gistfile1.clj

(defmacro with-ns
  "Evaluates f within ns. Calls (require 'ns) first."
  [ns f]
  `(do
     (require '~ns)
     (binding [*ns* (find-ns '~ns)]
       (eval '~f))))

gistfile2.clj

(defn trap-ns [ns f]
  (if (ns-exists ns)
    `(pig/with-ns ~ns ~f)
    f))

(defn trap* [keys values ns f]
  (->> f
    (trap-locals keys values)
    (trap-ns ns)))
  
(defmacro trap
  "Returns a form that, when evaluated, will reconsitiute f in namespace ns, in
the presence of any local bindings"
  ([f] `(trap '~(ns-name *ns*) ~f))
  ([ns f]
    (let [keys# (vec (keys &env))]
      `(trap* '~keys# ~keys# ~ns '~f))))