March 1999 { Second Workshop on Attribute Grammars and Their Applications { Waga99 on Eliminating Type 3 Circularities of Ordered Attribute Grammars

Ordered attribute grammars (OAGs for short) are a useful class of attribute grammars (AGs). For some attribute grammars, even though they are not circular, OAG circularity test reports that they are not ordered and fails to generate attribute evaluators because some approximation introduces circularities(called type 3 circularities in this paper). First we discuss that it is sometimes diicult for programmers to eliminate type 3 circularities by hand. Secondly, in order to reduce this diiculty, we propose a new AG class called OAG* that produces less type 3 circularities than OAG while preserving the positive characteristic of OAG. OAG* uses a global dependency graph GDS that provides a new approximation algorithm, which is diierent from the existing GAG and Eli/Liga systems. We also show that we obtained good results with our experimental implementation.