A spreadsheet interface for logic programming

We present PERPLEX, a programming environment intended for the end-user. In its design, the concepts of logic programming and spreadsheets are combined. Thus, on the one hand, logic programming becomes an interactive, incremental task where the user gets direct visual feedback, on the other hand, functionality and scope of a conventional spreadsheet program are considerably extended. In order to perform calculations and queries, constraints are imposed on the contents of the spreadsheet cells. New predicates can be defined using a programming-by-example technique: Rules are extracted from the user's solutions for example problems. Thus, concrete intermediate results take over the role of abstract logic variables in the programming process. PERPLEX has been successfully implemented on a Symbolics Lisp Machine.