gistfile1.txt

;;; the docstring doesn't quite match the implementation, but you get the idea.

(defmacro fold 
  "sugar on reduce, similar to how 'for' is a nicer version of 'map'.

  init is a symbol that evaluates to a value (local or var) or a vector of a symbol and an initial value. In the loop, init is bound to the result of the previous loop.

Binding can take any arguments supported by for, but should only bind one variable.
"
;;   (fold r [i (range 10)]   ;; existing symbol
;;       (+ r i))

;; (fold [r 0] [i (range 10)] ;; define new local
;;        (+ r i))
  [initial binding & body]
  (let [init-sym (if (symbol? initial)
                   initial
                   (first initial))
        init-val (if (symbol? initial)
                   initial
                   (second initial))]
    `(let [~init-sym ~init-val]
       (reduce (fn [~init-sym ~(first binding)]
                 ~@body) ~init-sym ~@(rest binding)))))