# zhsh

An implementation of the Zhang-Shasha algorithm for calculating
tree edit distance.

Here trees are s-expressions with NON-NULL leaves. 

I.e. Leaves are `(and leaf (atom leaf))` 

## Examples:

    ZHSH> (treedist '((the cat) (sat (on (the mat)))) 
                    '((the cat) (sat (on (the mat )))))
    0
    
    ZHSH> (treedist '((the cat) (sat (on (the mat)))) 
                    '((the cat) (sat (on (a mat )))))
    11
    
    ZHSH> (treedist '((the cat) (sat (on (the mat)))) 
                    '((the ordinary cats) (sit (on (a simple chair )))))
    21
    
    ZHSH> (treedist '((the cat) (sat (on (the mat)) (for (an hour)))) 
                    '((the ordinary cats) (sit (on (a simple chair)))))
    26