Derivative-Based Diagnosis of Regular Expression Ambiguity

TL;DR

This paper introduces a derivative-based approach using Brzozowski's derivatives to diagnose ambiguity in regular expressions, providing tools to generate parse trees and counter-examples, and compare disambiguation policies.

Contribution

It presents a novel derivative-based finite state transducer for diagnosing regular expression ambiguity and comparing disambiguation policies.

Findings

Can generate parse trees and minimal counter-examples

Allows comparison between POSIX and Greedy policies

Facilitates diagnosis of ambiguity in regular expressions

Abstract

Regular expressions are often ambiguous. We present a novel method based on Brzozowski's derivatives to aid the user in diagnosing ambiguous regular expressions. We introduce a derivative-based finite state transducer to generate parse trees and minimal counter-examples. The transducer can be easily customized to either follow the POSIX or Greedy disambiguation policy and based on a finite set of examples it is possible to examine if there are any differences among POSIX and Greedy.