Lox Interpreter

A Java implementation of the Lox programming language interpreter, following the design from "Crafting Interpreters" by Robert Nystrom.

Overview

This project implements a tree-walk interpreter for the Lox programming language. Lox is a dynamically-typed scripting language with features like:

• Variables and basic data types (numbers, strings, booleans)
• Arithmetic and logical operations
• Control flow (if/else statements, loops)
• Functions and closures
• Object-oriented programming with classes

Project Structure

learncompiler/
├── src/main/java/com/craftingintepreters/lox/
│   ├── Lox.java        # Main interpreter entry point
│   ├── Scanner.java    # Lexical analyzer (tokenizer)
│   ├── Token.java      # Token representation
│   └── TokenType.java  # Token type definitions
├── pom.xml            # Maven build configuration
└── README.md          # This file

Requirements

• Java 17 or later
• Maven 3.6+ (for building)

Building the Project

To build the project using Maven:

mvn clean compile

To create a JAR file:

mvn clean package

Running the Interpreter

Interactive Mode (REPL)

Run the interpreter without any arguments to start the interactive prompt:

java -cp target/classes com.craftingintepreters.lox.Lox

This will start a Read-Eval-Print Loop where you can type Lox expressions:

> print "Hello, World!";
Hello, World!
> var a = 5;
> print a + 3;
8

Script Mode

Run a Lox script file:

java -cp target/classes com.craftingintepreters.lox.Lox script.lox

Current Implementation Status

This implementation currently includes:

• ✅ Lexical Analysis: Complete tokenizer that recognizes all Lox tokens
• ✅ Token Types: Support for literals, operators, keywords, and identifiers
• ✅ Basic REPL: Interactive command-line interface
• ✅ File Execution: Ability to run Lox scripts from files
• ✅ Error Reporting: Basic error handling with line numbers

Lox Language Features

The scanner currently recognizes these language constructs:

Operators: +, -, *, /, =, ==, !=, <, <=, >, >=, !

Keywords: and, class, else, false, for, fun, if, nil, or, print, return, super, this, true, var, while

Literals: Numbers, strings, identifiers

Delimiters: (, ), {, }, ,, ., ;

Development

Running Tests

mvn test

Project Goals

This project serves as a learning exercise to understand:

• Lexical analysis and tokenization
• Recursive descent parsing
• Abstract syntax trees (AST)
• Tree-walk interpretation
• Programming language design principles

Next Steps

Future development will include:

• Parser implementation (syntax analysis)
• Abstract Syntax Tree (AST) generation
• Expression evaluation
• Statement execution
• Variable binding and environments
• Function calls and closures
• Object-oriented features

Resources

• Crafting Interpreters by Robert Nystrom
• Lox Language Specification

License

This project is for educational purposes. Please refer to the original "Crafting Interpreters" book for comprehensive explanations of the concepts implemented here.