Is there a way in the foreign function interface to pass to a function a struct by value? I explain it better. There are two ways in c to pass structs, as in the following example: /* begin c code */ struct couple{ int a; int b; }; //by value int print_couple (struct couple cpl) { printf("%d\n", cpl.a); printf("%d\n", cpl.b); return(0); } //by address int print_couple_ptr (struct couple *cpl) { printf("%d\n", cpl->a); printf("%d\n", cpl->b); return(0); } /* end c code */ Apparently in the ffi it is possible to import the second version, as: foreign import ccall "print_couple_ptr" printCouple::Ptr Couple->IO Int But not the first, as a struct it's not an atomic type. So how does one solve this issue? Cheers, Federico