The Definitive ANTLR 4 Reference, 2nd Edition

Matching an Arithmetic Expression Language

For our first grammar, we’re going to build a simple calculator. Doing something with expressions makes sense because they’re so common. To keep things simple, we’ll allow only the basic arithmetic operators (add, subtract, multiply, and divide), parenthesized expressions, integer numbers, and variables. We’ll also restrict ourselves to integers instead of allowing floating-point numbers.

Here’s some sample input that illustrates all language features:

tour/t.expr

193
a = 5
b = 6
a+b*2
(1+2)*3

In English, a program in our expression language is a sequence of statements terminated by newlines. A statement is either an expression, an assignment, or a blank line. Here’s ...