Well "walk the object graph with a visitor" goes back at least to early (reflection-based) Java XML serializers; a generated-code version of the same thing is not a huge leap. I find it a frustratingly imperative way of approaching the problem: you can't think about what happens without thinking about control flow, because the visit can't be defunctionalized as a value. You may not want to physically reify the generic representation of the value - there would be a performance cost to that - but having it available to think about helps keep your code (and understanding) clear, in the same way that when doing a series of transformations of a large collection you probably want to be able to conceptualise "the collection in between step 1 and step 2" even if you don't want to actually instantiate that in memory at runtime.