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Re: Wanted: mapcar() without nils

From: Nordlöw
Subject: Re: Wanted: mapcar() without nils
Date: Sat, 13 Jun 2009 11:24:37 -0700 (PDT)
User-agent: G2/1.0

This is my mockup:

(defun extract-elements (pred seq)
  "Extract a copy of SEQ containing all elements fullfilling
  (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.


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