Yet Another Frame-based Object-Oriented Language. YAFOOL is an object oriented language, based on ’frames’, and has been developed for applications in the field of Knowledge Representation (Artificial Intelligence and Expert Systems). It is written in LeL̲isp, and is rather a package of functions than a real language. This package allows simultaneously an object-oriented programming and a classical one (in LeL̲isp), as CEYX, LOOPS, or the Flavors.