February 2009 - Haskell-Cafe

ANNOUNCE: X Haskell Bindings 0.2
by Antoine Latter 22 Feb '09

22 Feb '09

I'd like to announce the 0.2.* series release of the X Haskell Bindings. This release, like the prior 0.1.* series focuses on making the API prettier. This does mean that there's a good chance this is a breaking release. Also, 0.2.* is based on the just-released version 1.4 of the XML descriptions of the X protocol. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb New this release: In the core protocol, a lot of the fields which previously were of type 'Word8' or 'Word16' now have appropriate higher-level types. For example, in the type GetWindowAttributesReply, the 'class' field was previously of type 'Word16', and is now of type 'WindowClass,' and the 'all_event_masks' field was of type 'Word32' and is now of type '[EventMask]'. These improvements haven't made their way out to the extensions yet, but the code-generation machinery is now in place for this to happen as the information makes its way into the XML protocol description. Related projects: X C Bindings: http://xcb.freedesktop.org/ -Antoine

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pkgenv - disposable, isolated pkg environments
by Paolo Losi 22 Feb '09

22 Feb '09

Hi all, I've been recently toying with a small tool inspired by the Python tool virtualenv [1]. What it basically allows to do is to setup isolated, disposable package environments. You can find a small session example in: http://www.haskell.org/haskellwiki/PkgEnv The main benefits should be: 1. allowing experimenting with package installations without "polluting" or breaking the default user package DB. When you're done you can simply remove the pkgenv directory => disposable 2. starting from a clean, fresh pkg "configuration" containing only system packages. This make cabal-install dependency analysis job much easier and predictable => isolated pkgenv now only runs on unix, even if it could be possible to port it to windows... To test it, download it from http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv chmod a+x and drop to an executable directory. Any feedback would be really appreciated. Is this useful at all? Are there better ways to reach the same goals? Pao 1. http://pypi.python.org/pypi/virtualenv

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Finding a PID in Windows
by Alexandru Scvortov 22 Feb '09

22 Feb '09

Quick question. In Linux, if you want to find the PID of a process, you use getProcessID from System.Posix.Process. How do you do the same under Windows? I cannot find the equivalent function in System.Win32 and searching Google does not yield any useful results. Thanks.

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instance MonadFix GenParser
by Paul Johnson 22 Feb '09

22 Feb '09

I want to write a parser for a Haskell-like type language. Amongst other things this means having a symbol table of top-level declarations. So for instance I want to be able to write in my type language: > type Foo = Bar Int > > data Bar a = Bar String a I can come up with a parser that identifies "Bar" in the type synonym as the name of another type. I could define a type to return from the parser which just has that as a string, but then I would have to write another data type which is essentially the same but replaces the string name with the actual data type, and a mapping function to use a symbol table to convert one into the other, like this: > data ParsedTypeExpr = ParsedTypeExpr {parsedBaseType :: String, parsedTypeArgs :: [String]} > > data TypeExpr = TypeExpr {baseType :: MyType, typeArgs :: [String]} > > convertTypeExpr :: (String -> MyType) -> ParsedTypeExpr -> TypeExpr I want to short-circuit this by looking up the definition of Bar in the parser. But that requires the symbol table to exist during the parse. I have to admit I haven't quite got my head around MonadFix yet, but if I understand it correctly I should be able to have a top level parser something like this: > parseDeclarations :: Parser [Declaration] > parseDeclarations = mdo > decls <- many ParseDeclaration symbols > let symbols = makeSymbolTable decls > return decls Unfortunately GenParser isn't an instance of MonadFix, so this won't work. Is there a good reason why GenParser can't be an instance of MonadFix? If not, what would the instance declaration be? Thanks, Paul.

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Re: Haskell-Cafe Digest, Vol 66, Issue 71
by David Yoffe 21 Feb '09

21 Feb '09

Hi D.R Plotkin, There are some nice mailing lists in haskell.org, include HUGS --- On Sat, 2/21/09, haskell-cafe-request(a)haskell.org <haskell-cafe-request(a)haskell.org> wrote: From: haskell-cafe-request(a)haskell.org <haskell-cafe-request(a)haskell.org> Subject: Haskell-Cafe Digest, Vol 66, Issue 71 To: haskell-cafe(a)haskell.org Date: Saturday, February 21, 2009, 7:01 PM Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. controlling timeout for Network.Socket.connect - how? (Belka) 2. Stacking StateTs (Luis O'Shea) 3. Haskellers on Twitter! (Daniel Peebles) 4. Fwd: Re: [Haskell-cafe] speed: ghc vs gcc (Khudyakov Alexey) 5. Re: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc (Bulat Ziganshin) 6. Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 7. Re: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 8. Re: Re: speed: ghc vs gcc (Daniel Fischer) 9. Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 10. Re: Stacking StateTs (David Menendez) 11. Re[2]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 12. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 13. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Sebastian Sylvan) 14. Re: Help using catch in 6.10 (John Meacham) 15. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Louis Wasserman) 16. The community is more important than the product (Don Stewart) 17. Re: Re[5]: [Haskell-cafe] Re: speed: ghc vs gcc (Sebastian Sylvan) 18. Re: Re: speed: ghc vs gcc (Daniel Fischer) 19. Re[7]: [Haskell-cafe] Re: speed: ghc vs gcc (Bulat Ziganshin) 20. Template Haskell compilation error on Windows (was Re: speed: ghc vs gcc) (Peter Verswyvelen) ---------------------------------------------------------------------- Message: 1 Date: Sat, 21 Feb 2009 11:26:51 -0800 (PST) From: Belka <lambda-belka(a)yandex.ru> Subject: [Haskell-cafe] controlling timeout for Network.Socket.connect - how? To: haskell-cafe(a)haskell.org Message-ID: <22139581.post(a)talk.nabble.com> Content-Type: text/plain; charset=us-ascii Hello, communion people! I have a problem and ask for an advice. I'm dealing with sockets on *Linux* platform (Network.Socket). The problem is that I can't fully control timeout for (connect :: Socket -> SockAddr -> IO ()) operation. On my system the timeout is - 3 seconds - I want to be able to change that in run-time. Well I managed to find out how to make it LESS THAN 3 seconds - using System.Timeout. But how to make timeout bigger (for example 9 seconds) is a mystery. (Notice: in order to achieve 9 seconds timeout - just repeating *connect* 3 times won't be effective for long-slow-way-connections. So it's not a solution.) The source code of Network.Socket.connect, taken from darcs: --------------------------------- -- Connecting a socket -- -- Make a connection to an already opened socket on a given machine -- and port. assumes that we have already called createSocket, -- otherwise it will fail. -- -- This is the dual to $bindSocket$. The {\em server} process will -- usually bind to a port number, the {\em client} will then connect -- to the same port number. Port numbers of user applications are -- normally agreed in advance, otherwise we must rely on some meta -- protocol for telling the other side what port number we have been -- allocated. connect :: Socket -- Unconnected Socket -> SockAddr -- Socket address stuff -> IO () connect sock@(MkSocket s _family _stype _protocol socketStatus) addr = do modifyMVar_ socketStatus $ \currentStatus -> do if currentStatus /= NotConnected then ioError (userError ("connect: can't peform connect on socket in status " ++ show currentStatus)) else do withSockAddr addr $ \p_addr sz -> do let connectLoop = do r <- c_connect s p_addr (fromIntegral sz) if r == -1 then do rc <- c_getLastError case rc of 10093 -> do -- WSANOTINITIALISED withSocketsDo (return ()) r <- c_connect s p_addr (fromIntegral sz) if r == -1 then (c_getLastError >>= throwSocketError "connect") else return r _ -> throwSocketError "connect" rc else return r connectBlocked = do #if !defined(__HUGS__) threadWaitWrite (fromIntegral s) #endif err <- getSocketOption sock SoError if (err == 0) then return 0 else do ioError (errnoToIOError "connect" (Errno (fromIntegral err)) Nothing Nothing) connectLoop return Connected --------------------------------- I know that controlling timeout is somehow connected to select(2) (I'm currently investigating this matter...), but it's not in the Network or Network.Socket libs (but in the libs that they FFI with). Hope I won't have to rewrite these low-level functions.... >__< Could anybody, please share some experience on how to adjust timeout for *connect*? Thanks in advance, Best regards, Belka -- View this message in context: http://www.nabble.com/controlling-timeout-for-Network.Socket.connect---how-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ------------------------------ Message: 2 Date: Sat, 21 Feb 2009 15:33:28 -0500 From: Luis O'Shea <loshea(a)gmail.com> Subject: [Haskell-cafe] Stacking StateTs To: haskell-cafe(a)haskell.org Message-ID: <3636FA2B-5BB1-47CC-B20F-85491A55E4F7(a)gmail.com> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed I've been experimenting with the state monad and with StateT, and have some questions about how to combine one state with another. This email is literate Haskell tested on GHCi, version 6.10.1. Also, sigfpe's post on monad transformers (http://blog.sigfpe.com/2006/05/ grok-haskell-monad-transformers.html) was very helpful. > import Control.Monad.State My question is basically whether the function modifyT (below) makes sense, whether some form of it already exists in a standard library, and (most importantly) whether it actually indicates that I'm thinking about StateT all wrong. > modifyT :: Monad m => > (s -> StateT t m s) > -> StateT t (StateT s m) () > modifyT f = do > x <- get > y <- lift get > (y',x') <- lift $ lift $ runStateT (f y) x > lift $ put y' > put x' Some context may be useful, so here is how I ended up thinking I needed modifyT. The state monad makes it easy to write stateful computations. For example here is a computation that has an Integer as its state and returns a String: > test1 :: State Integer String > test1 = do > modify (+ 1) > a <- get > return $ "foobar" ++ (show a) If the computation wants to do some IO then it makes sense to start with the IO monad and then apply the StateT transformer to it: > test2 :: StateT Integer IO String > test2 = do > modify (+ 1) > a <- get > lift $ print a > return $ "foobar" ++ (show a) So from now on I won't actually do any IO and will replace IO with an arbitrary monad m. Also instead of the fixed string "foobar" I'll have it take a String as a parameter: > test3 :: Monad m => String -> StateT Integer m String > test3 s = do > modify (+ 1) > a <- get > return $ s ++ (show a) A nice feature of all this is that it is easy to combine these computations: > test4 :: Monad m => StateT Integer m (String,String) > test4 = do > s1 <- test3 "foo" > s2 <- test3 "bar" > return $ (s1,s2) Now seeing as test3 takes a String and returns another String you can imagine using it to transform a String state. (I'm also going to assume that test3 is in another library so we don't want to alter how it's written.) So here is how you could use test3 in a computation that has (String,Integer) as its state: > test5 :: (Monad m) => m Integer > test5 = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s2) (x2*x2) > return x3 Then running test5 >>= print gives 17. The problem with test5, of course, is that we have manually threaded the state, with all the problems that implies. For example nothing prevents you from erroneously misthreading the state: > test5bad :: (Monad m) => m Integer > test5bad = do > (s1,x1) <- runStateT (test3 "") 0 > (s2,x2) <- runStateT (test3 s1) (2*x1 + 1) > (s3,x3) <- runStateT (test3 s1) (x2*x1) > return x3 Running test5bad >>= print gives 5. Obviously we want operate in a State monad with more state. One way to do this is to stack two StateTs on top of m. This is, finally, where I need the modifyT that we defined above -- it lets us "lift" test3 to a function that modifies the state of the top *two* StateTs. Now let's use it to rewrite test5: > test6 :: (Monad m) => StateT Integer (StateT String m) Integer > test6 = do > modifyT test3 > modify $ \x -> 2*x + 1 > modifyT test3 > modify $ \x -> x*x > modifyT test3 > x <- get > return x > > test7 :: (Monad m) => m Integer > test7 = evalStateT (evalStateT test6 0) "" As expected, running test7 >>= print gives 17. So, given that modifyT seems to be useful, does it, or something like it, already exists in the standard libraries? More likely, am I making a mountain of a molehill and is there a better way to structure all this? Thanks, Luis > main = do > test5 >>= print > test5bad >>= print > test7 >>= print ------------------------------ Message: 3 Date: Sat, 21 Feb 2009 16:14:15 -0500 From: Daniel Peebles <pumpkingod(a)gmail.com> Subject: [Haskell-cafe] Haskellers on Twitter! To: haskell-cafe(a)haskell.org Message-ID: <b1a8a5050902211314y74edbf39h97dcfa3188f80a60(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Hi all, I liked Brian O'Sullivan's blog post on twitter (http://www.serpentine.com/blog/2008/12/05/functional-programmers-on-twitter/) so I moved the Haskell subset of his list (along with a couple of additions) onto the haskell wiki, to make it easier for people to update. You can find the page at http://haskell.org/haskellwiki/Twitter. Please update with yourself or any other Haskellers we may have missed. Cheers, Dan ------------------------------ Message: 4 Date: Sun, 22 Feb 2009 00:58:59 +0300 From: Khudyakov Alexey <alexey.skladnoy(a)gmail.com> Subject: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc To: haskell-cafe(a)haskell.org Message-ID: <200902220058.59198.alexey.skladnoy(a)gmail.com> Content-Type: Text/Plain; charset="iso-8859-1" Oh I've again sent mail to wrong address ---------- Forwarded Message ---------- On Saturday 21 February 2009 02:42:11 you wrote: > On Sat, Feb 21, 2009 at 12:22 AM, Bulat Ziganshin > <bulat.ziganshin(a)gmail.com > > > wrote: > > > > Hello Khudyakov, > > > > Saturday, February 21, 2009, 2:07:39 AM, you wrote: > > > I have another question. Why shouldn't compiler realize that `sum > > > > [1..10^9]' > > > > > is constant and thus evaluate it at compile time? > > > > since we expect that compilation will be done in reasonable amount of > > time. you cannot guarantee this for list-involving computation > > it would be nice to have a compiler that can run forever, incrementally > generating faster and faster versions of the same program, until you press > a key or a timeout is reached. > > then you just let it run before you get to bed ;-) > > you could even pass it in a test data set to which it must be optimized; > after the program is compiled, the compiler runs and profiles it, measures > the results, and does another pass to make it faster. > I've just remembered another but related approach to optimization. It uses genetic algorithm to determine close to the best set of optimization options. Alternatively it could be used to find badly interacting options, pessimizations. Implementation for gcc is here: http://www.coyotegulch.com/products/acovea/ In fact I didn't tried it but I liked the idea. -- Khudaykov Alexey ------------------------------ Message: 5 Date: Sun, 22 Feb 2009 01:09:23 +0300 From: Bulat Ziganshin <bulat.ziganshin(a)gmail.com> Subject: Re: Fwd: Re: [Haskell-cafe] speed: ghc vs gcc To: Khudyakov Alexey <alexey.skladnoy(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <528706754.20090222010923(a)gmail.com> Content-Type: text/plain; charset=us-ascii Hello Khudyakov, Sunday, February 22, 2009, 12:58:59 AM, you wrote: >> you could even pass it in a test data set to which it must be optimized; >> after the program is compiled, the compiler runs and profiles it, measures >> the results, and does another pass to make it faster. it supported in gcc4 and icl at least > I've just remembered another but related approach to optimization. It uses > genetic algorithm to determine close to the best set of optimization options. afaik it used widely for tuning parameters of compression algorithms -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com ------------------------------ Message: 6 Date: Sun, 22 Feb 2009 02:21:09 +0300 From: Bulat Ziganshin <bulat.ziganshin(a)gmail.com> Subject: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc To: Louis Wasserman <wasserman.louis(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <989437740.20090222022109(a)gmail.com> Content-Type: text/plain; charset=us-ascii Hello Louis, Saturday, February 21, 2009, 4:16:10 AM, you wrote: > In the meantime, a brief summary: a minor correction: the best gcc result shown in the thread was 50x faster than Don's one, so you need to miltiple all ratios by a factor of 50 > Straightforward and simple Haskell code, written by an individual > aware of issues with tail recursion and stream fusion, is frequently > within 3x the speed of GCC code when compiled with appropriate > optimizations in GHC. yes, within 150x margin > When performance is an absolute necessity, > Haskell code can sometimes be manually modified (e.g. with manual > loop unrolls) to equal GCC in performance. yes, to make it only 50x slower while being only 7 times larger (i mean source lines) > Can we move on? yes, we can! :) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com ------------------------------ Message: 7 Date: Sat, 21 Feb 2009 17:30:23 -0600 From: Louis Wasserman <wasserman.louis(a)gmail.com> Subject: Re: Re[3]: [Haskell-cafe] Re: speed: ghc vs gcc To: Bulat Ziganshin <Bulat.Ziganshin(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <ab4284220902211530k1690103ay1a31f437a2c521f4(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Observation: The best gcc result shown in the thread, if I recall, precomputed the result of the full computation at compiletime and simply outputted it, when we looked at the assembly. While I will accept that this could be seen as an optimization GHC should have made, I do not accept that this will be the case with most everyday code a programmer writes, as most code is not used to simply compute arithmetic constants. For code that actively requires computation at runtime, I have seen no examples of an instance where well-optimized GHC is actually dozens or hundreds of times slower than GCC output. Louis Wasserman wasserman.louis(a)gmail.com On Sat, Feb 21, 2009 at 5:21 PM, Bulat Ziganshin <bulat.ziganshin(a)gmail.com>wrote: > Hello Louis, > > Saturday, February 21, 2009, 4:16:10 AM, you wrote: > > > In the meantime, a brief summary: > > a minor correction: the best gcc result shown in the thread was 50x > faster than Don's one, so you need to miltiple all ratios by a factor > of 50 > > > Straightforward and simple Haskell code, written by an individual > > aware of issues with tail recursion and stream fusion, is frequently > > within 3x the speed of GCC code when compiled with appropriate > > optimizations in GHC. > > yes, within 150x margin > > > When performance is an absolute necessity, > > Haskell code can sometimes be manually modified (e.g. with manual > > loop unrolls) to equal GCC in performance. > > yes, to make it only 50x slower while being only 7 times larger (i > mean source lines) > > > Can we move on? > > yes, we can! :) > > > -- > Best regards, > Bulat mailto:Bulat.Ziganshin@gmail.com > >

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Array use breaks when I make it unboxed?
by Phil 21 Feb '09

21 Feb '09

Hi, The code below compiles fine as it is, but if I change the import statement to: import Data.Array.Unboxed I get the following error: philip-beadlings-imac-g5:MonteCarlo phil$ ghc -O2 --make test.hs [2 of 5] Compiling InverseNormal ( InverseNormal.hs, InverseNormal.o ) InverseNormal.hs:28:38: No instance for (IArray a1 Double) arising from a use of `!' at InverseNormal.hs:28:38-40 Possible fix: add an instance declaration for (IArray a1 Double) In the first argument of `(*)', namely `c ! 1' In the first argument of `(+)', namely `c ! 1 * q' In the first argument of `(*)', namely `(c ! 1 * q + c ! 2)' ....and so on My understanding is that I should just be able to use them like-for-like? Anyone seen this before? Thanks, Phil. module InverseNormal where import Array a = listArray (1,6) [-3.969683028665376e+01, 2.209460984245205e+02, -2.759285104469687e+02, 1.383577518672690e+02, -3.066479806614716e+01, 2.506628277459239e+00] b = listArray (1,5) [-5.447609879822406e+01, 1.615858368580409e+02, -1.556989798598866e+02, 6.680131188771972e+01, -1.328068155288572e+01] c = listArray (1,6) [-7.784894002430293e-03, -3.223964580411365e-01, -2.400758277161838e+00, -2.549732539343734e+00, 4.374664141464968e+00, 2.938163982698783e+00] d = listArray (1,4) [7.784695709041462e-03, 3.224671290700398e-01, 2.445134137142996e+00, 3.754408661907416e+00] invnorm :: Double -> Double invnorm p | p < 0.02425 = let q = sqrt ( -2*log(p) ) in (((((c!1*q+c!2)*q+c!3)*q+c!4)*q+c!5)*q+c!6) / ((((d!1*q+d!2)*q+d!3)*q+d!4)*q+1) | p > (1-0.02425) = let q = sqrt ( -2*log(1-p) ) in -(((((c!1*q+c!2)*q+c!3)*q+c!4)*q+c!5)*q+c!6) / ((((d!1*q+d!2)*q+d!3)*q+d!4)*q+1) | otherwise = let q = p-0.5 r = q*q in (((((a!1*r+a!2)*r+a!3)*r+a!4)*r+a!5)*r+a!6)*q / (((((b!1*r+b!2)*r+b!3)*r+b!4)*r+b!5)*r+1)

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ANNOUNCE: wxFruit-0.1.2
by Henk-Jan van Tuyl 21 Feb '09

21 Feb '09

L.S., I have updated wxFruit to work with GHC 6.10; it can be downloaded from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wxFruit wxFruit is a graphical user interface that combines some of the power and versatility of wxHaskell with the elegance and simplicity of Fruit. The interface of wxFruit has a functional style, using arrows, whereas wxHaskell has an object oriented style. The package includes a demo game, PaddleBall: try to keep the ball in the game, using the mouse to move the paddle. The position of developer/maintainer is currently open. See also http://www.haskell.org/haskellwiki/WxFruit -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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Re[2]: [Haskell-cafe] Re: speed: ghc vs gcc
by Louis Wasserman 21 Feb '09

21 Feb '09

I am no longer sure that this conversation is producing useful information or a learning experience for any involved party, and suggest it ends. In the meantime, a brief summary: - Straightforward and simple Haskell code, written by an individual aware of issues with tail recursion and stream fusion, is frequently within 3x the speed of GCC code when compiled with appropriate optimizations in GHC. - When performance is an absolute necessity, Haskell code can sometimes be manually modified (e.g. with manual loop unrolls) to equal GCC in performance. - The amount of effort required for manually unrolling loops is greater than simply using standard GCC optimizations, and in practice few programmers will want to make this extra effort. For your everyday programmer, achieving that sort of performance is typically easier when writing in C. - If anybody wants a Haskell compiler to achieve GCC-level speeds while writing short and concise Haskell, it is preferable to add a ticket with examples already written out and exhaustively examined to minimize the effort Simon needs to make in working on the problem. GHC has had considerably fewer person-hours devoted to it than GCC, and only additional person-hours can improve it. - Even though it might not match with the amount of effort an average Haskell programmer would put into their code, it is *still* constructive to attempt to optimize Haskell code exhaustively and at a low level, if only to help us learn what sorts of transformations it would be useful for GHC to do automatically. This sort of information, I imagine, would be of significant use to Simon when attempting to improve GHC. Nobody is opining that everyday Haskell code will compile to code as speedy as GCC output. People *are* attempting to find out how Haskell code can be hacked at a low level to run as fast as GCC code, but not because they're claiming GHC output is as fast as GCC output. Rather, they're attempting to find out a) what sorts of approaches a really determined Haskell programmer can use to improve speed b) the sorts of optimizations a later version of GHC might be able to make, and c) what sort of code its optimizer might produce. This is not being reported as "fair Haskell vs C++ comparison" -- this is a collaborative effort to *improve* Haskell that was motivated by Bulat's original comparison. Can we move on? Louis Wasserman wasserman.louis(a)gmail.com

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Template Haskell compilation error on Windows (was Re: speed: ghc vs gcc)
by Peter Verswyvelen 21 Feb '09

21 Feb '09

I tried to compile the template Haskell loop unrolling trick from Claus Reinke on my machine which is running Windows and GHC 6.10.1, and I got linker errors. (note that compiling *without* -fvia-C works fine) Compiling under Cygwin did not solve it. Any ideas how I could get this working? I have no experience with TH yet so I might be missing something essential... Thanks, Peter c:\temp>ghc -O2 -fvia-C -optc-O3 -fforce-recomp Apply.hs Apply.o:ghc6140_0.hc:(.text+0x7d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x10d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x19d): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x571): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x609): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x6c9): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x789): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x82c): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x868): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x891): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0xd81): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0xe19): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0xed9): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0xf99): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarE_con_info' Apply.o:ghc6140_0.hc:(.text+0x103c): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x1078): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_closure' Apply.o:ghc6140_0.hc:(.text+0x10a1): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziSyntax_VarP_con_info' Apply.o:ghc6140_0.hc:(.text+0x14d0): undefined reference to `__stginit_templatezmhaskell_LanguageziHaskellziTHziSyntax_' Apply.o:ghc6140_0.hc:(.text+0x292): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' Apply.o:ghc6140_0.hc:(.text+0x6ab): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x76b): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x9bc): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' Apply.o:ghc6140_0.hc:(.text+0xebb): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0xf7b): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_a23_info' Apply.o:ghc6140_0.hc:(.text+0x11cc): undefined reference to `templatezmhaskell_LanguageziHaskellziTHziLib_lamE_info' C:\app\ghc-6.10.1/libHSrts.a(Main.o):Main.c:(.text+0x7): undefined reference to `__stginit_ZCMain' C:\app\ghc-6.10.1/libHSrts.a(Main.o):Main.c:(.text+0x36): undefined reference to `ZCMain_main_closure' collect2: ld returned 1 exit status >

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Help using catch in 6.10
by Victor Nazarov 21 Feb '09

21 Feb '09

Hello, cafe. I whant to switch to GHC 6.10 My application compiled fine with 6.8.3, but after switchin to 6.10, I've got errors about usage of catch function: Main.hs:165:14: Ambiguous type variable `e2' in the constraint: `Exception e2' arising from a use of `catch' at Main.hs:165:14-38 Probable fix: add a type signature that fixes these type variable(s) Main.hs:261:17: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `handle' at Main.hs:261:17-118 Probable fix: add a type signature that fixes these type variable(s) Relevant places in code are: ... getNSteps f = do text <- get entryNSteps entryText catch (readIO text >>= f) $ \_e -> do msgBox (Just window) [] MessageWarning ButtonsOk $ "Число шагов указано неверно: " ++ show text return () ... loadData :: IO ([Term], Map.Map String Term) loadData = do examples <- handle (\_e -> msgBox Nothing [] MessageWarning ButtonsOk "Ошибка чтения файла примеров" >> return []) $ do examplesLines <- fmap lines $ readFile "examples.txt" let parsings :: [Term] parsings = concatMap (fromEither . parse) examplesLines parse :: String -> Either ParseError Term parse = Parsec.parse (Lambda.parser >>= \t -> skipMany space >> eof >> return t) "" fromEither :: Either ParseError Term -> [Term] fromEither = either (const []) (\t -> [t]) return parsings ... -- Victor

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