September 2006 - 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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Compilation of big, computed tables
by Stefan Karrmann 24 Oct '06

24 Oct '06

Dear all, can ghc compile huge tables into efficient code if they are constant at compile time? Two examples may clearify the question: big1 :: UArray Int Char big1 = array (0,1000) $! map (\i -> (i,toEnum i)) [0..1000] big2 = sum [0..10000]::Int -- == 50005000 == n*(n+1)/2 where n = 10000 Both values are constant at compile time. As they are given by pure functions, the compiler could evaluate them and write the *result* into the object file 'foo.o'. This would save code size and run time. I peeked into 'foo.hc' but I didn't found 0x2fb0408 nor an array {0, 1, 2, 3, ..., 1000} or similar things. The function in big2 should show that the computation of the value could be very time consuming. If the compiler does not compute it, the source file could be generated by a helper program (or template Haskell?). The function in big1 should show that the conversion of the data into an array could be run-time, code-size and heap-size consuming. (You need the list (maybe explicitly - think of 1000 fixed pseudo-random numbers) and convert it into an array.) If the compiler generates the unboxed array directly it could be rather efficient. PS: I compiled with: ghc6 -c -O2 -keep-tmp-files -keep-hc-files foo.hs Regards, -- Stefan Karrmann

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Re: Haskell Weekly News: September 27, 2006
by Cyril Schmidt 24 Oct '06

24 Oct '06

Donald Bruce Stewart wrote: >Conference roundup > The [41]Commercial Users of Functional Programming workshop (CUFP), > held in association with [42]ICFP, attracted a record turn-out this > year. [...] > * Haskell programming at Credit Suisse. Howard Mansell talked about > Haskell programming at [44]Credit Suisse in New York. Sadly, I was unable to attend. Is the presentation, by any chance, available online? Pointers to other related info will be much appreciated. (Yes, I know that a report of the conference will be published, but that won't happen before December :( Regards, Cyril

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Haskell web forum
by Bulat Ziganshin 18 Oct '06

18 Oct '06

Hello haskell, i definitely think that to rise up Haskell popularity we need now to create web forum. comparing to mail lists, it allows to faster "include in communication" because all previous discussions are easily available and simplifies participation for "strangers" that just have several questions and don't want to subscribe/unsubscribe and setup mail filters. moreover, participation in web forums requires less technical knowledge and prevent spamming of mail address used i heard that nowadays completed solutions available that need just to install but i don't have experience of setting up and administering of web forum. can anyone set up web forum on haskell.org server? i can perform all user-level administration, wiping of spam messages and so on.. alternatively, is there a good place to set up "main" Haskell web forum? from my POV, main requirements should be availability of message base for archiving, and ability to create sub-forums. I plan to create Russian section here, in order to help russian-speaking developers to master Haskell -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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building shared objects
by Jeremy Wazny 13 Oct '06

13 Oct '06

Hi all, I'm wondering if anybody has had any success building shared objects from Haskell code on x86 Linux and/or Sparc Solaris. I have some Haskell source which I am trying to integrate into a C/C++ library which I am maintaining at the same time. The performance of the Haskell code is not an issue. The key limitation is that I need to be able to package the whole thing as a single .so object file. Put simply, I have a Haskell module which exports one of its functions via the FFI, using the ccall calling convention. I need to compile that module, and then link the resulting object, along with some other objects, into a single shared object. It seems there is no straightforward way to achieve this with any Haskell implementation on anything other than windows (by building a DLL.) A few possibilties have occurred to me, and I'd be interested to know if anybody has tried any of these with any success. 1. Use GHC with unregisterised libraries that have been compiled by gcc using -fPIC. I haven't been able to figure out how to actually build unregisterised libraries. I tried compiling the GHC 6.4.2 sources (using GHC 6.4.2) with `GhcUnregisterised = YES' in mk/build.mk, only to have the assembler fail. Has anyone else tried this recently? I sent a message to the GHC-users mailing list with more details, but haven't had a response yet. 2. Use nhc98 with libraries and run-time compiled with gcc and -fPIC. I have no idea whether this is feasible. 3. Link in a version of yhc's yhi interpreter, compiled with -fPIC. The shared object would have to produce some temporary files containing all of the pre-compiled byte code for the interpreter to read and execute. (We're already assuming that the platform the system runs on is completely trustworthy.) 4. Alternative 3 might also be possible using Hugs. I'm not sure that I can rely on any of these approaches - provided I can even get any of them working. Does anybody know of a good solution to this problem? The alternative is to admit defeat and rewrite all the Haskell code as C++, which is pretty depressing. Regards, Jeremy ____________________________________________________ Do you Yahoo!? Listen to your personal radio station on Yahoo!7 Music http://au.music.yahoo.com/launchcast/setup.asp

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ANNOUNCE: Haskell XML Toolbox Version 6.0
by Uwe Schmidt 05 Oct '06

05 Oct '06

Haskell XML Toolbox 6.0 I would like to announce a new version of the Haskell XML Toolbox for processing XML. main new features: * works with ghc 6.4.2 * better XPath integration * separate documentation for filter API and arrow API * arrow API slightly simplified More information and download: http://www.fh-wedel.de/~si/HXmlToolbox/index.html Please email comments, bugs, etc. to hxmltoolbox(a)fh-wedel.de Uwe -- University of Applied Sciences, Wedel, Germany http://www.fh-wedel.de/~si/index.html

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Common library for generic programming
by Johan Jeuring 03 Oct '06

03 Oct '06

Dear haskellers, Generic programming has been around for more than 10 years now. We think a lot of progress has been made in the last decade. As an example, there are more than 10 proposals for libraries or language extensions only for Haskell. The success of generic programming has also caused a problem: although generic programming has been applied in several applications, it lacks actual users for real-life projects (HaRe using Strafunski is maybe an exception). This is understandable: choosing a particular approach to generic programming for a real-life project is rather risky: few approaches that have been developed over the last decade are still supported, and there is a high risk that the chosen approach will not be supported anymore, or that at least it will change in a backwards incompatible way in a couple of years time. We have recently started an initiative to design a common library for generic programming, which should work together with most of the Haskell compilers, and for which we hope to guarantee support for a longer period. If you want to get involved (or just want to see the discussion), you can subscribe to the mailing list generics(a)haskell.org, see http://www.haskell.org/mailman/listinfo/generics -- Johan Jeuring and Andres Loeh

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Proceedings Haskell Workshop 1995
by Henrik Nilsson 29 Sep '06

29 Sep '06

Dear Haskellers, In celebration of the 10th Haskell Workshop, that took place in Portland, Oregon, on the 17th September 2006, the proceedings of the very first Haskell workshop, in La Jolla 1995, have now been made available off the Haskell Workshop home page: www.haskell.org/haskell-workshop/1995 Thanks to Paul Hudak for helping locating the proceedings and arranging for them to be scanned into PDF. All the best, /Henrik -- Henrik Nilsson School of Computer Science and Information Technology The University of Nottingham nhn(a)cs.nott.ac.uk 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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ANN: Efficient, dynamically compiled, lazy functional semantics on JVM, having tight integration with the Java language
by Luke Evans 29 Sep '06

29 Sep '06

Greetings denizens of the Haskell mailing list! Though this is not strictly an announcement about Haskell, it might be of interest to a number of folk here. The Research Group here at Business Objects has been beavering away since 1999 on a suite of technologies to allow us to represent certain kinds of business logic as reusable, composable pieces. One of the primary requirements was that a general runtime for such objects be embeddable within the Java environment (i.e. pure Java). These pieces of business logic (which we called "Gems" to give them a nice friendly face) are declarative 'functional' objects. So, the side effect of focusing on our goals was the creation of a high performance, general purpose functional language and runtime for the Java platform. Here are a few 'highlights' from our feature list: - A lazily evaluated, strictly-typed language called CAL, with many similarities to Haskell - A compiler capable of generating Java bytecode with efficient schemes - Many optimisations specific to targeting a dynamic, OO language platform, such as the JVM - A graphical language and tooling for interactively developing and testing Gems (also a good teaching tool) - Debugging features, with value inspection that doesn't force evaluation - Eclipse integration (still in progress) - Metadata on CAL entities - CALDoc (source embedded documentation) - Fully multithreaded compiler and runtime - Control of evaluation from Java, if required (suspension, resumption, exploring different parts of the result) - Dynamic compilation - use SDK to create Gems at runtime, or create ad hoc compositions that might represent specific data flows in an application - Easy integration to use Java types in CAL and to call regular Java logic - Exception support - Localisation and Internationalisation support Over the next few weeks, we will be publishing more technical information about our framework (codenamed Quark). As Business Objects is not a language or development tools vendor, we are investigating the possibilities around open sourcing the general language machinery. As part of figuring out the best way to approach this, we would be interested in hearing from anyone with a possible interest in this sort of thing (for teaching, application development, research, etc.). While we gather useful collateral, I have made a couple of videos available that we had to hand and could share quickly. Some of the content is designed for those new to the functional paradigm, but the videos do show quite a range of tool and language features. To take a look at these, point your browser at: http://homepage.mac.com/luke_e In precis, the videos demonstrate the following: Intro to Gems (parts 1 and 2) Some of the regular things you expect functional languages to do, created interactively in our graphical language designer called the Gem Cutter. We find this tool is used quite a bit by developers for experimentation and orientation when reasoning from scratch about problems. In the demo you can see real-time typing, Intellicut (our system for proposing legal compositions), a graphical way to handle partial application and recursion and a number of other features that may be interesting. CAL and ICE Shell This video is a whistlestop tour through some CAL language features as well as some of the features of the framework (as exposed through the interactive shell, ICE). In this demonstration, you can see some aspects of CAL syntax, the interface to Java types and methods, a quick demo of some tracing/debugging, a look at CALDoc, records/tuples, refactoring and some brief discussion on a range of other topics. I may post other videos over the next few days and weeks, along with papers, manuals and other artifacts, but I'll spare everyone from further announcements here lest that bugs people. [Videos are Quicktime/H264, if you aren't in the habit of watching Quicktime I believe most browsers will help you to get and install the plug-in. I can send people other formats on request, or indeed, at the original resolution which is easier to see!] Regards to all, Luke Evans Chief Scientist, VP Research. Business Objects

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