loop 是一个怪异的东西，它在源中定义了两次，一次在第 37 行。
;在引导过程中，我们没有 destructuring let、loop 或 fn，稍后将其重新定义。
clojure
(def
^{:macro true
:added "1.0"}
loop (fn* loop [&form &env & decl] (cons 'loop* decl)))
你获得的文档是从 loop 的第二次定义中获取的。
loop 的第一次定义钩入了一些编译器魔法。
然后在第 4599 行
(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)
bfs (reduce1 (fn [ret [b v g]]
(if (symbol? b)
(conj ret g v)
(conj ret g v b g)))
[] (map vector bs vs gs))]
`(let ~bfs
(loop* ~(vec (interleave gs gs))
(let ~(vec (interleave bs gs))
~@body)))))))
