The eval function is recursive.  So you can't use it to just evaluate the root node.  So... just don't use it.  Instad in your evaluate() method, evaluate the tree as you see fit.  You don't have to call eval at all.

Sean

On Feb 19, 2014, at 10:08 AM, Emre AYDO&#286;AN <[log in to unmask]> wrote:

> Thanks for your answer. I don't want to run nodes' evaluation function
> except root node. In other words I just want to run evaluation function for
> root node. In evaluation function, I will find same nodes between population
> tree and desired tree. I mean I will do pattern matching. And my fitness
> value is the number of same nodes between trees. 
> 
> Thanks,