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<title>.</title>
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</head><body>
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<p><span class="h1">Syntax</span>
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<br/><br/>
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Retro has more syntax than a traditional Forth due to ideas
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borrowed from ColorForth and some design decisions. This has
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some useful traits, and helps to make the language more
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consistent.
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<br/><br/>
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<span class="h2">Tokens</span>
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<br/><br/>
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Input is divided into a series of whitespace delimited tokens.
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Each of these is then processed individually. There are no
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parsing words in Retro.
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<br/><br/>
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Tokens may have a single character <strong>sigil</strong>, which Retro will
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use to decide how to process the token.
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<br/><br/>
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<span class="h2">Sigils</span>
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<br/><br/>
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Sigils are single characters added to the start of a token
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to guide the compiler. The use of these is a major way in
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which Retro differs from traditional Forth.
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<br/><br/>
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When a token is passed to <span class="tt">interpret</span>, Retro first takes the
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initial character and looks to see if there is a word that
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matches this. If so, it will pass the rest of the token to
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that word to handle.
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<br/><br/>
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In a traditional Forth, the interpret process is something
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like:
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<br/><br/>
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<tt class='indentedcode'>get token</tt>
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<tt class='indentedcode'>is token in the dictionary?</tt>
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<tt class='indentedcode'> yes:</tt>
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<tt class='indentedcode'> is it immediate?</tt>
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<tt class='indentedcode'> yes: call the word.</tt>
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<tt class='indentedcode'> no: are we interpreting?</tt>
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<tt class='indentedcode'> yes: call the word</tt>
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<tt class='indentedcode'> no: compile a call to the word</tt>
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<tt class='indentedcode'> no:</tt>
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<tt class='indentedcode'> is it a number?</tt>
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<tt class='indentedcode'> yes: are we interpreting?</tt>
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<tt class='indentedcode'> yes: push the number to the stack</tt>
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<tt class='indentedcode'> no: compile the number as a literal</tt>
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<tt class='indentedcode'> no: report an error ("not found")</tt>
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<br/><br/>
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In Retro, the interpret process is basically:
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<br/><br/>
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<tt class='indentedcode'>get token</tt>
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<tt class='indentedcode'>does the first character match a `sigil:` word?</tt>
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<tt class='indentedcode'> yes: pass the token to the sigil handler</tt>
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<tt class='indentedcode'> no: is token a word in the dictionary?</tt>
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<tt class='indentedcode'> yes: push the XT to the stack and call the</tt>
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<tt class='indentedcode'> class handler</tt>
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<tt class='indentedcode'> no: report an error ("not found")</tt>
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<br/><br/>
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All of the actual logic for how to deal with tokens is moved
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to the individual sigil handlers, and the logic for handling
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words is moved to word class handlers.
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<br/><br/>
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This means that sigils are used for a lot of things. Numbers?
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Handled by a <span class="tt">#</span> sigil. Strings? Use the <span class="tt">'</span> sigil. Comments?
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Use <span class="tt">(</span>. Making a new word? Use the <span class="tt">:</span> sigil.
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<br/><br/>
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The major sigils are:
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<tt class='indentedcode'>| Sigil | Used For |</tt>
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<tt class='indentedcode'>| ------ | ----------------------------- |</tt>
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<tt class='indentedcode'>| @ | Fetch from variable |</tt>
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<tt class='indentedcode'>| ! | Store into variable |</tt>
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<tt class='indentedcode'>| & | Pointer to named item |</tt>
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<tt class='indentedcode'>| # | Numbers |</tt>
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<tt class='indentedcode'>| $ | ASCII characters |</tt>
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<tt class='indentedcode'>| ' | Strings |</tt>
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<tt class='indentedcode'>| ( | Comments |</tt>
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<tt class='indentedcode'>| : | Define a word |</tt>
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<br/><br/>
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The individual sigils will be covered in more detail in the
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later chapters on working with different data types.
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<br/><br/>
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<br/><br/>
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Word classes are words which take a pointer and do something
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with it. These are covered in detail in their own chapter,
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but essentially they decide <strong>how</strong> to execute or compile specific
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types of words.
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<br/><br/>
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</p>
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</body></html>
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