How to Make a Lexical Scanner in Rust

Introduction

Lexical scanning, or lexing, is the first phase in the process of compiling a programming language. It involves converting a sequence of characters from source code into a sequence of tokens. In this blog post, I’ll walk you through how to create a lexical scanner (lexer) in Rust, a systems programming language known for its performance and safety. By the end of this tutorial, you’ll have a basic lexer that can tokenize simple arithmetic expressions.

Prerequisites

Before we start, make sure you have Rust installed. If you haven’t installed Rust yet, you can do so by following the instructions on the official Rust website.

Step 1: Setting Up Your Project

First, create a new Rust project:

cargo new lexer_example
cd lexer_example

Open the Cargo.toml file and add the following dependencies:

[dependencies]
regex = "1"

The regex crate will help us with pattern matching for our tokens.

Step 2: Defining the Token Types

Create a new file named lexer.rs in the src directory. This file will contain our lexer implementation. Start by defining the token types: