log.clj

(defprotocol Log
  (info [args]))

; We wanted to do this
(deftype TaggedLogger [metadata]
  Log
  (info [args] (apply clojure.tools.logging/info (conj metadata args))))
; but info et al. are macros so we can't use apply here

; Then I wrote this macro in order to wrangle the problem
(defmacro invoke-log [level args]
  (let [s (symbol (str "clojure.tools.logging/" level))]
    `(~s ~@args)))

; so we could then do
(deftype TaggedLogger [metadata]
  Log
  (info [args] (invoke-log info (conj metadata args))))

; but it emits the following log line
(info (TaggedLogger. "meta") (list "bar" "baz"))
; [2015-08-20 14:19:36,001][INFO][the-ns] (nREPL-worker-3) #<core$cons clojure.core$cons@1a4d2ef8> foo (bar baz)