common-lisp - SBCL 意外陷入浮点？

Question

考虑 Common Lisp 中的以下代码：

  (defun range (max &key (min 0) (step 1))
    (loop for n from min below max by step
          collect n))
  (reduce #'* (range 61 :min 1))

这给出了预期的 bignum 值 60！，即

8320987112741390144276341183223364380754172606361245952449277696409600000000000000

但是，以下代码（不包含我可以看到的任何浮点强制）会产生浮点答案：

  (defun fact (n)
    (if (= 0 n)
        1
        (* n (fact (- n 1)))))

  (fact 60)
  8.32098711274139e+81

问题是“为什么？” 和“我怎样才能fact在 SBCL（Steel-Bank Common Lisp）中编写一个简单的递归，产生一个 bignum 结果？”

Answer 1

The coercion happens on the emacs side. ob-lisp.el calls read on the result. Try evaluating this on the *scratch* buffer to see for your self

(read "8320987112741390144276341183223364380754172606361245952449277696409600000000000000")