Scala

Whoa, check out Scala. It's a programming language, and it's like Java and ML at the same time.

package test;

object HelloWorld {
  
  abstract class Expression;
  case class Num(x:int) extends Expression;
  case class Sum(e_1:Expression, e_2:Expression) extends Expression;
  
  def main(args : Array[String]) : Unit = {
    // TODO: Where is my auto-gen?
    System.out.println("Hello World!");       
    
    
    
    
    def do_it(e:Expression) : int = e match {
      case Num(x) => x
      case Sum(e_1, e_2) => do_it(e_1) + do_it(e_2)
    }
    
    System.out.println( Integer.toString( do_it(Sum(Num(5), Num(6))) ) );
  }
}