struct ElementType {
   int  size;
   void (*handler   )(void* ptr);
   void (*destructor)(void* ptr);
};

struct Element {
   struct ElementType* type_ptr
   void*               ptr;
};

struct NestedLoopList {
   int      length;
   Element* ptr;
   int      free_ptr;    /* 1 when ptr needs to be freed. */
   int      free_elems;  /* 1 when each element of ptr[] needs to be freed and destroyed. */
};

struct NestedLoopArrayArg {
   struct ElementType* type_ptr;
   int                 length;
   void*               ptr;
};

struct NestedLoopMixedArg {
   int             length;
   struct Element* ptr;
};

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

struct NestedLoopArg {
   int ptr_type;  /* 0 = array, 1 = mixed array, 2 = func */
   union {
      struct NestedLoopArrayArg array;
      struct NestedLoopMixedArg mixed;
      struct NestedLoopFuncArg  func;
   } ptr;
};