It works indeed. Thanks.
-Kenny
On Fri, Jun 12, 2009 at 3:50 PM, Jochem Berndsen
kenny lu wrote:
Hi,
I was trying to write a FFI wrapper for my Haskell program which manipulates
ByteString. But I am unable to compile/link it.
Here is the toy program.
{-# LANGUAGE ForeignFunctionInterface #-}
module B where
import Foreign.C.Types import Foreign.C.String import qualified Data.ByteString as BS
rev :: BS.ByteString -> BS.ByteString rev bstr = BS.reverse bstr
rev_hs :: CString -> IO CString rev_hs cstr = do { bstr <- BS.packCString cstr ; let bstr' = rev bstr ; cstr' <- newCString (show bstr') ; return cstr' }
foreign export ccall rev_hs :: CString -> IO CString
And here is the C counter-part.
#include "B_stub.h" #include
int main(int argc, char *argv[]) { char *str; hs_init(&argc, &argv);
str = rev_hs("it works."); printf("Rev: %s\n", str);
hs_exit(); return 0; }
Compiling B.hs alone seems fine, but errors popped up when I was trying to compile/link it with C.
$ ghc -c -O B.hs
$ ghc -optc-O test_b.c B.o B_stub.o -o test_b Undefined symbols: "___stginit_bytestringzm0zi9zi1zi4_DataziByteString_", referenced from: ___stginit_Lib_ in B.o "_bytestringzm0zi9zi1zi4_DataziByteString_zdwreverse_info", referenced from: _s19w_info in B.o "_bytestringzm0zi9zi1zi4_DataziByteStringziInternal_zdwshowsPrec_info", referenced from: _s19v_info in B.o
"_bytestringzm0zi9zi1zi4_DataziByteStringziInternal_zdwshowsPrec_closure",
referenced from: _Lib_zdwa_srt in B.o "_bytestringzm0zi9zi1zi4_DataziByteString_zdwa4_info", referenced from: _Lib_zdwa_info in B.o "_bytestringzm0zi9zi1zi4_DataziByteString_reverse_info", referenced from: _Lib_rev_info in B.o ld: symbol(s) not found collect2: ld returned 1 exit status
If I replace ByteString with the ordinary String, the above programs can be compiled and linked.
Can someone tell me what I did wrong here?
Add -package bytestring to the ghc command line options. I believe that adding --make also may work.
Regards, -- Jochem Berndsen | jochem@functor.nl GPG: 0xE6FABFAB