April 2018 - Haskell-Cafe

Fwd: Safe TCP accept loop
by Sumit Raja 30 May '18

30 May '18

Hi, I sent this to beginners but got no responses so I'm hoping someone here can help. I’ve looked at https://wiki.haskell.org/Concurrency_demos/Graceful_exit and used(2) Using throwTo without the use of block and unblock. It runs on 8.2.1 with my limited testing. I can’t find out much about what the > 7.x GHC replacement for block/unblock is other than mask. What does the unblock do in acceptConnections'? Does this method of handling an accept loop still need masking of async exceptions ? If so where does this need to be done? I've got a version with async running for my specific application (https://bitbucket.org/sumitraja/hvrr/src/6927216597a35a9a0d7f2e55cca83fa5b7…) but I don't know if I need to unmask at any point so was hoping for some guidance. Thanks Sumit

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Archival of community.haskell.org
by Mario Rogic 19 May '18

19 May '18

Hi all As announced back in 2015 <http://blog.haskell.org/post/7/the_future_of_community.haskell.org/> we have started archiving community.haskell.org services. We've created https://archives.haskell.org/, and the old projects mailing lists have been the first to be archived. Next on the list is the remainder of projects.haskell.org, and the code.haskell.org site. As always, you can email admin(a)h.o or hop on the #haskell-infrastructure freenode channel to provide feedback / concerns. Thanks - Mario

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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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<<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 29 Apr '18

29 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!

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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.

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