THE PROBLEM OF SUBSTITUTION.

One of the most significant features of programs designed for non-numeric calculation is that the size of expressions manipulated, and hence the amount of storage necessary, changes continually during the execution of the program. It is therefore usually not possible for the user to know ahead of time just how much output his program will produce, or whether the calculation will in fact fail because of lack of available computer memory. The key to keeping both the size of intermediate expressions and output under control often lies in the manner in which substitutions for variables and expressions declared by the programmer are implemented by the system. In this paper various methods which have been developed to perform these substitutions in the author's own system REDUCE are discussed. A brief discription of the REDUCE system is also given. (Author)
Presented at IBM Summer Institute on Symbolic Mathematics by Computer, Boston, Mass., Jul-Aug 68.