Question

(define myList ‘(a b c d e a f))

how can i return a list of all the occurrences of ‘a. in this case the returned value is ‘(a a)

Answer 1

You can simply iterate your list with a result list, and cons the searched element whenever you find a match:

racket@> (define (occurrences list elem)
           (define (iter list result)
             (cond ((null? list) result)
                   ((equal? (car list) elem)
                    (iter (cdr list) (cons elem result)))
                   (else (iter (cdr list) result))))
           (iter list '()))
racket@> (occurrences '(1 2 3) 1)
'(1)
racket@> (occurrences '(a b c d e a f) 'a)
'(a a)
racket@> 

By the way, I wrote this in Racket but it should work in any Scheme dialects/implementations.