An overview of the relational-functional language RELFUN

Abstract

This overview considers research and development in integrated declarative programming based on the design, semantics, implementation, and use of the RELFUN (RELational-FUNctional) language. RELFUN reciprocally extends Horn relations and call-by-value (eager) functions just enough to yield a unified operator concept. Relations acquire application nesting and higher-order notation; functions acquire non-groundness and non-determinism. Relations are defined by Horn-like clauses implicitly returning true; functions are defined by rules with an additional returned-value premise. This minimal relational-functional kernel then provides a platform for common extensions such as finite domains, avoiding their duplication as separate features of logic and functional languages. Operational (interpreter in pure LISP), procedural (SLV-resolution), fixpoint, and model-theoretic semantics were developed for pure RELFUN. The compiler system has a layered structure, ranging from source-to-source transformers to a declarative classifier, to a code generator for the WAM (Warren Abstract Machine). Applications include a library of declarative (hyper)graph operations, a CAD-to-NC transformer of geometry/plan terms, as well as sharable knowledge bases on materials science and engineering.