[Haskell-cafe] C++ interface with Haskell

[Miguel Lordelo]

Thanks,

I found on one site how to compile after creating the stub files with GHC:

First step:
*ghc -c -ffi haskell_file.hs*
Second step - here it is important to know and write where are the ghc
libraries:
*gcc -I /usr/local/lib/ghc-5.04.3/include -c C_file.c *
After that it is important to link my creted C_file with the stub file and
compile it:
*ghc -no-hs-main -o C_file C_file.o haskell_file.o haskell_file_stub.o*

The final result is C_file execution file...just enter C_file and the
program is running correctly.

This information: how to compile and to link C with Haskell and to call a
Haskell funtion from C was quite difficult.
But here is my result of googling throw the internet and to find something
usefull.

Next challange: link C++ with C and creating a usefull documentation and put
it online!

Ciao,
Miguel Lordelo.




On Fri, Apr 18, 2008 at 3:33 PM, Alfonso Acosta <alfonso.acosta at gmail.com>
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 <miguellordelo at gmail.com>:
> > 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.
> > > >
> > > >
> > > >
> > > >
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> >
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