July 2007 - Haskell-Cafe

i need wxHaskell compiled for ghc 6.6.1 on Windows
by Bulat Ziganshin 25 Jul '07

25 Jul '07

Hello haskell-cafe, can anyone provide wxHaskell already compiled/compilable with ghc 6.6.1 on Windows? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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GHC 6.6.1: Where is Graphics.SOE ?
by Dmitri O.Kondratiev 25 Jul '07

25 Jul '07

Olivier Boudry olivier.boudry(a)gmail.com wrote: (Wed Jul 18 11:56:56 EDT 2007) >Hi Dmitri, > >I built gtk2hs on Windows with GHC 6.6.1 and gtk2hs-0.9.11. Here's are the >steps that worked for me: (not sure I didn't missed some) > >First you need to install a GTK+ development package for windows. I think >mine comes from http://gladewin32.sourceforge.net/modules/wfdownloads/ > >Then you must have MSYS and MinGW installed on your computer. You'll find >information on how to install this here: >http://hackage.haskell.org/trac/ghc/wiki/Building/Windows. > >Once you've installed that stuff you can start a MSYS shell. You'll need to >set some environment variables for GTK (adapt to your path): >export GTK_BASEPATH=/c/GTK_2.0 >export GTK_CONFIG_PATH=/c/GTK_2.0/lib/pkgconfig > >Cd to the gtk2hs source directory and type: >./configure --prefix=/c/Progra~1/Haskell >make >make install > >Hope this helps. > >Good luck, > >Olivier. Oliver, thanks! I tried that, yet have some problems. I use: GHC 6.6.1, current development version of Gtk2hs (not sure what version), Gtk+ 2.10.11 (Win32) and latest available from MinGW distributions: MSYS-1.0.10.exe msysDTK-1.0.1.exe msys-autoconf-2.59.tar.bz2 msys-automake-1.8.2.tar.bz2 msys-libtool-1.5.tar.bz2 Problem 1. Gtk2hs build requires to run autoreconf. So in MSYS I have: $ autoreconf /usr/share/aclocal/autoopts.m4:22: warning: underquoted definition of AG_PATH_AUTOOPTS run info '(automake)Extending aclocal' or see http://sources.redhat.com/automake/automake.html#Extending%20aclocal configure.ac:101: error: possibly undefined macro: AC_MSG_ERROR If this token and others are legitimate, please use m4_pattern_allow. See the Autoconf documentation. autoreconf: /usr/bin/autoconf failed with exit status: 1 Notwithstanding this error autoreconf creates configure script. When I run it I get: Problem 2. $ ./configure --with-hc=/c/usr/ghc-6.6.1 --prefix=/c/usr/ghc-6.6.1 checking for a BSD-compatible install... /bin/install -c checking whether build environment is sane... yes checking for gawk... gawk checking whether make sets $(MAKE)... yes checking build system type... i686-pc-mingw32 checking host system type... i686-pc-mingw32 checking for style of include used by make... GNU checking for gcc... no checking for cc... no checking for cc... no checking for cl... no configure: error: no acceptable C compiler found in $PATH Questions: 1) Should I ignore autoreconf errors? 2) I thought that building Gtk2hs is done with GHC only. Is it right that build requires C compiler? 3) Any other ideas what is wrong with this build? Thanks! -- Dmitri O. Kondratiev dokondr(a)gmail.com http://www.geocities.com/dkondr

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[meta] the haskell wiki management
by Andrea Rossato 25 Jul '07

25 Jul '07

Hi, this is what happened to me recently. Recently I had the opportunity to join the community around XMonad, a project, you should know something about it, led by some well know haskellers. It's a very exiting project, and by joining it you have the opportunity to code with people who know Haskell very well. Moreover those guys are very friendly and willing to help newcomers like me. Thanks to them I came to build up some knowledge about X window programming in Haskell - Robert and Spencer being my two principal mentors. I have this problem of mine, that when I feel grateful to someone I must find a way to get even, and I thought that writing a tutorial for newcomers could be a form of paying back the XMonad community, a subgroup of the Haskell community after all. I though that using the Haskell wiki was appropriate, so I started writing down what I learned thanks to those guys. As you may understand writing a tutorial is time consuming: not only you have to write the code and the code must be possibly clear. But I have also another problem: English is not my mother tongue, I'm sure you know that by now. So, while writing - eventually it took me up to 20 hours of work to finish the tutorial -, I started a new wiki page and updated it as new stuff was written: "X Window Programming in Haskell" was the page title. Then suddenly, Sunday night, I could not find my page anymore. So I went to "recent changes" to find out that someone had decided to change the page title to "X window programming", right after editing it. Not to remove some of the huge amount of typos, not to rephrase a sentence that a (properly) English speaker could not understand, not to debug some code, not to improve the content. No, just to enforce a rule, written here: http://www.haskell.org/haskellwiki/HaskellWiki:Guidelines A rule that reads: "Titles should use sentence-style capitalization (see [1] - wikipedia). Capitalizing more words seems to be only appropriate in larger documents like books." "Seems to be only appropriate in larger documents like books." This makes me laugh, really. I got really upset and went to the talk page of the guy who moved the page to ask for an explanation. And I moved the page back to its original title: it was not a tutorial about x window programming, but about x window programming in Haskell. And so I found out these guidelines I was not even aware of. And that people were actually enforcing them. Now, that's fine, it is a wiki after all, and authorship must be forgotten. I didn't have this feeling when I discovered the wiki for the first time. In many tutorial you could and still can find a signature. You know, I'm an academic type of guy: I don't care about copyright at all, but I care a lot about authorship. I know, this is my fault. Now, what happened next? The guy I was upset with decided to change the rules and added this to the guidelines page: "When doing a signficant renaming of a page, (i.e., something more than just correcting the case as per the guidelines), use the "Discuss this page" link to suggest the new title and the reasons why. After a reasonable amount of time, if there are no objections, go ahead and move / rename the page." But five minutes later he also decided that it was time for the new rule to be violated by the rule setter himself, and renamed other tutorials of mine, something I've written a year ago or so, without making any suggestion in the discussion page. You know, changing a wiki page title means breaking all links to that page from other sites. So, changing an old page title, means taking that page off the Net. This is fine with me and my contributions to the Haskell wiki: useless stuff that is better not reading than reading. On the other side, I'm not going to stand such behaviour and I'm not going to write a single word on that wiki anymore. I removed my signature from the x window tutorial. I'm human too, I would add. Nonetheless I do not understand if this is an explicit policy of getting rid of unwanted contributors, like me, or just a stupid way of managing a collective resource like a wiki. Having a group of people in charge of setting, enforcing and violating rules at their will is a nice form of government, that usually pisses people off. And it is very difficult to adopt such an attitude to piss only unwanted people off. You usually end up repelling people you would like to attract too. I believe it is inevitable. This is the only reason I'm writing this. Sorry for such a long useless letter, but I've seen that the Haskell community loves to talk about maintaining itself, and so on. I thought that my 2 cents could be enjoyable too. Regards, Andrea Rossato

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partitions of a multiset
by Brent Yorgey 25 Jul '07

25 Jul '07

Hi all, I've written some code to generate set partitions: import Control.Arrow import Data.List -- pSet' S generates the power set of S, with each subset paired -- with its complement. -- e.g. pSet' [1,2] = [([1,2],[]),([1],[2]),([2],[1]),([],[1,2])]. pSet' :: [a] -> [([a],[a])] pSet' [] = [([],[])] pSet' (x:xs) = mp first ++ mp second where mp which = map (which (x:)) psRest psRest = pSet' xs -- partitions S generates a list of partitions of S. -- e.g. partitions [1,2,3] = [[[1,2,3]],[[1,2],[3]],[[1,3],[2]],[[1],[2,3]],[[1],[2],[3]]]. partitions :: [a] -> [[[a]]] partitions [] = [[]] partitions (x:xs) = (pSet' xs) >>= ((x:) *** partitions >>> uncurry (map . (:))) However, this version of partitions generates duplicates when given a multiset, for example: *Combinatorics> partitions [1,1,2] [[[1,1,2]],[[1,1],[2]],[[1,2],[1]],[[1],[1,2]],[[1],[1],[2]]] The partition [[1,2],[1]] is generated twice (order doesn't matter). I'd like to write a version of partitions which generates duplicate-free output even for input multisets, but haven't come up with a good method yet. Any ideas? -Brent PS Yes, this is for Project Euler. =)

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Re: [Haskell] Re: View patterns in GHC: Request for feedback
by Claus Reinke 24 Jul '07

24 Jul '07

>> unit :: Typ -> Maybe () >> arrow :: Type -> Maybe (Typ,Typ) >> size :: Typ -> Integer >> size (unit -> ()) = 1 >> size (arrow -> (t1,t2)) = size t1 + size t2 > Though I guess you would not object to: > > size (unit -> Just ()) = 1 > size (arrow -> Just (t1,t2)) = size t1 + size t2 > ? actually, i might!-) it is not just that, in general, you have to invent and declare those intermediate view types, but that their use obscures the overall pattern, once you start nesting abstract and concrete patterns (and if you don't nest them, view patterns don't add much). claus

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Dealing with large OOHaskell records
by Scott West 24 Jul '07

24 Jul '07

Hello all, Does anyone have any experience with using large-ish (20 element) OOHaskell records? I'm finding that as the records get large, compile times get fairly ridiculous. Is there some explicit typing I should be doing to help the type-checker? Thanks! Scott

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expension of fractions
by Arie Groeneveld 24 Jul '07

24 Jul '07

Hi, I don't know if this is the right place to post this, but here I go. I translated a BC-program found on the home page of Keith Matthews, http://www.numbertheory.org/keith.html. It's about the expension of a (not necessarily reduced) fraction m/n in base b. Looking at the result of my rewriting gives me the idea it isn't Haskelly enough. Anyways, here's my interpretation: -- period m/n base = (period length, preperiod digits, period digits) period :: Integer -> Integer -> Integer -> (Int, ([Integer], [Integer])) period m n base | m' >= n' = error $ show m ++ " >= " ++ show n | m' < 1 = error $ "m (" ++ show m ++ ") < 1" | n' < 1 = error $ "n (" ++ show n ++ ") < 1" | base <= 1 = error $ "base (" ++ show base ++ ") < 2" | otherwise = decimals [] [m'] where g = gcd m n m' = m `div` g n' = n `div` g decimals qs rs | i' /= -1 = (length rs - i', splitAt i' qsi) | otherwise = decimals qsi (rs++[ri]) where (qi,ri) = divMod (base * last rs) n i = findIndex (==ri) rs i' = if i == Nothing then -1 else fromJust i qsi = qs++[qi] Which comes from the BC program: (Keith Matthews) define period(m,n,b){ auto a[],g,i,p,j,c[] g=gcd(m,n) m=m/g;n=n/g if(m>=n){"m>=n:"; return(0)} if(m<1){"m<1:"; return(0)} if(n<1){"n<1:"; return(0)} if(b<=1){"b<=1:"; return(0)} i=0 c[0]=m flag=0 while(flag==0){ p=b*c[i] i=i+1 c[i]=p%n a[i]=p/n /*print "a[",i,"]=",a[i],"\n" /* the i-th digit */ if(i==1000){ print "limit of 1000 digits produced\n" return(0) } for(j=0;j<i;j++){ if(c[i]==c[j]){ flag=1 break } } } print "the expansion of ",m,"/",n," to base ",b,"\n" if(j){ print "preperiod digits: " for(k=1;k<=j;k++){ print a[k],"," } print "\n" } print "period digits: " for(k=j+1;k<=i;k++){ print a[k] if(k<i){ print "," } } print "\n" t=i-j "period-length = ";return(t) }

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Optimising UTF8-CString -> String marshaling, plus comments on withCStringLen/peekCStringLen
by Alistair Bayley 24 Jul '07

24 Jul '07

Hello cafe, D'ya fancy an optimisation exercise? In Takusen we currently marshal UTF8-encoded CStrings by first turning the CString into [word8], and then running this through a [Word8] -> String UTF8 decoder. We thought it would be more space-efficient (and hopefully faster) to marshal directly from the CString buffer, rather than use an intermediate list. We assumed it would be most space-efficient by working backwards from the end of the CString buffer, like the peekArray/peekArray0 functions in Foreign.Marshal.Array. So I implemented it and benchmarked against the original UTF8 marshaling function, which simply converts CString -> [Word] -> String. And to my surprise, the [Word8] -> String solution seems to be faster, and uses less memory, than the function which creates the String directly from the CString buffer. Now I appreciate that GHC's optimisations are quite effective (presumably deforestation should take credit here), but I thought I'd ask the haskell-cafe optimiser if we could do better with the direct-from-buffer function. I'm loath to start eyeballing GHC Core, but if needs must... The code is attached. I also have some comments/questions about the various CStringLen functions in Foreign.C.String. The Haddock comment for CStringLen states: "A string with explicit length information in bytes..." and for CWString something similar: "A wide character string with explicit length information in bytes..." I know this is a blatant lie, though, because the code (unless I've grossly misunderstood it) for newCStringLen, withStringLen, newCWStringLen, and withCWStringLen all return the number of Haskell Chars in the String i.e. the number of Unicode chars, NOT the number of bytes. However, for the sake of inconsistency, the peekC{W}StringLen functions take, respectively, the number of Word8 or Word16/Word32 elements (whether CWString is Word16 or Word32 depends on your plaform, apparently) in the C{W}String array/buffer. So the outputs from newCStringLen etc are not reliably usable as inputs to their duals (peekCStringLen etc.) The only cases that they do work in this way is where the CStrings are encoded with fixed-width encodings i.e. there are no surrogate units in the encoding. So we have three different approaches: 1. Haddock comments say bytes 2. with/newC{W}StringLen returns unicode char count 3. peekC{W}StringLen expects Word8 or Word16 count (1) and (3) can be considered equivalent, in the sense that if you know the number of Word16 units then you know the number of Word8 units, and vice versa. It'd be nice if we could have one consistent aproach. For a start, I think we should eliminate (2), because it's dead easy the get the number of unicode chars from a String (length, if you didn't know). So whether to settle on (1) or (3) depends on what the most likely use case is for the length information. Presumably it's going to be passed to a foreign function which expects the length either in bytes or in Word16/Word32 units. Does anyone have any evidence or opinion as to which case is the most common: bytes, or encoding units? Alistair

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Profiling and Threading: never the twain shall meet
by Dougal Stanton 24 Jul '07

24 Jul '07

Hi Haskellers, It seems that profiling and threading are not supported at the same time in GHC6.6. At least, it objects to using both the flags at the same time, and there's a Trac entry for that issue. So I just wanted to be sure that I really need threading. I'm passing text through some filters written in perl, just ordinary command line programs. I do it like this: > do > (hin, hout, herr, ph) <- runInteractiveProcess cmd args Nothing Nothing > forkIO $ hPutStr hin content >> hClose hin > out <- hGetContents hout > return (ph, out) which seems to require threading. If I compile without, it will hang indefinitely, I presume deadlocked. Is there a way this can be done without threading? But it's not a great issue for me if I can't do profiling in this case. I just wanted to try out the feature, and it seemed worthwhile checking I was doing this right. Cheers, Dougal.

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My Haskell ICFP '07 Programming Competition entry
by Antoine Latter 23 Jul '07

23 Jul '07

Hello, I'd just like to call attention to a few recent blog posts containing myself and my friend Creighton's entry into the ICFP '07 programming competition. Mainly because I'm looking to find someone who knows Haskell and the contest so they can tell me where my bug is :) Also, if anyone wants to see a Haskell approach towards the contest's DNA to RNA conversion, here you go. It's not always idiomatic HAskell, but that's what happens in a 72 hour contest. Any feedback would be appreciated. The bug (I believe) occurs somewhere in the implementation of "matchpattern", which is in the fourth URL. Bellow are the URLs of the Haskell source code (with comments included as blog posts). We only got as far as the DNA to RNA conversion algorithm. -Antoine http://panicsonic.blogspot.com/2007/07/icfp-07-post-mortem-i.html http://panicsonic.blogspot.com/2007/07/icfp-07-post-mortem-ii.html http://panicsonic.blogspot.com/2007/07/icfp-07-post-mortem-iii.html http://panicsonic.blogspot.com/2007/07/icfp-07-post-mortem-iv.html

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