44 lines
1 KiB
Text
44 lines
1 KiB
Text
# A Quick Tutorial
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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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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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A palindrome is a phrase which reads the same backward
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and forward.
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We first need a string to look at. Starting with something
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easy:
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```
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'anna
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```
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Looking in the Glossary, there is a `s:reverse` word for
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reversing a string. We can find `dup` to copy a value, and
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`s:eq?` to compare two strings. So testing:
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```
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'anna dup s:reverse s:eq?
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```
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This yields -1 (`TRUE`) as expected. So we can easily
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name it:
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```
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:palindrome dup s:reverse s:eq? ;
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```
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Naming uses the `:` prefix 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 (`;`) ending the definition. We can then use this:
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```
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'anna palindrome?
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```
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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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