package schemeFactory.visitor;

import schemeFactory.*;

/**
 * Reverses the host given the reverse of the list preceding the host.
 * Passes the accumulated reverse to the constructor.
 <pre>
 Note to students: try to write a version where the accumuated reverse is passed
 as the input parameter.  You will learn to appreciate the differences.
 </pre>
 @author D. X. Nguyen
 */
class HelpReverse implements IListAlgo {
    private AList _accReverse;  // acumulated reverse so far.

    public HelpReverse(AList accReverse) {
        _accReverse = accReverse;
    }

    /**
    * Returns the accumulated reverse because this is the end of the list.
    * @param host not used
    * @param input not used
    * @return IList
    */
    public Object emptyCase(AList host, Object input) {
        return _accReverse;
    }

    /**
    * Accumulates the reverse by cons-ing the host's first with the accumulated
    * reverse so far, and recur on the host's rest.
    * @param host the rest of the list to be reversed.
    * @param input the accumulated reverse of the list preceding host.
    * @return IList
    */
    public Object nonEmptyCase(AList host, Object input) {
        //_accReverse = new NEList(host.getFirst(), _accReverse);
        return host.getRest().execute (this, null);
    }
}