import java.lang.*;

/**A Function is an object that can be evaluated when applied
to an arg.
<p> Usage:<br>
	Implement a Function F that
	responds to 'of(args)' by returning the desired function
	of the arguments.  This class can have objects that
	can by (1) evaluated, (2) passed as arguments to methods.
<br>
	class F implements Function{
		public Object of(Object arg){
			return arg.doubleValue();
		}
	}
<br>
	Function f = new F;
<br>
	Integrators.simpson(f, 0,1);
<br>
	where Integrators.simpson(Function f, double lo, double hi)
	returns a double.
@author Dick Botting
@version 2.1
*/
interface Function{
	public Object of(Object arg);
}
/** The well known triangular number function */
class Triangle implements Function{
	public Triangle(){
		super();
	}
	public Object of(int n){
		return new Integer(n*(n+1)/2);
	}
	public Object of(Object arg){
		int n=((Integer)arg).intValue();
		return this.of(n);
	}
}
class TestFun {

    public static void main(String argv[]){
	Triangle triangle=new Triangle();
	Integer I= new Integer(1);
	Integer II=new Integer(2);
	p(triangle.of(1));
	p(triangle.of(2));
	p(triangle.of(3));

	p(new Triangle().of(4));
	p(new Triangle().of(new Integer(5)));

	p(dup(triangle, I));
	p(dup(triangle, II));

	p(summer(triangle, 1,4));
    }


    public static int summer(Function f, int lo, int hi){
	int sum=0;
	for(int i=lo; i<=hi; i++)
		sum+=((Integer)f.of(new Integer(i))).intValue();
	return (sum);
    }
    
    public static Object dup(Function F, Object x){
	return comp(F,F,x);
    }
    public static Object comp(Function F, Function G, Object x){
	return F.of( G.of(x));
    }
   
    private static void p(int i){
	p(new Integer(i));
    }
    private static void p(Object x){
	System.out.println(x);
    }
}