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Ranger.java

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// file:    Ranger.java
// author:  Robert M. Keller
// purpose: Example of a Function1 object

/**
 * A Ranger is a Function1 object that produces a list of number from a
 * start number up to including the argument number.  The start number
 * is specified in the constructor.  So a Ranger can be used as the argument
 * to map or mappend, for example.
 */

class Ranger implements Function1
{
/**
 * The starting number in the range to be produced.
 */

private Number start;
private Number increment;

/**
 * Create a Ranger with a specific start and increment.
 * @param _start the starting Number to be used.
 * @param _increment the increment Number to be used.
 */

Ranger(Number _start, Number _increment)
  {
  start = _start;
  increment = _increment;
  }


/**
 * Create an ascending list beginning with start, up to and including stop.
 * @param _start the starting Number to be used.
 * @param _stop the ending Number to be used.
 * @return a list consisting of start to stop, incremented by increment.
 */

public static OpenList range(Number start, Number stop, Number increment)
  {
  long startValue = ((Number)start).longValue();
  long stopValue  = ((Number)stop).longValue();

  if( startValue > stopValue )
    return OpenList.nil;

  long inc = ((Number)increment).longValue();

  return OpenList.cons(start, 
                       range(new Long(startValue +inc), stop, increment));
  }


/**
 * Apply this Ranger object to an Object x, which should be a Number.
 * If x is not a number, a ClassCastException will be thrown.
 *
 * @param x the Object to which this function is applied
 * @return a Double containing this Ranger's start times the argument's value
 */

public Object apply(Object stop)
  {
  return range(start, (Number)stop, increment);
  }
}

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