A Simple Reeective Interpreter Imsa '92 International Workshop on Reeection and Meta-level Architecture Tokyo, November 4-7, 1992 a Simple Reeective Interpreter

Procedurally reeective programming languages enable user programs to semantically extend the language itself, by permitting them to run at the level of the language implementation with access to their context. The reeective tower, rst introduced by Brian Smith 9, 10], is the principal architecture for such languages. It is informally described as an innnitely ascending tower of meta-circular interpreters, connected by a mechanism that allows programs at one level to run at the next higher level. Various accounts of the reeec-tive tower have been published, including a meta-circular deenition, operational deenitions, and denotational deeni-tions. We present an operational account of the main aspects of the reeective tower, which we claim is simpler than previous accounts. Our approach is to implement a nite tower where each level literally runs the level directly below it. A complete Scheme implementation is included.