Each of the steps will now be described in more detail. For example, a teacher might have the attributes age, sex and status. Alternatively, this could be typed into a file and the file loaded into Lisp-Stat. A history is automatically kept of the values of all attributes. Thus, for instance, you can access the status of a teacher two time steps ago, or display a graph showing the changing status of a teacher since the beginning of the simulation.
Temporary variables differ from attributes in that no history of their values is kept.
Each object in the simulation can carry out some computation every time step. This assumes that the object teacher has already been defined and that it has been given the attribute age . The example above uses two MLS functions. Set-attribute sets the value of an attribute. Prev-attribute recovers the value of the attribute at a previous time step.