In this blog, we’ll present a simple arithmetic expression parser implemented through an Antlr4 parser generator. It will be able to take in an input string (such as 2+4+-4+-2*10%9*7) to produce the result (-12.0).

You may be thinking, “Great, but what’s the point?” Well, to answer your question, as simple as this example may seem, the principles involved actually extend to use cases such as DSLs, transpilation, and anything else expressible by grammar rules.

This post has two parts. In part 1, we’ll discuss the background components of a parser. In part 2, we’ll cover building the demo and running it. If you already understand grammar parsing, you could skip part one.