All functionality of the simulation environment is always accessible by entering commands at the prompt of the VLISP interpreter. If a GUI is present, it correctly reflects the internal state produced by all commands entered, i.e., the text-input mode may be used simultaneously with the graphical user interface. In a typical application, a file is loaded at the beginning of the session that describes the tasks to perform, and the user enters commands to start and stop jobs, to view work-in-progress information, to switch between projects, etc.