- Haskell-Cafe - Haskell.org

Announce: Haskell Platform 8.4.2
by Gershom B 05 May '18

05 May '18

On behalf of the Haskell Platform team, I'm happy to announce the release of Haskell Platform 8.4.2 Now available at https://www.haskell.org/platform/ This includes GHC 8.4.2, cabal-install 2.2.0.0, and stack 1.7.1, all with substantial improvements since the last platform release. A full list of contents is available at https://www.haskell.org/platform/contents.html Thanks to all the contributors to this release, thanks to all the package and tool maintainers and authors, and a big thanks to the GHC team for all their hard work. There are (still) currently no 32 bit Windows builds available. We're looking into the issues preventing us from building an installer for that platform. The components all appear to work individually in such a case, and can be installed separately by users who so desire. A list of new GHC changes is available at: https://ghc.haskell.org/trac/ghc/blog/ghc-8.4.1-released and https://ghc.haskell.org/trac/ghc/blog/ghc-8.4.2-released A list of cabal changes is available at: https://hackage.haskell.org/package/cabal-install-2.2.0.0/changelog The cabal documentation page is at: https://www.haskell.org/cabal/users-guide/ A list of stack changes is at: https://docs.haskellstack.org/en/stable/ChangeLog/#v171 The stack documentation page is at: https://docs.haskellstack.org/en/stable/README/ Happy Haskell Hacking all, Gershom

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Picking up the CI buildnumber during build
by Magnus Therning 04 May '18

04 May '18

I'm looking for a way to pick up the CI buildnumber from the environment (e.g. $TRAVIS_BUILD_NUMBER) and use it as part of of the output of `my-tool --version`. I don't really know where to start looking, so I'm hoping someone on the list has already done something similar and can point me to a working example :) /M -- Magnus Therning OpenPGP: 0x927912051716CE39 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus I am always doing that which I cannot do, in order that I may learn how to do it. — Pablo Picasso

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Strange error with GADT DataKinds -- needs TypeInType!?
by Tom Ellis 04 May '18

04 May '18

Can anyone explain why the type instance for K is fine but the one for I needs TypeInType? (It does indeed work when I turn on TypeInType.) {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} data T a b where K :: b -> T a b I :: T a a type family F (a :: T ka kb) -- Data constructor ‘I’ cannot be used here -- (Perhaps you intended to use TypeInType) -- type instance F 'I = () type instance F ('K b) = ()

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emacs heads up
by Rustom Mody 03 May '18

03 May '18

There seems to be some significant developments in emacs' haskell mode Can I understand?? The run-haskell command is now evidently deprecated What is the new alternative? Or do we just stay with run-haskell? Context: - Teaching Haskell - Using emacs - Need a nice REPL - Not (immediately) getting into in stack cabal etc; though will be needed in due course

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[ANNOUNCE] GHC 8.4.2 released
by Ben Gamari 01 May '18

01 May '18

Hello everyone, The GHC team is pleased to announce the availability of GHC 8.4.2. The source distribution, binary distributions, and documentation for this release are available at https://downloads.haskell.org/~ghc/8.4.2 This release is a bug-fix release, fixing numerous regressions and bugs present in GHC 8.4.1. These include: * A regression resulting in some uses of `Control.Exception.evaluate` to be inappropriately optimised away (see #13930) * A regression resulting in segmentation faults of programs compiled with profiling (#14705) * A bug causing runtime system panics while running programs with retainer profiling (#14947) * The configure scripts now accepts a `--disable-dtrace` option, again allowing GHC to be bootstrapped on FreeBSD (#15040) * The version number of the `base` package has been bumped to 4.11.1.0 to reflect the addition of the `GHC.IO.FixIOException` type. This interface was added in 8.4.1 but the version bump was missed due to an oversight. * Support for DWARF debug information has been significantly improved (#14894, #14779) A more thorough list of the changes in this release can be found in the release notes, https://downloads.haskell.org/~ghc/8.4.2/docs/html/users_guide/8.4.2-notes.… Thanks to everyone who has contributed to developing, documenting, and testing this release! As always, let us know if you encounter trouble. How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating efficient code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces. GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://ghc.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://ghc.haskell.org/trac/ghc/wiki/Contributors Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://ghc.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://ghc.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-tickets There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see https://mail.haskell.org/cgi-bin/mailman/listinfo Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug

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3rd CfP: IFL 2018 (30th Symposium on Implementation and Application of Functional Languages)
by Jurriaan Hage 01 May '18

01 May '18

Hello, Please, find below the third call for papers for IFL 2018. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL --- ============================================================ ==================== IFL 2018 30th Symposium on Implementation and Application of Functional Languages University of Massachusetts Lowell, MA, USA September 5th-7th, 2018 http://iflconference.org ============================================================ ==================== ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2018 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Keynote Speakers * Adam Chlipala, Massachusetts Institute of Technology CSAIL * Arjun Guha, University of Massachusetts Amherst ### Submissions and peer-review Differently from previous editions of IFL, IFL 2018 solicits two kinds of submissions: * Regular papers (12 pages including references) * Draft papers for presentations ('weak' limit between 8 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. A set of regular papers will be conditionally accepted for publication. Authors of conditionally accepted papers will be provided with committee reviews along with a set of mandatory revisions. Regular papers not accepted for publication will be considered as draft papers, at the request of the author. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. Prior to the symposium: Authors of conditionally accepted papers and accepted presentations will submit a pre-proceedings version of their work that will appear in the draft proceedings distributed at the symposium. The draft proceedings does not constitute a formal publication. We require that at least one of the authors present the work at IFL 2018. After the symposium: Authors of conditionally accepted papers will submit a revised versions of their paper for the formal post-proceedings. The program committee will assess whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. Our interest is to ultimately accept all conditionally accepted papers. If you are an author of a conditionally accepted paper, please make sure that you address all the concerns of the reviewers. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected. ### Publication The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication ### Important dates Submission of regular papers: May 25, 2018 Submission of draft papers: July 17, 2018 Regular and draft papers notification: July 20, 2018 Deadline for early registration: August 8, 2018 Submission of pre-proceedings version: August 29, 2018 IFL Symposium: September 5-7, 2018 Submission of papers for post-proceedings: November 7, 2018 Notification of acceptance: December 22, 2018 Camera-ready version: February 10, 2019 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template Authors submit through EasyChair: https://easychair.org/conferences/?conf=ifl2018 ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organization and Program committee Chairs: Jay McCarthy & Matteo Cimini, University of Massachusetts Lowell, USA Program Committee: * Arthur Chargueraud, Inria, FR * Ben Delaware, Purdue University, USA * Christos Dimoulas, Northwestern University, USA * David Darais, University of Vermont, USA * Dominic Orchard, University of Kent, UK * Ekaterina Komendantskaya, Heriot-Watt University, UK * Garrett Morris, University of Kansas, USA * Heather Miller, EPFL & Northeastern University, CH & USA * Jeremy Yallop, University of Cambridge, UK * Keiko Nakata, SAP Innovation Center Potsdam, DE * Laura Castro, University of A Coruna, ESP * Magnus Myreen, Chalmers University of Technology, SWE * Natalia Chechina, Bournemouth University, UK * Peter Achten, Radboud Universiteit Nijmegen, NL * Peter-Michael Osera, Grinnell College, USA * Richard Eisenberg, Bryn Mawr College, USA * Trevor McDonell, University of New South Wales, AUS * Yukiyoshi Kameyama, University of Tsukuba, JAP ### Venue The 30th IFL is organized by the University of Massachusetts Lowell. The City of Lowell is located at the heart of the Merrimack Valley just 30 miles northwest of Boston. Lowell can be easily reached by train or taxi. See the website for more information on the venue. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organizers for their work, which is reused here. A part of IFL 2018 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

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<<loop>> as result of SemigroupMonoid changes
by Joey Hess 30 Apr '18

30 Apr '18

I tried to follow the instructions at https://prime.haskell.org/wiki/Libraries/Proposals/SemigroupMonoid and I got a <<loop>> when my code runs with ghc 8.2.2. My code looked like this: import Data.Monoid import Prelude data InfoVal v = NoInfoVal | InfoVal v deriving (Show) instance Monoid (InfoVal v) where mempty = NoInfoVal mappend _ v@(InfoVal _) = v mappend v NoInfoVal = v Following the "recommended variant" for compatible code, I changed that too: {-# LANGUAGE CPP #-} import Data.Monoid import qualified Data.Semigroup as Sem import Prelude data InfoVal v = NoInfoVal | InfoVal v deriving (Show) instance Monoid (InfoVal v) where mempty = NoInfoVal #if !(MIN_VERSION_base(4,11,0)) mappend = (<>) #endif instance Sem.Semigroup (InfoVal v) where _ <> v@(InfoVal _) = v v <> NoInfoVal = v This loops because <> comes from Data.Monoid not from Data.Semigroup, so mappend = mappend. Note that I diverged slightly from the instructions to get to this wrong code; I imported Data.Semigroup qualified. Without the qualification, the above code fails to compile, with Ambiguous occurrence ‘<>’ So, the transition instructions don't produce code that ghc 8.2.2 can build, and when the obvious fix is made to get it to compile, it compiles into a loop, that is *not* a loop when compiled with newer versions of ghc. -- see shy jo

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final call for papers: Trends in Functional Programming, 11-13 june 2018, Chalmers Campus Johanneberg, Gothenburg - deadline extended -
by Peter Achten 30 Apr '18

30 Apr '18

------------------------------------- F I N A L C A L L F O R P A P E R S ------------------------------------- ----- deadline extended ----- ======== TFP 2018 =========== 19th Symposium on Trends in Functional Programming 11-13 June, 2018 Chalmers Campus Johanneberg, Gothenburg http://www.cse.chalmers.se/~myreen/tfp2018/index.html The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below at scope). Please be aware that TFP uses two distinct rounds of submissions (see below at submission details). TFP 2018 will be the main event of a pair of functional programming events. TFP 2018 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 14. == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: Leading-edge, previously unpublished research work Position Articles: On what new trends should or should not be Project Articles: Descriptions of recently started new projects Evaluation Articles: What lessons can be drawn from a finished project Overview Articles: Summarizing work with respect to a trendy subject. Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2018 program chairs, Michał Pałka and Magnus Myreen. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Paper Submissions == We use EasyChair for the refereeing process. The link to the submission page is: https://easychair.org/conferences/?conf=tfp2018 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Pre-symposium formal review == Papers to be formally reviewed before the symposium should be submitted before an early deadline and receive their reviews and notification of acceptance for both presentation and publication before the symposium. A paper that has been rejected in this process may still be accepted for presentation at the symposium, but will not be considered for the post-symposium formal review. == Post-symposium formal review == Draft papers will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == Draft papers and papers submitted for formal review are submitted as extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which all authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site. == Important Dates == Submission (pre-symposium review): March 26, 2018 -- passed -- Submission (draft, post-symposium review): May 11, 2018 -- extended -- Notification (pre- and post-symposium review): May 13, 2018 -- extended -- Registration: June 3, 2018 TFP Symposium: June 11-13, 2018 TFPIE Workshop: June 14, 2018 Student papers feedback: June 21, 2018 Submission (post-symposium review): August 14, 2018 Notification (post-symposium review): September 20, 2018 Camera-ready paper (pre- and post-symposium review): November 30, 2018 == Program Committee == Program Co-chairs Michał Pałka, Chalmers University of Technology (SE) Magnus Myreen, Chalmers University of Technology (SE) Program Committee Soichiro Hidaka, Hosei University (JP) Meng Wang, University of Bristol (UK) Sam Tobin-Hochstadt, Indiana University Bloomington (US) Tiark Rompf, Purdue University (US) Patricia Johann, Appalachian State University (US) Neil Sculthorpe, Nottingham Trent University (UK) Andres Löh, Well-Typed LLP (UK) Tarmo Uustalu, Tallinn University of Technology (EE) Cosmin E. Oancea, University of Copenhagen (DK) Mauro Jaskelioff, Universidad Nacional de Rosario (AR) Peter Achten, Radboud University (NL) Dimitrios Vytiniotis, Microsoft Research (UK) Alberto Pardo, Universidad de la República (UY) Natalia Chechina, University of Glasgow (UK) Peter Sestoft, IT University of Copenhagen (DK) Scott Owens, University of Kent (UK)

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 30 Apr '18

30 Apr '18

Dear all, If you or one of your students recently completed a PhD in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, open access, deadline 25th May 2018. Please share! Best wishes, Graham Hutton ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 25th May 2018 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the PhD student and PhD advisor/supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 25th May 2018. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 1000 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting in the abstract, but do get in touch if this causes significant problems) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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[ANNOUNCE] New release of SBV (v7.7), now with symbolic characters and strings
by Levent Erkok 30 Apr '18

30 Apr '18

I'm pleased to announce v7.7 release of SBV, a library integrating modern SMT solvers into Haskell. The main feature in this version is support for symbolic characters, strings, and regular-expressions; initially contributed by Joel Burget. SBV can now deal with proofs of programs that work on strings, taking advantage of modern SMT solving techniques. This is the first time SBV is venturing out of the realm of "number" like types (bit-vectors, reals, integers, floats etc.), so I am excited about the new problem domains we can now model symbolically. A symbolic string is not a mere list of symbolic characters, but rather is a type on its own. While this departure seems not in the spirit of Haskell, this change of view brings a lot of expressive/proof power. Joel contributed two simple examples to illustrate: - A regular-expression crossword solver: https://hackage.haskell.org/package/sbv-7.7/docs/Documentation-SBV-Examples… - A simple SQL-injection analyzer: https://hackage.haskell.org/package/sbv-7.7/docs/Documentation-SBV-Examples… Support for strings/regular-expressions is rather new in the SMT solving arena. Furthermore, the logic is not known to be decidable, and thus the solvers might struggle with difficult queries. Currently, only Z3 and CVC4 support this logic. If you do play with it, you're likely to find issues in both SBV itself and possibly with the underlying solver as well. Please report if you run into anything that looks fishy. In any case, implementations are solid enough that you should be able to model and reason about non-trivial string-processing programs with relative ease. - Hackage: https://hackage.haskell.org/package/sbv - Homepage: http://leventerkok.github.io/sbv/ - Release notes: https://github.com/LeventErkok/sbv/blob/master/ CHANGES.md - SMTLib initiative: http://smtlib.cs.uiowa.edu/ Thanks to Joel Burget for doing the initial work for adding support for symbolic strings. Feedback and bug reports are most welcome! Happy reasoning! -Levent.

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ANN: stack-1.7.1
by Emanuel Borsboom 29 Apr '18

29 Apr '18

See https://haskellstack.org for installation and upgrade instructions. ### Changes since v1.6.5: Release notes: * aarch64 (64-bit ARM) bindists are now available for the first time. * Statically linked Linux bindists are no longer available, due to difficulty with GHC 8.2.2 on Alpine Linux. * 32-bit Linux GMP4 bindists for CentOS 6 are no longer available, since GHC 8.2.2 is no longer being built for that platform. Major changes: * Upgrade from Cabal 2.0 to Cabal 2.2 Behavior changes: * `stack setup` no longer uses different GHC configure options on Linux distributions that use GCC with PIE enabled by default. GHC detects this itself since ghc-8.0.2, and Stack's attempted workaround for older versions caused more problems than it solved. * `stack new` no longer initializes a project if the project template contains a stack.yaml file. Other enhancements: * A new sub command `ls` has been introduced to stack to view local and remote snapshots present in the system. Use `stack ls snapshots --help` to get more details about it. * `list-dependencies` has been deprecated. The functionality has to accessed through the new `ls dependencies` interface. See [#3669](https://github.com/commercialhaskell/stack/issues/3669) for details. * Specify User-Agent HTTP request header on every HTTP request. See [#3628](https://github.com/commercialhaskell/stack/issues/3628) for details. * `stack setup` looks for GHC bindists and installations by any OS key that is compatible (rather than only checking a single one). This is relevant on Linux where different distributions may have different combinations of libtinfo 5/6, ncurses 5/6, and gmp 4/5, and will allow simpifying the setup-info metadata YAML for future GHC releases. * The build progress bar reports names of packages currently building. * `stack setup --verbose` causes verbose output of GHC configure process. See [#3716](https://github.com/commercialhaskell/stack/issues/3716) * Improve the error message when an `extra-dep` from a path or git reference can't be found See [#3808](https://github.com/commercialhaskell/stack/pull/3808) * Nix integration is now disabled on windows even if explicitly enabled, since it isn't supported. See [#3600](https://github.com/commercialhaskell/stack/issues/3600) * `stack build` now supports a new flag `--keep-tmp-files` to retain intermediate files and directories for the purpose of debugging. It is best used with ghc's equivalent flag, i.e. `stack build --keep-tmp-files --ghc-options=-keep-tmp-files`. See [#3857](https://github.com/commercialhaskell/stack/issues/3857) * Improved error messages for snapshot parse exceptions * `stack unpack` now supports a `--to /target/directory` option to specify where to unpack the package into * `stack hoogle` now supports a new flag `--server` that launches local Hoogle server on port 8080. See [#2310](https://github.com/commercialhaskell/stack/issues/2310) Bug fixes: * The script interpreter's implicit file arguments are now passed before other arguments. See [#3658](https://github.com/commercialhaskell/stack/issues/3658). In particular, this makes it possible to pass `-- +RTS ... -RTS` to specify RTS arguments used when running the script. * Don't ignore the template `year` parameter in config files, and clarify the surrounding documentation. See [#2275](https://github.com/commercialhaskell/stack/issues/2275). * Benchmarks used to be run concurrently with other benchmarks and build steps. This is non-ideal because CPU usage of other processes may interfere with benchmarks. It also prevented benchmark output from being displayed by default. This is now fixed. See [#3663](https://github.com/commercialhaskell/stack/issues/3663). * `stack ghci` now allows loading multiple packages with the same module name, as long as they have the same filepath. See [#3776](https://github.com/commercialhaskell/stack/pull/3776). * `stack ghci` no longer always adds a dependency on `base`. It is now only added when there are no local targets. This allows it to be to load code that uses replacements for `base`. See [#3589](https://github.com/commercialhaskell/stack/issues/3589#issuecomment) * `stack ghci` now uses correct paths for autogen files with [#3791](https://github.com/commercialhaskell/stack/issues/3791) * When a package contained sublibraries, stack was always recompiling the package. This has been fixed now, no recompilation is being done because of sublibraries. See [#3899](https://github.com/commercialhaskell/stack/issues/3899). * The `get-stack.sh` install script now matches manual instructions when it comes to Debian/Fedora/CentOS install dependencies. * Compile Cabal-simple with gmp when using Nix. See [#2944](https://github.com/commercialhaskell/stack/issues/2944) * `stack ghci` now replaces the stack process with ghci. This improves signal handling behavior. In particular, handling of Ctrl-C. To make this possible, the generated files are now left behind after exit. The paths are based on hashing file contents, and it's stored in the system temporary directory, so this shouldn't result in too much garbage. See [#3821](https://github.com/commercialhaskell/stack/issues/3821). ### Thanks to all our contributors for this release: * Alexey Kuleshevich * Andrei Dziahel * Andrew Cowie * Daniel Bergey * David Baynard * Domen Kožar * Don Waldhalm * Emanuel Borsboom * Geoffrey Noel * Ivan Kasatenko * Jan von Loewenstein * Joshua Simmons * Kirill Elagin * Krishnan Parthasarathi * Luke Murphy * Matt Spaulding * Matthias Braun * Maximilian Tagher * Michael Sloan * Michael Snoyman * Mihai Maruseac * Mike Pilgrem * Mitchell Rosen * Nicolas Mattia * Niklas Hambüchen * Oleg Grenrus * Reuben D'Netto * Robert J. Macomber * Sibi Prabakaran * silky * Simon Hengel * Tero Laxström * tswelsh * Yuji Yamamoto

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ANN: network-2.7.0.0
by evan＠evan-borden.com 28 Apr '18

28 Apr '18

Announcing network-2.7.0.0 https://hackage.haskell.org/package/network-2.7.0.0 The 2.7.0.0 release is mostly communicating change. There are a few new APIs, but much of this release is dedicated to preperation for 3.0.0.0. Many long standing functions and modules with tacit deprecation have been officially marked as such. Change log: * Obsoleting the Network module. * Obsoleting the Network.BSD module. * Obsoleting APIs: MkSocket, htonl, ntohl, getPeerCred, getPeerEid, send, sendTo, recv, recvFrom, recvLen, inet_addr, inet_ntoa, isConnected, isBound, isListening, isReadable, isWritable, aNY_PORT, iNADDR_ANY, iN6ADDR_ANY, sOMAXCONN, sOL_SOCKET, sCM_RIGHTS, packFamily, unpackFamily, packSocketType * Do not closeFd within sendFd [#271](https://github.com/haskell/network/pull/271) * Exporting ifNameToIndex and ifIndexToName from Network.Socket. * New APIs: setCloseOnExecIfNeeded, getCloseOnExec and getNonBlock * New APIs: isUnixDomainSocketAvailable and getPeerCredential * socketPair, sendFd and recvFd are exported even on Windows. Upcoming changes in 3.0.0.0 will include: * Functions and modules marked as deprecated in 2.7.0.0 will be removed. * New APIs introduced in 2.7.0.0 will be present in 3.0.0.0. * Socket addresses will have an extensible API. * Linux, BSD and Windows will all have the same API. 3.0.0.0 has been implemented, but we will wait a sufficient period of time before releasing it. As always thanks to network contributors!

1 0

mallocForeignPtrArray with check against buffer overflows
by Henning Thielemann 27 Apr '18

27 Apr '18

I like to test whether some low-level routines overwrite non-allocated memory area. On the Amiga there was the program Mungwall that surrounded memory blocks with some byte patterns at allocation and checked the integrity of those patterns at deallocation. This would also be possible in Haskell with a modified mallocForeignPtrArray. Has someone already implemented this idea? If yes, how could I easily switch between the mallocForeignPtrArray version with such debugging support and the plain function? It would be unfeasible to re-compile a lot of packages only for debugging. Ideally the test-suite of a package would use the debugging version of mallocForeignPtrArray and the library part would use plain allocation. I thought about using valgrind but I remember this often gave many false positive bug reports for Haskell programs.

3 5

Object assignment and equivalence
by Alfred Matthews 26 Apr '18

26 Apr '18

Numerically, wondering if there are design implications to or via defining integers (1,12) as let mod(1)=0, 0<x<=12 as opposed to let mod(1):=0, 0<x<=12 or 0<x<=12, let mod(1)==0 I think I mean mathematically, since none are anything more than Haskell pseudocode. Possibly this makes only metaphorical sense. Thanks in advance. Alfred.

1 0

Block editor for Haskell
by Alex McLean 26 Apr '18

26 Apr '18

Hi all, I'm wondering if anyone has made a 'block editor' for Haskell, i.e. a syntax-aware text editor where you make a program by snapping together type-compatible words, usually with a mouse. Something similar to Scratch for example: https://scratch.mit.edu/ Any leads appreciated! Best wishes alex

4 3

HaRe : informal poll
by Alan & Kim Zimmerman 26 Apr '18

26 Apr '18

Currently HaRe (on hackage) supports GHC 7.10 and 8.0 There is a new version ready to roll, with GHC 8.2 and 8.4 support. But due to the complexities of the build environment (details here[1] for anyone who cares) it will not be able to support earlier GHC versions. Will this be a problem for anyone? Alan [1] https://github.com/haskell/cabal/pull/5275

1 0

Numerical Programming in Functional Languages (CfP)
by dominic＠steinitz.org 26 Apr '18

26 Apr '18

I’m the chair this year for the first(!) ACM SIGPLAN International Workshop on Numerical Programming in Functional Languages (NPFL), which will be co-located with ICFP this September in St. Louis, Missouri, USA. Please consider submitting something! All you have to do is submit between half a page and a page describing your talk. There will be no proceedings so all you need do is prepare your slides or demo. We do plan to video the talks for the benefit of the wider world. We have Eva Darulova <https://people.mpi-sws.org/%7Eeva/> giving the keynote. The submission deadline is Friday 13th July but I and the Committee would love to see your proposals earlier. See here <https://icfp18.sigplan.org/track/npfl-2018-papers> for more information. Please contact me if you have any questions! Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com Twitter: @idontgetoutmuch

1 0

need to find generated reflex/reflex-dom docs
by Michael Litchard 26 Apr '18

26 Apr '18

I've installed reflex-platform on ubuntu via nix, and am pretty sure I have local docs installed. I located this file /nix/store/hv5zkh1gmhklk4sgwhd8gy1q79l37zpc-reflex-dom-0.4-doc/share/doc/html/index.html But it doesn't lead to very much. I'm thinking I didn't do a full doc install. I'd like some advice on how to make sure I've got a complete local install of reflex docs.

2 1

how to catch/bracket in yesod-1.6?
by waldmann 25 Apr '18

25 Apr '18

Dear Cafe, I wonder what's the recommended way to catch an exception, clean up resources, etc., in a yesod Handler. I was using Control.Monad.Catch.bracket_ in legacy code but now I get "No instance for (Control.Monad.Catch.MonadMask (HandlerFor App))" - J

3 2

ML4PL '18, 1st Call for Submissions
by Artem Pelenitsyn 25 Apr '18

25 Apr '18

******************************************************************************** | | | The 2nd International Workshop on Machine Learning Techniques | | for Programming Languages (ML4PL '18) | | | | July 18th 2018, Amsterdam, Netherlands | | Collocated with ECOOP & ISSTA | | | ******************************************************************************** A workshop on machine learning techniques applied to programming language-related research and development. This workshop puts an emphasis on identifying open problem rather than presenting solution, and encourages discussion amongst the participants. Attendance will be limited to ensure that meeting retains an interactive character. Workshop web-site: https://conf.researchr.org/track/ecoop-issta-2018/ML4PL-2018-papers Submission web-site: https://ml4pl18.hotcrp.com/ ********************************** SCOPE *********************************** Over the last years, we have seen a rapid growth in the use of machine-learning technologies in programming languages and systems. This growth is driven by the need to design programming languages to analyze, detect patterns, and make sense of Big Data, along with the increasing complexity of programming language tools, including analyzers and compilers, and computer architectures. The scale of complexity in available unstructured data and system tools has reached a stage where simple heuristics and solutions are no longer feasible or do not deliver adequate performance. At the same time, statistical and machine learning techniques have become mainstream. This workshop is a broad forum to bring together researchers with interests in the intersection of programming languages and system tools with machine learning. Topics of interest include (but are not limited to): * Program analysis + machine learning * Programming languages + machine learning * Compiler optimizations + machine learning * Computer architecture + machine learning * Probabilistic programming languages * Design space exploration Submissions should take the form of talk abstract or 2-page problem statements. Materials of accepted talks will be published in ACM DL. --------------- IMPORTANT DATES --------------- Submission deadline: Wednesday, May 18th, 2018, AOE Notification (tentative): Monday, June 1st, 2018 ML4PL Workshop: Wednesday, July 18th, 2018 ----------------- PROGRAM COMMITTEE ----------------- * Miltiadis Allamanis (Microsoft Research, Cambridge, United Kingdom) * Lasse Blaauwbroek (Czech Institute for Informatics Robotics and Cybernetics, Czech Republic) * Yoav Goldberg (Bar Ilan University, Israel) * Georgy Lukyanov (Newcastle University, United Kingdom) * Alex Polozov (Microsoft Research, United States) * Mark Santolucito (Yale University, United States) * Meital Zilberstein (Technion, Israel) ------------------------------ ORGANIZING COMMITTEE & CONTACT ------------------------------ * Hila Peleg (Technion, Israel) * Artem Pelenitsyn (Czech Technical University in Prague, Czech Republic) Please, address any questions to Artem (a.pelenitsyn(a)gmail.com)

1 0

WST 2018 - Last Call for Papers (deadline: April 30, 2018)
by Salvador Lucas 25 Apr '18

25 Apr '18

========================================================================== WST 2018 - Call for Papers 16th International Workshop on Termination July 18-19, 2018, Oxford, United Kingdom http://wst2018.webs.upv.es/ ========================================================================== NEW: James Worrell and Akihisa Yamada, WST 2018 invited speakers 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 held as part of the 2018 Federated Logic Conference (FLoC 2018) http://www.floc2018.org/ IMPORTANT DATES: * submission deadline: April 30, 2018 * notification: May 28, 2018 * final version due: June 11, 2018 * workshop: July 18-19, 2018 TOPICS: The 16th 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 INVITED SPEAKERS: James Worrell - University of Oxford "Termination Checking and Invariant Synthesis for Affine Programs" Akihisa Yamada - NII Japan "Towards a Unified Method for Termination" 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 2018, the Termination Competition will run in parallel with FLoC 2018. More details will be provided in a dedicated announcement on the competition. PROGRAM COMMITTEE: Cristina Borralleras - U. de Vic Ugo Dal Lago - U. degli Studi di Bologna Carsten Fuhs - Birkbeck, U. of London Samir Genaim - U. Complutense de Madrid Juergen Giesl - RWTH Aachen Raul Gutiérrez - U. Politecnica de València Keiichirou Kusakari - Gifu University Salvador Lucas (chair) - U. Politecnica de Valencia Fred Mesnard - U. de La Reunion Aart Middeldorp - U. of Innsbruck Albert Rubio - U. Politecnica de Catalunya Rene Thiemann - U. of Innsbruck Caterina Urban - ETH Zürich 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=wst2018 Please, use LaTeX and the LIPIcs style file http://drops.dagstuhl.de/styles/lipics/lipics-authors.tgz to prepare your submission.

1 0

In which format should GHC expose documentation via its .hi-files?
by Simon Jakobi 24 Apr '18

24 Apr '18

Hi! In preparation for the coding phase of the Hi Haddock proposal that I want to implement, I need a decision on the format in which we should expose haddocks in GHC's .hi interface files. Please visit https://github.com/haskell/haddock/issues/805, ask questions, make suggestions and help me find a timely decision! :) Cheers, Simon

1 0

Selda: confused about type signtures
by Marc Busqué 24 Apr '18

24 Apr '18

Hi! I'm using [selda](https://hackage.haskell.org/package/selda) package in order to deal with database backends. Selda uses `TypeOperators` language extension, and it introduces `:*:` type operator constructor which take concrete types like `RowID` or `Text` . It also has a `Table` type constructor which takes anything built with `:*:`). On the other hand, `SeldaM` is selda custom monad transformer with `IO` at the bottom. I have following helper function which just wraps a call to the SQLite backend. `dBPath` is just the database file path: ``` withDB :: SeldaM a -> IO a withDB act = do path <- dBPath withSQLite path act ``` I want to wrap selda API in custom functions to be more resilient to changes. Right now I'm trying to abstract selecting all rows for a given table (maybe it seems brittle, but it is just a toy project in order to learn Haskell): ``` list table = withDB $ query (select table) ``` Not adding a type signature to `list` produces following compilation error: ``` • Non type-variable argument in the constraint: selda-0.1.12.1:Database.Selda.Column.Columns (selda-0.1.12.1:Database.Selda.Column.Cols s a) (Use FlexibleContexts to permit this) • When checking the inferred type list :: forall s a. (selda-0.1.12.1:Database.Selda.Column.Columns (selda-0.1.12.1:Database.Selda.Column.Cols s a), selda-0.1.12.1:Database.Selda.Compile.Result (selda-0.1.12.1:Database.Selda.Column.Cols s a)) => Table a -> IO [selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s a)] ``` If I try to add what I think would be the correct signature: ``` list :: Table a -> IO [a] ``` The error changes to: ``` • Couldn't match type ‘a’ with ‘selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s0 a)’ ‘a’ is a rigid type variable bound by the type signature for: list :: forall a. Table a -> IO [a] at src/Hedger/Category.hs:35:1-25 Expected type: SeldaM [a] Actual type: selda-0.1.12.1:Database.Selda.Backend.Internal.SeldaT IO [selda-0.1.12.1:Database.Selda.Compile.Res (selda-0.1.12.1:Database.Selda.Column.Cols s0 a)] • In the second argument of ‘($)’, namely ‘query (select table)’ In the expression: withDB $ query (select table) In an equation for ‘list’: list table = withDB $ query (select table) • Relevant bindings include table :: Table a (bound at src/Hedger/Category.hs:36:6) list :: Table a -> IO [a] (bound at src/Hedger/Category.hs:36:1) | 36 | list table = withDB $ query (select table) ``` However, if I constraint the type signature to act just for a given table, it compiles without errors: ``` type CategoriesSchema = RowID:*:Text list :: Table CategoriesSchema -> IO [CategoriesSchema] ``` Why is that it works with concrete types but not with a type variable that takes the same concrete type in its both placeholders? Thanks in advance, Marc Busqué http://waiting-for-dev.github.io/about/

4 18

Munich Haskell Meeting, 2018-04-26 @ 19:30
by Leah Neukirchen 23 Apr '18

23 Apr '18

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, April 26 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-apr-2018/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> http://leah.zone

1 0

New Version of hmatrix (more ODE solvers)
by dominic＠steinitz.org 22 Apr '18

22 Apr '18

I am pleased to announce a new version of hmatrix: 0.19.0.0. This is not intended to be a breaking change but a lot of modules have been modified to ensure that continuous integration (which has now been set up) is green. Support for SUNDIALS <https://computation.llnl.gov/projects/sundials> has been added. It should be possible to replace Numeric.GSL.ODE with Numeric.Sundials.ARKode.ODE and have your program work as before bearing in mind that the methods and error control might differ (even for those with the same names!). The packages that comprise hmatrix are: hmatrix hmatrix-gsl hmatrix-special hmatrix-sparse hmatrix-glpk hmatrix-tests hmatrix-sundials I am planning to split these up into separate projects to make it easier for contributors. To this end, I have created an hmatrix <https://github.com/haskell-numerics> organisation in github. Please contact me if you wish to become a member. I strongly recommend anyone solving ODEs to look as hmatrix-sundials as the underlying package provides many more methods, more documentation and more diagnostic information (great when your 200 variable model fails). It is a truism that any sufficiently sophisticated ODE solver package is a domain specific language (I include the ODE solving part of GSL here). The current interface both to GSL and to SUNDIALS is somewhat rudimentary but will hopefully evovle to a nicer DSL (something at which Haskell excels). Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com Twitter: @idontgetoutmuch

1 0

Selda, type operators and heterogeneous lists
by Marc Busqué 20 Apr '18

20 Apr '18

Hi there! I'm using [selda](https://github.com/valderman/selda) package to deal with relational databases. This package represents database tables in haskell in a type-safe way. And to do so it leans on type operators. For example, here they are two different tables: ``` categories :: Table (RowID:*:Text) expenses :: Table (RowID:*:Text:*:Double:*:RowID) ``` As both of them belong to different types, I can't put them in a single list out of the box: ``` [categories, expenses] --- not valid!! ``` I'm aware of [different solutions](https://wiki.haskell.org/Heterogenous_collections) to deal with it, but they don't convince me: - Algebraic data types: I think in this situation it is specially a burden having to play type-switching... There can exist a lot of different table schemas and they may change at any moment. - Universal type: I see it as a kind of hack - Existential types: I have read that usually it is an anti-pattern, and in this case I don't understand how it should work, because types are constructed with `:*:` operator. So my question if it exists some natural way to treat types built with type operators as a single type. I have to recognize I don't understand well how all this stuff about type operators works. I have read something but I still don't get it. So any direction with it would be very gratifying, too :) Thanks in advance. Marc Busqué http://waiting-for-dev.github.io/about/

4 7

ANN: stack-1.7 RELEASE CANDIDATE
by Emanuel Borsboom 20 Apr '18

20 Apr '18

This is the second release candidate for stack-1.7 (the first was short-lived and never widely announced). Binaries for supported platforms are available here: https://github.com/commercialhaskell/stack/releases/tag/v1.7.0.3 <https://github.com/commercialhaskell/stack/releases/tag/v1.7.0.3>. You easily upgrade to it using: `stack upgrade --binary-version=1.7.0.3` ## Changes since v1.6.5: Release notes: * aarch64 (64-bit ARM) bindists are now available for the first time. * Statically linked Linux bindists are no longer available, due to difficulty with GHC 8.2.2 on Alpine Linux. * 32-bit Linux GMP4 bindists for CentOS 6 are no longer available, since GHC 8.2.2 is no longer being built for that platform. Major changes: * Upgrade from Cabal 2.0 to Cabal 2.2 Behavior changes: * `stack setup` no longer uses different GHC configure options on Linux distributions that use GCC with PIE enabled by default. GHC detects this itself since ghc-8.0.2, and Stack's attempted workaround for older versions caused more problems than it solved. * `stack new` no longer initializes a project if the project template contains a stack.yaml file. Other enhancements: * `stack unpack` now supports a `--to /target/directory` option to specify where to unpack the package into * `stack hoogle` now supports a new flag `--server` that launches local Hoogle server on port 8080. See [#2310](https://github.com/commercialhaskell/stack/issues/2310) * A new sub command `ls` has been introduced to stack to view local and remote snapshots present in the system. Use `stack ls snapshots --help` to get more details about it. * `list-dependencies` has been deprecated. The functionality has to accessed through the new `ls dependencies` interface. See [#3669](https://github.com/commercialhaskell/stack/issues/3669) for details. * Specify User-Agent HTTP request header on every HTTP request. See [#3628](https://github.com/commercialhaskell/stack/issues/3628) for details. * `stack setup` looks for GHC bindists and installations by any OS key that is compatible (rather than only checking a single one). This is relevant on Linux where different distributions may have different combinations of libtinfo 5/6, ncurses 5/6, and gmp 4/5, and will allow simpifying the setup-info metadata YAML for future GHC releases. * The build progress bar reports names of packages currently building. * `stack setup --verbose` causes verbose output of GHC configure process. See [#3716](https://github.com/commercialhaskell/stack/issues/3716) * Improve the error message when an `extra-dep` from a path or git reference can't be found See [#3808](https://github.com/commercialhaskell/stack/pull/3808) * Nix integration is now disabled on windows even if explicitly enabled, since it isn't supported. See [#3600](https://github.com/commercialhaskell/stack/issues/3600) * `stack build` now supports a new flag `--keep-tmp-files` to retain intermediate files and directories for the purpose of debugging. It is best used with ghc's equivalent flag, i.e. `stack build --keep-tmp-files --ghc-options=-keep-tmp-files`. See [#3857](https://github.com/commercialhaskell/stack/issues/3857) * Improved error messages for snapshot parse exceptions Bug fixes: * When a package contained sublibraries, stack was always recompiling the package. This has been fixed now, no recompilation is being done because of sublibraries. See [#3899](https://github.com/commercialhaskell/stack/issues/3899). * The `get-stack.sh` install script now matches manual instructions when it comes to Debian/Fedora/CentOS install dependencies. * Compile Cabal-simple with gmp when using Nix. See [#2944](https://github.com/commercialhaskell/stack/issues/2944) * `stack ghci` now replaces the stack process with ghci. This improves signal handling behavior. In particular, handling of Ctrl-C. To make this possible, the generated files are now left behind after exit. The paths are based on hashing file contents, and it's stored in the system temporary directory, so this shouldn't result in too much garbage. See [#3821](https://github.com/commercialhaskell/stack/issues/3821). * The script interpreter's implicit file arguments are now passed before other arguments. See [#3658](https://github.com/commercialhaskell/stack/issues/3658). In particular, this makes it possible to pass `-- +RTS ... -RTS` to specify RTS arguments used when running the script. * Don't ignore the template `year` parameter in config files, and clarify the surrounding documentation. See [#2275](https://github.com/commercialhaskell/stack/issues/2275). * Benchmarks used to be run concurrently with other benchmarks and build steps. This is non-ideal because CPU usage of other processes may interfere with benchmarks. It also prevented benchmark output from being displayed by default. This is now fixed. See [#3663](https://github.com/commercialhaskell/stack/issues/3663). * `stack ghci` now allows loading multiple packages with the same module name, as long as they have the same filepath. See [#3776](https://github.com/commercialhaskell/stack/pull/3776). * `stack ghci` no longer always adds a dependency on `base`. It is now only added when there are no local targets. This allows it to be to load code that uses replacements for `base`. See [#3589](https://github.com/commercialhaskell/stack/issues/3589#issuecomment) * `stack ghci` now uses correct paths for autogen files with [#3791](https://github.com/commercialhaskell/stack/issues/3791)

1 0

building ghc-8.4.2 from source: undefined reference to 'mpz_powm_sec'
by Johannes Waldmann 20 Apr '18

20 Apr '18

Dear Cafe, I am getting this when building ghc-8.4.2 from source, with ghc-8.2.2: ghc-8.4.2/libraries/integer-gmp/dist-install/build/libHSinteger-gmp-1.0.2.0_p.a(wrappers.p_o):wrappers.c:function integer_gmp_powm_sec: error: undefined reference to 'mpz_powm_sec' collect2: error: ld returned 1 exit status `gcc' failed in phase `Linker'. (Exit code: 1) make[1]: *** [iserv/ghc.mk:104: iserv/stage2_p/build/tmp/ghc-iserv-prof] Error 1 This may be due to some mis-config on my part, because I'm getting this on one machine only, and it works on others. Still, perhaps you have seen this before, and could help me with an educated guess on what may have caused this. It is especially puzzling because this install of ghc-8.2.2 seems to work perfectly fine for all of my projects. Thanks - J.W.

2 2

Integer representation
by David Feuer 19 Apr '18

19 Apr '18

Is there any way to determine whether Integer comes from integer-gmp or integer-simple? I'm playing with the idea of using the underlying representation to get more compact/efficient tries, but I need to be able to find out what that representation is.

4 6

ANN: RISC-V ISA Formal Spec (written in Haskell)
by Rishiyur Nikhil 19 Apr '18

19 Apr '18

Title: RISC-V ISA Formal Specification Speaker: Thomas Bourgeat, MIT Venue: 8th RISC-V Workshop, Barcelona Date: Monday May 7, 2018 Abstract: In this tutorial we will demonstrate several flavors of a formal specification of the RISC-V ISA, written in Haskell. We will present the important part of the code, use it as a software simulator, automatically transform it into a coq specification (used to prove the correctness of a small imperative language), and automatically synthesize it to circuit (to model check against other designs). If time permits, we will show how the same code can be used to explore some non-determinism in the specification. Registration info: https://riscv.org/workshops/

1 0

Is there a reason that template-haskell does not expose its own parser for using in quasi-quoters?
by Christopher Done 16 Apr '18

16 Apr '18

I.e. something like parseExpr :: String -> Either String Exp It seems that a lot of trivial extensions could be made nicely if this was so. An example might be: [ne| 1, 2, 3, ... |] for a non-empty list statically checked to be non-empty. In there I could put any Haskell code. But presently I need to use HSE which isn't quite GHC Haskell and has a large foot-print. The alternative splice $(ne [| [1, 2, 3, ... ] |]) is rather unwieldy.

1 0

JOB | Permanent Web Developer (New York)
by James Tobin 16 Apr '18

16 Apr '18

Hello, I'm working with an established financial technology employer that is looking to hire a permanent web developer with significant Java client side experience to join their New York office. Consequently, I had hoped that some members of this mailing list may like to discuss further off-list using "JamesBTobin (at) Gmail (dot) Com". Kind regards, James

3 2

Call for Participation: Summer School on Advanced Functional Programming
by Alejandro Serrano Mena 16 Apr '18

16 Apr '18

# Call for Participation SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Utrecht, the Netherlands, 27-31 August 2018 http://www.afp.school ## 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. 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: * Johan Jeuring * Alejandro Serrano Mena * Doaitse Swierstra * Wouter Swierstra Guest lectures: * Manuel Chakravarty * Koen Claessen * Gabriele Keller ## 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. ## DATES Registration deadline: 1 August, 2017 School: 27-31 August ## COSTS €1700 - Housing and registration €1500 - Registration only We offer a €1000 discount for students and staff members affiliated with a university. ## SCHOLARSHIPS If you’re struggling to finance your trip to Utrecht, please let us know. We have a 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

1 0

2nd call for papers: Trends in Functional Programming, 11-13 june 2018, Chalmers Campus Johanneberg, Gothenburg
by Peter Achten 16 Apr '18

16 Apr '18

------------------------------------- 2 N D C A L L F O R P A P E R S ------------------------------------- ======== TFP 2018 =========== 19th Symposium on Trends in Functional Programming 11-13 June, 2018 Chalmers Campus Johanneberg, Gothenburg http://www.cse.chalmers.se/~myreen/tfp2018/index.html The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below at scope). Please be aware that TFP uses two distinct rounds of submissions (see below at submission details). TFP 2018 will be the main event of a pair of functional programming events. TFP 2018 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 14. == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: Leading-edge, previously unpublished research work Position Articles: On what new trends should or should not be Project Articles: Descriptions of recently started new projects Evaluation Articles: What lessons can be drawn from a finished project Overview Articles: Summarizing work with respect to a trendy subject. Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2018 program chairs, Michał Pałka and Magnus Myreen. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Paper Submissions == We use EasyChair for the refereeing process. The link to the submission page is: https://easychair.org/conferences/?conf=tfp2018 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Pre-symposium formal review == Papers to be formally reviewed before the symposium should be submitted before an early deadline and receive their reviews and notification of acceptance for both presentation and publication before the symposium. A paper that has been rejected in this process may still be accepted for presentation at the symposium, but will not be considered for the post-symposium formal review. == Post-symposium formal review == Draft papers will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == Draft papers and papers submitted for formal review are submitted as extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which all authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site. == Important Dates == Submission (pre-symposium review): March 26, 2018 -- passed -- Submission (draft, post-symposium review): April 26, 2018 -- open -- Notification (pre- and post-symposium review): May 3, 2018 Registration: June 3, 2018 TFP Symposium: June 11-13, 2018 TFPIE Workshop: June 14, 2018 Student papers feedback: June 21, 2018 Submission (post-symposium review): August 14, 2018 Notification (post-symposium review): September 20, 2018 Camera-ready paper (pre- and post-symposium review): November 30, 2018 == Program Committee == Program Co-chairs Michał Pałka, Chalmers University of Technology (SE) Magnus Myreen, Chalmers University of Technology (SE) Program Committee Soichiro Hidaka, Hosei University (JP) Meng Wang, University of Bristol (UK) Sam Tobin-Hochstadt, Indiana University Bloomington (US) Tiark Rompf, Purdue University (US) Patricia Johann, Appalachian State University (US) Neil Sculthorpe, Nottingham Trent University (UK) Andres Löh, Well-Typed LLP (UK) Tarmo Uustalu, Tallinn University of Technology (EE) Cosmin E. Oancea, University of Copenhagen (DK) Mauro Jaskelioff, Universidad Nacional de Rosario (AR) Peter Achten, Radboud University (NL) Dimitrios Vytiniotis, Microsoft Research (UK) Alberto Pardo, Universidad de la República (UY) Natalia Chechina, University of Glasgow (UK) Peter Sestoft, IT University of Copenhagen (DK) Scott Owens, University of Kent (UK)

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WST 2018 - Call for Papers (extended deadline: April 30, 2018)
by Salvador Lucas 14 Apr '18

14 Apr '18

========================================================================== WST 2018 - Call for Papers 16th International Workshop on Termination July 18-19, 2018, Oxford, United Kingdom http://wst2018.webs.upv.es/ ========================================================================== NEW: Deadline extended to April 30, 2018 NEW: Akihisa Yamada, WST 2018 invited speaker 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 held as part of the 2018 Federated Logic Conference (FLoC 2018) http://www.floc2018.org/ IMPORTANT DATES: * submission deadline: April 30, 2018 (extended) * notification: May 28, 2018 * final version due: June 11, 2018 * workshop: July 18-19, 2018 TOPICS: The 16th 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 2018, the Termination Competition will run in parallel with FLoC 2018. More details will be provided in a dedicated announcement on the competition. PROGRAM COMMITTEE: Cristina Borralleras - U. de Vic Ugo Dal Lago - U. degli Studi di Bologna Carsten Fuhs - Birkbeck, U. of London Samir Genaim - U. Complutense de Madrid Juergen Giesl - RWTH Aachen Raul Gutiérrez - U. Politecnica de València Keiichirou Kusakari - Gifu University Salvador Lucas (chair) - U. Politecnica de Valencia Fred Mesnard - U. de La Reunion Aart Middeldorp - U. of Innsbruck Albert Rubio - U. Politecnica de Catalunya Rene Thiemann - U. of Innsbruck Caterina Urban - ETH Zürich INVITED SPEAKERS: Akihisa Yamada - NII Japan 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=wst2018 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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Performance of TL-calculations
by Dmitry Olshansky 13 Apr '18

13 Apr '18

Hello, cafe, The main problem I have when using promising type-level calculation is compile time. E.g. I have > type T = ... :: [Symbol] Now I don't know the order of Symbols in T. But I want to sort it before using for some reasons. I can define > type T1 = Sort T -- where Sort is from Singletons library but T1 is only type synonym and long type-level calculation will be done in any places where I use T1. So I will have problems with compile-time performance. Probably I would overcome this if I can define > class X x where ... > instance X T1 where ... but I can't do it because can't define instances for (non-injective) Type Families. Is there any workaround? Are there any plans to make it better? Are there any hidden problems to make an analog of CAF on the type level? Best regards, Dmitry

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OneTuple unmaintained
by ☂Josh Chia (謝任中) 13 Apr '18

13 Apr '18

OneTuple needs an update for compatibility with GHC 8.4. I emailed the listed maintained but the email bounced. I would like to take over the package if there are no other takers. Josh

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using type variables in type declarations inside function
by Dennis Raddle 12 Apr '18

12 Apr '18

Let's say I've written a function on three types. myFunc :: a -> b -> c myFunc x y z = ... where helper :: a -> [b] helper xx = ... Notice that I'm attempting to declare 'helper' using my type variables. I've noticed that this results in an error. Is this actually possible, and how? D

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Unplanned Hackage Downtime
by Gershom B 12 Apr '18

12 Apr '18

I made a terrible administrative snafu, and we need to take some time to restore Hackage. Luckily we have better mirroring in place now, so cabal-install should be able to fall back automatically to mirrors. If this does not work, you can use http://objects-us-west-1.dream.io/hackage-mirror/ or http://hackage.fpcomplete.com/ manually. Best (and sincere apologies), Gershom

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hackage style
by Ben Franksen 11 Apr '18

11 Apr '18

The new hackage style has nice colors but severe problems w.r.t. readability. The right column with the package meta data causes the Readme text to be cut off. This make it almost impossible to read it. I attached a screenshot for illustration. Cheers Ben

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Join a transformer
by Michael Snoyman 11 Apr '18

11 Apr '18

I'm wondering if this pattern exists and has a name. We have the concept of joining a Monad: join :: Monad m => m (m a) -> ma How about joining a monad transformer? joinT :: (Monad m, MonadTrans t) => t (t m) a -> t m a I believe implementing this in terms of MonadTransControl[1] might be possible, but I was wondering if there's an already existing idiom for this. Michael [1] http://haddocks.fpcomplete.com/fp/7.4.2/20130301-40/monad-control/Control-M…

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downgrading GHC version on a Mac
by Dennis Raddle 11 Apr '18

11 Apr '18

I'm on a MacBook Pro. I'm not very familiar with software installation. Up until now I've been using Stack for GHC work, and it seems to take care of having the right version of GHC. Now I'm going to use GHCJS, and I need to have a system GHC installed (I believe). At some point in the past I installed the Haskell Platform for Mac, and I have GHC 8.01. But I want to downgrade that to 7.10 so that I don't have to worry about compatibility with GHCJS. How do I go about uninstalling GHC 8 and installing 7.10 in its place? Can I use Homebrew? D

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looking for a particular paper
by Michael Litchard 10 Apr '18

10 Apr '18

Could someone provide a copy of the following paper? Safe Client/Server Web Development with Haskell Mark Mazumder <https://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=%22Authors…> ; Timothy Braje <https://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=%22Authors…>

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GHC Core / STG to supercombinators
by Csaba Hruska 09 Apr '18

09 Apr '18

Hello, I wonder what is the easiest way to compile Haskell to supercombinators (top level functions) using GHC as a library. Is it possible to use GHC simplifier to transform the parsed Haskell source to supercombinators? i.e. to do - eta expansion - closure conversion - lambda lifting Or should it be written from scratch? Is Core or STG suited better for this purpose? Thanks, Csaba

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stack and GHCJS
by Dennis Raddle 08 Apr '18

08 Apr '18

Now I'm trying to use stack to install and run GCHJS. Can someone help me figure out this error? I first created project 'proj01' using the ghcjs template via stack new proj01 ghcjs Then I typed stack build It ran for a while, then gave an error messages that starts "While building custom Setup.hs for package semigroupoids-5.0.0.4 using .... <very long description>, Process exited with code ExitFailure 1" But it didn't halt. Instead it started compiling Main.hs, and ended up saying "at least the following dependencies are missing: tagged >= 0.8.5 && <1 && ==0.8.1" I tried adding "tagged" to the extra-deps in the stack.yaml, but it didn't help. While I'm posting, is there a resource that explains background to this? I don't know much about "packages," "snapshots," "dependencies", means of specifying versions, cabal, or YAML files. Everything I find online seems to assume some background knowledge of these things. For instance the stack documentation talks about snapshots, but I can't find an explanation that I understand for what a "snapshot" actually is. Ditto for all these many concepts that go into configuring and building. D

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PatternSignatures (rant)
by Johannes Waldmann 06 Apr '18

06 Apr '18

Dear all, (this is a rant - please ignore) why has "PatternSignatures" been renamed to "ScopedTypeVariables" (in ghc-6.10)? show me the alleged "type variable" in this code: do x :: Int <- [ 1 .. 10 ] ; return $ x^2 and why on earth do I need to use a language extension at all to get to the most basic thing of declarative programming: to declare the type of an identifier? This seriously hurts (me, at least) when teaching Haskell. Thanks - J.W.

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Windows: how to perform cleanup actions when the console window closes
by Peter Dedecker 06 Apr '18

06 Apr '18

So I looked at this some more, and determined a few things: - Ctrl-C did not do anything in the original program because the main thread was blocked on a socket accept() call, which seemingly could not be interrupted for an asynchronous exception. - I fixed this by having the main thread initialize everything, then running the main body of code in an async and waiting on that. Apparently this wait is interruptible, so Ctrl-C works, bracket nicely cleans up, and the application exits. Good! - Then I added a console handler to capture 'close' events. Here is the code for the handler: f mainThreadID event = case event of ControlC -> putStrLn "HANDLER" >> throwTo mainThreadID UserInterrupt Break -> putStrLn "HANDLER" >> throwTo mainThreadID UserInterrupt Close -> putStrLn "HANDLER" >> throwTo mainThreadID ThreadKilled >> threadDelay maxBound _ -> pure () Where the 'threadDelay' call serves simply to give the main thread time to exit. This works fine for ControlC and Break, but fails for Close: the program exists immediately, and no cleanup is run. So I still haven't solved how to clean up when the window close button is hit. Any thoughts? Thanks Peter

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ANN: Yampa 0.11
by Ivan Perez 06 Apr '18

06 Apr '18

Dear all, I'm happy to announce version 0.11 of Yampa! Yampa is a mature and robust FRP implementation that has been used to create mobile, desktop, and web games and applications, including games that use devices like wiimotes and kinect, as well as free and commercial mobile games available on iTunes and Google Play. (For reference, see [1-4].) This version includes documentation for all modules and all definitions. We have closed a total of 29 issues. Thanks to @ptvirgo for contributing to this release. A limitation of Haddock prevents us from achieving 100% coverage. Help with that would be appreciated [5, 6]. This version has been tested against all major GHC versions, from 7.6 to 8.4. A minor change in the low-level interface has triggered a major version bump (0.11). I would expect all projects that use Yampa to work by, at most, adapting the version constraints in the cabal files. Everybody is welcome to collaborate. The github repo includes some simple issues especially suitable for beginners, and we are working on the next major version. We are also exploring different research ideas related to FRP, and actively look for research collaborators. Hope you all enjoy it. Happy Haskelling! Ivan [1] https://github.com/ivanperez-keera/Yampa [2] https://github.com/ivanperez-keera/haskanoid [3] https://github.com/ksaveljev/yampa-2048 [4] https://haskell.games [5] https://github.com/haskell/haddock/issues/123 [6] https://github.com/ivanperez-keera/Yampa/issues/72

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Windows: how to perform cleanup actions when the console window closes
by Peter Dedecker 06 Apr '18

06 Apr '18

Hi Joachim, > You need to intercept the various events that may cause a console > windows to be closed; this is done via the Windows API call > SetConsoleCtrlHandler . > https://stackoverflow.com/a/30843219/6944068 gives an overview very informative, thanks! > I don't know how to register a Haskell function as a Windows callback, > that will have to be answered by somebody else. With your tips, I came across https://hackage.haskell.org/package/base-4.11.0.0/docs/GHC-ConsoleHandler.h…. (The documentation doesn't work, but you can look at the source to see the gist of it). I think this may do what you describe. The documentation for this function says that > When the event is received, if the > 'Handler' value is @Catch f@, then a new thread will be spawned by > the system to execute @f e@, where @e@ is the 'ConsoleEvent' that > was received. I wonder if I can add a handler function that detects Control-C and Close events, and responds by throwing a userInterrupt exception to the main thread, and then sleeping forever. The main thread then sees an asynchronous exception, the bracket cleanup action fires (which is my goal here), main thread shuts down and the program stops. Will try to experiment with that later. Thanks again Peter

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Windows: how to perform cleanup actions when the console window closes
by Peter Dedecker 06 Apr '18

06 Apr '18

Hello all, I have a console (command-line) Haskell application that communicates with some hardware equipment. The equipment needs to be initialized when my program starts, and needs to be cleanly shut down when the program ends. This is the basic structure of the program: main = readAvailableEquipment >>= \descs -> withEquipment descs $ \availableEquipment -> <<< more initialization then an infinite loop as a sockets-based server, communicating with the hardware via availableEquipment >>> withEquipment is defined as withEquipment descs action = bracket (initializeEquipment descs) closeEquipment action Basically I want closeEquipment to be executed when the program shuts down. The program is stopped by the user closing the console window (hitting the upper right 'X' in the Windows title bar). I would expect that the 'closeEquipment' action is performed since it is in the cleanup part of the 'bracket', but my testing suggests that these actions never execute. Incidentally, stopping the program via Ctrl-C doesn't work. I have tested this with GHC 8.2.2 installed via Stack (LTS 11.3). This is on Windows 10. Summary question and TLDR: how do I reliably perform cleanup actions in a Windows console program that is closed by the user by clicking the 'X' symbol in the window title bar? Thanks! Peter

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