January 2017 - Haskell-Cafe

Re: [Haskell-cafe] Haskell with C++: removing runtime dependencies on Windows 10.
by David Banas 20 Jan '17

20 Jan '17

Hi Deech, Not sure this is helpful, as I haven’t tested it on Windows 10, but here are the gcc/ghc compile/link options I use for a project that has a similar need: CC = gcc CFLAGS += -I/usr/lib/ghc-7.4.2/include/ -g -fPIC HC = ghc HC_OPTS = -cpp -O3 $(EXTRA_HC_OPTS) EXTRA_HC_OPTS = -package parsec -dynamic -fPIC -rtsopts HC_LOPTS = -shared -dynamic -package parsec -lHSrts -lm -lffi -lrt -db

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Strange encoding issue with Text and Servant
by Jan von Löwenstein 20 Jan '17

20 Jan '17

Hi, I have got a two places with a `QueryParam "q" Text` and call it with a Text that contains a `=` literal. In one place the `=` is correctly encoded as %3D, in the other I see a `!D(MISSING)`. This has to happen somewhere in Servant or the lower layers. Both Texts print out nicely with an `=` sign if I just print them to stdout. Google does not find `!D(MISSING)` anywhere. Any idea what could possibly be the problem here? Best Jan

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monad prompt example missing
by Michael Litchard 19 Jan '17

19 Jan '17

There's an example from the Monad.Prompt documentation https://hackage.haskell.org/package/MonadPrompt-1.0.0.5/docs/Control-Monad-… That is a dead link. http://paste.lisp.org/display/53766 Does anyone have a copy of this example, and of course any other ones you may know of.

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Haskell with C++: removing runtime dependencies on Windows 10.
by aditya siram 19 Jan '17

19 Jan '17

Hi, I am trying to create an executable on Windows 10 with some Haskell->C++ bindings I wrote but having trouble getting rid of some runtime DLL dependencies. I'm currently compiling and linking using the MSYS2 and GHC environment that ships with Windows Stack installer but no matter what I do I end up with the following dependencies: $ ldd <executable> ... libwinpthread-1.dll => /c/Users/user/AppData/Local/Programs/stack/x86_64-windows/ghc-8.0.1/mingw/bin/libwinpthread-1.dll (0x64940000) libstdc++-6.dll => /c/Users/user/AppData/Local/Programs/stack/x86_64-windows/ghc-8.0.1/mingw/bin/libstdc++-6.dll (0x6fc40000) libgcc_s_seh-1.dll => /c/Users/user/AppData/Local/Programs/stack/x86_64-windows/ghc-8.0.1/mingw/bin/libgcc_s_seh-1.dll (0x61440000) I have verified that the standalone versions of those libs are in available in stack install: libstdc++: ../stack/x86_64-windows/ghc-8.0.1/mingw/lib/gcc/x86_64-w64-mingw32/5.2.0/libstdc++.a ../stack/x86_64-windows/ghc-8.0.1/mingw/lib/gcc/x86_64-w64-mingw32/5.2.0/libstdc++.dll.a ../stack/x86_64-windows/ghc-8.0.1/mingw/lib/gcc/x86_64-w64-mingw32/5.2.0/libgcc.a libgcc: ../stack/x86_64-windows/ghc-8.0.1/mingw/lib/gcc/x86_64-w64-mingw32/5.2.0/libgcc_eh.a ../stack/x86_64-windows/ghc-8.0.1/mingw/lib/gcc/x86_64-w64-mingw32/5.2.0/libgcc_s.a libpthread: ../stack/x86_64-windows/ghc-8.0.1/mingw/x86_64-w64-mingw32/lib/libpthread.a ../stack/x86_64-windows/ghc-8.0.1/mingw/x86_64-w64-mingw32/lib/libpthread.dll.a I've unsuccessfully tried to link them into the executable using many combinations of `-optl-static`, `-optl-static-gcc`, and `-optl-static-stdc++` and also passing along these libraries " raw" to the linker like: `ghc-Options: -pgml g++ "-optl-Wl,--whole-archive" "-optl-Wl,-Bstatic" "-optl-Wl,-lstdc++" "-optl-Wl,-Bdynamic" "-optl-Wl,--no-whole-archive" Short of shipping these DLL with the executable (which I'd really rather not do) I'm running out of ideas so any suggestions would be appreciated. Thanks! -deech

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Haskell Weekly - 01/18/2017
by Haskell Weekly 19 Jan '17

19 Jan '17

View this email in your browser (http://us10.campaign-archive2.com/?u=49a6a2e17b12be2c5c4dcb232&id=d1f16b3bf…) ** Haskell Weekly (http://news.us10.list-manage1.com/track/click?u=49a6a2e17b12be2c5c4dcb232&i…) ------------------------------------------------------------ ** Issue 38 (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) ------------------------------------------------------------ Welcome to Haskell Weekly! Haskell (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) is an advanced, purely functional programming language. This is a weekly summary of what’s going on in its community. You can subscribe to the email newsletter (http://news.us10.list-manage1.com/track/click?u=49a6a2e17b12be2c5c4dcb232&i…) or the Atom feed (/haskell-weekly.atom) . Want to contribute to Haskell Weekly? Send us a message on Twitter (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) or open an issue on GitHub (http://news.us10.list-manage1.com/track/click?u=49a6a2e17b12be2c5c4dcb232&i…) . ** News from the Haskell community ------------------------------------------------------------ * Brent Yorgey’s new programming languages course (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) My new PL course is now finished, and all the course materials are freely available. Working through all the exercises should be a great option for anyone wishing to learn some basics of programming language design and implementation. * CLaSH 0.7 released: GHC 8 support and more (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) Our company has been hired to do FPGA development work, and best of all, we get to use CLaSH. As a consequence, I cannot put as much time into CLaSH development as during my days as a PhD/PostDoc. However, we do now get to use CLaSH in industry! And as part of the contract there is time to find and fix bugs in CLaSH! * safe-prelude: a thought experiment (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) This is a thought experiment in a different point in the alternative prelude design space. After my blog post on readFile, I realized I was unhappy with the polymorphic nature of readFile in classy-prelude. Adding that with Haskell Pitfalls I’ve been itching to try something else. * Selecting a platform: JavaScript vs Elm vs PureScript vs GHCJS vs Scala.js (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) There are not many people who have worked on production applications in multiple frontend FP systems, and lived to tell the tale. So here goes, my guide to selecting a functional programming platform for the browser. * The design and use of QuickCheck (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) The typical examples you’ll find online have deceptively simple code. The examples make it hard to learn how their succinct tests are possible, and how to customize them when things go wrong. This guide puts it all together piece by piece so you can use QuickCheck with confidence. * Monads made difficult (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) This is a short, fast and analogy-free introduction to Haskell monads derived from a categorical perspective. This assumes you are familiar with Haskell and basic category theory. * Constraint kinds (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) In this blog post, I will show some examples of using the ConstraintKinds GHC extension. Classes and contexts were not first-class citizens in Haskell, but the introduction of the Constraint kind has changed this and allows them to be used as parameters of types. * Expressive types, not oppressive types (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) Uncle Bob looks at advanced type systems and sees them as more oppressive rather than more expressive. Being able to describe whether or not a function can return null is an opportunity, not a constraint. * LiquidHaskell (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) LiquidHaskell (LH) refines Haskell’s types with logical predicates that let you enforce critical properties at compile time. ** Package of the week ------------------------------------------------------------ This week’s package of the week is dump-core (http://news.us10.list-manage.com/track/click?u=49a6a2e17b12be2c5c4dcb232&id…) , a GHC plugin for rendering Core. Send us a message on Twitter (http://news.us10.list-manage2.com/track/click?u=49a6a2e17b12be2c5c4dcb232&i…) to nominate next week’s package! ============================================================ Copyright © 2017 Haskell Weekly, All rights reserved. You are receiving this email because you opted in at our website haskellweekly.news. Our mailing address is: Haskell Weekly 13140 Coit Rd Ste 405 Dallas, TX 75240 USA Want to change how you receive these emails? You can ** update your preferences (http://news.us10.list-manage.com/profile?u=49a6a2e17b12be2c5c4dcb232&id=ffb…) or ** unsubscribe from this list (http://news.us10.list-manage.com/unsubscribe?u=49a6a2e17b12be2c5c4dcb232&id…) Email Marketing Powered by MailChimp http://www.mailchimp.com/monkey-rewards/?utm_source=freemium_newsletter&utm…

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Approaches for a DSL for API-level testing
by Damian Nadales 19 Jan '17

19 Jan '17

Hello, I'm writing an embedded DSL for API level testing. The idea in a nutshell is that I can write tests like the following one: createProjectCreates = do p <- createProject "foobar" ps <- getProjects ps `shouldContain` p Here http://stackoverflow.com/questions/41740658/separating-concerns-in-a-dsl-us… I show a sketch of the solution I'm working on, and the issues I'm running into. I wonder whether there are other approaches to embedded DSL writing in Haskell that allows for a better compositionality and separation of concerns. Thanks! Damian.

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[ANNOUNCE] Glasgow Haskell Compiler 8.0.2 is available!
by Ben Gamari 18 Jan '17

18 Jan '17

=============================================== The Glasgow Haskell Compiler -- version 8.0.2 =============================================== The GHC team is happy to at last announce the 8.0.2 release of the Glasgow Haskell Compiler. Source and binary distributions are available at http://downloads.haskell.org/~ghc/8.0.2/ This is the second release of the 8.0 series and fixes nearly two-hundred bugs. These include, * Interface file build determinism (#4012). * Compatibility with macOS Sierra and GCC compilers which compile position-independent executables by default * Compatibility with systems which use the gold linker * Runtime linker fixes on Windows (see #12797) * A compiler bug which resulted in undefined reference errors while compiling some packages (see #12076) * A number of memory consistency bugs in the runtime system * A number of efficiency issues in the threaded runtime which manifest on larger core counts and large numbers of bound threads. * A typechecker bug which caused some programs using -XDefaultSignatures to be incorrectly accepted. * More than two-hundred other bugs. See Trac [1] for a complete listing. * #12757, which lead to broken runtime behavior and even crashes in the presence of primitive strings. * #12844, a type inference issue affecting partial type signatures. * A bump of the `directory` library, fixing buggy path canonicalization behavior (#12894). Unfortunately this required a major version bump in `directory` and minor bumps in several other libraries. * #12912, where use of the `select` system call would lead to runtime system failures with large numbers of open file handles. * #10635, wherein -Wredundant-constraints was included in the -Wall warning set A more detailed list of the changes included in this release can be found in the release notes, https://downloads.haskell.org/~ghc/8.0.2/docs/html/users_guide/8.0.2-notes.… Please note that this release breaks with our usual tendency to avoid major version bumps of core libraries in minor GHC releases by including an upgrade of the `directory` library to 1.3.0.0. Also note that, due to a rather serious bug (#13100) affecting Windows noticed late in the release cycle, the Windows binary distributions were produced using a slightly patched [2] source tree. Users compiling from source for Windows should be certain to include this patch in their build. This release is the result of six months of effort by the GHC development community. We'd like to thank everyone who has contributed code, bug reports, and feedback to this release. It's only due to their efforts that GHC remains a vibrant and exciting project. [1] https://ghc.haskell.org/trac/ghc/query?status=closed&milestone=8.0.2&col=id… [2] http://downloads.haskell.org/~ghc/8.0.2/0001-SysTools-Revert-linker-flags-c… How to get it ~~~~~~~~~~~~~ Both the source tarball and binary distributions for a wide variety of platforms are available at, http://www.haskell.org/ghc/ Background ~~~~~~~~~~ Haskell is a standardized lazy functional programming language. The Glasgow Haskell Compiler (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. Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, can be found on the GHC wiki http://ghc.haskell.org/trac/ghc/wiki/Platforms 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 getting started with hacking on GHC are available from GHC's developer site, http://ghc.haskell.org/trac/ghc/ Community Resources ~~~~~~~~~~~~~~~~~~~ There are mailing lists for GHC users, develpoers, and monitoring bug tracker activity; 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-devs 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 the #ghc and #haskell of the Freenode IRC network, 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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Re: [Haskell-cafe] Control.Parallel seemingly randomly behaviour
by Johannes Waldmann 18 Jan '17

18 Jan '17

Hi Juan, I am interested in this because I use Control.Parallel in teaching currently. But - * what is your actual Main program / main function (it was not included in your message?) * what is your actual cabal / stack config file? * on what machine (OS, CPU) are you running this (it seems pretty slow)? * have you looked at eventlogs with threadscope? - J.

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Yesod devel issue: cannot satisfy -package-key main
by Geraldus 18 Jan '17

18 Jan '17

Hi folks! I haven't used Yesod quite a while; now when I'm trying to run development server of freshly scaffolded PostgreSQL stack's template I see this error message: Rebuilding application... (using cabal) Starting development server... *<command line>: cannot satisfy -package-key main* (use -v for more information) Exit code: ExitFailure 1 I've found several issues on the web, however I wasn't able to resolve this. I've tried to upgrade my Yesod binary first via `stack install yesod-bin`. Now I have: stack exec yesod version *yesod-bin version: 1.4.18.7* stack --version *Version 1.1.2 x86_64 hpack-0.14.0* I also tried to comment out the test suite section in cabal file, but devel server still fails to run. Can someone clarify how to deal with this?

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Re: [Haskell-cafe] Hyper-recursion?
by Olaf Klinke 18 Jan '17

18 Jan '17

If I may step into this discussion, I'd like to suggest you start modelling your world of parcels more concretely, as data types. From there it should be easier to grasp our hyper-recursion. Question: Does every parcel have its own time, or is there a universal clock ticking in the background? If you have a uiversal clock, you could model your world as a linear series of state changes, stretching infinitely into the past and future. Hence two streams going out form a "now" would be the overarching data type. This has been used e.g. for doubly linked lists. Doesn't functional reactive programming use a similar model? Question: How does one identify a parcel of land? Is it a polygon of coordinates in some reference system? Hence can the state be seen as a finite set of (Polygon,Owner) pairs? Question: What is more important: The state or the state change? If the state is more important, a kind of graph might be the appropriate data structure. If the change is important, it might be interesting to model the world (and time) as a network of functions. Question to all mathematicians on this list: Suppose (again assuming a universal clock) there is a type (a set?) X and a function change :: Integer -> (X -> X) where the state of "now" is to be understood as the value now = change 0 . change (-1) . change (-2) . {...ad infinitum} Under which circumstances does this determine the value of "now"? The only instance I can think of are contractions on a (compact) metric space. (Brouwer's/Banach's fixed point theorems) I second the contributors who suggest that this has not much to do with recursion nor corecursion. To me, the essence of recusion is self-reference. A function building e.g. an infinite stream from a seed is not self-referential in itself, it is the resulting data that is self-referential. Olaf

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