在工作中，我们有些情况下需要混合同步序列，如果某个序列比另一个短，我们希望在同步结束后将较长的序列的元素附加到较短序列的后面。
以下代码可以用来实现 -- 现有 interleave 函数的微小变体
(defn interleave-all
"Like interleave, but stops when the longest seq is done, instead of
the shortest."
{:copyright "Rich Hickey, since this is a modified version of interleave"}
([] ())
([c1] (lazy-seq c1))
([c1 c2]
(lazy-seq
(let [s1 (seq c1) s2 (seq c2)]
(cond
(and s1 s2) ; there are elements left in both
(cons (first s1) (cons (first s2)
(interleave-all (rest s1) (rest s2))))
s1 ; s2 is done
s1
s2 ; s1 is done
s2))))
([c1 c2 & colls]
(lazy-seq
(let [ss (filter identity (map seq (conj colls c2 c1)))]
(concat (map first ss) (apply interleave-all (map rest ss)))))))
