Re: which articles are sold?

Lieven Marchand wrote:

if we have this list:
(a <sold> b c d <sold> e f g <sold>)
that shows that article a, d and g are sold and the rest are not how
can we put all the sold articles in one list:
(a d g)

 
More homework?
 
(loop for (first next) on '(a <sold> b c d <sold> e f g <sold>)
      when (eql next '<sold>)
      collect first)

Scheme:

(define items '(a <sold> b c d <sold> e f g <sold> h i <sold>))

(filter-map
  (lambda(x y) (and (eq? '<sold> y) x))
  items
  (cdr items))

 ===>
(a d g i)