August 2007 - Haskell-Cafe

Java 1.5 parser in Haskell
by tim.b 06 Aug '07

06 Aug '07

Does anyone know of a fairly complete Java 1.5 parser and abstract syntax in Haskell? I've looked around quite a bit to no avail. Thanks, - Tim -- View this message in context: http://www.nabble.com/Java-1.5-parser-in-Haskell-tf4227017.html#a12025365 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Type without a data constructor?
by Rahul Kapoor 06 Aug '07

06 Aug '07

Most examples for defining algebraic types include data constructors like so: data Tree a = Tip | Node a (Tree a) (Tree a) I by mistake defined a type which did not specify a data constructor : data SearchCondition = Term Bool | SearchCondition :||: (Term Bool) data Term a = Constant a sc :: SearchCondition sc = Term True is ok, but sc :: SearchCondition sc = Constant True is not (though this is what I intended to capture!). So the question is what are types with no constructors good for? A simple example would be appreciated. Rahul

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[Fwd: PADL 2008: Call for Papers]
by Paul Hudak 06 Aug '07

06 Aug '07

-------- Original Message -------- Subject: PADL 2008: Call for Papers Date: Sat, 4 Aug 2007 19:25:58 -0500 (CDT) From: Gopal Gupta <gupta(a)utdallas.edu> [ Colleagues, note that this will be the 10th PADL; We strongly urge you to submit papers, the deadline is only 3 weeks way] CALL FOR PAPERS!!! Tenth International Symposium on Practical Aspects of Declarative Languages 2008 (PADL '08) http://www.ist.unomaha.edu/padl2008/ San Francisco, USA January 7-8, 2008 Co-located with ACM POPL'08 Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to vastly different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raises numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include: * innovative applications of declarative languages; * declarative domain-specific languages and applications; * practical applications of theoretical results; * new language developments & their impact on applications; * evaluation of implementation techniques on practical applications; * novel uses of declarative languages in the classroom; and * practical experiences PADL 08 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. PADL 08 will be co-located with the ACM POPL. IMPORTANT DATES AND SUBMISSION GUIDELINES Paper Submission: August 24, 2007 Notification: September 27, 2007 Camera-ready: October 23, 2007 Symposium: January 7-8, 2008 Authors should submit an electronic copy of the full paper (written in English) in Postscript (Level 2) or PDF. Papers must be no longer than 15 pages, written in 11-point font and with single spacing. Since the final proceedings will be published as Lecture Notes in Computer Science by Springer Verlag, authors are strongly encouraged to use the LNCS paper formatting guidelines for their submission. Each submission must include on its first page the paper title; authors and their affiliations; contact author's email and postal addresses, telephone and fax numbers, abstract, and three to four keywords. The keywords will be used to assist us in selecting appropriate reviewers for the paper. If electronic submission is impossible, please contact the program chair for information on how to submit hard copies. MOST PRACTICAL PAPER AWARD The Most Practical Paper award will be given to the submission that is judged by the program committee to be the best in terms of practicality, originality, and clarity of presentation. The program committee may choose not to make an award, or to make multiple awards. Contacts: For information about papers and submissions, please contact the Program Chair: Paul Hudak PC co-Chair - PADL 2008 Department of Computer Science Yale University P.O. Box 208285 New Haven, CT 06520 - 8285 Email: hudak(a)cs.yale.edu David S. Warren PC co-Chair - PADL 2008 Department of Computer Science Stony Brook University Stony Brook, NY Email: warren(a)cs.sunysb.edu For other information about the conference, please contact: Hai-Feng Guo General Chair - PADL 2008 Department of Computer Science College of Information Science & Technology University of Nebraska at Omaha Omaha, NE, U.S.A. Email: haifengguo(a)mail.unomaha.edu Sponsored by: COMPULOG Americas (http://www.cs.nmsu.edu/~complog) and University of Nebraska at Omaha

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ICFP07 Call for Participation
by Matthew Fluet (ICFP Publicity Chair) 06 Aug '07

06 Aug '07

===================================================================== Call for Participation The 12th ACM SIGPLAN International Conference on Functional Programming (ICFP 2007) http://www.informatik.uni-bonn.de/~ralf/icfp07.html Freiburg, Germany, 1-3 October 2007 ===================================================================== ICFP 2007 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Preliminary program: * http://www.informatik.uni-bonn.de/~ralf/schedule.html * Invited speakers: + John Hughes (Chalmers University of Technology) + Frank Pfenning (Carnegie Mellon University) + John Lloyd (Australian National University) * The Program committee has *deliberately* created extra breaks so as to give participants more time to talk with colleagues. Schedule including related workshops: * 30 Sep: ACM SIGPLAN Haskell Workshop * 30 Sep: ACM SIGPLAN Workshop on Scheme and Functional Programming * 1-3 Oct: ICFP07 * 4 Oct: ACM SIGPLAN Commercial Users of Functional Programming * 4 Oct: ACM SIGPLAN Workshop on Mechanizing Metatheory * 5 Oct: ACM SIGPLAN Erlang Workshop * 5 Oct: ACM SIGPLAN Workshop on ML * 5 Oct: ACM SIGPLAN Programming Languages meets Program Verification Registration information: * http://proglang.informatik.uni-freiburg.de/ICFP2007/registration.shtml * Early registration deadline: September 7, 2007 Accommodations information: * http://proglang.informatik.uni-freiburg.de/ICFP2007/accommodation.shtml * Conference reservation/rate deadline: September 1, 2007 * September/October is Freiburg's main tourist season; participants are advised to book rooms as early as possible. Conference organizers: * General Chair: Ralf Hinze (Universität Bonn) * Program Chair: Norman Ramsey (Harvard University) * Local Arrangements Chair: Peter Thiemann (Universität Freiburg) * Workshop Co-Chairs: Graham Hutton (University of Nottingham) and Matthias Blume (Toyota Technological Institute at Chicago) * Programming Contest Chair: Johan Jeuring (Universiteit Utrecht) * Publicity Chair: Matthew Fluet (Toyota Technological Institute at Chicago)

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Zippers, Random Numbers & Terrain
by Thomas Conway 06 Aug '07

06 Aug '07

Hi All, To amuse myself while waiting for test-runs to complete, I was thinking about random terrain generation. I came across a bunch of nice posts by Torben Mogensen, where he describes a neat way of constructing random terrains by recursively subdividing right angled isosceles triangles. It got me thinking - it's all well and good subdividing to give more detail as you zoom in, but what about when you zoom out? This got me thinking that it would be cool to make an infinite terrain generator using a zipper, so you can zoom in/out infinitely, and by implication, infinitely in any direction. One of the key components that seems to be necessary is a random number generator zipper. In Mogensen's scheme, you have a number associated with each point, and when you subdivide, you create a new RNG seed from the numbers at each end of the hypotenuse which you are bisecting. These numbers are used to generate height variation. The trick, is to make the combination order independent (e.g. xor). This is easy for zooming in, but it's not clear how to do this for zooming out. It's probably sufficient to assume a (parameterizable) hashing/mixing scheme, and to simply number the nodes in some deterministic fashion. The subdivision is binary, so we could number the children deterministically. If we use "decimals", from some arbitrary starting point, we can extend in the "fractional" direction when we zoom in, and extend in the "whole number" direction. I'm only just discovering zippers, so my question to the learned members of this forum is: Am I on the right track? Is a scheme like this going to work? cheers, Tom -- Dr Thomas Conway drtomc(a)gmail.com Silence is the perfectest herald of joy: I were but little happy, if I could say how much.

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how to make haskell faster than python at finding primes?
by Alex Jacobson 06 Aug '07

06 Aug '07

This implementation of calculating 10000 primes (compiled with GHC -O2) is 25% slower than the naive python implementation. Shouldn't it be faster? Am I doing something obviously stupid? primes = map (\(x,_,_)->x) $ filter (\(_,isP,_)->isP) candidates candidates = (2,True,[]):(3,True,[]): map next (tail candidates) next (candidate,isP,modCounts) = let newCounts = map incrMod2 modCounts in -- accumulate mods (candidate+2 -- we only need to bother with odd numbers ,(isPrime newCounts) -- track whether this one is prime ,if isP then (candidate,2):newCounts else newCounts) -- add if prime isPrime = and . map ((/=0).snd) incrMod2 (p,mc) = let mc' = mc+2 in if mc'<p then (p,mc') else if mc'>p then (p,1) else (p,0) Note: It is shorter than the python, but I would have assumed that GHC could deliver faster as well. -Alex-

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Navigating Haddock
by David Pollak 06 Aug '07

06 Aug '07

Howdy, As I'm starting to learn the Haskell libraries, I'm having a less than fun time trying to figure out what functions operate on what types. For example, in the documentation for HaXml, there's a description of Document: http://www.cs.york.ac.uk/fp/HaXml/HaXml/Text-XML-HaXml-Types.html#4 However, I can't find any links to what functions accept document as a parameter. Am I missing some magic? A couple of other questions... Can ByteStrings be substituted anywhere that takes a String (e.g., HaXml xmlParse)? Is there a way to deal with UTF-8 encoded byte arrays converting them to Strings other than http://www.gatago.org/fa/haskell/52409638.html ? Thanks, David -- lift, the fast, powerful, easy web framework http://liftweb.net

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c2hs and structs?
by Magnus Therning 06 Aug '07

06 Aug '07

I can't seem to find any information on how to deal with C functions that return a (pointer to a) struct. C2hs tells me there's no automatic support for marshalling structs (I'm using version 0.14.5). If I'm to do it by hand, is there a preferred way? (E.g. make the type adhere to the type Storable.) /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus(a)therning.org Jabber: magnus.therning(a)gmail.com http://therning.org/magnus Unreadable code, Why would anyone use it? Learn a better way. -- Geoff Kuenning's contribution to the 2004 Perl Haiku Contest, Haikus about Perl - 'Dishonerable Mention' winner

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Perfect example
by Jon Harrop 06 Aug '07

06 Aug '07

Any suggestions for a perfect example that uniquely demonstrates the benefits of the Haskell language compared to other languages? -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. OCaml for Scientists http://www.ffconsultancy.com/products/ocaml_for_scientists/?e

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Re: creating graphics the functional way
by Shin-Cheng Mu 06 Aug '07

06 Aug '07

On 05/08/07, Frank Buss <fb(a)frank-buss.de> wrote: > Is it possible to write functions with an arbitrary number of > arguments? > Would be nice if the average function would accept any number of pixel > values. You may be interested to see Oleg Kiselyov's discussion on polyvariadic functions in Haskell: http://okmij.org/ftp/Haskell/types.html#polyvar-fn sincerely, Shin

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