April 2007 - Haskell - Haskell.org

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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CfP: 2nd CEFP Functional Programming School, June 23-30, 2007
by HORVATH Zoltan 11 Jun '07

11 Jun '07

2nd Central-European Functional Programming School CEFP 2007 Cluj-Napoca, June 23-30, 2007 http://cs.ubbcluj.ro/cefp2007/ First Announcement - Call for participation - Call for PhD student presentation Aims and Scopes: The Central-European Functional Programming School (CEFP) is an intensive summer school series in the field of functional programming. The main goal is to bring together computer scientists, researchers, graduate and especially PhD students. The school would like to promote the research and the education of the functional programming languages, software technologies and programming methodologies. The second CEFP school will be organized by the Babeş-Bolyai University (Cluj-Napoca / Kolozsvár / Klausenburg) between 23-30 June, 2007. The previous school was held in Budapest, Hungary, July, 2005. The invited lecturers are prominent researchers in the field, and they will present state-of-the-art functional programming techniques. Beside the lectures practical courses will be held. The school includes a workshop for PhD students to present their work and get feed-back from the lecturers. Invited Lecturers: Rinus Plasmeijer (Radboud University Nijmegen, The Netherlands): iTasks: Defining Interactive Workflows for the Web Werner Kluge (Christian-Albrechts-Universität zu Kiel, Germany): Abstract Lambda Calculus Machines Marko van Eekelen (Radboud University Nijmegen, The Netherlands): Proving Properties of Lazy Functional Programs Tim Sheard (Portland State University, USA): The Omega Programming Language Ralf Hinze (Universität Bonn, Germany): Generics Three additional short courses will be given: Zoltán Horváth (Eötvös Loránd University, Budapest, Hungary): Refactoring Erlang Programs Zoltán Csörnyei (Eötvös Loránd University, Budapest, Hungary): Lambda-Calculus Horia F. Pop (Babeş-Bolyai University, Cluj-Napoca, Romania): A Tutorial on Object Orientedness in Functional Programming Submissions: PhD students are invited to submit the abstract of their presentations to be included in the workshop programme. Each presentation can be of max. 25 minutes. The full paper version can be submitted after the summer school. It is under negotiation to publish the revised lectures and the selected and reviewed papers in LNCS Volume. Venue: Cluj-Napoca / Kolozsvár / Klausenburg, formerly the capital of Transylvania, is one of the most beautiful medieval cities with a huge multicultural and historical inheritance. Surrounded by marvelous hills and mountains, the city provides fascinating environment for experiencing the unique ambience of a diversified culture, society and nature. Registration and costs: The registration fee (260 Euro) includes the course materials distributed during the school, the post-school volume, lunches, the excursion and the summer school banquet. For further information, accommodation possibilities and registration please visit the web-page of the event: http://www.cs.ubbcluj.ro/cefp2007. The deadline for registration and submissions is 1 June 2007.

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how to include GHC/Hugs specific module/function?
by Paul L 30 Apr '07

30 Apr '07

What I'm trying to do is something like below, except that #ifdef doesn't really work.. #ifdef __GLASGOW_HASKELL__ import GHC.Prim unsafePtrEq = reallyUnsafePtrEquality# #endif #ifdef __HUGS__ import Hugs.IOExts (unsafePtrEq) #endif Any help is greated appreciated! Regards, Paul Liu

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ANN: The Monad.Reader - Issue7
by Wouter Swierstra 30 Apr '07

30 Apr '07

I am pleased to announce that the latest issue of The Monad.Reader is now available: http://www.haskell.org/haskellwiki/The_Monad.Reader Issue 7 consists of the following four articles: * Matthew Naylor A Recipe for controlling Lego using Lava * Yaron Minsky Caml Trading: Experiences in Functional Programming on Wall Street * Duncan Coutts Book Review: “Programming in Haskell” by Graham Hutton * Dimitry Golubovsky, Neil Mitchell, Matthew Naylor Yhc.Core – from Haskell to Core The Monad.Reader is a quarterly magazine about functional programming. It is less-formal than journal, but somehow more enduring than a wiki page or blog post. If you'd like to submit something to the next issue of The Monad.Reader, please get in touch. I haven't fixed the deadline for the next issue just yet; I hope to send out an official call for copy in the coming weeks. Wouter 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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Newbie: what are the advantages of Haskell?
by phiroc＠free.fr 30 Apr '07

30 Apr '07

Hello, what are the advantages of haskell over semi-functional programming languages such as Perl, Common Lisp, etc.? What are the mysterious "side effects" which are avoided by using Haskell, which everyone talks about? Null pointers? Don't you ever get null pointers in Haskell, including when doing IO? Aren't Haskell's advantages outweighed by its complexity (Monads, etc.) and rigidity? Last but not least, I would like to learn from those among you who are former PERL developers, why you switched to Haskell. Many thanks. phiroc

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ANNOUNCE: photoname
by Dino Morelli 29 Apr '07

29 Apr '07

photoname - rename and move photo files based on EXIF data photoname is a command-line utility for renaming/moving photo image files. The new folder location and naming are determined by two things: the photo shoot date information contained within the file's EXIF tags and the usually-camera-assigned serial number, often appearing in the filename. This software requires Bjorn Bringert's exif binding library to build. (http://www.cs.chalmers.se/~bringert/darcs/haskell-exif/doc/) get photoname: darcs get http://ui3.info/darcs/photoname http://ui3.info/d/proj/photoname.html Binary available as well for Debian i386 users: http://ui3.info/d/proj/photoname/photoname_002-1_i386.deb -- .~. Dino Morelli /V\ email: dino(a)ui3.info /( )\ irc: dino- ^^-^^ preferred distro: Debian GNU/Linux http://www.debian.org

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Re: Newbie: what are the advantages of Haskell?
by Taillefer, Troy (EXP) 28 Apr '07

28 Apr '07

Mike, It has affected my Java/C/C++ programming a lot. 1. I am much more careful how I combine ( inherit, compose, aggregate ) code because of potential side affects 2. It has helped to find certain types of bugs in Java code more easily that come up because of subtle effects introduced by combining code together 3. It has helped me to write code that is more composable 4. Haskell has increased my awareness of how important type safety is So I use Java Generics more now to enforce more type safety when I can (sometimes I am stuck deploying to java 1.4) (I also use C++ templates to do the same thing for C++) But these are often feel like hacks Haskell's type system is a thing of pure beauty haven't seen anything quite like it in any other PL (ML and OCAML are as close as I have seen but still fall short) and Generics and Templates really can't compare You really want the compiler to help you out as much it can. Have it tell you when you are doing something that you shouldn't be doing. By the way Mike thanks you just totally cheered me up I guess I just needed to sit back and think about what I have learned and how valuable it is to me. Troy -----Original Message----- From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of mike clemow Sent: Friday, April 27, 2007 4:16 PM To: haskell(a)haskell.org Subject: Re: [Haskell] Re: Newbie: what are the advantages of Haskell? Troy, As a Java chimp embarking on the Haskell journey myself, I'd be interested in hearing about specific ways that learning Haskell has changed the way you program Java. How do you employ the "very interesting concepts" that you have learned through your study of Haskell in your Java programming? Do you employ them at all? _Can_ they be employed in Java? Has it made you a better Java programmer? Cheers, Mike On 4/27/07, Taillefer, Troy (EXP) <troy.taillefer(a)lmco.com> wrote: > >Admittedly, this is phrased in an inflammatory manner, however, the > original sentiment >>is actually pointing out an advantage of Java > over Haskell. Here is the original >>>.paragraph in context: > > This not the first inflammatory comment he has made > > >>But, Sebastian is right. > Sebastian will be right when I see Chimpanzees coding in Java :) > > >> The leap is worth it. > I am not so sure it was for me. > I guess It depends on what you are looking for I have spent the last > year learning Haskell and I have learned some very interesting concepts. > I can't help but wish that Haskell turned out to be a more practical > language for me to code something useful in every time I looked for > Haskell libraries I was a disappointed. > I can't help feeling that last year might have been better spent > learning Erlang (which is this years language for me to learn). > > I really enjoy Functional programming (at least until I try to do > something serious then frustration sets in). I can't produce software > in a timely and cost effective fashion without a large body of high > quality, documented and maintained libraries. > > I get the feeling that Haskell is for researchers to explore ideas > about programming in but no one is interested in doing The grind work > of cranking out useful basic libraries. > I guess you need borrow some of those Java Chimps :). > > Am I the only person on the list that feels this way ? > > I guess I am feeling a bit bitter of spending so much time on Haskell > and having so little to show for it. > > Troy > > > -----Original Message----- > From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] > On Behalf Of Al Falloon > Sent: Friday, April 27, 2007 12:19 PM > To: haskell(a)haskell.org > Cc: haskell(a)haskell.org > Subject: [Haskell] Re: Newbie: what are the advantages of Haskell? > > Taillefer, Troy (EXP) wrote: > > Java sense (i.e. "cut out any feature that can't be understood in > > five > > > minutes by a chimp") > > > > Got to love comments like this they are constructive, objective, > > mature and accurate. > > > > Glad we have your expert opinion to give us the gospel. > > > > Can I get an amen? How about a Hallelujah ? > > Admittedly, this is phrased in an inflammatory manner, however, the > original sentiment is actually pointing out an advantage of Java over > Haskell. Here is the original paragraph in context: > > Sebastian Sylvan wrote: > > I can sometimes feel that Haskell looses out on not being user > > friendly in the Java sense (i.e. "cut out any feature that can't be > > understood in five minutes by a chimp"). Some things do take some > > effort to learn, but there is a huge payoff for it (it's really > > powerful!). But yeah, there might be plenty of folks who will never > > bother learning about them, and they won't understand your code. > > IOW: Java's advanced features are separable from its basic features. > I.e. you can teach Java without teaching generics or anonymous inner > classes. In Haskell, OTOH, you can't even learn how to do IO without > learning Monads, or at least glossing over oddities like a new syntax. > And thats not even getting into issues like statelessness and lazy > evaluation. > > So for a new user, Java is the better language. You can get into its > features slowly and as you see the need for them. Haskell requires you > to learn a number of mind-bending concepts right up front. Java has a > gentle learning curve and Haskell has a vertical jump. > > But, Sebastian is right. The leap is worth it. Its the same as what > someone once said about LISP: even if you never get to use Haskell > regularly, you will be a better programmer when you finally "get it". > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell > -- http://clembie.livejournal.com http://shadowofaculture.blogspot.com http://deadlylittlepills.com _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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Re: [Haskell] Re: Newbie: what are the advantages of Haskell?
by mike clemow 28 Apr '07

28 Apr '07

On 4/27/07, Taillefer, Troy (EXP) <troy.taillefer(a)lmco.com> wrote: [snip] > By the way Mike thanks you just totally cheered me up I guess I just > needed to sit back and think about what I have learned and how valuable > it is to me. There had to be some reason you were still hanging around on this list. ;-) I think that one can make a really good case for learning Haskell on the basis that knowing how to program in Haskell will make you a better programmer in any language. There's some recognition about that regarding functional programming in business; I know Jane St. Capital only hires programmers with FP experience and uses Ocaml on the inside because they know that programmers who can program in these languages produce good code. I'm glad to hear that your experience with Haskell has made you a better Java programmer and it cheers me up to think that there's something inherently beneficial to learning the language per se, even if there aren't a lot of libraries to make it as productive as other languages _yet_. Cheers, Mike

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