struct NestedLoopList {
   int   elem_size;
   int   length;
   void* ptr;
   int   free_ptr;  /* 0 = no, 1 = yes */
};

struct NestedLoopArrayArg {
   int   elem_size;
   int   length;
   void* ptr;
};

struct NestedLoopFuncArg 
   void  (*ptr)(struct NestedLoopList* list_ptr, void* pad);
   void* pad;
};

struct NestedLoopArg {
   int ptr_type;  /* 0 = array, 1 = func */
   union {
      struct NestedLoopArrayArg array;
      struct NestedLoopFuncArg  func;
   } ptr;
};