;反序 (  ) -> (  )

(define (rvs x)

  (let recur ((x x)(res '()))

    (if (null? x)

        res

        (recur (cdr x) (cons (car x) res)))))

;长度 (  ) ->

(define (len x)

  (let recur ((x x)(y ))

    (if (null? x)

        y

        (recur (cdr x) (+ y )))))

;合并列表 (x ...) (y ...) -> (x ... y ...)

(define (apd x y)

  (let recur ((x x))

    (if (null? x)

        y

        (cons (car x) (recur (cdr x))))))

;切割教程版

(define (tail x n)

  (if (zero? n)

      x

      (tail (cdr x) (- n ))))

;引用 (   )  ->

(define (ref x n)

  (if (=  n)

      (car x)

      (ref (cdr x) (- n ))))

;成员查询  (   ) -> (  )

(define (mem i x)

  (let recur ((x x))

    (if (null? x)

        #f

        (if (equal? (car x) i)

            x

            (recur (cdr x))))))

;类字典查询 k2 ((k1 v1)(k2 v2)(k3 v3)...) ->(k2 v2)

(define (asq k x)

  (let recur ((x x))

    (if (null? x)

        #f

        (if (equal? (caar x) k)

            (car x)

            (recur (cdr x))))))

(define x '(1 2 3 4))

(define y '(5 6 7 8))

(append x y)

(apd x y)

(length x)

(len x)

(reverse x)

(rvs x)

(list-tail '(1 2 3) 1)

(tail '(1 2 3) 1)

(list-ref '(1 2 3) 2)

(ref '(1 2 3) 2)

(member  '(1 2 3 4))

(mem  '(1 2 3 4))

(assv  '((2 3) (5 7) (11 13)))

(asq  '((2 3) (5 7) (11 13))) 

(       )

(       )

(   )

(   )

( )

( )

(  )

(  )

( )

( )

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