Recursive parser optimization by rewriting context-free grammars

Abstract

The analysis of programming languages is a fundamental activity in the process of comprehending, maintaining, documenting and reengineering old software. However, the analysis may sometimes be inefficient because of the parsing methodology adopted. Prolog parsers, for instance, have two main drawbacks: the time spent on extracting information as a result of the backtracking mechanism, and the large memory occupation involved. This paper presents an algorithm that optimizes a top-down parser by imposing a set of rules on the grammar to be analyzed. A methodology is then defined for rewritting a context-free grammar ( LL( n) n > = 1), and a tool that can achieve this is illustrated. This tool, called FACTOTUM, has been implemented in LPA Prolog, and works on a PC (IBM-MSDOS) through the Windows medium. FACTOTUM is composed of nearly 250 productions, and is an important part of another reverse engineering tool called RE_Tool (Giannone and Maresca, 1995) which can analyze codes in a multilanguage environment. RE_Tool has been implemented in the software engineering laboratories of DIS at the University of Naples Federico II, where it is currently under experimentation.