[Haskell-cafe] C variable access via FFI
I have a bunch of global variables in C I would like to directly read and write from Haskell. Is this possible with FFI, or must I write a bunch of C wrapper functions for the interface, i.e. a 'get' and a 'set' for each variable? I'm building a simulator for one of our embedded systems. The C is embedded code for an ECU -- the global variables are sensor and control IO. I'm using Haskell to integrate the C with vehicle models and to provide the user interface. With the help of the SDL hackage lib, I'm able to feed analog and discrete inputs from a gamepad into the simulator, which then runs the embedded code and streams VCD data into GTKWave, providing waveform visualization in realtime. Pretty fun stuff. -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] memory needed for SAX parsing XML
Jason Dagit wrote: On Mon, Apr 19, 2010 at 3:01 AM, Daniil Elovkov daniil.elov...@googlemail.com mailto:daniil.elov...@googlemail.com wrote: Hello haskellers! I'm trying to process an xml file with as little footprint as possible. SAX is alright for my case, and I think that's the lightest way possible. So, I'm looking at HaXml.SAX I'm surprised to see that it takes about 56-60 MB of ram. This seems constant relative to xml file size, which is expected. Only slightly depends on it as I recursively traverse the list of sax events. But it seems like too much. For me these sorts of problems always involve investigation into the root cause. I'm just not good enough at predicting what is causing the memory consumption. Thankfully, GHC has great tools for this sort of investigative work. The book real-world haskell documents how to use those tools: http://book.realworldhaskell.org/read/profiling-and-optimization.html If you haven't already, I highly recommend looking at the profiling graphs. See if you can figure out if your program has any space leaks. No, I didn't profile it yet. I just made up the simplest example (while evaluating a few xml parsers) and saw the result. Given the triviality of the example I considered it could be a feature of HaXml SAX parser, and that somebody would say that it is indeed so. The size of the file is from 1MB to 20MB. The code is something like this main = do (fn:_) - getArgs h - openFile fn ReadMode c - hGetContents h let out = proc $ fst $ saxParse fn c putStrLn out getChar For such a simple program you won't run into any problem with lazy IO, but as your program grows in complexity it will very likely come back to bite you. If you're not familiar with lazy IO, I'm referring to the hGetContents. Some example problems: Thanks, I'm aware of that. Speaking of this, I've always felt a bit uncomfortable about lazy IO. I've just looked at the safe-lazy-io package now. I think iteratees are slowly catching on as an alternative to lazy io. Basically, the iteratee approach uses a left fold style to stream the data and process it in chunks, including some exception handling. Unfortunately, I think it may also require a special sax parser that is specifically geared towards iteratee use. Having an iteratee based sax parser would make processing large xml streams very convenient in haskell. Hint, hint, if you want to write a library :) (Or, maybe it exists, I admit that I haven't checked.) Iteratees seem like a natural thing if we want to completely avoid unsafeInterleaveIO. But the presence of the latter is so good for modularity. We can glue IO code and pure code of the type String - a so seamlessly. In case of iteratees, as I understand, pure functions of the type String - a would no longer be usable with IO String result. The signature (and the code itself) would have to be changed to be left fold. Another (additional) approach would be to encapsulate unsafeInterleaveIO within some routine and not let it go out into the wild. lazilyDoWithIO :: IO a - (a - b) - IO b It would use unsafeInterleave internally but catch all IO errors within itself. I wonder if this is a reasonable idea? Maybe it's already done? So the topic is shifting... -- Daniil Elovkov ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] newbie question how to pass data
Hi If you are working with characteristic functions (Point - Bool or Point - Colour...) the common way to do this is to manufacture a Num instance for functions. This gives you syntax overloading of the (+, -, *) operators. Similarly you might want to overload (or have to overload) Floating, Fractional... Examples using this technique are Jerzy Karczmarczuk's Clastic, Conal Elliott's Vertigo, Tangible Values, Pan etc. To overload Num you have to define Show and Eq instances for functions as well. Something along the lines of this is adequate: type CF = (Double,Double) - Bool instance Show CF where show _ = function instance Eq CF where (==) _ _ = error No Eq on Characteristic functions instance Num CF where f + g = \pt - f pt + g pt -- ... negate f = \(x,y) - f (negate x, negate y) -- ... rest follows this pattern, Floating, Fractional similar If you characteristic function is Point - Bool then you also need a Num instance for Bool. All that said, I think your formulation of func above is slightly wrong to fit this style. Its forming a function (- Point) to point rather than a characteristic function Point - Bool. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] newbie question how to pass data
Great job Stephen. Thank for explaining . I got it to work. On Tue, Apr 20, 2010 at 9:21 AM, Stephen Tetley stephen.tet...@gmail.comwrote: Hi If you are working with characteristic functions (Point - Bool or Point - Colour...) the common way to do this is to manufacture a Num instance for functions. This gives you syntax overloading of the (+, -, *) operators. Similarly you might want to overload (or have to overload) Floating, Fractional... Examples using this technique are Jerzy Karczmarczuk's Clastic, Conal Elliott's Vertigo, Tangible Values, Pan etc. To overload Num you have to define Show and Eq instances for functions as well. Something along the lines of this is adequate: type CF = (Double,Double) - Bool instance Show CF where show _ = function instance Eq CF where (==) _ _ = error No Eq on Characteristic functions instance Num CF where f + g = \pt - f pt + g pt -- ... negate f = \(x,y) - f (negate x, negate y) -- ... rest follows this pattern, Floating, Fractional similar If you characteristic function is Point - Bool then you also need a Num instance for Bool. All that said, I think your formulation of func above is slightly wrong to fit this style. Its forming a function (- Point) to point rather than a characteristic function Point - Bool. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Mujtaba Ali Alboori ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: hamming distance allocation
Daniel Fischer wrote: Heinrich Apfelmus: For instance, your expression can be replaced by filter (/=0) [hammingX x y | (x:xs) - tails example, y - xs] which cuts the total running time in half. It's still quadratic in the length of example . I'm sure there are faster algorithms out there that can bring it down to O(n log n) if you want. I don't think so. You can't calculate the Hamming distance of x and z from the distances between x and y and y and z, so you'd have to consider all pairs of distinct strings, wouldn't you? And there I was sure about something once, only to see that it's actually really doubtful... ;) The thing about the Hamming distance is that it's not a black box, so you can't get a lower bound by counting the number of minimum calls to hamming that have to be made. You are essentially arguing that the different Hamming distances are independent, which they are not. Not to mention that there are also black-box restrictions like the triangle inequality d(x,z) = d(x,y) + d(y,z) but that one is probably harmless. In short, the situation is similar to how the sorting bound O(n*log n) does not apply to radix sort. Still, you are right to question my O(n*log n) claim; so far, my attempts at finding such an algorithm myself have failed. More precisely, the goal is to make a histogram of the possible hamming distances. We need at least O(n*w) time to do that, where n is the number of strings and w their maximum length; after all, we have to touch every character. For simplicity, that the characters are just one bit each. Furthermore, we can assume that w = log n, otherwise there are lots of duplicate strings which can be grouped together. In this notation, the simple algorithm takes O(n^2*w) time. I did find a straightforward divide-and-conquer algorithm to tally small Hamming distances, but it's not good enough for the whole histogram. Here's the specification: countHemming :: Int - [Bool] - [Bool] countHemming d xs ys = length [() | x-xs, y-ys, hamming x y == d] In other words, countHemming d xs ys counts the number of pairings (x,y) whose Hamming distance is exactly d . Now, the idea is that this can be made faster for small d . For instance, for d == 0 , we are essentially just calculating the number of different elements of xs and ys . By requiring that xs and ys be sorted, this can be done in linear time countHemming 0 xs ys = ... a variation on merge xs ys And for slightly larger d , we can partition the lists by their first bits and continue recursively countHemming _ [] [] = 0 countHemming d xs ys = countHemming (d-1) x0 y1 + countHemming (d-1) x1 y0 + countHemming d x0 y0 + countHemming d x1 y1 where (x0,x1) = partitionByHead xs (y0,y1) = partitionByHead ys partitionByHead xs = (behead True xs, behead False xs) behead b xs = [bs | (b':bs) - xs, b == b'] To estimate the running time, we set n = length (xs ++ ys) and let T(d,n) = running time of countHamming d xs ys We started with T(0,n) = O(n) and want to discuss the recursive case. The idea is that each list is divided in half, so we get T(d,n) = 2*T(d-1,n/2) + 2*T(d,n/2) From this, we can calculate T(1,n) = 2*T(0,n/2) + 2*T(1,n/2) = O(n) + 2*T(1,n/2) -- remember quicksort! = O(n*log n) T(2,n) = O(n*log n) + 2*T(2,n/2) = O(n*(log n)^2) and so on, yielding T(d,n) = O(n*(log n)^d) Alas, this can be used to search a dictionary while accounting for spelling errors, but it's no good to calculate a full histogram because it becomes prohibitively expensive when d ~ w/2 ~ (log n)/2 . Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] C variable access via FFI
On Tue, Apr 20, 2010 at 8:48 AM, Tom Hawkins tomahawk...@gmail.com wrote: I have a bunch of global variables in C I would like to directly read and write from Haskell. Is this possible with FFI, or must I write a bunch of C wrapper functions for the interface, i.e. a 'get' and a 'set' for each variable? I believe Maurício C. Antunes' bindings-DSL has support for automating reading from and writing to global variables. Look at the Detailed usage guide from the home page of: http://hackage.haskell.org/package/bindings-DSL regards, Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] C variable access via FFI
Tom Hawkins wrote: I have a bunch of global variables in C I would like to directly read and write from Haskell. Is this possible with FFI, Yes it is, as explained in section 4.1.1. in the FFI specification [1]. An import for a global variable int bar would look like this: foreign import ccall bar bar :: Ptr CInt The difference to an import of a function int foo() is the extra . HTH, Bertram [1] http://www.cse.unsw.edu.au/~chak/haskell/ffi/ffi/ffise4.html#x7-170004.1.1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Asynchronous exception wormholes kill modularity
On 09/04/2010 12:14, Bertram Felgenhauer wrote: Simon Marlow wrote: On 09/04/2010 09:40, Bertram Felgenhauer wrote: timeout t io = mask $ \restore - do result- newEmptyMVar tid- forkIO $ restore (io= putMVar result) threadDelay t `onException` killThread tid killThread tid tryTakeMVar result I'm worried about the case when this function is called with exceptions already blocked. Then 'restore' will be the identity, and exceptions will continue to be blocked inside the forked thread. You could argue that this is the responsibility of the whole chain of callers (who'd have to supply their own 'restore' functions that will have to be incorporated into the 'io' action), but that goes against modularity. In my opinion there's a valid demand for an escape hatch out of the blocked exception state for newly forked threads. It could be baked into a variant of the forkIO primitive, say forkIOwithUnblock :: ((IO a - IO a) - IO b) - IO ThreadId I agree with the argument here. However, forkIOWithUnblock reintroduces the wormhole, which is bad. The existing System.Timeout.timeout does it the other way around: the forked thread sleeps and then sends an exception to the main thread. This version work if exceptions are masked, regardless of whether we have forkIOWithUnblock. Arguably the fact that System.Timeout.timeout uses an exception is a visible part of its implementation: the caller must be prepared for this, so it is not unreasonable for the caller to also ensure that exceptions are unmasked. But it does mean that a library cannot use System.Timeout.timeout invisibly as part of its implementation. If we had forkIOWithUnblock that would solve this case too, as the library code can use a private thread in which exceptions are unmasked. This is quite a nice solution too, since a private ThreadId is not visible to anyone else and hence cannot be the target of any unexpected exceptions. So I think I'm convinced that forkIOWithUnblock is necessary. It's a shame that it can be misused, but I don't see a way to avoid that. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Agata-0.2.0
Hi, Have you seen the derive package? It also generates QuickCheck instances in virtually the same way - plus it can generate source code and do lots of other types of instances. http://community.haskell.org/~ndm/derive/ Thanks, Neil 2010/4/20 Bas van Dijk v.dijk@gmail.com: 2010/4/19 Jonas Almström Duregård jonas.dureg...@gmail.com: If this is to be used with QuickCheck maybe it should be named that way. Certainly worth considering. There seems to be no convenient way of renaming packages on Hackage though, is there? AFAIK hackage has support for deprecating packages in favor of others. This functionality is not exposed to regular users but you could mail one of the maintainers (Ross Paterson) to rename your package. Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Agata-0.2.0
Jonas,
You can also derive (Co)Arbitrary instances automatically using the
regular-extras package based on the Regular generic programming library.
The advantage of using a library like Regular is that you do not have to write
any Template Haskell code. The library generates a nice algebraic generic view
on your datatype that you can use to write your generic functions. The Regular
library itself of course uses TH internally, but this is done once and all
datatype generic functions can piggy bag on the same TH derivation. For
example, look at Generics.Regular.Functions.Arbitrary, this module is really
concise.
Nice work though!
Gr,
Sebastiaan
On Apr 18, 2010, at 1:43 AM, Jonas Almström Duregård wrote:
I'm pleased to announce Agata (Agata Generates Algebraic Types Automatically)!
Avoiding excessive details, usage is best described by a small example:
{-#LANGUAGE TemplateHaskell #-}
import Test.QuickCheck
import Test.AgataTH
data X a b = X [Either a b] deriving Show
data Y = Y deriving Show
data Z = Z deriving Show
$(agatath $ deriveall [''X,''Y,''Z])
main = sample (arbitrary :: Gen (X Y Z))
This code derives instances of Test.QuickCheck.Arbitrary for the data
types X, Y and Z.
http://hackage.haskell.org/package/Agata
Regards Jonas
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Profiling
Dear all, I am trying to compile a project with the "-prof -auto-all" profile options. But the compiler returns: "Could not find module `Text.ParserCombinators.Parsec.Language':Perhaps you haven't installed the profiling libraries for package `parsec-3.1.0'?Use -v to see a list of the files searched for." When I build the project without the "-prof -auto-all", the project compiles without any error or warning. I build GHC (6.10.4) from source, without changing any build option. Thanks in advance for any help, Rodrigo. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Profiling
rodrigo.bonifacio rodrigo.bonifa...@uol.com.br writes: Could not find module `Text.ParserCombinators.Parsec.Language': Perhaps you haven't installed the profiling libraries for package `parsec-3.1.0'? Use -v to see a list of the files searched for. How did you install parsec? You need to rebuild it with profiling library support. If you used cabal-install, you have two options: 1) set library-profiling to True in ~/.cabal/config and then cabal install parsec --reinstall 2) cabal install parsec --reinstall --enable-library-profiling When I build the project without the -prof -auto-all, the project compiles without any error or warning. I build GHC (6.10.4) from source, without changing any build option. This has nothing to do with GHC. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: GUI (was: Re: [Haskell-cafe] DLL on Windows)
:-( - it seems that cabal install wx isn't how you install it on Windows, not by a long shot. I'm currently a Gtk2hs user. If wx got to the point where cabal install wx either installed wx, including all it's non-Haskell dependencies, or printed out a message you're a windows user who hasn't installed wxWidgets, here's a handy url for you to click and run then run cabal install wx again I'd be tempted to switch. I realise that the platform differences makes it annoying, but it would be generally handy for Windows users. I do appreciate the work the wx people are doing for Windows users - it is generally going in the right direction :-) Thanks, Neil On Mon, Apr 19, 2010 at 2:54 AM, Jeremy O'Donoghue jeremy.odonog...@gmail.com wrote: On 18/04/2010, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Sonntag 18 April 2010 21:41:06 schrieb Daniel Fischer: wx-config should have been installed as part of the wxWidgets package. Is that not included in the windows-installer of wxWidgets? Seems it's not so. http://www.haskell.org/haskellwiki/WxHaskell/Building says Windows users should also get the Windows port of wx-config. ( http://sites.google.com/site/wxconfig/ Sadly, the Windows port of wxWidgets doesn't contain wx-config (all of the Unix variants have it - it's a shell script), which is a major problem as this by far the simplest way for the build system to work out the options used to build wxWidgets. The Windows port of wx-config is an attempt to fix this problem, but only currently supports gcc, hence the restriction to using MinGW (although I guess Cygwin would probably work). If wxHaskell could be installed with one cabal command that would be incredibly cool :-) Well, it's just one cabal command if you have all non-Haskell requirements installed as needed. An option I am looking at is creating a basic Windows installer for wxHaskell which would contain a compiled copy of wxWidgets and a copy of wx-config, and which would run cabal install wxWidgets out of the box. (basic here means you probably don't get to choose anything at all - not even where the wxWidgets libraries get installed) Provided that I don't need to maintain a source distribution, this might be a good way forward for some Windows users. The installer would be updated for 'significant' wxWidgets updates (you would be able to 'cabal install wx' at any time wxHaskell is updated once you have all of the libraries) Any interest - please let me know. Regards Jeremy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Profiling
Hi Ivan, I tried doing cabal install parsec = 3 --reinstall --enable-library-profiling This complained about bytestring ... so I did this - cabal install bytestring --reinstall --enable-library-profiling And this complained about base - Data/ByteString.hs:278:7: Could not find module `GHC.ST': Perhaps you haven't installed the profiling libraries for package `base'? Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: bytestring-0.9.1.5 failed during the building phase. The exception was: exit: ExitFailure 1 [kash...@trinity318 ~]$ cabal install base --reinstall --enable-library-profiling Resolving dependencies... cabal: internal error: impossible Am I missing something? On Tue, Apr 20, 2010 at 6:59 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: rodrigo.bonifacio rodrigo.bonifa...@uol.com.br writes: Could not find module `Text.ParserCombinators.Parsec.Language': Perhaps you haven't installed the profiling libraries for package `parsec-3.1.0'? Use -v to see a list of the files searched for. How did you install parsec? You need to rebuild it with profiling library support. If you used cabal-install, you have two options: 1) set library-profiling to True in ~/.cabal/config and then cabal install parsec --reinstall 2) cabal install parsec --reinstall --enable-library-profiling When I build the project without the -prof -auto-all, the project compiles without any error or warning. I build GHC (6.10.4) from source, without changing any build option. This has nothing to do with GHC. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Asynchronous exception wormholes kill modularity
On 04/20/10 06:56, Simon Marlow wrote: On 09/04/2010 12:14, Bertram Felgenhauer wrote: Simon Marlow wrote: On 09/04/2010 09:40, Bertram Felgenhauer wrote: timeout t io = mask $ \restore - do result- newEmptyMVar tid- forkIO $ restore (io= putMVar result) threadDelay t `onException` killThread tid killThread tid tryTakeMVar result I'm worried about the case when this function is called with exceptions already blocked. Then 'restore' will be the identity, and exceptions will continue to be blocked inside the forked thread. You could argue that this is the responsibility of the whole chain of callers (who'd have to supply their own 'restore' functions that will have to be incorporated into the 'io' action), but that goes against modularity. In my opinion there's a valid demand for an escape hatch out of the blocked exception state for newly forked threads. It could be baked into a variant of the forkIO primitive, say forkIOwithUnblock :: ((IO a - IO a) - IO b) - IO ThreadId I agree with the argument here. However, forkIOWithUnblock reintroduces the wormhole, which is bad. The existing System.Timeout.timeout does it the other way around: the forked thread sleeps and then sends an exception to the main thread. This version work if exceptions are masked, regardless of whether we have forkIOWithUnblock. Arguably the fact that System.Timeout.timeout uses an exception is a visible part of its implementation: the caller must be prepared for this, so it is not unreasonable for the caller to also ensure that exceptions are unmasked. But it does mean that a library cannot use System.Timeout.timeout invisibly as part of its implementation. If we had forkIOWithUnblock that would solve this case too, as the library code can use a private thread in which exceptions are unmasked. This is quite a nice solution too, since a private ThreadId is not visible to anyone else and hence cannot be the target of any unexpected exceptions. So I think I'm convinced that forkIOWithUnblock is necessary. It's a shame that it can be misused, but I don't see a way to avoid that. [forkIOWithUnblock in the implementation of 'timeout'?] I thought that System.Timeout.timeout runs the IO in the original thread for a good reason. Was it just so that it could receive asynchronous exceptions correctly? Or also so that myThreadID returned the correct value? If just the former is what we're concerned about, we *could* make it behave differently when exceptions are unblocked vs. when it's uninterruptible, except that they can be restored to an unblocked state somewhere within the io. [Oh wait, Simon was suggesting that the library should run forkIOWithUnblock as a wrapper to its use of 'timeout'.] Yes, that sounds relatively safe. None of the exceptions thrown to the original thread will be discharged unexpectedly as a result of this unblocking, because of the forkIO. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Profiling
Am Dienstag 20 April 2010 18:59:23 schrieb C K Kashyap: Hi Ivan, I tried doing cabal install parsec = 3 --reinstall --enable-library-profiling This complained about bytestring ... so I did this - cabal install bytestring --reinstall --enable-library-profiling And this complained about base - Data/ByteString.hs:278:7: Could not find module `GHC.ST': Perhaps you haven't installed the profiling libraries for package `base'? Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: bytestring-0.9.1.5 failed during the building phase. The exception was: exit: ExitFailure 1 [kash...@trinity318 ~]$ cabal install base --reinstall --enable-library-profiling Resolving dependencies... cabal: internal error: impossible Am I missing something? You cannot reinstall or upgrade core libs (basically, what comes with the compiler). If your GHC came from a system package (and I think the binaries from the GHC page include profiling libs and they're built by default when building GHC from source, so you wouldn't have that problem), you probably don't have installed the package with the profiling libraries, something like yum/apt-get install libghc??-prof should get you the profiling libraries for base, bytestring and a few others, then cabal install parsec = 3 --reinstall --enable-library-profiling should work. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bulk Synchronous Parallel
2010/04/19 Gregory Crosswhite gcr...@phys.washington.edu: Thanks for the link; my ultimate interest, though, is in an architecture that could scale to multiple machines rather than multiple cores with shared memory on a single machine. Has there been any interest and/or progress in making DPH run on multiple machines and other NUMA architectures? I wonder what it would take to do this. One approach is some compiler magic that provides you with an RTS that can communicate with other RTSen over TCP and chunks the computation appropriately. Or maybe you give it a chunk size and it gives you some number of executables that find one another using Bonjour. Values not on this node are found via some hashing scheme (the same scheme used to chunk in the first place). There is a lot to know about this problem area. It would be a great alternative to OpenMPI. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Profiling
Thanks Daniel, that worked. On Tue, Apr 20, 2010 at 11:24 PM, Daniel Fischer daniel.is.fisc...@web.dewrote: Am Dienstag 20 April 2010 18:59:23 schrieb C K Kashyap: Hi Ivan, I tried doing cabal install parsec = 3 --reinstall --enable-library-profiling This complained about bytestring ... so I did this - cabal install bytestring --reinstall --enable-library-profiling And this complained about base - Data/ByteString.hs:278:7: Could not find module `GHC.ST': Perhaps you haven't installed the profiling libraries for package `base'? Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: bytestring-0.9.1.5 failed during the building phase. The exception was: exit: ExitFailure 1 [kash...@trinity318 ~]$ cabal install base --reinstall --enable-library-profiling Resolving dependencies... cabal: internal error: impossible Am I missing something? You cannot reinstall or upgrade core libs (basically, what comes with the compiler). If your GHC came from a system package (and I think the binaries from the GHC page include profiling libs and they're built by default when building GHC from source, so you wouldn't have that problem), you probably don't have installed the package with the profiling libraries, something like yum/apt-get install libghc??-prof should get you the profiling libraries for base, bytestring and a few others, then cabal install parsec = 3 --reinstall --enable-library-profiling should work. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: hamlet 0.0.0
Hi all, I'd like to announce the first release of Hamlet[1], a templating system which is fully compile-time checked. Templates are parsed via quasi-quoting, giving you greater confidence in the validity of your templates. The syntax is inspired by Haml[2]; however, it is most definitely its own language, avoiding embedding of arbitrary code in favor of a more strict view-logic separation. Finally, it has a goal of allowing high performance uses; to facilitate this, it allows calling monadic code from inside the template, and can use enumerators for traversing elements. While these features could be abused to allow templates to perform unintended side-effects, the performance gains allowed by them are sometimes essential. I have started a documentation site for all Yesod-related packages[3], and in particular there is a Hamlet section[4]. I've also put up a small blog post[5] on this release, which explains how Hamlet fits into the Yesod ecosystem. (For those not in the know, Yesod is a web framework I'm working on.) Michael [1] http://hackage.haskell.org/package/hamlet-0.0.0 [2] http://haml-lang.com/ [3] http://docs.yesodweb.com/ [4] http://docs.yesodweb.com/hamlet/ [5] http://www.snoyman.com/blog/entry/hamlet-is-born/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Agata-0.2.0
Hi Neil and Sebastiaan,
Thanks for the constructive criticism ;).
As far as i can tell, derive only works for regular and linear
recursive types and Regular uses frequencies to regulate size. (Also
Regular doesn't seem to work for QuickCheck-2).
I think I may have used a too simple example in my original post. Here
is a more complicated one:
data TrinaryTree a =
Branch a (TrinaryTree a) (TrinaryTree a) (TrinaryTree a)
| Empty deriving Show
$(agatath $ derive ''TrinaryTree)
With the derive tool, generated values would typically be infinite.
With Regular, the user would need to specify frequencies, and even
then the generator would be useless because of the low frequency
required for Branch to ensure termination (most generated trees
would be empty, and almost none would contain several branches).
Most of the work i have done on Agata is to make a class that
resembles arbitrary (i.e. can be used to construct generators) but
where the instances can be defined mechanically from the definition of
instantiated types. The reason i didn't use Generics for defining the
instances is that I was unsure if/how it distinguishes mutually
recursive fields.
Another feature of Agata generators is improved scalability compared
to other QuickCheck generators, especially for nested collection data
types (analog to a and such). The details of how this works in
Agata will one day be explained in the documentation, but the
principle is explained in my masters thesis[1].
Regards,
Jonas
[1] http://gupea.ub.gu.se/bitstream/2077/22087/1/gupea_2077_22087_1.pdf
2010/4/20 Sebastiaan Visser sfvis...@cs.uu.nl:
Jonas,
You can also derive (Co)Arbitrary instances automatically using the
regular-extras package based on the Regular generic programming library.
The advantage of using a library like Regular is that you do not have to
write any Template Haskell code. The library generates a nice algebraic
generic view on your datatype that you can use to write your generic
functions. The Regular library itself of course uses TH internally, but this
is done once and all datatype generic functions can piggy bag on the same TH
derivation. For example, look at Generics.Regular.Functions.Arbitrary, this
module is really concise.
Nice work though!
Gr,
Sebastiaan
On Apr 18, 2010, at 1:43 AM, Jonas Almström Duregård wrote:
I'm pleased to announce Agata (Agata Generates Algebraic Types
Automatically)!
Avoiding excessive details, usage is best described by a small example:
{-#LANGUAGE TemplateHaskell #-}
import Test.QuickCheck
import Test.AgataTH
data X a b = X [Either a b] deriving Show
data Y = Y deriving Show
data Z = Z deriving Show
$(agatath $ deriveall [''X,''Y,''Z])
main = sample (arbitrary :: Gen (X Y Z))
This code derives instances of Test.QuickCheck.Arbitrary for the data
types X, Y and Z.
http://hackage.haskell.org/package/Agata
Regards Jonas
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does the transformers/mtl 'Error' class exist?
On Sat, Apr 17, 2010 at 2:52 PM, Henning Thielemann
schlepp...@henning-thielemann.de wrote:
Ryan Ingram schrieb:
It's used in the implementation of fail for those monads.
class Monad m where
...
fail :: String - m a
fail = error -- default implementation
which is then used to desugar do-notation when pattern matching fails:
do
Left x - something
return x
=
something = \v - case v of { Left x - return x ; _ - fail
Pattern match failure ... }
You can argue about whether fail belongs in Monad (and many people
have), but that's why it is how it is.
I also prefered to not support the fail method in this way and wrote:
http://hackage.haskell.org/packages/archive/explicit-exception/0.1.4/doc/html/Control-Monad-Exception-Synchronous.html
I find that having pattern match desugar to fail, and supporting
fail, can lead to extremely concise, clear code.
For example, an excerpt from some type checking/inference code I wrote:
data Equal a b = (a ~ b) = Refl
data Typ a where
TInt :: Typ Int
TBool :: Typ Bool
TList :: Typ a - Typ [a]
TArrow :: Typ a - Typ b - Typ (a - b)
eqT :: Typ a - Typ b - Maybe (Equal a b)
eqT TInt TInt = return Refl
eqT TBool TBool = return Refl
eqT (TList a) (TList b) = do
Refl - eqT a b
return Refl
eqT (TArrow a1 a2) (TArrow b1 b2) = do
Refl - eqT a1 b1
Refl - eqT a2 b2
return Refl
eqT _ _ = fail not equal
This relies heavily on the pattern match desugaring to case, which
brings the type equality (a ~ b) into scope, and fail returning
Nothing. For example, the list case:
desugaring eqT (TList TInt) (TList TInt), with all operations on the
Maybe monad inlined and simplified
we have
ta = TList TInt :: Typ a, tb :: TList TInt :: Typ b, for some a, b
eqT = case ta of
...
(TList ta1) -
-- now we have a ~ [a1] for some a1
case tb of
...
(TList tb1) -
-- now we have b ~ [b1] for some b1
case eqT ta1 tb1 of
Just Refl -
-- now we have a1 ~ b1, which gives us [a1] ~ [b1], which gives us a ~ b
Just Refl
_ - Nothing
-- ryan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what does the '~' mean ?
On Thu, Apr 15, 2010 at 10:59 PM, zaxis z_a...@163.com wrote: instance (BinaryDefer a, BinaryDefer b) = BinaryDefer (a,b) where put (a,b) = put2 a b get = get2 (,) size x = let ~(a,b) = x in size a + size b putFixed (a,b) = putFixed2 a b getFixed = getFixed2 (,) in `size` function, what does the `~` mean ? This is kind of a funny question, because in this case the ~ doesn't mean anything at all. Pattern matches in let are automatically irrefutable/lazy. A better way to write this is size ~(a,b) = size a + size b which is equivalent to size x = size a + size b where (a,b) = x which is equivalent to size x = let (a,b) = x in size a + size b which is equivalent to size x = let a = case x of (v,_) - v b = case x of (_,v) - v in size a + size b If a or b never get evaluated, the case statements (which will fail on bottom values) don't happen. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] C variable access via FFI
On Tue, Apr 20, 2010 at 01:48:16AM -0500, Tom Hawkins wrote: I have a bunch of global variables in C I would like to directly read and write from Haskell. Is this possible with FFI, or must I write a bunch of C wrapper functions for the interface, i.e. a 'get' and a 'set' for each variable? Yup. foo.c: int my_int; Foo.hs: foreign import my_int my_int_ptr :: Ptr Int foo = do poke my_int_ptr 4 x - peek my_int_Ptr John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: forkable-monad 0.1
Dear Haskellers, I'm happy, and only slightly intimidated, to announce the initial release of forkable-monad. The short version is that forkable-monad exports a replacement forkIO that lets you do this: type MyMonad = ReaderT Config (StateT Ctx IO) startThread :: MyMonad ThreadId startThread = forkIO threadMain threadMain :: MyMonad () threadMain = forever $ liftIO $ putStrLn Painless monad stack forking! Note the lack of monad stack deconstruction and reconstruction to transport it over to the new thread. You'll find the details in the Haddock documentation for the module. forkable-monad is available: * On hackage: http://hackage.haskell.org/package/forkable-monad * Via cabal: cabal install forkable-monad * Source and issue tracker: http://code.google.com/p/forkable-monad/ Feedback is of course welcome. As this is my first published Haskell code and Hackage upload, I expect there will be quite a bit! - Dave ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Re: instance Eq (a - b)
I don't mind the 0.0 == -0.0 case, its the NaN /= NaN one that gets me. ;) The former just says that the equivalence relation you are using isn't structural. The latter breaks the notion that you have an equivalence relation by breaking reflexivity. Eq doesn't state anywhere that the instances should be structural, though in general where possible it is a good idea, since you don't have to worry about whether or not functions respect your choice of setoid. Ultimately, I find myself having to play a bit unsafe with lazy bytestrings more often than I'd like to admit. Use of toChunks should always be careful to be safe to work regardless of the size of the chunks exposed, and can also rely on the extra-logical fact enforced by the bytestring internals that each such chunk is non-empty. It greatly facilitates 'lifting' algorithms that work over strict bytestrings to work over their lazy kin, and its omission would deal a terrible blow to the practical usability and efficiency of the bytestring library. I frankly would be forced to reimplement them from scratch in several packages were it gone. Ultimately, almost any libraries relies on a contract that extends beyond the level of the type system to ensure they are used them correctly. A malformed 'Ord' instance can wreak havoc with Set, a non-associative 'Monoid' can leak structural information out of a FingerTree. Similarly, the pleasant fiction that x == y == f x == f y -- only holds if the Eq instance is structural, and toChunks can only 'safely' be used in a manner that is oblivious to the structural partitioning of the lazy bytestring. -Edward Kmett On Mon, Apr 19, 2010 at 6:02 PM, Ashley Yakeley ash...@semantic.org wrote: Why is a function that gets a bunch of strict ByteStrings out of a lazy one exposed? In any case, it sounds like a similar situation to (==) on Float and Double. There's a mismatch between the Haskellish desire for a law on (==), and the convenient desire for -0.0 == 0.0, or for exposing toChunks. Which one you prefer depends on your attitude. My point is not so much to advocate for the Haskellish viewpoint than to recognise the tension in the design. Float and Double are pretty ugly anyway from a Haskell point of view, since they break a bunch of other desirable properties for (+), (-) and so on. The theoretical reason for using floating point rather than fixed point is when one needs relative precision over a range of scales: for other needs one should use fixed point or rationals. I added a Fixed type to base, but it doesn't implement the functions in the Floating class and I doubt it's as fast as Double for common arithmetic functions. It would be possible to represent the IEEE types in a Haskellish way, properly revealing all their ugliness. This would be gratifying for us purists, but would annoy those just trying to get some numeric calculations done. -- Ashley Yakeley On Mon, 2010-04-19 at 15:32 -0400, Edward Kmett wrote: Because it is the most utilitarian way to get a bunch of strict ByteStrings out of a lazy one. Yes it exposes an implementation detail, but the alternatives involve an unnatural amount of copying. -Edward Kmett On Sat, Apr 17, 2010 at 6:37 PM, Ashley Yakeley ash...@semantic.org wrote: Ketil Malde wrote: Do we also want to modify equality for lazy bytestrings, where equality is currently independent of chunk segmentation? (I.e. toChunks s1 == toChunks s2 == s1 == s2 but not vice versa.) Why is toChunks exposed? -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing listhaskell-c...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Move MonadIO to base
On Tue, 20 Apr 2010, wren ng thornton wrote: -- | The isomorphic Haskell98 version class Monad m = MonadJoinIO m where -- | Embed the IO into the monad m joinIO :: IO (m a) - m a -- | Extract the IO computation to the top level, -- rendering the m pure from IO. partIO :: m a - IO (m a) -- | The isomorphisms joinIO' m = morphIO (m =) morphIO' f = joinIO (f partIO) To establish an isomorphism, you also need to define partIO from morphIO. For example, I don’t see how I could define partIO :: IO a - IO (ReaderT r IO a) that extracts effects into the outer IO, because the effects depend on some unknown state of type r. By the way: This bounced because I have different emails registered for cafe@ and libraries@, so forwarding it along to the cafe. You can sign up both addresses for the list, then log in to the Mailman web interface ( http://www.haskell.org/mailman/listinfo/haskell-cafe → Unsubscribe or edit options) and disable mail delivery on one of them. Then you get one copy of each message but you can post from either address. Anders ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bulk Synchronous Parallel
On Apr 20, 2010, at 11:05 AM, Jason Dusek wrote: Thanks for the link; my ultimate interest, though, is in an architecture that could scale to multiple machines rather than multiple cores with shared memory on a single machine. Has there been any interest and/or progress in making DPH run on multiple machines and other NUMA architectures? I wonder what it would take to do this. Erlang. ;0) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
