We pick up again our dicussion of streams, and show how a careful use of state can memoize computed elements, i.e., save their value so that it does not need to be recomputed the next time it is needed. Memoization ensures that a suspended expression is evaluated at most once. When a suspension is forced for the first time, its value is stored in a reference cell and simply returned when the suspension is forced again. The implementation that we present makes a subtle and elegant use of a "self-modifying" code technique with circular references.