81 lines
3.2 KiB
HTML
81 lines
3.2 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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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/errors</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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white-space: pre; display: block; width: 100%; }
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.indentedcode { margin-left: 2em; margin-right: 2em; }
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.codeblock {
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background: #dedede; color: #111; font-family: monospace;
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box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
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padding: 7px;
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display: block;
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}
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.indentedlist { margin-left: 2em; color: #000; }
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span { white-space: pre; }
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.colon { color: #000; background: #dedede; }
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.ptr { color: #000; font-weight: bold; background: #dedede; }
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.fetch { color: #000; font-style: italic; background: #dedede; }
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.store { color: #000; font-style: italic; background: #dedede; }
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.char { color: #000; background: #dedede; }
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.inst { color: #000; background: #dedede; }
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.defer { color: #000; background: #dedede; }
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.prim { color: #000; font-weight: bolder; background: #dedede; }
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.tt { white-space: pre; font-family: monospace; background: #dedede; }
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.h1, .h2, .h3, .h4 { white-space: normal; }
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.h1 { font-size: 125%; }
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.h2 { font-size: 120%; }
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.h3 { font-size: 115%; }
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.h4 { font-size: 110%; }
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.hr { display: block; height: 2px; background: #000000; }
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</style>
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</head><body>
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<p><span class="h1">Errors</span>
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<br/><br/>
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RETRO does only minimal error checking.
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<br/><br/>
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<span class="h2">Non-Fatal</span>
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<br/><br/>
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A non-fatal error will be reported on <strong>word not found</strong> during
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interactive or compile time. Note that this only applies to
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calls: if you try to get a pointer to an undefined word, the
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returned pointer will be zero.
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<br/><br/>
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<span class="h2">Fatal</span>
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<br/><br/>
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A number of conditions are known to cause fatal errors. The
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main ones are stack overflow, stack underflow, and division
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by zero.
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<br/><br/>
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On these, RETRO will generally exit. For stack depth issues,
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the VM will attempt to display an error prior to exiting.
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<br/><br/>
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In some cases, the VM may get stuck in an endless loop. If this
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occurs, try using CTRL+C to kill the process, or kill it using
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whatever means your host system provides.
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<br/><br/>
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<span class="h2">Rationale</span>
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<br/><br/>
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Error checks are useful, but slow - especially on a minimal
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system like RETRO. The overhead of doing depth or other checks
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adds up quickly.
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<br/><br/>
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As an example, adding a depth check to <span class="tt">drop</span> increases the
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time to use it 250,000 times in a loop from 0.16 seconds to
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1.69 seconds.
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<br/><br/>
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</p>
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</body></html>
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