September 2007 - Haskell

Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 07 Apr '11

07 Apr '11

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

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Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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The real Monad Transformer
by Henning Thielemann 13 Nov '08

13 Nov '08

It was argued that people avoid Haskell because of terms from Category theory like 'Monad'. This problem can now be solved by a wrapper which presents all the WWW without monads! Start e.g. at http://saxophone.jpberlin.de/MonadTransformer?source=http%3A%2F%2Fwww%2Ehas… Of course the tool is written in Haskell, that is, Haskell helps solving problems which only exist because of Haskell. Bug reports and feature requests can be tracked at https://sourceforge.net/projects/parallelweb

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Seemingly impossible Haskell programs
by Graham Hutton 29 Sep '07

29 Sep '07

Readers of this list may enjoy the following note by Martin Escardo, which shows how to write a number of "seemingly impossible Haskell programs" that perform exhaustive searches over spaces of infinite size, by exploiting some ideas from topology: http://math.andrej.com/2007/09/28/seemingly-impossible-functional-programs/… Have fun! Graham +-----------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | School of Computer Science | | University of Nottingham Web : www.cs.nott.ac.uk/~gmh | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB, UK Phone : +44 (0)115 951 4220 | +-----------------------------------------------------------------+ 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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ANNOUNCE: mpd-0.1 library
by Ben Sinclair 28 Sep '07

28 Sep '07

Hello, I am pleased to announce the first release of mpd, a client protocol implementation for MPD*. Hackage page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mpd-0.1 API ref: http://turing.une.edu.au/~bsinclai/code/libmpd-haskell/dist/doc/html/mpd/ -Ben * http://www.musicpd.org/

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Job programming in F#
by Simon Peyton-Jones 27 Sep '07

27 Sep '07

Want to be paid to write functional programs? My colleagues here at Cambridge are looking for you. See below. Simon A position has arisen within our Applied Games Team in Cambridge for a Software Development Engineer (SDE). The role of the SDE will be to design, implement and maintain solutions based on new technology in the very competitive web search and advertising arena. In this position you will be working closely with researchers to analyze very large data sets, and with product teams to have the research applied. Please see job description attached for full details. Any machine learning or functional programming experience (particularly F#) is highly desirable, however not essential as training will be provided for the right candidate. Background: We are establishing a virtual team for applied research between adCenter's Research & Mining group and Microsoft Research Cambridge's Applied Games group. The mission of the team is to conduct applied research into problems relevant for Microsoft's online advertisement business and to transfer resulting technology to adCenter. 1. Design, implement and maintain solutions. 2. Assist researchers to analyze data and provide rapid prototypes for new technology. 3. Transferring technology to product teams. Knowledge, Skills and Experience 1) Essential Experience * Three years SQL Server Programming experience. * Three years .Net Programming experience. 2) Technical / Functional Skills * Knowledge of SQL programming. * Knowledge of C# and .Net programming. * Experience with Agile methods 3) Personal Attributes / Interpersonal Skills * Good communication skills ideally with some client facing experience. * Self-motivated. * Willingness to travel. * Interest in cutting edge research Special Requirements/Additional Information Must be willing to live and work in the UK; but also be prepared to travel frequently to the US. Any machine learning or functional programming experience particularly F# is highly desirable but not essential as training will be provided for the right candidate. To apply please send your current curriculum vitae (CV) to our Human Resources Department by email: cambhr(a)microsoft.com

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Re: [Haskell-cafe] PROPOSAL: Rename haskell@ to haskell-announce@
by Claus Reinke 25 Sep '07

25 Sep '07

[cc-ed to haskell@, as this discussion is about haskell@] > There are four things sent to the haskell list@ > > 1) Calls for papers > 2) Annoucements > 3) Oleg's stuff (which are really announcements of a library or technique) > 4) Off topic stuff > > I'm initially only proposing to mop up category 4, which I am pretty > sure the haskell@ people don't want to see. i still keep all haskell[-cafe] email in one folder, and tend to reply on the list a post comes from;-) but iirc, those who proposed the split were not looking for a pure announcement list: (*) the idea was to have a low-traffic window into all haskell developments of wider interests, while also establishing a free-form forum for general discussion/newbie questions. so everything that would be of interest to all haskellers, including those too busy to follow haskell-cafe, would go to haskell, everything else would go to haskell-cafe. but even those topics starting out on haskell are meant to migrate to haskell-cafe after a few posts at most. in other words, people were meant to subscribe either to haskell or to haskell+haskell-cafe, and posting to haskell was meant to be a flag able to raise a topic briefly over the general din in haskell-cafe. see also the welcome messages: http://www.haskell.org/mailman/listinfo/haskell http://www.haskell.org/mailman/listinfo/haskell-cafe (note that the second is slightly misleading: *everything* is off-topic on haskell@ after a few exchanges, i think; note also that crossposting was explicitly ruled out) > I did wonder whether this discussion should take place > on the haskell@ list or the haskell-cafe@ one - the great > ambiguity of the lists. this discussion should have started out on haskell@. and since it is entirely about changing haskell@, it probably should have stayed there as well. it is not very helpful to discuss changes to a specific list on another list!-) however, it has become a problem, and i don't know whether everyone on haskell-cafe is really subscribed to haskell as well anymore. so posting announcements only to haskell might miss the majority of haskeller on cafe, the crossposting some have started to resort to is expressly discourage in the haskell-cafe 'charta', newcomers don't know where to post or where to subscribe, threads sometimes linger on haskell@ instead of migrating to haskell-cafe, etc. as i indicated, i wasn't a fan of the split, but it had its merits: the free discussion on haskell-cafe is nice, and the intention of haskell@ as a highlights channel for busy haskellers was understandable, even if it doesn't seem to work any more. if my interpretation of the split intentions (*) is accurate, my proposal to alleviate the current confusion would be: - do not assume everyone is on haskell@ as well - do not prohibit cross-postings anymore, but give clear instructions about when to use them - for most haskellers, haskell-cafe has become the main channel, so do not post only to haskell@ - for most specific discussions, there are specific lists, so there seems little need for haskell@ as a general discussion forum => all posts meant for either haskell or haskell-cafe go to haskell-cafe => threads that are likely to be of interest to everyone on both lists may be highlighted on haskell@, either by crossposting the first (and only the first) email in the thread, or by posting a brief discussion announcement/summary to haskell@ that way, there'd be no confusion about where to post (always haskell-cafe), or whether to crosspost (permitted, but only for thread starters) and no limitation to formal announcements and cfps only (whenever something of wider interest starts on -cafe, interesting techniques or discussions, or events, or announcements, also send a brief invitation to haskell@). and busy haskellers can see on haskell@ whenever there is a thread on haskell-cafe that they might want to read/join. does this sound workable? claus

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downtime for monk ({darcs, hackage, cvs}.haskell.org) Monday from 3pm UTC
by Ian Lynagh 24 Sep '07

24 Sep '07

Hi all, The machine called monk, which serves as darcs.haskell.org hackage.haskell.org cvs.haskell.org haskell.galois.com will be down from 3pm UTC on Monday 24th for an OS and RAM upgrade. If you know of any important services run on the machine other than darcs, CVS, trac, hackage and darcsweb then please let us know. Thanks Ian

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ANN: Haskell S3 Library 0.1
by Greg Heartsfield 24 Sep '07

24 Sep '07

Hello, This is the first release of hS3, a Haskell interface to Amazon's Simple Storage Service. One week from conception to this release, it is still rough around the edges, but the basic functionality does work. Get it from Hackage: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hS3-0.1> A brief writeup with links to documentation and the darcs repo is on my blog: <http://scsibug.com/2007/09/23/haskell-s3-library/> Thanks, Greg Heartsfield

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Math behind Haskell
by Tomas Caithaml 24 Sep '07

24 Sep '07

Hi all. When I was playing with Haskell and reading stuff about it, I noticed that there is a lot of information in a form of research papers and a lot of mathematics involved. I must confess that I quite like this academic approach. Well, I thought that while I am still at university I could take some math classes to help me better understand these things and broaden my horizon. Any suggestion what could be relevant? I came up with: * Lambda calculus - the basis of functional languages * Category theory - where all these mysterious things like monads, arrows, and functors come from. * Topology (?) - don't know; I thought it is important rather in mathematical analysis (which I don't like much) but I have seen somewhere some references to it in context of CS. Any other suggestions? Thanks, Tom.

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