The translator pattern-external functionality with homomorphic mappings

The author describes how one can express homomorphic translations with an object-oriented design. This includes a uniform approach to the addition of external functionality to data structures. He presents the tradeoffs of distributing intrinsic and extrinsic properties to data structures and external functions respectively. A mini-architecture (design pattern) for the emulation of multi-dispatching functions is presented in order to allow the definition of local translation functions. Actually, he presents a variant of the Visitor pattern, but adds the idea of maintaining a homomorphism between source and target and introduces a target structure between source structure and target semantics. Combined, these concepts pave the way to incremental evaluation.