January 2020 - Haskell-Cafe

stack: pandoc fails to build as dependency
by Olaf Klinke 06 Aug '20

06 Aug '20

Dear cafe, I am baffled to learn that stack does not provide builds as reproducible as advertised. I have a project that depends on pandoc. It builds fine on my Debian 9 machine. Then I check out the project on a Debian 8 machine. Downloading and building pandoc-2.7.3 with the latest stack-2.1.3 on the Debian 8 machine runs fine. Now I create a new project, using the same stack.yaml as in the pandoc-2.7.3 package, except now pandoc-2.7.3 is an extra-dep. The project's only module contains nothing but: module Test where import Text.Pandoc Building this project with the same stack results in a linker error: pandoc > Preprocessing executable 'pandoc' for pandoc-2.7.3.. pandoc > Building executable 'pandoc' for pandoc-2.7.3.. pandoc > [1 of 2] Compiling Main pandoc > [2 of 2] Compiling Paths_pandoc pandoc > Linking .stack-work/dist/x86_64-linux/Cabal-2.4.0.1/build/pandoc/pandoc ... pandoc > collect2: error: ld returned 1 exit status pandoc > `gcc' failed in phase `Linker'. (Exit code: 1) This seems to be independent of the LTS version (the stack.yaml in pandoc-2.7.3 says lts-13.17 although lts-13.17 contains pandoc-2.5 and pandoc-2.7.3 is available only in 14.9). Can somebody hint what I am doing wrong? Should I file a bug report? Thanks Olaf

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[ANNOUNCE] GHC 8.8.2 is now available
by Ben Gamari 25 Feb '20

25 Feb '20

Hello everyone, The GHC team is proud to announce the release of GHC 8.8.2. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.8.2 Release notes are also available [1]. This release fixes a handful of issues affecting 8.8.1: - A bug (#17088) in the compacting garbage collector resulting in segmentations faults under specific circumstances. Note that this may affect user programs even if they did not explicitly request the compacting GC (using the -c RTS flag) since GHC may fallback to compacting collection during times of high memory pressure. - A code generation bug (#17334) resulting in GHC panics has been fixed. - A bug in the `process` library causing builds using `hsc2hs` to fail non-deterministically on Windows has been fixed (Trac #17480) - A typechecker bug (#12088) resulting in programs being unexpectedly rejected has been fixed. - A bug in the implementation of compact normal forms resulting in segmentation faults in some uses (#17044) has been fixed. - A bug causing GHC to incorrectly complain about incompatible LLVM versions when using LLVM 7.0.1 has been fixed (#16990). As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] https://downloads.haskell.org/ghc/8.8.2/docs/html/users_guide/8.8.2-notes.h…

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Haskell positions available at Luminous Computing.
by David Banas 01 Feb '20

01 Feb '20

Hi all, I have 3 Haskell openings on my team at Luminous Computing, Inc. https://www.luminouscomputing.com/ <https://www.luminouscomputing.com/> We are using Haskell to build our tools (chip design, architecture explorer, and customer design compiler). And I’m looking for a different individual to own each tool. Of course, in a start-up flexibility is key, but that’s the official notion of how things would be arranged. Please, take a brief look at our web site. And, if you think you might be interested, let me know, so we can chat and explore a potential fit. Thanks, David Banas Chief Architect Luminous Computing, Inc.

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Call for Papers: PACMPL issue ICFP 2020
by Sam Tobin-Hochstadt 30 Jan '20

30 Jan '20

PACMPL Volume 4, Issue ICFP 2020 Call for Papers accepted papers to be invited for presentation at The 25th ACM SIGPLAN International Conference on Functional Programming Jersey City, USA http://icfp20.sigplan.org/ ### Important dates Submissions due: 3 March 2020 (Tuesday) Anywhere on Earth https://icfp20.hotcrp.com Author response: 21 April (Tuesday) - 24 Apri (Friday) 14:00 UTC Notification: 8 May (Friday) Final copy due: 1 July (Wednesday) Conference: 18 August (Sunday) - 23 August (Friday) ### About PACMPL Proceedings of the ACM on Programming Languages (PACMPL <https://pacmpl.acm.org/>) is a Gold Open Access journal publishing research on all aspects of programming languages, from design to implementation and from mathematical formalisms to empirical studies. Each issue of the journal is devoted to a particular subject area within programming languages and will be announced through publicized Calls for Papers, like this one. ### Scope [PACMPL](https://pacmpl.acm.org/) issue ICFP 2020 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Topics of interest include (but are not limited to): * Language Design: concurrency, parallelism, and distribution; modules; components and composition; metaprogramming; macros; pattern matching; type systems; type inference; dependent types; session types; gradual typing; refinement types; interoperability; domain-specific languages; imperative programming; object-oriented programming; logic programming; probabilistic programming; reactive programming; generic programming; bidirectional programming. * Implementation: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimization; garbage collection and memory management; runtime systems; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources. * Software-Development Techniques: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling; build systems; program synthesis. * Foundations: formal semantics; lambda calculus; program equivalence; rewriting; type theory; logic; category theory; monads; continuations; control; state; effects; names and binding; program verification. * Analysis and Transformation: control flow; data flow; abstract interpretation; partial evaluation; program calculation. * Applications: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; graphics and multimedia; GPU programming; scripting; system administration; security. * Education: teaching introductory programming; parallel programming; mathematical proof; algebra. Submissions will be evaluated according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. PACMPL issue ICFP 2020 also welcomes submissions in two separate categories — Functional Pearls and Experience Reports — that must be marked as such when submitted and that need not report original research results. Detailed guidelines on both categories are given at the end of this call. Please contact the principal editor if you have questions or are concerned about the appropriateness of a topic. ### Preparation of submissions **Deadline**: The deadline for submissions is **Tuesday, March 3, 2020**, Anywhere on Earth (<https://en.wikipedia.org/wiki/Anywhere_on_Earth>). This deadline will be strictly enforced. **Formatting**: Submissions must be in PDF format, printable in black and white on US Letter sized paper, and interpretable by common PDF tools. All submissions must adhere to the "ACM Small" template that is available (in both LaTeX and Word formats) from <https://www.acm.org/publications/authors/submissions>. For authors using LaTeX, a lighter-weight package, including only the essential files, is available from <http://sigplan.org/Resources/Author/#acmart-format>. There is a limit of **25 pages for a full paper or Functional Pearl** and **12 pages for an Experience Report**; in either case, the bibliography will not be counted against these limits. Submissions that exceed the page limits or, for other reasons, do not meet the requirements for formatting, will be summarily rejected. Supplementary material can and should be **separately** submitted (see below). See also PACMPL's Information and Guidelines for Authors at <https://pacmpl.acm.org/authors.cfm>. **Submission**: Submissions will be accepted at <https://icfp20.hotcrp.com/> Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. **Author Response Period**: Authors will have a 72-hour period, starting at 14:00 UTC on **Tuesday, April 21, 2020**, to read reviews and respond to them. **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). **Authorship Policies**: All submissions are expected to comply with the ACM Policies for Authorship that are detailed at <https://www.acm.org/publications/authors/information-for-authors>. **Republication Policies**: Each submission must adhere to SIGPLAN's republication policy, as explained on the web at <http://www.sigplan.org/Resources/Policies/Republication>. ### Review Process This section outlines the two-stage process with lightweight double-blind reviewing that will be used to select papers for PACMPL issue ICFP 2020. We anticipate that there will be a need to clarify and expand on this process, and we will maintain a list of frequently asked questions and answers on the conference website to address common concerns. **PACMPL issue ICFP 2020 will employ a two-stage review process.** The first stage in the review process will assess submitted papers using the criteria stated above and will allow for feedback and input on initial reviews through the author response period mentioned previously. At the review meeting, a set of papers will be conditionally accepted and all other papers will be rejected. Authors will be notified of these decisions on **May 8, 2020**. Authors of conditionally accepted papers will be provided with committee reviews (just as in previous conferences) along with a set of mandatory revisions. After four weeks (June 5, 2020), the authors will provide a second submission. The second and final reviewing phase assesses whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. The intent and expectation is that the mandatory revisions can be addressed within four weeks and hence that conditionally accepted papers will in general be accepted in the second phase. The second submission should clearly identify how the mandatory revisions were addressed. To that end, the second submission must be accompanied by a cover letter mapping each mandatory revision request to specific parts of the paper. The cover letter will facilitate a quick second review, allowing for confirmation of final acceptance within two weeks. Conversely, the absence of a cover letter will be grounds for the paper’s rejection. **PACMPL issue ICFP 2020 will employ 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 judgement 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. ### Information for Authors of Accepted Papers * As a condition of acceptance, final versions of all papers must adhere to the new ACM Small format. The page limit for the final versions of papers will be increased by two pages to help authors respond to reviewer comments and mandatory revisions: **27 pages plus bibliography for a regular paper or Functional Pearl, 14 pages plus bibliography for an Experience Report**. * Authors of accepted submissions will be required to agree to one of the three ACM licensing options: open access on payment of a fee (**recommended**, and SIGPLAN can cover the cost as described next); copyright transfer to ACM; or retaining copyright but granting ACM exclusive publication rights. Further information about ACM author rights is available from <http://authors.acm.org>. * PACMPL is a Gold Open Access journal. It will be archived in ACM’s Digital Library, but no membership or fee is required for access. Gold Open Access has been made possible by generous funding through ACM SIGPLAN, which will cover all open access costs in the event authors cannot. Authors who can cover the costs may do so by paying an Article Processing Charge (APC). PACMPL, SIGPLAN, and ACM Headquarters are committed to exploring routes to making Gold Open Access publication both affordable and sustainable. * ACM offers authors a range of copyright options, one of which is Creative Commons CC-BY publication; this is the option recommended by the PACMPL editorial board. A reasoned argument in favour of this option can be found in the article [Why CC-BY?](https://oaspa.org/why-cc-by/) published by OASPA, the Open Access Scholarly Publishers Association. * We intend that the papers will be freely available for download from the ACM Digital Library in perpetuity via the OpenTOC mechanism. * ACM Author-Izer is a unique service that enables ACM authors to generate and post links on either their home page or institutional repository for visitors to download the definitive version of their articles from the ACM Digital Library at no charge. Downloads through Author-Izer links are captured in official ACM statistics, improving the accuracy of usage and impact measurements. Consistently linking to the definitive version of an ACM article should reduce user confusion over article versioning. After an article has been published and assigned to the appropriate ACM Author Profile pages, authors should visit <http://www.acm.org/publications/acm-author-izer-service> to learn how to create links for free downloads from the ACM DL. * The official publication date is the date the papers 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. * At least one author of each accepted submission will be expected to attend and present that paper at the conference. The schedule for presentations will be determined and shared with authors after the full program has been selected. Presentations will be videotaped and released online if the presenter consents. In extraordinary circumstances, at the discretion of the principal editor, alternative presentation methods may be approved for specific papers. The canonical example is where all authors are denied visas to the ICFP host country, in which case a nonauthor may be deputized to present, or various electronic substitutes may be considered. We list these options in the interest of transparency, but please keep in mind that, most years, no exceptions are granted. This option is not meant, e.g., to excuse cases where authors find themselves double-booked with other meetings (so, at the time of submitting a paper, please do keep the days of the conference reserved on at least one author’s calendar). ### Artifact Evaluation Authors of papers that are conditionally accepted in the first phase of the review process will be encouraged (but not required) to submit supporting materials for Artifact Evaluation. These items will then be reviewed by an Artifact Evaluation Committee, separate from the paper Review Committee, whose task is to assess how the artifacts support the work described in the associated paper. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Authors of accepted papers will be encouraged to make the supporting materials publicly available upon publication of the papers, for example, by including them as "source materials" in the ACM Digital Library. An additional seal will mark papers whose artifacts are made available, as outlined in the ACM guidelines for artifact badging. Participation in Artifact Evaluation is voluntary and will not influence the final decision regarding paper acceptance. ### Special categories of papers In addition to research papers, PACMPL issue ICFP solicits two kinds of papers that do not require original research contributions: Functional Pearls, which are full papers, and Experience Reports, which are limited to half the length of a full paper. Authors submitting such papers should consider the following guidelines. #### Functional Pearls A Functional Pearl is an elegant essay about something related to functional programming. Examples include, but are not limited to: * a new and thought-provoking way of looking at an old idea * an instructive example of program calculation or proof * a nifty presentation of an old or new data structure * an interesting application of functional programming techniques * a novel use or exposition of functional programming in the classroom While pearls often demonstrate an idea through the development of a short program, there is no requirement or expectation that they do so. Thus, they encompass the notions of theoretical and educational pearls. Functional Pearls are valued as highly and judged as rigorously as ordinary papers, but using somewhat different criteria. In particular, a pearl is not required to report original research, but, it should be concise, instructive, and entertaining. A pearl is likely to be rejected if its readers get bored, if the material gets too complicated, if too much specialized knowledge is needed, or if the writing is inelegant. The key to writing a good pearl is polishing. A submission that is intended to be treated as a pearl must be marked as such on the submission web page, and should contain the words "Functional Pearl" somewhere in its title or subtitle. These steps will alert reviewers to use the appropriate evaluation criteria. Pearls will be combined with ordinary papers, however, for the purpose of computing the conference's acceptance rate. #### Experience Reports The purpose of an Experience Report is to help create a body of published, refereed, citable evidence that functional programming really works -- or to describe what obstacles prevent it from working. Possible topics for an Experience Report include, but are not limited to: * insights gained from real-world projects using functional programming * comparison of functional programming with conventional programming in the context of an industrial project or a university curriculum * project-management, business, or legal issues encountered when using functional programming in a real-world project * curricular issues encountered when using functional programming in education * real-world constraints that created special challenges for an implementation of a functional language or for functional programming in general An Experience Report is distinguished from a normal PACMPL issue ICFP paper by its title, by its length, and by the criteria used to evaluate it. * Both in the papers and in any citations, the title of each accepted Experience Report must end with the words "(Experience Report)" in parentheses. The acceptance rate for Experience Reports will be computed and reported separately from the rate for ordinary papers. * Experience Report submissions can be at most 12 pages long, excluding bibliography. * Each accepted Experience Report will be presented at the conference, but depending on the number of Experience Reports and regular papers accepted, authors of Experience reports may be asked to give shorter talks. * Because the purpose of Experience Reports is to enable our community to accumulate a body of evidence about the efficacy of functional programming, an acceptable Experience Report need not add to the body of knowledge of the functional-programming community by presenting novel results or conclusions. It is sufficient if the Report states a clear thesis and provides supporting evidence. The thesis must be relevant to ICFP, but it need not be novel. The review committee will accept or reject Experience Reports based on whether they judge the evidence to be convincing. Anecdotal evidence will be acceptable provided it is well argued and the author explains what efforts were made to gather as much evidence as possible. Typically, more convincing evidence is obtained from papers which show how functional programming was used than from papers which only say that functional programming was used. The most convincing evidence often includes comparisons of situations before and after the introduction or discontinuation of functional programming. Evidence drawn from a single person's experience may be sufficient, but more weight will be given to evidence drawn from the experience of groups of people. An Experience Report should be short and to the point: it should make a claim about how well functional programming worked on a particular project and why, and produce evidence to substantiate this claim. If functional programming worked in this case in the same ways it has worked for others, the paper need only summarize the results — the main part of the paper should discuss how well it worked and in what context. Most readers will not want to know all the details of the project and its implementation, but the paper should characterize the project and its context well enough so that readers can judge to what degree this experience is relevant to their own projects. The paper should take care to highlight any unusual aspects of the project. Specifics about the project are more valuable than generalities about functional programming; for example, it is more valuable to say that the team delivered its software a month ahead of schedule than it is to say that functional programming made the team more productive. If the paper not only describes experience but also presents new technical results, or if the experience refutes cherished beliefs of the functional-programming community, it may be better to submit it as a full paper, which will be judged by the usual criteria of novelty, originality, and relevance. The principal editor will be happy to advise on any concerns about which category to submit to. ### ICFP Organizers General Chair: Stephanie Weirich (University of Pennsylvania, USA) Artifact Evaluation Co-Chairs: Ben Lippmeier (UNSW, Australia) Brent Yorgey (Hendrix College, USA) Industrial Relations Chair: Alan Jeffrey (Mozilla Research, USA) Programming Contest Organiser: Igor Lukanin (Kontur, Russia) Publicity and Web Chair: Sam Tobin-Hochstadt (Indiana University, USA) Student Research Competition Chair: Youyou Cong (Tokyo Institute of Technology, Japan) Workshops Co-Chair: Leonidas Lampropoulos (University of Maryland, USA) Jennifer Hackett (University of Nottingham, UK) Conference Manager: Annabel Satin (P.C.K.) ### PACMPL Volume 4, Issue ICFP 2020 Principal Editor: Adam Chlipala (MIT, USA) Review Committee: Andreas Abel (Gothenburg University, Sweden) Nada Amin (Harvard University, USA) Edwin Brady (University of St. Andrews, UK) William E. Byrd (University of Alabama at Birmingham, USA) David Darais (University of Vermont) Richard A. Eisenberg (Bryn Mawr College, USA) Matthew Fluet (Rochester Institute of Technology, USA) Makoto Hamana (Gunma University, Japan) Fritz Henglein (Department of Computer Science, University of Copenhagen (DIKU) and Deon Digital, Denmark) Jan Hoffmann (Carnegie Mellon University, USA) Robbert Krebbers (Delft University of Technology, Netherlands) Neel Krishnaswami (Computer Laboratory, University of Cambridge, UK) Geoffrey Mainland (Drexel University, USA) Magnus O. Myreen (Chalmers University of Technology, Sweden) Atsushi Ohori (Tohoku University, Japan) Frank Piessens (KU Leuven, Belgium) Nadia Polikarpova (University of California San Diego, USA) Jonathan Protzenko (Microsoft Research, USA) Jerome Simeon (Clause, France) KC Sivaramakrishnan (IIT Madras, India) External Review Committee: Danel Ahman (University of Ljubljana, Slovenia) Aws Albarghouthi (University of Wisconsin-Madison, USA) Kenichi Asai (Ochanomizu University, Japan) Patrick Bahr (IT University of Copenhagen, Denmark) Stephanie Balzer (Carnegie Mellon University, USA) Jean-Philippe Bernardy (University of Gothenburg, Sweden) Sandrine Blazy (Univ Rennes-IRISA, France) Benjamin Canou (OCamlPro, France) Giuseppe Castagna (CNRS - Université de Paris, France) Jesper Cockx (TU Delft, Netherlands) Youyou Cong (Tokyo Institute of Technology, Japan) Leonardo De Moura (Microsoft Research, USA) Sebastian Erdweg (JGU Mainz, Germany) Ronald Garcia (University of British Columbia, Canada) Jennifer Hackett (University of Nottingham, UK) Troels Henriksen (University of Copenhagen, Denmark) Gabriele Keller (Utrecht University, Netherlands) Delia Kesner (IRIF, France / University of Paris Diderot, France) Shriram Krishnamurthi (Brown University, United States) Jan Midtgaard (University of Southern Denmark, Denmark) Andrey Mokhov (Jane Street, USA) J. Garrett Morris (University of Kansas, USA) Stefan Muller (Carnegie Mellon University, USA) Rasmus Ejlers Møgelberg (IT University of Copenhagen, Denmark) Cyrus Omar (University of Chicago, USA) Dominic Orchard (University of Kent, UK) Ivan Perez (NIA / NASA Formal Methods) Brigitte Pientka (McGill University, Canada) Juan Pedro Bolívar Puente (Independent Consultant, Sinusoidal Engineering) Norman Ramsey (Tufts University, USA) Christine Rizkallah (UNSW Sydney, Australia) Tiark Rompf (Purdue University, USA) Guido Salvaneschi (Technische Universität Darmstadt, Germany) Tom Schrijvers (KU Leuven, Belgium) Chung-chieh Shan (Indiana University, USA) Vincent St-Amour (Northwestern University, USA) Aaron Stump (The University of Iowa, USA) Nicolas Tabareau (Inria, France) Ross Tate (Cornell University, USA) Dimitrios Vytiniotis (DeepMind, UK) John Wiegley (DFINITY, USA) Beta Ziliani (FAMAF, UNC and CONICET, Argentina)

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Do new versions of GHC work on older versions of macOS?
by Troels Henriksen 30 Jan '20

30 Jan '20

When new versions of GHC come out, I suppose they work on the newest macOS. But what is the oldest macOS they will support? Is there a policy in place? If not, do they tend to work in practice? I am particularly concerned with the binary distributions. -- \ Troels /\ Henriksen

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Domain modeling
by Jean Lopes 30 Jan '20

30 Jan '20

Hi! I'm trying to encode a domain which is full of simple records, and a lot of field name clashes. Here is a simple example, a.k.a. 1:1 with the domain-spec: data C001 { > -- other stuff > indMov :: Bool > } > data C170 { > -- other stuff > indMov :: Bool > } There is ~148 records with this field (indMov), all with the same meaning. What are my options to encode this in Haskell? - Prefix all record fields to avoid name clashes? - Use *DuplicateRecordFields*? - Typeclasses??? - other options I am not aware of? which would you prefer? and why of course :) Thanks, Jean Lopes

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Compilers written in Haskell?
by David Banas 28 Jan '20

28 Jan '20

Can anyone provide a list of compilers written in Haskell? Sent from my iPhone

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Need help using a typeclass within an existing API
by Debasish Ghosh 27 Jan '20

27 Jan '20

Hi - (Apologies for the long post) I need some help integrating a typeclass based functionality within an existing API. I am using Control.Monad.Validate for my validation of objects. Here's a simple function based on this .. debit :: forall m. (MonadReader Env m, MonadValidate [Error] m) => Y.Dense "USD" -> Account -> m Account debit amount = updateBalance ((-1) * amount) Now I want to make a change in the API where I would like to fetch the account from some database based on account number. For this I have a typeclass as below .. class (Monad m) => AccountDB m where query :: Text -> m (Maybe Account) .. elided details and I am using persistent - so I have an instance of this class as follows .. -- | Instance of AccountDB for `SqlPersistT` (which is `ReaderT SqlBackend`) instance (MonadIO m) => AccountDB (SqlPersistT m) where query ano = get (AccountKey ano) .. other details elided My question is how can I integrate this typeclass within the above API ? I tried as yet another constraint in the function .. debit :: forall m. (MonadReader Env m, MonadValidate [Error] m, AccountDB m) => Y.Dense "USD" -> Text -> m Account debit amount accNo = do maybeAccount <- query accNo maybe (refuteErr $ InvalidAccountNumber accNo) (updateBalance ((-1) * amount)) maybeAccount This compiles but I don't get the proper instance of the typeclass when I run it - possibly due to the reason that the "m" cannot be the same for AccountDB as the other constraints. And I don't want to hardcode SqlPersistT in the function debit as I would like to be able to run it with other instances of the typeclass as well (example for testing I may like to test against a HashMap). What would be an idiomatic approach to this kind of composition ? Any help will be appreciated. regards. -- Debasish Ghosh http://manning.com/ghosh2 http://manning.com/ghosh Twttr: @debasishg Blog: http://debasishg.blogspot.com Code: http://github.com/debasishg

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Issues requesting permission to publish packages
by Victor Adossi 27 Jan '20

27 Jan '20

Hi Haskell-Cafe, I recently tried to upload a package to hackage and sent an email to hackage-trustees(a)haskell.org to request to be added to the uploaders group. Unfortunately my email was undelivered due to an SPF Failure -- here's what the error emailed to me looks like: > <one-of-the-maintainers(a)personal-email.com> (expanded from > <hackage-trustees(a)haskell.org>): host > host.personal-email.com[xxx.xxx.xxx.xxx] said: 550 5.7.23 > <one-of-the-maintainers(a)personal-email.com>: Recipient address > rejected: Message rejected due to: > SPF fail - not authorized. Please see > http://www.openspf.net/Why?s=mfrom;id=vados@vadosware.io;ip=<IP of > haskell.org server>;r=<UNKNOWN> > (in reply to RCPT TO command) It looks like the SPF settings on my domain forbid the bounce off of hackage-trustees to the individual trustee that was picked. Two points: - This seems like an unintended leaking of information (I have one of the emails of the trustees, via the error message) - How else can I request the ability to become a package uploader? Thanks, Victor

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Munich Haskell Meeting, 2020-01-27 @ 19:30
by Leah Neukirchen 26 Jan '20

26 Jan '20

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, January 27 at Augustiner-Gaststätte Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jan-2020/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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