80 lines
4 KiB
HTML
80 lines
4 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head>
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<title>doc/book/techniques/pointers</title>
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<style type="text/css">
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* { color: #000; background: #fff; max-width: 700px; }
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tt, pre { background: #dedede; color: #111; font-family: monospace;
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</head><body>
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<p><span class="h1">Working With Pointers</span>
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<br/><br/>
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<span class="h2">Sigil</span>
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<br/><br/>
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Pointers are returned by the <span class="tt">&</span> sigil.
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<br/><br/>
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<span class="h2">Examples</span>
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='str'>'Base</span> var </span><br/>
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<span class="tt"><span class='ptr'>&Base</span> <span class='prim'>fetch</span> </span><br/>
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<span class="tt"><span class='num'>#10</span> <span class='ptr'>&Base</span> <span class='prim'>store</span> </span><br/>
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<span class="tt"> </span><br/>
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<span class="tt"><span class='num'>#10</span> <span class='ptr'>&n:inc</span> <span class='prim'>call</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Notes</span>
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<br/><br/>
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The use of <span class="tt">&</span> to get a pointer to a data structure (with a
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word class of <span class="tt">class:data</span>) is not required. I like to use it
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anyway as it makes my intent a little clearer.
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<br/><br/>
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Pointers are useful with combinators. Consider:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='colon'>:abs</span> <span class='prim'>dup</span> n:negative? <span class='imm'>[</span> n:negate <span class='imm'>]</span> <span class='prim'>if</span> <span class='imm'>;</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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Since the target quote body is a single word, it is more
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efficient to use a pointer instead:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='colon'>:abs</span> <span class='prim'>dup</span> n:negative? <span class='ptr'>&n:negate</span> <span class='prim'>if</span> <span class='imm'>;</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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The advantages are speed (saves a level of call/return by
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avoiding the quotation) and size (for the same reason).
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This may be less readable though, so consider the balance
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of performance to readability when using this approach.
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</p>
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</body></html>
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