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copied!<p>Let's step through an example; maybe that will help. :-) For simplicity, I'm just going to use <code>list</code> as the collector/continuation, which will just return a list with the arguments to the continuation.</p> <pre><code>(multirember&co 'foo '(foo bar) list) </code></pre> <p>At the start,</p> <pre><code>a = 'foo lat = '(foo bar) col = list </code></pre> <p>At the first iteration, the <code>(eq? (car lat) a)</code> condition matches, since <code>lat</code> is not empty, and the first element of <code>lat</code> is <code>'foo</code>. This sets up the next recursion to <code>multirember&co</code> thusly:</p> <pre><code>a = 'foo lat = '(bar) col = (lambda (newlat seen) (list newlat (cons 'foo seen)) </code></pre> <p>At the next iteration, the <code>else</code> matches: since <code>lat</code> is not empty, and the first element of <code>lat</code> is <code>'bar</code> (and not <code>'foo</code>). Thus, for the next recursion, we then have:</p> <pre><code>a = 'foo lat = '() col = (lambda (newlat seen) ((lambda (newlat seen) (list newlat (cons 'foo seen))) (cons 'bar newlat) seen)) </code></pre> <p>For ease of human reading (and avoid confusion), we can rename the parameters (due to lexical scoping), without any change to the program's semantics:</p> <pre><code>col = (lambda (newlat1 seen1) ((lambda (newlat2 seen2) (list newlat2 (cons 'foo seen2))) (cons 'bar newlat1) seen1)) </code></pre> <p>Finally, the <code>(null? lat)</code> clause matches, since <code>lat</code> is now empty. So we call</p> <pre><code>(col '() '()) </code></pre> <p>which expands to:</p> <pre><code>((lambda (newlat1 seen1) ((lambda (newlat2 seen2) (list newlat2 (cons 'foo seen2))) (cons 'bar newlat1) seen1)) '() '()) </code></pre> <p>which (when substituting <code>newlat1 = '()</code> and <code>seen1 = '()</code>) becomes</p> <pre><code>((lambda (newlat2 seen2) (list newlat2 (cons 'foo seen2))) (cons 'bar '()) '()) </code></pre> <p>or (evaluating <code>(cons 'bar '())</code>)</p> <pre><code>((lambda (newlat2 seen2) (list newlat2 (cons 'foo seen2))) '(bar) '()) </code></pre> <p>Now, substituting the values <code>newlat2 = '(bar)</code> and <code>seen2 = '()</code>, we get</p> <pre><code>(list '(bar) (cons 'foo '())) </code></pre> <p>or, in other words,</p> <pre><code>(list '(bar) '(foo)) </code></pre> <p>to give our final result of</p> <pre><code>'((bar) (foo)) </code></pre>

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