Make True and False as subtypes of Boolean in Scala (Note that the "object" keyword is the Scala way to declare a singleton class)

Boolean.scala

abstract class Boolean {
  	def == (other: Boolean): Boolean;
  	def != (other: Boolean): Boolean;
  	def && (other: Boolean): Boolean;
	def || (other: Boolean): Boolean;
	def unary_! (): Boolean;
}

object True extends Boolean {
	def == (other: Boolean) = other;
	def != (other: Boolean) = !other;
	def && (other: Boolean) = other;
	def || (other: Boolean) = True;
	def unary_! () = False;
	
	override def toString() = "True";
}

object False extends Boolean {
	def == (other: Boolean) = !other;
	def != (other: Boolean) = other;
	def && (other: Boolean) = False;
	def || (other: Boolean) = other;
	def unary_! () = True
	
	override def toString = "False";
}

object Test {
	def main(args: Array[String]) = {
		println("True == True --> " + (True == True));
		println("True == False --> " + (True == False));
		println("!True --> " + !True);
		println("False == !True --> " + (False == !True));
		println("!True && (True || False) --> " + (!True && (True || False)));
		println("!True || True && False || !False --> " + (!True || True && False || !False));
	}
}