No errors, but the returned value res (or the dereferenced res) makes no
sense (not 10,11,12).
My idea was: the result of the function(a ByteString of Word8) must be
locked. No garbage collection. But newStablePtr does not return a pointer.
So I have to convert the newStablePtr to a real pointer and then coerce this
in the C program to a pointer to a array of word8.?
I've tried to return the ByteString in the Haskell function. But now the
compiler complains: Unacceptable result type in foreign declaration :