- Haskell-Cafe - Haskell.org

Filter by several predicates at once
by Dougal Stanton 18 Jan '08

18 Jan '08

Are the functions > passall, passany :: [a -> Bool] -> a -> Bool > passall ps v = and $ map ($v) ps > passany ps v = or $ map ($v) ps or something similar defined anywhere? Such that one can write > filter (passany tests) [0..10] > filter (passall tests) [0..10] where > tests = [>5, odd] Or is there a better way of filtering by several predicates for each value without using > filter p3 . filter p2 . filter p1 or > filter (\v -> p1 v && p2 v && p3 v) vs Cheers, D -- Dougal Stanton dougal(a)dougalstanton.net // http://www.dougalstanton.net

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HPC of several modules?
by Magnus Therning 17 Jan '08

17 Jan '08

How do I get reports on coverage of all modules in a program? The documentation I've found http://blog.unsafeperformio.com/?p=18 and http://www.haskell.org/ghc/docs/latest/html/users_guide/hpc.html both do coverage of a single module. Going the naive route of first making sure there are no compiled modules in my source tree (i.e. removing all .o and .hi files) then running 'ghc --make -fhpc MyTool.hs' succeeds in building the program, and I get a MyTool.tix and a .mix file in .hpc/ for each module after running it, but how do I get 'hpc' to produce reports containing more than just Main? 'hpc6 markup MyTool' includes only Main 'hpc6 markup MyTool Main My.Module' includes only Main 'hpc6 markup MyTool My.Module' results in an error: Writing: hpc_index.html hpc6: Prelude.foldr1: empty list None of the arguments shown by 'hpc6 help markup' stands out as a clear candidate either... 'hpc6 report --per-module MyTool' generates this: -----<module Main>----- 80% expressions used (386/479) 100% boolean coverage (0/0) 100% guards (0/0) 100% 'if' conditions (0/0) 100% qualifiers (0/0) 100% alternatives used (0/0) 100% local declarations used (0/0) 100% top-level declarations used (17/17) Where are my other modules??? Any and all help is appreciated. /M

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announcing darcs 2.0.0pre2
by David Roundy 17 Jan '08

17 Jan '08

I am pleased to announce the availability of the second prerelease of darcs two, darcs 2.0.0pre2. This release fixes several severe performance bugs that were present in the first prerelease. These issues were identified and fixed thanks to the helpful testing of Simon Marlow and Peter Rockai. We also added support for compilation under ghc 6.4, so even more users should be able to test this release. As before, some information about the prerelease is available at: http://wiki.darcs.net/index.html/DarcsTwo You can either use darcs to grab the latest darcs, or you can download a tarball at: http://darcs.net/darcs2.0.0pre2.tar.gz A few outstanding performance issues are: 1. darcs whatsnew performance has dropped for hashed repositories due to no longer tracking file-modification times. We need to reenable this feature, but it's not quite clear how best to do so. 2. darcs get on a hashed repository is not as fast as the older darcs get --partial. We could fix this by enabling the downloading of a single file _darcs/pristine.hashed.tar.gz. This eliminates the potential benefits of caching file downloads on darcs get (currently a second "get" of the same remote repository is almost free if you've enabled a global cache), so we may want to make this behavior optional. I hope we can get even more testing with this release, and look forward to finding and fixing any remaining performance regressions (or bugs, of course)! David

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Poisx select support
by Galchin Vasili 17 Jan '08

17 Jan '08

Hello, In the ghc libraries directory I can't find the Haskell .hs/.lhsthat implements Posix select. ?? I found Select.c. Regards, Vasili

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haskelldb basic documentation needed
by Immanuel Normann 17 Jan '08

17 Jan '08

with the release update haskelldb-0.9 -> haskelldb-0.10 several things have changed. Unfortunately the API documentation does not give enough information in generall. Is there any additional uptodate documentation around? In particular the fundamental function "connect" hast a new signature: *connect* :: (forall m a . MonadIO<http://hackage.haskell.org/packages/archive/mtl/1.1.0.0/doc/html/Control-Mo…>m => [( String<http://hackage.haskell.org/packages/archive/base/3.0.0.0/doc/html/Data-Char…>, String<http://hackage.haskell.org/packages/archive/base/3.0.0.0/doc/html/Data-Char…>)] -> (Database<file:///usr/share/doc/haskelldb-0.10/Database-HaskellDB-Database.html#t%3ADatabase>-> m a) -> m a) I don't know what pairs of strings this function needs. The API description is to unspecific: The connect<file:///usr/share/doc/haskelldb-0.10/Database-HaskellDB-DriverAPI.html#v%3Aconnect>function takes some driver specific name, value pairs use to setup the > database connection, and a database action to run. What are the specific name value pairs needed (for a connection to a mysql db )? Immanuel

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Re: [Haskell] Simulating client server communication with recursive monads
by Ryan Ingram 17 Jan '08

17 Jan '08

(redirected to haskell-cafe) mfix is "value" recursion, not "effect" recursion. It allows you to "tie-the-knot" with data being constructed recursively even in a monadic context. When you are using the Writer monad like this, the bind operation between statements in a "do" construct is just ++. "simulation" in your message is > simulation:: Writer [String] () > simulation = mdo > a <- server cr > cr <- client $ take 10 a > return () This is really just the following: > simulation :: Writer [String] () > simulation = Writer result where > ( a, a_out ) = runWriter (server cr) > ( cr, cr_out ) = runWriter (client $ take 10 a) > result = ( (), a_out ++ cr_out ) With "mdo" you are allowed to have the values refer to each other; the right hand side of "( a, a_out ) = ..." can refer to "cr" and vice versa. But there's no way to follow the thread of computation between the server and the client with this style. -- ryan

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ANNOUNCE: Haddock version 2.0.0.0
by David Waern 17 Jan '08

17 Jan '08

Dear Haskell community, I'm proud to announce the release of Haddock 2.0.0.0! http://www.haskell.org/haddock http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.0.0.0 Changes in version 2.0.0.0: * The GHC API is used as the front-end * Haddock now understands all syntax understood by GHC 6.8.2 * Haddock can generate documentation for some of the language extensions in GHC 6.8.2 * Format of module attributes has changed. The only way of specifiying module attributes is via a new OPTIONS_HADDOCK pragma. Example: {-# OPTIONS_HADDOCK hide, prune #-} * Haddock understands literate source files * Add a small library to read Haddock's interface files * Add a flag -B for passing the path to the GHC lib dir * Add a flag --optghc for passing options to GHC * Add a flag --ghc-version for printing the GHC version * Remove --use-package, --allow-missing-html, --ghc-pkg, in favour of only supporting --read-interface * Remove --package flag, the GHC flag -package-name can be used instead * Remove --no-implicit-prelude flag, the GHC flag -XNoImplicitPrelude can be used instead * Hoogle support temporarily removed It should be noted that this version of Haddock is not compatible with interface files from previous versions. Also, currently, when Haddock comes across a GHC language extension that it doesn't know how to render as HTML, it will bail out. If this happens to you, bug me about it, or help out by sending a patch. On the development side, Haddock has been slightly refactored for easier code navigation, and has the beginnings of a test suite. Haddock also ships with (as noted in the list of changes) a small, experimental library that can be used to read its interface files. Tools and IDE-type applications can use this library to e.g. look up the documentation for identifiers. The code repository is at http://code.haskell.org/haddock. David

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Yi editor tutorial
by Andrew Birkett 17 Jan '08

17 Jan '08

Hi, I've recently started using Yi, the haskell editor. I found it slightly non-trivial to get started, so I've written up my installation method and a "beginners guide" tutorial which I hope will be of interest to other people who'd like to try Yi. It lives at: http://nobugs.org/developer/yi/ Let me know if it's useful or if you have suggestions (to andy(a)nobugs.org) Andrew -- - http://www.nobugs.org -

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ANN: GLFW-0.3 released
by Paul L 16 Jan '08

16 Jan '08

GLFW is a Haskell module for GLFW OpenGL framework. It provides an alternative to GLUT for OpenGL based Haskell programs. The current 0.3 version is for download from hackageDB at: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/GLFW-0.3 Same as the previous 0.2 version it requires Cabal 1.2 or later for installation (which comes as default in GHC 6.8 or later). The installation is now conforming to the standard Cabal steps. New addition is the Haddock documentation for all interface functions. There is also a sample program to demonstrate its usage on the Haskell wiki site for GLFW: http://haskell.org/haskellwiki/GLFW Any feedbacks is welcome! I've only tested it on a limited number of platforms + GHC combinations, so if you have installation issue, please let me know. Thank you! -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

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Re: Simulating client server communication with recursive monads
by apfelmus 16 Jan '08

16 Jan '08

[redirected to haskell-cafe] Jan Stranik wrote: > Do you know what is the theoretical foundation for having mfix process > side-effects in the lexical order as opposed to execution order? > Could you point me to some papers, if you know of any off top your head? http://www.cse.ogi.edu/pacsoft/projects/rmb/ Regards, apfelmus

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hmp3 1.4: ncurses mp3 player in Haskell
by Don Stewart 16 Jan '08

16 Jan '08

4 years after its original release, and with almost daily use, I'm pleased to announce a new release of hmp3, the Haskell mp3 player. The goal of this project was a more stable, resize-friendly mp3 player for the console, that didn't compromise on efficiency or the user interface. This release, version 1.4, introduces pcre support for searching for tracks and albums, and improves support for ghc 6.8. Install: $ cabal install hmp3 Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmp3 Homepage: http://www.cse.unsw.edu.au/~dons/hmp3.html Repos: http://code.haskell.org/~dons/code/hmp3 Cheers, Don --- Take direct action against bad code: program Haskell!

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High-readibility version of "CONS should not evaluate its arguments?"
by Benjamin L. Russell 16 Jan '08

16 Jan '08

While reading the paper "A History of Haskell: Being Lazy With Class" (Paul Hudak, John Hughes, Simon Peyton Jones, Philip Wadler: The Third ACM SIGPLAN History of Programming Languages Conference (HOPL-III) San Diego, California, June 9-10, 2007) (http://research.microsoft.com/~simonpj/papers/history-of-haskell/history.pdf) I came across a reference (in Part I, Section 2.1: The Call of Laziness) to the paper ""CONS should not evaluate its arguments" (D. P. Friedman and D. S. Wise, in Automata, Languages, and Programming, S. Michaelson and R. Milner, Eds. Edinburgh: Edinburgh University Press, 1976, pp. 257-284), and looked for a highly readable version. However, all I could come across was Technical Report TR44 at the Indiana Department of Computer Science, at http://www.cs.indiana.edu/cgi-bin/techreports/TRNNN.cgi?trnum=TR44. This version appears as small, light typewritten type on horizontally placed double pages, and is very hard to read. Does anybody know where I can find a version of this paper with higher readability?

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ErrorT and catchError question
by Adam Smyczek 16 Jan '08

16 Jan '08

Hi, I'm trying to use ErrorT transformer based on Don Stewart's Shell example: http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10#programmable-semicolons It's probably a trivial question, but I cannot figure out how to implement the catchError function in: instance MonadError String Shell where throwError = error . ("Shell failed: "++) catchError l h = ??? Thanks for help, Adam

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jumping to code every and anywhere : what about installing tagfile and source ?
by Marc Weber 15 Jan '08

15 Jan '08

I feel this is the right place to think about this? (I'll crosspost a small announcement on ghc as well pointing to this thread) Copied from http://hackage.haskell.org/trac/hackage/ticket/207#preview: == Introduction == I personally depend on tags because the source code only tells what is really going on. So it would be incredible useful to not only get information using ghci after loading libs but also beeing able to jump to all functions you might be using anywhere (The only solution providing this in all cases is uning tags, right? Because cpp defines can introduce new functions.. To be able to jump to the code source must be installed along with libs (the way you can optionally install haddock docs) == Use case: == setup configure --with-tags --install-source (or something like that) setup build && setup install do this for each dependency given in the .cabal file (VIM:) let tags+=system('ghc-pkg --query-tagfile-location haskell98-1.0.0.0') == Issues: == * Which tool to generate tag files? * ghc(i) when targeting ghc * the hasktags program shipping with ghc * some others? * Tagfile path type relative or absolute? * absolute: After moving/ installing the sources the tagfile must be patched * relative: Do editors take the right base directory to find source files? * When to invoke the tagfile generating program? * Perfect case would be after all preprocessing has been done (Thus the tagging program should understand line number changing comments!) * Template Haskell? ( This is really tricky I think ) * Hmm sorted tagfiles would be useful as well :) == alternatives ? == If you do not think this is useful (mandatory?) how do you lookup code? (Yes I know hoogle :) perhaps using Eclipse or Visual Studio? I'd like to start implementing this somehow the next weeks. So don't hesitate and start discussing Marc Weber

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fast fractional part of floating point number - modf?
by Henning Thielemann 15 Jan '08

15 Jan '08

Is there a fast and reliable way to compute the fraction of a floating point number? I can implement fraction x = snd (properFraction x :: (Int, Double)) or fraction x = x - fromIntegral (truncate x :: Int) (actually I need 'floor' not 'truncate' but this is another issue) but these need considerably more time than fraction x = x - GHC.Float.int2Double (GHC.Float.double2Int x) Is there a fast 'fraction' built-in function? Or do I have to use FFI to modf ?

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\_ -> not equivalent to const $
by Luke Palmer 15 Jan '08

15 Jan '08

In attempting to devise a variant of cycle which did not keep its argument alive (for the purpose of cycle [1::Int..]), I came across this peculiar behavior: import Debug.Trace cycle' :: (a -> [b]) -> [b] cycle' xs = xs undefined ++ cycle' xs > take 20 $ cycle' (const $ 1:2:3:4:trace "x" 5:[]) [1,2,3,4,x 5,1,2,3,4,5,1,2,3,4,5,1,2,3,4,5] Nuts. Oh, but wait: > take 20 $ cycle' (\_ -> 1:2:3:4:trace "x" 5:[]) [1,2,3,4,x 5,1,2,3,4,x 5,1,2,3,4,x 5,1,2,3,4,x 5] Hey, it worked! Can someone explain what the heck is going on here? Luke

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Computer Science Books using Haskell
by PR Stanley 15 Jan '08

15 Jan '08

Hi Can the list recommend books that use Haskell - or any FP language but preferably Haskell - to illustrate the principles of compilers and/or algorithms? I think most of you would understand if I said that I'd prefer FP code instead of funny math symbols that don't translate into ANSI characters with the current OCR technology, unless, of course, you know of a book available in latex code. Rather than rushing straight to Google I thought I'd first draw on the wealth of knowledge that exists on this list. Cheers Paul

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QuickCheck properties: export or not?
by Paul Johnson 15 Jan '08

15 Jan '08

I was recently sent a patch for my Ranged Sets library which exported all the QuickCheck properties. I'd left them unexported on the grounds that they clutter up the documentation (although simplified versions are included in the documentation) and you can easily run them with the standard "quickcheck" script. The contributor, gwern0(a)gmail.com suggested an explicit test harness instead. I'm not unduly bothered one way or the other, but I thought I'd ask the community: what is the best practice here? Paul.

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Displaying # of reductions after each computation in ghci?
by Fernando Rodriguez 15 Jan '08

15 Jan '08

Hi, Is there a way to configure ghci to display the number of reuctions after each compution (as in winhugs)? Thanks!

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Getting frantic with FranTk
by Torsten Otto 15 Jan '08

15 Jan '08

Howdy, with a just-in-time-learning approach I managed to teach my class of advanced high schoolers the basics of functional programming using Haskell (I had only used Scheme before). Now to show them that Haskell is not a weirdo esoteric command line only language, I thought I'd end the class with spoken output (easy enough with the System module and "say" in Mac OS) and a GUI for input using FranTk. There is however something very basic I'm missing: I have Hugs installed at /opt/local/bin/hugs in MacOS 10.4/10.5. What do I do to get Hugs to recognize FranTk? I have downloaded it, but I can't even get the demo to work, none of the imports can be found: module Main where import FranTk import qualified StaticTypes as S import IOExts For Windows, there's a .bat to use, but I can't figure out how to get it to work on a Unix-system like Mac OS. I seems to be more than just to include the path when starting Hugs... Thanks in advance for any hints, regards, Torsten Otto

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Strange GLFW linker problem on Linux
by Peter Verswyvelen 15 Jan '08

15 Jan '08

Because apparently GHC works much better on Linux than Windows, I switched to that platform. I'm currently trying Fedora 8. So now I'm completely alone in the dark: no experience with Haskell, no experience with Linux; I left decades of experience with Microsoft products behind me ;-) I tried compiling GFLW (used by SOE) and a Haskell test app on my laptop, and that worked fine. Then I installed Fedora on my desktop, installed all development tools, and GLFW (both the C library and Haskell wrapper) also compiled and linked fine, but when trying to link the test app to GLFW, I got linker errors (see below). It seems these symbols are defined in libXrandr, but I have both the binary as the devel package installed: [root@localhost dev]# yum list installed | grep Xrandr libXrandr.i386 1.2.2-1.fc8 installed libXrandr-devel.i386 1.2.2-1.fc8 installed So I have no idea what to do. The main difference between the laptop and desktop is that I installed the NVidia drivers on the desktop manually (first installed the kernel-devel package, and then downloaded and installed the linux driver from the nvidia website) Any hints? Thanks, Peter Linker errors reported by ghc --make Main.hs: /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformRefreshWindowParams': x11_window.c:(.text+0x803): undefined reference to `XRRGetScreenInfo' x11_window.c:(.text+0x80d): undefined reference to `XRRConfigCurrentRate' x11_window.c:(.text+0x81b): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformCloseWindow': x11_window.c:(.text+0xb7a): undefined reference to `XRRGetScreenInfo' x11_window.c:(.text+0xb9d): undefined reference to `XRRSetScreenConfig' x11_window.c:(.text+0xba6): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformPollEvents': x11_window.c:(.text+0x115b): undefined reference to `XRRUpdateConfiguration' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformOpenWindow': x11_window.c:(.text+0x1fa5): undefined reference to `XRRSelectInput' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwPlatformGetVideoModes': x11_fullscreen.c:(.text+0x1ca): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x1db): undefined reference to `XRRConfigSizes' x11_fullscreen.c:(.text+0x219): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwSetVideoModeMODE': x11_fullscreen.c:(.text+0x329): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x344): undefined reference to `XRRConfigCurrentConfiguration' x11_fullscreen.c:(.text+0x394): undefined reference to `XRRSetScreenConfigAndRate' x11_fullscreen.c:(.text+0x3ac): undefined reference to `XRRSetScreenConfig' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwGetClosestVideoMode': x11_fullscreen.c:(.text+0x3fa): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x408): undefined reference to `XRRConfigSizes' x11_fullscreen.c:(.text+0x48f): undefined reference to `XRRConfigRates' x11_fullscreen.c:(.text+0x4dc): undefined reference to `XRRFreeScreenConfigInfo' x11_fullscreen.c:(.text+0x512): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwSetVideoModeMODE': x11_fullscreen.c:(.text+0x3be): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_init.o): In function `_glfwPlatformInit': x11_init.c:(.text+0xea): undefined reference to `XRRQueryExtension' collect2: ld returned 1 exit status

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First Israel Haskell Event
by B K 15 Jan '08

15 Jan '08

Hello all, A Haskell gathering will take place for the first time in Israel: Friday, January 18 2008 at 11:00 AM Village Green, 33 Jaffa Rd, (corner of Rivlin St), Jerusalem This will be an informal event where everyone can introduce themselves and talk about their thoughts on Haskell. Everyone and anyone are invited. If you are in the area then please stop by, and email me with any questions. Looking forward to an enlightening time, Benny

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Re: [Haskell-cafe] Yi editor tutorial
by gwern0＠gmail.com 15 Jan '08

15 Jan '08

On 2008.01.14 13:34:42 +0000, Andrew Birkett <andy(a)nobugs.org> scribbled 0.8K characters: > gwern0(a)gmail.com wrote: >> I'm going through them now, and I like them a lot. (Maybe I'll finally >> begin doing stuff with Yi!) >> Is there any particular reason you didn't put your tutorials on the >> Haskell wiki? I'd think they'd be good there. > > Cool, thanks. :-) > > I agree it'll be a good idea to move it to the wiki, and I'll do that soon. > On my own site, I can make lots of little changes locally and then > atomically (well, quickly at least!) rsync the new version up onto the > server. It makes life easier when I'm likely to change around the top > level structure. The wiki makes a lot of sense though, because it's > central and other people can extend the tutorial and fix bugs. I'd say editing a wiki is even easier. :) But if you want to wait until you've gotten it to a state where you're happy with it, that's good too. > It's also nice to be able to check the server logs and gauge interest too > (about 5000 hits since yesterday). > > Andrew True, but the interest won't last forever; so maybe after the Reddit links go quiescent? -- gwern rico Glock telex million propellants Warfare Ortega CNN 8182 Vauxhall

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cabal and hpc?
by Greg Fitzgerald 15 Jan '08

15 Jan '08

Has the Haskell Program Coverage tool been integrated into Cabal? That is, is there anything like "runhaskell Setup.hs coverage" to generate a coverage report? Thanks, Greg

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All equations must have the same arity - why?
by Neil Mitchell 15 Jan '08

15 Jan '08

Hi, It's nice to write functions in point free style: f = sort . nub But sometimes I have to add an extra case, on a certain value: f [] = [1] f = sort . nub But now these equations have different arities, and its rejected by Haskell. Why does this not simply desugar to: f [] = [1] f x = (sort . nub) x i.e. lift the arities to the longest argument list. Is there a reason this isn't done? Thanks Neil

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Code folding in Emacs
by Johan Tibell 15 Jan '08

15 Jan '08

It would be pretty neat for Haskell hacking if the Emacs Haskell mode could do the following. Imagine you have written some code like so: -- | The parse state. data S = S {-# UNPACK #-} !B.ByteString -- current chunk L.ByteString -- rest of the input {-# UNPACK #-} !Int64 -- bytes read -- | The 'Parser' monad is just a State monad carrying around the -- input ByteString. newtype Parser a = Parser { unParser :: S -> Consumed (Reply a) } -- | Match byte that fulfills predicate. satisfy :: (Word8 -> Bool) -- ^ Predicate that byte must fulfill. -> Parser Word8 -- ^ Matched byte. satisfy p = Parser $ \(S s ss pos) -> if B.null s then (if L.null ss then Empty (Error (ParseError pos)) else case L.splitAt 1 ss of (consuming,rest) -> let now = B.concat . L.toChunks $ consuming b = B.head now in if p b then Consumed $ Ok b (S (B.tail now) rest (pos + 1)) else Empty $ Error $ ParseError pos ) else let b = B.head s in if p b then Consumed $ Ok (B.head s) (S (B.tail s) ss (pos + 1)) else Empty $ Error $ ParseError pos Now you want an overview of your source file. One way would be to replace all the implementation parts with ellipses, like so: -- | The parse state. data S = S {-# UNPACK #-} !B.ByteString -- current chunk L.ByteString -- rest of the input {-# UNPACK #-} !Int64 -- bytes read -- | The 'Parser' monad is just a State monad carrying around the -- input ByteString. newtype Parser a = Parser { unParser :: S -> Consumed (Reply a) } -- | Match byte that fulfills predicate. satisfy :: (Word8 -> Bool) -- ^ Predicate that byte must fulfill. -> Parser Word8 -- ^ Matched byte. satisfy p = ... Binding a haskell-fold-source function to a key chain would enable you to get a quick overview of your module showing only the comments and type signatures. I've used the little function from http://emacs.wordpress.com/2007/01/16/quick-and-dirty-code-folding/ but it doesn't work well together with indented type signatures like in the example above. Anyone with strong Emacs-fu that knows how one could implement such a function? -- Johan

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[IETF Apps meeting] A Theory of Templating Languages
by Stephane Bortzmeyer 14 Jan '08

14 Jan '08

The IETF (http://www.ietf.org/) holds a meeting of its Application Area and is looking for papers. In a position paper, Joe Gregorio asked for information about the theory of templating languages. Giving the interest here in DSLs and conceptualization, he may find on this list the help he wants and the references he searches: >From: "Joe Gregorio" <joe(a)bitworking.org> >Date: December 14, 2007 8:20:17 AM PST >Subject: Re: Position papers due Dec 14 > >Here is my brief position paper: > >Working on the URI Templating specification has made me realize that >there is a pretty substantial hole >in computer science theory: a lack of a theory of templating >languages. For example, the current version of >URI Templates is not Turing-complete, which excludes a whole bunch of >possible attacks. In the specification I state: > > On the balance, the template processing is not Turing complete, >thus avoiding a number of > security issues, ala the billion-laughs attack of XML DTDs. > >I was rightly called out on this on the W3C URI mailing list: > > This reads a little odd, as not being Turing-complete is not >sufficient > to avoid the attack. (And DTDs are not Turing-complete either.) > >The criticism is correct. The problem is that I don't know of any >finer grained levels of classifications >of templating languages than Turing/non-Turing, and not only for >security reasons, but for general capabilities. > >For example, if there were classes of templating languages, I could >say that URI Templates fell into 'class X', and >if that class had a known set of limitations and capabilities then I >could say that URI Templates thus had those >limitations and capabilities. The weakness to the billion laughs >attack comes from two facets of DTD usage, the >first being that templates can be defined in terms of other templates, >and the second is that the depth of template >definition, in terms of other templates, isn't limited. But the >converse isn't true, that is, I don't have a general >theory of templating to lean on that says since URI Template >expansions are never defined in terms of other >expansions then URI Templates are immune to such resource >exhaustion attacks. > >I did find one paper that makes a start at such work, "Enforcing >Strict Model-View Separation in Template Engines", >but the theory is a little weak and it focuses on the nebulous idea of >separation of model and view, as opposed to >a classification of capabilities and limitations. In addition there >seems to not be a lot of work on sub-turing languages, >and most interestingly the contemporary work that is being done is on >Membrane Computing Systems, which >is in turn motivated by studying cell evolutions and chemical >reactions. I am bringing this topic forward in the >hopes of learning of other pointers into the literature, and also >learning if this problem applies to others >in the Apps area, of if I'm all alone with this problem in URI >Templates. ----- End forwarded message -----

2 1

Re: [Haskell-cafe] [newbie question] Memoization automatic in Haskell?
by Hugh Perkins 14 Jan '08

14 Jan '08

On Jan 12, 2008 10:54 PM, Henning Thielemann <lemming(a)henning-thielemann.de> wrote: > > On Sat, 12 Jan 2008, Hugh Perkins wrote: > > > I guess that Haskell's referential transparence means the answers to > > the isPerfectSquare will be cached, ie automatically memoized? (not > > sure if is correct term?) > > http://www.haskell.org/haskellwiki/Memoization > Interesting... but I dont understand... I thought that referential transparence meant that once the answer to a function has been calculated once, it will always be the same, and that the interpreter can, and will, cache this answer? So, if I call f( 20 ) once, for some, arbitrary, f, it will have to go away and calculate f(20), but if I call it multiple times, it will just return the value it already calculated?

11 13

How to add ENV variable in runhaskell shell script
by Steve Lihn 14 Jan '08

14 Jan '08

Hi, In perl scripts (unix), one can do == #!/usr/local/bin/perl BEGIN { $ENV{LD_LIBRARY_PATH} = ...; } do my perl stuff == The setting of ENV variable before the program runs allows me to fix the shell environments. In this case, I need to specify where to look for the shared library. How do I do this in Haskell if I am writing the same script using: == #!/path/to/runhaskell {- how to set LD_LIBRARY_PATH = ... ? -} do my haskell stuff == Thanks, Steve

5 4

Possibility to port vshaskell to VS2008?
by Philipp Riemer 14 Jan '08

14 Jan '08

Because my university is in the MSNDAA-program I could download the new Visual Studio 2008 Professional, what I've done today. Now I tried to install the vshaskell-extension to start learning Haskell but the installer only quits with the message that (of course) VS2005 is not installed. Now is my question if I have to download the "old" VS2005 or if it is somehow possible to get this extension running with VS9.0? I already tried to use the EclipseFP-plugin so I already have (win)hugs, ghc and haddoc installed (if it helps for the problem above). The problem with this plugin was that Ctrl+Space does apparently not work for code hints and because I'm just started to learn the language, I don't know every keyword... So I have to look it up everytime somewhere, I want to implement something new. The fact that Prelude.hs and others are plain text are a great help, but what I have seen in the screenshot at http://www.haskell.org/visualhaskell/screenshots.html would be much better...

3 3

Solving a geometry problem with Haskell
by Rafael Almeida 14 Jan '08

14 Jan '08

Hello, I have been browsing through the problems at projecteuler.net and I found one that seemed interesting. It's the problem 176, I'll state it here: The four rectangular triangles with sides (9,12,15), (12,16,20), (5,12,13) and (12,35,37) all have one of the shorter sides (catheti) equal to 12. It can be shown that no other integer sided rectangular triangle exists with one of the catheti equal to 12. Find the smallest integer that can be the length of a cathetus of exactly 47547 different integer sided rectangular triangles. I thought I've solved it nicely, only to find later on that my solution was too slow (it has been running for almost three days now). While I was creating my solution I used literate haskell, which I think helped me a bunch to think about the problem. I wrote it originally in portuguese -- the portuguese literate version has all the attempts I've made until getting to the final one. For posting it here I've translated the reasoning around the attempt that solved the problem -- although it does it very slow -- into a new .lhs file: http://www.dcc.ufmg.br/~rafaelc/problem176.lhs After some profiling I found out that about 94% of the execution time is spent in the ``isPerfectSquare'' function. So I began researching about better ways to write that functio. Someone pointed to me on #haskell that the C library gmp has such a function. So I went ahead and wrote a C version of the program using gmp: http://www.dcc.ufmg.br/~rafaelc/problem176.c It's not the prettiest C code, as I did it really quickly, simply translating haskell code into C, but I believe it works. That C solution has been running for more than one hour now and no solution has come up yet. So I don't think it's worthed even writing a faster isPerfectSquare in haskell. As I was translating from Portuguese to English I revisited my logic and I can't see any problems with it. I think the problem is only of slowness, really. Does anyone have a better idea for how I should try to solve this problem? I'm all out of ideas. []'s Rafael

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Re: All equations must have the same arity - why?
by Jonathan Cast 14 Jan '08

14 Jan '08

On 13 Jan 2008, at 4:56 PM, jerzy.karczmarczuk(a)info.unicaen.fr wrote: > Jonathan Cast writes: >> On 13 Jan 2008, at 4:15 PM, Achim Schneider wrote: > ... never mind... >> I'm glad you are capable of ever so nobly assigning the purest >> imaginable motives to the designers of Haskell. You are an >> inspiration to us all. jcc > > Jonathan, please... > You see as well as anybody else what is the point of this discussion. > Perhaps it is not as bad as discussing with Cristian Baboi, but still. Very well, I'll be good. jcc (Meant to send this to the list first time...)

1 0

Add "number of downloads" to hackageDB page?
by Hugh Perkins 14 Jan '08

14 Jan '08

I seem to remember a thread about this a while back actually, but... Any chance of adding the number of downloads to the hackageDB page? For those packages that are included in ghc, hugs etc, perhaps add a green tick with "included in ghc", "included in hugs", etc? That way it should be relatively easier to know for newbies which packages are more or less mature/stable. Optional: perhaps include a tick-box/dropdown to only show packages with more than a certain (configurable) number of downloads?

2 1

Possibilities for website construction using Haskell?
by Hugh Perkins 14 Jan '08

14 Jan '08

What are the possibilities for website construction using Haskell?

5 8

hash-cons
by Tony Finch 14 Jan '08

14 Jan '08

I've been thinking about hashlife recently. I've written part of a fairly didactic C implementation <http://dotat.at/prog/misc/hashlife.c> but I there are more interesting things that can be done with it. In particular, the core calc2() function is essentially implementing lazy evaluation, so it ought to be possible to write it even more nicely in Haskell. However it relies crucially on a hash-cons aka intern aka memoized constructor find(). How can one implement this in Haskell? Google doesn't turn up anything very helpful. If I can solve the hash cons problem, then it ought to be fairly straightforward to use Parallel Haskell to speed up the algorithm on multicore machines. Tony. -- f.a.n.finch <dot(a)dotat.at> http://dotat.at/ PORTLAND: SOUTH 7 TO SEVERE GALE 9 VEERING SOUTHWEST 5 TO 7. ROUGH OR VERY ROUGH. RAIN AT FIRST, THEN SQUALLY SHOWERS. MODERATE OR GOOD.

1 0

Patterns overlapped?
by Fernando Rodriguez 14 Jan '08

14 Jan '08

Hi, When I compile this code, ghc complains about some overlapped patterns in function depth. What on Earth is ghc talking about? O:-) data BinTree a = EmptyTree | NodeBT a (BinTree a) (BinTree a) deriving Show emptyBT = EmptyTree depth emptyBT = 0 depth (NodeBT _ left right) = max (1 + depth left) (1 + depth right)

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Access to list
by Fernando Rodriguez 14 Jan '08

14 Jan '08

Hi, If I define the follwoing functions: car (x:_) = x car [] = [] cdr (_:xs) = xs cdr [] = [] and try to apply them to some list, such as car [1,2,3] I get this odd error: <interactive>:1:9: No instance for (Num [a]) arising from the literal `3' at <interactive>:1:9 Possible fix: add an instance declaration for (Num [a]) In the expression: 3 In the first argument of `car', namely `[1, 2, 3]' In the expression: car [1, 2, 3] What am I doing wrong this time? :-P Thanks

5 5

Comments and suggestions on code
by Andre Nathan 13 Jan '08

13 Jan '08

Hello I've just found time to finish writing my first "real world" program, so I thought I'd post it here and ask for insight on general issues such as if there's anything that isn't done "the Haskell way", or if there's something that could be done more efficiently. The code is at the bottom of this message and also at http://hpaste.org/4893. I realize it's a bit long, so if anyone could just skim through it and see if there's anything really ugly or stupid and point it out, it would be of great help :) Just to make it easier to follow the code, its idea is simple: - Build a process tree by reading entries from /proc (represented as a map); - Compare each child of the init process against a whitelist (which comes from a configuration file); - For each child not in the whitelist, send it a KILL signal. The idea here is to run this on webservers and try to catch bad customers who try to run daemons from their accounts, the typical script kiddie stuff. Anyway, there's one specific question I'd like to ask. I'm using "StateT PsTree IO" to keep program state (the process tree). IO is necessary because all information is read from /proc files. Now consider the following function: appendChild :: Pid -> Pid -> StateT PsTree IO Bool appendChild ppid pid = do tree <- get let PsInfo psData children = mapLookup ppid tree put $ Map.insert ppid (PsInfo psData (pid:children)) tree return True It changes the program state by modifying a process tree entry, but it does no I/O at all. The return type is there basically to match the return type of the function which calls it (insertParent), which calls functions that do I/O. Is there anyway to avoid the "IO" in appendChild's signature (other than making it a pure function by passing the process tree as a parameter and returning a modified map)? I would also like to try ways to improve efficiency, maybe trying a hash table instead of a map for the state, and also using bytestrings. I guess I could try making it parallel, since each child of init can be checked independently. Anyway, this is already longer than I thought it would be (I hope I'm not abusing too much :) The code follows. Thanks in advance for any comments or suggestions. Andre module Main where import qualified Data.Map as Map import Directory import Control.Monad.State import Maybe import System.Environment import System.IO import System.Posix.Files import System.Posix.Signals import System.Posix.Unistd import System.Posix.User import Text.Printf import Text.Regex import Text.Regex.Posix type Pid = FilePath type Uid = String type PsData = Map.Map String String type PsChildren = [Pid] type KillFunction = PsTree -> Pid -> IO () data PsInfo = PsInfo PsData PsChildren type PsTree = Map.Map Pid PsInfo type Whitelist = Map.Map FilePath String mapLookup :: (Ord a) => a -> Map.Map a b -> b mapLookup k = fromJust . Map.lookup k -- Process Tree construction parentPid :: PsInfo -> Pid parentPid (PsInfo psData _) = mapLookup "PPid" psData getProcInfo :: String -> PsData -> PsData getProcInfo line psData = do case line =~~ "^([A-Za-z]+):[[:space:]]+(.*)$" of Nothing -> psData Just ([_, key, value]:_) -> Map.insert key value psData getIds :: String -> PsData -> (String, String) getIds id psData = (rId, eId) where (rId:eId:_) = words (mapLookup id psData) processData :: String -> PsData processData procData = addIds psData where psData = foldr getProcInfo Map.empty (lines procData) addIds psData = Map.union psData (idMap psData) idMap psData = Map.fromList [("RUid", rUid), ("EUid", eUid), ("RGid", rGid), ("EGid", eGid)] (rUid, eUid) = getIds "Uid" psData (rGid, eGid) = getIds "Gid" psData readLink :: String -> IO String readLink link = catch (readSymbolicLink link) (\e -> return "?") procInfo :: Pid -> IO PsInfo procInfo pid = do let dir = "/proc/" ++ pid ++ "/" procData <- readFile $ dir ++ "status" exe <- readLink $ dir ++ "exe" cwd <- readLink $ dir ++ "cwd" cmd <- readFile $ dir ++ "cmdline" let cmd' = subRegex (mkRegex "[^a-zA-z[:space:]\\/\\.-]") cmd " " info = processData procData adminInfo = Map.fromList [("Exe", exe), ("Cwd", cwd), ("Cmd", cmd')] return $ PsInfo (Map.union info adminInfo) [] addProc :: Pid -> StateT PsTree IO PsInfo addProc pid = do info <- lift $ procInfo pid modify (Map.insert pid info) return info appendChild :: Pid -> Pid -> StateT PsTree IO Bool appendChild ppid pid = do tree <- get let PsInfo psData children = mapLookup ppid tree put $ Map.insert ppid (PsInfo psData (pid:children)) tree return True insertParent :: Pid -> Pid -> StateT PsTree IO Bool insertParent ppid pid = do tree <- get if Map.member ppid tree then appendChild ppid pid else do built <- insertInTree ppid if built then appendChild ppid pid else return False insertPid :: Pid -> StateT PsTree IO Bool insertPid "1" = do info <- addProc "1" return True insertPid pid = do info <- addProc pid let ppid = parentPid info if ppid == "0" then return False else insertParent ppid pid insertInTree :: Pid -> StateT PsTree IO Bool insertInTree pid = do tree <- get if Map.member pid tree then return True else insertPid pid buildTree :: FilePath -> StateT PsTree IO Bool buildTree entry | entry =~ "^[0-9]+$" = insertInTree entry | otherwise = return False createTree :: IO PsTree createTree = do entries <- getDirectoryContents "/proc" execStateT (mapM_ buildTree entries) Map.empty -- Process Tree pretty-printing treeStr :: PsTree -> PsChildren -> Int -> String -> String treeStr tree children level str = foldr append str children where append pid s = treeStr tree children' (level + 1) newstr where PsInfo _ children' = mapLookup pid tree pad = take (4 * level) [' ', ' ' ..] newstr = s ++ "\n" ++ pad ++ pid printTree :: PsTree -> Pid -> IO () printTree tree pid = putStrLn (treeStr tree children 1 pid) where PsInfo _ children = mapLookup pid tree -- Process killing tryToKill :: PsTree -> KillFunction -> Pid -> Uid -> Uid -> Bool -> IO Bool tryToKill tree killFun pid "0" allowedUid killed = do -- The process may be starting, give it a second chance. sleep 10 -- conservative value. let PsInfo psData _ = mapLookup pid tree if allowedUid /= mapLookup "EUid" psData then killFun tree pid >> return True else return (killed || False) tryToKill tree killFun pid _ _ _ = killFun tree pid >> return True buildWhitelist :: String -> Whitelist -> Whitelist buildWhitelist line whitelist = do case line =~~ "^[ \t]*([^: \t]+)[ \t]*:[ \t]*([^ \t]+)[ \t]*$" of Nothing -> error "Invalid configuration file" Just ([_, exe, user]:_) -> Map.insert exe user whitelist readWhiteList :: FilePath -> IO Whitelist readWhiteList file = do contents <- readFile file return $ foldr buildWhitelist Map.empty (lines contents) allowedUidForExecutable :: Whitelist -> FilePath -> IO Uid allowedUidForExecutable whitelist exe = do case Map.lookup exe whitelist of Nothing -> return "0" Just user -> do entry <- getUserEntryForName user return $ show (userID entry) processBastard :: PsTree -> Whitelist -> KillFunction -> Bool -> Pid -> IO Bool processBastard tree whitelist killFun killed pid = do let PsInfo psData _ = mapLookup pid tree euid = mapLookup "EUid" psData exe = mapLookup "Exe" psData allowedUid <- allowedUidForExecutable whitelist exe if euid /= allowedUid then tryToKill tree killFun pid euid allowedUid killed else return killed withEachBastard :: PsTree -> Whitelist -> KillFunction -> IO Bool withEachBastard tree whitelist killFun = foldM (processBastard tree whitelist killFun) False children where (PsInfo _ children) = mapLookup "1" tree printWarnings :: Pid -> PsData -> IO () printWarnings pid psData = do let exe = mapLookup "Exe" psData let cmd = mapLookup "Cmd" psData let cwd = mapLookup "Cwd" psData let ppid = mapLookup "PPid" psData let euid = mapLookup "EUid" psData let ruid = mapLookup "RUid" psData let egid = mapLookup "EGid" psData if ruid /= euid then hPrintf stderr "PID %s: RUID=%s, EUID=%s\n" pid ruid euid else return () hPrintf stderr "Killing proc %s (%s, UID=%s, GID=%s), child of %s\n" pid exe euid egid ppid hPrintf stderr " Process command line: %s\n" cmd hPrintf stderr " Process working directory: %s\n" cwd killTree :: KillFunction killTree tree pid = do let PsInfo psData children = mapLookup pid tree printWarnings pid psData signalProcess sigKILL (read pid) mapM_ (killTree tree) children killBastards :: PsTree -> Whitelist -> Int -> IO () killBastards tree whitelist n = do runAgain <- withEachBastard tree whitelist killTree if runAgain && n > 1 then do sleep 2 killBastards tree whitelist (n - 1) else return () -- Configuration printConfig :: KillFunction printConfig tree pid = do let PsInfo psData _ = mapLookup pid tree exe = mapLookup "Exe" psData euid = mapLookup "EUid" psData entry <- getUserEntryForID (read euid) putStrLn $ exe ++ ": " ++ (userName entry) -- main helpers config :: PsTree -> IO () config tree = do withEachBastard tree Map.empty printConfig return () pstree :: PsTree -> IO () pstree tree = do printTree tree "1" -- In newer kernels, process 2 is kthreadd, which is not a child -- of init. let info = mapLookup "2" tree if parentPid info /= "1" then printTree tree "2" else return () kill :: PsTree -> IO () kill tree = do whitelist <- readWhiteList "killbastards.conf" killBastards tree whitelist 5 main :: IO () main = do args <- getArgs tree <- createTree case args of ["config"] -> config tree ["pstree"] -> pstree tree [] -> kill tree

3 18

ANNOUNCE: pcre-light, a light, portable regular expression library for Haskell
by Don Stewart 13 Jan '08

13 Jan '08

pcre-light A light regular expression library, using Perl 5 compatible regexes I'm pleased to announce the first release of pcre-light. This library provides a simple, efficient interface to PCRE regular expressions, via either strict ByteStrings or classical Strings. Compilation and matching of regular expressions is done via two functions: compile :: ByteString -> [PCREOption] -> Either String Regex match :: Regex -> ByteString -> [PCREExecOption] -> Maybe [ByteString] A convenience interface for 'Char8' Strings is also provided. == Examples == Although the operations by default take ByteStrings, we can avoid unnecessary 'pack' calls using GHC's support for ByteStrings literals, enabled with -XOverloadedStrings: > :m + Text.Regex.PCRE.Light > :m + Data.ByteString.Char8 > :set -XOverloadedStrings > let Right r = compile "the quick brown fox" [] > match r "the quick brown fox" [] Just ["the quick brown fox"] > match r "the quick brown FOX" [] Nothing We can also enable various matching extensions, > let Right r = compile "the quick brown fox" [caseless] > match r "the quick brown FOX" [] Just ["the quick brown FOX"] Subpatterns, and fancy Perl regex extensions are happily supported: > let Right r = compile "^(abc){1,2}zz" [] > match r "abczz" [] Just ["abczz","abc"] Where the subpattern bound by ( ) was returned as the second element of the list. > let Right r = compile "\\w+(?=\t)" [] > match r "the quick brown\t fox" [] Just ["brown"] You can do lots of silly things with this: > let Right r = compile "^(a()+)+" [] > match r "aaaa" Just ["aaaa", "a", ""] The full set of compile and runtime PCRE extensions are supported. == Get it == * Stable tarballs, (on Hackage, of course): http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pcre-light * Cabal install it! Using the new 'cabal-install', you can automatically download, build and install the package: $ cabal update $ cabal install pcre-light Downloading 'pcre-light-0.1'... Configuring pcre-light-0.1... Preprocessing library pcre-light-0.1... Building pcre-light-0.1... Registering pcre-light-0.1.. And off we go! For more information about cabal-install, see the hackage page for this excellent tool. * Darcs repository: http://code.haskell.org/~dons/code/pcre-light/ * Documentation: http://code.haskell.org/~dons/docs/pcre-light/ * Stability The library takes correctness seriously, and comes with a reasonable testsuite (with plans to greatly extend it), and code coverage data for those tests (using GHC's new -fhpc flag). You can see the test coverage results here: http://code.haskell.org/~dons/tests/pcre-light/hpc_index.html Yours in code, Don P.S. I'd like to encourage other authors to distribute code coverage results for their libraries! hpc is an invaluable tool to ensure high quality libraries for the Haskell community. P.P.S. Consider consider contributing your own light bindings to useful C libraries. The more we have, the more certain and sustainable Haskell development will be :) P.P.P.S. Thanks to #haskell for testing and advice.

1 0

the trivial monad- thoughts and a question
by Brian Hurt 13 Jan '08

13 Jan '08

So, I've been playing around with what I call the trivial monad: module TrivialMonad where data TrivialMonad a = M a recover :: TrivialMonad a -> a recover (M x) = x instance Monad TrivialMonad where (M x) >>= f = f x (M x) >> f = f return x = M x fail s = undefined This is actually a surprisingly usefull little sucker- it allows you to "demonadify" code. Which is usefull when you have some places where you want to use the code within a monad, and some places where you don't. You write the base bit of code monadically, and then demonadify it as needed. The first question I have is it is possible to implement this guy without wrapping the value in a constructor? What I'd like to do is replace the: data TrivialMonad a = M a with something like: type TrivialMonad a = a and then be able to junk the recover function. The second question I have is: is there any hope of getting something like this into the standard library? Thanks, Brian

5 4

ANN: Haskell Cryptographic Library 4.1.0
by Dominic Steinitz 13 Jan '08

13 Jan '08

I'd like to announce the release of a new version of the library following various contributions (contributors are bcc'd). Additions include: BubbleBabble, TEA, HMAC and more large word support. It no longer includes Base64. This is provided by http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc-0.10.1. Many thanks to all contributors. Dominic. PS I always mention this but the library really needs to be reviewed holistically and possibly restructured given the advent of bytestrings. If anyone would like to volunteer to do this or take over as library maintainer, please let me know.

1 0

Gtk2HS and GHC 6.8.2
by Peter Verswyvelen 12 Jan '08

12 Jan '08

It seems GHC 6.8.2 fixes a couple of bugs in GHC 6.8.1. Gtk2HS does not yet detect my GHC 6.8.2 installation, but I guess it is 100% compatible. Is it possible to get the Gtk2HS installer detect GHC 6.8.2? I'm on Windows. Thanks, Peter

2 2

Linq (FP in C#)
by Hugh Perkins 12 Jan '08

12 Jan '08

Linq went live in C# in November, as part of .Net 3.5. It adds lots of FP-things to C#. It's really fun to be able to use Haskell-ish things in C#. Manipulating lists and collections just got *much* easier. Things it does: - map, fold, filter are all there (they're called "select", "agregate", "where") - limited support for laziness (since .Net 2.0; you can write a lazy "zip" function; I couldnt figure out how to write a lazy "unzip" function) - you can extend the methods available on all lists and collections - lambda expressions - type inferrence (technically, this is part of .Net 3.x, rather than specific to Linq). Things it doesnt do: - recursion doesnt seem particularly optimized (quick 2 minute test, I could be wrong) - no way to enforce purity It's an interesting vindication of the ideas in Haskell that C#, a big mainstream language, has integrated ideas from it, and that they're in production today.

2 1

Typo in ByteString documentation
by Johan Tibell 12 Jan '08

12 Jan '08

In Data.ByteString.Unsafe in the documentation of unsafePackAddress the documentation reads: "Use unsafePackAddress if you know the length of the string statically." I assume that unsafePackAddressLen is the being function referred to here. If I was sitting in front of my laptop I would send you a patch. :) -- Johan

1 0

where is the FFI glue code for STM?
by Galchin Vasili 12 Jan '08

12 Jan '08

Hello, I see where the top level code (written in Haskell)for STM. I have found STM.c;however, I can't seem to find the FFI glue code.? Thanks, Vasili

2 1

Not to load Prelude
by Maurício 12 Jan '08

12 Jan '08

Hi, Is it possible not to load Prelude module when compiling a Haskell module? Or instruct ghc to “unload” it? Thanks, Maurício

8 11

Next PDXFunc Meeting (Portland/Oregon FP Group): Monday, January 14, 7pm, CubeSpace
by Don Stewart 12 Jan '08

12 Jan '08

Join us at the next meeting of pdxfunc, the Portland Functional Programming Study Group, on Monday, 14th January, at CubeSpace. ------------------------------------------------------------------------ We'll have presentations, demos and discussions. We welcome programmers interested in all functional languages and our meetings have content for coders of all skill levels. If interested, please also subscribe to our mailing list at http://groups.google.com/group/pdxfunc PRESENTATIONS (1) Justin Bailey: Exploring Haskell's space and time profiling tools A presentation on the space and time profiling tools available for GHC Haskell, featuring slides and interactive demos. Heap profiling tools and methods will be discussed, along with a demonstration of how to use them to detect a space leak. Time profiling tactics will be covered using "cost-centre" annotations to help select candidates for optimization. Recommendations will be given on how to read the "Core" language with an eye for optimization. Justin Bailey (jgbailey(a)gmail.com) has been programming professionally for 12 years, and is currently a Computer Science master's student at Portland State University. Until 2006, he coded exclusively with object-oriented languages like Java and C#, but then discovered Haskell and hasn't looked back. He's released a Haskell library for building command-line applications called HCL, made contributions to several other Haskell libraries, and continues to hack Haskell every day he can. (2) Iavor Diatchki: Writing parsing combinators with Haskell A presentation on parsing combinators, given as a hands-on demonstration for developing a small library to parse JSON data using Haskell. The entire process will be shown from scratch, starting with defining the concept of JSON values, using pretty-printer combinators to turn values into strings, and finally using parser combinators to turn strings into values. Iavor S. Diatchki is an engineer at Galois Inc., where he uses functional programming for the development of high assurance software. Iavor obtained his PhD degree in 2007. His research focused on various aspect of using functional languages for the development of low-level systems software such as OS kernels.

1 0

Field updates in a state monad
by Michael Roth 12 Jan '08

12 Jan '08

Hello list, still playing with monads and states, I have the following question: Given: import Control.Monad.State.Lazy data MyData = MyData { content :: String } foobar :: State MyData String foobar = do gets content Ok, that looks nice and tidy. But: foobar2 :: State MyData () foobar2 = do modify $ \x -> x { content = "hello haskell"} ...looks not so nice. Exists there a way to write this cleaner without writing countless "set_xyz" helper functions? Michael

5 4

Re: [Haskell-cafe] Re: Why purely in haskell?
by Miguel Mitrofanov 11 Jan '08

11 Jan '08

> However, the fact that (0 / 0) == (0 / 0) yields False is quite shocking. Just for the record: the following is from Firebug (JavaScript debugger for Firefox) session: >>> a = 0/0 NaN >>> a == a false >>> a === a false

4 3

Haskell-mode 2.4
by Stefan Monnier 11 Jan '08

11 Jan '08

Here's for Xmas, version 2.4 of the Haskell-mode package. Haskell-mode is an Elisp package to support editing Haskell in Emacs. See the home page at http://www.iro.umontreal.ca/~monnier/elisp/ -- Stefan Changes since 2.3: * Update license to GPLv3. * New derived major mode for .hsc files. * Removed the C-c C-r binding to reload a file. You can still call inferior-haskell-reload-file (and/or bind it to your favorite key, including C-c C-r) or you can now use C-u C-c C-l. * C-c C-d looks up the symbol at point in the Haddock docs. * Haddock comments are highlighted with font-lock-doc-face if it exists. * Use `tex' rather than `latex' for haskell-literate. * inf-haskell.el tries to find the root of the module hierarchy to determine the root of a project (either by looking for a Cabal file or relying on the `module' declaration line). If all works well, this will make C-c C-l automatically switch to the root dir, so that dependencies in other directories are automatically found. If it doesn't, complain and/or set inferior-haskell-find-project-root to nil. * The new command haskell-hoogle helps you query Hoogle from Emacs.

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