November 2004 - Glasgow-haskell-users

Export through FFI Haskell List to C array (by MarshalAlloc)
by David Lo 09 Nov '04

09 Nov '04

Dear all, Anyone has ever tried exporting Haskell list to C array ? I read in the FFI for MarshalAlloc, it is mentioned that Haskell lists are typically passed as C arrays to C functions. However, how can we do that ? I have a list of Int (i.e. [Int]) which I would like to pass as int[] in C. Please kindly advise how to proceed. Best Regards, David Lo

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Looing for advice on profiling
by Duncan Coutts 09 Nov '04

09 Nov '04

Hi all, I'm looking for some advice on profiling and any suggestion on what might be going on with this program. I'm profiling c2hs, Manuel Chakravarty's FFI preprocessor with an eye to reducing its time and space usage. I'm also trying to add binary serialisation. c2hs basically works by parsing a load of C header files, building up maps of info on function & type names. It then scans a .chs file and produces a .hs file using the info it gained from the C header files. Producing the .hs file is fairly quick once all the symbol maps have been constructed. Parsing the C headers and gathering the info is fairly slow. So building a project that uses lots of .chs files is quite slow because it re-parses the header files each time. We originally modified c2hs to do multiple .chs files in one go so the work could be shared however this style is not compatible with most build tools (ie automake). Another approach is to dump a representation of the symbol maps after parsing the header files and then reading this back for each .chs file. So enough background, here's the issues: doing the binary serialisation seems to be incredibly slow and I can't figure out why. I'm now using the Binary module pinched from the ghc sources and instances derived by DrIFT for all the c2hs data structures. I've also derived NFData instances (DeepSeq) so that I can make sure that the data to be serialised is already fully evaluated. I inserted timing points in the program so see what's taking so long. Here's a sample output: c2hs/c2hs +RTS -M400m -H300m -RTS -C-I/usr/include/glib-2.0 -C-I/usr/lib/glib-2.0/include --precomp=glib.precomp glib.h starting c2hs elapsed time: 0.00 (start) elapsed time: 0.00 (about to run cpp) elapsed time: 0.01 (about to parse header) elapsed time: 1.90 (about to emit warnings) elapsed time: 1.90 (about to deepSeq header) elapsed time: 5.24 (about to serialise header) elapsed time: 52.47 (finnished serialising header) elapsed time: 52.47 (finnish) glib.h (and it's includes after cpp'ing) is about 3k lines. So it takes a few seconds to parse the file and a few more to deepSeq the whole structure. However after that it takes a long time to serialise the structure. glib.h is quite small in comparison to gtk/gtk.h which is about 25k lines. So gtk.h takes ages. In fact it uses so much memory serialising that it cannot complete on my machine with -H450m (the max I can set it to on my 512Mb machine without swap thrashing). When I run it in the original mode that does no serialisation it completes fine in about 1min. The binary file produced for glib.h in the end is about 4Mb which is not huge I'd say. We're using String rather than FastString so that slows things down a bit and takes more space but even so. (I modified the Binary module to store lists in length + elems format rather than 0 for [], 1 for (:) format and chars to use just one byte so strings are not stored too inefficiently). The file size for gtk.h is about 20Mb (tested on a machine with more memory). When I do time profiling, the big cost centres come up as putByte and putWord. When I profile for space it shows the large FiniteMaps dominating most everything else. I originally guessed from that that the serialisation must be forcing loads of thunks which is why it shows up so highly on the profile. However even after doing the deepSeq before serialisation, it takes a great deal of time, so I'm not sure what's going on. The retainer profiling again shows that the FiniteMaps are holding on to most stuff. A major problem no doubt is space use. For the large gtk/gtk.h, when I run with +RTS -B to get a beep every major garbage collection, the serialisation phase beeps continuously while the file grows. Occasionally it seems to freeze for 10s of seconds, not dong any garbage collection and not doing any file output but using 100% CPU, then it carries on outputting and garbage collecting furiously. I don't know how to work out what's going on when it does that. I don't understand how it can be generating so much garbage when it is doing the serialisation stuff on a structure that has already been fully deepSeq'ed. Any ideas? Where should I direct my investigation? I can supply tarballs and profiling results and graphs if that would be helpful. Unfortunately the code base is quite big which makes things difficult. Duncan

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RE: GHC CVS HEAD bug!
by Simon Peyton-Jones 09 Nov '04

09 Nov '04

Good point. I've fixed this (HEAD only), and added a test so it won't recur. Thanks! Simon | -----Original Message----- | From: glasgow-haskell-users-bounces(a)haskell.org [mailto:glasgow-haskell-users- | bounces(a)haskell.org] On Behalf Of Keean Schupke | Sent: 03 November 2004 10:08 | To: glasgow-haskell-users(a)haskell.org | Subject: GHC CVS HEAD bug! | | The CVS HEAD branch of GHC seems to ignore the fixity of | type constructors imported from another module... This breaks | compiling of code that uses this feature: | | module1: | | type a :+ b = (a,b) | infixr 1 :+ | | module2: | | a :: Int :+ Float :+ Double | a = undefined | | Gives a the wrong type. | | Keean | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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RE: proposal for ghc-pkg to use a directory of .conf files
by Simon Marlow 08 Nov '04

08 Nov '04

On 06 November 2004 10:10, Sven Panne wrote: > Duncan Coutts wrote: >> I can knock up a proof of concept patch if anyone thinks this is a >> good idea. It should be totally backward compatible, it's ok to use >> both, but ditro packagers might like to enforce a policy of using a >> directory of package files for external libraries. > > OK, just send us a patch and if there are no objections we can merge > it into the HEAD. In some ways this looks like a good idea, but it contradicts some of the ideas in the Cabal proposal. There, we were treating the package database as an abstract entity hidden behind the ghc-pkg interface. All interaction with the database would be done via ghc-pkg. The advantages of this abstraction are the usual ones: we might want to change the representation, and the ghc-pkg tool provides a good place to add backwards compatibility if necessary. However, I'm prepared to be persuaded. The "just put a file in this directory" approach to installation is very compelling, being much more transparent. But bear in mind that if we pick this route, then backwards compatibility has to be built into the file format (I think it might be already, but we're planning changes in this area to better support Cabal). Also, there needs to be a way to find the location to install the file - asking ghc or ghc-pkg is the usual way. Cheers, Simon

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RE: foreign export stdcall on user-defined type and function
by Simon Marlow 08 Nov '04

08 Nov '04

On 08 November 2004 02:49, David Lo wrote: > I'm new in haskell. I'm assigned to see that a piece of Haskell code > need to be callable from C#. I find that I can convert Haskell to DLL > using ghc --mk-dll. > > I find it is fine for simple function but for the following errors are > reported. > > foreign export stdcall doComp :: Pattern -> CString -> IO () > doComp :: Pattern -> CString -> IO () > > foreign export stdcall evalDisplay :: RealFrac a => CString -> > (Int->VMC (Maybe a)) -> IO () > evalDisplay :: RealFrac a => CString -> (Int->VMC (Maybe a)) -> IO () It would help if you posted the entire code, rather than just a snippet. We can't tell for sure where the errors are without seeing the definitions for some of the types you've used, for example. > The errors are as follows: > > Compiling Main ( CPL.hs, interpreted ) > > CPL.hs:29: > Unacceptable argument type in foreign declaration: > forall a b c. (Ind a c, Compare c b) => Pat a b > When checking declaration: > foreign export stdcall "doComp" doComp :: Pattern-> CString > -> IO () The error indicates that you have declared a foreign exported function with a type that does not have a direct translation into a C type. The legal types for foreign exported functions are described in the FFI specification, which can be found online here: http://www.cse.unsw.edu.au/~chak/haskell/ffi/ffi.pdf > CPL.hs:107: > Unacceptable argument type in foreign declaration: {RealFrac a} > When checking declaration: > foreign export stdcall "evalDisplay" evalDisplay :: forall a. > (RealFrac a) => CString-> (Int -> VMC (Maybe a)) -> IO () > > CPL.hs:107: > Unacceptable argument type in foreign declaration: > Int -> VMC (Maybe a) > When checking declaration: > foreign export stdcall "evalDisplay" evalDisplay :: forall a. > (RealFrac a) =>CString-> (Int -> VMC (Maybe a)) -> IO () > > I would like to inquire on how to use foreign function stdcall on self > defined data structure and function. Can I just simply cast them to > string ? Perhaps you could give more details about what you want to do. What Haskell functions do you want to export to C#, and what types do they have (both in Haskell and C#)? If you want to export Haskell data structures to C#, then you have to "marshal" the data into C#, by converting the Haskell representation into a representation that C# can understand. Using strings is one possibility, but it's unlikely to be the best. Cheers, Simon

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Re: [Haskell-cafe] Re: Double -> CDouble, realToFrac doesn't work
by MR K P SCHUPKE 08 Nov '04

08 Nov '04

>I would be very careful of adding non-rationals to the Rational type. Why is there no Irrational class. This would make more sense for Floats and Doubles than the fraction based Rational class. We could also add an implementation of infinite precision irrationals using a pair of Integers for exponent and mantissa. Keean.

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RE: happy and OPTIONS pragmas
by Simon Marlow 08 Nov '04

08 Nov '04

On 04 November 2004 18:21, Ian Lynagh wrote: > However, if a .y file starts: > > { > {-# OPTIONS -w #-} > -- Foo > {-# OPTIONS -w #-} > module Parser (parse) where > } > > then the generated .hs file starts: > > -- parser produced by Happy Version 1.14 > -- Foo > {-# OPTIONS -w #-} > module Parser (parse) where > > so the pragma before my comment has been eaten and the 2 comments mean > that ghc doesn't see the pragma, so gives me all the warnings anyway. > > Can happy be changed so my pragma gets through please? Thanks, will be fixed in the next Happy release (fix is in CVS). Cheers, Simon

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foreign export stdcall on user-defined type and function
by David Lo 08 Nov '04

08 Nov '04

Dear all, I'm new in haskell. I'm assigned to see that a piece of Haskell code need to be callable from C#. I find that I can convert Haskell to DLL using ghc --mk-dll. I find it is fine for simple function but for the following errors are reported. foreign export stdcall doComp :: Pattern -> CString -> IO () doComp :: Pattern -> CString -> IO () foreign export stdcall evalDisplay :: RealFrac a => CString -> (Int->VMC (Maybe a)) -> IO () evalDisplay :: RealFrac a => CString -> (Int->VMC (Maybe a)) -> IO () The errors are as follows: Compiling Main ( CPL.hs, interpreted ) CPL.hs:29: Unacceptable argument type in foreign declaration: forall a b c. (Ind a c, Compare c b) => Pat a b When checking declaration: foreign export stdcall "doComp" doComp :: Pattern-> CString -> IO () CPL.hs:107: Unacceptable argument type in foreign declaration: {RealFrac a} When checking declaration: foreign export stdcall "evalDisplay" evalDisplay :: forall a. (RealFrac a) => CString-> (Int -> VMC (Maybe a)) -> IO () CPL.hs:107: Unacceptable argument type in foreign declaration: Int -> VMC (Maybe a) When checking declaration: foreign export stdcall "evalDisplay" evalDisplay :: forall a. (RealFrac a) =>CString-> (Int -> VMC (Maybe a)) -> IO () I would like to inquire on how to use foreign function stdcall on self defined data structure and function. Can I just simply cast them to string ? Thank you in advance for your help and attention. Best Regards, David

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typechecking too eager?
by Keean Schupke 07 Nov '04

07 Nov '04

The following code should compile (If the constructor is valid, so is the function): data Test = Test (forall a . a) test a = Test a However this fails to compile with the following error: Test.hs:9:9: Inferred type is less polymorphic than expected Quantified type variable `a' escapes It is mentioned in the environment: test :: a -> Test (bound at Test.hs:9:0) a :: a (bound at Test.hs:9:5) In the first argument of `Test', namely `a' In the definition of `test': test a = Test a I think this should only generate an error once the value of 'a' is known not to be undefined. Keean.

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Terminal does not reset correctly with System.Console.SimpleLineEditor
by Einar Karttunen 07 Nov '04

07 Nov '04

Hello It appears that the console is not reset correctly with System.Console.SimpleLineEditor. The terminal does not echo characters until it is reset. The following program demonstrates it: import System.Console.SimpleLineEditor main = initialise >> getLineEdited "prompt> " >>= print >> restore This occurs with the Debian ghc package version 6.2.1 and the binary cvs snapshot of 20041017, both on i386 linux and in an xterm. - Einar Karttunen

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