lispobject.java

计算机代数系统

package net.sf.yacas;


/** class LispObject is the base object class that can be put in
 *  linked lists. It either has a pointer to a string, obtained through
 *  String(), or it is a holder for a sublist, obtainable through SubList(),
 *  or it is a generic object, in which case Generic() returns non-NULL.
 *  Only one of these three functions should return a non-NULL value.
 *  It is a reference-counted object. LispPtr handles the reference counting.
 */
abstract class LispObject 
{
  public  LispPtr Next()
	{
	  return iNext;
	}

  /** Return string representation, or NULL if the object doesn't have one.
    *  the string representation is only relevant if the object is a
    *  simple atom. This method returns NULL by default.
    */
  public abstract String String() throws Exception;
  /** If this object is a list, return a pointer to it.
    *  Default behaviour is to return NULL.
    */
  public LispPtr SubList()
	{
	  return null;
	}
  public GenericClass Generic()
	{
	  return null;
	}

  /** If this is a number, return a BigNumber representation
    */
  public BigNumber Number(int aPrecision) throws Exception
	{
	  return null;
	}

  public abstract LispObject Copy(boolean aRecursed) throws Exception;

  /** Return a pointer to extra info. This allows for annotating
    *  an object. Returns NULL by default.
    */
  public LispPtr ExtraInfo()
	{
	  return null;
	}
  public abstract LispObject SetExtraInfo(LispPtr aData);

  public boolean Equal(LispObject aOther) throws Exception
	{
		// next line handles the fact that either one is a string
		if (String() != aOther.String())
			return false;

		//So, no strings.
		LispPtr iter1 = SubList();
		LispPtr iter2 = aOther.SubList();
		if (!(iter1 != null && iter2 != null))
		  return false;

		// check all elements in sublist
		while (iter1.Get()!= null && iter2.Get()!=null)
		{
			if (! iter1.Get().Equal(iter2.Get() ))
				return false;
				
			//TODO FIXME oddly enough the following lines were not present in the C++ code!
			iter1 = iter1.Get().Next();
			iter2 = iter2.Get().Next();
		}
		//One list longer than the other?
		if (iter1.Get()== null && iter2.Get()==null)
			return true;
		return false;
	}
//TODO FIXME shouldn't these be removed from the Yacas main source tree too?    void SetFlag(int aFlag);
//TODO FIXME shouldn't these be removed from the Yacas main source tree too?    void ResetFlag(int aFlag);

	LispPtr   iNext = new LispPtr();
}