Implementation of language enhancements

Data abstractions have been proposed as a means to enhance program modularity. The implementation of such new features to an existing language is typically handled by either rewriting large portions of an existing compiler or by using a preprocessor to translate the extensions into the standard language. The first technique is expensive to implement while the latter is usually slow and clumsy to use. In this paper a data abstraction addition to PL 1 is described and a hybrid implementation is given. A minimal set of primitive features are added to the compiler and the other extensions are added via an internal macro processor that expands the new syntax into the existing language.