Re: scheme-question about unnesting list

[David Nalesnik]

Hi Harm,

On Fri, Apr 10, 2015 at 7:28 AM, Thomas Morley <address@hidden> wrote:

Hi,

consider the following list:

(define ls
  (list
   "a"
   (list
     (cons 'x "xx")
     (cons 'y "yy")
     (list 1 2 3))
   (cons 'z "zz")))

I want to unnest it one level.
It can be done with the procedure 'unnest-list-one-lvl', which I
defined for that purpose:

(define (unnest-list-one-lvl l)
  (append-map
    (lambda (e)
      (if (list? e)
          e
          (list e)))
    l))

(unnest-list-one-lvl ls)

-> ("a" (x . "xx") (y . "yy") (1 2 3) (z . "zz"))


Question:
Is there a better, easier way?

What's wrong with the way you're doing it?

I mean, you could do something like this:

 (define (unnest-a-level ls)

   (let loop ((ls ls) (result '()))

     (cond

      ((null? ls) result)

      ((list? (car ls)) (loop (cdr ls) (append result (car ls))))

      (else (loop (cdr ls) (append result (list (car ls))))))))

but it's not as concise!

DN