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retroforth/doc/html/chapters/general/syntax.html
crc 5c52887aa8 fix #101: epub: chapter names are not rendered 
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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head>
<title>doc/book/general/syntax</title>
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</head><body>
<p><span class="h1">Syntax</span>
<br/><br/>
Retro has more syntax than a traditional Forth due to ideas
borrowed from ColorForth and some design decisions. This has
some useful traits, and helps to make the language more
consistent.
<br/><br/>
<span class="h2">Tokens</span>
<br/><br/>
Input is divided into a series of whitespace delimited tokens.
Each of these is then processed individually. There are no
parsing words in Retro.
<br/><br/>
Tokens may have a single character <strong>sigil</strong>, which Retro will
use to decide how to process the token.
<br/><br/>
<span class="h2">Sigils</span>
<br/><br/>
Sigils are single characters added to the start of a token
to guide the compiler. The use of these is a major way in
which Retro differs from traditional Forth.
<br/><br/>
When a token is passed to <span class="tt">interpret</span>, Retro first takes the
initial character and looks to see if there is a word that
matches this. If so, it will pass the rest of the token to
that word to handle.
<br/><br/>
In a traditional Forth, the interpret process is something
like:
<br/><br/>
<tt class='indentedcode'>get&nbsp;token</tt>
<tt class='indentedcode'>is&nbsp;token&nbsp;in&nbsp;the&nbsp;dictionary?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;yes:</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;is&nbsp;it&nbsp;immediate?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yes:&nbsp;call&nbsp;the&nbsp;word.</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;no:&nbsp;&nbsp;are&nbsp;we&nbsp;interpreting?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yes:&nbsp;call&nbsp;the&nbsp;word</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;no:&nbsp;&nbsp;compile&nbsp;a&nbsp;call&nbsp;to&nbsp;the&nbsp;word</tt>
<tt class='indentedcode'>&nbsp;&nbsp;no:</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;is&nbsp;it&nbsp;a&nbsp;number?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yes:&nbsp;are&nbsp;we&nbsp;interpreting?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yes:&nbsp;push&nbsp;the&nbsp;number&nbsp;to&nbsp;the&nbsp;stack</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;no:&nbsp;&nbsp;compile&nbsp;the&nbsp;number&nbsp;as&nbsp;a&nbsp;literal</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;no:&nbsp;&nbsp;report&nbsp;an&nbsp;error&nbsp;("not&nbsp;found")</tt>
<br/><br/>
In Retro, the interpret process is basically:
<br/><br/>
<tt class='indentedcode'>get&nbsp;token</tt>
<tt class='indentedcode'>does&nbsp;the&nbsp;first&nbsp;character&nbsp;match&nbsp;a&nbsp;`sigil:`&nbsp;word?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;yes:&nbsp;pass&nbsp;the&nbsp;token&nbsp;to&nbsp;the&nbsp;sigil&nbsp;handler</tt>
<tt class='indentedcode'>&nbsp;&nbsp;no:&nbsp;&nbsp;is&nbsp;token&nbsp;a&nbsp;word&nbsp;in&nbsp;the&nbsp;dictionary?</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yes:&nbsp;push&nbsp;the&nbsp;XT&nbsp;to&nbsp;the&nbsp;stack&nbsp;and&nbsp;call&nbsp;the</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;class&nbsp;handler</tt>
<tt class='indentedcode'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;no:&nbsp;&nbsp;report&nbsp;an&nbsp;error&nbsp;("not&nbsp;found")</tt>
<br/><br/>
All of the actual logic for how to deal with tokens is moved
to the individual sigil handlers, and the logic for handling
words is moved to word class handlers.
<br/><br/>
This means that sigils are used for a lot of things. Numbers?
Handled by a <span class="tt">#</span> sigil. Strings? Use the <span class="tt">'</span> sigil. Comments?
Use <span class="tt">(</span>. Making a new word? Use the <span class="tt">:</span> sigil.
<br/><br/>
The major sigils are:
<br/><br/>
<tt class='indentedcode'>|&nbsp;Sigil&nbsp;&nbsp;|&nbsp;Used&nbsp;For&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;------&nbsp;|&nbsp;-----------------------------&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;@&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Fetch&nbsp;from&nbsp;variable&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;!&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Store&nbsp;into&nbsp;variable&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;&amp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Pointer&nbsp;to&nbsp;named&nbsp;item&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;#&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Numbers&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;$&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;ASCII&nbsp;characters&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;'&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Strings&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;(&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Comments&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<tt class='indentedcode'>|&nbsp;:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;Define&nbsp;a&nbsp;word&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;|</tt>
<br/><br/>
The individual sigils will be covered in more detail in the
later chapters on working with different data types.
<br/><br/>
<span class="h2">Word Classes</span>
<br/><br/>
Word classes are words which take a pointer and do something
with it. These are covered in detail in their own chapter,
but essentially they decide <strong>how</strong> to execute or compile specific
types of words.
<br/><br/>
</p>
</body></html>
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