loop macro, wrapping let

loop-let.clj

(require '[clojure.walk :as walk])
(walk/macroexpand-all '(loop [[x & xs] xs a 3]))

(let* [G__1249 xs
       vec__1250 G__1249
       x (clojure.core/nth vec__1250 0 nil)
       xs (clojure.core/nthnext vec__1250 1)
       a 3]
  (loop* [G__1249 G__1249 a a]
    (let* [vec__1251 G__1249
           x (clojure.core/nth vec__1251 0 nil)
           xs (clojure.core/nthnext vec__1251 1)
           a a])))

(loop* [G__1249 xs a a]
  (let* [vec__1251 G__1249
         x (clojure.core/nth vec__1251 0 nil)
         xs (clojure.core/nthnext vec__1251 1)
         a a]))

(defmacro loop
  "Evaluates the exprs in a lexical context in which the symbols in
  the binding-forms are bound to their respective init-exprs or parts
  therein. Acts as a recur target."
  {:added "1.0", :special-form true, :forms '[(loop [bindings*] exprs*)]}
  [bindings & body]
    (assert-args
      (vector? bindings) "a vector for its binding"
      (even? (count bindings)) "an even number of forms in binding vector")
    (let [db (destructure bindings)]
      (if (= db bindings)
        `(loop* ~bindings ~@body)
        (let [vs (take-nth 2 (drop 1 bindings))
              bs (take-nth 2 bindings)
              gs (map (fn [b] (if (symbol? b) b (gensym))) bs)]
          `(loop* ~(vec (interleave gs vs))
                  (let ~(vec (interleave bs gs))
                    ~@body))))))