Crosscut

Using a free-form approach to structural code editing, makes changes to the syntax tree challenging. But there's an alternative: You don't let the user add and remove nodes freely. If they add a node, the editor also adds its required children. They can't remove a required child without also removing the parent. And they can't add extra children.

I'm calling this restricted (versus free-form) structural code editing. It is much easier on the compiler, since it doesn't need to cover as many edge cases. And updating a node becomes much simpler.

You no longer need to compile children after changing a node, because if the node changed, new (and suitable) children have been created. You don't need to re-compile a parent after its children changed, because changes to children can't make the parent invalid. The compiler becomes more efficient, and much more manageable.