extend-protocol

(extend-protocol Protocol Type (method [target & args] body...) ...)

Adds rows to a protocol's table without redefining the type: one stored lambda per method per type, like defmethod rows (a repeated type's later rows win, like the oracle). Targets are the kinds class answers (String, Number, Boolean, Keyword, Symbol, Character, Map, Vector, Set, List/Seq, plus nil and Object as the miss default; package-qualified spellings such as java.lang.String or clojure.lang.IPersistentMap too) and known record/deftype names; anything else (an Instant, a Date, ...) is a named refusal.