Inter_Sim, an interactive tool for developing and running discrete simulation models by interpreting a descriptive language, is presented. A running simulation, when halted, remains suspended. Aftern extension, alteration, or investigation of the description, the simulation runs from the suspended state. Thus the user views the simulation model as a running model, rather than a piece of static text. The strengths and weaknesses of such an approach are discussed; other methods of interactive development are reviewed
