foreach
int (*foreach)(int, char *, int, char *, int, char *);
if ((*incallback->foreach)((int)out.status,
foreach(list, it)
foreach(list, it) {
ypcb.foreach = printit;
ypallcb.foreach = pushit; /* callback function */
Callback.foreach = yptest_foreach;
callback.foreach = ypxfr_foreach;