Circular reference attributed grammars — their evaluation and applications

Abstract

This paper presents a combination of Reference Attributed Grammars (RAGs) and Circular Attribute Grammars (CAGs). While RAGs allow the direct and easy specification of nonlocally dependent information, CAGs allow iterative fixed-point computations to be expressed directly using recursive (circular) equations. We demonstrate how the combined formalism, Circular Reference Attributed Grammars (CRAGs), can take advantage of both these strengths, making it possible to express solutions to many problems in an easy way. We exemplify with the specification and computation of the nullable, first, and follow sets used in parser construction, a problem which is highly recursive and normally programmed by hand using an iterative algorithm. We also present a general demand-driven evaluation algorithm for CRAGs and some optimizations of it. The approach has been implemented and experimental results include computations on a series of grammars including that of Java 1.2. We also revisit some of the classical examples of CAGs and show how their solutions are facilitated by CRAGs.

An Introductory Tutorial on JastAdd Attribute Grammars

“…In this tutorial, we particularly cover reference attributes [Hed00], parameterized attributes [Hed00,Ekm06], circular attributes [Far86,MH07] and collection attributes [Boy96,MEH09].…”

Decorated Attribute Grammars: Attribute Evaluation Meets Strategic Programming

“…This makes them unsuitable for traditional AGs. However, by extending the formalism with [23,4], it becomes possible to use declarative AG equations to specify such analyses [25]. Circular attribute equations can be solved by fixed point iteration, as long as their underlying data forms a lattice.…”

“…We implemented this in a decorator that evaluates circular attributes. However, due to a lack of space to fully explain the rather intricate algorithm that underlies it (see [23,4]), we do not include it here, and refer the interested reader to the technical report that accompanies this paper [17].…”

“…1 JastAdd uses reference attributes [12], which we also use in a number of decorators. Its extensions include collection attributes [22] and circular computations [23]. These are built into the JastAdd implementation; there is no user-level mechanism to define similar extensions.…”

“…A different kind of remote attribute is provided by reference attribute grammars that allow references directly to arbitrary non-local nodes and their attributes [12], allowing for attributes that look up a particular node or collection of nodes. Finally, some attribute grammar systems support equations with circular dependencies that are evaluated to a fixed point [4,23].…”