example.clj

;; manual

(def fuel (atom 10))

(loop []
  (when (zero? (swap! fuel dec))
    (fail "out of fuel!"))
  (recur))


;; auto

(loop []
  (check-fuel! 10)
  (recur))

fuel.clj

(def fuel (atom {}))

(defmacro check-fuel! [n]
  (assert (int? n))
  (let [tank (assoc (select-keys (meta &form) [:line :column])
                    :file *file*)]
    (assert (and *file* (= (count tank) 3)))
    (swap! fuel assoc tank n)
    `(do
       (swap! fuel update '~tank dec)
       (when (zero? (@fuel '~tank))
         (swap! fuel assoc '~tank ~n)
         (fail "out of fuel!")))))