Green Card support for Haskell calls/callbacks is definitely useful
(and on the ToDo list, I believe.)
However, GHC has for a long time supported the calling Haskell code
from C, here's a little sample demonstrating how to do it:
foo.lhs
...
type Callback = StablePtr (PrimIO ())
mkCallback :: (Int -> PrimIO Int) -> IO Callback
mkCallback act = do
makeStablePtr ( do
v <- _casm_ `` %r = cback_arg1; ''
res <- act v
_casm_ `` cback_res = (int)%0; '' res )
foo.c
typedef long HaskellCodePtr;
typedef void *(*(*FunPtr)())();
extern FunPtr startPerformIO();
extern void enterStablePtr (HaskellCodePtr, FunPtr);
static int cback_arg1;
static int cback_res;
int invokeHaskellCallback(cback, i)
HaskellCodePtr cback;
int i;
{
cback_ arg1 = res1;
enterStablePtr (cback, startPerformIO);
return (cback_res);
}
Not Pretty, But It Works (sm).
--Sigbjorn
Graeme Moss writes:
> Dave Tweed wrote:
> > David Elworthy wrote:
> > > The Green Card manual says there is zero demand for calling Haskell from
> > > C. Well, here is an increment to that: there is now 1 demand.
> >
> > Better make that 1 1/2. I'd like to be able to call Haskell from C (well,
>
> I can't resist: make that 2 1/2. My benchmarking kit for functional
> data structures, Auburn, see
>
> http://www.cs.york.ac.uk/~gem/auburn/
>
> works a lot better at the moment if we use a Green Card extension that
> allows C to call Haskell. The York release of nhc does support such
> an extension, see
>
> http://www.cs.york.ac.uk/fp/
>
> Simon L Peyton Jones wrote:
> |Something will happen here, although not that fast. Getting C to
> |call Haskell is part of getting COM to call Haskell, which we want
> |to do.
>
> Good.
>
> Graeme.
