In addition to the basic command structure outlined above, MOSES provides many features of a programming language. In MOSES, one can alter the flow of either command or description input, make logical checks, define variables, create macros, etc. All of these features operate on both commands and descriptions, so that with this language, one can automate the definition of a model as well as build a set of specific commands he needs to perform repetitive tasks. The language described here is an interpreted, string based language. In other words, all of the functions described here are performed before control is passed to the command interpreter.