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simple function: stack overflow in hugs vs none in ghc
by Tom Pledger 23 Sep '07

23 Sep '07

John Lask wrote: : | The following code causes a "C stack overflow" in hugs (version 20051031) | but not in ghc (version 6.6) | The point of the exercise is to process a very large file lazily, | returning the consumed and unconsumed parts (i.e. basic parser combinators). : | > sqnc p ts = let ( r, ts' ) = p ts in case r of | > Nothing -> ([],ts') | > Just x -> let (r',ts'') = (sqnc p ts') in (x:r', ts'' ) : I don't know how ghc is avoiding the stack overflow, but it looks like it's caused by strict pattern matching. The first call to sqnc wants reassurance that the second call is returning a pair (as opposed to _|_) before deciding that it's OK to return a pair. Try putting a tilde in the recursive call, to make the pattern lazy. let ~(r',ts'') = ... There's a recent thread on lazy patterns in the haskell-cafe list, too. http://www.haskell.org//pipermail/haskell-cafe/2007-September/031974.html Regards, Tom

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simple function: stack overflow in hugs vs none in ghc
by john lask 21 Sep '07

21 Sep '07

Hi hoping someone can shed some light on this: The following code causes a "C stack overflow" in hugs (version 20051031) but not in ghc (version 6.6) The point of the exercise is to process a very large file lazily, returning the consumed and unconsumed parts (i.e. basic parser combinators). The simplified (stylised example of the problem) is displayed bellow. test1 (on a large file) will succeed in ghc but fail in hugs test2 on same file will succeed in both ghc and hugs the problem appears to be retaining a hold on the unconsummed portion and returning it. maybe something to do with updating CAFS, all too subtle for me. The question: is there any changes that can be made to the code to make test1 work in hugs without changing the essence of the function. >test1 = readFile "big.dat" >>= (\x->print $ parse x) >test2 = readFile "big.dat" >>= (\x->print $ fst $ parse x) big.dat is just some large data file say 1MB. (not particularly large by todays standards!) >parse x = sqnc item x > where > > item =( \ ts -> case ts of > [] -> ( Nothing, []) > ts -> ( Just (head ts), tail ts) ) > > sqnc p ts = let ( r, ts' ) = p ts in case r of > Nothing -> ([],ts') > Just x -> let (r',ts'') = (sqnc p ts') in ( >x:r', ts'' ) _________________________________________________________________ Advertisement: Search for local singles online at Lavalife http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Flavalife9%2Eninemsn%2Ecom%2…

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Postdoctoral Fellowship in Functional Programming
by Graham Hutton 19 Sep '07

19 Sep '07

+--------------------------------------------------------------------+ POSTDOCTORAL RESEARCH FELLOW IN FUNCTIONAL PROGRAMMING School of Computer Science University of Nottingham, UK Applications are invited for a 3-year postdoctoral research fellowship in functional programming, to work with Dr Graham Hutton on the EPSRC-funded project "Reasoning About Exceptions and Interrupts". Most modern programming languages provide special features for detecting and managing unexpected events, in the form of exception and interrupt handling primitives. Despite their importance, the issue of provable correctness for programs involving these features has received little attention, but is particularly crucial given the difficulty of writing correct programs in this setting. The aim of this project is to address this problem within the context of modern functional programming languages such as Haskell and Epigram. Applicants for this position will require a PhD in Computer Science, and research experience in functional programming. Additional desirable attributes include experience in formal semantics, program verification, concurrency theory, or theorem provers. The successful applicant will work in collaboration with Dr Graham Hutton in the Foundations of Programming group in Nottingham, a leading centre for research on formal approaches to software construction and verification. The group currently comprises 7 academic staff, 5 research staff, and 13 PhD students. Salary will be within the range 25,134 - 32,796 pounds per year, depending on qualifications and experience. The post is available immediately, and will be offered on a fixed-term contract for 3 years. Further details regarding the position and how to apply are available from Dr Graham Hutton, http://www.cs.nott.ac.uk/~gmh. Closing date for applications: 12th October 2007. +--------------------------------------------------------------------+ | Dr Graham Hutton Email : gmh(a)cs.nott.ac.uk | | School of Computer Science | | University of Nottingham Web : www.cs.nott.ac.uk/~gmh | | Jubilee Campus, Wollaton Road | | Nottingham NG8 1BB, UK Phone : +44 (0)115 951 4220 | +--------------------------------------------------------------------+ 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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Functor ((,) a)
by Janis Voigtlaender 19 Sep '07

19 Sep '07

Hi, the Prelude docs found via http://haskell.org/hoogle/hoodoc.cgi?module=Prelude&name=Functor&mode=class claim that there is an instance Functor ((,) a) And yet, I get (in GHC, but similarly in Hugs): Prelude> fmap (+1) (undefined,2) <interactive>:1:0: No instance for (Functor ((,) a)) arising from use of `fmap' at <interactive>:1:0-22 Possible fix: add an instance declaration for (Functor ((,) a)) In the expression: fmap ((+ 1)) (undefined, 2) In the definition of `it': it = fmap ((+ 1)) (undefined, 2) What do I have to import to get the Functor ((,) a) instance? (Of course, I can define it myself, but this is not the point.) Thanks, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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Update: HaL2 Videos, Second Talk: Wolfgang Jeltsch now in full length
by klaus meier 18 Sep '07

18 Sep '07

Hello, we updated the video given at HaL2 (http://iba-cg.de/haskell.html) "Second Talk: Wolfgang Jeltsch (TU Cottbus) talks about Grapefruit, a Haskell-library for the declarative description of graphic user interfaces." because the last one was accidentally truncated. Greetings, Klaus Meier

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ANNOUNCE: SparseCheck
by Matthew Naylor 18 Sep '07

18 Sep '07

Dear Haskellers, You might be interested in SparseCheck, a library for typed, depth-bounded logic programming in Haskell allowing convenient expression of test-data generators for properties with sparse domains. http://www.cs.york.ac.uk/~mfn/sparsecheck/ SparseCheck is a based on a library called LP (to be presented at the Haskell Workshop) that was developed jointly with Emil Axelsson. Matthew.

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Swapping parameters and type classes
by Andrzej Jaworski 18 Sep '07

18 Sep '07

Well, the corridors are better known for the men in power:-) Why don't leave this entry as Reception for the uninitiated and move on to Announcements and ... Curiosity? Regards, -A.J.

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PLAN-X 2008 second call for papers and demos
by Ioana Manolescu 18 Sep '07

18 Sep '07

(Apologies for cross-posting) Call for Papers and Demos ========================= PLAN-X 2008 --- Programming Language Techniques for XML ACM SIGPLAN Workshop colocated with POPL 2008 San Francisco, California, USA - 9 January 2008 http://gemo.futurs.inria.fr/events/PLANX2008/ *** *** New: Submission is now open! *** http://gemo.futurs.inria.fr/events/PLANX2008/myreview/ *** The PLAN-X 2008 workshop is the forum to present and discuss bleeding-edge research at the intersection of programming language and data base technology with an emphasis on tree-shaped data structures and their XML representation. Topics of interest are all aspects of XML processing and querying: theories, methodologies, paradigms, language designs, types, analyses, runtime aspects, implementations, tools, applications. This edition of PLAN-X is particularly interested in blending the XML processing approaches developed by the programming languages and data management communities. Expressive power and high performance are among the common goals that these communities pursue. We encourage the submission of crosscutting contributions that apply techniques from one community to problems from the other. The primary criteria for paper selection are originality, relevance, and timeliness to ensure that we can enjoy reports on ongoing and unfinished work with high potential in the workshop. Submissions =========== We seek submissions in two categories * regular papers (10 pages, 30 minutes presentation) * demo papers (4 pages, 10 minutes plenary presentation + 30 minutes slot for individual discussions shared with other demos) For details see the submission instructions on http://gemo.futurs.inria.fr/events/PLANX2008/?page=subm Important Dates =============== Submission deadline 15 October 2007 Notification 30 November 2007 Final papers due 14 December 2007 Program Committee ================= Véronique Benzaken Université de Paris-Sud 11, France Alin Deutsch University of California, San Diego, USA Wenfei Fan University of Edinburgh, UK Mary Fernandez ATT Research, USA Haruo Hosoya University of Tokyo, Japan Ralf Lämmel Universität Koblenz, Germany Sebastian Maneth National ICT and UNSW, Sydney, Australia Jim Melton Oracle Corporation, USA Michael Schwartzbach University of Aarhus, Denmark Jérôme Vouillon CNRS, France Ioana Manolescu (general chair) Gemo group, INRIA Futurs, France Peter Thiemann (program chair) University of Freiburg, Germany

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Swapping parameters and type classes
by Mads Lindstrøm 18 Sep '07

18 Sep '07

Hi all If I have this type: data Foo a b = ... and this class class Bar (x :: * -> *) where ... I can imagine two ways to make Foo an instance of Bar. Either I must "apply" the 'a' or the 'b' in (Foo a b). Otherwise it will not have the right kind. To "apply" the 'a' I can do: instance Bar (Foo a) where ... But what if I want to "apply" the 'b' ? How do I do that ? Greetings, Mads Lindstrøm

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ANN: ListLike, a generic interface over list-like structures
by John Goerzen 18 Sep '07

18 Sep '07

Hi, I'm pleased to announce the first release of ListLike, a generic interface to the various list-like structures in Haskell. This grew out of the annoyance at having to handle Strings and ByteStrings differently in my code, and has expanded on well past there. ListLike implements an API very similar to Data.List, but based on a typeclass. The module ships with instance definitions for lists, ByteStrings, lazy ByteStrings, Arrays, and even Maps. Additional classes are available for types that implement some additional features: String-like behavior, infinite list capability, and I/O. Finally, an extensive set of default functions is provided. Only minimal effort -- as little as four functions -- are needed to make your list-like type an instance of ListLike. ListLike is backed by an extensive suite of QuickCheck tests wrapped in HUnit, which tests virtually every function against every type. As of right now, 1567 test cases are executed, and all pass. Homepage: http://software.complete.org/listlike/ Download from: http://software.complete.org/listlike/downloads API ref: http://software.complete.org/listlike/static/doc/ Hackage page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ListLike-1.0.0 -- John

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