READ_TOGGLE

READ_TOGGLE(C command_tail)

Y result

READ_TOGGLE gives TRUE if the specified command tail exists in the list of command tails. As with READ_TAIL you can only call this function once per command tail - checking for the command tail causes it to be removed from the list of command tails supplied to he program.

{given command tails of −GEORGE −FRED −HENRY B}
READ_TOGGLE("CHARLES") = FALSE
READ_TOGGLE("FRED") = TRUE