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Re: [Haskell-cafe] An example of enumerator processing some data between input and output
by oleg＠okmij.org 20 Apr '11

20 Apr '11

Paul Sujkov wrote: > I played a bit with the enumerator package, and I'm quite stuck with the > question how to duplex data to two (or more) consumers Many packages have the combinator named enumPair (or something like that). Here is one example http://okmij.org/ftp/ftp/Streams.html#1enum2iter The combinator is quite useful for logging, for dumping the contents of the stream as it is being processed. > actually I need to pipeline output of one consumer to another > (outputting text after making some internal representation - with Show > instance - with the parseData). You need enumeratees, which convert one stream into another. There are many examples of those: e.g., converting a stream of bytes into a stream of lines, or a stream of compressed/encoded data into the plaintext stream. You enumerator package probably has them. The Stream.html page also describes many examples of enumeratees.

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by nanardon＠nanardon.zarb.org 20 Apr '11

20 Apr '11

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Unicode normalization
by wren ng thornton 20 Apr '11

20 Apr '11

Hello all, I'm in need of a Unicode normalization function, Utf8 NFC for ByteString in particular. From some quick Googling around it looks like the only available option is to use ICU in some form. The text-icu package has a nice binding to it, but unfortunately that means a lot of redundant conversions (Utf8 ByteString -> Text; Text -> Utf8 ByteString) and an additional rather large non-Haskell dependency[1]. Is ICU really the only available implementation of normalization? The TR15 doesn't really give a complete algorithm and only hints at the "numerous opportunities for optimization" implicit in the complexity of the spec. [1] Which is especially annoying on OSX since OSX does ship with libicu in a public location, but it doesn't provide header files and apparently it's incomplete somehow, meaning you'd have to reinstall it for text-icu to use (and hilarity ensues when your copy gets out of sync with the OS's). -- Live well, ~wren

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CFT -- Haskell Implementors' Workshop 2011
by Ben Lippmeier 20 Apr '11

20 Apr '11

Call for Talks ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2011 Tokyo, Japan, September 23rd, 2011 The workshop will be held in conjunction with ICFP 2011 http://www.icfpconference.org/icfp2011/ Important dates Proposal Deadline: 22nd July 2011 Notification: 8th August 2011 Workshop: 23rd September 2011 The Haskell Implementors' Workshop is to be held alongside ICFP 2011 this year in Tokyo, Japan. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. This relatively new workshop reflects the growth of the user community: there is a clear need for a well-supported tool chain for the development, distribution, deployment, and configuration of Haskell software. The aim is for this workshop to give the people involved with building the infrastructure behind this ecosystem an opportunity to bat around ideas, share experiences, and ask for feedback from fellow experts. We intend the workshop to have an informal and interactive feel, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2011. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop we hope to study the underlying technology. We want to bring together anyone interested in the nitty gritty details necessary to turn a text file into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and Tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for a relatively short talk. We are aiming for 20 min talks with 10 mins for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 200 words to benl(a)cse.unsw.edu.au We will also have a lightning talks session which will be organised on the day. These talks will be 2-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers ---------- * Rebekah Leslie (Portland State University) * Ben Lippmeier - co-chair (University of New South Wales) * Andres Loeh (Well-Typed LLP) * Oleg Lobachev (University of Marburg) * Neil Mitchell - co-chair (Standard Chartered) * Dimitrios Vytiniotis (Microsoft Research)

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HXT and xhtml page encoded in cp1251
by Dmitry V'yal 19 Apr '11

19 Apr '11

Greetings, I'm writing a small webcrawler. Usually I used tagsoup for such tasks but this time I decided to give hxt a try. Unfortunately, I ran into the troubles with character encodings. The site I'm targeting uses cp1251, which is the one of the most popular among sites in Russian. Pages contain the following meta tag <meta http-equiv="content-type" content="text/html; charset=windows-1251" /> The readDocument arrow fails with the following message: fatal error: encoding scheme not supported: "WINDOWS-1251" Can someone suggest a workaround for my use case? Best regards, Dmitry

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Painless parallelization.
by Grigory Sarnitskiy 19 Apr '11

19 Apr '11

Hello, I'm searching a way to benefit from modern hardware in my programs. I consider parallel programing to be actually easier than sequential one. Parallel computation allows to avoid sophisticated algorithms that were developed to gain performance on sequential architecture. It should also allow to stop bothering about using immutable objects --- immutable parallel arrays should be as fast as mutable ones, right? (provided there is enough cores) So what are the options to write a pure functional parallel code with the level of abstraction I used in Haskell? So far I've found Data Parallel Haskell for multicore CPU's and Data.Array.Accelerate for GPU's. It would be nice to have something at the release state, rather than some beta.

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An example of enumerator processing some data between input and output
by Paul Sujkov 19 Apr '11

19 Apr '11

Hi haskellers, I played a bit with the enumerator package, and I'm quite stuck with the question how to duplex data to two (or more) consumers using combinators from xml-enumerator (for example) package. What I mean is: main = withFile "out.xml" WriteMode $ \h -> parseFile "in.xml" decodeEntities $ (joinI $ renderText $$ iterHandle h) >> (force "data required" parseData) where parseData is a simple xml-enumerator parser. Combining consumers in such a way I can get text being output to the file "out.xml" (like in the example given) or parsed with parseData (if I switch the order of the consumers), but not both. Can anybody tell me how to make a pipe (input -> process -> output) to have text both parsed and then put back to the file? While pretty straightforward with the arrow approach, it doesn't seem obvious to me with the iteratees :( -- Regards, Paul Sujkov

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Stack overflow in simple code with getStdRandom / randomR (GHC)
by Volker Stolz 19 Apr '11

19 Apr '11

The following three-liner creates a stack overflow (on my machine, MacOS), and I'm a bit puzzled as to why: > import System.Random > > main = do > mapM (const (getStdRandom (randomR (0, 50000::Int)))) [0..10000000] botanix:~ stolz$ ./a.out Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. Yes, the list is quite long, but somehow I'd expected mapM to chug slowly along...printing "Hello World" doesn't create a stack overflow either, after all. My Haskell-foo has become a bit rusty, but I was wondering where I am missing a point or two here (and I couldn't find the correct profiler incantation that would give me more than a big black blob for the main-CAF). GHC is 6.12.3 on MacOS. Cheers, Volker

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ANNOUNCE: cereal-0.3.1.0
by Trevor Elliott 19 Apr '11

19 Apr '11

Hi Everyone, I'm proud to announce version 0.3.1.0 of the cereal binary-(de)serialization library [1]! This version includes some new functionality contributed by Lemmih, that adds support for partial parses in the Get monad. The changes don't modify the API presented in 0.3.0.0, instead adding a new runPartialGet function for the Get monad when partial parses are desired. [1] http://hackage.haskell.org/package/cereal-0.3.1.0

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Another(!) PhD Position at Strathclyde
by Conor McBride 19 Apr '11

19 Apr '11

Hot on the heels of Patricia Johann's advertisement, here's another PhD Position in the Mathematically Structured Programming Group, Deparment of Computer and Information Sciences at the University of Strathclyde to be supervised by Dr. Conor McBride and Prof. Neil Ghani on something related to Designing Precision with Dependent Types. We invite applications for one PhD position within the Mathematically Structured Programming group at the University of Strathclyde. The group comprises Prof. Neil Ghani, Dr. Patricia Johann, Dr. Conor McBride, Dr. Peter Hancock, Dr. Robert Atkey, and five PhD students. The PhD project involves THEORETICAL and PRACTICAL issues in FUNCTIONAL PROGRAMMING with DEPENDENT TYPES. Dependent type systems allow us to construct precise variations on general-purpose datatypes which address the specific needs of particular programming problems, thus opening a new "precision" axis in the design space of programs and data. We seek equipment to help programmers explore this axis, determining what is needed to shift the level of precision at which existing functions operate and which properties are guaranteed in return. The project thus represents an opportunity to study mathematical abstractions with a concrete engineering motivation. The PhD position is for 3 years, starting in October 2011. The position is a fully-funded post for a UK or EU student, and includes coverage both of fees and an EPSRC-level stipend for each of the three years. More information about the department is available at http://www.strath.ac.uk/cis The University of Strathclyde (http://www.strath.ac.uk) is slap bang in the middle of Glasgow, a thronging metropolis of wit and daring. Scotland is a hive of activity in Computer Science: we have active collaborations with researchers at Edinburgh, Heriot-Watt, Glasgow and St. Andrews. This is the time and the place to make an impact. Requests for further information and other informal enquiries can be sent to: Conor McBride conor at cis.strath.ac.uk Please get in touch as soon as you can. We hope to appoint in early May.

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