Simple aggregator macro

gistfile1.clj

(defmacro aggregate
  "Simple aggregation. Iterates over seq, binding values to
  seq-bind. agg-bind is initially initial-val, but is bound to the value
  of body after each iteration, and returned as the final value."
  [agg-bind initial-val
   [seq-bind seq]
   & body]
  `(reduce
    (fn [~agg-bind ~seq-bind]
      (do ~@body))
    ~initial-val
    ~seq))

(aggregate a {:sum 0}
           [i (range 10)]
           {:sum (+ i (:sum a))})
;; => {:sum 45}


(aggregate [count sum] [0 0]
           [i (range 10)]
           [(inc count) (+ sum i)])
;; => [10 45]