July 2010 - Haskell-Cafe

Re: [Haskell-cafe] Hot-Swap with Haskell
by austin seipp 16 Jul '10

16 Jul '10

Sorry Andy! CC'ing to the rest of -cafe in case anybody notices (I need to stop haskelling so early in the morning...) On Fri, Jul 16, 2010 at 8:59 AM, austin seipp <as(a)0xff.ath.cx> wrote: > You also may like one project I wrote, an IRC bot that used hs-plugins > to do hot code reloading (only works on GHC 6.8.) Inspired by > lambdabot, it could swap the entire running program as well as its own > plugins, on the fly and maintain state pretty successfully. I haven't > touched the source code in a long time - it was one of my first bigger > Haskell projects after reading Dons paper about yi. I tried a bunch of > things with various versions of it. > > If I wrote the code again today (providing plugins worked) it would > likely be 1/10th the size and more manageable as I have become much > better at Haskell, but oh well. Looking over it now though, most of > the code is pretty simple. :) > > http://code.haskell.org/infinity/src/ > > On Fri, Jul 16, 2010 at 8:04 AM, Andy Stewart <lazycat.manatee(a)gmail.com> wrote: >> Bartek Ćwikłowski <paczesiowa(a)gmail.com> writes: >> >>> Hello Andy, >>> >>> 2010/7/16 Andy Stewart <lazycat.manatee(a)gmail.com>: >>> >>>> There are some problems with re-compile solution: >>>> >>>> 1) You can't save *all* state with some FFI code, such as gtk2hs, you >>>> can't save state of GTK+ widget. You will lost some state after >>>> re-launch new entry. >>> >>> For my 2008 GSOC application I wrote a demo app that used hot code >>> reloading and it maintained gtk state just fine. The code (and video) >>> is available at http://paczesiowa.dw.pl/ , it worked in ghc 6.8 and >>> needed hs-plugins, so it won't work now, but the approach should work. >> Wow, thanks for your hint, i will wait dons fix hs-plugins then try this >> cool feature.. >> >> Thanks, >> >> -- Andy >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > > -- > - Austin > -- - Austin

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Haskell Platform dependency hell
by Kevin Jardine 16 Jul '10

16 Jul '10

I have Haskell Platform 2010.1.0.0 installed under Windows and I often find that Haskell breaks if I try upgrading some of the current modules. For example, after using cabal to upgrade to the latest version of Network.CGI, I can no longer compile any code and instead get this message: cabal.exe: dependencies conflict: ghc-6.12.1 requires array ==0.3.0.1 however array-0.3.0.1 was excluded because ghc-6.12.1 requires array ==0.3.0.0 The only way I have found to fix this problem in the past has been to uninstall the Haskell Platform and start over. Can anyone tell me: a. why does this occur, and b. what can I do to stop it from occurring again? Is it the case that the Haskell Platform is simply not upgradable and that I need to wait for the next release? Kevin

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ANNOUNCE: highlighting-kate 0.2.7
by John MacFarlane 16 Jul '10

16 Jul '10

I'm pleased to announce a new release of highlighting-kate [1], a syntax highlighting library based on syntax definitions from the kate editor. !! Important note !! The new release uses new, two-letter class names in its HTML output. If you use highlighting-kate, you will need to update your css files. Three sample css files can be found in the css directory of the source. This release also incorporates improvements to the kate syntax definition for Haskell by Nicolas Wu. There are two minor API changes: 1. A new function, languagesByFilename, has been added. This will give better results than languagesByExtension for things like "Makefile" or "CMake.txt". 2. A new formatting option, OptDetailed, has been added. Use this only if you need access to detailed, language-specific lexical information, and not generic styles. [1]: http://hackage.haskell.org/package/highlighting-kate

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point-free ADT pattern matching ?
by Alexey Karakulov 16 Jul '10

16 Jul '10

I wonder if pattern matching could be less verbose. Maybe this sounds weird, but here is example of what I mean: > type A = (Int, String) > > f :: String -> A -> A > f s (i,s') = (i, s ++ s') > > data B = B Int String deriving Show > >g :: String -> B -> B >g s (B i s') = B i $ s ++ s' Types A/B and functions f/g are quite similar: (x :: A) or (x :: B) means that x contains some integer and string values, and f/g functions take some string and prepend it to the string part of x. The code for f and g has the same level of verbosity, but -- ta-dah! -- we can use arrows and define f in a highly laconic manner: > import Control.Arrow > f' :: String -> A -> A > f' = second . (++) So my queastion is how I could define (g' :: String -> B -> B) in the same way.

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Haddock anchors
by Mark Lentczner 15 Jul '10

15 Jul '10

I've been re-working on the Haddock HTML back end to get it to generate "semantic markup" and legal XHTML. One of the problems is that the anchors that Haddock currently generate aren't always legal in HTML, XHTML, or XML. I'd like to fix the anchor generation so that they are. If I do, then links between old and new generated Haddock pages will land on the right page, but won't always get to the right spot on the page. Will this be a problem for anyone? On one's own machine, I imagine we can come up with a simple script that will just rebuild all the Haddock docs and that will take care of it. What about on Hackage? Eventually, as packages update, the issue will diminish. Can we just bulk re-build the haddock for the latest rev of all packages? - Mark Mark Lentczner http://www.ozonehouse.com/mark/ IRC: mtnviewmark

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cryptohash and an incremental API
by Thomas M. DuBuisson 15 Jul '10

15 Jul '10

Vincent, Due to spam-like comments on -cafe I hadn't been subscribed for a while and missed your cryptohash discussion! Particularly: > The main reason for this library is the lack of incremental api exposed by > current digest libraries, and filling the void about some missing digest > algorithms; Also the speed comes as a nice bonus. I've been working on a new crypto library specifically to provide a unified API for packages implementing cryptographic algorithms. You can see the discussions on libraries(a)haskell.org [1] [2]. Please feel free to take a look, comment, contribute, and hopefully move to the interface. I should be finishing up BlockCipher modes and adding hash tests soon. Cheers, Thomas [1] http://www.haskell.org/pipermail/libraries/2010-May/013688.html [2] http://www.haskell.org/pipermail/libraries/2010-June/013782.html

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Expression dye
by Andrew Coppin 15 Jul '10

15 Jul '10

I'm trying to write a function that builds a series of results in a very complicated way. Eventually I ended up writing things like > newtype Dye = Dye String deriving (Eq, Show) > > instance Num Dye where > (Dye x) + (Dye y) = Dye (x ++ " + " ++ y) > (Dye x) - (Dye y) = Dye (x ++ " - " ++ y) > (Dye x) * (Dye y) = Dye (x ++ " * " ++ y) > abs (Dye x) = Dye ("abs " ++ x) and so on. In this way, you can do something like > sum [Dye "x", Dye "y", Dye"z"] and get "0 + x + y + z" as the result. (In reality you probably want to keep track of bracketing and so forth.) In this way, you can take functions that accept any Num instance and feed the "dye" through them to see what they're actually computing on a given run. Has anybody ever put anything like this on Hackage? I'd prefer to not invent this stuff if somebody has already done it... (The small problem with the approach above, of course, is that as soon as the function wants to do comparisons or take flow control decisions, you've got trouble. It's not impossible to solve, but it *is* a lot of work...)

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IFL 2010: 3rd CFP and 1st Call for Participation
by Don Stewart 14 Jul '10

14 Jul '10

3RD CALL FOR PAPERS and 1ST CALL FOR PARTICIPATION 22nd Symposium on Implementation and Application of Functional Languages (IFL 2010) September 1-3, 2010 Utrecht University Alphen aan den Rijn, The Netherlands http://www.cs.uu.nl/ifl2010 ******************************************************************************************* ** Submission and Registration are now both OPEN ** ** If you intend to participate in IFL 2010, help us by registering as soon as possible. ** ** ** ** Submission closes July 25, Registration closes August 1 ** ******************************************************************************************* After a first successful visit to the USA, the Symposium on Implementation and Application of Functional Languages returns to Europe for its 22nd edition. The hosting institution is Utrecht University in the Netherlands, although the conference itself will take place in the ornithological theme park Avifauna in Alphen aan den Rijn, situated conveniently close to Schiphol (Amsterdam Airport). The symposium dates are September 1-3, 2010. The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2010 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Following the IFL tradition, IFL 2010 will use a post-symposium review process to produce formal proceedings which will be published by Springer Verlag in the Lecture Notes in Computer Science series. All participants in IFL 2010 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues. Here we follow the ACM Sigplan republication policy as defined on http://www.sigplan.org/republicationpolicy.htm. The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. After the symposium, authors will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal review process. These revised submissions will be reviewed by the program committee using prevailing academic standards to select the best articles, which will appear in the formal proceedings. INVITED SPEAKER Johan Nordlander of Lulea University, the designer and developer of the Timber language, is the invited speaker at IFL 2010. Timber is a functional programming language that draws some of its concepts from object-oriented programming, and has built-in facilities for concurrent execution. The language is specifically targeted at implementing real-time embedded systems. TOPICS IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools. If you are not sure that your work is appropriate for IFL 2010, please contact the PC chair at jur(a)cs.uu.nl. Topics of interest include, but are not limited to: language concepts type checking contracts compilation techniques staged compilation runtime function specialization runtime code generation partial evaluation (abstract) interpretation generic programming techniques automatic program generation array processing concurrent/parallel programming concurrent/parallel program execution functional programming and embedded systems functional programming and web applications functional programming and security novel memory management techniques runtime profiling and performance measurements debugging and tracing virtual/abstract machine architectures validation and verification of functional programs tools and programming techniques industrial applications of functional programming PAPER SUBMISSIONS Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English, conform to the Springer-Verlag LNCS series format and not exceed 16 pages. The draft proceedings will appear as a technical report of the Department of Computer Science of Utrecht University. SPONSORS IFL 2010 is sponsored by Microsoft Research. As a result we can offer decreased participation fees for Master students and PhD students who plan to attend or present at IFL 2010. PETER LANDIN PRIZE The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. IMPORTANT DATES Draft proceedings submission deadline July 25, 2010 Registration deadline August 1, 2010 IFL 2010 Symposium September 1-3, 2010 Submission for review process deadline October 25, 2010 Notification Accept/Reject December 22, 2010 Camera ready version February 17, 2011 PROGRAM COMMITTEE Jost Berthold University of Copenhagen (DIKU), Denmark Olaf Chitil University of Kent, UK John Clements California Polytechnic State University, USA Matthew Fluet Rochester Institute of Technology, USA Andy Gill Kansas University, USA Jurriaan Hage (Chair) University of Utrecht, Netherlands Bastiaan Heeren Open University, Netherlands Ralf Hinze University of Oxford, UK John Hughes Chalmers University of Technology, Sweden Yukiyoshi Kameyama University of Tsukuba, Japan Gabriele Keller University of New South Wales, Australia Pieter Koopman Radboud University Nijmegen, Netherlands Luc Maranget INRIA, France Simon Marlow Microsoft Research, UK Marco T. Morazán Seton Hall University, USA Rex Page University of Oklahoma, USA Ricardo Peña Universidad Complutense de Madrid, Spain Sven-Bodo Scholz University of Hertfordshire, UK Tom Schrijvers Catholic University of Leuven, Belgium Don Stewart Galois, USA Wouter Swierstra Vector Fabrics, Netherlands Don Syme Microsoft, UK Peter Thiemann University of Freiburg, Germany Phil Trinder Heriott-Watt University, Scotland Janis Voigtländer University of Bonn, Germany Viktória Zsók Eötvös Loránd University, Hungary

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Call for Copy: Monad.Reader Issue 17
by Brent Yorgey 14 Jul '10

14 Jul '10

Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 17 will be: **Friday, October 1, 2010** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (byorgey at cis.upenn.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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Comments on Haskell 2010 Report
by Alex Stangl 14 Jul '10

14 Jul '10

based upon final version PDF created 7/6/2010 11:44:27 1. I.E. and e.g. should be followed by commas -- unless UK usage differs from US standards. (Page 3 and elsewhere, although FFI chapter seems to have the commas.) Also, inconsistent mix of British and American usage throughout (-ize and -ise, flavour, behaviour, behavior, analyse, color, colour, finaliser, finalizer, etc.) 2. Inconsistent spelling (lowercase/uppercase in section 1.4; lower-case/upper-case in section 2.4) 3. In section 3.11, boolean misspelled boolen. 4. LaTeX macros involving @ showing up in text. See sects 3.12, 6.4.2, 11.1, and in Chapter 9. 5. In section 3.15.2, reference to third bullet seems like it should be fourth bullet. 6. In section 3.17.2, the example that is supposed to return [undefined,undefined,undefined] seems like it really ought to return undefined, although I can see in the description above for ~apat matching where the other interpretation would hold. I actually tried this in GHC 10.4.2, binding the result to a variable and then applying the function length to it, and it comes back with undefined, whereas performing "length [undefined,undefined,undefined]" returns 3. So it appears that in this case, at least GHC 10.4.2 is returning undefined rather than [undefined,undefined,undefined]. 7. In section 6.3.4, "[LT..]" needs whitespace in the middle to parse correctly. 8. I'm curious about last part of section 6.4.3 that says 0**y is undefined. It seems to work reasonably under GHC, returning 0 in every case except 0**0, which returns 1 (the ^0 == 1 rule taking precedence, apparently.) Saying 0**0 is undefined seems reasonable, but why 0**y? 9. In section 6.4.6, statement about b^(d-1) <= m < b^d doesn't seem to hold when m < 0. Should it be |m| in the equation, rather than m? 10. Section 7.1 uses "function" in places where it ought to use "action". It seems more correct to describe print as returning an action that outputs a value. Most of the "Input Functions" (e.g., getChar, getLine, getContents, readLn) should be described as actions, not functions. It switches to using the term "operation", which seems better, but then reverts back to "function". 11. In section 8.4, variable misspelled varibale. 12. In section 8.5.1, in "we require that chname ends on .h", "on" should be "in". 13. Also in section 8.5.1, dependent misspelled "dependant". 14. Last paragraph of section 8.5,1 has extra "a" -- "... defined to a accept a ...". Following sentence has a semicolon where it should have a comma. 15. In section 10.3, "(i.e. the programmer..." has no closing paren. 16. In section 10.4, "... other lines are comment", "comments" sounds better. This occurs twice. 17. Also in section 10.6, anything misspelled "anyything". 18. In Chapter 15, it would be more clear to describe "bit i" as producing a value with the ith bit set, and all other bits clear. 19. In section 20.3.1, caveats about finiteness of lists similar to ones given for "and" and "or" could also apply to "any" and "all". Ditto for elem, notElem, etc. Maybe a single paragraph could summarize this short-circuiting behavior for all of them. 20. In heading for 20.9.2, quotes around "Set" are not balanced. Both are closing quotes. Ditto for 20.10.1, 20.10.2. 21. In section 29.1.1, "finaliser" and "finalizer" used in same paragraph. 22. In section 38.2, first occurrence of 'dual' has mismatched quotes. 23. In section 41.1, quotes around "perform" are mismatched. Word "function" is mildly misused again here. 24. In section 41.3.1, it would be nice to document what happens if act terminates abnormally, and then a secondary exception occurs during the closing of the handle. Oftentimes systems lose the primary exception and propagate out the secondary exception, whereas in reality we may be more interested in the original primary exception. 25. In section 41.4.4, bullet before isPermissionError isn't rendered correctly. Alex

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