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Computer Camp for kids 13 - 15 years old in Colorado featuring Functional Reactive Programming
by John Peterson 12 Feb '10

12 Feb '10

Western State College in Colorado has a computer camp for kids aged 13 - 15. Although we don't use Haskell (it's Python on the inside) the underlying engine is Functional Reactive Programming. We use a 3-D game engine to explore more than just programming - we cover a lot of math and physics. We have a very unique camp - every day includes 3 - 4 hours of recreation in the area: rafting, rock climbing, kayaking, mountain biking. Our website is at http://western.edu/academics/computerscience/computer-camp.html The camp is the last week of June. See the website for further details. We're trying to get the software in releasable form - should be ready to go in a few months. This is the fourth year of our camp and FRP has been an ideal way to introduce novices to computing. John (PS - all recreational activities at our camp are approved by Simon PJ - http://haskell.org/haskellwiki/Simon_Has_Fun)

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ANN: hledger 0.8 released
by Simon Michael 12 Feb '10

12 Feb '10

hledger 0.8 is out! http://hledger.org http://hledger.org/MANUAL.html#installing Bug fixes, refactoring and Hi-Res Graphical Charts. (See Roman Cheplyaka's blog: http://www.reddit.com/r/haskell/comments/b0w0q/using_the_hledger_package_to…) Best - Simon Release notes: ...................... * parsing: in date=date2, use first date's year as a default for the second * add: ctrl-d doesn't work on windows, suggest ctrl-c instead * add: --no-new-accounts option disallows new accounts (Roman Cheplyaka) * add: re-use the previous transaction's date as default (Roman Cheplyaka) * add: a command-line argument now filters by account during history matching (Roman Cheplyaka) * chart: new command, generates balances pie chart (requires - fchart flag, gtk2hs) (Roman Cheplyaka, Simon Michael) * register: make reporting intervals honour a display expression (#18) * web: fix help link * web: use today as default when adding with a blank date * web: re-enable account/period fields, they seem to be fixed, along with file re-reading (#16) * web: get static files from the cabal data dir, or the current dir when using make (#13) * web: preserve encoding during add, assuming it's utf-8 (#15) * fix some non-utf8-aware file handling (#15) * filter ledger again for each command, not just once at program start * refactoring, clearer data types Stats: 62 days since last release, 2 contributors, 76 commits, 3464 lines of non-test code, 97 tests, 53% test coverage

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Hackage download statistis
by Maurício CA 12 Feb '10

12 Feb '10

Hi, all, Some time ago a download statistic of hackage was made available, and analysed in a few ways. Googling for it still find that at a Galois web page. I though that, since the tools to get that were there, this would be output once in a while, but it seems it hasn't been done since then. Does anyone know if there are plans about that? Thanks, Maurício

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Seen on reddit: or, foldl and foldr considered slightly harmful
by Johann Höchtl 12 Feb '10

12 Feb '10

In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he "considers foldl and foldr" harmful as they hinder parallelism because of "Process first element, then the rest" Instead he proposes a divide and merge aproach, especially in the light of going parallel. The slides at http://docs.google.com/viewer?url=http%3A%2F%2Fresearch.sun.com%2Fprojects%… [Bware: Google docs] are somewhat geared towards Fortress, but I wonder what Haskellers have to say about his position. Greetings, Johann

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ANN: Happstack 0.4.1
by Jeremy Shaw 11 Feb '10

11 Feb '10

Happstack 0.4.1 STABLE is now available. We recommend that all users of Happstack update to 0.4.1 immediately. Migration from Happstack 0.3 should be trivial. There was one race condition in happstack-state which could cause a state event to fail under heavy congestion. Happstack is the Haskell Application Server Stack. It is a scalable framework for developing web applications. It is similar in purpose to Django, RoR, Turbogears, Grails, Seaside, etc. Using less buzzwords, it is a collection of libraries which can be used to develop a self-contained server application which does not require SQL or Apache (though it can integrate with both). It includes: * an HTTP server * a rich DSL for deconstructing HTTP Requests and generating Responses * HTML/XML/etc templating via HStringTemplate, HSP, or Text.XHtml * a persistent data store based on user defined Haskell data types with ACID properties and state migration * and more!! Happstack's modular nature means it is easy to integrate unrelated 3rd party modules such as Pandoc, or to add support for an alternative templating system. Additionally, it does not exclude you from using SQL, or supporting other protocols besides HTTP. HOMEPAGE: http://www.happstack.com/ SUPPORTED PLATFORMS: Happstack supports GHC 6.8, 6.10, and 6.12, under GNU/Linux, FreeBSD, OS X, and Windows. GHC 6.12 currently requires a minor patch to HJScript. Details here: http://groups.google.com/group/haskell-server-pages/browse_thread/thread/56… INSTALL: 1. ensure that ~/.cabal/bin is in your $PATH 2. cabal update 3. cabal install happstack * see SUPPORTED PLATFORMS for information about GHC 6.12 NOTABLE CHANGES: For a complete list of changes see: http://www.patch-tag.com/r/mae/happstack/snapshots/all/history Removed: * happstack-contrib has been completely removed. If you were using something in it, please complain on the mailing list. * removed Happstack.Server.S3 -- newer, better maintained S3 libraries are on hackage now * removed unsupported spread-based multimaster support fileServe: * now with sendfile() support! On supported platforms sendfile allows files to be served from the disk to the network in a zero-copy fashion. This means faster transfers, less memory and CPU usage, and no file handle leaks. (hopefully). sendfile uses native sendfile() support on Linux, Windows, OS X, and FreeBSD. Other platforms will use a sendfile emulation mode. We recommend that you use sendFile instead of sendFileStrict or sendFileLazy, unless you have specific needs and know some reason why you must use sendFileStrict or sendFileLazy. * FileServe internals majorly refactored. FileServe now provides a modular way of building your own fileServe-like functions. Also includes functions for serving a single file instead of the contents of a directory. * added more complete list of mime-types * automatically redirect from foo to foo/ if foo is a directory * filter . and .. from request path, but allow filenames and directories which start with . happstack-server: * ServerMonad instance for ErrorT * Added ServerMonad, FilterMonad, and WebMonad for XMLGenT * Added secure flag to cookies. Defaults to False. * fix supportsIPv6 to work with newer versions of network library * simpleHTTPWithSocket + bindPort for H.S.SimpleHTTP (you can use this to start the server as root, bind to the socket, and then drop privileges.) * Fixed Accept-Encoding parser to accepts encodings with a - in them. Added additional tests to acceptEncodingParserTest * fix so basicAuth sets correct response code and headers. * SimpleHTTP: added trailingSlash. Guard which checks that Request URI ends with a / * decode body of PUT requests not just POST * added ifModifiedSince guard * added host and withHost guards to SimpleHTTP (similar to dir and path, but for the requested hostname) other: * happstack-state: Correct an embarrassing race condition bug. * happstack-data: Exported getSafeGet and getSafePut * happstack: add state transition code to guestbook (add email to form, handler, and state), and tar of example _local state before transition experimental: * happstack-state: now has experimental replication support using Amazon Web Services. This support is disabled by default. This feature is highly experimental, may not work, and may even be completely removed in future versions (though, hopefully not). THANKS: Alex Jacobson David Himmelstrup / Lemmih Matthew Elder / mae Antoine Latter Erik Hesselink Pasqualino 'Titto' Assini Nils / McManiaC Thomas Hartman Creighton Hogg / wchogg John MacFarlane Jochem Berndsen / koeien MightByte And everyone who filed bug reports, tested RC1 and RC2, and anyone else I missed.

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Examples/docs for simulated annealing bindings
by Dougal Stanton 11 Feb '10

11 Feb '10

I found the HsASA library [1] on Hackage, but there's no documentation and it's not particularly intuitive. I can't see any obvious way of choosing initial config or generating new configurations. Google reveals no one using it. Does anyone have ideas? [1]: http://hackage.haskell.org/package/HsASA-0.1 Cheers, D -- Dougal Stanton dougal(a)dougalstanton.net // http://www.dougalstanton.net

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Streamed creation of STArray from list?
by Jason Dagit 11 Feb '10

11 Feb '10

Hello, I was wondering if there is a trick for generating a new STArray from a list in such a way that you do not have to hold both the list and array in memory? http://www.haskell.org/ghc/docs/latest/html/libraries/array-0.3.0.0/Data-Ar… As far as I can tell, that is the interface for creating ST Arrays. For example, newListArray looks almost perfect: *newListArray* :: (MArray<http://www.haskell.org/ghc/docs/latest/html/libraries/array-0.3.0.0/Data-Ar…>a e m, Ix<http://www.haskell.org/ghc/docs/latest/html/libraries/base-4.2.0.0/Data-Ix.…>i) => (i, i) -> [e] -> m (a i e) If I know the length of the list, I might expect newListArray to have the memory behavior I want. In my case, the code calls (length xs) to calculate the length of the list. As I understand it, that will force the spine of the list into memory. Can this be avoided? The only trick that comes into mind is the one used by the C++ vector class where you dynamically resize the array and copy the values to the new array. That's potentially a lot of copying, right? Is some other array better suited for this, such as vector or uvector? Thanks, Jason

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Haskell and the Job Market, e.g. with Google
by Hans van Thiel 11 Feb '10

11 Feb '10

Hello, Somewhat in response to the original post about Haskell engineers I, II and III. This confirms the remark that Haskell experience is now being appreciated, though not (yet) used (very much). Steven Grant, recruiter from Google, asked me to bring to his attention anyone who might be suitable, so that's what I'm doing. <start quote> We are currently aggressively recruiting for a large number of engineers in EMEA. I spotted your extensive open source experience and was particularily interested to see you have worked with Haskell. I am not looking for a Haskell developer but more interested in people that have worked in exotic languages such as Haskell or Erlang or Scheme. The roles we have are heavily open sourced based and will be mainly working with Python, C, Linux, shell etc and are based in Dublin, London or Zurich. If you have any interest in discussing these further, drop me an email to stevengrant(a)google.com and we can discuss. <end quote> >From a second email: <start quote> The job specs are below. http://www.google.ie/support/jobs/bin/answer.py?answer=34884 http://www.google.ie/support/jobs/bin/answer.py?answer=34883 The roles are within a very specialist team within Google. They are a hybrid type role and are responsible for making our products reliable scalable and more efficient. <end quote> Get in touch with Steven: Steven Grant European IT Staffing Phone: +353 1 543 5083 Google Ireland Ltd., Barrow Street, Dublin 4, Ireland Registered in Dublin, Ireland Registration Number: 368047 I think this is interesting even to those who are not looking for a job right now, since it shows the current mind-set regarding Haskell, at a major and leading IT company. Best Regards, Hans van Thiel

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If monads are single/linearly threaded, doesn't that reduce parallelism?
by caseyh＠istar.ca 11 Feb '10

11 Feb '10

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HDBC convert [SqlValue] without muchos boilerplate
by Iain Barnett 11 Feb '10

11 Feb '10

Hi, I'm trying to get to grips with HDBC and have the following problem. When I run a query that returns a result set, each row comes back as a [SqlValue]. Naively, I thought the following function would convert a [SqlValue] into a string, but instead I get the error below. convrow2 :: [SqlValue] -> String convrow2 (x:xs) = foldl (\i j -> i ++ " | " ++ show j ) (show (fromSql x)) xs Prelude> :l TasksSimple.lhs [1 of 1] Compiling Main ( TasksSimple.lhs, interpreted ) TasksSimple.lhs:126:65: No instance for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) arising from a use of `fromSql' at TasksSimple.lhs:126:65-73 Possible fix: add an instance declaration for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) In the first argument of `show', namely `(fromSql x)' In the second argument of `foldl', namely `(show (fromSql x))' In the expression: foldl (\ i j -> i ++ " | " ++ show j) (show (fromSql x)) xs Failed, modules loaded: none. I tried looking at how to add an instance declaration for convertible, but was stumped. This code, however, works in GHCi. Would anyone know how to convert from [SqlValue] in a straightforward way without having to specify every field "by hand" ? I don't fancy doing this for each sql statement I need to run. convrow1 :: [SqlValue] -> String convrow1 [tasksid,title,added] = show ( (fromSql tasksid)::Integer ) ++ " | " ++ fromSql title ++ " | " ++ show ((fromSql added)::LocalTime) Any help is much appreciated, especially as I haven't looked at any Haskell in a while and wasn't any good with it before! Regards, Iain This is my set up: GHC is 6.10.4 HDBC is HDBC-2.1.1, HDBC-2.2.2, HDBC-postgresql-2.1.0.0,HDBC-postgresql-2.2.0.0 Convertible is convertible-1.0.5, convertible-1.0.8 OSX 10.6

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