Lisp函数调用错误

Question

我写了一个这样的 Lisp 函数:

(defun power (base exponent)
  (if (= exponent 0)
      1
    (* base (power (- exponent 1)))))

然而，当我尝试调用它时，出现了一些错误:

CL-USER 2 > (power 2 3)

Error: POWER got 1 arg, wanted at least 2.
  1 (abort) Return to level 0.
  2 Return to top loop level 0.

Type :b for backtrace or :c <option number> to proceed.
Type :bug-form "<subject>" for a bug report template or :? for other options.

CL-USER 3 : 1 > (power 2)

Error: POWER got 1 arg, wanted at least 2.
  1 (abort) Return to level 1.
  2 Return to debug level 1.
  3 Return to level 0.
  4 Return to top loop level 0.

Type :b for backtrace or :c <option number> to proceed.
Type :bug-form "<subject>" for a bug report template or :? for other options.

CL-USER 4 : 2 > (power 2 3 4)

Error: POWER got 3 args, wanted 2.
  1 (continue) Ignore the extra arg.
  2 (abort) Return to level 2.
  3 Return to debug level 2.
  4 Return to level 1.
  5 Return to debug level 1.
  6 Return to level 0.
  7 Return to top loop level 0.

Type :b for backtrace or :c <option number> to proceed.
Type :bug-form "<subject>" for a bug report template or :? for other options.

这是怎么回事？如果我给它两个参数，它认为我给了它一个。如果我给它三个，它就认为我给了它三个。如果我给它一个，它就认为我给了它一个...

Answer 1

只有一个参数的递归调用:

(power (- exponent 1))

应该是这样的:

(power base (- exponent 1))