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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.lang.scheme
Subject: Re: how to write append from primitives?
Message-ID: <1991May28.202106.23617@Think.COM>
Date: 28 May 91 20:21:06 GMT
References: <1650003@hpkslx.mayfield.HP.COM>
Sender: news@Think.COM
Reply-To: barmar@think.com
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 19

In article <1650003@hpkslx.mayfield.HP.COM> ted@hpkslx.mayfield.HP.COM (Ted Johnson) writes:
>How would one write append, using just car, cons, and cdr?

Here's a two-argument append.  The n-argument version is left as an
exercise for the reader:

(defun append (list1 list2)
  (if (null list1)
      list2
      (cons (car list1)
	    (append (cdr list1) list2))))

Unfortunately, this isn't tail recursive.  It could be made so without too
much work, but I don't feel like doing it at the moment.
-- 
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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