当我使用 (avg-bids 4000 10 5) 调用以下 Clojure 代码时，会导致 java.lang.StackOverflowError 。我试图找出原因，因为 sum-bids 是作为尾递归函数编写的，所以应该可以工作。使用 Clojure 1.2。
有谁知道为什么会发生这种情况？
(ns fixedprice.core
(:use (incanter core stats charts)))
(def *bid-mean* 100)
(defn bid [x std-dev]
(sample-normal x :mean *bid-mean* :sd std-dev))
(defn sum-bids [n offers std-dev]
(loop [n n sum (repeat offers 0)]
(if (zero? n)
sum
(recur (dec n) (map + sum (reductions min (bid offers std-dev)))))))
(defn avg-bids [n offers std-dev]
(map #(/ % n) (sum-bids n offers std-dev)))
map是懒惰的，并且您正在通过以下方式构建非常深层嵌套的映射映射recur。回溯有点神秘，但仔细观察你可以看到地图，地图，地图......
Caused by: java.lang.StackOverflowError
at clojure.lang.LazySeq.seq(LazySeq.java:56)
at clojure.lang.RT.seq(RT.java:450)
at clojure.core$seq.invoke(core.clj:122)
at clojure.core$map$fn__3699.invoke(core.clj:2099)
at clojure.lang.LazySeq.sval(LazySeq.java:42)
at clojure.lang.LazySeq.seq(LazySeq.java:56)
at clojure.lang.RT.seq(RT.java:450)
at clojure.core$seq.invoke(core.clj:122)
at clojure.core$map$fn__3699.invoke(core.clj:2099)
at clojure.lang.LazySeq.sval(LazySeq.java:42)
at clojure.lang.LazySeq.seq(LazySeq.java:56)
at clojure.lang.RT.seq(RT.java:450)
at clojure.core$seq.invoke(core.clj:122)
at clojure.core$map$fn__3699.invoke(core.clj:2099)
at clojure.lang.LazySeq.sval(LazySeq.java:42)
at clojure.lang.LazySeq.seq(LazySeq.java:56)
at clojure.lang.RT.seq(RT.java:450)
at clojure.core$seq.invoke(core.clj:122)
at clojure.core$map$fn__3699.invoke(core.clj:2099)
修复它的一种方法是放置doall围绕它来战胜懒惰。
(defn sum-bids [n offers std-dev]
(loop [n n sum (repeat offers 0)]
(if (zero? n)
sum
(recur (dec n) (doall (map + sum (reductions min (bid offers std-dev))))))))
user> (avg-bids 4000 10 5)
(100.07129114746716 97.15856005697917 95.81372899072466 94.89235550905231 94.22478826109985 93.72441188690516 93.32420819224373 92.97449591314158 92.67155818823753 92.37275046342015)
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