A direct execution PROLOG system

Abstract

This paper presents a direct execution PROLOG system. It does syntax check at token level and reports errors even before a clause is completed. It does consistency checking whenever rules and facts are entered, and waits for corrective action from the user so that errors cannot snowball. The user can trace the unification process in detail. He can examine the backtracking path and/or the value of the instantiated variables at any point. The system is written in PASCAL.