Using procedures in list processing

Abstract

In many situations the atoms in a list can require a considerable amount of storage space or can be difficult to evaluate. When handling algorithms which only refer to a few atoms of a list much time and space can be wasted if the whole list is stored. In this paper an attempt is made to store lists as procedures which are only evaluated if absolutely necessary. The difficulties which arise when programming such a list processor in Algol 68 are caused by inherent scoping problems. A solution is presented for linear lists together with an example based on the processing of an infinite list.