January 2003 - Haskell

Enum on Float/Double
by George Russell 23 Oct '03

23 Oct '03

The situation with Enum on Ratio is pretty bad but at least it's not hopeless, since rational numbers are at least exact. But for Float/Double it seems to be a total disaster area. Since it seems to be impossible to abolish Enum Float/Double altogether, would it at least be possible to make it rather more useful, by making succ x return the next representable float after x (or x if x is non-finite) and pred x the previous representable float. This would (a) be useful; (b) make mathematical sense; (c) is tricky to implement with the existing primitives. Before someone else points it out, this is of course unimplementable should someone in the future implement infinite-precision reals in Haskell, but as (barring a solution to the halting problem) Eq would be as well, that does not bother me. My preference would be for succ (+-0) to return the smallest positive real, since then you could define succ x to be the unique y with x < y and forall z . z < y => not (x < z), where such a y exists, and I'm not sure if the Haskell standard knows about signed zeros. Feri wrote > Everybody working with floats should know their quirks While in an ideal world, everyone who represented a mouse position or anything else as a float should have a PhD in numerical analysis, in practice they do not. Indeed I think the Haskell Library Report contains quite a few examples of floating point code which a numerical analyst would have written rather better. So I don't think it's good enough to treat every Float/Double operation as if it had an implicit "UNSAFE" flag indicating that the compiler was entitled to wierd behaviour only comprehensible to experts, as seems to be the case with floating enumerations now.

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time since the epoch
by Mike T. Machenry 24 Feb '03

24 Feb '03

I am looking for a simple way to get the current days sincethe epoch. Most language's standard time library have a get-seconds function that returns the number of seconds since the epoch, thus the function is for example in scheme: (define (days-since-epoch) ((get-seconds) / (* 60 60 24))) But it seems that in haskell the standard definition for the time library will not give me seconds since the epoch. There is technically enough information in the CalendarTime structure to calculate it, but it is a pretty complicated algorithm. Not to mention the fact that it is the exact opposite of the algorithm used to get that information in the first place, so I'd like to not have to undo it and just get the seconds as they are. Thanks for the help -mike

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Database Mailing List
by Dominic Steinitz 21 Feb '03

21 Feb '03

There seems to be a small group of Haskell users who are interested in building and using interfaces to databases. Would it be possible to set up a mailing list for those interested? I'd be happy to administer it if required (although someone would have to show / tell me what needs doing). Dominic Steinitz

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Re: seeking ideas for short lecture on type classes
by Norman Ramsey 04 Feb '03

04 Feb '03

> > In a fit of madness, I have agreed to deliver a 50-minute lecture > > on type classes to an audience of undergraduate students. These > > students will have seen some simple typing rules for F2 and will > > have some exposure to Hindley-Milner type inference in the context > > of ML. > > Will they have had exposure to more "traditional" OO programming? If > so, it might be useful to note the difference between Haskell type > classes and C++/Java/whatever classes, namely that Haskell decouples > types and the interfaces that they support. The advantage is that you > can extend a type with a new interface at any point, not just when you > define the type. Hmm --- you are talking about the `instance' declarations, right? A fact that I know but don't understand the implication of is that Haskell dispatches on the static type of a value, whereas OO languages dispatch on the dynamic type of a value. But I suspect I'll leave that out :-) N

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ANNOUNCE: Helium, for learning Haskell
by Arjan van IJzendoorn 03 Feb '03

03 Feb '03

=================================== Helium (for learning Haskell) 1.0 =================================== We are pleased to announce the first public release of the Helium system, consisting of a language, compiler and interpreter designed especially for education in functional programming. It is being developed at the Software Technology group of the Institute of Information and Computing Sciences of Utrecht University in the Netherlands. CURRENT RELEASE The language is a (large) subset of Haskell 98. Most notable difference is the absence of type classes. Without type classes, types are simpler and more specific type errors can be given. The compiler gives high-quality error messages with exact locations and sometimes hints (e.g. in the case of misspelled names). Warnings are given for unused parameters, shadowing and more. The most sophisticated part is the type checker which uses a novel constraint-based inferencer to improve type error messages. The compiler generates portable byte codes for the Lazy Virtual Machine (cf. JVM for Java) resulting in a system that is a magnitude faster than Hugs. The Helium interpreter "Hi" is a Hugs-like application which is built on top of the compiler. Together these features make Helium a fine tool for teaching environments. We have experienced that friendlier compiler messages make learning functional programming more fun for our students. More information and downloads can be found at the Helium homepage: http://www.cs.uu.nl/~afie/helium/index.html FUTURE ENHANCEMENTS - User manuals for the different tools - (Closed world) type classes - A more visually pleasing and powerful interpreter - More libraries (e.g. GUI) - Binary distributions for more platforms With kind regards, the Helium team

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looking for research opportunities
by Michael Emmi 31 Jan '03

31 Jan '03

I am a senior undergraduate student, and a firm (moral) supporter of Haskell, and am on the lookout for exciting places to do graduate research. The areas of programming language design & implementation, and of course the declarative paradigm, are of most interest. Would anyone be able to suggest a few places? Mike

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Reminder: Fun of Programming early reg 7th Feb
by Jeremy Gibbons 31 Jan '03

31 Jan '03

THE FUN OF PROGRAMMING A symposium in honour of Professor Richard Bird's 60th birthday Examination Schools, Oxford 24th and 25th March 2003 Professor Richard Bird is well known for his contributions to functional programming: for his two textbooks, his "Functional Pearls" column in the Journal of Functional Programming, his work on synthesizing programs from specifications, his influence in the design of the language Haskell and its predecessors, and so on. This symposium is to celebrate Richard Bird's work on the occasion of his sixtieth birthday. The symposium will coincide with the publication by Palgrave of an eponymous book. This book is intended as much as a textbook for an advanced course in functional programming as it is a festschrift; its twelve chapters cover applications (pretty printing, musical composition, hardware description, graphical design) and techniques (the design of efficient data structures, interpreters for little languages, program testing and optimization) in functional programming. The contributors to the book will give short lectures at the symposium, and every participant at the symposium will receive a copy of the book. The symposium will take place from 10.30am on Monday 24th March 2003 to 4pm on Tuesday 25th, in Oxford's historical Examination Schools. The registration fee includes participation, buffet lunch and tea and coffee on both days, a formal dinner on the Monday night in Worcester College, and a copy of the book. There is a lower price for early registration; the capacity of the lecture room is limited and offered on a first-come first-served basis, so early registration is recommended. The speakers are as follows: Chris Okasaki (West Point) John Hughes (Chalmers) Jeremy Gibbons (Oxford) Paul Hudak (Yale) Oege de Moor (Oxford) Simon Peyton Jones (Microsoft) Conal Elliott Mary Sheeran (Chalmers) Mike Spivey (Oxford) Ross Paterson (City) Philip Wadler (Avaya) Ralf Hinze (Bonn) For further details, including registration information, see the website at http://www.comlab.ox.ac.uk/oucl/research/areas/ap/fop/ In particular, there is an early registration deadline (with reduced fee) of 7th February 2003, and a late registration deadline of 7th March. Jeremy Gibbons and Oege de Moor (organizers) -- Jeremy.Gibbons(a)comlab.ox.ac.uk Oxford University Computing Laboratory, TEL: +44 1865 283508 Wolfson Building, Parks Road, FAX: +44 1865 273839 Oxford OX1 3QD, UK. URL: http://www.comlab.ox.ac.uk/oucl/people/jeremy.gibbons.html

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First APPSEM-II Workshop
by Graham Hutton 31 Jan '03

31 Jan '03

+---------------------------------------------------------------------+ CALL FOR PARTICIPATION First APPSEM-II Workshop 26-28 March 2003 Nottingham, United Kingdom Registration deadline: 26 FEBRUARY 2003 The first annual workshop of the IST working group APPSEM-II (Applied Semantics II) will be held in Nottingham from 26-28 March 2003. All members of the working group are invited to attend, but participation of non-members from both academia and industry with interests in application-oriented programming language semantics is actively encouraged. The purpose of the workshop is to present new results and plan future work in each of the nine themes of the group: A - Program structuring: object-oriented programming, modules (Didier Remy, Gavin Bierman); B - Proof assistants, functional programming, and dependent types (Thierry Coquand); C - Program analysis, generation, and configuration (Neil Jones); D - Specification and verification methods (Uday Reddy); E - Types and type inference in programming (Fritz Henglein); F - Games, sequentiality, and abstract machines (Pierre-Louis Curien); G - Semantic methods for distributed computing (Glynn Winskel); H - Resource models and web data (Peter O'Hearn, Philippa Gardner); I - Continuous phenomena in Computer Science (Achim Jung). For each theme there will be a session of presentations, organised by the theme leader (in parentheses above). There will also be a number of invited presentations, an industrial panel session, a brainstorming session, a business meeting, and a banquet. Following on from the workshop an informal proceedings will be published on the web. Further details are available from the workshop web page (see below). The registration deadline is 26 FEBRUARY 2003. Early registration is advisable, as the number of places is limited. Note that the fun of programming symposium in honour of Richard Bird's 60th birthday will be held in Oxford during the two days before the workshop, so participants may like to combine both events. Useful links: First APPSEM-II workshop: http://www.cs.nott.ac.uk/~gmh/appsem03.html APPSEM-II working group: http://www.tcs.informatik.uni-muenchen.de/~mhofmann/appsem2/ Fun of programming symposium: http://web.comlab.ox.ac.uk/oucl/research/areas/ap/fop/ Graham Hutton Workshop Organiser +---------------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | School of Computer Science and IT Web : www.cs.nott.ac.uk/~gmh | | University of Nottingham | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB Phone : +44 (0)115 951 4220 | | United Kingdom Fax : +44 (0)115 951 4254 | +---------------------------------------------------------------------+

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ANNOUNCE: haskell modules
by Markus.Schnell＠infineon.com 31 Jan '03

31 Jan '03

I have made a haskell module for HMM (hidden markov models) demonstration. If somebody is interested, you can find it at http://www.markusschnell.com/haskell.html Not meant for production code, there are better implementations. (Hal?) There's also a module for maintaining demo and development versions for your programs. Have a look at it, comments (or better versions) are welcome. Markus -- Markus Schnell

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ANNOUNCE: DSP Libraries for Haskell
by Matthew Donadio 30 Jan '03

30 Jan '03

Hi all, I would like to annouce the availability of Haskell libraries for digital signal processing, spectral estiation, and frequency estimation. This project is a reincarnation of a project started several years ago, but went dormant for a while. The URL is http://users.snip.net/~donadio/haskell/ The home pages lists everything that is available. Of particular interest is: -- Module for LU decomposition of matrices (LU solver, matrix inversion, etc) -- Cholesky solver -- FFT module that is not limited to N=2^v. It includes Radix-2 decimation in time FFT for N=2^v Radix-2 decimation in frequency FFT for N=2^v Cooley-Tukey FFT for composite N Prime factor algorithm for composite N Rader's algorithm using direct convolution for prime N Rader's algorithm using FFT convolution fpr prime N Hard-coded FFT for a few small values of N Inverse FFT defined in terms of the FFT 2N-point real FFT computed with N-point FFT More algorithms will be appearing over time, as well as some demo applications. -- Matthew Donadio (m.p.donadio(a)ieee.org)

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