🦀 Rlox — A Tree-Walk Interpreter in Rust

This is a Rust implementation of the Lox programming language from Crafting Interpreters by Robert Nystrom.

It follows the tree-walk interpreter model and supports the features up to classes (without inheritance).
The project demonstrates how an interpreter can be built from scratch, including scanning, parsing, and evaluation.

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⚙️ Installation

There’s no published binary or package for Rlox — the interpreter can only be run by cloning the repository and using Cargo directly.

# Clone the repository
git clone https://github.com/abrishk26/rlox.git
cd rlox

# Run a Lox file
cargo run -- examples/basics.lox

⚠️ Make sure to include -- before the file path so Cargo passes it to your program and not to itself.

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🔧 Built-in Functions

Rlox provides the following built-in functions:

• print(arg1, arg2, ...) — prints all arguments concatenated with spaces, without a newline.
• println(arg1, arg2, ...) — prints all arguments concatenated with spaces, with a newline.
• input([prompt]) — reads a line from the user. Optionally displays prompt if provided.

Example:

print("Enter your name: ");
var name = input();
println("Hello, " + name + "!");

var age = input("Enter your age: ");
println("You are " + age + " years old.");

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🧩 Example Snippets

Here are simple Lox programs you can use to test the interpreter.
None of these examples use inheritance — they’re all self-contained demonstrations.

1. Basic Arithmetic

print(2 + 3 * 4);     // 14
println((10 - 4) / 3);  // 2
print(5 > 2);         // true
println("lox" + "lang"); // "loxlang"

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2. Variables and Scope

var greeting = "Hello";
var name = "World";
println(greeting + ", " + name);

{
  var greeting = "Hi";
  println(greeting); // "Hi"
}

println(greeting); // "Hello"

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3. Functions

fun add(a, b) {
  return a + b;
}

println(add(2, 3)); // 5

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4. While Loop

var i = 0;
while (i < 3) {
  println(i);
  i = i + 1;
}

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5. Closures

fun makeCounter() {
  var count = 0;
  fun inc() {
    count = count + 1;
    println(count);
  }
  return inc;
}

var counter = makeCounter();
counter(); // 1
counter(); // 2

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6. Classes and Methods

class Person {
  init(name, age) {
    this.name = name;
    this.age = age;
  }

  sayHi() {
    println("Hi, I'm " + this.name + " and I'm " + this.age + " years old.");
  }
}

var p = Person("John", 40);
p.sayHi();

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7. Property Access

class Box {
  init(value) {
    this.value = value;
  }

  show() {
    println("Value: " + this.value);
  }
}

var b = Box("Rust");
b.show();       // "Value: Rust"
b.value = "Lox";
b.show();       // "Value: Lox"

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8. Error Examples

// Undefined variable
println(notDefined); // runtime error

// Calling a non-function
var x = 123;
x(); // should error: Can only call functions and classes.

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