PLox

Plox is a Python implementation of the Lox Programming Language, which was created by Bob Nystrom for his book - "Crafting Interpreters".

Using Lox

This is a very brief primer on how to use "Lox". For more detailed documentation, please refer to "Crafting Interpreters" - Chapter 3 - The Lox Programming Language".

Input and Output

Being a simple language created for the sake of teaching compiler design, Lox only support one I/O operation - printing on screen.

The print statement is baked right into the core library itself. Since it's a statement, and not a function, it should be called without the parentheses.

In fact, we are ready for out very first program:

print "Hello, world!";

Comments

Anything after // is ignored as a comment.

Data Types

There are four basic data types:

• Strings - Anything quoted in double quotes is considered a string.
• Numbers - All numbers are stored as double precision floating point numbers.
• Boolean - It wouldn't make much sense to create a programming language which can't support with logic. And For logic, we need Boolean - true and false. It follows Ruby style - only nil and false are "treated" as false (for eg. let's say in an if condition), everything else is considered true.
• nil - It represents no value. What None is to Python, what null is to Java, nil is to Lox.

Variables

Lox is a dynamically typed language, and no data type is associated with variables.

A variable can be declared using:

var hello = "Hello!";

However, the initializer isn't necessary. You may choose to initialize the variable later on. For eg.:

var my_var;
// More code
my_var = "This is the best variable I named!"

Functions

Defining a function is fun using the keyword fun:

fun greet(person, host){
    print "Hello, have a good day, " + person;
    print "From,";
    print host;
}

Calling a function:

my_function("dear 'loxer'", "Rahul");

Classes

[Coming Soon]

Installation

plox can be installed using pip.

Clone the repository using git:

$ git clone https://github.com/RJ722/plox && cd plox

Create a virtualenv and install using pip:

$ virtualenv venv
$ source venv/bin/activate
(venv) $ pip install -e .

Try it out in an interactive prompt:

(venv) $ plox

Why didn't you just use the Java implementation?

The simple answer is that I don't know Java well enough.

Also, I believe that I would learn better if rather than merely copying code, I write it myself, and writing in another language enabled me to do just that. Due to this, I cannot vouch for the correctness of the code. It is solely based on my understanding of Bob's ideas.

Is this complete?

Not yet, Classes and Inheritance (Chapter 12 and 13) are still a WIP. You might want to watch the repo for updates.

I also (rather ambitiously) plan to complete all the Challenges listed at the end of the chapters and publish the solutions online.

Why isn't there a LICENSE?

The book "Crafting Interpreters"* licenses all of it's code under the permissible MIT License, but all the text and the aesthetics are covered under CC BY-NC-ND 4.0. I was a little confused with this because Lox didn't fall into neither. Also, I couldn't find a coherent licensing policy from looking at the other ports, so I have emailed Bob (original author and creator).

Source code is open source, because there's no reason it shouldn't be, but I'd request you all to please wait for Bob's reply in case you want to use this code.

Similar Projects

Lox is hugely popular and the interpreter has been developed in 30+ languages. Some of them can be found here.