February 2015 - Haskell-Cafe

Composition and type magic
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 24 Feb '15

24 Feb '15

Hi everyone, I defined a function for discrete convolution, i.e conv xs = sum . zipWith (*) xs . reverse And I was wondering, can it be done without explicitly passing in the xs (eta-reduction)? I've seen people play with (.).(.) and foldl foldl foldl and was thinking that maybe something similar might be used here. -- Regards Sumit Sahrawat

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7 PhD studentships in Nottingham
by Graham Hutton 24 Feb '15

24 Feb '15

Dear all, The School of Computer Science in Nottingham is advertising 7 fully-funded PhD studentships for "home" students (or EU students who have been ordinarily resident in the UK for 3 years prior to the start of the programme). Applicants in the area of the Functional Programming lab (fp.cs.nott.ac.uk) are encouraged! If you are interested in applying, please contact a potential supervisor in the FP lab prior to submitting your application: Venanzio Capretta - type theory, mathematical logic, corecursive structures, proof assistants, dependently-typed programming. Henrik Nilsson - functional reactive programming, modelling and simulation, domain-specific languages, probabilistic languages. Thorsten Altenkirch and Graham Hutton - not planning to take on any further new PhD students this year. Best wishes, Graham +-----------------------------------------------------------+ 7 Fully-Funded PhD Studentships School of Computer Science University of Nottingham, UK http://www.nottingham.ac.uk/jobs/currentvacancies/ref/SCI1433 Applications are invited for up to 7 fully-funded PhD studentships for "home" students (or EU students who have been ordinarily resident in the UK for 3 years prior to the start of the programme) in the School of Computer Science at the University of Nottingham, starting on 1st October 2015. The topics for the studentships are open, but should relate to the interests of one of the School's research groups: Agents Lab; Automated Scheduling, Optimisation and Planning; Computer Vision Lab; Functional Programming Lab; Intelligent Modelling and Analysis; Mixed Reality Lab; Networked Systems. The studentships are for three years, include a stipend of Â£13,863 per year and tuition fees, and are available to students who qualify as "home" applicants in terms of their fee status. Applicants are normally expected to have a first-class Masters or Bachelors degree in Computer Science or a related discipline, and must obtain the support of a potential supervisor in the School prior to submitting their application. Initial contact with supervisors should be made at least two weeks prior to the closing date for applications. Applications should be submitted via the postgraduate applications website: http://www.nottingham.ac.uk/pgstudy/apply/apply-online.aspx. As part of your personal statement, please include an outline research proposal (max 1 page). Informal enquiries may be addressed to Christine.Fletcher(a)nottingham.ac.uk. Closing date for applications: Tuesday 31st March 2015 +-----------------------------------------------------------+ 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 send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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how can I do this the best
by Roelof Wobben 24 Feb '15

24 Feb '15

Hello, Im busy with a programm which translates log files to another format. I also have to look if the lines in the old one have the rigtht format. Schould I check the format and also if another field contains a I, E or W. Or schould I do the checking in one clause and make another case on the rest ? Roelof

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The Future of Community.Haskell.Org
by Gershom B 23 Feb '15

23 Feb '15

This message is intended to kick off a discussion on the state of the Community.Haskell.Org server and possible future plans. Included below is the text of a blog post on the infra blog ( https://blog.haskell.org/post/the_future_of_community_haskell_org/) We would especially like input and feedback from those who use or rely on any community.haskell.org services or accounts. We don't want to leave you in the lurch, and want to make sure that you feel your needs can be taken care of smoothly, even as we look to wind things down. Feedback is welcome via email (to admin(a)h.o) as a post on the blog, or via the reddit discussion ( http://www.reddit.com/r/haskell/comments/2wwc42/the_future_of_communityhask… ) - - - Community.haskell.org is a server in our ecosystem that comparatively few know about these days. It actually was, to my knowledge, a key part of how the whole haskell.org community infrastructure got set up way back when. The sparse homepage still even says: "This server is run by a mysterious group of Haskell hackers who do not wish to be known as a Cabal, and is funded from money earned by haskell.org mentors in the Google Summer-of-Code programme." At a certain point after this server was created, it ceased to be run by a "mysterious group of Haskell hackers" and instead became managed officially by the haskell.org Committee that we know today. You can see the original announcement email in the archives <https://mail.haskell.org/pipermail/haskell/2010-November/022375.html>. The community server, first set up in 2007 <https://mail.haskell.org/pipermail/haskell/2007-June/019592.html> played a key role back before the current set of cloud-based services we know today was around. It provided a shared host which could provide many of the services a software project needs -- VCS hosting, public webspace for documentation, issue trackers, mailing lists, and soforth. Today, the server is somewhat of a relic of another time. People prefer to host projects in places like github, bitbucket, or darcs hub <http://hub.darcs.net/>. Issue trackers likewise tend to be associated with these hosts, and there are other free, hosted issue trackers around as well. When folks want a mailing list, they tend to reach for google groups. Meanwhile, managing a big box full of shell account has become a much more difficult, riskier proposition. Every shell account is a security vulnerability waiting to happen, and there are more adversarial "scriptkiddie" hackers than ever looking to claim new boxes to spam and otherwise operate from. Managing a mailman installation is likewise more difficult. There are more spammers out there, with better methods, and unmaintained lists quickly can turn into ghost towns filled with pages of linkspam and nothing but. The same sad fate falls on unmaintained tracs. As a whole, the internet is a more adversarial world for small, self-hosted services, especially those whose domain names have some "google juice". We think it would be good to, to the extent possible, get out of the business of doing this sort of hosting. And indeed, very few individuals tend to request accounts, since there are now so many nicer, better ways of getting the benefits that community.haskell.org once was rare in providing. So what next? Well, we want to "end of life" most of community.haskell.org, but in as painless a way as possible. This means finding what few tracs, if any, are still active, and helping their owners migrate. Similarly for mailing lists. Of course we will find a way to continue to host their archives for historical purposes. Similarly, we will attempt to keep source repositories accessible for historical purposes, but would very much like to encourage owners to move to more well supported code hosting. One purpose that, until recently, was hard to serve elsewhere was in hosting of private darcs repositories with shared access -- such as academics might use to collaborate on a work in project. However, that capability is now also provided on http://hub.darcs.net. At this point, we can't think of anything in this regard that is not better provided elsewhere -- but if you can, please let us know. On webspace, it may be the case that a little more leniency is in order. For one, it is possible to provide restricted accounts that are able to control web-accessible files but have no other rights. For another, while many open source projects now host documentation through github pages or similar, and there are likewise many services for personal home pages, nonetheless it seems a nice thing to allow projects to host their resources on a system that is not under the control of a for-profit third party that, ultimately is responsible to its bottom line and not its users. But all this is open for discussion! Community.haskell.org was put together to serve the open source community of Haskell developers, and its direction needs to be determined based on feedback regarding current needs. What do you think? What would you like to see continued to be provided? What do you feel is less important? Are there other good hosted services that should be mentioned as alternatives? And, of course, are you interested in rolling up your sleeves to help with any of the changes discussed? This could mean simply helping out with sorting out the mailman and trac situation, inventorying the active elements and collaborating with their owners. Or, it could mean a more sustained technical involvement. Whatever you have to offer, we will likely have a use for it. As always, you can emailadmin(a)h.o or hop on the #haskell-infrastructure freenode channel to get involved directly. Cheers, Gershom

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GHC 7.10 will use Plan FTP
by Simon Peyton Jones 23 Feb '15

23 Feb '15

Colleagues You will remember (see this email<https://mail.haskell.org/pipermail/libraries/2015-February/024925.html>) that the Haskell community has been engaged in a debate about proposed changes to the Haskell Prelude, the Plan-List or Plan-FTP debate<https://ghc.haskell.org/trac/ghc/wiki/Prelude710>. We decided to hold an open survey to get feedback from the community. Simon Marlow and Simon PJ were asked to make a decision in the light of that feedback. The survey closed on 21 Feb, so it's time to decide. Bottom line: we recommend Plan FTP. There are strong arguments in both directions. For the record, our own personal instincts were both in the conservative, Plan List direction. But the survey gave some pretty compelling feedback, and was far more unequivocal than we expected. Some details * Over 800 people participated in the survey. That's a lot for an 11-day window. Many wrote several paragraphs of supporting information. Thank you for participating so actively! * Overall, 82% of respondents were in favour of FTP, a 4:1 majority. Simon and I found this level of unanimity quite surprising - and it made our task much easier. We clearly under-estimated the Haskell community's appetite for absorbing change when they approve of the direction of travel. * Herbert helped us by doing a rough categorisation into hobbyist/non-hobbyist responses. o The first interesting fact is that there were a lot of non-hobbyist responses: in fact a majority (58%) of the responses were from non-hobbyists. So increasingly people are using Haskell for real work. o The support for Plan FTP among hobbyists was overwhelming (over 87%). But it was still very strong indeed among non-hobbyists (over 79%). Caveat: time was short, so the hobby/non-hobby categorisation is extremely approximate. But since the results are so unambiguous, even the crude results are helpful. * We tried filtering out responses that were blank in the name field and both text boxes. The 82% majority did not budge. What happens now * GHC 7.10 will embody Plan FTP. * The Core Libraries committee, freshly energised and informed by this episode, is drafting new guidelines to clarify what it does, and how it works; and to help avoid a repetition of the recent drama. * The responses. In the survey we said "We won't publish either textual responses or personally-identifying information without your consent. The full responses will be made available only to a limited few." However, the English-language comments are a remarkable snapshot of the Haskell community, and it would be a shame to discard them without deeper study. We propose to make them available to the Core Libraries Committee, to inform their future choices. If anyone else wants to digest the comments into a summary report, we think that would be a service to the community, and (in our view, provided they are a reputable person etc) would fall under the "available to a limited few" rubric. If that appeals to you, write to us. If you object even to such limited sharing, write to us too. This wasn't an entirely easy process, especially because it happened so late in the release cycle. But although many people felt quite strongly about List vs FTP, the whole debate has involved light rather than heat; people have concentrated on the technical issues, rather than yelling. Overall, it's been very encouraging to see the resilience, transparency, and constructive tone of the community. We really appreciate that - thank you. Simon Marlow and Simon Peyton Jones

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Re: [Haskell-cafe] how can I do this the best
by Roelof Wobben 23 Feb '15

23 Feb '15

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Re: [Haskell-cafe] how can I do this the best
by Roelof Wobben 23 Feb '15

23 Feb '15

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Haskell implementation of longest path algorithm
by Jeremy 23 Feb '15

23 Feb '15

Compared to the Nim code [https://github.com/logicchains/LPATHBench/blob/master/nim.nim] for a longest path algorithm, Haskell [https://github.com/logicchains/LPATHBench/blob/master/hs.hs] looks horrendously verbose and ugly, even if you ignore the pragmas and imports. Is this idiomatic Haskell style? Could it be clearer, but has to be written that way for performance - although it still takes 3.7x as long as the Nim version [https://github.com/logicchains/LPATHBench/blob/master/writeup.md]? I posted this to the beginners group last week, but no reply, so trying again here. -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-implementation-of-longest-path… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: Lambdabot 5.0
by Bertram Felgenhauer 22 Feb '15

22 Feb '15

Dear Haskell users, after a long hiatus, I'm pleased to announce that we have just released Lambdabot 5.0 on hackage. Lambdabot is an IRC bot that can also be used offline; it provides tools for querying information about and even for producing Haskell code. To install it, use the following command: cabal install lambdabot-haskell-plugins lambdabot (cabal install lambdabot *should* work, but instead seems to send cabal's dependency solver onto a wild goose chase from which it fails to return.) * What's new Lambdabot is now maintained by a team, currently consisting of James Cook and me. The repository and bugtracker have moved to https://github.com/lambdabot/lambdabot The most significant change compared to lambdabot 4.3 is that lambdabot has been refactored and split into multiple packages. As a result, lambdabot has become easier to customize: simply edit the source files (Main.hs and Modules.hs) in the lambdabot package, and optionally add your own plugins. Other notable changes include - The code snippets provided by @src have been updated. (thanks to Artyom) - Support for IRC server authentication. - Pinging the IRC server regularly in order to detect one-sided disconnects. There have also been many minor tweaks and bug fixes. * What's next There are still a number of open issues on the bugtracker, so you can expect another release soon. Have fun with lambdabot, Bertram and James

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Looking for a new release manager for cabal
by Johan Tibell 22 Feb '15

22 Feb '15

(bcc: haskell-cafe) Hi, After about 3 years of cabal releases I'm looking for someone else to take over the responsibility as cabal release manager. As a release manager I try to keep on top of pull requests, make releases, and make sure bugs get triaged and bugfixes get release. Anyone interested? -- Johan

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