May 2007 - Haskell - Haskell.org

Inaugural London HUG meeting; attendee list suggestion
by Bayley, Alistair 22 May '07

22 May '07

Tomorrow evening's London Haskell User Group meeting has a reasonable list of attendees (inferred from the comments): http://www.londonhug.net/2007/04/26/announcement-first-meeting-of-the-lo ndon-haskell-user-group/ I think it'd be a good idea to do what the BCS-SPA does, and maintain a wiki-page where attendees can add/remove themselves e.g. http://bcs-spa.org/cgi-bin/view/SPA/MakingSenseOfInformalInformation (scroll down to bottom of page, above map) This gives a current picture of who's planning to attend, which might be useful if you want to catch up with particular people. Should we start something here, perhaps? http://www.haskell.org/haskellwiki/London_Haskell_User_Group/Events/2007 0426 Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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AngloHaskell 2007
by Philippa Cowderoy 21 May '07

21 May '07

I'd like to announce AngloHaskell 2007, or at least the start of the process of organising it! Last year there was a get-together organised around the interviews for the job of GHC maintainer. There were talks, with a largely pragmatic flavour, and there was plenty of socialising. It was fun, and doing it again seems a good idea. In the vein of last year's process, organising an event this year shall take place on the Haskell Wiki page at: http://www.haskell.org/haskellwiki/AngloHaskell and on IRC, in #anglohaskell on irc.freenode.net So far this is almost all the detail available, as neither date nor venue have been set - a summer date seems good though, and by the time we're organised I imagine late July or August looks most likely. Simon Peyton-Jones has offered to ask Microsoft Research for space to give talks in. This worked well last year, but if anyone else wants to offer a venue that's fine! -- flippa(a)flippac.org The task of the academic is not to scale great intellectual mountains, but to flatten them.

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not-so-newbie question
by Wolfgang De Meuter 20 May '07

20 May '07

Dear all, I used to be a Gofer freak on my Mac back in the mid-nineties. Recently I have regained interest in FP and I'm trying to get hold of an implementation of Haskell on my G4. I must say that this hunt has been quite frustrating until now. I don't know unix and I'm unwilling to learn it just to install a Haskell interpreter. Apart from an old GHC 6.4.2, *every* implementation that I have downloaded so far is full of installation scripts, and stuff like that. Does anyone know of a site where I can download a simple MacOsX binary application? Download&double-click is really the only thing I want to do before starting to program in Haskell. Cheers Wolf

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Announce: Yi 0.2.0 released
by Jean-Philippe Bernardy 18 May '07

18 May '07

Hello folks, I'm very pleased to announce the 0.2.0 release of the Yi editor. Yi is a text editor written and extensible in Haskell. The goal of Yi is to provide a flexible, powerful and correct editor core dynamically scriptable in Haskell. Yi is not a finished product, but "release early, release often", and it's been way too long since last time :). Besides, Yi has interesting aspects that deserve wider exposure. * Yi is an haskell interpreter. Very much like emacs is a Lisp interpreter, this makes really easy to dynamically hack, experiment and modify Yi. All tools and goodies written in haskell are also readily available from the editor. This is implemented by binding to the GHC api. * Frontends. Yi can use either gtk2hs or vty as frontends, so users can choose their favourite interface. * "Emulation modes". The primary emulation modes for Yi are vim and emacs. Keybindings for vi, mg and nano and other are also provided. Other editor interfaces can be written by the user to extend Yi. Download from Hackage: http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Editor (please note that you need yi and either of the yi-vty or yi-gtk backends) More information is available on: http://haskell.org/haskellwiki/Yi Darcs repo: http://www.cse.unsw.edu.au/~dons/yi/ Yi homepage: http://www.cse.unsw.edu.au/~dons/yi.html Patches, comments, criticism welcome... as always! CREDITS: The following people have contributed to Yi: Allan Clark Alson Kemp Andrii Zvorygin Bastiaan Zapf Ben Moseley Cale Gibbard Don Stewart Duncan Coutts Harald Korneliussen Henning Guenther Jason Dagit Jean-Philippe Bernardy Mario Lang Mark Wotton Samuel Bronson Shae Erisson Simon Winwood Spencer Janssen Stefan O'Rear Suleiman Souhlal Taral Tim Newsham Tuomo Valkonen Vivian McPhail Yang Zhang (If I've forgotten you, please tell me -- there are a few patches I could not trace back to their author) This release also marks my taking over the maintenance of Yi. Many thanks to Donald Bruce Stewart for creating and bringing up Yi so far. -- Jean-Philippe Bernardy

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ANNOUNCE: Dimensional 0.4 -- Statically checked physical dimensions
by Björn Buckwalter 17 May '07

17 May '07

Dear all, I am pleased to announce version 0.4 of Dimensional (working name). Dimensional is a library providing data types for performing arithmetic with physical quantities and units. Information about the physical dimensions of the quantities/units is embedded in their types and the validity of operations is verified by the type checker at compile time. The boxing and unboxing of numerical values as quantities is done by multiplication and division with units. The library is designed to, as far as is practical, enforce/encourage best practices [1] of unit usage. Since the previous formal announcement [2] (version 0.1) Dimensional has gone through several structural and stylistic improvements but usage remains fundamentally unchanged. Noteworthy changes are a vastly solidified 'NumType' module, a complete(?) set of elementary functions and a 'Prelude'-replacement for users' convenience. There is also an experimental 'Extensible' module supporting user-defined dimensions. Additional structural changes and additions (primarily of units) are planned and the library will continue to have an unstable API until the 1.0 release. However, apart from module reshuffling no changes are anticipated that would break user code. Additional information and code is available from the project web site [3]. Thank you, Bjorn Buckwalter [1] http://physics.nist.gov/Pubs/SP811/ [2] http://www.haskell.org/pipermail/haskell/2006-December/018993.html [3] http://code.google.com/p/dimensional/

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Commercial Users of Functional Programming: call for speakers
by Simon Peyton-Jones 16 May '07

16 May '07

Folks, This is just to remind you about the closing date for offers of talks at the 2007 Commercial Users of Functional Programming workshop http://cufp.galois.com/ The closing date is 1st June, in a couple of weeks. The workshop itself is on Oct 4, colocated with ICFP at Freiburg, Germany. CUFP is a workshop for people who use functional programming (in some guise), because it's the best way to get the job done, rather than because it's a cool research topic. It's a very informal workshop. No papers, no proceedings -- just stand up and tell us how it is for you. But you have to tell us in advance so we can plan the day. Please get in touch with me or Kathleen Fisher (details at the URL above). You can also nominate someone else. That's even easier. (But ask them first.) And plan to come, too! Simon

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Implicit Parameters in Instance Declarations
by Ashley Yakeley 15 May '07

15 May '07

Would horrible things happen if implicit parameters were allowed as contexts in instance declarations? instance (?limit :: Int) => Eq Thing where ... -- Ashley Yakeley

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Core language inlined?
by Marcel Manthe 14 May '07

14 May '07

Hey, GHC seems to have a very powerful core language, which makes implementing language features less painful. As further applications of Core were mentioned: let other languages use it and build new features upon it. Here's a silly idea: Would it be possible to use Haskell and Core in parallel, in the same module or at least in the same program? Can Core integrate smoothly with Haskell? The benifitz of such feature would at least be: * Easy implementation and testing of new language features * Use language features that are used too seldom to justify an implementation in haskell * Some code may be easier to implement/understand, when it is in core form Any comments? Marcel Manthe -- View this message in context: http://www.nabble.com/Core-language-inlined--tf3751489.html#a10601250 Sent from the Haskell - Haskell mailing list archive at Nabble.com.

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Fun in the Afternoon (Cambridge, Thursday)
by Conor McBride 14 May '07

14 May '07

Relayed from Alan Mycroft: The "Fun in the afternoon" termly functional programming event takes place in Cambridge this thurday. For more details (including travel) see: http://sneezy.cs.nott.ac.uk/fun/ STOP PRESS: Microsoft are kindly providing a buffet lunch for those arriving for 12:30 (this is in the reception of the Microsoft Research building 100m behind (East of) the Computer Lab (turn left at our reception and go round the side of our building). First come first served! For those of us coming later, there will be a room in the Computer Laboratory to buy or eat our own sandwiches. Programme: 2.00pm Andy Gordon (MSR, Cambridge) Baltic: Service Combinators for Farming Virtual Machines We consider the problem of managing server farms largely automatically, in software. Automated management is gaining in importance with the widespread adoption of virtualization technologies, which allow multiple virtual machines per physical host. We consider the case where each server is service-oriented, in the sense that the services it provides, and the external services it depends upon, are explicitly described in metadata. We describe the design, implementation, and formal semantics of a library of combinators whose types record and respect server metadata. Our implementation consists of a typed functional script built with our combinators, in control of a Virtual Machine Monitor hosting a set of virtual machines. Our combinators support a range of operations including creation of virtual machines, their interconnection using typed endpoints, and the creation of intermediaries for tasks such as load balancing. Our combinators also allow provision and reconfiguration in response to events such as machine failures or spikes in demand. We describe a series of programming examples run on our implementation, based on existing server code for order processing, a typical data centre workload. To obtain a formal semantics for any script using our combinators, we provide an alternative implementation of our interface using a small concurrency library. Hence, the behaviour of the script plus our libraries can be interpreted within a statically typed process calculus. Assuming that server metadata is correct, a benefit of typing is that various server configuration errors are detected statically, rather than sometime during the execution of the script. [Based on joint work with Karthikeyan Bhargavan, Microsoft Research and Iman Narasamdya, University of Manchester] ========= 3.00 coffee ========= 3.30 Joao Fernando Ferreira, University of Nottingham Recounting the Rationals: Twice! In this talk we present an algorithm that enables the rationals to be enumerated in two different ways. One way is known and is called Calkin-Wilf-Newman enumeration; the second is new and corresponds to a flattening of the Stern-Brocot tree of rationals. We show that both enumerations stem from the same simple algorithm. In this way, we construct a Stern-Brocot enumeration algorithm with the same time and space complexity as Calkin-Wilf-Newman enumeration. ========= 4.00 Ben Rudiak-Gould, University of Cambridge Why eager and lazy are not quite dual Writing down a denotational semantics for strict and non-strict ML is a tricky business: in particular, it is not always clear what should be lifted or why. We have previously shown how a simple continuation-based intermediate language is useful for compiling strict and non-strict languages to a single virtual machine (_Haskell is Not Not ML_, ESOP '06). In this talk I will show how the negation-based type system of this language can usefully model the habitation of types in ML and Haskell, and in two variations of Haskell semantics: Haskell without seq, and "dual Haskell" where code is represented by data and data by code. ========= 4.30 Tarmo Uustalu, Institute of Cybernetics, Tallinn Firmly antifounded Recursive coalgebras are a simple formulation of wellfounded recursion and termination. In an attempt to learn about antifounded recursion and productivity, we play with their dual concept. Since Set is not self-dual, this is not without surprises. (Joint work with Venanzio Capretta and Varmo Vene.) See you for Fun on Thursday... Alan 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: Foreign.AppleScript version 0.1
by Wouter Swierstra 14 May '07

14 May '07

* Foreign.AppleScript * version 0.1 I'd like to announce the first public release of Foreign.AppleScript, a library for compiling and executing AppleScript from Haskell. AppleScript is a scripting language available on all modern Apple computers. It can be used to script most applications on running on MacOS X. Using AppleScript you can, for instance: * write dirt-cheap GUIs; * use Apple's built-in text-to-speech to read out text; * play your favourite iTunes tracks; * open URLs in your standard webbrowser. Unfortunately, AppleScript isn't the world's greatest general purpose programming language. Using Foreign.AppleScript, however, you can pimp your Haskell apps with all neat stuff AppleScript can do. How to get it? Darcs: darcs get http://www.cs.nott.ac.uk/~wss/repos/ForeignAppleScript Tarball: www.cs.nott.ac.uk/~wss/repos/ForeignAppleScript/dist/ AppleScript-0.1.tar.gz Haddock: http://www.cs.nott.ac.uk/~wss/repos/ForeignAppleScript/dist/doc/ html/ Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ AppleScript-0.1 There are a few small examples included with the source files. Implementation: At the moment, the binding is very restricted. Essentially, there is a function: > runAppleScript :: String -> IO ExitCode That will compile and execute any String of AppleScript you pass it. The result is an ExitCode, indicating whether or not the script succeeded. I have some ideas about how to improve this simple interface, allowing you to access the result of executing the AppleScript. This still needs a bit of work, before I can release it. It would be pretty interesting to try and write a typed combinator library to help generate AppleScript code. If you have any ideas about this, please do get in touch. Patches and suggestions are very welcome. Finally, I'd like to thank Duncan Coutts for helping me cabalize the code. Have fun! 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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