December 2015 - Haskell-Cafe

costate
by Peter Padawitz 31 Dec '15

31 Dec '15

When is cobinding in the costate/funarg/incontext comonad (c -> a,c) (see papers by Kieburtz, Uustalu, Vene, Orchard, Mycroft, …) preferable to (better-known) currying? f <<= (g,x) is equivalent to (curry f g,x) ! HNY, Peter

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Make this code more idiomatic?
by David Turner 31 Dec '15

31 Dec '15

Hi, I'd like to use the Control.Parallel.Strategies machinery to evaluate parts of a big record-based data structure in the background. The following code is the sort of thing that I've ended up with - it makes a spark that forces the actuals field of a user object, in the sense that it forces all of the elements to WHNF. (At least, that's what I hope it's doing!) updateActuals user = runEval $ do newActuals <- rparWith (evalTraversable rseq) $ calculateActuals user return user { actuals = newActuals } However, I'm concerned that runEval is marked as "for Strategy programmers" and that I should be using some collection of combinators instead of dropping down to this level. But I just can't work out how to combine the available combinators to do the same thing. In particular, all the articles I've found about this seem to end up adding `using` something to the end of one key line of code to achieve near-perfect parallelisation, but now that I come to do it myself I'm stuck! I think I'm looking for something like: updateActuals user = user { actuals = newActuals } `using` ... Can anyone help me fill in the blank there? Many thanks, David

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ANN: wxInstall Achelanne and wxHaskell 0.92.2.0
by Henk-Jan van Tuyl 30 Dec '15

30 Dec '15

L.S., I am happy to announce a new version of wxHaskell: 0.92.2.0 and new installation packages for wxHaskell on Windows: wxInstall Achelanne 0.1 (32 bit and 64 bit) Changes in wxHaskell since 0.92.1: - Solved warnings for wxcore, wxdirect, wxc - Added support for Pickerctrl, Hyperlinkctrl and some Streams in wxc and wxcore - Solved several bugs - Added some image Functions in wxc and wxcore - Added enumerateFonts function in wxcore - Updated wxBITMAP_TYPE_ constants - Adapted to GHC 7.10.3 Thanks to everyone who contributed! wxInstall Achelanne[0] is created because GHC 7.10.3 for Windows is accompanied with a newer GCC: 5.2.0. A detailed description can be found at the wxHaskell-for-Windows homepage[1]. What is wxHaskell? ------------------ wxHaskell[2] is a portable and native GUI library for Haskell. The goal of the project is to provide an industrial strength GUI library for Haskell, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore built on top of wxWidgets – a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel. Links ----- See the homepage of wxHaskell for more information: https://wiki.haskell.org/WxHaskell The packages are: - wxc https://hackage.haskell.org/package/wxc - wxdirect https://hackage.haskell.org/package/wxdirect - wxcore https://hackage.haskell.org/package/wxcore - wx https://hackage.haskell.org/package/wx Regards, Henk-Jan van Tuyl [0] http://sourceforge.net/projects/wxhaskell/files/wxInstall/ [1] https://wiki.haskell.org/WxHaskell/Windows#Installing_the_easy_way [2] https://wiki.haskell.org/WxHaskell -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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I need repositories that contain commited erroneous code
by Rick Klomp 30 Dec '15

30 Dec '15

Hi Haskell community, For my master thesis project I need change logs that I can use to derive what changes have been made to fix certain compilation errors. Unfortunately so for me, good repository etiquette is to never commit erroneous code. However, there are bound to be plenty of repos where this etiquette isn't/hasn't been followed (in non-main branches). My question to you is if you currently know or at some point in the near future (new data will be useful until somewhere early summer 2016) come to know of repos that fit the description, could you point me to them? Much appreciated! Or if you are willing to share a personal project with me (where obviously this repo etiquette is much less significant), then that would be immensely helpful to me! I promise to only use the metadata (but you'll have to believe me on my word). Thanks in advance for your help. Best regards, Rick Klomp

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Re: [Haskell-cafe] Preventing sharing
by Oleg 28 Dec '15

28 Dec '15

> -fno-full-laziness fixes the space leak issue in your iterative deepening > example. Yes, and I think it has been mentioned that the flag is a blunt weapon as it affects the whole module... > This isn't a problem with laziness. It's a problem with performing a time > optimization which is a space pessimization. In the absence of the > "optimization" there is no problem. How come it isn't the problem with laziness?! Recall, that pure call-by-name calculus is observationally undistinguishable from the call-by-need (i.e., lazy) calculus. The only reason to have laziness is to avoid recomputations of argument computations should an argument be used more than once -- at the cost of taking memory to store the result of the first evaluation. Thus "performing a time optimization which is a space pessimization" is exactly what laziness is all about -- as the article mentioned earlier argued. Laziness isn't an absolute good -- it is a time-space trade-off, which is not always beneficial.

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[ANN] Flashy-Haskell: Advanced Haskell syntax for Vim
by mwnx 27 Dec '15

27 Dec '15

In case anyone is interested, I just published a syntax extension I use for vim. It adds on to the default "haskell.vim" syntax file and enables some more advanced colouring. Here's the link to the github page, with visual examples: https://github.com/mwnx/flashy-haskell I rewrote the whole thing before publishing so there might be quite a few bugs due to a lack of real world testing, but I'll strive to fix any reported bugs rapidly. It also doesn't seek to completely and perfectly interpret Haskell's syntax. As a result, some of the more unusual syntactic constructs might not benefit from the extra colouring. -- mwnx GPG: AEC9 554B 07BD F60D 75A3 AF6A 44E8 E4D4 0312 C726

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Q: language-c upstream repo
by Ivan Zakharyaschev 26 Dec '15

26 Dec '15

Hello! I've been interested in hacking language-c library a bit for my needs. (If it turns out useful and successful, I'll tell about it.) And I've cloned the repo listed at https://hackage.haskell.org/package/language-c-0.4.7 , namely: http://code.haskell.org/language-c Apart from my special hacks, I've also fixed some typos and so on. But then I discovered that if I want to publish them on hub.darcs.net , I need a darcs-2 repo, and the initial one which I used for cloning is a darcs-1 repo. I could do the conversion to darcs-2, but I read that it is not reproducible: run several times on the same set of patches it will give different results. As I've discovered also a language-c repo at hub.darcs.net which looks like an upstream repo: http://hub.darcs.net/visq/language-c , I'm in doubt whether I should continue making my patches against the darcs-1 repo which is said to be upstream at hackage or against http://hub.darcs.net/visq/language-c whichis not officially declared as the upstream but looks more fresh. ..if I want to be able to send some of my patches upstream. Best regards, Ivan

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ANN: stack-1.0.0
by Emanuel Borsboom 25 Dec '15

25 Dec '15

A Christmas present: we’re calling this version 1.0! This is a minor enhancement and bug fix release, but since Stackage LTS 4 is about to be cut we thought it was time to give Stack a version number that reflects its readiness for production use. Enhancements: - Added flag --profile flag: passed with stack build, it will enable profiling, and for --bench and --test it will generate a profiling report by passing +RTS -p to the executable(s). Great for using like stack build --bench --profile (remember that enabling profile will slow down your benchmarks by >4x). Run stack build --bench again to disable the profiling and get proper speeds - Added flag --trace flag: just like --profile, it enables profiling, but instead of generating a report for --bench and --test, prints out a stack trace on exception. Great for using like stack build --test --trace - Nix: all options can be overriden on command line #1483 <https://github.com/commercialhaskell/stack/issues/1483> - Nix: build environments (shells) are now pure by default. - Make verbosity silent by default in script interpreter mode #1472 <https://github.com/commercialhaskell/stack/issues/1472> - Show a message when resetting git commit fails #1453 <https://github.com/commercialhaskell/stack/issues/1453> - Improve Unicode handling in project/package names #1337 <https://github.com/commercialhaskell/stack/issues/1337> - Fix ambiguity between a stack command and a filename to execute (prefer stack subcommands) #1471 <https://github.com/commercialhaskell/stack/issues/1471> - Support multi line interpreter directive comments #1394 <https://github.com/commercialhaskell/stack/issues/1394> - Handle space separated pids in ghc-pkg dump (for GHC HEAD) #1509 <https://github.com/commercialhaskell/stack/issues/1509> - Add ghci —no-package-hiding option #1517 <https://github.com/commercialhaskell/stack/issues/1517> - stack new can download templates from URL #1466 <https://github.com/commercialhaskell/stack/issues/1466> Bug fixes: - Nix: stack exec options are passed properly to the stack sub process #1538 <https://github.com/commercialhaskell/stack/issues/1538> - Nix: specifying a shell-file works in any current working directory #1547 <https://github.com/commercialhaskell/stack/issues/1547> - Nix: use --resolver argument - Docker: fix missing image message and ‘—docker-auto-pull’ - No HTML escaping for “stack new” template params #1475 <https://github.com/commercialhaskell/stack/issues/1475> - Set permissions for generated .ghci script #1480 <https://github.com/commercialhaskell/stack/issues/1480> - Restrict commands allowed in interpreter mode #1504 <https://github.com/commercialhaskell/stack/issues/1504> - stack ghci doesn’t see preprocessed files for executables #1347 <https://github.com/commercialhaskell/stack/issues/1347> - All test suites run even when only one is requested #1550 <https://github.com/commercialhaskell/stack/pull/1550> - Edge cases in broken templates give odd errors #1535 <https://github.com/commercialhaskell/stack/issues/1535> - Fix test coverage bug on windows

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Re: [Haskell-cafe] Formatting strict Text
by Mark Fine 25 Dec '15

25 Dec '15

I've been using Formatting <http://hackage.haskell.org/package/formatting> recently. Mark On Wed, Dec 23, 2015 at 5:13 PM, fr33domlover <fr33domlover(a)riseup.net> wrote: > Hello, > > I have code which uses Text.Printf.printf with String. Now I'm moving the > code > to use strict Text everywhere (I picked strict since all my strings are > very > short, mostly less than 400 chars). What should I use instead of printf > now? > > One solution I found is the text-format package, which seems to simply > split a > Text on occurences of "{}" and insert values there. Are there other simple > and > efficient options? All I need is to append Text values and sometimes Ints > too, > so it's enough to have > > (1) efficient append and concat > (2) A function that is :: Int -> Text > > Why is strict Text not a Monoid instance? And Builder has no `toStrictText` > function? There is a function to convert Int to Builder and a Buildable > instance for Int, but for a simple Int->Text it seems I'm left with an ugly > `T.pack . show`. > > > Suggestions / advice / comments on this? > > Thanks in advance :) > > fr33 > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > >

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Installation instructions for ghc 7-10-3 on Windows
by Lian Hung Hon 24 Dec '15

24 Dec '15

Dear Haskellers, How can I install just ghc on Windows? Especially with regards to the network package? Before this I used minghc, but the github page says its now dead. Sincerely, Hon

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