struct NestedLoopArg* arg = (NestedLoopArg*)calloc(2, sizeof(NestedLoopArg));

args[0].ptr_type           = 0;  /* array */
args[0].ptr.array.type_ptr = &IntType;
args[0].ptr.array.length   = 5;
args[0].ptr.array.ptr      = calloc(arg[0].array.length, arg[0].array.elem_size);

args[1].ptr_type           = 1;  /* mixed array */
args[1].ptr.mixed.length   = 4;
args[1].ptr.mixed.ptr      = (Element*)calloc(arg[0].array.length, sizeof(struct Element));
{
   ... populate args[1].mixed.ptr[] ...
}

args[2].ptr_type           = 2;  /* func */
args[2].ptr.func.ptr       = my_func;
struct MyFuncPad arg2_pad;
arg2_pad.count = 5;
args[2].ptr.func.pad       = &arg2_pad;

NestedLoops(args);

... free memory allocated for args ...