Multi-plan attribute grammars

We identify a new class of non-circular attribute grammars, called the multi-plan attribute grammars, for which static evaluation plans can be computed. The class of multi-plan attribute grammars is larger than all currently known classes of non-circular attribute grammars with static evaluation plans. The decision procedure and the procedure for computing evaluation plans take essentially polynomial time under a new, more practical criterion (but the procedures still take exponential time based on the traditional criterion). The multi-plan attribute grammars lead to a new way to classify well-defined attribute grammars into a hierarchy based on the look-ahead behavior of the evaluators. Our work confirms a result of Riis and Skyum, which says that all well-defined attribute grammars can be evaluated with static evaluators.