September 2006 - Haskell-Cafe

Re: Haskell DLL crashes Excel
by Cyril Schmidt 26 Sep '06

26 Sep '06

A few people recently asked how to pass a string between a Haskell DLL and Excel. I attach the proof-of-concept code that I wrote a while ago; it demonstrates passing a string from Excel to Haskell and the other way. Most of the C++ code is taken from code examples at http://msdn.microsoft.com Beware, though, that the code has never been thoroughly tested. I ran it, and it did not crash -- that's almost all I can say. I even do not know if it leaks any memory. Use it at your own peril. The tar file contains a sample Excel sheet, and the sources of two DLLs: a COM DLL which interfaces with Excel, and a Haskell DLL which is invoked by the COM DLL. You will need Visual Studio 7.1 to build the COM DLL. The Haskell DLL exports one function, hString2String, which takes a C-style string, and returns the reverse of it. To build the Haskell DLL, run build.bat. To build (and register) the COM DLL, open Excel2Haskell.sln in Visual Studio, and hit Build. Once the two libraries are built, open Worksheet.xls and see how the function is invoked. Note that the COM DLL can be used not only by Excel, but by any other program or script that understands COM. For example, VBA scripts in Word, or VB and Javascript run by Wscript or Cscript. Hope this helps. Regards, Cyril ___

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Haskell.org down
by dons＠cse.unsw.edu.au 26 Sep '06

26 Sep '06

Just in case it has gone unnoticed, haskell.org seems to have been down for a few hours now. Do we have an admin looking into this? -- Don

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Haskell.org down (again)
by dons＠cse.unsw.edu.au 26 Sep '06

26 Sep '06

Something's going on. Haskell.org seems to be down again. That's the 3rd time in 4 days. -- Don

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haskell.org down again
by Pasqualino 'Titto' Assini 26 Sep '06

26 Sep '06

_____ From: HostTracker Notifier [mailto:noreply@host-tracker.com] Sent: 26 September 2006 01:19 To: tittoassini(a)gmail.com Subject: Error Alert Hello, The following url is down: http://haskell.org the error detected is: Http error:Http_client.No_reply Error was detected at 2006-09-26 01:14:41 Your login:titto -- Best regards, http://host-tracker.com/ support team uid:957058 tid:188350 eid:188350-209-0-0-4eee7afa9e44102989dd000c7651f68b

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Curious Functor Class
by Ashley Yakeley 26 Sep '06

26 Sep '06

Is there anything useful about the class of functors which foralls can move across? In other words, functors f, for which for any function g there is this isomorphism f (forall a. g a) <=> forall a. f (g a) In this Haskell snippet I've called the class Hoistable and the isomorphism is (hoist,unhoist): newtype All g = MkAll (forall a. g a); class (Functor f) => Hoistable f where { hoist :: forall g. (f (All g) -> (forall a. f (g a))); hoist = fmap (\(MkAll ga) -> ga); unhoist :: forall g. ((forall a. f (g a)) -> f (All g)); }; Functors that can be made instances of Hoistable: data Singleton a = MkSingleton newtype Identity a = MkIdentity a (->) p -- forall p. data Pair a = MkPair a a data Extra p a = MkExtra p a -- forall p. data Compose p q a = MkCompose (p (q a)) -- forall p q. (Hoistable p,Hoistable q) => On the other hand, Maybe and Either cannot. The key seems to be in only having one "form", i.e. no "|"s in the definition. Does this class actually have a use, or is it merely a curiosity? -- Ashley Yakeley Seattle WA

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Re: Haskell DLL crashes Excel
by Cyril Schmidt 25 Sep '06

25 Sep '06

Nikunj, The symptoms that you describe hint at some incorrect pointer handling. I believe the culprit is that pesky BSTR. I will try to dig up the code that I wrote a while ago to pass a BSTR to Haskell. Meanwhile, another hint. The GHC FAQ 1.4.1 says: "For utterly horrible reasons, programs that use more than 128Mb of heap won't work when compiled dynamically on Windows (they should be fine statically compiled)." (See http://haskell.org/haskellwiki/GHC:FAQ#My_program_that_uses_a_really_large_….) I have no clue what those horrible reasons might be, but you can limit the heap used by the Haskell DLL by setting the environment variable GHCRTS=-M128m Regards, Cyril ___ > | From: Gupta, Nikunj (London) [mailto:Nikunj_Gupta@ml.com] > | Sent: 25 September 2006 10:31 > | To: Simon Peyton-Jones > | Subject: RE: [Haskell-cafe] Haskell DLL crashes Excel > | > | Hello Simon, > | > | Nice to hear from you. I haven't really been working with Haskell but > I > | posted the message to that list since that was the only list I was > able > | to locate even remotely referring to the problem I was facing. > | I have a c++ code which I try to compile as a dll. When debugging the > | code works fine but as soon as I compile it for release and launch an > | independent process not attached to VC++ it crashes. Do you have any > | suggestions with regards to the project settings that might be causing > | the same. > | > | Any sort of help would be much appreciated > | Regards > | Nikunj >

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Writing forum software in Haskell
by David House 25 Sep '06

25 Sep '06

Hi all. The recent thread on email vs. forums inspired a bit of interest to get some forum software on haskell.org. Were we to go ahead with this, I think it'd be great to have this software written in Haskell itself. I'd also love to be involved in a collaboration should one be drummed up to write this kind of thing. Therefore, my questions: * What kind of forum are we aiming at? In my eyes, it'd be less like the bloated phpBBs out there full of oversized signatures and avatars, and more like the minimalistic bbPress on show at, for example, the WordPress support forums [1]. * What would be a compulsory feature list? * What would be a list of things to avoid like the plague? * Which web platform (HAppS, Hope, ...) would make the most appropriate target? Appreciate thoughts and opinions. -- -David House, dmhouse(a)gmail.com

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job writing security software in Haskell
by Andrew Pimlott 25 Sep '06

25 Sep '06

Planning Systems, Inc. has a job opportunity for Haskell programmers. My synopsis is below, and the official description is at http://www.plansys.com/careers/job_details.cfm?JobID=28 Write Haskell code for a US government contractor. Projects include a high-assurance authorization system build around Soutei: http://okmij.org/ftp/Prolog/#Soutei Job is located in Monterey, CA, Slidell, LA, or Portsmouth, VA; working remotely is probably not an option. US citizenship required. Desirable experience: - Haskell - Logic programming - Formal methods - Network security - Web services I welcome you to ask me for more information, and please pass this along to Haskellers looking for a job who can meet the citizenship and (re-)location requirements. Andrew

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Haskell DLL crashes Excel
by Andreas Marth 25 Sep '06

25 Sep '06

Hi everybody! As you might now already know I try to let VBA call Haskell via a DLL. The function returns a String. Everything works fine now if I call the function only once. If I call it more often Excel crashes soon. Does any body have any idea what is going wrong or how I can find out. (I am a medium skilled Haskell user but no VBA programmer.) My code for Haskell (Calculate.hs): module Calculate where import Foreign.C.String (CString, peekCString, newCString) import Data.Word (Word8, Word16, Word32) import Data.Bits (shiftR, (.&.)) import Foreign.Marshal.Array (newArray) import Foreign.Ptr (Ptr, plusPtr) type BSTR8 = Ptr Word8 createBSTR8 :: String -> IO BSTR8 createBSTR8 s = do let len :: Word32 = fromIntegral (length s) low_l :: Word8 = fromIntegral (len .&. 0xFFFF) low_h :: Word8 = fromIntegral (shiftR len 8 .&. 0xFFFF) high_l :: Word8 = fromIntegral (shiftR len 16 .&. 0xFFFF) high_h :: Word8 = fromIntegral (shiftR len 24 .&. 0xFFFF) arr <- newArray ([low_l,low_h,high_l,high_h] ++ map (fromIntegral . fromEnum) s ++ [0]) return $! plusPtr arr 4 testL :: Int -> CString -> IO BSTR8 testL n cs = do s <- peekCString cs createBSTR8 $ concat $ take n $ repeat s foreign export stdcall testL :: Int -> CString -> IO BSTR8 --------------------------------------------------------------- My VBA code (in Excel 2000): Option Explicit Dim h1 As String Dim a As Long Dim b As Long Private Declare Function testL Lib "P:\Daten\Code\Calculate.dll" (ByVal n As Long, ByVal str As String) As String Sub Test() a = 0 b = 10 h1 = "" Do While a <= 15 h1 = testL(b, "What is going on here?") a = a + 1 Debug.Print a Debug.Print h1 Loop End Sub ----------------------------------------------------------- And my DllMain.c: #include <windows.h> #include <Rts.h> extern void __stginit_Calculate(void); static char* args[] = { "ghcDll", NULL }; /* N.B. argv arrays must end with NULL */ BOOL STDCALL DllMain ( HANDLE hModule , DWORD reason , void* reserved ) { if (reason == DLL_PROCESS_ATTACH) { /* By now, the RTS DLL should have been hoisted in, but we need to start it up. */ startupHaskell(1, args, __stginit_Calculate); return TRUE; } if (reason == DLL_PROCESS_DETACH) { shutdownHaskell(); return TRUE; } return TRUE; } ---------------------------------------------------------------- And I compile the DLL with: ghc -c --make -fglasgow-exts -static Calculate.hs ghc -c -fglasgow-exts -static *.c ghc --mk-dll -o Calculate.dll *.o -static -optdll--def -optdllCalculate.def ------------------------------------------------------------------ Nearly forgot Calculte.def: LIBRARY Calculate EXPORTS testL = testL@8 ----------------------------------------------------------------- The DLL is stable regarding the length of the input string and thelength of the return string (determined with b). But crashes for larger(?) a's. At my computer it crashes with a >9. There seems to be a connection between b and a. If b is 10 then a>9 crashes a<10 is fine. If b=1000 then a<5 is okay a>4 crashes. If b =100 then a<5 is okay, a>5 crashes and a=5 crashes with an error "Statement in 0x778cb032 points to 0x00000000 the function 'written' could not be done ..." And a second one "Statement in 0x778cc441 points to 0x00000000 the function 'written' could not be done ..." (My translation of the german errors.) If anybody knows what is going wrong or can give me a hint how to find out what is going wrong it would be very helpful. Thanks Andreas

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Re: [Haskell] BitSyntax for Haskell
by Einar Karttunen 25 Sep '06

25 Sep '06

On 23.09 15:00, Adam Langley wrote: > Erlang's bit syntax[1] is a great for building and breaking up binary > structures. I've knocked up something similar (although a little > clumsy) for Haskell: > > http://www.imperialviolet.org/binary/bitsyntax/ > http://www.imperialviolet.org/binary/bitsyntax/BitSyntax.hs > > I'm sure that this isn't the best possible way to do this, but it > suffices at this stage for many problems. This looks very nice. Here are some feature wishes: BitBlock: add a way to encode length prefixed ByteStrings. For the decoding part: * Provide a monadic interface * Add a test part to ReadType: Test :: ReadType a -> (a -> Bool) -> ReadType Test (or a -> m ()) in the monadic case. * Add a way to limit the size of a LengthPrefixed: e.g. [Unsigned 4, LengthPrefixed] is very unsafe, the app should have a way to control the maximum length. - Einar Karttunen

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