The Meta-Level Architecture

We designed the meta-level architecture of ABCL/R3 so that various language constructs such as the ones shown in Section 3, are straightforwardly implemented at the meta-level as language extensions. Its major features are as follows:

• Meta-interpreters of base-level methods and functions are represented as objects, providing an object-oriented programming model of base-level execution. They can be customized to introduce syntax and semantics extensions into the language.
• A meta-object gives the meta-level representation of an object, including its class name, instance variables, method definitions, and message queue, all of which can be manipulated as first class data.

In addition to above two major features, there are mechanisms to facilitate simple and modular meta-level programming:

• Meta-level arguments can be passed between meta-level programs, which avoids modifying the structure of base-level programs.
• A reflective annotation serves as a programmable directive to the meta-level from the base-level programs. In addition, the interpretation of annotations is also defined in the meta-level interpreters.