使用 lazy-seq 的 Clojure 尾递归

Question

您能否更全面、更清晰地解释一下，lazy-seq 如何按照此文档页面使尾递归“安全”？

https://clojuredocs.org/clojure.core/lazy-seq

;; The following defines a lazy-seq of all positive numbers.  Note that 
;; the lazy-seq allows us to make a recursive call in a safe way because
;; the call does not happen immediately but instead creates a closure.

user=> (defn positive-numbers 
    ([] (positive-numbers 1))
    ([n] (lazy-seq (cons n (positive-numbers (inc n))))))
#'user/positive-numbers

user=> (take 5 (positive-numbers))
(1 2 3 4 5)

Answer 1

如果您查看 lazy-seq 的实现，您会发现它确实返回了一个闭包(一个保留一段上下文的函数):

(list 'new 'clojure.lang.LazySeq (list* '^{:once true} fn* [] body))

所以 (cons n (positive-numbers (inc n)) 中对 positive-numbers 的调用不会立即求值，而是延迟到闭包被调用。