Programming with First-Class Contexts

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9302114 Friedman Contexts are a perfect means for expressing variable sharing across multiple lexical scopes. A context is a syntax tree with nonterminal leaves, called holes, that are to be filled later with terms (which are contexts as well). Unlike substitution, filling a context's hole with a term causes the term's free variables to be captured by the context's bound variables. First- class contexts thus are a basis for incremental development of information-sharing program pieces. Giving contexts first-class status facilitates separate compilation of contexts. The target code can be reused on different instantiations of the context's free variables or be reused on resolving its different filling terms' free variables. Contextual programming brings compilation, linking (context filling), and evaluation under the user's control. It is a conceptually simple and yet very general programming paradigm. In particular, modular and object-oriented programming are both special cases of contextual programming. This research has both formal and experimental components. Formal reasoning systems furnish a platform for analyzing and comparing contextual programming with other programming language concepts and mechanisms. Experiments are expected to generate insightful information to evaluate design decisions, uncover deficiencies, and develop a better understanding of contextual programming. ***