Balancing theEuLisp metaobject protocol

The challenge for the metaobject protocol designer is to balance the conflicting demands of efficiency, simplicity, and extensibility. It is impossible to know all desired extensions in advance; some of them will require greater functionality, while others require greater efficiency. In addition, the protocol itself must be sufficiently simple that it can be fully documented and understood by those who need to use it.This paper presents the framework of a metaobject protocol forEuLisp which provides expressiveness by a multi-leveled protocol and achieves efficiency by static semantics for predefined metaobjects and modularizing their operations. TheEuLisp module system supports global optimizations of metaobject applications. The metaobject system itself is structured into modules, taking into account the consequences for the compiler. It provides introspective operations as well as extension interfaces for various functionalities, including new inheritance, allocation, and slot access semantics.While the overall goals and functionality are close to those of Kiczaleset al. [9], the approach shows different emphases. As a result, time and space efficiency as well as robustness have been improved.This article is a revised and extended version of [4]The work of this paper was supported by the joint project APPLY, Ilog SA, the University of Bath, the British Council/DAAD ARC program, and theEuLisp working group.The joint project APPLY is funded by the German Federal Ministry for Research and Technology (BMFT). The partners in this project are the University of Kiel, the Fraunhofer Institute for Software Engineering and Systems Engineering (ISST), the German National Research Center for Computer Science (GMD), and VW-Gedas.