Author: Vinod Pahuja

In Part 1 of the series on PEG implementation, I explained the basics of Parser Expression Grammar and how to implement it in JavaScript. This second part of the series is focused on implementation in Java using the parboiled library. We will try to build the same example for parsing arithmetic expressions but using different syntax and API.

QuickStart

parboiled is a lightweight and easy-to-use library to parse text input based on formal rules defined using Parser Expression Grammar. Unlike other parsers that use external grammar definition, parboiled provides a quick DSL (domain-specific language) to define grammar rules that can be used to generate parser rules on the runtime. This approach helps to avoid separate parsing and lexing phases and also does not require additional build steps.

Parsing is an age-old technique used to analyze and extract meaning from languages (both natural and programming). Parser is a type of compiler that converts the stream of text into syntax or parse tree that conforms to some predefined grammar rules.

There are various classifications to categorize these techniques, and plenty of content is available to explain them. So, for now, I am focusing on Parser Expression Grammar (which is the most recent research in parsing grammar). Also, I will try to explain the ways to implement a PEG parser.