我正在尝试构建一个函数，将底部的以下过程编码为1和0并且任何人都可以帮助找到我收到错误消息mpair的原因：0。
function handleEvent(){
}
searchbox.onsubmit = handleEvent;
searchbtn.onclick = handleEvent;
(define (symbols tree)
(if (leaf? tree)
(list (symbol-leaf tree))
(caddr tree)))
(define (right-branch tree) (cadr tree))
(define (left-branch tree) (car tree))
(define (leaf? object)
(eq? (car object) 'leaf))
(define (member? x set)
(not (equal? (member x set) false)))
(define (encode-branch symbol tree)
(let ((left (left-branch tree))
(right (right-branch tree)))
(cond ((member? symbol (symbols left)) (list 0 left))
((member? symbol (symbols right)) (list 1 right))
(else (error symbol tree)))))
(define (encode symbol tree)
(if (leaf? tree) '()
(let ((new-branch (encode-branch symbol tree)))
(cons (car new-branch) (encode symbol (cadr new-branch))))))