// Can represent a first-class function in Java as an object 
// with a single "apply" method.
interface Fun {
  public Object apply (Object x); 
}

// Representing the linear function ax + b as an object
// with instance variables a and b:
class Linear implements Fun {

  private int a, b; // integer instance variables

  public Linear (int a, int b) {
    this.a = a;
    this.b = b;
  }

  public Object apply (Object x) {
    // Must deal with hassle of unwrapping integers from wrapping 
    // integers into instances of the integer wrapper class. Yuck!
    // Doesn't it make you feel like you need to take a shower?
    return new Integer (a * ((Integer) x).intValue() + b); 
  }

}

public class Mapper {

  // Handy way to abbreviate "ObjectList." as "OL."
  public static ObjectList OL; 

  public static ObjectList map (Fun f, ObjectList L) {
    if (OL.isEmpty(L)) {
      return L;
    } else {
      return OL.prepend(f.apply(OL.head(L)), map(f, OL.tail(L)));
    }
  }

  // Parse a string representation of an integer list into a list of IntegerObjects. 
  public static ObjectList parseIntList (String s) {
    return map (// Example of "anonymous inner class"
		new Fun() {
		  public Object apply (Object x) {
		    return new Integer ((String) x); 
                  }
		}, 
		OL.fromString(s)); // fromList returns a list of strings
  }

  public static void main (String [] args) {
    if (args[0].equals("linear1")) {
      int a = Integer.parseInt(args[1]);
      int b = Integer.parseInt(args[2]);
      ObjectList L = parseIntList(args[3]);
      System.out.println(map(new Linear(a,b), L)); 
    } else if (args[0].equals("linear2")) {
      final int a = Integer.parseInt(args[1]); // Java requires these be be final
      final int b = Integer.parseInt(args[2]); // in order to close over them
      // Create an anonymous linear function 
      Fun f = new Fun() {
	  public Object apply (Object x) {
	    return new Integer (a * ((Integer) x).intValue() + b); 
	  }
	};
      ObjectList L = parseIntList(args[3]);
      System.out.println(map(f, L));
    } else {
      System.out.println("unrecognized option"); 
    }
  }

  /* Examples of running the above
     [fturbak@jaguar java] java Mapper linear1 2 3 [1,2,3,4,5]
     [5,7,9,11,13]
     [fturbak@jaguar java] java Mapper linear2 2 3 [1,2,3,4,5]
     [5,7,9,11,13]
  */

}