[Haskell-cafe] C++ interface with Haskell

[Isaac Dupree]

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 <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
>>>>
>>>
>>
>> _______________________________________________
>>  Haskell-Cafe mailing list
>>  Haskell-Cafe at haskell.org
>>  http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
>