Double Ended Lists Package

Overview

This package creates a data type called Del and provides 47 subprograms for manipulating values of this type. Basically Dels are finite sequences and the operations provided are similar to to those of Singly Linked Lists (Chapter 6), but some operations such as concatenation are more efficient (constant time rather than linear in the length of the arguments). In addition, more security against certain kinds of semantic errors is provided, since the package user does not have direct access to pointer values. For example, with Singly Linked Lists it is possible using the Set Next operation to create a circular list, causing other operations to loop indefinitely, but this is not possible with Dels.