I think you are looking for something like this:
#lang racket
(require test-engine/racket-tests)
(define (remove-empty-lists lst)
(cond
[(null? lst) '()] ; Check for end of list
[(null? (first lst)) (remove-empty-lists (rest lst))] ; Skip null
sublist
[(not (list? (first lst))) ; Leave non-lists alone
(cons (first lst) (remove-empty-lists (rest lst)))]
[else ; Process the sublists recursively
(cons (remove-empty-lists (first lst))
(remove-empty-lists (rest lst)))]))
(check-expect (remove-empty-lists '()) '())
(check-expect (remove-empty-lists '(a)) '(a))
(check-expect (remove-empty-lists '(a b c)) '(a b c))
(check-expect (remove-empty-lists '(())) '())
(check-expect (remove-empty-lists '(() a)) '(a))
(check-expect (remove-empty-lists '(a ())) '(a))
(check-expect (remove-empty-lists '(a (b () c) d)) '(a (b c) d))
(check-expect (remove-empty-lists '((a) (b c) () (e () f (g ())) h (() i
j)))
'((a) (b c) (e f (g)) h (i j)))
(test)
Justin
On Tue, Nov 15, 2016 at 10:52 PM, <[email protected]> wrote:
> Hi,
>
> I have a list of sublists. Some of the sublists are empty.
> The list should be processed recursevly and the resulting
> list should no longer contain empty sublists.
>
> The code I have so far looks like:
>
> (define (step-through-list lst)
> (if (empty? lst)
> lst
> (cons (process-sublist (car lst)) (step-through-list (cdr lst)))
>
> ....but "car" would feed empty sublists to process-sublist as any other
> sublist. How can I "silently" skip empty sublists and even get out of
> the recursion without harm (if the last sublist is empty) without
> switching to iteration?
> Is there something like "car-not-empty" ? ;)
> Or do I oversee the obvious here...? ;)))
>
> Thank you vary much for any help in advance!
> Cheers
> Meino
>
>
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