(define (tree-walk walker proc tree) (walker (lambda (elt) (if (list? #?=elt) (tree-walk walker proc elt) (proc elt))) tree)) (define (numbers-only-for-tree walker) (lambda (proc lis) (walker proc #?=(my-filter (lambda (x) (or (number? x) …

(define (my-length lis) (define (loop a n) (if (null? a) n (loop (cdr a) (+ 1 n)))) (loop lis 0)) (define (my-length lis) (if (null? lis) 0 (+ 1 (my-length (cdr lis))))) (my-length '(1 2 (4 5) 3)) (define (my-filter pred lis) (define (loop…