March 2003 - FFI - Haskell.org

Re: Comparing [Fun]Ptrs
by Sven Panne 06 Mar '03

06 Mar '03

Volker Stolz wrote: > [...] > class ToPtr a where > toPtr :: a -> Ptr b > [...] The problem with a class like this is that you can't define any sensible instances, apart from the trivial one for Ptr itself. There is no guarantee at all that e.g. a FunPtr, an Int, ... fits into a Ptr and there are actually platforms where this is not the case. It's perhaps OK as a hack, but it has no place in a general FFI library, Cheers, S.

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by Ami 06 Mar '03

06 Mar '03

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[Fwd: Re: Foreign import]
by Gustavo Villavicencio 06 Mar '03

06 Mar '03

I have continued reading the bibliography on ffi but I cannot find the solution. Please, can anyone help me?. gustavo -------- Original Message -------- Subject: Re: Foreign import From: "Gustavo Villavicencio" <gustavov(a)ucse.edu.ar> Date: Tue, March 4, 2003 8:35 pm To: <chak(a)cse.unsw.edu.au> Thanks Manuel The error message is as follows -------------------------------------- CallIncr.o: In function `sWM_entry': CallIncr.o:(.text+0xc5): undefined reference to `incr' collect2: ld returned 1 exit status -------------------------------------- where 'incr' is a toy function defined in 'mylib.h'. Obviously, in the foreign declaration I have changed 'myfun' by 'incr'. The compilation command is the typical ghc -ffi -c CallIncr.hs followed by ghc -ffi CallIncr.o which generate the previous error. Thanks again, gustavo Manuel M T Chakravarty said: > "Gustavo Villavicencio" <gustavov(a)ucse.edu.ar> wrote, > >> I'm a new ffi user and I have some problems with foreign import >> declaration. I'm don't have any problem to access C standard >> functions. However, I cannot access to my own functions in mylib.h by >> means of >> >> foreign import "mylib.h myfun" hmyfun :: ... >> >> May be I'm omitting some compilation step or parameter also, since >> I'm applying the same compilation process to call C standard >> functions. >> >> I'm working with ghc 5.04 on SuSe Linux 7.0. > > You should say what goes wrong. Eg, paste the error > messages of the compiler and/or linker into your email. > > Manuel

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Comparing [Fun]Ptrs
by Volker Stolz 06 Mar '03

06 Mar '03

Hi, I'm looking for a way of comparing Ptrs to null *elegantly*. The FFI distinguishes between 'Ptr a' and 'FunPtr a', so testing would mean writing ((==) null[Fun]Ptr). This is rather tedious and a predicate 'isNull' might be in order so that it's possible to write when (isNull p) $ ... or throwIOErrorIf isNull ... , especially without having to worry about comparing against the correct null pointer (FunPtr or Ptr). That's something where a class can help, but I'm not sure whether such a specialised class is desired... I'd like to add the following class and instances/functions to Foreign.Ptr if nobody objects, they'd make code much more readable and concise: class ToPtr a where toPtr :: a -> Ptr b isNull :: ToPtr a => a -> Bool isNull = (==) nullPtr . toPtr The ToPtr class was suggested my Simon M. in favour of an even more specialised class PtrCmp which just has nullPtr :: PtrCmp a => isNull a -> Bool. -- Volker Stolz * http://www-i2.informatik.rwth-aachen.de/stolz/ * PGP * S/MIME

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Foreign import
by Gustavo Villavicencio 05 Mar '03

05 Mar '03

Hi, I'm a new ffi user and I have some problems with foreign import declaration. I'm don't have any problem to access C standard functions. However, I cannot access to my own functions in mylib.h by means of foreign import "mylib.h myfun" hmyfun :: ... May be I'm omitting some compilation step or parameter also, since I'm applying the same compilation process to call C standard functions. I'm working with ghc 5.04 on SuSe Linux 7.0. Any help will be welcome. gustavo

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need help with ffi function pointers
by David Sankel 03 Mar '03

03 Mar '03

Hello, I'm working on interfacing a c library that has the notion of callbacks. I have a C function: f_setCallback( void (funptr*) () ); I would like to allow a haskell developer to have an interface like the following: callback :: IO () callback = putStr "Called!\n" main :: IO () main = do setCallback callback -- etc. Is this possible via. ffi? If so, how would I do it code wise? Thanks, David J. Sankel

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Example: Binding C++ to Haskell using the ffi
by David Sankel 03 Mar '03

03 Mar '03

Here is some example code doing just that. It uses ghc. Questions: Can one think of better ways to interface generic c++ libraries to Haskell? What do you think of the ->> member function operator? for the ffi people: Has any though gone into cplusplus? If so, how would it interface? Would stubs on the c++ side be generated or would it use the code directly. Later, David J. Sankel

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by Erick Parker R. 02 Mar '03

02 Mar '03

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The best Cigar ever made, you must read this
by Karen Dever R. 01 Mar '03

01 Mar '03

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