An internal memory uses a resource identifier to identify which functional program from an external memory is to be loaded into an overlay space of the internal memory. In executing a program statement of a main program to perform a particular functional operation without identifying a corresponding functional program, a prelude stored in a prelude space of the internal memory provides a resource identifier for the functional operation. The resource identifier identifies a corresponding functional program to perform the particular functional operation and the identified functional program is then loaded into the overlay space to be executed.