[Haskell-cafe] C++ interface with Haskell

[Miguel Lordelo]

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 <isaacdupree at charter.net>
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:
>
> > 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
> > C++.
> > 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
> > 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.
> >
> >
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
>
>
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