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From: Joerg Mertens <joerg-mertens@t-online.de>
Newsgroups: comp.lang.lisp
Subject: Re: Faster remove-duplicates with sorted list.
Date: Fri, 21 Jun 2024 21:42:07 +0200
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Joerg Mertens <joerg-mertens@t-online.de> wrote:

>   (loop for element in list
>         for last-element-key = nil then element-key
>         for element-key = (funcall key element)
>         for result = nil then (funcall test element-key last-element-key)
>         unless result collect element))

This is clearer:

(defun uniquify-sorted-list (list &key (key #'identity) (test #'eql))
  (loop for element in list
        for element-key = (funcall key element)
            and last-element-key = nil then element-key
        for result = nil then (funcall test element-key last-element-key)
        unless result collect element))

I forgot that the loop way to step two clauses in parallel is to
combine them with an `and´.