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Applicative banana brackets
by martin 14 Dec '15

14 Dec '15

Hi, while learning about all the type classes and their relationships I came across something I found weird. If I understand it correctly, banana brackets where originally developed for Applicatives. The intent was to enable us to write something like (| (\a b c -> a + b + c), [3], [1,2], [5,0,7] |) and have it translated to liftA3 (\a b c -> a + b + c) [3] [1,2] [5,0,7] or alternatively, to allow us to write something like (| (pure $ \a b c -> a + b + c), [3], [1,2], [5,0,7] |) and have it translated directly to pure (\a b c -> a + b + c) <*> [3] <*> [1,2] <*> [5,0,7] A variant of banana brackets is implemented in ghc, but only for Arrows as part of -XArrowSyntax. Arrows are just the intersection of Applicative and Category, so this implementation seems to be a specialization. What's worse, I don't think -XRebindableSyntax extends to banana brackets. But why? Is it hard to have the notation work with both? (After all, the relationship between Arrows and Applicatives is not easily expressed in Haskell.) Was the demand for (Applicative) bananas not big enough? Is it just a relic? And more to the point: I have not looked at the ghc code base at all yet, but it's on my bucket list to hack on it one day. Right now, a generalization of banana brackets seems like a simple enough low pressure first project, but I fear that it might break code or that there is some pitfall I'm not seeing. Can anybody shed a bit of light on this? Thanks and cheers, Martin L. P.S.: If the list receives this mail several times, I apologize. The list management tool seems to be confused by gmail vs. googlemail. That's what you get for using non-Haskell software. ;)

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[NL-FP 2016] Final CFP: Dutch Functional Programming Day 2016
by Atze Dijkstra 14 Dec '15

14 Dec '15

[My apologies for multiple received copies of the same message] Final Call for Participation: Dear all, The next Dutch Functional Programming day (NL-FP 2016) will be held on Friday, January 8, 2016 at the Utrecht University, The Netherlands. The program of the day now is online (see the below webpage). At the end of the day we will have a joint dinner. Besides the program, on the web page http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome <http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome> for the day you’ll also find the registration, which is by letting me know via email (with a subject header that begins with [NL-FP 2016]) whether you want to (1) participate, (2) join dinner, also see the webpage for additional details. There is still room for a demo or poster during lunch/break time. If you intend to participate, please let me know before the end of this year because we like to know how many people we can expect. Hope to meet you all in Utrecht at the next FP Day! Best regards, - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze <http://www.cs.uu.nl/~atze> . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)uu.nl <mailto:atze@uu.nl> ............... / |___\

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Problem running the ping example from "Parallel and Concurrent Programming in Haskell"
by s nedunuri 13 Dec '15

13 Dec '15

hello I am trying out the examples in Chapter 14 of the book, and was able to install and build the parconc-examples package fine. However when I try running the (very first example) ping program I get the following error: ping.exe: bind: failed (Cannot assign requested address (WSAEADDRNOTAVAIL)) It appears that the failure is in the main function: distribMain (\_ -> master) Main.__remoteTable Any ideas? thanks PS I am running Haskell Platform 7.10.2-a on Windows 7

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ANNOUNCE: bank-holidays-england: Calculation of bank holidays in England and Wales
by David Turner 12 Dec '15

12 Dec '15

Hi all, A very belated announcement of a little library that implements the frankly daft rules for calculating the dates of bank holidays in England and Wales. With apologies to the Welsh for the abbreviated package name, and to the Scots for not including yours too. http://hackage.haskell.org/package/bank-holidays-england Comments and feature requests are most welcome. Cheers, David

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ANNOUNCE: alarmclock-0.2.0.8: wake up at a certain time
by David Turner 12 Dec '15

12 Dec '15

Hi all, A very belated announcement of a little library for efficiently waking up at a certain time. I've found this useful for things like timeouts, scheduling retries, cache expiry and so on. Not a lot to say, really, it does what it says on the tin! http://hackage.haskell.org/package/alarmclock Comments and feature requests are most welcome. Cheers, David

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[ANNOUNCE] Glasgow Haskell Compiler version 7.10.3
by Ben Gamari 11 Dec '15

11 Dec '15

Hello everyone, We are pleased to announce the release of GHC 7.10.3: https://downloads.haskell.org/~ghc/7.10.3/ There can be found source tarballs and binary distributions for 64-bit and 32-bit modern Linux (GMP 5.0 or later), CentOS (GMP 4.0), Windows, and 64-bit Mac OS X platforms. These binaries and tarballs have an accompanying SHA256SUMS file signed by my GPG key id (0x97DB64AD). Significant fixes in release include changes to the simplifier's treatment of rules, the handling of Mac OS X frameworks, and support for response files to work around the restrictive command line length limit on Windows. As always, a full accounting of the changes present in this release can be found in the release notes [1]. The previous release, 7.10.2, was well-behaved save a couple notable bugs; while we have merged a good number of bug fixes in 7.10.3 they were were largely low risk and so we expect that this release should be similiarly stable. A notable exception is the upgrade of the Windows compiler toolchain to GCC 5.2. Typically we would refrain from making such large changes in a point release but Windows users have been long suffering at the hand of the old toolchain (e.g. lack of response file support, #8596, and lack of SEH support). We expect that this change should fix far more than breaks. Unfortunately, due to some oversights in the release process there are two source tarballs for this release. The first, ghc-7.10.3-src.tar.{bz2,xz}, does not include the release notes in the users guide. This is fixed in the second patchlevel release, ghc-7.10.3a-src.tar.{bz2,xz}. It is recommended that users wanting a source release use the ghc-7.10.3a-src tarballs. GHC 7.10.3 will very likely be the last release in the GHC 7 series. In the coming weeks we will be beginning the release process for GHC 8.0, which will include a number of exciting features including the merger of kinds with types, injective type families, imporved DWARF debugging information, applicative-do syntax, a Strict language extension synonyms mechanism, and more. See the GHC 8.0.1 status page for details [2]. Happy compiling! Cheers, - Ben [1] http://downloads.haskell.org/~ghc/7.10.3/docs/html/users_guide//release-7-1… [2] https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-8.0.1

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Audio search library; and debugging help!
by Richard Lewis 11 Dec '15

11 Dec '15

Hi there, For a little while I've been working on an audio search library. It wraps over a C++ library written by some of my colleagues. It's nearing the state where someone other than me might actually be able to use it. So this message is partly an annoucement: <https://github.com/TransformingMusicology/libaudioDB-haskell> I'd be very interested to hear if anyone has a go at installing it and running the "tests". But this message is also a request for help, because I'm actually stuck with a bug. I've created a fork of the above repo here: <https://github.com/ironchicken/libaudioDB-haskell> which includes an extra commit which adds quite a few tracing statements. So if anyone feels up to trying to help me with my bug, then this would be the repo to use. The bug goes something like this: One of the features I need to implement is so-called "query rotation". The library implements audio feature searching. For some kinds of multi-dimensional audio features, it's useful to execute queries with them repeatedly moving the values between the dimensions each time to get a kind of exhaustive search. As a specific example (and for those who know a little music theory), there's a feature known as chroma which gives a measure of the signal energy in each of the 12 pitch classes for each window in the audio. If you search with a vector of chroma features, you will only find results that are at exactly the same pitch. But if you shift the chroma search vector around 11 times, you can effectively search for the query vector in every transposition (that's "transposition" as in to transpose in music theory). Anyway, I've tried to capture this in the library by allowing a call to the Sound.Audio.Database.Query.query function to include a QueryTransformer, which is essentially a function which takes a query and returns a new query. And then one instance of this is the function S.A.D.Query.mkSequenceQueryWithRotation which uses another helper function, S.A.D.Query.mkSequenceQueryMutateDatum. This function takes a Ptr to a query, and scribbles over the memory to replace its contents with an altered query vector: the result of some mutation function. Now, what originally alerted me to there being anything wrong with this was that, when I execute a rotated query, I'm getting exactly the same results as for a non-rotated query. As I started investigating, the first thing I found was that the altered feature vectors were not being altered in the way I expected. If I printed them and traced the path of a single value, it wasn't moving step-wise between the bins, but instead jumping around between them randomly. I eventually put in enough putStrLn and trace calls to find that, I think, each time the query is transformed, instead of doing just one transformation, it does as many transformations as times it has iterated: i.e., first iteration it does one transformation, second iteration it does two transformations, and so on. The recursive (sort of iterative?) query transformation is implemented in S.A.D.Query.queryWithTransformPtr. But I'm now at a loss to say whether there's anything actually wrong with this function. So, I think this is the end of my message. I appreciate that this is a very specific problem. I know it's normally helpful to try and abstract a problem into something in terms of Foos and Bars, but I'm not sure I can do this here. As a result, it would be a significant undertaking for anyone to try and help out. So I would be even more grateful than usual if anyone could! (And that's not really meant as a grovelling plea, it's actually more of a warning: you probably shouldn't try and help me.) Thanks, Richard -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Richard Lewis Computing, Goldsmiths' College t: +44 (0)20 7078 5203 @: lewisrichard http://www.transforming-musicology.org/ 905C D796 12CD 4C6E CBFB 69DA EFCE DCDF 71D7 D455 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

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Darcs Hacking Sprint #10 (January 15th-17th, Seville)
by Guillaume Hoffmann 10 Dec '15

10 Dec '15

Dear Hackers I'm glad to announce that the 10th Darcs Sprint that will be in Seville, on January 15-17 at the ETS de Ingeniería Informática, Universidad de Sevilla. Please check the details at: http://darcs.net/Sprints/2016-01 Here are three things to know 1. Everybody is welcome to join us. We'd love to have you, whatever your Haskell or Darcs hacking experience. Also, if you've got a wacky idea for the future of version control, or a cool use for the Darcs library, you should join us too :-) 2. Please let us know if you're attending: * add your name to http://wiki.darcs.net/Sprints/2016-01 * send me (privately) your full name and some official identification number for access to the university on Saturday and Sunday. 3. We can reimburse travel costs (within reason!). Let us know if you'd like a reimbursement, and save your receipts. Many thanks to everybody who participated in our fundraising drives or who gave money on the side. Thanks also to the Software Freedom Conservancy for making fundraising and reimbursements so painless! If you can't join us in person, but you'd like to cheer us on, say hello at http://darcs.net/Donations ! see you in one month! Guillaume

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Looking for maintainers for emacs-haskell-tutorial
by Alejandro Serrano Mena 10 Dec '15

10 Dec '15

Dear Haskell-Café, Some time ago, and as part of my Google Summer of Code project, I wrote a tutorial about setting up Emacs to work with Haskell [ https://github.com/serras/emacs-haskell-tutorial/blob/master/tutorial.md] The tutorial is now a bit outdated and several issues are pending solution [ https://github.com/serras/emacs-haskell-tutorial/issues] However, due to other (young, crying) obligations I don't have the time needed to maintain the tutorial anymore, all by myself. Thus, I would like to ask whether somebody is willing to maintain the tutorial up-to-date, and take care of the issues. Or simply, whether somebody is willing to help in doing so. Regards, Alejandro

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setting up property tests
by Michael Litchard 10 Dec '15

10 Dec '15

I've got a little project, based off of fizzbuzz, that I would like to write property tests for using either QuickCheck or SmallCheck. Could someone have a look at https://github.com/mlitchard/fizzbuzzfib/blob/master/src/FizzBuzz.hs and help me sort out how to write property tests?

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