- Glasgow-haskell-users

Haskell function with String arguments in DLL
by Christian Lescher 17 Oct '00

17 Oct '00

I'm trying to build a DLL with a Haskell function of type String -> String, that should be called from outside (e.g. VBA), but it still doesn't work. I'm afraid I need an example or some kind of 'step by step instruction'. Who can help me? (I use GHC 4.08.1.) Christian

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RE: Exposing Haskell functions with string arguments in a DLL
by Simon Marlow 16 Oct '00

16 Oct '00

You can use CString.packString and CString.packStringIO, but be aware that (a) these functions return ByteArrays, so you need to adjust your foreign export definitions accordingly (b) because they use ByteArray, these functions are GHC specific and any use of them is non-portable. GHC currently doesn't supply a portable way to marshal strings from Haskell to C. However, you can quite easily write your own using eg. the functions from Storable. Cheers, Simon > -----Original Message----- > From: Lescher Christian [mailto:christian.lescher@icn.siemens.de] > Sent: Monday, October 16, 2000 12:20 PM > To: Simon Marlow; 'glasgow-haskell-users(a)haskell.org' > Subject: AW: Exposing Haskell functions with string arguments in a DLL > > > Thanks!! What about the other direction? (Haskell function > with string result) > > Christian > > > -----Urspr> üngliche Nachricht----- > > Von: Simon Marlow [SMTP:fldrsimonmar@microsoft.com] > > Gesendet am: Montag, 16. Oktober 2000 13:07 > > An: 'Lescher Christian'; 'glasgow-haskell-users(a)haskell.org' > > Betreff: RE: Exposing Haskell functions with string > arguments in a DLL > > > > > > > How can I convert string arguments (null-terminated strings) > > > to Haskell's [Char]? I saw there is some CString module in > > > package lang of GHC, but I didn't found any documentation > > > about it (e.g. packStringIO...?). > > > > For converting a static null-terminated C string to a > Haskell String, use > > CString.unpackCString. If you need to free the memory used > by the original > > C string afterwards, use CString.unpackCStringIO. > > > > Cheers, > > Simon >

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AW: Exposing Haskell functions with string arguments in a DLL
by Lescher Christian 16 Oct '00

16 Oct '00

Thanks!! What about the other direction? (Haskell function with string result) Christian > -----Urspr> üngliche Nachricht----- > Von: Simon Marlow [SMTP:fldrsimonmar@microsoft.com] > Gesendet am: Montag, 16. Oktober 2000 13:07 > An: 'Lescher Christian'; 'glasgow-haskell-users(a)haskell.org' > Betreff: RE: Exposing Haskell functions with string arguments in a DLL > > > > How can I convert string arguments (null-terminated strings) > > to Haskell's [Char]? I saw there is some CString module in > > package lang of GHC, but I didn't found any documentation > > about it (e.g. packStringIO...?). > > For converting a static null-terminated C string to a Haskell String, use > CString.unpackCString. If you need to free the memory used by the original > C string afterwards, use CString.unpackCStringIO. > > Cheers, > Simon

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RE: Exposing Haskell functions with string arguments in a DLL
by Simon Marlow 16 Oct '00

16 Oct '00

> How can I convert string arguments (null-terminated strings) > to Haskell's [Char]? I saw there is some CString module in > package lang of GHC, but I didn't found any documentation > about it (e.g. packStringIO...?). For converting a static null-terminated C string to a Haskell String, use CString.unpackCString. If you need to free the memory used by the original C string afterwards, use CString.unpackCStringIO. Cheers, Simon

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RE: C main
by Sigbjorn Finne 13 Oct '00

13 Oct '00

Brett Letner <bletner(a)revbiz.com> writes: > > So if I understand this correctly, I'm doing it wrong, but that's o.k. > because even if I wasn't it still wouldn't work :) > > This brings up a larger question, should I even be trying to do this? > Yes, linking in Haskell code in the way you tried is the most convenient way of going about embedding Haskell code into C/C++ apps (well, at least that's the intention ;-) You can package up Haskell code in a DLL and call it that way, but that requires extra steps. I posted some instructions on how to build ghc-compiled DLLs on this mailing list a couple of weeks ago; you may find them useful here. If you're really desperate, what you tried to do works with ghc-4.05. It depends on using another version of cygwin (gcc, really) than 4.08, so I wouldn't recommend doing this if you haven't already got it installed. hth --sigbjorn

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RE: C main
by Sigbjorn Finne 13 Oct '00

13 Oct '00

Simon Marlow writes: > > > > Could someone instruct me on (or point me to) the correct ghc > > command line for calling haskell from C? > > ... > > You can use ghc just like you would use gcc to compile up > your C program, > then use ghc again to link the whole program with the Haskell > module(s). The -no-hs-main flag shouldn't be necessary, as > far as I can tell. eg. > > $ ghc -c main.c > $ ghc -c HaskellStuff.hs > $ ghc main.o HaskellStuff.o > That will (sort of) work if you also insist that HaskellStuff.hs implements Main.main. As the name suggests, -no-hs-main takes care of the case when HaskellStuff.hs doesn't. (Well almost, the 4.08 driver contains a bug in setupLinkOpts(); __init_PrelMain should be handled the same way as PrelMain_mainIO_closure. ) In either case, you need to make sure that the RTS is started up, since you're not using the RTS-supplied main(). The HDirect distribution contains an example of this in examples/server/, but notice that the 4.08 RTS' startupHaskell() signature has changed to also take an extra 'module root' argument. However, even with that change, 4.08 compiled code crashes when running (4.05 works fine), which leads me to believe there's something else going on here :-) This is on the same platform that Brett originally reported the problem on. --sigbjorn btw, 4.05 contained a bug in this area which made -no-hs-main only work when linking with -static. 4.08 seems to have inherited it, i.e., in prepareWin32DllLink(), the condition for pushing Main.dll_o and PrelMain.dll_o onto @Link_file should be ($linking_main && !$NoHaskellMain) and not just $linking_main

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RE: How to get BlockedOnDeadMVar exception?
by Simon Marlow 13 Oct '00

13 Oct '00

> On Fri, Oct 13, 2000 at 04:01:00AM -0700, Simon Marlow wrote: > > Sure it's implemented. However, a main thread will never > get this exception > > (at the moment). Try this example in 4.08.1: > > Funny, it works and almost looks the same like my code. Only > {Ee}xception: > I was using a getLine-loop for preventing the main thread > from exiting. > Could this be the reason I don't get the exception? probably: the exception is generated as a result of the thread being discovered unreachable during garbage collection. If there's no garbage collection, eg. because the program is waiting for I/O, then the exception is never raised. Which brings up an interesting subject: should the RTS start a GC after it has been waiting for I/O for a certain length of time? If so, how long? Cheers, Simon

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RE: How to get BlockedOnDeadMVar exception?
by Simon Marlow 13 Oct '00

13 Oct '00

> I didn't succeed in getting (or catching?) this exception through an > obvious example. Is this exception thrown at all or just NYI? > > Is this exception thrown at all or just NYI? Sure it's implemented. However, a main thread will never get this exception (at the moment). Try this example in 4.08.1: module Main where import Exception import Concurrent main = do id <- myThreadId forkIO (catchAllIO (do m <- newEmptyMVar; takeMVar m) (\e -> raiseInThread id e)) catchAllIO (print (sum [1..1000000])) (\e -> print e) Cheers, Simon

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How to get BlockedOnDeadMVar exception?
by Volker Stolz 13 Oct '00

13 Oct '00

I didn't succeed in getting (or catching?) this exception through an obvious example. Is this exception thrown at all or just NYI? Is this exception thrown at all or just NYI? Volker -- Volker Stolz * stolz(a)i2.informatik.rwth-aachen.de * PGP + S/MIME

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RE: C main
by Simon Marlow 12 Oct '00

12 Oct '00

> Greetings - > > Could someone instruct me on (or point me to) the correct ghc > command line > for calling haskell from C? > From the documentation, it seems like "ghc -fglasgow-exts > -no-hs-main main.c > foo.hs" should work, but > that still gives me a multiple definition of "main". > > I'm running ghc 4.08.1 on Windows NT. You can use ghc just like you would use gcc to compile up your C program, then use ghc again to link the whole program with the Haskell module(s). The -no-hs-main flag shouldn't be necessary, as far as I can tell. eg. $ ghc -c main.c $ ghc -c HaskellStuff.hs $ ghc main.o HaskellStuff.o Cheers, Simon

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