2021-01-21 13:40:28 +01:00
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</head><body>
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2022-06-03 12:41:52 +02:00
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<p><br/><br/>
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2021-05-17 19:04:42 +02:00
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Programming in Retro is all about creating words to solve
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2021-01-21 13:40:28 +01:00
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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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2021-03-30 13:58:25 +02:00
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Naming uses the <span class="tt">:</span> sigil to add a new word to the dictionary.
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2021-01-21 13:40:28 +01:00
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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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2021-05-17 19:04:42 +02:00
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any of the words already provided by the Retro system.
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2021-01-21 13:40:28 +01:00
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</p>
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</body></html>
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