Lox

A tree-walk interpreter for the Lox language, built in Java by following Part II (jlox) of Crafting Interpreters by Robert Nystrom.

This is a learning project — not a production tool.

What's implemented

All chapters from Part II of the book are covered:

Chapter	Feature	Status
4	Scanning (lexer)	✅
5–6	Parsing (recursive descent)	✅
7	Evaluating expressions	✅
8	Statements and state (variables, scoping)	✅
9	Control flow (if, while, for)	✅
10	Functions and closures	✅
11	Resolving and binding (static analysis pass)	✅
12	Classes (methods, this, constructors)	✅
13	Inheritance (super, method lookup chain)	✅

Extensions beyond the book

• Ternary operator (condition ? a : b) — a book challenge, fully wired through parser, resolver, and interpreter
• Nested block comments (/* /* ... */ */) — tracks nesting depth
• String + number concatenation ("value: " + 42 → "value: 42")
• Single-character string comparison ("a" < "b" using char codes)

Building and running

Requires Java and Maven.

mvn package

Run a file:

java -cp target/lox-1.0.0-Alpha.0.jar com.lox.Lox main.lox

Start the REPL:

java -cp target/lox-1.0.0-Alpha.0.jar com.lox.Lox

Example

main.lox:

class D {
  cook() {
    print "Fry until golden brown.";
  }
}

class B < D {
  cook() {
    super.cook();
    print "Pipe full of custard and coat with chocolate.";
  }
}

var b = B();
b.cook();

Output:

Fry until golden brown.
Pipe full of custard and coat with chocolate.

Grammar

See grammar.md for the full BNF grammar.