Re[2]: [Haskell-cafe] C++ interface with Haskell

Hello Isaac, Friday, April 18, 2008, 7:27:56 PM, you wrote: absolutely true! it's required if you use new/delete and other things supported by c++ RTS

if you'd normally be linking using g++, you'll need (IIRC) -lstdc++ added to linking-ghc's command line

Alfonso Acosta wrote:

...

Although you could use gcc to link the code I wouldn't recommend it (mainly for the problems you are currently having)

SImply call GHC to compile both the C and Haskell code. It will take care of finding the headers and supplying the necessary linker arguments.

ghc -ffi -c foo.hs myfoo_c.c

BTW, you don't need to compile viaC

2008/4/17 Miguel Lordelo :

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Well Isaac...I became now a little bit smarter then yesterday!!!

I show you the example that I found and on which I?m working with.

File: foo.hs module Foo where

foreign export ccall foo :: Int -> IO Int

foo :: Int -> IO Int foo n = return (length (f n))

f :: Int -> [Int] f 0 = [] f n = n:(f (n-1))

To get the C wrapper you insert the following command: ghc -ffi -fvia-C -C foo.hs

After execution you will have these following additional files:

foo.hc foo.hi foo_stub.c foo_stub.h foo_stub.o

What I did next was to create a file named: myfoo_c.c, where I will call the foo function (implemented in Haskell). (you can see this example on http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html ) But the problem is to compile with gcc (must I put any flag or whatever set something)

The gcc output is: myfoo_c.c:2:19: error: HsFFI.h: No such file or directory

I downloaded this header file from: (I know that is not the correct way, but it was the only idea that occurs at the moment) http://www.koders.com/c/fidD0593B84C41CA71319BB079EFD0A2C80211C9337.aspx

I compiled again and the following return error appears: myfoo_c.c:(.text+0x1c): undefined reference to `hs_init' myfoo_c.c:(.text+0x31): undefined reference to `foo' myfoo_c.c:(.text+0x50): undefined reference to `hs_exit' collect2: ld returned 1 exit status

These functions are necessary to setup GHC runtime (see: http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html )

What I want to know is how to compile myfoo_c.c?! Is it with GCC or GHC?!

Chears, Miguel Lordelo.

On Wed, Apr 16, 2008 at 9:16 PM, Isaac Dupree wrote:

...

perhaps

haskell: foreign export "foo_func" foo :: Int -> IO Int -- I forget the rest of the syntax here

C++:

extern "C" { int foo_func(int i); }

int some_cplusplus_function() { int bat = 3; int blah = foo_func(bat); return blah; }

Is that all you need to do?

Miguel Lordelo wrote:

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Hi all,

Well...somehow I'm a beginner in Haskell. But actually my interest in Haskell will increase if it is possible to call a haskell function in

...

Something like GreenCard ( http://www.haskell.org/greencard/ ) simplifying the task of interfacing Haskell programs to external libraries (usually). But is there also a task to interface a foreign language with Haskell, but calling Haskell functions. Or c2hs which is an interface generator that simplifies the development of Haskell bindings to C libraries.

I want to know this, because in my company some guys are doing some testing with Frotran and MatLab and I want to show them the power of haskell and

C++. the

...

software which we are using is implemented in C++ (there is the reason to make Haskel -> C++).

I read somewhere that the only way for C++ calling a haskell function is to create a binding between Haskell and C and from C to C++, but a easy "Hello World" example was not there. Unfortunatelly I couldn't found anything usefull, like an complete example, or how to compile the code from haskell to C to C++.

Can sombody help me, please :P

Chears, Miguel Lordelo.

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