运行lisp程序遇到：should be a lambda expression，如何解决？

(defun int-to-binary (alist)
    (setq n (- length(alist) 1))
    (setq result 0)
    (loop for x in alist
        do(setq result (+ result (* x (expt 2 n)))
        (setq n (- n 1))
        )
    )
    (format t "~d" result)

(int-to-binary '(1 0 1 1))

报错如下：

*** - SYSTEM::%EXPAND-FORM: (SETQ RESULT (+ RESULT (* X (EXPT 2 N)))) should be a lambda expression

这个程序是要解决如下问题的：

Write a LISP function binary-to-int that converts a binary number that is given as list
comprising only 0 and 1 into a integer. For example:
(binary-to-int ’()) returns nil, because the empty set is not a representation of a binary number.
(binary-to-int ’(1 0)) returns 2
(binary-to-int ’(0 1)) returns 1
(binary-to-int ’(0)) returns 0
(binary-to-int ’(1 1 1 0)) returns 14

http://www.itkeyword.com/doc/9211980630815971796/common-lisp-error-should-be-lambda-expression