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3.8 KiB
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63 lines
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3.8 KiB
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<title>CLiki: Issue APPLY-EXAMPLE-WRONG</title>
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<span class="hidden">CLiki - Issue APPLY-EXAMPLE-WRONG</span>
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<div id="content"><div id="content-area"><div id="article-title">Issue APPLY-EXAMPLE-WRONG</div><div id="article">This example for <a href="https://www.cliki.net/site/HyperSpec/Body/fun_apply.html" class="hyperspec">APPLY</a> is wrong, because it assumes particular behavior of <a href="https://www.cliki.net/site/HyperSpec/Body/fun_type-of.html" class="hyperspec">TYPE-OF</a>:
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<pre>
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(defun foo (size &rest keys &key double &allow-other-keys)
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(let ((v (apply #'make-array size :allow-other-keys t keys)))
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(if double (concatenate (type-of v) v v) v)))
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(foo 4 :initial-contents '(a b c d) :double t)
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=> #(A B C D A B C D)
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</pre>
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The call to FOO will signal an error if TYPE-OF returns a type containing the length (4). This causes a type conflict in CONCATENATE, because the new sequence length should be 8. If TYPE-OF returns a type without the length, then FOO will behave as shown above.<p>To get the intended effect, it could do something like one of these:<p><pre>
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(concatenate `(vector ,(array-element-type v) *) v v)
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(concatenate `(vector ,(array-element-type v) ,(* 2 size)) v v)
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</pre><p><hr>
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