External Representations of Objects of User-Defined Type

Abstract

The portable programming language (PPL) is one of a number of recently designed programming languages that enable the user to define new types by giving their representations and operations in terms of those of previously available types. Such provisions for the construction of objects of user-defined type have been discussed elsewhere; this work concerns the related problem of the external representations of such objects, both on input-output media and as written constants within the program text. We introduce an enhancement to the PPL design allowing specification of the external representations of objects of user-defined type. This extension to the PPL design means that objects of user-defined type can be read, written, and used as constants exactly as if their representations had been selected by the writer of the PPL compiler. The implementation and use of the added facilities are also discussed.