An extension of the interpreter pattern to define domain-parametric rewriting systems

The Interpreter design pattern providesan elegant and natural way of implementing systemsbased on term-rewriting in a OO fashion. The ideais simply associating each term of a language, eitherterminal or non-terminal, with a correspondingclass provided with a suitable simplify() method.Reducing a term to a normal form is thus performedthrough a series of recursive calls to such a method.The main weakness of this approach is that it does nottake into account similarities existing among differentdomains, thus enforcing programmers to pollutegeneric and domain-specific rules. The resulting codeif often wordy, hard to maintain, non-reusable. In thispaper we adapt the Interpreter pattern so that a cleanseparation between generic (common to differentdomains) and domain-specific rules is possible. Thenew pattern significantly helps design even complexrewriting systems. A running example which refersto a generic Logical domain is used throughout thepaper. An application to High Level Petri nets analysisis sketched. Without any loss of generality we refer toJava as representative of a large class of languages.