Factories are data

To elaborate, factories are maps with a type metadata to distinguish them. You can assoc things into their template on the fly for instance. As the trait discussion highlights there's some non obvious aspects to how intuitively they should work, so I think it's helpful to encapsulate that and provide an api that handles common cases. I'd love to see a good proposal of what this would look like leveraging "just Clojure". My sense is that in that case you don't need a library at all, just write the code that generates your data.