Syntactic Abstraction in Scheme

Naive program transformations can have surprising e ects due to the interaction between introduced identi er references and previously existing identi er bindings, or between introduced bindings and previously existing references. These interactions can result in the inadvertent binding, or capturing, of identi ers. A further complication results from the fact that the transformed program may have little resemblance to the original program, making correlation of source and object code di cult. We address both the capturing problem and the problem of source-object code correlation. Previous approaches to the capturing problem have been both inadequate and overly restrictive, and the problem of source-object code correlation has been largely unaddressed. Our approach is based on a new algorithm for implementing syntactic transformations along with a new representation for syntactic expressions. It allows the programmer to de ne program transformations using an unrestricted, general-purpose language, while at the same time it helps the programmer avoid capturing problems and maintains a correlation between the original code and the transformed code.