re: lisp newbie here

Alex Mizrahi wrote:

> in kmrcl package you can find such implementations:
>
> (defun alist-plist (alist)
> (apply #'append (mapcar #'(lambda (x) (list (car x) (cdr x))) alist)))

Racket:

(flatten '((k . 2) (key . 3)))
=> '(k 2 key 3)

On 05/26/2012 03:01 PM, WJ wrote:
> Alex Mizrahi wrote:
>
>> in kmrcl package you can find such implementations:
>>
>> (defun alist-plist (alist)
>> (apply #'append (mapcar #'(lambda (x) (list (car x) (cdr x))) alist)))
>
> Racket:
>
> (flatten '((k . 2) (key . 3)))
> => '(k 2 key 3)
CL-USER> (defun alist->plist (alist)
(loop for (car . cdr) in alist
collect car
collect cdr))
ALIST-TO-PLIST
CL-USER> (alist->plist '((1 . 2) (3 . 4) (5 . 6)))
(1 2 3 4 5 6)
CL-USER>

The loop solution seems pretty clean and efficient to me.
This first one is dreadfull as it conses up two cons cells for each
alist element only to delete them afterward. Also it only works if the
alist size is less than half the largest number of arguments to a
function which means it is is not reliable is the alist has more than
500 elements or so.

A flatten that works on improper trees is interesting, however.