The Use of Recursive Procedures in ALGOL 60

Abstract

This chapter discusses the use of recursive procedures in ALGOL 60. It also discusses two classes of useful applications of recursive procedures, indirect recursivity and direct recursivity. The implementation of recursive procedures is usually considered difficult, furthermore it has been reported that the object programs produced by compilers that allow recursive procedures are less efficient. In any case, the implementation problem for recursive procedures has been solved by Dijkstra and also by Sattley and Ingerman, and accordingly ambitious compiler-builders will certainly include recursive procedures. However, if restrictions have to be made, then recursive procedures will be one of the first features to be omitted. This will not even entirely forbid their actual use. Indeed, in all realistic examples presented in the chapter, the total depth of recursivity was rather low, and therefore such examples could still be treated non-recursively by providing a sufficient number of copies of the procedures in question for the translation process. In view of this possibility the decision of the ALCOR group, not to implement the recursive procedures, is certainly well founded.