Generalized recursive data structures

Summary Recursive data types are data types which are defined in terms of themselves, such as lists and trees. There is a single access path to each component in a recursive data structure.Generalized recursive data structures may include multiple access paths to some parts of the data structure. Two way lists, threaded trees and circular lists are generalized recursive data types. The extra access paths in a generalized recursive data structure are uniquely determined by the type of the structure and the main paths through the structure.An extension to Pascal in which generalized recursive data structures may be defined is described.