October 2011 - Haskell-Cafe

Haskell vs. Dart
by Kevin Jardine 11 Oct '11

11 Oct '11

After Google's disappointing Dart announcement yesterday, I decided to tweak them a bit and mention Haskell and functional programming languages as an alternative: https://plus.google.com/u/0/111705054912446689620/posts/UcyLBH7RLXs Comments on the post are welcome!

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Is there a DFA library?
by Alex Rozenshteyn 11 Oct '11

11 Oct '11

I couldn't find one on hackage that isn't better described as a RegEx library. I'm looking for things like minimization, completion, etc. kinda like http://www.cis.upenn.edu/~cis639/docs/xfst.html However, I may have just missed it. -- Alex R

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ANN: ircbot 0.1.1
by Jeremy Shaw 11 Oct '11

11 Oct '11

Hello, I have just released a new library on hackage called ircbot. (Because that is what Haskell really needs -- another irc bot library). http://hackage.haskell.org/package/ircbot A demo app is here: http://patch-tag.com/r/stepcut/ircbot/snapshot/current/content/pretty/demo.… The demo is pretty non-thrilling. 98% of it is parsing command-line arguments, and then it calls a simple bot with two parts: pingPart - part that handles server PING/PONG requests dicePart - a simple part that lets you roll dice Here is an example session: <stepcut> synthea: dice 3d4+12 <synthea> You rolled 3 4-sided dice with a +12 modifier: [1,3,4] => 20 The primary reason this library exists is that a long time ago, I needed a way to log the #happs channel. So I coded up a little logging bot using the irc library from hackage. Then later I decided to fork the irc logging out of the happstack.com server itself and into a resuable irc bot library. The library has the following features: 1. a reconnect loop that tries really hard to make sure the bot notices if it is disconnected and tries to reconnect. 2. a channel logging facility that automatically rolls over to a new log file every day. 3. a BotMonad class and BotPartT monad which make it easy to create handlers for incoming messages: http://patch-tag.com/r/stepcut/ircbot/snapshot/current/content/pretty/Netwo… Each bot part is run in its own thread. Incoming messages are delivered to all the parts. That is useful because some parts, like the seen command, need to see every incoming message, even if they do not actively respond to them. Because the parts are handled by different threads, they do not block each other. By default, each part is single-threaded. That is because some parts may need to see multiple messages and see them in the order they originally arrived. However, a part can easily call forkIO to handle each incoming Message and avoid blocking when appropriate. 4. a wrapper that let's you use Parsec to parse an incoming message. It is used by the dicePart: http://patch-tag.com/r/stepcut/ircbot/snapshot/current/content/pretty/Netwo… Using parsec gives you an easy way to specify syntax errors: <stepcut> synthea: dice <synthea> unexpected end of input; expecting dice <num-dice>d<num- sides>[+<modifier>] Future work: 1. The library is based around the old String based irc library. Would be nice to upgrade to something that used ByteStrings+Text+Builder. Practically speaking.. it's IRC. The maximum line length is 510 characters, and the bot typically needs to handle, at most, a few messages per second. So, space and time issues would only be a practical concern if your bot is joining hundreds of channels. But, that is no excused not to use Text :) Perhaps the fastirc library? 2. The channel logging feature needs some minor changes so that more than one channel at a time can be logged 3. the bot needs to do something sane if the nick it wants is already in use. It should also support nick registration. 4. needs automatic help text generation 5. documentation 6. It should be possible to support dynamically reloadable plugins. Most of the technology exists in happstack-plugins + plugins. We just need to finish splitting happstack-plugins into two packages. 7. clustering support. ircbot does not have any built-in persistent storage. It should work fine with acid-state, SQL, etc. When acid- state gets multimaster replication support, it would be nice if there was an automatic failover system. Basically, you could have two or more bots in the channel using acid-state replication. Queries would normally be answered by the primary bot, but if the primary bot goes offline, the secondary bot could answer the queries instead. 8. windows support - the channel logging feature uses the unix package, which is not supported on Windows. The rest of the code is already portable. Anyway. Enjoy! - Jeremy

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PEPM'12 Deadline Extension
by Simon Thompson 11 Oct '11

11 Oct '11

Apologies for multiple postings of this announcement. PEPM'12 - DEADLINE EXTENSION Due to a number of requests for extensions, the deadline for submission to PEPM'12 has been extended until 23:59 GMT on Sunday 16 October. We would like to remind you about three aspects of PEPM. Journal Special Issue There will be a journal special issue for PEPM'12. PEPM'09 has already appeared in Higher-order and Symbolic Computation (HOSC, online-first edition this year), and the special issue based on PEPM'10 papers has just been delivered to the HOSC editorial team. Short papers We're looking for short papers (up to 4pp) and tool papers as well as full research papers. All categories of papers will appear in the formal ACM proceedings. Tool papers The main purpose of a tool paper is to display other researchers in the PEPM community a completed, robust and well-documented tool; more guidance on the format and expected contact is given on the PEPM 2012 web site. In contrast with regular PEPM submissions, PEPM tool demo papers may include work that has been published elsewhere. In the ideal case, the technical foundations of the tool will have been published previously, and the submitted PEPM tool paper will report on follow-on work that has produced a robust tool that has been applied to interesting examples. The PEPM program committee will consider accepting tool demo papers that describe tools that have been presented at other conferences/ workshops if these conferences/ workshops belong to a different community (the authors should acknowledge the previous demos and justify the benefits of presenting the tool again for the PEPM audience). Call For Papers ACM SIGPLAN 2012 Workshop on Partial Evaluation and Program Manipulation January 23-24, 2012. Philadelphia, Pennsylvania, USA (co-located with POPL'12) http://www.program-transformation.org/PEPM12 Paper submission deadline: Sunday, October 16, 2011, 23:59, GMT The PEPM Symposium/Workshop series aims to bring together researchers and practitioners working in the broad area of program transformation, which spans from refactoring, partial evaluation, supercompilation, fusion and other metaprogramming to model-driven development, program analyses including termination, inductive programming, program generation and applications of machine learning and probabilistic search. PEPM focuses on techniques, supporting theory, tools, and applications of the analysis and manipulation of programs. Each technique or tool of program manipulation should have a clear, although perhaps informal, statement of desired properties, along with an argument how these properties could be achieved. Topics of interest for PEPM'12 include, but are not limited to: - Program and model manipulation techniques such as: supercompilation, partial evaluation, fusion, on-the-fly program adaptation, active libraries, program inversion, slicing, symbolic execution, refactoring, decompilation, and obfuscation. - Program analysis techniques that are used to drive program/model manipulation such as: abstract interpretation, termination checking, binding-time analysis, constraint solving, type systems, automated testing and test case generation. - Techniques that treat programs/models as data objects including metaprogramming, generative programming, embedded domain-specific languages, program synthesis by sketching and inductive programming, staged computation, and model-driven program generation and transformation. - Application of the above techniques including case studies of program manipulation in real-world (industrial, open-source) projects and software development processes, descriptions of robust tools capable of effectively handling realistic applications, benchmarking. Examples of application domains include legacy program understanding and transformation, DSL implementations, visual languages and end-user programming, scientific computing, middleware frameworks and infrastructure needed for distributed and web-based applications, resource-limited computation, and security. To maintain the dynamic and interactive nature of PEPM, we will continue the category of `short papers' for tool demonstrations and for presentations of exciting if not fully polished research, and of interesting academic, industrial and open-source applications that are new or unfamiliar. Student attendants with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses and other support. All accepted papers, short papers included, will appear in formal proceedings published by ACM Press and will be included in the ACM Digital Library. Selected papers may later on be invited for a journal special issue dedicated to PEPM'12. Submission Categories and Guidelines Authors are strongly encouraged to consult the advice for authoring research papers and tool papers before submitting. The PC Chairs welcome any inquiries about the authoring advice. Regular research papers must not exceed 10 pages in ACM Proceedings style. Short papers are up to 4 pages in ACM Proceedings style. Authors of tool demonstration proposals are expected to present a live demonstration of the described tool at the workshop (tool papers should include an additional appendix of up to 6 extra pages giving the outline, screenshots, examples, etc. to indicate the content of the proposed live demo at the workshop). Important Dates - Paper submission: Sunday, October 16, 2011, 23:59, GMT - Author notification: Tue, November 8, 2011 - Workshop: Mon-Tue, January 23-24, 2012 Invited Speakers - Markus Pueschel (ETH Zurich, Switzerland) - Martin Berger (University of Sussex, UK) Program Chairs - Oleg Kiselyov (Monterey, CA, USA) - Simon Thompson (University of Kent, UK) Program Committee Members - Emilie Balland (INRIA, France) - Ewen Denney (NASA Ames Research Center, USA) - Martin Erwig (Oregon State University, USA) - Sebastian Fischer (National Institute of Informatics, Japan) - Lidia Fuentes (Universidad de Malaga, Spain) - John Gallagher (Roskilde University, Denmark and IMDEA Software, Spain) - Dave Herman (Mozilla Research, USA) - Stefan Holdermans (Vector Fabrics, the Netherlands) - Christian Kaestner (University of Marburg, Germany) - Emanuel Kitzelmann (International Computer Science Institute, USA) - Andrei Klimov (Keldysh Institute of Applied Mathematics, Russian Academy of Sciences) - Shin-Cheng Mu (Academia Sinica, Taiwan) - Alberto Pardo (Universidad de la Repu'blica, Uruguay) - Kostis Sagonas (Uppsala University, Sweden and National Technical University of Athens, Greece) - Anthony M. Sloane (Macquarie University, Australia) - Armando Solar-Lezama (MIT, USA) - Aaron Stump (The University of Iowa, USA) - Kohei Suenaga (University of Kyoto, Japan) - Eric Van Wyk (University of Minnesota, USA) - Kwangkeun Yi (Seoul National University, Korea) Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Three questions to graphviz
by kaffeepause73 11 Oct '11

11 Oct '11

First of all - thanks a lot for this package, graphviz is an awesome tool and having this interface library is really convenient. There a three point where I could use some help: 1. when I try to create a label with e.g.: textLabelValue "Hallo" - the compiler complains he can't match string with data.text.lazy.internal -- I have idea how to create lazy internal text ! 2. I know how to rotate the whole diagram (with landscape or rotate 90), but not how to keep all the text in unrotated position -- is there a command to do this ? 3. When I create a symmetric tree with two directions on the two sides. The tree gets completely messed up when I enter the right directions. (left graph ok but wrong edge dirs, right graph with correct dirs but gemetry scambled). - It has todo with ranking order which is based on the direction of the edges. I can fake it with reversing the arrows in the diagram, but my original graph data is coming directed ... Cheers Phil http://haskell.1045720.n5.nabble.com/file/n4888818/GraphA.jpg http://haskell.1045720.n5.nabble.com/file/n4888818/GraphC.jpg -- View this message in context: http://haskell.1045720.n5.nabble.com/Three-questions-to-graphviz-tp4888818p… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Implementing a new primtype
by Paul Monday 10 Oct '11

10 Oct '11

There seems to be plenty of documentation around on implementing a new primop, much of it needs some tweaking as files have moved and such. I can't seem to find any documentation about how to implement primtypes though. For example, I want to experiment with a new primtype "DV#", my assumption that the type was first declared in the primops.txt.pp seems incorrect. So I'm trying to backtrack a bit and see where primtypes first appear, I'm hoping someone can at least give me a pointer :-) For example: ./compiler/prelude/primops.txt.pp Add the following: primtype DoubleVec# a Compiles fine Add a primop on the type: primop ExtractDoubleVecOp "extractDoubleVec#" GenPrimOp DoubleVec# -> Int# -> Double# And suddenly it's not as friendly. I expected a compile issue since I hadn't added it to CgPrimOps.hs yet, but this is not that compile problem: make -r --no-print-directory -f ghc.mk phase=1 phase_1_builds /usr/bin/gcc -E -undef -traditional -P -Iincludes -x c compiler/prelude/primops.txt.pp | grep -v '^#pragma GCC' > compiler/prelude/primops.txt "inplace/bin/genprimopcode" --data-decl < compiler/prelude/primops.txt > compiler/primop-data-decl.hs-incl "inplace/bin/genprimopcode" --primop-tag < compiler/prelude/primops.txt > compiler/primop-tag.hs-incl "inplace/bin/genprimopcode" --primop-list < compiler/prelude/primops.txt > compiler/primop-list.hs-incl "inplace/bin/genprimopcode" --has-side-effects < compiler/prelude/primops.txt > compiler/primop-has-side-effects.hs-incl "inplace/bin/genprimopcode" --out-of-line < compiler/prelude/primops.txt > compiler/primop-out-of-line.hs-incl "inplace/bin/genprimopcode" --commutable < compiler/prelude/primops.txt > compiler/primop-commutable.hs-incl "inplace/bin/genprimopcode" --code-size < compiler/prelude/primops.txt > compiler/primop-code-size.hs-incl "inplace/bin/genprimopcode" --can-fail < compiler/prelude/primops.txt > compiler/primop-can-fail.hs-incl "inplace/bin/genprimopcode" --strictness < compiler/prelude/primops.txt > compiler/primop-strictness.hs-incl "inplace/bin/genprimopcode" --primop-primop-info < compiler/prelude/primops.txt > compiler/primop-primop-info.hs-incl genprimopcode: ppType: can't handle: TyApp "DoubleVec#" [] make[1]: *** [compiler/primop-primop-info.hs-incl] Error 1 make[1]: *** Deleting file `compiler/primop-primop-info.hs-incl' make: *** [all] Error 2 So, I'm thinking the type needs to be better defined but I haven't tracked it down yet (I'm working on it though ;-) Any clues? Paul Monday Parallel Scientific, LLC. paul.monday(a)parsci.com

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Question: Lazy Incremental Evaluation and Haskell?
by Benjamin Redelings I 10 Oct '11

10 Oct '11

Hi all, I'm not sure this is the right forum for this question. If so, please let me know where else might be more appropriate. My question is, roughly, is there already an existing framework for incremental evaluation in Haskell? That is, if I write a program using Haskell, and then change a small part of this program, can the modified program re-use any results which are calculated by the first, unmodified program? This would be really useful for CPU-intensive statistical software and other scientific computing. For example, if I have the expression (x+y)+z, where x=1, y=2, and z=4, then I need not recalculate (x+y) when z changes. However, (x+y)+z must still be recalculated. This is useful in speeding up statistical software that optimizes a complex function of many arguments, when only one argument changes at a time. It is also useful for Markov chain Monte Carlo (MCMC) since usually one changes only one argument at a time there as well. I haven't seen much work on this using the lambda calculus for this since JH Field's Ph.D. Thesis "Incremental Reduction in the Lambda Calculus". There are a number of programs that represent the calculation as a static DAG (directed, acyclic graph), but this can't handle functions very well. I'm currently trying to write an interpreter that could do this correctly, but I don't want to reinvent the wheel. Can anyone point me to where I could find more information about how to do this in a Haskell framework? thanks! -BenRI -- Benjamin Redelings

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Question on definition of `parse' function in Parsec library.
by Captain Freako 10 Oct '11

10 Oct '11

Hi all, In this definition from the Parsec library: parse :: (Stream s Identity t) => Parsec s () a -> SourceName -> s -> Either ParseError aparse p = runP p () what's the significance of `Identity t'? (`t' isn't used anywhere.) Thanks, -db

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Seeking Feedback on Crypto Learning Project Ideas
by Daniel Kelly 10 Oct '11

10 Oct '11

Hi, I am a Haskell newbie looking for a small to medium size Haskell project that I can use as a learning tool, and would appreciate some feedback. I want to design and build something new, from scratch, that could actually be of practical use and that hasn't been done before (in Haskell, that is). I want to end up with a library package that could be uploaded to Hackage. I also want it to be something cryptography related, since this is a strong interest of mine. I'm particularly interested in exploring the possibilities of being able to pass basic crypto algorithms, to very generic higher-order functions quite naturally in Haskell. I would like to know a) if these ideas have been done (in Haskell) that I'm not aware of, b) which would be most useful/interesting to fellow Haskellers, c) guesstimates of the amount of work involved in each, d) suitability for learning language concepts, and e) any other helpful suggestions you might have Some specific project ideas I have been kicking around that i would appreciate feedback on: 1. An implementation of Shamir's Secret Sharing: http://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing 2. A Haskell binding to LibTomCrypt (Opinions for/against LibTom? - it looks unusually complete.) 3. A generic secure channel, where you pass your choice of basic algorithms (hash, symmetric, asymmetric, compression, etc) to higher order function 4. A Haskell implementation of Trevor Perrin's CryptoID's: http://trevp.net/cryptoID/index.html 5. A Haskell implementation of a generic Proof of Work system: http://en.wikipedia.org/wiki/Proof-of-work_system as a building block for anti-spam/anti-denial-of-service systems such as hashcash. 6. Some other generic high level interface to basic algorithms (looking for ideas here). I would also welcome any other project ideas along these lines that you might have. Thank you in advance. Dan Kelly

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Simple design question using Wai
by Arnaud Bailly 10 Oct '11

10 Oct '11

Hello, I am trying to move a web application I wrote that initially used raw sockets for doing HTTP by "hand" to a more sensible Wai-based framework, and I am running into a design issue. I initially thought it would be a good idea to be able to support various I/O methods so I defined a layer called CommandIO (this is a game application) to insulate business-level code from the detials of reading commands and outputting results to the outside world. Here is the signature for this simple monad: class (Monad io) => CommandIO io where readCommand :: io Command writeResult :: CommandResult -> io () then I have an interpret function which looks like: interpret :: (CommandIO io, Map t) => Commands t io CommandResult which reads a command from the io, execute it producing a CommandResult, then request output from the io using writeResult. This works nicely using Reader-based data containing a Handle, both for HTTP-based and console-based I/O. But when I try to move to WAI, I am a little bit stuck. The core of Wai is an application which rougly has type Request -> Response and this basically breaks my (simple) model of read commands / write results. I suspect there might be a way to stick to my current model using enumerators/streams for I/O and a custom type for encapsulating the underlying state of the HTTP exchange. I also thought about reversing the dependency : ensuring that interpret does not need to know about low-level I/O and only dealing with Command/CommandResult, with I/O being handled by wrappers. Thanks in advance for any insights, Arnaud PS: the code is on github: http://github.com/abailly/crete1941. Not that I deem it ready for prime-time though...

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