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    <section class="sect1" title="Enumeration types" epub:type="subchapter" id="Enumerations">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both">Enumeration types</h2>
          </div>
        </div>
      </div>
      <p>An enumeration type is a set of named atomic enumeration values
that are distinct from other values.  You define the type
using <code class="literal">define-enum</code>, and you reference enumeration values
using colon notation:
</p>
      <pre class="screen">(define-enum colors (red blue green))
(define favorite-color colors:green)
</pre>
      <p>Displaying an enum just prints the enum name,
but readable output using <code class="literal">write</code> (or the <code class="literal">~s</code> <code class="literal">format</code>
specifier) prepends the type name:
</p>
      <pre class="screen">(format "~a" favorite-color) ⇒ "green"
(format "~s" favorite-color) ⇒ "colors:green"
</pre>
      <p>The static <code class="literal">values</code> method returns a Java array of the enumeration
values, in declaration order, while <code class="literal">ordinal</code> yields the index
of an enumeration value:
</p>
      <pre class="screen">(colors:values) ⇒ [red blue green]
((colors:values) 1) ⇒ blue
(favorite-color:ordinal) ⇒ 2
</pre>
      <p>If you invoke the enumeration type as a function,
it will map the name (as a string) to the corresponding value.
(This uses the <code class="literal">valueOf</code> method.)
</p>
      <pre class="screen">(colors "red") ⇒ red
(colors "RED") ⇒ throws IllegalArgumentException
(eq? favorite-color (colors:valueOf "green")) ⇒ #t
</pre>
      <p>Kawa enumerations are based on Java enumerations.
Thus the above is similar to a Java5 <code class="literal">enum</code> declaration,
and the type <code class="literal">colors</code> above extends <code class="literal">java.lang.Enum</code>.
</p>
      <p class="synopsis" kind="Syntax"><span class="kind">Syntax</span><span class="ignore">: </span><a id="idm139667871660096" class="indexterm"/> <code class="function">define-enum</code> <em class="replaceable"><code>enum-type-name</code></em> <em class="replaceable"><code><em class="replaceable"><code>option-pair</code></em></code></em><em class="replaceable"><code>...</code></em> <em class="replaceable"><code><span class="bold"><strong>(</strong></span></code></em><em class="replaceable"><code>enum-value-name</code></em> <em class="replaceable"><code>...</code></em><em class="replaceable"><code><span class="bold"><strong>)</strong></span></code></em> <em class="replaceable"><code><em class="replaceable"><code>field-or-method-decl</code></em></code></em><em class="replaceable"><code>...</code></em></p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>This declares a new enumeration type <em class="replaceable"><code>enum-type-name</code></em>,
whose enumerations values are the <em class="replaceable"><code>enum-value-name</code></em> list.
You can specify extra options and members using
<em class="replaceable"><code>option-pair</code></em> and <em class="replaceable"><code>field-or-method-decl</code></em>,
which are as in <code class="literal">define-simple-class</code>.
(The <em class="replaceable"><code>define-enum</code></em> syntax is similar to a
<code class="literal">define-simple-class</code> that extends <code class="literal">java.lang.Enum</code>.)
</p>
        </blockquote>
      </div>
      <p>(Note that R6RS has a separate Enumerations library <code class="literal">(rnrs enum)</code>.
Unfortunately, this is not compatible with standard Java enums.
R6RS enums are simple symbols, which means you cannot distinguish
two enum values from different enumeration types if they have the
same value, nor from a vanilla symbol.  That makes them less useful.)
</p>
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