At runtime, the function created by the macroexpansion captures lexical scope from wherever it's called, and is stored in the atom.

compiletime-closures.clj

(def protos (atom nil))

(defn build-func [[name args body]]
 (list 'fn name args body))

(defmacro bleh [fbody]
  `(let [f# ~(build-func fbody)]
    (do (reset! protos f#) f#)))

(macroexpand-1 '(bleh (foo [y] (+ x y))))

(let [x 100
      func (bleh (foo [y] (+ x y)))]
    (func 15))
;; closure created above stored in atom (i.e. protocol map)
(@protos 80)