Transforming sequences using threaded morphisms.

Sequences are very useful structures in programming languages. Functional programming languages allow the convenient definition of transformations between sequence algebras and other types of data algebra. Sequence homomorphisms are an important class of such transformations. However, not all desired transformations can be expressed as homomorphisms. This paper describes a class of transformation which is a generalisation of homomorphisms: sequence morphisms with threads. This class is shown to contain a number of interesting sub-classes of transformation. The morphisms are described using a simple functional programming language and are applied to the design and implementation of a simple object-oriented programming language feature.