Hi john I'm facing the following situation and I was wondering if a simple heuristic could not improve the situation (where edge cases will always be a problem). I got a hierarchy of expressions implementing evaluate and I wanted to add a parameter (the binding). So Add Parameter worked but broke evaluate recursive methods. Here is a part of the book I'm writing [[[ EConstant >> testEvaluate self assert:(EConstant new value: 5) evaluate equals: 5 ]]] is transformed as follows: [[[ EConstant >> testEvaluate self assert: ((EConstant new value: 5) evaluateWith: Dictionary new) equals: 5 ]]] Your tests should nearly all pass except the ones on variables. Why do they fail? Because the refactoring transformed message sends ==evaluate== but ==evaluateWith: Dictionary new== and this even in methods ==evaluate==. [[[ EAddition >> evaluateWith: anObject ^ (right evaluateWith: Dictionary new) + (left evaluateWith: Dictionary new) ]]] [[[ EAddition >> evaluateWith: anObject ^ (right evaluateWith: anObject) + (left evaluateWith: anObject) ]]] And I was wondering if a good heuristic would be to change the parameter. Now I have the impression that the refactoring is done it two passes. So this is more tricky than it looks. Stef