Abstract A computer software system for interactive data processing is described. Data are transferred between functions (‘operators’). Execution flow is designed in a semi-graphical language. Data are composed of arbitrary data types in sequences of any length. The system works as an interpreter and the user may define or modify its current operation without delay. Lucidity is increased by the possibility of building complex functions (‘macros’) from simpler ones. Once such a construction has been made, the functions included can be made transparent to the user. Portability is emphasized by using only standard PASCAL. To promote flexibility, entirely new procedures and data types can be introduced. Both short- and long term solutions are thus supported.