package lrs;

/**
 * Mutable linear recursive structure.
 * @author Dung X. Nguyen  Copyright 2000 - All rights reserved.
 * @author Alan L. Cox
 * @since 02/13/01
 * @dependency lrs.IAlgo
 */
public class LRStruct
{
    private ANode _head;

    public LRStruct()
    {
	_head = EmptyNode.singleton;
    }

    /**
     * @return the String describing this list
     */
    public final String toString()
    {
	return _head.toString(this);
    }

    /**
     * @return the object at the front of the list
     */
    public final Object getFirst()
    {
	return _head.getFirst(this);
    }

    /**
     * @param data the object that replaces the one at the front of the list
     */
    public final void setFirst(Object data)
    {
	_head.setFirst(data, this);
    }

    /**
     * @return the rest of the list
     */
    public final LRStruct getRest()
    {
	return _head.getRest(this);
    }

    /**
     * @param tail the list that becomes the rest of the list
     */
    public final void setRest(LRStruct tail)
    {
	_head.setRest(tail, this);
    }

    /**
     * @param data an object to insert at the front of the list
     */
    public final void insertFront(Object data)
    {
	_head.insertFront(data, this);
    }

    /**
     * @return the object removed from the front of the list
     */
    public final Object removeFront()
    {
	return _head.removeFront(this);
    }

    /**
     * The hook required by the visitor pattern.
     *
     * @param visitor The visitor object.
     * @param input An input that is passed to the visitor.
     * @return The result of the visitor.
     */
    public final Object execute(IAlgo visitor, Object input)
    {
	return _head.execute(visitor, input, this);
    }

// Package access only:

    /**
     * Initializes this LRStruct object with the given head node.
     *
     * @param head null != head.
     */
    LRStruct(ANode head)
    {
	_head = head;
    }

    /**
     * This is the ``set state'' method required
     * by the state pattern.
     *
     * @param head The ANode that becomes the head of the list.
     */
    final void setHead(ANode head)
    {
	_head = head;
    }

    /**
     * This is the ``get state'' method required
     * by the state pattern.
     *
     * @return The ANode at the head of the list.
     */
    final ANode getHead()
    {
	return _head;
    }
}