Requirements for Extensible Languages

This paper gathers requirements to an extensible programming lan-guage by systematically examining examples used in scientific pa-pers on language extensions and extensible languages. Obviously, such an examination cannot be complete, but nevertheless, clear tendencies manifest themselves, and it is clear that no single exten-sible language or extension technique has ever tried to cover all re-quirements. The contribution of this paper is a classification of a number of examples from the literature, a classification scheme that clarifies the requirements to extensible languages, and points out new areas of research. It will be discussed to what extent the differ-ent categories can be supported by current object oriented abstrac-tion mechanisms, and what are the requirements to an extensible language to be able to handle each category.