retroforth/doc/html/chapters/techniques/characters.html
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<p><span class="h1">Working With Characters</span>
<br/><br/>
RETRO provides words for working with ASCII characters.
<br/><br/>
<span class="h2">Sigil</span>
<br/><br/>
Character constants are returned using the <span class="tt">$</span> sigil.
<br/><br/>
<span class="h2">Namespace</span>
<br/><br/>
Words operating on characters are in the <span class="tt">c:</span> namespace.
<br/><br/>
<span class="h2">Classification</span>
<br/><br/>
RETRO provides a number of words to determine if a character
fits into predefined groups.
<br/><br/>
The primary words for this are:
<br/><br/>
&bull; <span class="tt">c:consonant?</span><br/>
&bull; <span class="tt">c:digit?</span><br/>
&bull; <span class="tt">c:letter?</span><br/>
&bull; <span class="tt">c:lowercase?</span><br/>
&bull; <span class="tt">c:uppercase?</span><br/>
&bull; <span class="tt">c:visible?</span><br/>
&bull; <span class="tt">c:vowel?</span><br/>
&bull; <span class="tt">c:whitespace?</span><br/>
<br/><br/>
There are also corresponding "not" forms:
<br/><br/>
&bull; <span class="tt">c:-consonant?</span><br/>
&bull; <span class="tt">c:-digit?</span><br/>
&bull; <span class="tt">c:-lowercase?</span><br/>
&bull; <span class="tt">c:-uppercase?</span><br/>
&bull; <span class="tt">c:-visible?</span><br/>
&bull; <span class="tt">c:-vowel?</span><br/>
&bull; <span class="tt">c:-whitespace?</span><br/>
<br/><br/>
All of these take a character and return either a <span class="tt">TRUE</span> or
<span class="tt">FALSE</span> flag.
<br/><br/>
<span class="h2">Conversions</span>
<br/><br/>
A few words are provided to convert case. Each takes a character
and returns the modified character.
<br/><br/>
&bull; <span class="tt">c:to-lower</span><br/>
&bull; <span class="tt">c:to-number</span><br/>
&bull; <span class="tt">c:to-upper</span><br/>
&bull; <span class="tt">c:toggle-case</span><br/>
<br/><br/>
RETRO also has <span class="tt">c:to-string</span>, which takes a character and
creates a new temporary string with the character.
<br/><br/>
<span class="h2">I/O</span>
<br/><br/>
Characters can be displayed using <span class="tt">c:put</span>.
<br/><br/>
<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='char'>$a</span> c:put </span><br/>
<span class="tt">```</span></span><br/><br/>
With the default system on BSD, Linux, and macOS (and other
Unix style hosts), <span class="tt">c:get</span> is provided to read input. This
may be buffered, depending on the host.
</p>
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