[Haskell-cafe] C++ interface with Haskell
Bulat Ziganshin
bulat.ziganshin at gmail.com
Fri Apr 18 11:17:18 EDT 2008
Hello Miguel,
Friday, April 18, 2008, 7:06:07 PM, you wrote:
you may look into my freearc.org project
overall, nothing complex as far as you got it :) i use
ghc -c c_file.cpp
ghc --make main.hs c_file.o
in order to call from C++ to Haskell or vice versa you should define
function in C++ as having extern "C" linkage. i recommend you to
declare function in header file which is able to compile either in C++
mode (used in first step) or C mode (used in second step, when
compiling main.hs):
#ifdef __cplusplus
extern "C" {
#endif
void myfunc(void);
#ifdef __cplusplus
}
#endif
then you use either "foreign import" haskell statement to use C++ func
from haskell or "foreign export" for other way. i also recommend you
to use main procedure written in haskell and run from this procedure
your main C function - this is the simplest way to initialize Haskell
runtime system. that's all
> 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.
>> > >
>> > >
>> > >
>> > > ------------------------------------------------------------------------
>> > >
>> > >
>> > > _______________________________________________
>> > > Haskell-Cafe mailing list
>> > > Haskell-Cafe at haskell.org
>> > > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> > >
>> >
>> >
>>
>>
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>
>
--
Best regards,
Bulat mailto:Bulat.Ziganshin at gmail.com
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