December 2006 - Haskell-Cafe

Parsec: Where's +++?
by Greg Fitzgerald 02 Dec '06

02 Dec '06

Koen Claessen's "Parallel Parsing Processes," suggests their parsing combinators have been integrated into Parsec. If so, where is the +++ operator hiding? If not, does anyone know of a parsing library with a choice operator that does breadth-first search? Also, how do I determine what instances a datatype supports? Is Parsec an instance of Applicative? Thanks, Greg

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The Data.Array.* hierarchy is unsafe (or, Segfaulting for fun and profit)
by Spencer Janssen 02 Dec '06

02 Dec '06

I've discovered a problem in the array libraries that allows one to read arbitrary memory locations without the use of any unsafeFoo functions. Both GHC and Hugs are affected. > import Data.Array.IArray > import Data.Array.Unboxed Here is a poorly behaved instance of Ix: inRange and index ignore the bounds supplied. > newtype EvilIx = E Int deriving (Eq, Ord) > instance Ix EvilIx where > inRange _ _ = True > index _ (E i) = i > range (E x, E y) = map E $ range (x, y) One can read arbitrary memory locations, eventually indexing far enough to cause a segmentation fault. > main = print [a ! E (2^i) | i <- [0..]] > where > a :: UArray EvilIx Int > a = array (E 0, E 0) [] This problem is not specific to UArrays: > main' = print [a ! E (2^i) | i <- [0..]] > where > a :: Array EvilIx String > a = array (E 0, E 0) [] The issue is that the array operators trust the Ix instance to manage boundaries correctly. The solution is to double check the value returned by index with the actual length of the array. I volunteer to write the fix, if I can extract some hints from more knowledgeable folk. There's sizeOfByteArray#, is there an analog for an Array#? I need to know how to find the length of Hugs array primitives too. Cheers, Spencer Janssen

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Command line utility that shrinks/simplifies functions applications ?
by Jason Dagit 02 Dec '06

02 Dec '06

On 11/30/06, Pepe Iborra <mnislaih(a)gmail.com> wrote: > > > On 30/11/2006, at 17:04, Spencer Janssen wrote: > > > I believe you're talking about the `pl' plugin for lambdabot. Lambdabot has > an offline mode, visit the homepage for the source: > > http://www.cse.unsw.edu.au/~dons/lambdabot.html > > > > > There is also a web interface to lambdabot, but I can't seem to find the > link. > http://lambdabot.codersbase.com/ > > It's really nice, I use it all the time. Thanks, we had fun putting lambdabot on the web (I have some other plans for it now too, but no time!). It had been a long time since I updated that instance of lambdabot but your email prompted me to do that today. The instance at that url now supports, redo, undo and unpl and has been synched with the official version of lambdabot 4p284. Thanks, Jason

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why are implicit types different? (cleanup)
by S. Alexander Jacobson 01 Dec '06

01 Dec '06

Why do g and g' have different types? g x y = let ?f = \x-> x in ?f x ++ (show (?f y)) g :: [Char] -> [Char] -> [Char] g' :: (Show t) => [Char] -> t -> [Char] g' x y = let f = \x-> x in f x ++ (show (f y)) Is there a way I can use implicit types and let g be as general as g'? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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First Call for Papers: TFP 2007, New York
by TFP 2007 01 Dec '06

01 Dec '06

CALL FOR PAPERS Trends in Functional Programming 2007 New York, USA April 2-4, 2007 http://cs.shu.edu/tfp2007/ OR http://tltc.shu.edu/tfp2007/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results through acceptance by extended abstracts. A formal post-symposium refereeing process then selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2007 is co-hosted by Seton Hall University and The City College of New York (CCNY) and will be held in New York, USA, April 2-4, 2007 at the CCNY campus. SCOPE OF THE SYMPOSIUM The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles leading-edge, previously unpublished research work Position Articles on what new trends should or should not be Project Articles descriptions of recently started new projects Evaluation Articles what lessons can be drawn from a finished project Overview Articles summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Articles on the following subject areas are particularly welcomed: o Dependently Typed Functional Programming o Validation and Verification of Functional Programs o Debugging for Functional Languages o Functional Programming and Security o Functional Programming and Mobility o Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications o Functional Languages for Telecommunications Applications o Functional Languages for Embedded Systems o Functional Programming Applied to Global Computing o Functional GRIDs o Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) o Interoperability with Imperative Programming Languages o Novel Memory Management Techniques o Parallel/Concurrent Functional Languages o Program Transformation Techniques o Empirical Performance Studies o Abstract/Virtual Machines and Compilers for Functional Languages o New Implementation Strategies o any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2007 program chair, Marco T. Morazan, at tfp2007(a)shu.edu. SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the review of extended abstracts (6 to 10 pages in length) by the program committee. Accepted abstracts are to be completed to full papers before the symposium for publication in the draft proceedings and on-line. Further details can be found at the TFP 2007 website. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we intend to continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. IMPORTANT DATES Abstract Submission: February 1, 2007 Notification of Acceptance: February 20, 2007 Registration Deadline: March 2, 2007 Camera Ready Full Paper Due: March 9, 2007 TFP Symposium: April 2-4, 2007 PROGRAMME COMMITTEE John Clements California Polytechnic State University, USA Marko van Eekelen Radboud Universiteit Nijmegen, The Netherlands Benjamin Goldberg New York University, USA Kevin Hammond University of St. Andrews, UK Patricia Johann Rutgers University, USA Hans-Wolfgang Loidl Ludwig-Maximilians Universität München, Germany Rita Loogen Philipps-Universität Marburg, Germany Greg Michaelson Heriot-Watt University, UK Marco T. Morazán (Chair) Seton Hall University, USA Henrik Nilsson University of Nottingham, UK Chris Okasaki United States Military Academy at West Point, USA Rex Page University of Oklahoma, USA Ricardo Pena Universidad Complutense de Madrid, Spain Benjamin C. Pierce University of Pennsylvania, USA John Reppy University of Chicago, USA Ulrik P. Schultz University of Southern Denmark, Denmark Clara Segura Universidad Complutense de Madrid, Spain Jocelyn Sérot Université Blaise Pascal, France Zhong Shao Yale University, USA Olin Shivers Georgia Institute of Technology, USA Phil Trinder Heriot-Watt University, UK David Walker Princeton University, USA ORGANIZATION Symposium Chair: Henrik Nilsson, University of Nottingham, UK Programme Chair: Marco T. Morazan, Seton Hall University, USA Treasurer: Greg Michaelson, Heriot-Watt University, UK Local Arrangements: Marco T. Morazan, Seton Hall University, USA ************************************************************************************ Dr. Marco T. Morazan TFP 2007 Program Committee Chair http://tltc.shu.edu/tfp2007/ http://cs.shu.edu/tfp2007/

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Re: [Haskell] ANNOUNCE: Visual Haskell prerelease 0.2
by Johannes Waldmann 01 Dec '06

01 Dec '06

> > Not only the interfaces [Visual Studio vs. Eclipse] > > are completely different, but an entirely new > > set of interoperability problems would need to be solved. ... I still don't see what would be the fundamental difference. (Except perhaps that the Eclipse interfaces are easily available and well documented so it is at least possible to describe the interface problems...) The main advantage (Visual Haskell over eclipsefp) at the moment is that VH uses incremental (on-the-fly) typechecking/compilation while eclipsefp calls the compiler for whole modules? What source text transformations (refactorings) does VH support? Best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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Re: How to get subset of a list?
by oleg＠pobox.com 01 Dec '06

01 Dec '06

Huazhi (Hank) Gong wrote: > Like given a string list s="This is the string I want to test", I want to get > the substring. In ruby or other language, it's simple like s[2..10], but how > to do it in Haskell? Quite simply, actually: > infixl 1 %% > str %% idxs = map (str !!) idxs That is it. Not the most efficient, but gets the job done. > tstring = "This is the string I want to test" > test1 = tstring %% [2..10] *Sub> test1 "is is the" > However, like I want to choose s[1,3,6,10] or something like this. > Are there some straightforward function or operator for doing this > job? Yes, see above. > test2 = tstring %% [1,3,6,10] *Sub> test2 "hsse" Indices don't have to be in the increasing order > test3 = tstring %% [10,6,3,1] *Sub> test3 "essh" or in any order... > test4 = tstring %% [10,6,3,1]++[2..10] *Sub> test4 "esshis is the" Of course if one cares about the overhead of running code (rather than the overhead of writing code), one would probably ask, as several posters did, if the list of characters is the right data structure and if the problem indeed calls for random access to the elements of the list.

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