82 lines
3.8 KiB
HTML
82 lines
3.8 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>.</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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.text { color: #000; white-space: pre; background: #dedede; }
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.colon { color: #000; background: #dedede; }
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.note { color: #000; background: #dedede; }
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.str { color: #000; text-decoration: underline; background: #dedede; }
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.num { color: #000; background: #dedede; font-weight: bold; font-style: italic; }
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.fnum { color: #000; font-weight: bold; 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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.imm { color: #000; font-weight: bold; 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><br/><br/>
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Programming in Retro is all about creating words to solve
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the problem at hand. Words operate on data, which can be
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kept in memory or on the stack.
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<br/><br/>
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Let's look at this by solving a small problem: writing a
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word to determine if a string is a palindrome.
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<br/><br/>
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A palindrome is a phrase which reads the same backward
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and forward.
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<br/><br/>
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We first need a string to look at. Starting with something
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easy:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='str'>'anna</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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Looking in the Glossary, there is a <span class="tt">s:reverse</span> word for
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reversing a string. We can find <span class="tt">dup</span> to copy a value, and
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<span class="tt">s:eq?</span> to compare two strings. So testing:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='str'>'anna</span> <span class='prim'>dup</span> s:reverse s:eq? </span><br/>
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<span class="tt">```</span></span><br/><br/>
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This yields -1 (<span class="tt">TRUE</span>) as expected. So we can easily
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name it:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='colon'>:palindrome?</span> <span class='prim'>dup</span> s:reverse s:eq? <span class='imm'>;</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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Naming uses the <span class="tt">:</span> sigil to add a new word to the dictionary.
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The words that make up the definition are then placed, with a
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final word (<span class="tt">;</span>) ending the definition. We can then use this:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='str'>'anna</span> palindrome? </span><br/>
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<span class="tt">```</span></span><br/><br/>
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Once defined there is no difference between our new word and
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any of the words already provided by the Retro system.
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</p>
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</body></html>
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