- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] The range operator
by PR Stanley 07 Apr '08

07 Apr '08

At 12:28 07/04/2008, you wrote: >On Fri, Apr 4, 2008 at 10:49 PM, Andrew Coppin ><andrewcoppin(a)btinternet.com> wrote: > > More to the point, the range y..z goes in steps of y-z. ;-) >[x,y..z] goes in steps of y-x ;-), [y..z] goes in steps of 1 >(depending on the type). Could you elaborate please? >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe

2 1

Memory allocation in extractor function (newbie question)
by Alexander Kireyev 07 Apr '08

07 Apr '08

Hello, While trying to write a program for the countPaths Code Jam problem I ran into what seems to me as a weird behaviour in terms of memory allocation. The task is to count the number of way you can spell a certain "word" by walking some path on a board of letters. Being a newbie I started with a very straightforward recursive approach, which is not effective, but still helps to improve understanding of Haskell basics. Quite naturally I quickly hit the point where the program becomes too slow, so I tried to profile and optimize the code. I used 3 data types: data GridEntry = GridEntry {letter :: Char, neighbors :: [Point]} data Area = Area {letters :: (Array (Int, Int) GridEntry), width :: Int, height :: Int} data Point = Point { x :: Int, y :: Int} deriving (Show, Eq) With the recursive approach I had to retrieve GridEntries (a letter in a certain point of grid together with the list of its neighbours on the grid) a lot. Quite surprisingly I saw that this operation was overly expensive in my program. The most time was spent in these 2 functions: countPathsFrom :: Area -> Int -> String -> Point -> Int countPathsFrom _ count [] _ = count countPathsFrom area count (l:[]) point = count + if (letter (letterAt area point) == l) then 1 else 0 countPathsFrom area count (l:ls) point = let gridPt = letterAt area point points = neighbors gridPt in if (letter gridPt == l) then countForPoints area ls count points else count letterAt :: Area -> Point -> GridEntry letterAt area (Point x y) = letters area ! (x, y) The profiling log (./paths +RTS -P) shows the following time/space behaviour for them: countPathsFrom Main 181 11830476 37.8 52.3 59.5 82.2 28 1325013312 letterAt Main 184 11830476 21.6 29.9 21.6 29.9 16 757150464 What puzzles me here is how the function letterAt generates 64 bytes of garbage per call. Since there are no side-effects in this section of program - and noone can damage the 'area' structure - I would expect the compiler/runtime to use a reference to the data in the 'area' structure when returning values from letterAt. Instead it seems to make a copy of GridEntry and return that. The question here is whether (why?) this behaviour is normal and if it is possible to optimize the code in such cases. Thanks in advance, -Alexander

2 1

The range operator
by PR Stanley 07 Apr '08

07 Apr '08

Hi folks [x, y..z] What's the role of x? Cheers, Paul

5 4

REMINDER: Next Hackathon (Hac4) starts in 4 days
by Thomas Schilling 07 Apr '08

07 Apr '08

Hi Haskell Hackers! There are only 4 days left until the fourth Hackathon (http:// www.haskell.org/haskellwiki/Hac4) at Chalmers University in Gothenburg, Sweden. If you haven't registered, yet, please do so now! Registration deadline: Tuesday, April 8, 2008 To register, go to http://www.haskell.org/haskellwiki/Hac4/Register and follow the steps. For all those already registered, here's a short (not nearly complete) checklist: * Make sure you have an account on code.haskell.org. (See http:// www.haskell.org/haskellwiki/Hac4/Projects for how to do that.) * Decide what to work on if you haven't yet. (See http:// www.haskell.org/haskellwiki/Hac4/Projects for ideas.) * Make sure your laptop is working and that you take all required extra equipment. (If your wireless driver sucks, we can probably find some cables and a switch here.) * It would be good to have all the code you want to work on already on your computer. Also make sure it builds with your compiler version. If your distro doesn't have binaries, maybe install some software in advance, like Gobby or profiled versions of GHC, newest version of gtk2hs or whatever seems appropriate. It would just be a shame to waste hours of precious hacking time. * Make a backup. Just in case. ;) * Many hostels want a confirmation a few days before arrival, don't forget. * If you need some phone numbers of locals, check the wiki site, if you need some more help from us locals, you can ask us at our IRC channel #haskell-hac4. We're looking forward to a fun weekend! / The Hac4 Team

1 0

Re: [Haskell-cafe] ANN: Hayoo! beta 0.1
by Timo B. Hübel 07 Apr '08

07 Apr '08

On Sunday 06 April 2008 20:31:09 you wrote: > Overall feedback: Cool! So far, I like Hayoo!, and I'm therefore > interested in Holumbus. Is there some technical overview available? Currently, only what you can find on http://holumbus.fh-wedel.de but we will try to extend the site in the near future. > transcript of my short test of hayoo, including nitty-picky feedback: > [...] Thanks for this extensive feedback, some of these are known issues we're already working on which will be fixed soon. The others are on my TODO list now :) Regards, Timo

1 0

Role based access control via monads or arrows or... something
by porrifolius 06 Apr '08

06 Apr '08

Hello. I've been playing around trying to write a framework to support/enforce access control to resources. So far my efforts have yielded little but bruised forehead and compressed plaster-board. What I'd like is a solution that: (1) prevents access to resources except via a fine-grained permissions checking gateway (2) supports on-the-fly permissions eg Bob can see Fred's salary (3) supports dynamic role constraints eg Bob can't be both appointor and appointee of secret agent status (4) allows lack of permission to optionally act as a filter rather than cause an abort, eg Bob viewing all salaries returns Fred's but doesn't return Tom's rather than aborting altogether because Bob lacks the permission over Tom (5) well defined behaviour when checking permissions for actions that change permissions (6) it must be pure, no need for IO. (7) ideally required permissions would appear (and accumulate) in type signatures via inference so application code knows which are required and type checker can reject static/dynamic role constraint violations I've attempted a solution using arrows based loosely upon ideas in [1] and [2]. I can't figure out how to make it work, even if I did get it working I now suspect it can be done far more simply, and I don't think it could ever provide feature (7). For what it's worth it's attached. Ideally you kind folk could help me come up with a type-level solution to satisfy (7), so you could have something like: deptAveSal :: (HasPerms subject? Read Salary [person]?, HasPerm subject? Read Employees dept?, HasRole subject? Manager dept?) => Department -> Salary Failing that how to do it in a more simple fashion? I now think that a State-like monad exposing only functions taking values in a wrapper type that carries required permissions may be sufficient, but still probably couldn't satisfy (7). Failing that my existing attempt has me stumped for a few reasons: how do I get hold of the subject and resource so I can build the correct permission in Test? eg the Person whose Salary is needed in salary, and who's trying to get it where do I get the System from in Test? eg fakeSystem in personByName how to implement the filter functionality in RBAC? Parametric over container types? I think that perhaps the Validator would need to be a monad that holds the initial state of the System to provide a stable set of permissions/roles and that the subject and System should also be threaded through the arrows for use/modification. Any help you can offer for my aching cranium will be _much_ appreciated. Thanks. [1] Encoding Information Flow in Haskell - Peng Li, Steve Zdancewic. http://www.seas.upenn.edu/~lipeng/homepage/flowarrow.html [2] A Library for Secure Multi-threaded Information Flow in Haskell - Alejandro Russo, Tsa-chung Tsai, John Hughes. http://www.cs.chalmers.se/~russo/publications.html

6 7

Beginners arrow question
by Paul Johnson 06 Apr '08

06 Apr '08

I'm using arrows for the first time, with HXT. I think I'm getting the hang of it, but one problem has me stumped. I have a function "lookupFormatter" which takes a string and returns an arrow, and I want to use that arrow. Something like this: myProblem :: (ArrowXml a) -> a XmlTree String myProblem = proc xml do name <- getAttrValue "name" -< xml fmt <- arr lookupFormatter -< name fmt -< xml But I can't figure out how to do it. I get "fmt: not in scope". Can anyone help? Thanks, Paul.

5 4

Problems installing OpenAL / compiling an OpenAL program
by Henk-Jan van Tuyl 06 Apr '08

06 Apr '08

L.S., I downloaded OpenAL from Hackage and tried to compile a program that uses it (on a Windows XP computer). I got a long list of messages in the linking phase; I found a related ticket, http://hackage.haskell.org/trac/ghc/ticket/1140 with a patch. I applied the patch manually and removed the package and installed it again. The problem remained. The output from the compiler run: ghc -Wall --make TestOpenAL.hs -i"C:\Programs\Haskell\Libs" -dcore-lint -o TestO penAL.exe [1 of 1] Compiling Main ( TestOpenAL.hs, TestOpenAL.o ) TestOpenAL.hs:57:8: Warning: This binding for `s' shadows an existing binding In a pattern binding in a 'do' expression Linking TestOpenAL.exe ... C:\Program Files\Haskell\OpenAL-1.3.1.1\ghc-6.8.2/libHSOpenAL-1.3.1.1.a(Buffer.o )(.text+0x1de):fake: undefined reference to `alGetBufferi@12' C:\Program Files\Haskell\OpenAL-1.3.1.1\ghc-6.8.2/libHSOpenAL-1.3.1.1.a(Buffer.o )(.text+0x5f7):fake: undefined reference to `alBufferData@20' C:\Program Files\Haskell\OpenAL-1.3.1.1\ghc-6.8.2/libHSOpenAL-1.3.1.1.a(Buffer.o )(.text+0xa4e):fake: undefined reference to `alGetBufferi@12' C:\Program Files\Haskell\OpenAL-1.3.1.1\ghc-6.8.2/libHSOpenAL-1.3.1.1.a(Source.o )(.text+0x1b9):fake: undefined reference to `alSourcei@12' C:\Program Files\Haskell\OpenAL-1.3.1.1\ghc-6.8.2/libHSOpenAL-1.3.1.1.a(Source.o )(.text+0x30d):fake: undefined reference to `alIsSource@4' Etcetera. Then I downloaded OpenAL with the command: darcs get http://darcs.haskell.org/packages/OpenAL/ Trying to install this gives: Libs\OpenAL>runhaskell Setup.hs configure Configuring OpenAL-1.3.1.1... Libs\OpenAL>runhaskell Setup.hs build Preprocessing library OpenAL-1.3.1.1... Building OpenAL-1.3.1.1... Sound/OpenAL/Config.hs:40:0: HsOpenALConfig.h: No such file or directory My questions are: 1) How do I get a proper package installed? 2) How do I find tickets for a certain package? 3) Is there an automatic way of applying patches from the tickets? 4) Is the darcs repository version incomplete? -- Met vriendelijke groet, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

1 0

lhs2TeX --> html?
by Conal Elliott 06 Apr '08

06 Apr '08

Has anyone fiddled with hooking up lhs2TeX a tex->html tool like jsMath, for lovely code in a web page? - Conal

1 0

Re: [Haskell] Some old and quite old news.
by gwern0＠gmail.com 06 Apr '08

06 Apr '08

On 2008.04.05 17:42:00 +0400, Serguey Zefirov <s_zefirov(a)ipmce.ru> scribbled 0.6K characters: > gwern0(a)gmail.com пишет: >> Hmm. I'm having trouble getting it through SVN: >> >> gwern@localhost:1003~>svn co http://thesz.mskhug.ru/browser/hiersort [ >> 1:44PM] >> svn: PROPFIND request failed on '/browser/hiersort' >> svn: PROPFIND of '/browser/hiersort': 200 OK (http://thesz.mskhug.ru) >> >> Is there some trick that as a Darcser I don't know about? >> > Actually, I do not know too. Maybe, just a version mismatch? > > Did you tried to access files using just a web browser? > > I CC'd that to myself at home and will try to resolve matters ASAP. At > least I will make a tarball and post it somewhere at MskHUG website. > > Thank you for your interest. ;) Well, I looked at some of the files with a browser, and that worked fine. It's just when I tried to do a checkout that fails. I've asked the guys in #svn, and they said the 'real' repo is elsewhere, so I went and asked #trac where the real repo's URL is. One of them said 12:37 < thatch> gwern: the faq can't cover it. Trac only knows the local filesystem path to the repo, not its web-accessible path. So I dunno. After some guessing, thatch came up with <http://thesz.mskhug.ru/svn/hiersort/> as the repo URL. It's downloading now, although slowly. -- gwern Z7 Service NSG Sayeret FIPS140-1 encryption data-haven continuous black-bag illuminati

1 0

DEFUN08: Call for Talks & Tutorials (co-located w/ ICFP08)
by Matthew Fluet (ICFP Publicity Chair) 05 Apr '08

05 Apr '08

Call for Talks and Tutorials ACM SIGPLAN 2008 Developer Tracks on Functional Programming http://www.deinprogramm.de/defun-2008/ Victoria, BC, Canada, 25, 27 September, 2008 The workshop will be held in conjunction with ICFP 2008. http://www.icfpconference.org/icfp2008/ Important dates Proposal Deadline: June 27, 2008, 0:00 UTC Notification: July 14, 2008 DEFUN 2008 invites functional programmers who know how to solve problems with functional prorgamming to give talks and lead tutorials at the The ICFP Developer Tracks. We want to know about your favorite programming techniques, powerful libraries, and engineering approaches you've used that the world should know about and apply to other projects. We want to know how to be productive using functional programming, write better code, and avoid common pitfals. We invite proposals for presentations in the following categories: How-to talks: 45-minute "how-to" talks that provide specific information on how to solve specific problems using functional programming. These talks focus on concrete examples, but provide useful information for developers working on different projects or in different contexts. Examples: - "How I made Haskell an extension language for SAP R/3." - "How I replaced /sbin/init by a Scheme program." - "How I hooked up my home appliances to an Erlang control system." - "How I got an SML program to drive my BMW." General language tutorials Half-day general language tutorials for specific functional languages, given by recognized experts for the respective languages. Technology tutorials Half-day tutorials on techniques, technologies, or solving specific problems in functional programming such as: - how to make the best use of specific FP programming techniques - how to inject FP into a development team used to more conventional technologies - how to connect FP to existing libraries / frameworks / platforms - how to deliver high-performance systems with FP - how to deliver high-reliability systems with FP Remember that your audience will include computing professionals who are not academics and who may not already be experts on functional programming. Presenters of tutorials will receive free registration to ICFP 2008. Submission guidelines Submit a proposal of 150 words or less for either a 45-minute talk with a short Q&A session at the end, or a 300-word-or-less proposal for a 3-hour tutorial, where you present your material, but also give participants a chance to practice it on their own laptops. Some advice: - Give it a simple and straightforward title or name; avoid fancy titles or puns that would make it harder for attendees to figure out what you'll be talking about. - Clearly identify the level of the talk: What knowledge should people have when they come to the presentation or tutorial? - Explain why people will want to attend: is the language or library useful for a wide range of attendees? Is the pitfall you're identifying common enough that a wide range of attendees is likely to encounter it? - Explain what benefits attendees are expected to take home to their own projects. - For a tutorial, explain how you want to structure the time, and what you expect to have attendees to do on their laptops. List what software you'll expect attendees to have installed prior to coming. Submit your proposal in plain text electronically to defun-2008-submission-AT-deinprogramm.de by the beginning of Friday, June 27, Universal Coordinated Time. Organizers Kathleen Fisher AT&T Labs Simon Peyton Jones Microsoft Research Mike Sperber (co-chair) DeinProgramm Don Stewart (co-chair) Galois

1 0

Doing without IORef
by Jinwoo Lee 05 Apr '08

05 Apr '08

Hi, Recently I wrote a code that uses readline library (System.Console.Readline). I had to maintain a state (file path) and do IO throughout the code, so I decided to use StateT monad. The problem was that in order to retrieve the current state (file path) inside the handler that had been registered by using bindKey function of readline, I had to resort back to using IORef rather than using the state stored in the StateT monad. It's because the handler for bindKey should have the type of Int -> Char -> IO Int. Here is my code snippet. type MyState a = StateT FilePath IO a rootDir :: FilePath rootDir = "/root/" main :: IO () main = do hSetBuffering stdout NoBuffering execStateT (do pwd <- get pwdRef <- lift $ newIORef pwd lift $ bindKey '\t' (tabHandler pwdRef) lift $ bindKey '\^L' ctlLHandler commandLoop pwdRef) rootDir return () tabHandler :: IORef FilePath -> Int -> Char -> IO Int tabHandler pwdRef _ _ = do *pwd <- readIORef pwdRef* insertText pwd return 0 ... commandLoop :: IORef FilePath -> MyState () commandLoop pwdRef = commandLoop' where commandLoop' = do pwd <- get *lift $ writeIORef pwdRef pwd* maybeLine <- lift $ readline $ makePrompt $ dropTrailingPathSeparator pwd case maybeLine of Nothing -> return () Just "exit" -> return () Just line -> do let tokens = words line case tokens of [] -> commandLoop' ("exit":_) -> return () _ -> do lift $ addHistory line processLine tokens commandLoop' ... Is there any way in which I can do without IORef in tabHandler and commandLoop (written in red and bold, if you can see)? Thanks, Jinwoo -- Jinwoo Lee Always remember that you are unique. Just like everyone else.

7 13

Strange behavior of float literals
by Vladimir Reshetnikov 05 Apr '08

05 Apr '08

The float literal 1e-100000000000000000000000000000000000000000000 in GHC evaluates to 1.0, and 1e-999999999999999999999999999999999999999999999 evaluates to 10.0. Is it a bug, or a documented overflow behavior? What it the correct place to submit bug reports concerning GHC? -- Thank you, Vladimir Reshetnikov (aka nikov), Microsoft MVP

3 2

HDBC, character encoding
by Adrian Neumann 05 Apr '08

05 Apr '08

Hi, I wrote a CGI program to access a Postgres database using HDBC. The database stores books and I want to display those from a certain author. Everything works fine, unless I search for someone with an umlaut in his name. Böll, for example. I have a function like this > bookByAuthor :: Connection -> AutorName -> IO [[String]] > bookByAuthor c aName = do > writeFile "./err.log" ((show aName)++" "++(show $ toSql aName)) > rows <- quickQuery c "SELECT * FROM buecher WHERE lower (autor_name) LIKE ? ORDER BY autor_name, buch_name" [toSql $ map toLower $ '%':aName++"%"] > return $ map (map fromSql) rows It returns me a SqlError. However, doing the same in ghci works perfectly. I can't understand why. err.log contains > "b\195\182ll" SqlString "b\195\182ll" which is ok I think. Since > quickQuery c "SELECT * FROM buecher WHERE lower(autor_name) LIKE ? ORDER BY autor_name, buch_name" [toSql "%b\195\182%"] works in ghci. I have tried "b\246ll", but that doesn't even work in ghci, although the database-encoding is utf-8. This all is really annoying... Adrian

6 8

Bug in Hugs, Haskell behavior question
by Fritz Ruehr 05 Apr '08

05 Apr '08

In lab the other day I was showing pattern bindings to a student and broached a limiting case, one with no variables to be bound in the pattern. I was surprised to find that Hugs crashed when I tried a pattern binding at top level like this: (2,[1,4],5) = (2,[1,4],5) It also crashed on the simpler: [2] = [2] On the other hand, this turns out to be acceptable: 2 = 2 In fact, even this goes through without a hitch! 2 = 3 I'm not sure from the language definition yet whether this last should give an "Unmatched pattern" error, but if it's intended behavior, it does look a little odd. Would anyone care to argue for or against allowing this? In any case, the more structured patterns cause the latest (Sep 06) Hugs release to crash, with "INTERNAL ERROR: compileGlobalFunction". (GHC allows the strange "2 = 3" and handles the structured ones fine, including even "(1,[2,3],4) = (4,[3,37],42)". I haven't checked any other compilers.) -- Fritz

4 4

mostly for Neil: tagsoup problems
by Magnus Therning 05 Apr '08

05 Apr '08

Neil, and others, Does the cabal file for Tagsoup require a version of Cabal newer than 1.1.6? In case it does it doesn't say so. I suspect this is the cause of the rather cryptic error message: "setup: tagsoup.cabal:20: 'Executable' stanza starting with field 'ghc-options'". I also noticed that the Haddock-umentation on Neil's side is for version 0.1, while Hackage has version 0.4. I was rather confused by that at first, since the module names had changed :) /M

2 1

Re: [Haskell-cafe] Windows CE, Xscale Compiler?
by PR Stanley 04 Apr '08

04 Apr '08

At 14:37 04/04/2008, you wrote: >And how would I cross compile something for that platform with ghc? >(There seems to be no port, which is fine) > > Don't look at me mate. :-) >PR Stanley schrieb: >>I'm surprised you can't use the Glasgow implementation on CE. >>At 13:55 04/04/2008, you wrote: >>>Is there any Haskell compiler for Windows CE on a XScale platform? >>>I googled around a bit and found references to a Hugs >>>implementation but couldn't find any place to download it. >>> >>>I have the opportunity to program a teledrive[1] and would very >>>much like to avoid something disfunctional like C. >>> >>>[1] http://www.iavproducts.com/de/produkte/teledrive/teledrive.php >>> >>> >>> >>> >>>_______________________________________________ >>>Haskell-Cafe mailing list >>>Haskell-Cafe(a)haskell.org >>>http://www.haskell.org/mailman/listinfo/haskell-cafe >>_______________________________________________ >>Haskell-Cafe mailing list >>Haskell-Cafe(a)haskell.org >>http://www.haskell.org/mailman/listinfo/haskell-cafe > > > >

1 0

Windows CE, Xscale Compiler?
by Adrian Neumann 04 Apr '08

04 Apr '08

Is there any Haskell compiler for Windows CE on a XScale platform? I googled around a bit and found references to a Hugs implementation but couldn't find any place to download it. I have the opportunity to program a teledrive[1] and would very much like to avoid something disfunctional like C. [1] http://www.iavproducts.com/de/produkte/teledrive/teledrive.php

2 1

trying to install ghc-6.8.2 both binaries and sources
by michael＠schmong.org 04 Apr '08

04 Apr '08

I am operating under the assumption that Idid have a broken gcc. I installed a new one This is what happened when I tried compiling ghc-6.8.2 make all /usr/bin/ghc -H16m -O -w -I. -Iinclude -Rghc-timing -ignore-package Cabal -ignore-package filepath -I../libraries -fglasgow-exts -no-recomp -c System/FilePath/Posix.hs -o System/FilePath/Posix.o -ohi System/FilePath/Posix.hi cc1: error: unrecognized option `-fno-unit-at-a-time' <<ghc: 129595404 bytes, 17 GCs, 2640525/5069484 avg/max bytes residency (3 samples), 20M in use, 0.00 INIT (0.00 elapsed), 0.59 MUT (0.80 elapsed), 0.09 GC (0.14 elapsed) :ghc>> make[2]: *** [System/FilePath/Posix.o] Error 1 make[1]: *** [boot] Error 2 make: *** [stage1] Error 1 this is exactly what happened prior to installing a new gcc. Here's what config.log says $ ./configure --prefix=/home/michael ## --------- ## ## Platform. ## ## --------- ## hostname = schmong.org uname -m = i686 uname -r = 2.6.16.33-vpsX uname -s = Linux uname -v = #2 SMP Tue Jan 23 22:53:20 EST 2007 /usr/bin/uname -p = unknown /bin/uname -X = unknown /bin/arch = i686 /usr/bin/arch -k = unknown /usr/convex/getsysinfo = unknown hostinfo = unknown /bin/machine = unknown /usr/bin/oslevel = unknown /bin/universe = unknown PATH: /usr/local/bin PATH: /usr/bin PATH: /bin PATH: /usr/bin/X11 PATH: /usr/games PATH: /usr/lib ## ----------- ## ## Core tests. ## ## ----------- ## running configure, to aid debugging if configure makes a mistake. It was created by The Glorious Glasgow Haskell Compilation System configure 6.8. 2, which was generated by GNU Autoconf 2.59. Invocation command line was $ ./configure --prefix=/home/michael ## --------- ## ## Platform. ## ## --------- ## hostname = schmong.org uname -m = i686 uname -r = 2.6.16.33-vpsX uname -s = Linux uname -v = #2 SMP Tue Jan 23 22:53:20 EST 2007 /usr/bin/uname -p = unknown /bin/uname -X = unknown /bin/arch = i686 /usr/bin/arch -k = unknown /usr/convex/getsysinfo = unknown hostinfo = unknown /bin/machine = unknown /usr/bin/oslevel = unknown /bin/universe = unknown PATH: /usr/local/bin PATH: /usr/bin PATH: /bin PATH: /usr/bin/X11 PATH: /usr/games PATH: /usr/lib ## ----------- ## ## Core tests. ## ## ----------- ## configure:1502: checking build system type configure:1520: result: i686-pc-linux-gnu configure:1528: checking host system type configure:1542: result: i686-pc-linux-gnu configure:1550: checking target system type configure:1564: result: i686-pc-linux-gnu configure:2121: checking for ghc configure:2139: found /usr/bin/ghc configure:2151: result: /usr/bin/ghc configure:2175: checking version of ghc The Glorious Glasgow Haskell Compilation System, version 6.6 configure:2204: result: 6.6 configure:2217: checking for ghc-pkg matching /usr/bin/ghc configure:2229: result: /usr/bin/ghc-pkg configure:2275: checking whether ghc has readline package configure:2286: result: yes configure:2296: checking for nhc configure:2329: result: no configure:2296: checking for nhc98 configure:2329: result: no configure:2338: checking for hbc configure:2371: result: no configure:2508: checking for ld configure:2526: found /usr/bin/ld configure:2538: result: /usr/bin/ld configure:2642: checking for path to top of build tree configure:2667: result: /home/michael/src/ghcsrc/ghc-6.8.2 configure:2728: checking whether #! works in shell scripts configure:2745: result: yes configure:2796: checking for perl configure:2814: found /usr/bin/perl configure:2826: result: /usr/bin/perl configure:2852: checking if your perl works in shell scripts configure:2870: result: yes configure:2875: checking for python configure:2893: found /usr/bin/python configure:2905: result: /usr/bin/python configure:2959: checking for gcc configure:2985: result: /home/michael/bin/gcc configure:3229: checking for C compiler version configure:3232: /home/michael/bin/gcc --version </dev/null >&5 gcc (GCC) 3.4.6 Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. configure:3235: $? = 0 configure:3237: /home/michael/bin/gcc -v </dev/null >&5 Reading specs from /home/michael/lib/gcc/i686-pc-linux-gnu/3.4.6/specs I have also tried to install the binaries, this may be more promising. ./configure --prefix=$HOME checking build system type... i686-pc-linux-gnu checking host system type... i686-pc-linux-gnu checking target system type... i686-pc-linux-gnu Which we'll further canonicalise into: i386-unknown-linux checking for path to top of build tree... pwd: timer_create: Operation not supported configure: error: cannot determine current directory this is exactly what happened when I tried to install the binaries with the old gcc. Here's the config.log $ ./configure --prefix=/home/michael ## --------- ## ## Platform. ## ## --------- ## hostname = schmong.org uname -m = i686 uname -r = 2.6.16.33-vpsX uname -s = Linux uname -v = #2 SMP Tue Jan 23 22:53:20 EST 2007 /usr/bin/uname -p = unknown /bin/uname -X = unknown /bin/arch = i686 /usr/bin/arch -k = unknown /usr/convex/getsysinfo = unknown /usr/bin/hostinfo = unknown /bin/machine = unknown /usr/bin/oslevel = unknown /bin/universe = unknown PATH: /usr/local/bin PATH: /usr/bin PATH: /bin PATH: /usr/bin/X11 PATH: /usr/games PATH: /usr/lib ## ----------- ## ## Core tests. ## ## ----------- ## configure:1692: checking build system type configure:1710: result: i686-pc-linux-gnu configure:1732: checking host system type configure:1747: result: i686-pc-linux-gnu configure:1769: checking target system type configure:1784: result: i686-pc-linux-gnu configure:1907: checking for path to top of build tree configure:1923: error: cannot determine current directory ## ---------------- ## ## Cache variables. ## ## ---------------- ## ac_cv_build=i686-pc-linux-gnu ac_cv_env_CC_set=set ac_cv_env_CC_value=/home/michael/bin/gcc ac_cv_env_CFLAGS_set= ac_cv_env_CFLAGS_value= ac_cv_env_CPPFLAGS_set= ac_cv_env_CPPFLAGS_value= ac_cv_env_CPP_set= ac_cv_env_CPP_value= ac_cv_env_LDFLAGS_set= ac_cv_env_LDFLAGS_value= ac_cv_env_build_alias_set= ac_cv_env_build_alias_value= ac_cv_env_host_alias_set= ac_cv_env_host_alias_value= ac_cv_env_target_alias_set= ac_cv_env_target_alias_value= ac_cv_host=i686-pc-linux-gnu ac_cv_target=i686-pc-linux-gnu ## ----------------- ## ## Output variables. ## ## ----------------- ## ArCmd='' CC='/home/michael/bin/gcc' CFLAGS='' CPP='' CPPFLAGS='' DEFS='' ECHO_C='' ECHO_N='-n' ECHO_T='' EXEEXT='' GccExtraViaCOpts='' GccVersion='' HaveGcc='' INSTALL_DATA='' INSTALL_PROGRAM='' INSTALL_SCRIPT='' LDFLAGS='' LIBOBJS='' LIBS='' LN_S='' LTLIBOBJS='' OBJEXT='' PACKAGE_BUGREPORT='' PACKAGE_NAME='' PACKAGE_STRING='' PACKAGE_TARNAME='' PACKAGE_VERSION='' PATH_SEPARATOR=':' PerlCmd='' RANLIB='' SHELL='/bin/sh' SedCmd='' TargetPlatform='i386-unknown-linux' ac_ct_CC='' bindir='${exec_prefix}/bin' build='i686-pc-linux-gnu' build_alias='' build_cpu='i686' build_os='linux-gnu' build_vendor='pc' datadir='${datarootdir}' datarootdir='${prefix}/share' docdir='${datarootdir}/doc/${PACKAGE}' dvidir='${docdir}' exec_prefix='NONE' exeext='' fp_prog_ar_raw='' hardtop='' host='i686-pc-linux-gnu' host_alias='' host_cpu='i686' host_os='linux-gnu' host_vendor='pc' htmldir='${docdir}' includedir='${prefix}/include' infodir='${datarootdir}/info' libdir='${exec_prefix}/lib' libexecdir='${exec_prefix}/libexec' localedir='${datarootdir}/locale' localstatedir='${prefix}/var' mandir='${datarootdir}/man' oldincludedir='/usr/include' pdfdir='${docdir}' prefix='/home/michael' program_transform_name='s,x,x,' psdir='${docdir}' sbindir='${exec_prefix}/sbin' sharedstatedir='${prefix}/com' sysconfdir='${prefix}/etc' target='i686-pc-linux-gnu' target_alias='' target_cpu='i686' target_os='linux-gnu' target_vendor='pc' ## ----------- ## ## confdefs.h. ## ## ----------- ## #define PACKAGE_NAME "" #define PACKAGE_TARNAME "" #define PACKAGE_VERSION "" #define PACKAGE_STRING "" #define PACKAGE_BUGREPORT "" configure: exit 1 whew. Okay can anyone give me ideas on how to proceed? I have also verified I have the correct libreadline.so.5, libncurses.so.5. michael litchard

2 1

Re: [Haskell-cafe] [GSoC] Porting HaRe to use the GHC API
by Chaddaï Fouché 04 Apr '08

04 Apr '08

2008/4/1, Claus Reinke <claus.reinke(a)talk21.com>: > as for the project, the are actually two APIs to consider, > GHC's and HaRe's, and the main stumbling points are those > things that are not in those APIs (explicitly or at all): > > <snip> Many thanks for the valuable insights. I intend to work in close collaboration with the Kent team, indeed I'll do an internship over the summer with Simon Thompson ! Don't worry on this point. Of course I'll also try to work with the GHC developers on the subject of the GHC API. My objective is to make it work on the 6.8 API but if it appears that certain functions would be useful in the future API I'll be sure to report this to the GHC team. If I can, I would also like to be present during the discussion between the two Simon. Another notion I was interested in was to be able to reproduce a sequence of multi-module refactorings even in the absence of the initial module. It would allow to present a kind of "interface diff" for a distribution which would allow the developer of a module which depends on the distribution to update the call to this library. Of course it wouldn't be perfect and wouldn't convey the semantic modifications of the interface but it would help for all the renaming and usual modifications of external interfaces. To refactor modules that use CPP, I can see some possibilities : transforming the macro into placeholders (undefined) and inversing the transformation after the refactoring, trying every combination of the variables for the #ifdef/ifndef, forgetting those that don't compile and confronting the refactorisation of the others to see if they merge... That would need some work and would probably be very inefficient as it is But all of that should wait after we get HaRe working with the GHC API. :-) -- Chaddaï

2 1

compile-time question
by Galchin Vasili 04 Apr '08

04 Apr '08

hello, I have added new function definitions to the namespace of an existing module. I did 1: runhaskell Setup.hs configure 2. runhaskell Setup.hs build 3) runhaskell Setup.hs install successfully so that a Linux .a(rchive) is installed. I write a small test case that references one of the new functions; however, when I build the test case, I get an "Out of scope" message indicated that at ghc(i) compile time the new function symbol cannot be found. Why? kind regards, Vasili

2 1

Precedence (Part 2)
by PR Stanley 04 Apr '08

04 Apr '08

Hi folks > let f = sum.map (^2).filter even > f [1..4] 20 So far so good! > sum.map (^2).filter even [1..4] returns an error. How is it that the composition above as part of a function equation doesn't return any errors while on its own it requires parentheses? I can understand the need for the parentheses - the composition operator takes two arguments/operand,s each of which is a mapping which must correspond to specific domain and range requirements i.e. (b->c -> (a->b) -> (a->c) Why aren't the parentheses required in the function definition? Cheers, Paul

4 4

Typing with co/contra-variance.
by Ben Lippmeier 04 Apr '08

04 Apr '08

Hi all, I have some quick questions for the type theory people: If I write an expression: (if .. then 23 else "Erk") In Haskell this would be an error, but perhaps I can assign it the type 'Top' (or 'Any') and then use reflection ala Data.Dynamic to inspect the type of this object at runtime and cast it back to something useful... But if I write: isEven "Erk" where isEven :: Int -> Bool isEven i = case i of 1 -> False 2 -> True ... Then this would be a genuine type error, because the case-expression demands an actual Int at runtime. Questions: 1) Could I perhaps wave my arms around and say something about the Int in the type of isEven being in a contra-variant position? Is this what is actually happening?, and can someone point me to a good paper? 2) This seems simpler than real intersection types, which I know are problematic. If I only want 'Top' and not a real object system like in Scala or Java, then can I just add this to a HM/unification style inference algorithm and expect it to work? I'm thinking the unifier only needs to know the variance of the types it's unifying to decide whether to throw an error or return Top - or will there be problems with higher order functions etc? I had a read through the subtyping chapter in "Types and Programming Languages" by Pierce - it gives the typing rules but don't mention inference or implementations. Scala seems to have this (http://www.scala-lang.org/intro/variances.html) but as I understand it, their system doesn't support full type inference without user supplied annotations... BTW: searching for 'the any type' in Google helps even less than you might expect :) Thanks, Ben.

4 3

installing ghc-6.8.2
by michael＠schmong.org 04 Apr '08

04 Apr '08

It seems there is no ghc 6.8.2 for my version of debian. So I am compiling from source. I ran config with no problem. make generated some errors. I omit all output except the end. Let me know if Ileft something important out please. make all /usr/bin/ghc -H16m -O -w -I. -Iinclude -Rghc-timing -ignore-package Cabal -ignore-package filepath -I../libraries -fglasgow-exts -no-recomp -c System/FilePath/Posix.hs -o System/FilePath/Posix.o -ohi System/FilePath/Posix.hi cc1: error: unrecognized option `-fno-unit-at-a-time' <<ghc: 129595956 bytes, 17 GCs, 2640537/5069484 avg/max bytes residency (3 samples), 20M in use, 0.00 INIT (0.00 elapsed), 0.67 MUT (0.76 elapsed), 0.11 GC (0.14 elapsed) :ghc>> make[2]: *** [System/FilePath/Posix.o] Error 1 make[1]: *** [boot] Error 2 make: *** [stage1] Error 1 so it's this line that seems of the most interesting cc1: error: unrecognized option `-fno-unit-at-a-time' any tips on how to deal with this would be most helpful. Michael Litchard

4 4

Type constraints for class instances
by Krzysztof Skrzętnicki 03 Apr '08

03 Apr '08

Hello everyone, I'm working on a small module for comparing things incomparable with Ord. More precisely I want to be able to compare equal infinite lists like [1..]. Obviously (1) compare [1..] [1..] = _|_ It is perfectly reasonable for Ord to behave this way. Hovever, it doesn't have to be just this way. Consider this class class YOrd a where ycmp :: a -> a -> (a,a) In a way, it tells a limited version of ordering, since there is no way to get `==` out of this. Still it can be useful when Ord fails. Consider this code: (2) sort [ [1..], [2..], [3..] ] It is ok, because compare can decide between any elements in finite time. However, this one (3) sort [ [1..], [1..] ] will fail because of (1). Compare is simply unable to tell that two infinite list are equivalent. I solved this by producing partial results while comparing lists. If we compare lists (1:xs) (1:ys) we may not be able to tell xs < ys, but we do can tell that 1 will be the first element of both of smaller and greater one. You can see this idea in the code below. --- cut here --- {-# OPTIONS_GHC -O2 #-} module Data.YOrd where -- Well defined where Eq means equality, not only equivalence class YOrd a where ycmp :: a -> a -> (a,a) instance (YOrd a) => YOrd [a] where ycmp [] [] = ([],[]) ycmp xs [] = ([],xs) ycmp [] xs = ([],xs) ycmp xs'@(x:xs) ys'@(y:ys) = let (sm,gt) = x `ycmp` y in let (smS,gtS) = xs `ycmp` ys in (sm:smS, gt:gtS) ycmpWrap x y = case x `compare` y of LT -> (x,y) GT -> (y,x) EQ -> (x,y) -- biased - but we have to make our minds! -- ugly, see the problem below instance YOrd Int where ycmp = ycmpWrap instance YOrd Char where ycmp = ycmpWrap instance YOrd Integer where ycmp = ycmpWrap -- ysort : sort of mergesort ysort :: (YOrd a) => [a] -> [a] ysort = head . mergeAll . wrap wrap :: [a] -> [[a]] wrap xs = map (:[]) xs mergeAll :: (YOrd a) => [[a]] -> [[a]] mergeAll [] = [] mergeAll [x] = [x] mergeAll (a:b:rest) = mergeAll ((merge a b) : (mergeAll rest)) merge :: (YOrd a) => [a] -> [a] -> [a] merge [] [] = [] merge xs [] = xs merge [] xs = xs merge (x:xs) (y:ys) = let (sm,gt) = x `ycmp` y in sm : (merge [gt] $ merge xs ys) --- cut here --- I'd like to write the following code: instance (Ord a) => YOrd a where ycmp x y = case x `compare` y of LT -> (x,y) GT -> (y,x) EQ -> (x,y) But i get an error "Undecidable instances" for any type [a]. Does anyone know the way to solve this? Best regards Christopher Skrzętnicki

5 9

ANN: hdbc-odbc 1.1.4.1
by John Goerzen 03 Apr '08

03 Apr '08

Hi folks, HDBC-ODBC 1.1.4.1 has been uploaded to http://software.complete.org/hdbc-odbc and to Hackage. Bryn Keller reported a build problem on Windows with GHC 6.8.x, which has been fixed. -- John

1 0

FW: Haskell
by Simon Peyton-Jones 03 Apr '08

03 Apr '08

Dear Haskell Cafe members Here's an open-ended question about Haskell vs Scheme. Don't forget to cc Douglas in your replies; he may not be on this list (yet)! Simon -----Original Message----- From: D. Gregor [mailto:kerrangster@gmail.com] Sent: 30 March 2008 07:58 To: Simon Peyton-Jones Subject: Haskell Hello, In your most humble opinion, what's the difference between Haskell and Scheme? What does Haskell achieve that Scheme does not? Is the choice less to do with the language, and more to do with the compiler? Haskell is a pure functional programming language; whereas Scheme is a functional language, does the word "pure" set Haskell that much apart from Scheme? I enjoy Haskell. I enjoy reading your papers on parallelism using Haskell. How can one answer the question--why choose Haskell over Scheme? Regards, Douglas

14 21

Template Haskell -- when are things evaluated?
by Emil Axelsson 03 Apr '08

03 Apr '08

Hello all! Up until yesterday I thought I understood the basics of Template Haskell, but now I'm a little confused. Consider the following code module A where a1 = [| (2::Int) + 2 |] a2 = let x = (2::Int) + 2 in [| x |] a3 = [| y |] where y = (2::Int) + 2 z = (2::Int) + 2 a4 = [| z |] module B where import A a1S = $a1 a2S = $a2 a3S = $a3 a4S = $a4 I'd have thought that in all four cases the addition was evaluated at compile-time, but compiling with -ddump-splices reveals that this is only the case for a2 and a3. Is there a general reliable rule for when things are evaluated? Thanks, / Emil

3 5

Re: [Haskell-cafe] Function Precedence
by PR Stanley 03 Apr '08

03 Apr '08

>Think about this: > >map (+1) [1..10] > >What should it do? > take (+1) and return a function which takes a list as its > argument and finally return a list. >How about: > >f 1 2 3 > >Should that be f (1 (2 3)), or ((f 1) 2) 3? The latter, of course, but that's not really what I'm driving at. I'm asking why we can't have a function treated differently with regard to the precedence and associativity rules. f 1 2 is indeed ((f 1) 2). Why not f 1 g 2 == ((f 1) (g 2))? Cheers, Paul

5 6

[Newbie] Problem with Data.Map (or something else ?)
by Bruno Carnazzi 02 Apr '08

02 Apr '08

Dears Haskellers, As an Haskell newbie, I'm learning Haskell by trying to resolve Euler Project problems (http://projecteuler.net/ ). I'm hanging on problem 14 (Collatz problem). I've written the following program... Which does not end in a reasonable time :( My algorithm seems ok to me but I see that memory consumption is gigantic... Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) In a more general way, how can I troubleshoot these kind of problem ? Here's the code : import qualified Data.List as List import qualified Data.Map as Map f n | even n = n `div` 2 | otherwise = 3 * n + 1 chain m n = let chain' cn cm | Map.member cn m = Map.map (+ (m Map.! cn)) cm | otherwise = chain' (f cn) $! Map.insert cn 1 (Map.map (+1) cm) in chain' n Map.empty chains n = List.foldl' (\m i -> Map.union m (chain m i)) (Map.singleton 1 1) [2..n] maxCollatz c1@(_,l1) c2@(_,l2) | l1 < l2 = c2 | otherwise = c1 maxChain = List.foldl' maxCollatz (0,0) . Map.toList . chains main = let n = 1000000 in putStrLn $ show $ maxChain n Hope someone can help me, I really don't see what is th problem... Best regards, Bruno.

6 9

How can I represent 4x4 map in haskell
by iliali16 02 Apr '08

02 Apr '08

Hi can you please tell me how can I represent 4x4 map in haskell.Should I show it as a list of lines and each line to be a list of char or I am mistaken? Thanks in advance! -- View this message in context: http://www.nabble.com/How-can-I-represent-4x4-map-in-haskell-tp16396273p163… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

6 9

unix support
by Galchin Vasili 02 Apr '08

02 Apr '08

Hello, On my personal computer, I added some functionality to the unix package and now I want to test this functionality. Basically I did a cabal install to the global env on my laptop. I just ran a session of ghci: vigalchin@ubuntu:~$ ghci GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m System.Posix Prelude System.Posix> :t openFd openFd :: FilePath -> OpenMode -> Maybe FileMode -> OpenFileFlags -> IO Fd Prelude System.Posix> :t mqOpen <interactive>:1:0: Not in scope: `mqOpen' There is a signature for openFd (existing functionality) but not mqOpen (new functionality!) The new functionality got some warnings vis-a-vis Storage because I have defined "alignment" and something else yet. However, when I did "runhaskell Setup.hs install" everything seemed to get installed. ??? Thanks, B.

1 0

function type def
by PR Stanley 02 Apr '08

02 Apr '08

HI It's one of those things - I know sort of instinctively why it is so but can't think of the formal rationale for it: f g x = g (g x) :: (t -> t) -> (t -> t) Why not (t -> t) -> t -> (t -> t) to take account of the argument x for g? Cheers Paul

3 3

Haskell vs Scheme
by Greg Meredith 02 Apr '08

02 Apr '08

Douglas, Excellent questions you posed to Simon P-J -- who then forwarded them to the Haskell Cafe list. By way of answering i should say i was a Schemer from the get-go; it was really the first programming language i studied as an undergraduate majoring in maths at Oberlin in the early 80's. Eventually, i went on to design and build my own language (at MCC with Christine Tomlinson, the principal investigator) called Rosette. While Scheme was Sussman and Abelson's way of making sense of Hewitt's ideas in a sequential setting Rosette was our way of doing the full banana -- including the actor-based form of concurrency as well as both structural and 3-Lisp-style procedural reflection and a whole host of other advanced features. So, i was naturally profoundly frustrated when the world at large turned to languages like C, C++ and even Java. i have been waiting more than 20 years for the industry to catch up to the joys of advanced language design. Now that the industry has taken a shine to functional languages again i have been spending more time with the various modern flavors and have to say that while each of the major contenders (ML, OCaml, Erlang, Scala, Haskell) have something to be said for them, Haskell stands out among them. Haskell enjoys a particular form of mental hygiene that few other languages enjoy. Its syntax, by comparison with Scheme, is remarkably concise -- and, the importance of syntax is almost impossible to gauge because at the end of the day it is code one is staring at ;-). The chief semantic differences that make a difference to my mind may be classified as follows. - types - monads - meta-programming In order, then: at its outset Haskell made a strong commitment to a potent (static) typing scheme. Even if types can be layered on Scheme, the two language design vectors are remarkably different and give programming a different feel. As a result of my academic and professional training i have come to rely heavily on types as a development discipline. In fact, if i cannot devise a sensible type "algebra" for a given (application) domain then i feel i don't really have a good understanding of the domain. One way of seeing this from the Schemer point if view is that the deep sensibility embodied in the Sussman and Abelson book of designing a DSL to solve a problem is further refined by types. Types express an essential part of the grammar of that language. In Haskell the close connection between typing and features like pattern-matching are also part of getting a certain kind of coherence between data and control. Again, this can be seen as taking the coherence between data and control -- already much more evident in Scheme than say C or C++ or even Java -- up a notch. Haskell's language-level and library support for monads are really what set this language apart. i feel pretty confident when i voice my opinion that the most important contribution to computing (and science) that functional programming has made in the last 15 years has been to work out practical presentations of the efficacy of the notion of monad. As a Schemer i'm sure you understand the critical importance of composition and compositional design. The monad provides an important next step in our understanding of composition effectively by making the notion parametric along certain dimensions. This allows a programmer to capture very general container patterns and control patterns (as well as other phenomena) with a very concise abstraction. Again, this could be layered onto Scheme, but Haskell embraced monad as a central abstraction at the language design level and this leads to very different approaches to programming. Now, the place where Haskell and the other statically typed functional languages have some catching up to do is meta-programming. Scheme, Lisp and other languages deriving from the McCarthy branch of the investigation of lambda-calculus-based programming languages enjoy a much longer and deeper investigation of meta-programming constructs. While MetaOCaml stands out as a notable exception i think it safe to say that 3-Lisp and Brown are pretty strong evidence of the long history and much richer investigation of meta-programming notions along the McCarthy branch than along the Milner branch. The industry as a whole, i think, has embraced the value of meta-programming -- witness (structural) reflection in such mainstream languages as Java and C#. And the Milner branch family of languages are moving rapidly to catch up -- see the efforts on generic programming like S P-J's SYB or TemplateHaskell -- but the deep coherence evident in the simplicity of the monadic abstraction has not met up with the deep coherence of 3-Lisp, yet. Anyway, that's my two cents... but i note that US currency is not worth what it used to be. Best wishes, --greg Message: 21 Date: Tue, 1 Apr 2008 11:18:25 +0100 From: Simon Peyton-Jones <simonpj(a)microsoft.com> Subject: [Haskell-cafe] FW: Haskell To: Haskell Cafe <haskell-cafe(a)haskell.org> Cc: "kerrangster(a)gmail.com" <kerrangster(a)gmail.com> Message-ID: < 638ABD0A29C8884A91BC5FB5C349B1C32AB9FA8B7B(a)EA-EXMSG-C334.europe.corp.microsoft.com > Content-Type: text/plain; charset="us-ascii" Dear Haskell Cafe members Here's an open-ended question about Haskell vs Scheme. Don't forget to cc Douglas in your replies; he may not be on this list (yet)! Simon -----Original Message----- From: D. Gregor [mailto:kerrangster@gmail.com] Sent: 30 March 2008 07:58 To: Simon Peyton-Jones Subject: Haskell Hello, In your most humble opinion, what's the difference between Haskell and Scheme? What does Haskell achieve that Scheme does not? Is the choice less to do with the language, and more to do with the compiler? Haskell is a pure functional programming language; whereas Scheme is a functional language, does the word "pure" set Haskell that much apart from Scheme? I enjoy Haskell. I enjoy reading your papers on parallelism using Haskell. How can one answer the question--why choose Haskell over Scheme? Regards, Douglas -- L.G. Meredith Managing Partner Biosimilarity LLC 806 55th St NE Seattle, WA 98105 +1 206.650.3740 http://biosimilarity.blogspot.com

1 0

[GSoC] Student applications deadline extended one week
by Don Stewart 02 Apr '08

02 Apr '08

Hey all, As you might know, the Google Summer of Code application submission period is open. Google has decided to extend the deadline for initial student applications by one week, http://groups.google.com/group/google-summer-of-code-announce/browse_thread… If you've thought about submitting, and are interested in hacking on Haskell for 3 months this summer, and bootstrapping into the Haskell developer community, check our project wiki, http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 and get your applications into google this week! -- Don

3 3

all threads are blocked by recvFrom
by Vitaliy Akimov 02 Apr '08

02 Apr '08

Hello, I have a problem with building multithreaded UDP server. If main thread is waiting for new request in recvFrom all other threads are blocked too. I've checked every variant with forkIO,forkOS,-threaded etc, nothing's helped. After reading GHC docs I've understood this is happened becouse foreign function call from recvFrom (network library) is marked to be unsefe, so it's execution blocks every other thread. How can I resolve it? Thank you. Vitaliy.

3 12

Unescaping with HaXmL (or anything else!)
by Anton van Straaten 01 Apr '08

01 Apr '08

I want to unescape an encoded XML or HTML string, e.g. converting " to the quote character, etc. Since I'm using HaXml anyway, I tried using xmlUnEscapeContent with no luck, e.g. with HaXml 1.19.1: let (CString _ s _) = head $ xmlUnEscapeContent stdXmlEscaper $ [CString False "This is a "quoted string"" ()] in s The result is unchanged, i.e. "This is a "quoted string"". Am I doing something wrong, or are my expectations wrong, or is this a bug? Or, is there any other library that includes a simple unescape function for XML or HTML? (The Network.URI module includes an unescape function, but that's specific to URIs, naturally.) Anton

3 2

ANN: wxHaskell 0.10.3
by Jeremy O'Donoghue 01 Apr '08

01 Apr '08

The wxHaskell development team is pleased to announce the release of wxHaskell 0.10.3, a Haskell binding for the wxWidgets GUI library. The Haskell support is built on a reasonably complete C language binding, which could be used as the basis for wxWidgets support on other languages/platforms which do not have easy mechanisms for linking with C++ code. The feature set is the same as wxHaskell 0.10.3 rc1 and rc2, with a number of additional bugfixes. This is the first full release since June 2005, and is the result of a great deal of work by a new team of contributors. Highlights of 0.10.3 include: - Support for Unicode builds of wxWidgets - Support for additional widgets including calendar, toolbar divider, styled text control (wxScintilla), media control - Support for clipboard, drag and drop - Support for 64bit (Linux) targets - Support for wxWidgets 2.6.x (support for wxWidgets 2.4.2 if you compile from source). wxWidgets 2.8 is not yet supported - Support for building with GHC 6.6.x and 6.8.x - Parts of wxHaskell are now built with Cabal - New test cases - Removed support GHC version < 6.4 - Profiling support - Smaller generated binary sizes (using --split-objs) Binary packages are available from the wxHaskell download site at http://sourceforge.net/project/showfiles.php?group_id=73133, for the following platforms: - Debian - Windows - OS X (Intel and PPC platforms) - Source code .tar.gz and .zip - Documentation (cross-platform) The wxHaskell libraries (wxcore and wx) are also available from Hackage (http://hackage.haskell.org) About wxHaskell --------------- wxHaskell is a Haskell binding to the wxWidgets GUI library for recent versions of the Glasgow Haskell Compiler. It provides a native look and feel on Windows, OS X and Linux, and a medium level programming interface. The main project page for wxHaskell is at http://wxhaskell.sourceforge.net. The latest source code for wxHaskell can always be obtained from http://darcs.haskell.org/wxhaskell. There are developer (wxhaskell-devel(a)lists.sourceforge.net and user (wxhaskell-users(a)lists.sourceforge.net) mailing lists, and a wiki page at http://haskell.org/haskellwiki/WxHaskell which can provide more information to those interested. wxHaskell was originally created by Daan Leijen. The contributors to this new release include: - Eric Kow - shelarcy - Arie Middelkoop - Mads Lindstroem - Jeremy O'Donoghue - Lennart Augustson The C language binding for wxHaskell was derived from an original C language binding created for the Eiffel programming language by the ELJ project (http://elj.sourceforge.net) -- Jeremy O'Donoghue jeremy.odonoghue(a)gmail.com

1 0

[GSoC] X Haskell bindings
by Roman Cheplyaka 01 Apr '08

01 Apr '08

Hi! I've written a draft proposal for GSoC on XCB Haskell Bindings[1]. I'd appreciate any feedback. Especially I need help with "Milestones" section. I'm not quite sure how it should look like for such project. 1. http://ro-che.info/docs/xhsb.txt -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock...

4 4

Seeking Daan Leijen
by John Goerzen 01 Apr '08

01 Apr '08

I tried to email this to Daan, but his mail is bouncing... Subject: http://legacy.cs.uu.nl/daan/parsec.html Hi Daan, I noticed Parsec 3.0.0 on Hackage, and went to your homepage to read about the new package. But it looks like your homepage still has the old version put out in 2003. This might cause confusion for some that are looking for new releases at your website. Thanks, -- John PS... The HaXml website has the same problem, and has an incompatible API with the version in Hackage... Some Linux distros are using one, some the other.

2 1

HTTP client libraries
by John Goerzen 31 Mar '08

31 Mar '08

Hi folks, I was recently looking for HTTP client libraries for Haskell. I investigated several, and it seems that there aren't any really ready for primetime. Am I missing anything? Here's what I found: * Bjorn's String-based HTTP It eats RAM. Does not appear to read data lazily, returns a String, and may have a memory leak as well. Does not appear to be suited for anything except very small file downloads. * nominolo's ByteString port of Bjorn's HTTP Appears to exist only in a darcs repo linked from his personal blog. Makes me hesitant to use it in production code, for fear that it won't be around long-term. * tagsoup Broken in many ways. Does not support chunked encoding that is mandated by HTTP RFC. Will be incompatible with numerous HTTP servers, and the manual states as much. Port 80 hardcoded. * network-minihttp Doesn't appear to actually be very useful as a client. Also, as far as I have been able to deduce, none of these have built-in support for https (SSL) URLs. There is also a Curl binding (or two?) floating around, which I haven't investigated. It would be nicer to have a native Haskell solution. Or should I just go write one? -- John

7 11

lexicographic order
by Simeon Mattes 31 Mar '08

31 Mar '08

Hello everyone, I would like to ask something that I found in the ebook "a Gentle Introduction to Haskell". http://haskell.org/tutorial/stdclasses.html#sect8.4 data Tree a = Leaf a | Branch (Tree a) (Tree a) instance (Ord a) => Ord (Tree a) where (Leaf _) <= (Branch _) = True (Leaf x) <= (Leaf y) = x <= y (Branch _) <= (Leaf _) = False (Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' The latter specifies a lexicographic order: Constructors are ordered by the order of their appearance the data declaration, and the arguments of a constructor are compared from left to right. Although I have tried to make sense what lexicographic order means I haven't figured out. Maybe an example with a simple application of this would be helpful. To be honest I can't understand what the symbol <= really means. Thanks -- View this message in context: http://www.nabble.com/lexicographic-order-tp16381434p16381434.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 6

Possible to automatically determine typeclass membership?
by Ryan Ingram 31 Mar '08

31 Mar '08

Is it possible in Haskell + GHC extensions to use reflection techniques to determine typeclass membership? I'm thinking of things like the following: Idea 1: > data MaybeEq a = NoEq a | Eq a => HasEq a > checkEq :: (some typeclass constraint) => a -> MaybeEq a (such that checkEq x returns HasEq x if and only if x has an Eq instance.) Idea 2: > data HTrue > data HFalse > class MaybeEq a b | a -> b > instance Eq a => MaybeEq a HTrue > instance (otherwise) => MaybeEq a HFalse -- ryan

3 2

Wumpus World
by iliali16 31 Mar '08

31 Mar '08

Hi guys I have to build the wumpus world problem. I didn't start yet since this is the first time in my life I have to do something like that and I feel not confident in starting it. So I have basic idea of what prolog and haskell can do and I know a bit of Java. I am wandering if you can tell me which one is best to use to build this problem.Thanks couse I am really confused -- View this message in context: http://www.nabble.com/Wumpus-World-tp16310198p16310198.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

8 11

SoC project: Python-Haskell bridge - request for feedback
by Michał Janeczek 31 Mar '08

31 Mar '08

Hi, I am a student interested in participating in this year's SoC. At http://tsk.ch.uj.edu.pl/~janeczek/socapp.html (and also below in this email) you can find a draft of my project proposal. I'd like to ask you to comment on it, especially the deliverables part. Are you interested in such a project, and if yes, what features would be most important to you? Is anything missing, or should something get more priority or attention? Regards, Michal Python-Haskell bridge ===================== Description ----------- This project will seek to provide a comprehensive, high level (and thus easy to use) binding between Haskell and Python programming languages. This will allow using libraries of either side from each language. Benefits for Python ------------------- * Robust, high assurance components It might be beneficial to implement safety-critical components in a strongly, statically typed language, using Python to keep them together. Cryptography or authentication modules can be an example. * Performance improvements for speed-critical code Haskell compiled to native code is typically an order of magnitude faster than Python. Aside from that, advanced language features (such as multicore parallel runtime, very lightweight threads and software transactional memory) further serve in improving the performance. Haskell could become a safe, high level alternative to commonly used C extensions. * Access to sophisticated libraries While its set of libraries is not as comprehensive as that of Python, Haskell can still offer some well tested, efficient libraries. Examples might be rich parser combinator libraries (like Parsec) and persistent, functional data structures. QuickCheck testing library could also be used to drive analysis of Python code. Benefits for Haskell -------------------- The project would benefit Haskell by providing it with access to an impressive suite of libraries. It also has a potential to help Haskell adoption, by mitigating risk of using Haskell in a project. Deliverables ------------ * A low level library to access Python objects from Haskell * A set of low level functions to convert built-in data types between Haskell and Python (strings, numbers, lists, dictionaries, functions, generators etc.) * A higher level library allowing easy (transparent) access to Python functions from Haskell, and wrapping Haskell functions for Python to access * A way to easily derive conversion functions for user-defined data types/objects. Functions derived in such a way should work well with both low level and high level access libraries * Documentation and a set of examples for all of above Optional goals -------------- These are of lower priority, and might require a fair amount of work. I would like to implement most of them, if technically feasible. If they don't fit into Summer of Code timeframe, I am planning to finish afterwards. * A Python module for accessing functions from Haskell modules without manual wrapping (such wrapping should be already easy thanks to the high level library). It'd be accomplished through GHC api - if it allows it. The Haskell side of the high level library will already support such mode of operation * Extend and refactor the code, to make it support other similar dynamic languages. This is a lot of work, and definitely out of the scope of Summer of Code project, but some design decisions may be influenced by this. Related projects ---------------- They (and quite possibly some others) will be referenced for ideas. * MissingPy Provides a one way, low level binding to Python. Some of the code can be possibly reused, especially data conversion functions. It doesn't seem to export all features, in particular function callbacks are not supported * HaXR XML-RPC binding for Haskell. It could provide inspiration for reconciling Haskell and Python type systems, resulting in a friendly interface * rocaml A binding between Ruby and OCaml

6 13

Haskell job opening
by Chris Smith 31 Mar '08

31 Mar '08

MindIQ Corporation is looking for a Haskell programmer. Details can be found at http://cdsmith.twu.net/jobposting.html. This isn't "officially" announced yet, but it will be in a few days. >From the announcement: Why You Want This Job * You can program in Haskell and get a salary for it. * Work from home. Choose your hours. Travel only if you want to. * Build a new software application from scratch. * Chance to work some (but not entirely) on open source stuff. * Small company, no bureaucracy, but quite stable (around since 1986). * You will be "Lead Software Developer" within a very short time. Hope this is of interest. -- Chris Smith Lead Software Developer, MindIQ Corporation

1 0

[GSoC] Porting HaRe to use the GHC API
by Chaddaï Fouché 31 Mar '08

31 Mar '08

For those unfamiliar with it, HaRe[1] is a refactoring tool in Haskell for Haskell. It already supports a wide range of useful refactoring and have Emacs and Vim bindings. Unfortunately, HaRe currently uses the Programmatica front-end to do his parsing, and Programmatica only knows Haskell 98, which make the tool far less useful for those that use GHC extensions in their programs. Moreover, Haskell' is bound to arrive one day and will encompass some of those extensions. My proposal for the SoC is to port HaRe (its parsing and refactoring) to use the GHC API instead of Programmatica. The advantages are : * GHC API already supports (by definition) all the GHC extensions, HaRe could be used for any Haskell program. * GHC development is unlikely to stop in the foreseeable future, thus HaRe could evolve with the language rather than having to catch up from time to time. * A certain number of refactoring can be added that exploit the GHC extensions * The GHC API is becoming a mature and generally useful tool, having more libraries that use it can't hurt its growth There already has been some works done to port HaRe to the GHC API in 2005 that did not run to completion but the API has evolved for the better since then and using this report [2] and the current API, I hope to complete the port during the summer. I'm familiarizing myself with the GHC API, Programmatica, Strafunski and HaRe and I'll do an internship at the university of Kent for three months in the summer, which should place me in the best situation to do this work. Refactoring is an important feature of the modern IDE, often quoted by the newcomers who search for the best environment to develop in Haskell. HaRe addresses this point but isn't usable for most programs actually written, which is really a shame (consult the list of supported and future refactoring [3] to get a taste of what you're missing...). Comments, reactions ? You can also propose refactoring, if I complete the port early, I'll try to add some refactoring to HaRe. [1] http://www.cs.kent.ac.uk/projects/refactor-fp/hare.html [2] http://www.cs.kent.ac.uk/pubs/2005/2266/ [3] http://www.cs.kent.ac.uk/projects/refactor-fp/catalogue/ -- Chaddaï Fouché, student in M1, majoring in CS, Ecole Normale Supérieure in Lyon.

3 2

Equality constraints in type families
by Hugo Pacheco 31 Mar '08

31 Mar '08

Hi all, I have encoded a type family such that: type family F a :: * -> * and a function (I know it is complicated, but I think the problem is self explanatory): hyloPara :: (Functor (F a), Functor (F d), F d a ~ F a (a,a), F d c ~ F a (c,a)) => d -> (F d c -> c) -> (a -> F d a) -> a -> c hyloPara d g h = g . fmap (hyloPara d g h) . h it all works fine. However, if I change the declaration to (changed F d c for the "supposedly equivalent" F a (c,a)): hyloPara :: (Functor (F a), Functor (F d), F d a ~ F a (a,a), F d c ~ F a (c,a)) => d -> (F a (c,a) -> c) -> (a -> F d a) -> a -> c and I get Occurs check: cannot construct the infinite type: c = (c, a) When generalising the type(s) for `hyloPara' This really messes up my notions on equality constraints, is it the expected behavior? It would be essential for me to provide this definition. Thanks, hugo

8 46

Functional dependencies with Type Classes
by Henning Günther 31 Mar '08

31 Mar '08

Hi, suppose there are two (identical) classes: > class Res a b | a -> b where > getRes :: a -> b and > class Res2 t where > type Member t > getRes2 :: t -> Member t It is easy to automatically make every instance of Res2 an instance of res: > instance Res2 a => Res a (Member a) where > getRes x = getRes2 x However, declaring every instance of Res an instance of Res2 seems impossible, as the following doesn't compile > instance Res a b => Res2 a where > type Member a = b > getRes2 x = getRes x Question is: How to do this? The reason I need it is because I use a library which uses functional dependencies, but my classes shall be type families. Regards, Henning

3 2

Monad instance for Data.Set
by oleg＠okmij.org 31 Mar '08

31 Mar '08

The following code solves exactly the problem of implementing (restricted) MonadPlus in terms of Data.Set: http://okmij.org/ftp/Haskell/DoRestrictedM.hs The code is written to demonstrate the do-notation. We write the monadic code as usual: > test1s_do () = do > x <- return "a" > return $ "b" ++ x and then instantiate it for Maybe String: > test1sr_do :: Maybe String > test1sr_do = unRM $ test1s_do () > -- Just "ba" or for Data.Set: > test2sr_do :: Set.Set String > test2sr_do = unSM $ test1s_do () > -- fromList ["ba"] It seems GHC 6.10 will support the do-notation even for the generalized monads.

4 4