October 2008 - Haskell-Cafe

Restricted file reading monad
by George Pollard 04 Oct '08

04 Oct '08

Hello all, I'm currently working on a (toy) ID3 [1] tag reader, which made me think of a library which might be quite useful. The structure of an ID3 tag goes something like this: Header: - total size of tag - other header info A series of frames, each with: - total size of frame - other header info - frame data Since the ID3 tag as a whole has size information, I need to pass that into the frame-reading functions to ensure that I never read past the end of the total header. This exact same requirement is present within the frame-reading function itself; it must read the frame data without reading past the end of the frame. It would be nice to have some kind of monad or similar so that I could do: > readTag = do > size <- -- read size > -- read other header info > withLimit size $ -- read frames then the read-frames function would be able to do its work without having to worry about size-checking all the time, as this would be implicit. (And similarly with the frame-reading functions as well.) This could easily be extended to: > f x = readManyWithLimit size readerFunction where readManyWithLimit would return a list of results of applying the reader function as many times as possible within the size limit (and possibly returning some kind of error if the reader function 'bails early' and doesn't gobble right up to the end of the size limit). The thing is, I've not implemented a monad of any substantial size so I don't have a clue where to start. Calling it FileReader (for want of a better name), I guess it would almost be the same as a parsing monad, so the type would have a reference to the file Handle and the current index into the file, as well as the last point that it's allowed to read up to. So, umm... a rather open-ended question, but how would I go about this? [1]: http://www.id3.org/Developer_Information

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Haddock Feature Proposal
by Jason Dagit 04 Oct '08

04 Oct '08

Hello, I was just thinking about how many devs put "TODO ...", "FIXME ...", or "HACK..." into comments. Do others think this could be nice optional information for Haddock to display? I think it could give people an idea for how mature, stable or clean an api is just by inspecting the above items when they are present. Thoughts? Thanks, Jason

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outdated OpenSPARC webpage
by Wolfgang Jeltsch 04 Oct '08

04 Oct '08

Hello, the webpage under <http://haskell.org/opensparc/> ist outdated. There is still the line saying that students can now apply. Who is responsible for this page? Wouldn’t it be better to move this page to the wiki so that keeping it up to date is easier? Best wishes, Wolfgang

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Haskell Weekly News: Issue 88 - October 4, 2008
by Brent Yorgey 04 Oct '08

04 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081004 Issue 88 - October 04, 2008 --------------------------------------------------------------------------- Welcome to issue 88 of HWN, a newsletter covering developments in the [1]Haskell community. An extra-short HWN this week, so you get an extra ten minutes to do something else during the time you would have normally spent reading the HWN! HWN-editor-approved activities for your ten minutes include eating cookies, playing [2]Fantastic Contraption, and writing a type checker in the type system while eating cookies. Announcements Arch Haskell News: Oct 4 2008. Don Stewart [3]sent out the newest Arch Haskell news --- now with 609 Haskell packages! Announcing OneTuple-0.1.0. John Dorsey [4]announced the release of the ground-breaking [5]OneTuple library, which adds the long neglected one-tuple to Haskell. It also turns out that the denizens of Haskell-cafe are completely unable to refrain from turning jokes into long-winded technical discussions about strictness and lifted types. Haskell protocol-buffers version 0.3.1. Chris Kuklewicz [6]announced the release of [7]protocol-buffers 0.3.1, with some functionality also split off into [8]protocol-buffers-descriptor and [9]hprotoc. The 'hprotoc' compiler for proto files to Haskell source code now takes a "-u" command-line option. When given, this turns on code generation to support loading, storing, and saving unknown fields. Discussion Stacking monads. Andrew Coppin began a long [10]discussion on monads, monad transformers, Applicative, MonadPlus, and related topics. planning for ghc-6.10.1 and hackage. Duncan Coutts began a [11]discussion on how to make the transition to GHC 6.10 as painless as possible, especially as it relates to the new base-4 package and Cabal. Proposal #2629: Data.List: Replace nub; add nubOrd, nubInt, nubWith. Bart Massey [12]proposed refactoring nub into a 'nubWith' function which can be specialized to efficient versions for Int and Ord. Blog noise [13]Haskell news from the [14]blogosphere. * Luke Palmer: [15]Laziness and the monad laws. Luke explains why making a Functor or Monad instance too lazy can be just as bad as making it too strict. * Paul R Brown: [16]The Haskell Platform and Lessons Learned Elsewhere. * Eric Kow (kowey): [17]darcs weekly news #6. * Mads Lindstroem: [18]Overlapping Instances in Haskell. * >>> Bill Six: [19]Dabbling with Haskell. Bill explores palindromic pangrams using Haskell. Quotes of the Week * ozy`: [on RWH] most authors are like "FUNCTIONAL PROGRAMMING IS FUNCTIONAL!!!" whereas these guys are more like "yeah but practical programming is practical. map wash_dish dishes" * BMeph: * wants an "Everything I know about computing I learned from sigfpe" T-shirt * OlegFacts: Oleg can evaluate bottom. With his fists. * quicksilver: my computer starts to play 'Dies Irae' when shapr gets ops, automatically. About the Haskell Weekly News New editions are posted to [20]the Haskell mailing list as well as to [21]the Haskell Sequence and [22]Planet Haskell. [23]RSS is also available, and headlines appear on [24]haskell.org. To help create new editions of this newsletter, please see the information on [25]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [26]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://fantasticcontraption.com/ 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45786 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45586 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OneTuple 6. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10134 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers… 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hprotoc 10. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45634 11. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/15339 12. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10133 13. http://planet.haskell.org/ 14. http://haskell.org/haskellwiki/Blog_articles 15. http://luqui.org/blog/archives/2008/10/03/laziness-and-the-monad-laws/ 16. http://mult.ifario.us/p/the-haskell-platform-and-lessons-learned-elsewhere 17. http://koweycode.blogspot.com/2008/10/darcs-weekly-news-6.html 18. http://lindstroem.wordpress.com/2008/09/27/inheritance-in-composites-and-ov… 19. http://billsix.blogspot.com/2008/10/dabbling-with-haskell.html 20. http://www.haskell.org/mailman/listinfo/haskell 21. http://sequence.complete.org/ 22. http://planet.haskell.org/ 23. http://sequence.complete.org/node/feed 24. http://haskell.org/ 25. http://haskell.org/haskellwiki/HWN 26. http://code.haskell.org/~byorgey/code/hwn/

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An important question to Simon P. Jones
by Vag 04 Oct '08

04 Oct '08

Dear Simon! Can you please give an authoritative explanation, in the nutshell, what is exact relationship between object-oriented programming and proposed lightweight extensible records? Thanks in advance, sincerely yours, Vag.

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NewLines in string
by Serge D. Mechveliani 04 Oct '08

04 Oct '08

People, Here is a certain naive question about string setting in a Haskell program. I have the functions parseProgram :: String -> Program apply :: Program -> Term -> Term -- interpreter, and try to build the example modules for them as in the following example: ---------------------------------------------------------------- module Main where program = parseProgram " isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo " main = let {data = ... :: Term; res = apply program data} in putStr $ concat ["data = ", shows data "\n", "res = ", shows res "\n"] ---------------------------------------------------------------- -- that is set a string (an object program example), parse it to a program, apply this program and print the result. But in reality, the above string must be set like this: (2) "\ \ isOrdered nil -> true;\ \ isOrdered (X:nil) -> true;\ \ isOrdered (X:Y:Ys) -> \ \ isOrd (X > Y) (isOrdered (Y:Ys));\ \\ \ isOrd true bo -> false;\ \ isOrd false bo -> bo\ \" -- because otherwise Haskell treats the NewLine characters in the above string in an unneeded way. But with (2), the program Main occurs hard to read. One could try to improve this by using readFile. Form the file data.txt -------------------------------- isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo ----------------------------------------- and combine readFile "data.txt", the `do' construct, pearseProgram, apply, putStr. But this needs adding one more file, and this also changes the programming style in defining examples. Now, what is the difference? 1. readFile reads string from file, with treating NewLine as needed. 2. The Haskell compiler reads the expression parseProgram " isOrdered nil > true; ... " from the input Haskell program with treating NewLine in the string in a different way. I wonder: how to remove most of backslashes in the program (2) ? Thank you in advance for your comments. ----------------- Serge Mechveliani mechvel(a)botik.ru

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maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Hello, Here is a site I discovered a while back for another language ... I guess in the back of my mind this more where I was going vis-a-vis scientific computing .... http://www.enthought.com/ Kind regards, Vasili

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Re: [Haskell-cafe] maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Let me recuse myself .... What is the nature of the open source license? Vasili On Fri, Oct 3, 2008 at 8:39 PM, Jeff Wheeler <jeff(a)nokrev.com> wrote: > On Oct 3, 2008, at 8:26 PM, Galchin, Vasili wrote: > > Here is a site I discovered a while back for another language ... I >> guess in the back of my mind this more where >> I was going vis-a-vis scientific computing .... http://www.enthought.com/ >> > > I interned at Enthought over this last summer; it's a very cool place. Many > of the open-source scientific libraries could be rewritten in Haskell > without significant difficulty, and this actually seems like a decent idea. > > SciPy and NumPy are the two most significant libraries worth thinking > about, in my opinion. Some of the other software, e.g. Traits, is less > relevant to scientific software in the context of Haskell. > > Much of their stack, especially Traits, TraitsGUI, and application > libraries are designed to help write applications quickly without much > programming experience. With these tools, it's easy for scientists, without > knowing much Python, to write large programs that work well for most of > their purposes. > > Jeff Wheeler >

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Announcing OneTuple-0.1.0
by John Dorsey 03 Oct '08

03 Oct '08

Fellow Haskellers, Much attention has been paid over the years to the regrettable omission of singleton tuples from Haskell. I am pleased to announce OneTuple, a humble implementation of the singleton tuple for Haskell. Now you can: * Wrap a single value of any type in a OneTuple ! * Pattern match to retrieve your value ! * Solve any of the software problems that cannot be solved without the singleton tuple ! * Enjoy instances for all the classes normal tuples have, plus more ! * Proclaim feature parity with Python ! Note: the singleton tuple does not support tuple syntax. Contributions are welcome. The project could use a tutorial, and a decent test suite. Strict singleton tuples are planned for the next version. Enjoy! Regards, John Dorsey

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pure Haskell database
by Manlio Perillo 03 Oct '08

03 Oct '08

Hi. I need a simple, concurrent safe, database, written in Haskell. A database with the interface of Data.Map would be great, since what I need to to is atomically increment some integer values, and I would like to avoid to use SQLite. Thanks Manlio Perillo

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