Job Link: https://soostone-inc.workable.com/jobs/678589 The Soostone Team

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looking for yesod-newsfeed example
by Johannes Waldmann 16 Jan '19

16 Jan '19

Dear Cafe, I want to add news feeds to a yesod application. Is there some example code that shows real-life usage of https://hackage.haskell.org/package/yesod-newsfeed ? Thanks - J.W.

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How to set ghc options while building Setup.hs in cabal package?
by Magicloud Magiclouds 16 Jan '19

16 Jan '19

Hi, I have some code in Setup.hs in a cabalized project. I'd like them to be warning-free. But I could not find a way to set -Wall. I tried ghc-options in ~/.cabal/config. But seems like it did not kick in. ``` /bin/ghc --make -fbuilding-cabal-package -odir /home/shida/src/Personal/cairo-core/dist-newstyle/build/x86_64-linux/ghc-8.6.3/cairo-core-1.16.0/setup -hidir /home/shida/src/Personal/cairo-core/dist-newstyle/build/x86_64-linux/ghc-8.6.3/cairo-core-1.16.0/setup -i -i/home/shida/src/Personal/cairo-core/. -optP-include -optP/home/shida/src/Personal/cairo-core/dist-newstyle/build/x86_64-linux/ghc-8.6.3/cairo-core-1.16.0/setup/setup_macros.h -hide-all-packages -no-user-package-db -package-db /home/shida/.cabal/store/ghc-8.6.3/package.db -package-db /home/shida/src/Personal/cairo-core/dist-newstyle/packagedb/ghc-8.6.3 -package-id Cabal-2.4.0.1 -package-id base-4.12.0.0 -package-id directory-1.3.3.0 -package-id filepath-1.4.2.1 -package-id haskell-src-exts-1.21.0-f3e84a9ee8883b0dcaaaaba712d74996854b441aa843a4dedc055c685debcfdb /home/shida/src/Personal/cairo-core/dist-newstyle/build/x86_64-linux/ghc-8.6.3/cairo-core-1.16.0/setup/setup.hs -o /home/shida/src/Personal/cairo-core/dist-newstyle/build/x86_64-linux/ghc-8.6.3/cairo-core-1.16.0/setup/setup -threaded ``` -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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intero flymake not working
by Dennis Raddle 16 Jan '19

16 Jan '19

I recently updated a stack project to a later version of GHC, and Intero isn't quite behaving the same as before. I can't see any evidence that flycheck or flymake is working. Any idea what to look for? Mike

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PPDP 2019 CFP - Principles and Practice of Declarative Programming
by František Farka 15 Jan '19

15 Jan '19

[Apologies for cross-posting; please circulate] ====================================================================== CALL FOR PAPERS -- PPDP 2019 21st International Symposium on Principles and Practice of Declarative Programming 7–9 October 2019, Porto, Portugal Collocated with FM'19 http://ppdp2019.macs.hw.ac.uk ====================================================================== Important Dates --------------- Title and abstract registration 26 April 2019 (AoE) Paper submission 3 May 2019 (AoE) Rebuttal period (48 hours) 3 June 2019 (AoE) Author notification 14 June 2019 Final paper version 15 July 2019 Conference 7–9 October 2019 About PPDP ---------- The PPDP 2019 symposium brings together researchers from the declarative programming communities, including those working in the functional, logic, answer-set, and constraint handling programming paradigms. The goal is to stimulate research in the use of logical formalisms and methods for analyzing, performing, specifying, and reasoning about computations, including mechanisms for concurrency, security, static analysis, and verification. Scope ----- Submissions are invited on all topics related to declarative programming, from principles to practice, from foundations to applications. Topics of interest include, but are not limited to - Language Design: domain-specific languages; interoperability; concurrency, parallelism, and distribution; modules; probabilistic languages; reactive languages; database languages; knowledge representation languages; languages with objects; language extensions for tabulation; metaprogramming. - Implementations: abstract machines; interpreters; compilation; compile-time and run-time optimization; memory management. - Foundations: types; logical frameworks; monads and effects; semantics. - Analysis and Transformation: partial evaluation; abstract interpretation; control flow; data flow; information flow; termination analysis; resource analysis; type inference and type checking; verification; validation; debugging; testing. - Tools and Applications: programming and proof environments; verification tools; case studies in proof assistants or interactive theorem provers; certification; novel applications of declarative programming inside and outside of CS; declarative programming pearls; practical experience reports and industrial application; education. The PC chair (Ekaterina Komendanstkaya <e.komendantskaya(a)hw.ac.uk>) will be happy to advise on the appropriateness of a topic. Submission Categories --------------------- Submissions can be made in three categories: regular Research Papers, System Descriptions, and Experience Reports. Submissions of Research Papers must present original research which is unpublished and not submitted elsewhere. They must not exceed 12 pages ACM style 2-column (including figures, but excluding bibliography). Work that already appeared in unpublished or informally published workshop proceedings may be submitted (please contact the PC chair in case of questions). Research papers will be judged on originality, significance, correctness, clarity, and readability. Submission of System Descriptions must describe a working system whose description has not been published or submitted elsewhere. They must not exceed 10 pages and should contain a link to a working system. System Descriptions must be marked as such at the time of submission and will be judged on originality, significance, usefulness, clarity, and readability. Submissions of Experience Reports are meant to help create a body of published, refereed, citable evidence where declarative programming such as functional, logic, answer-set, constraint programming, etc., is used in practice. They must not exceed 5 pages **including references**. Experience Reports must be marked as such at the time of submission and need not report original research results. They will be judged on significance, usefulness, clarity, and readability. Supplementary material may be provided in a clearly marked appendix beyond the above-mentioned page limits. Reviewers are not required to study any material beyond the respective page limit. Format of a Submission ---------------------- For each paper category, you must use the most recent version of the "Current ACM Master Template" which is available at <https://www.acm.org/publications/proceedings-template>. The most recent version at the time of writing is 1.48. You must use the LaTeX sigconf proceedings template as the conference organizers are unable to process final submissions in other formats. In case of problems with the templates, contact ACM's TeX support team at Aptara <acmtexsupport(a)aptaracorp.com>. Authors should note ACM's statement on author's rights (http://authors.acm.org/) which apply to final papers. Submitted papers should meet the requirements of ACM's plagiarism policy (http://www.acm.org/publications/policies/plagiarism_policy) Requirements for Publication ---------------------------- At least one author of each accepted submission will be expected to attend and present the work at the conference. The pc chair may retract a paper that is not presented. The pc chair may also retract a paper if complaints about the paper's correctness are raised which cannot be resolved by the final paper deadline. Program Committee Chair ----------------------- Ekaterina Komendantskaya Heriot-Watt University, UK Program Committee ----------------- Henning Basold CNRS, ENS de Lyon, France Jasmin Christian Blanchette Vrije Universiteit Amsterdam, The Netherlands Maria Paola Bonacina University of Verona, Italy Dmitry Boulytchev Saint–Petersburg University, Russia William Byrd University of Alabama at Birmingham, USA Ornela Dardha University of Glasgow, UK Marco Gaboardi University at Buffalo, SUNY, USA Arie Gurfinkel University of Waterloo, Canada Zhenjiang Hu National Institute of Informatics, Japan Moa Johansson Chalmers University of Technology, Sweden Neelakantan Krishnaswami University of Cambridge, UK Ralf Lämmel University of Koblenz · Landau, Germany Anthony Widjaja Lin University of Oxford, UK Aart Middeldorp University of Innsbruck, Austria Gopalan Nadathur University of Minnesota, USA Keisuke Nakano Tohoku University, Japan Dominic Orchard University of Kent, UK Alberto Pardo University of the Republic, Uruguay Aleksy Schubert University of Warsaw, Poland Peter J. Stuckey The University of Melbourne, Australia Tarmo Uustalu Reykjavik University, Iceland Local Chair ----------- José Nuno Oliveira INESC TEC & University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. Publicity Chair --------------- František Farka University of St Andrews & Heriot-Watt University, UK

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ANN: New Haskell.org Committee Member
by George Wilson 15 Jan '19

15 Jan '19

Following the nomination period and discussion, the Haskell.org committee has selected the following member for a new three-year term, expiring 2021: * Emily Pillmore As per the rules of the committee, this discussion was held among the current members of the committee, and the outgoing member of the committee who was not seeking reappointment. Thank you to all the many candidates who submitted a self-nomination. We received a number of strong nominations. We would encourage all those who nominated themselves to consider self-nominating again in the future. The outgoing member is Gershom Bazerman. He served not one but two terms for the Haskell.org committee, and he was chair during his last term. During this long period, Gershom has undeniably made the community a better place with his leadership and efforts. Thank you for your service! Since Gershom was our chair, the committee, including the new member, will hold a discussion and elect a new chair from amongst ourselves. Regards, George Wilson

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