(diagram) Check if there is an item in one list in the second list with do cicle

The do cycle in the racket has an interesting structure:

(do ([id init-expr step-expr-maybe] ...)
    (stop?-expr finish-expr ...)
  expr ...)

The documentation for r5rs gives an example:

(let ((x '(1 3 5 7 9)))
  (do ((x x (cdr x))
       (sum 0 (+ sum (car x))))
      ((null? x) sum)))

This operator returns 25, the sum of the elements in the loop. xin a loop, do is initialized to xin let, and then iteratively sets to cdritself each time through the loop. suminitialized to 0 and accumulates the value car xevery time through. A stop condition is when the iteration variable is empty and the return value is the sum.

, , . . - . , , ( ):

(define (find5 lst)
  (do ([x lst (rest x)]
       [found #f (or found (eq? 5 (first x)))])
    ((null? x) found)))

sum, or found. , first rest car cdr , . , .

(find5 '(1 2 3 4 6))

#f, . :

(find5 '(1 2 3 4 5 6))

#t.

do ?