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    <title>Evaluating Scheme expressions from Java</title>
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    <section class="sect1" title="Evaluating Scheme expressions from Java" epub:type="subchapter" id="Evaluating-Scheme-expressions-from-Java">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both">Evaluating Scheme expressions from Java</h2>
          </div>
        </div>
      </div>
      <p>The following methods are recommended if you need to evaluate a
Scheme expression from a Java method.
(Some details (such as the ‘<code class="literal">throws</code>’ lists) may change.)
</p>
      <p class="synopsis" kind="Static method"><span class="kind">Static method</span><span class="ignore">: </span><a id="idm139667870741808" class="indexterm"/> <span class="returnvalue">void</span> <code class="function">Scheme.registerEnvironment</code> ()</p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Initializes the Scheme environment.  Maybe needed if you
try to load a module compiled from a Scheme source file.
</p>
        </blockquote>
      </div>
      <p class="synopsis" kind="Static method"><span class="kind">Static method</span><span class="ignore">: </span><a id="idm139667870738128" class="indexterm"/> <span class="returnvalue">Object</span> <code class="function">Scheme.eval</code> (<span class="type">InPort</span> <em class="replaceable"><code><em class="replaceable"><code>port</code></em></code></em>, <span class="type">Environment</span> <em class="replaceable"><code><em class="replaceable"><code>env</code></em></code></em>)</p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Read expressions from <em class="replaceable"><code>port</code></em>, and evaluate them in the
<em class="replaceable"><code>env</code></em> environment, until end-of-file is reached.
Return the value of the last expression,
or <code class="literal">Interpreter.voidObject</code> if there is no expression.
</p>
        </blockquote>
      </div>
      <p class="synopsis" kind="Static method"><span class="kind">Static method</span><span class="ignore">: </span><a id="idm139667870731264" class="indexterm"/> <span class="returnvalue">Object</span> <code class="function">Scheme.eval</code> (<span class="type">String</span> <em class="replaceable"><code><em class="replaceable"><code>string</code></em></code></em>, <span class="type">Environment</span> <em class="replaceable"><code><em class="replaceable"><code>env</code></em></code></em>)</p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>Read expressions from <em class="replaceable"><code>string</code></em>, and evaluate them in the
<em class="replaceable"><code>env</code></em> environment, until the end of the string is reached.
Return the value of the last expression,
or <code class="literal">Interpreter.voidObject</code> if there is no expression.
</p>
        </blockquote>
      </div>
      <p class="synopsis" kind="Static method"><span class="kind">Static method</span><span class="ignore">: </span><a id="idm139667870724448" class="indexterm"/> <span class="returnvalue">Object</span> <code class="function">Scheme.eval</code> (<span class="type">Object</span> <em class="replaceable"><code><em class="replaceable"><code>sexpr</code></em></code></em>, <span class="type">Environment</span> <em class="replaceable"><code><em class="replaceable"><code>env</code></em></code></em>)</p>
      <div class="blockquote">
        <blockquote class="blockquote">
          <p>The <em class="replaceable"><code>sexpr</code></em> is an S-expression (as may be returned by <code class="literal">read</code>).
Evaluate it in the <em class="replaceable"><code>env</code></em> environment, and return the result.
</p>
        </blockquote>
      </div>
      <p>For the <code class="literal">Environment</code> in most cases you could use
‘<code class="literal">Environment.current()</code>’.  Before you start, you
need to initialize the global environment,
which you can do with
</p>
      <pre class="screen">Environment.setCurrent(new Scheme().getEnvironment());
</pre>
      <p>Alternatively, rather than setting the global environment,
you can use this style:
</p>
      <pre class="screen">Scheme scm = new Scheme();
Object x = scm.eval("(+ 3 2)");
System.out.println(x);
</pre>
      <section class="sect2" title="Using javax.script portable Java scripting" epub:type="division" id="idm139667870715120">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title">Using <code class="literal">javax.script</code> portable Java scripting</h3>
            </div>
          </div>
        </div>
        <p>Kawa also supports the standard
<a class="ulink" href="http://docs.oracle.com/javase/8/docs/api/javax/script/package-summary.html" target="_top"><code class="literal">javax.script</code></a> API.
The main advantage of this API is if you want your users to be able to choose
between multiple scripting languages.  That way you can support Kawa
without Kawa-specific programming.
</p>
        <p>For example the standard JDK tool <a class="ulink" href="http://docs.oracle.com/javase/8/docs/technotes/tools/unix/jrunscript.html" target="_top">jrunscript</a> provides a
read-eval-print-loop for any language that implements the  <code class="literal">javax.script</code>
API.  It knows nothing about Kawa but can still use it:
</p>
        <pre class="screen">$ jrunscript -cp kawa.jar -l scheme
scheme&gt; (cadr '(3 4 5))
4
</pre>
        <p>(Of course the <code class="literal">jrunscript</code> REPL isn’t as  nice as the one that
Kawa provides.  For example the latter can handle multi-line inputs.)
</p>
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