(define traverse (lambda (combine do seed) 
                   (lambda (x) 
                     (cond ((eq? x '()) seed)
                           (#t (combine (do (car x)) 
                                         ((traverse combine do seed) (cdr x))))))))
(define mapsquare (traverse cons (lambda (x) (* x x)) '()))
(mapsquare '(1 -2 3))

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