Re: Wanted: mapcar() without nils

[Thierry Volpiatto]

Hi, you can use loop: (easier)

ELISP> (mapcar #'(lambda (x) (when (stringp x) x)) '("a" "b" "c" 1 2 "d" 3))
("a" "b" "c" nil nil "d" nil)

ELISP> (loop for i in '("a" "b" "c" 1 2 "d" 3) when (stringp i) collect i)
("a" "b" "c" "d")

Nordlöw <per.nordlow@gmail.com> writes:

> This is my mockup:
>
> (defun extract-elements (pred seq)
>   "Extract a copy of SEQ containing all elements fullfilling
> PRED."
>   (delq nil (mapcar `(lambda (elm) (when (,pred elm)) elm) seq)))
> ;; Use: (extract-elements 'symbolp '(a b 1 2)) => '(a b)
> ;; Use: (extract-elements 'numberp '(a b 1 2)) => '(1 2)
>
> But why does my test-cases return '(a b 1 2) all the time? The first
> should return (a b) and second (1 2).
> I have tried edebugging it but because mapcar is a builtin I didn't
> get any help that way.
>
> /Nordlöw
>

-- 
A + Thierry Volpiatto
Location: Saint-Cyr-Sur-Mer - France