[antlr-interest] How to implement an IF

[Terence Parr]

howdy Joerg, i just tweaked CommonTreeNodeStream to make rewind/ 
release work properly.  The seek is there also (already I guess).   
Wait, it says:

		if ( index<this.index() ) {
             throw new IllegalArgumentException("can't seek backwards  
in node stream");
		}

which is true.  You can't seek backwards w/o knowing your state in  
the past (whence the treestate objects).  What we need for  
interpreters is to do away with the small lookahead array and just  
suck all tokens from CommonTreeNodeStream into an array like  
CommonTokenStream does.

Perhaps we need another class BufferedTreeNodeStream that sucks from  
a TreeNodeStream and buffers them so you can seek with an index  
change.  Make sense?  If so, i'll build it real quick.

I also want to update this to use Object not Tree as the type of  
nodes to be more generic.

Ter