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    <title>Unicode character classes and conversions</title>
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    <section class="sect1" title="Unicode character classes and conversions" epub:type="subchapter" id="Unicode">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both">Unicode character classes and conversions</h2>
          </div>
        </div>
      </div>
      <p>Some of the procedures that operate on characters or strings ignore the
difference between upper case and lower case.  These procedures have
<code class="literal">-ci</code> (for “case insensitive”) embedded in their names.
</p>
      <section class="sect2" title="Characters" epub:type="division" id="idm139667874766096">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title">Characters</h3>
            </div>
          </div>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874765024" class="indexterm"/> <code class="function">char-upcase</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874762064" class="indexterm"/> <code class="function">char-downcase</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874759104" class="indexterm"/> <code class="function">char-titlecase</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874756144" class="indexterm"/> <code class="function">char-foldcase</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p>These procedures take a character argument and return a character
result.
</p>
            <p>If the argument is an upper–case or title–case character, and if there
is a single character that is its lower–case form, then
<code class="literal">char-downcase</code> returns that character.
</p>
            <p>If the argument is a lower–case or title–case character, and there is
a single character that is its upper–case form, then <code class="literal">char-upcase</code>
returns that character.
</p>
            <p>If the argument is a lower–case or upper–case character, and there is
a single character that is its title–case form, then
<code class="literal">char-titlecase</code> returns that character.
</p>
            <p>If the argument is not a title–case character and there is no single
character that is its title–case form, then <code class="literal">char-titlecase</code>
returns the upper–case form of the argument.
</p>
            <p>Finally, if the character has a case–folded character, then
<code class="literal">char-foldcase</code> returns that character.  Otherwise the character
returned is the same as the argument.
</p>
            <p>For Turkic characters <code class="literal">#\x130</code> and <code class="literal">#\x131</code>,
<code class="literal">char-foldcase</code> behaves as the identity function; otherwise
<code class="literal">char-foldcase</code> is the same as <code class="literal">char-downcase</code> composed with
<code class="literal">char-upcase</code>.
</p>
            <pre class="screen">(char-upcase #\i)               ⇒  #\I
(char-downcase #\i)             ⇒  #\i
(char-titlecase #\i)            ⇒  #\I
(char-foldcase #\i)             ⇒  #\i

(char-upcase #\ß)               ⇒  #\ß
(char-downcase #\ß)             ⇒  #\ß
(char-titlecase #\ß)            ⇒  #\ß
(char-foldcase #\ß)             ⇒  #\ß

(char-upcase #\Σ)               ⇒  #\Σ
(char-downcase #\Σ)             ⇒  #\σ
(char-titlecase #\Σ)            ⇒  #\Σ
(char-foldcase #\Σ)             ⇒  #\σ

(char-upcase #\ς)               ⇒  #\Σ
(char-downcase #\ς)             ⇒  #\ς
(char-titlecase #\ς)            ⇒  #\Σ
(char-foldcase #\ς)             ⇒  #\σ
</pre>
            <div class="blockquote">
              <blockquote class="blockquote">
                <p><span class="emphasis"><em>Note:</em></span> <code class="literal">char-titlecase</code> does not always return a title–case
character.
</p>
              </blockquote>
            </div>
            <div class="blockquote">
              <blockquote class="blockquote">
                <p><span class="emphasis"><em>Note:</em></span> These procedures are consistent with Unicode’s
locale–independent mappings from scalar values to scalar values for
upcase, downcase, titlecase, and case–folding operations.  These
mappings can be extracted from <code class="filename">UnicodeData.txt</code> and
<code class="filename">CaseFolding.txt</code> from the Unicode Consortium, ignoring Turkic
mappings in the latter.
</p>
                <p>Note that these character–based procedures are an incomplete
approximation to case conversion, even ignoring the user’s locale.  In
general, case mappings require the context of a string, both in
arguments and in result.  The <code class="literal">string-upcase</code>,
<code class="literal">string-downcase</code>, <code class="literal">string-titlecase</code>, and
<code class="literal">string-foldcase</code> procedures perform more general case conversion.
</p>
              </blockquote>
            </div>
          </blockquote>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874736480" class="indexterm"/> <code class="function">char-ci=?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>1</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>2</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>3</sub></code></em> <em class="replaceable"><code>…</code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874730864" class="indexterm"/> <code class="function">char-ci&lt;?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>1</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>2</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>3</sub></code></em> <em class="replaceable"><code>…</code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874725248" class="indexterm"/> <code class="function">char-ci&gt;?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>1</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>2</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>3</sub></code></em> <em class="replaceable"><code>…</code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874719632" class="indexterm"/> <code class="function">char-ci&lt;=?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>1</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>2</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>3</sub></code></em> <em class="replaceable"><code>…</code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874714016" class="indexterm"/> <code class="function">char-ci&gt;=?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>1</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>2</sub></code></em> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em><em class="replaceable"><code><sub>3</sub></code></em> <em class="replaceable"><code>…</code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p>These procedures are similar to <code class="literal">char=?</code>, etc., but operate on the
case–folded versions of the characters.
</p>
            <pre class="screen">(char-ci&lt;? #\z #\Z)             ⇒ #f
(char-ci=? #\z #\Z)             ⇒ #f
(char-ci=? #\ς #\σ)             ⇒ #t
</pre>
          </blockquote>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874706736" class="indexterm"/> <code class="function">char-alphabetic?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874703776" class="indexterm"/> <code class="function">char-numeric?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874700816" class="indexterm"/> <code class="function">char-whitespace?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874697856" class="indexterm"/> <code class="function">char-upper-case?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874694896" class="indexterm"/> <code class="function">char-lower-case?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874691936" class="indexterm"/> <code class="function">char-title-case?</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p>These procedures return <code class="literal">#t</code> if their arguments are alphabetic,
numeric, whitespace, upper–case, lower–case, or title–case
characters, respectively; otherwise they return <code class="literal">#f</code>.
</p>
            <p>A character is alphabetic if it has the Unicode “Alphabetic” property.
A character is numeric if it has the Unicode “Numeric” property.  A
character is whitespace if has the Unicode “White_Space” property.  A
character is upper case if it has the Unicode “Uppercase” property,
lower case if it has the “Lowercase” property, and title case if it is
in the Lt general category.
</p>
            <pre class="screen">(char-alphabetic? #\a)          ⇒  #t
(char-numeric? #\1)             ⇒  #t
(char-whitespace? #\space)      ⇒  #t
(char-whitespace? #\x00A0)      ⇒  #t
(char-upper-case? #\Σ)          ⇒  #t
(char-lower-case? #\σ)          ⇒  #t
(char-lower-case? #\x00AA)      ⇒  #t
(char-title-case? #\I)          ⇒  #f
(char-title-case? #\x01C5)      ⇒  #t
</pre>
          </blockquote>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874685344" class="indexterm"/> <code class="function">char-general-category</code> <em class="replaceable"><code><em class="replaceable"><code>char</code></em></code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p>Return a symbol representing the Unicode general category of
<em class="replaceable"><code>char</code></em>, one of <code class="literal">Lu</code>, <code class="literal">Ll</code>, <code class="literal">Lt</code>, <code class="literal">Lm</code>,
<code class="literal">Lo</code>, <code class="literal">Mn</code>, <code class="literal">Mc</code>, <code class="literal">Me</code>, <code class="literal">Nd</code>, <code class="literal">Nl</code>,
<code class="literal">No</code>, <code class="literal">Ps</code>, <code class="literal">Pe</code>, <code class="literal">Pi</code>, <code class="literal">Pf</code>, <code class="literal">Pd</code>,
<code class="literal">Pc</code>, <code class="literal">Po</code>, <code class="literal">Sc</code>, <code class="literal">Sm</code>, <code class="literal">Sk</code>, <code class="literal">So</code>,
<code class="literal">Zs</code>, <code class="literal">Zp</code>, <code class="literal">Zl</code>, <code class="literal">Cc</code>, <code class="literal">Cf</code>, <code class="literal">Cs</code>,
<code class="literal">Co</code>, or <code class="literal">Cn</code>.
</p>
            <pre class="screen">(char-general-category #\a)         ⇒ Ll
(char-general-category #\space)     ⇒ Zs
(char-general-category #\x10FFFF)   ⇒ Cn  
</pre>
          </blockquote>
        </div>
      </section>
      <section class="sect2" title="Deprecated in-place case modification" epub:type="division" id="idm139667874668368">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title">Deprecated in-place case modification</h3>
            </div>
          </div>
        </div>
        <p>The following functions are deprecated; they really don’t
and cannot do the right thing, because in some languages
upper and lower case can use different number of characters.
</p>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874666400" class="indexterm"/> <code class="function">string-upcase!</code> <em class="replaceable"><code>str</code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p><span class="emphasis"><em>Deprecated:</em></span> Destructively modify <em class="replaceable"><code>str</code></em>, replacing the letters
by their upper-case equivalents.
</p>
          </blockquote>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874662304" class="indexterm"/> <code class="function">string-downcase!</code> <em class="replaceable"><code>str</code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p><span class="emphasis"><em>Deprecated:</em></span> Destructively modify <em class="replaceable"><code>str</code></em>, replacing the letters
by their upper-lower equivalents.
</p>
          </blockquote>
        </div>
        <p class="synopsis" kind="Procedure"><span class="kind">Procedure</span><span class="ignore">: </span><a id="idm139667874658208" class="indexterm"/> <code class="function">string-capitalize!</code> <em class="replaceable"><code>str</code></em></p>
        <div class="blockquote">
          <blockquote class="blockquote">
            <p><span class="emphasis"><em>Deprecated:</em></span> Destructively modify <em class="replaceable"><code>str</code></em>, such that the letters that start a new word
are replaced by their title-case equivalents, while non-initial letters
are replaced by their lower-case equivalents.
</p>
          </blockquote>
        </div>
      </section>
    </section>
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