Using the re-export paradigm to build composable Ada software components

In the construction of reusable software components, transitive composability of parameterized abstractions is important for achieving the functionality desired. We have argued in a previous paper ( "Composable Ada Software Components and the Re-Export Paradigm" , which was published in a preceding issue of Ada Letters) that the paradigm we call "re-export" is the best technique for building robust, composable components in Ada which come close to meeting our standards for software quality. That paper discusses in detail the techniques which Ada provides that are appropriate for composing abstractions using re-export and the difficulties which are encountered in their construction. Because we do not have the space to recapitulate here, our previous paper must be read to provide the necessary context for understanding this one.A concrete example of re-export is presented here in which we attempt to design an abstraction using composable components. After analyzing the successes and shortcomings of this example, we conclude by presenting our view of the current realities of composition in Ada and outlining the general requirements for effective composition of software in Ada.