For failure maps, I’ve found it useful to have a :tried key, which is the parameter that in some sense “caused” the err, or a map of params if there are multiple.

I also usually have an error :type key.

I’ve also found it useful to distinguish between expected errs and those that should end execution more quickly. Clojure allows hierarchical keys with “derive” so I inherit these from a top level error key and set them as the :type. (Why not use exceptions - because I’ve already got exit flow and error reporting built around the maps.)