Lox programming language

The walk-tree interpreter

Original implementation: Crafting Interpreters book.

This implementation is not compatible with the original one, see the differences here.

Lox is an interpreted, dynamically typed, object-oriented, programming language designed by Robert Nystrom.

This was made for learning purposes, as an exercise to better understand the Rust programming language and compilers/interpreters in general.

Language features:

• Variables
• First-class functions
• Closures
• Classes
• Inheritance
• Control flow structures (if, while, for loop)
• Builtin functions

Examples

print "Hello, world!";

class Hello {
    // Class constructor
    init(world) {
        self.world = world;
    }

    // Bound method
    say() {
        print "Hello" + this.world;
    }

    // Static method
    static world() {
        print "Hello static world";
    }
}

// Prints "Hello static world"
Hello.world();

let hello = Hello("world");

// Prints "Hello world"
hello.say();

Run

Cargo is required.

# Clone the repo
# Build with cargo
cargo build --release

# Run the REPL
./target/release/jlox

# Run some script
./target/release/jlox examples/script.jlox

Differences from the original implementation

Functionality	Original	Ours
Inheritance	<	extends
Variable declaration	var	let
Function declaration	fun	fn
Integer types	double	32-bit int and 64-bit float
Dynamic array	not implemented	let arr = [0] * 3; // evals to [0, 0, 0]
Comma operator	not implemented	let a, b = 1, 2; (only in assignments for now)
Static methods	not implemented	static
Pipe operator	not implemented	2 |> mul(2) |> sub(1)
If statement	if (true) // some code	if true { // some code }

Builtin functions

• Clock Returns the current system time as milliseconds.

Usage:

print clock();

• Read Reads a line from stdin and returns as a string.

Usage:

print "write something: ";

let prompt = read();
print "you wrote: " + prompt;

To-do

• import/use
• typeof
• instanceof
• Compound assignment expressions (+=, -=, *=, /=)
• Implement indexing for strings
• (std) FileSystem