What is Lox?

Lox is a programming language by Bob Nystrom written for the book Crafting Interpreters. It is an excellent book that teaches how to build lexers, parsers and interpreters. After reading the book and having implemented the interpreter for Lox in Java, I decided to make a playground for it which runs the code on the Java Interpreter for Lox hosted on a server.

// Hello, Welcome to the Lox Playground
// Use this space to play around with the language.


print "Hi, Thank you for coming to my site.";

View Source

Documentation

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");