Playground

Lox

Lox is the language Bob Nystrom builds in Crafting Interpreters, a book about writing lexers, parsers and interpreters. I worked through it and wrote my own interpreter for Lox in Java. Everything you run below is sent to that interpreter.

Lox editor

Examples

main.lox⌘ + Enter to run

// Welcome to the Lox playground.
// Everything here runs on the Java interpreter I wrote for Lox.

var name = "world";
print "Hello, " + name + "!";

var answer = 6 * 7;
print answer;

Output

Press Run to send this program to the interpreter.

View source

Language reference

Everything Lox can do, with a snippet for each. Copy any of it into the editor above.

General

Lox's syntax is a member of the C family. It is a dynamically typed language. Braces { } denotes a block of code and // is used for comments.

{
  // Hi these
  // are comments
  // in Lox
}

Variables

Lox supports booleans, numbers, strings and nil. Variables can be declared with the 'var' keyword.

var a = "Hello!"; //String
var b = 123; // Integer
var c = 45.5; // Decimal
var d = true; // Boolean
var e = nil; // nil

Arithmetic

Lox supports the following basic arithmetic operators.

var a = 10;
var b = 5;

var add = a + b; // 15
var sub = a - b; // 5
var mul = a * b; // 50
var div = a / b; // 2

Conditional

Lox supports if-else-if ladders.

var a = 10;
var b = 5;

if ( a > b ) {
  print "a is greater";
} else if ( b > a) {
  print "b is greater";
} else {
  print "a and b are equal.";
}

Loops

Lox supports for loops and while loops.

for (var i = 1; i <= 10; i=i+1) {
  print i;
}

var j = 0;
while (j<=10) {
  print j;
  j = j + 1;
}

Functions

You can create functions with the 'fun' keyword.

fun calculateTip(amount,tipPercent) {
  return (tipPercent/100 * amount);
}

var amount = 175;
var tipPercent = 10;

print calculateTip(amount,tipPercent); //17.5

Classes

You can create classes with the 'class' keyword and initilaize them with the 'innit' method. 'this' keyword is used to refer to the current object

class Person {
  init(name, age) {
    this.name = name;
    this.age = age;
  }
  greeting() {
    print "Hi, I am " + this.name;
  }
}

var person = Person("Swapnil", 24);
person.greeting();

Inheritance

Lox supports single inheritance. When you declare a class, you can specify a class that it inherits from using '<' operator.

class Person {
  init(name, age) {
    this.name = name;
    this.age = age;
  }
  greeting() {
    print "Hi, I am " + this.name;
  }
}

class Student < Person {
  init(name, age, studentId) {
    super.init(name, age);
    this.studentId = studentId;
  }
  greetProfessor(prof) {
    print "Hi Professor " + prof + ", I am " + this.name;
  }
}
var student = Student("Swapnil", 24, 12345);
student.greeting();
student.greetProfessor("Max");