- Haskell-Cafe - Haskell.org

Interruptible threads with IO loops
by Fedor Gogolev 22 Dec '11

22 Dec '11

Hello. I'm trying to get some threads that I can stop and get last values that was computed (and that values are IO values, in fact). Here is my first approach: module Main where import Control.Concurrent (MVar, threadDelay, forkIO, newMVar, putMVar, readMVar) tick :: Int -> IO Int tick v = return $ v + 1 loop :: MVar Bool -> a -> (a -> IO a) -> IO a loop var init loopfun = do next <- loopfun init shouldStop <- readMVar var case shouldStop of True -> return next False -> loop var next loopfun runLoop :: Int -> IO () runLoop timeout = do var <- newMVar False forkIO $ threadDelay timeout >> putMVar var True value <- loop var 0 tick print value main :: IO () main = runLoop 30000000 The problem is that it looks a little messy and what's worse it leaks memory. So I'm wondering if there is a better approach to do so or some fix to memory leak.

6 7

Mitigating state-threading through an application loop
by Michael Serra 22 Dec '11

22 Dec '11

Hello Haskellers, I'm implementing a simple tree-manipulating (for sports tournaments) application prototype, with SDL for graphics and simple user interaction. For reference, I've posted the code on hpaste. <http://hpaste.org/55506> My question is about code organization: everything was simple and elegant until I started writing the program's display/event loop. Every function in this section has to be passed the same parameters - the application window to draw on, the font to display text with, the tree representing the current application state, etc. The font is an especially egregious example of the problem, because it's only used by one function but to get there it must be threaded through all of them (looking at the hpaste, you will see I don't want to call openFont on every invocation of drawTexts; what's needed is to call it once in main and have the resulting value available to drawTxt. So my question: how can I mitigate the ugliness of this state-threading? I understand this is one purpose for monads; am I supposed to implement a monad transformer for this? I think it would be great if I could define a type AppState as a tuple of the various things I need to thread, and specify some kind of automatic as-pattern, so that every function taking this AppState parameter would implicitly have its components bound to certain preset names. I've never seen anyone do this however. What is the right solution?

4 3

ANNOUNCE: partial-lens 0.0.1
by roconnor＠theorem.ca 22 Dec '11

22 Dec '11

Do you miss null references from your old imperative programming days? Wish that the worlds best imperative language had null references? Now your wishes have come true with the new partial-lens package! partial-lens augment edwardk's data-lens package with partial lens. Partial lenses are like regular lenses but have the possibility of not referencing anything. In other words, null references are possible. One notable different with null references from this package is that you can set them without getting a run-time error. Instead setting a null reference is a no-op; however it is possible to determine if setting failed from the return value of the assignment operation. Actually I don't have any applications for partial lenses myself, so if you find this library useful, please let me know. I wrote this mostly because we know what partial lenses are in theory (they are the coalgebras of the (Identity :+: Store b) comonad) but I wanted to see what a real library would look like. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

2 3

Test
by Ertugrul Söylemez 21 Dec '11

21 Dec '11

This is a test. Please disregard. -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

1 0

OOM when linking, increasingly a problem
by Magnus Therning 21 Dec '11

21 Dec '11

I've started to run out of memory when linking certain packages. The culprits at the moment are crypto-api (Crypto.CPoly) and Agda-executable. A bit of searching revealed that adding ghc-options: -dynamic to the Agda-executable .cabal could allow me to link that package. And it worked. crypto-api is a library package, so I some similar trick isn't really a possibility there :( Is there anything I can do about this? System: Linux (ArchLinux) GHC version: 7.0.3 /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

2 3

PADL 2012 Final Call for Participation
by Claudio Russo 21 Dec '11

21 Dec '11

Final Call for Participation ============================ 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 You are cordially invited to PADL'12. 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 and constraints. PADL'12 is sponsored by Association for Logic Programming with cooperation of ACM SIGPLAN and support by Microsoft Research. Registration ============ To register for PADL'12, please follow the instructions at: https://regmaster3.com/2012conf/POPL12/register.php The early registration deadline is December 24, 2011. The registration fee will cover a copy of the symposium proceedings, refreshments, and an informal dinner. Hotel Information ================= PADL will be co-located with POPL at the Sheraton Society Hill Hotel in Philadelphia. Please visit POPL's web site to make reservations at the special conference rate. Program ======= The symposium will include invited talks by Boon Thau Loo and Don Stewart, and 19 technical papers selected from 41 submissions. The preliminary program is as follows: Invited Talk (9:00-10:00) * Boon Thau Loo Recent Advances in Declarative Networking Break (10:00-10:30) Session 1: Applications (10:30-12:00) * Mayer Goldberg and Guy Wiener A Declarative Approach for Software Modeling * Sergio Antoy and Michael Hanus Contracts and Specifications for Functional Logic Programming * Pedro M. Martins, Julie A. McCann and Susan Eisenbach The Environment as an Argument Lunch (not provided) (12:00-13:30) Session 2: Logic Programming (13:30-15:30) * Yuliya Lierler, Shaden Smith, Mirek Truszczynski and Alex Westlund Weighted-Sequence Problem: ASP vs CASP and Declarative vs Problem-Oriented Solving * Marcello Balduccini and Yuliya Lierler Practical and Methodological Aspects of the Use of Cutting-Edge ASP Tools * Christian Theil Have and Henning Christiansen Efficient tabling of structured data using indexing and program transformation * Dario Campagna, Beata Sarna-Starosta and Tom Schrijvers Optimizing Inequality Joins in Datalog with Approximated Constraint Propagation Break (15:30-16:00) Session 3: Parallelism and Concurrency (16:00-17:30) * Elvira Albert, Puri Arenas and Miguel Gomez-Zamalloa Symbolic Execution of Concurrent Objects in CLP * Pablo Chico De GuzmÃ¡n, Amadeo Casas, Manuel Carro and Manuel Hermenegildo A Segment-Swapping Approach for Executing Trapped Computations * Michael Lesniak Palovca: Describing and Executing Graph Algorithms in Haskell Informal PADL Dinner (Place: TBA) Tuesday, January 24, 2012 Breakfast (8:00-9:00) Invited Talk (9:00-10:00) * Don Stewart Make Things Now! Pragmatic Functional Programming in Haskell Break (10:00-10:30) Session 4: Domain Specific Languages I (10:30-12:00) * Kenny Zhu, Kathleen Fisher and David Walker LearnPADS++: Incremental Inference of Ad Hoc Data Formats * Jeroen Bransen, Arie Middelkoop, Atze Dijkstra and S. Doaitse Swierstra The Kennedy-Warren algorithm revisited: ordering Attribute Grammars * Nicholas Coleman Distributed Policy Specification and Interpretation with Classified Advertisements Lunch (not provided) (12:00-13:30) Session 5: Domain Specific Languages II (13:30-15:30) * Andy Gill and Bowe Neuenschwander Handshaking in Kansas Lava using Patch Logic * Daniel Winograd-Cort, Hai Liu and Paul Hudak Virtualizing Real-World Objects in FRP * Edwin Brady and Kevin Hammond Resource-safe Systems Programming with Embedded Domain Specific Languages * David Broman and Henrik Nilsson Node-Based Connection Semantics for Equation-Based Object-Oriented Modeling Languages Break (15:30-16:00) Session 6: Numerics (16:00-17:00) * Paul Tarau A Declarative Specification of Tree-based Symbolic Arithmetic Computations * Vincent St-Amour, Sam Tobin-Hochstadt, Matthew Flatt and Matthias Felleisen Typing the Numeric Tower

1 0

Re: [Haskell-cafe] The Riddle of the Buddhist Monk
by Patrick Browne 20 Dec '11

20 Dec '11

1 0

The Riddle of the Buddhist Monk
by Patrick Browne 20 Dec '11

20 Dec '11

2 2

CfP: Extended Submission Deadline TAP 2012 (International Conference on Test and Proofs)
by Achim D. Brucker 20 Dec '11

20 Dec '11

(Apologies for duplicates) ************************************************************ *** TAP 2012 offers extended submission deadlines due to *** *** numerous requests received: *** *** Abstract submission: January 11, 2012 *** *** Paper submission: January 18, 2012 *** ************************************************************ *** TAP 2012 solicits both full papers and (industrial) *** *** experience/tool papers *** *** in combining proofs and (security) testing. *** ************************************************************ CALL FOR PAPERS Full and short Research Paper, Industrial Experience Papers, Tool Papers Abstract submission: Jan 11, 2012, Paper submission Jan 18, 2012 6th INTERNATIONAL CONFERENCE ON TEST AND PROOFS (TAP 2012) http://lifc.univ-fcomte.fr/tap2012/ May 31 - June 1, 2012, Prague, Czech Republic Part of the TOOLS Federated Conferences 2012 http://tools2012.fit.cvut.cz/ The TAP conference is devoted to the convergence of proofs and tests, to the application of techniques from both sides and their combination for the advancement of software quality. Test and Proof seem to be contradictory techniques: if you have proved your program to be correct, it is fruitless to comb it for bugs; and if you are testing it, that is surely a sign that you have given up on any hope to prove its correctness. Accordingly, proofs and tests have, since the onset of software engineering research, been pursued by distinct communities. However, the development of both approaches lead to the discovery of common issues and to the realization that each may need the other. The emergence of model checking has been one of the first signs that contradiction may yield to complementarity. Further evidence give test data generation techniques from models or programs which boil down to constraint resolution techniques for relatively large formula; the advent of powerful SMT solvers have therefore powered new testing techniques. Finally, since formal, proof-based verification is costly, testing invariants and background theories can be helpful to detect errors early and to improve cost effectivity. Summing up, in the past few years an increasing number of research efforts have encountered the need for combining proofs and tests, dropping earlier dogmatic views of incompatibility and taking instead the best of what each of these software engineering domains has to offer. The TAP conference aims to bring together researchers and practitioners working in the converging fields of testing and proving, and will offer a generous allocation of papers, panels and informal discussions. Topics of interest cover theory definitions, tool constructions and experimentations and include (other topics related to TAP are welcome): - Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing - Program proving with the aid of testing techniques - New problematics in automated reasoning emerging from specificities of test generation - Verification and testing techniques combining proofs and tests - Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming - Model-based testing and verification - Generation of specifications by deduction - Automatic bug finding - Debugging of programs combining static and dynamic analysis - Formal frameworks - Tool descriptions and experience reports - Case studies combining tests and proofs - Applying combination of test and proof techniques to new application domains such as validating security procotols or vulnerability detection of programs Important Dates: ================ Abstract submission (extended): January 11, 2012 Paper submission (extended): January 18, 2012 Notification: March 2, 2012 Camera ready version: March 19, 2012 TAP conference: May 31 - June 1, 2012 TOOLS conferences (TOOLS, ICMT, SC, TAP): May 29 - June 01, 2012 Conference Chairs: Bertrand Meyer Program Chairs: Achim D. Brucker and Jacques Julliand Program Committee (to be extended): =================================== Nazareno Aguirre, Bernhard K. Aichernig, Paul Ammann, Dirk Beyer, Nikolaj Bjorner, Robert Clarisó, Marco Comini, Catherine Dubois, Gordon Fraser, Angelo Gargantini, Alain Giorgetti, Patrice Godefroid, Martin Gogolla, Arnaud Gotlieb, Reiner Hähnle, Bart Jacobs, Thierry Jéron, Gregory Kapfhammer, Nikolai Kosmatov, Victor Kuliamin, Karl Meinke, Jeff Offutt, Holger Schlingloff, T.H. Tse, Margus Veanes, Luca Viganò, Burkhart Wolff, Fatiha Zaidi Submission: =========== Please submit your papers via http://lifc.univ-fcomte.fr/tap2012/. TAP 2012 will accept two types of papers: - Research papers: full papers with at most 16 pages in LNCS format (pdf), which have to be original, unpublished and not submitted elsewhere. - Short contributions: work in progress, (industrial) experience reports or tool demonstrations, position statements; an extended abstract with at most 6 pages in LNCS format (pdf) is expected. Accepted papers will be published in the Springer LNCS series and will be available at the conference. The contents of previous TAP proceedings is available at: http://www.informatik.uni-trier.de/~ley/db/conf/tap/ -- Dr. Achim D. Brucker, SAP Research, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, Fax: +49-6227 78-50502, http://www.brucker.ch

1 0

Splitting off many/some from Alternative
by Gregory Crosswhite 20 Dec '11

20 Dec '11

Hey everyone, I am sure that it is too late to do more than idly speculate about this, but could we split the some/many methods out from Alternative? They simply don't make sense except in a subset of possible Alternatives --- in most cases they just result in an infinite loop. That is to say, it is not just that they are extraneous functionality, but most of the time they are *impossible* functionality to even implement! In a way, it is a lie to be including them in Alternative since people making use of the class might incorrectly (but quite reasonably!) assume that any type that is an instance of Alternative *has* a well-defined some and many method, when this is actually the exception rather than the rule. It is only recently that I have been able to grok what some and many are even about (I think), and they seem to only make sense in cases where executing the Alternative action results in a portion of some input being consumed or not consumed. "some v" means "consume at least one v and return the list of items consumed or fail", and "many v" means "consume zero or more v and return the list of items consumed or the empty list of none are consume". It thus makes sense for there to be some subclass of Alternative called something like "Consumptive" that contains these methods. The majority of "Alternative" instances would no longer have these methods, and again that would actually be an improvement since in such cases some/many were unworkable and did nothing but cause infinite loops anyway. Normally it would be unthinkable to even consider such a change to the base libraries, but I suspect that there are not more than a couple of packages out there that make active use of the some/many instances of Alternative; it is really only parser packages that need some/many, and users most likely use the versions included with the packages themselves rather than the Alternative version. Could we verify that this is the case, and if so split them away? I thought I heard a trick whereby people were able to grep all the source on Hackage, but I can't remember what it was. :-) Just a thought. :-) Thanks, Greg

15 37