I am not really familiar with Unison, but I presume it works like this: Only the code itself is hashed. The then-current name is then added as an annotation. When you refer to a name, the language compiler looks up the hash currently associated with that name and stores the hash instead of the name. When code is rendered, the name associated with the hash at render-time is looked up and displayed. That way if the name is changed, all of the renderings generated after that automagically use the new name.

It's actually quite a clever idea.