Adding abstract datatypes to Meta-IV

Abstract

Program structure is an important issue in program design. Reuse and flexibility are properties that depend on structure. Some notion of a module is needed to structure a program at a higher level than that of individual functions or procedures.

Meta-IV does not contain facilities to express the grouping of related entities corresponding to modules in a final program. Such facilities are needed, if structure is to be specified along with functionality.

Abstract datatypes are collections of (primarily) functional components. An abstract datatype may reflect an intended grouping of entities in a final program, in particular when no entity in the group is an assignable variable. Abstract datatypes are useful also for descriptions when assignable variables are needed.

We propose one way to add abstract datatype facilities to Meta-IV. We do not propose facilities for introducing hidden, assignable variables, because the abstract datatype extensions should be agreed upon first.

The paper draws heavily on fairly recent research results. It shows how Meta-IV can be extended in agreement with the results. Emphasis is put on the kind of concepts needed for the extension. However, the paper does not explain the underlying theory and does not contain new results of independent theoretical interest.

The intended audience is the group of experienced users of Meta-IV. A number of remarks address various subgroups, e.g. some are mostly of interest to those with special interest in the theoretical background. If a remark uses unfamiliar terminology, it should be standard terminology for some subgroup. Consequently the remark may be skipped be others. Remarks are kept brief and sketchy, just to give indications which may be pursued by studying the references. Illustrations are given in remarks also.