Let me be specific. I agree trees(or json) in general can have a fixed set of general purpose ops. This particular paper though, the author claims changing the type of a record struct is itself an operation. This allows to treat it as a special kind, thereby applying it means it has to touch a whole other set of nodes. This is just one example, there could be ops like this tailored for the structure he is working with which is what got me into thinking :)
Let me be specific. I agree trees(or json) in general can have a fixed set of general purpose ops. This particular paper though, the author claims changing the type of a record struct is itself an operation. This allows to treat it as a special kind, thereby applying it means it has to touch a whole other set of nodes. This is just one example, there could be ops like this tailored for the structure he is working with which is what got me into thinking :)