23.3 Reference counting

Mutator function: Marpa_Tree marpa_t_ref (Marpa_Tree t)

On success, increases the reference count by 1. Not needed by most applications.

Return value: On success, t. On hard failure, NULL.

Destructor function: void marpa_t_unref (Marpa_Tree t)

Decreases the reference count by 1, destroying t once the reference count reaches zero.