Zipper-Based Attribute Grammars and Their Extensions

Abstract

Attribute grammars are a suitable formalism to express complex software language analysis and manipulation algorithms, which rely on multiple traversals of the underlying syntax tree. Recently, Attribute Grammars have been extended with mechanisms such as references and high-order and circular attributes. Such extensions provide a powerful modular mechanism and allow the specification of complex fix-point computations. This paper defines an elegant and simple, zipper-based embedding of attribute grammars and their extensions as first class citizens. In this setting, language specifications are defined as a set of independent, off-the-shelf components that can easily be composed into a powerful, executable language processor. Several real examples of language specification and processing programs have been implemented in this setting.

Embedding attribute grammars and their extensions using functional zippers

“…In the following sections of the paper, we describe how the analysis of the LET language can be implemented in Haskell using the zipper-based AG embedding techniques of [9] together with the extensions we provide. In particular, Sections 3, 4 and 5 focus on challenge 1) above while Section 6 focuses on challenge 2).…”

“…In other words, repeatedly calculate attributes on the symbol table until all of the variables are solved. 9 Therefore, to process this LET program we need a circular, fixed-point evaluation strategy. The general idea is to start with a bottom value, ⊥, and compute approximations of the final result until it is not changed any more, that is, the least fixed point: x = ⊥; x = f(x); x = f(f(x)); ... is reached.…”

“…Firstly, attribute grammars are embedded in regular programming languages with AG fragments as first-class values in the language: they can be analyzed, reused and compiled independently [7][8][9][10][11]. First class AGs provide: i) A full component-based approach to AGs where a language is specified/implemented as a set of reusable off-the-shelf components; ii) Semantic-based modularity, while some traditional AG systems use a (restricted) syntactic approach to modularity.…”

“…In this work, we present the first embedding of HOAGs, RAGs and CAGs as first class attribute grammars, an embedding which is also powerful enough to express bidirectional transformations. Indeed, we revise the zipper-based AG embedding proposed in [9] to extend it with the bidirectional capabilities of [19]. We have used this embedding in a number of applications, e.g., in developing techniques for a language processor to implement bidirectional AG specifications and to construct a software portal.…”

“…In the remainder of the paper, we start by revising the concise embedding of AGs in Haskell of [9]. This embedding relies on the extremely simple mechanism of functional zippers.…”