Sophie: sbcl-1.0.31-1mdv2010.0 i586

sbcl-1.0.31-1mdv2010.0.i586.rpm

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<h3 class="section">3.2 Components</h3>

<p><a name="index-component-11"></a><a name="index-system-12"></a><a name="index-system-designator-13"></a><a name="index-g_t_002asystem_002ddefinition_002dsearch_002dfunctions_002a-14"></a>
A <dfn>component</dfn> represents a source file or (recursively) a
collection of components.  A <dfn>system</dfn> is (roughly speaking) a
top-level component that can be found via <code>find-system</code>.

   <p>A <dfn>system designator</dfn> is a string or symbol and behaves just like
any other component name (including with regard to the case conversion
rules for component names).

<div class="defun">
&mdash; Function: <b>find-system</b><var> system-designator &amp;optional </var>(<var>error-p t</var>)<var><a name="index-find_002dsystem-15"></a></var><br>
<blockquote>
        <p>Given a system designator, <code>find-system</code> finds and returns a
system.  If no system is found, an error of type
<code>missing-component</code> is thrown, or <code>nil</code> is returned if
<code>error-p</code> is false.

        <p>To find and update systems, <code>find-system</code> funcalls each element
in the <code>*system-definition-search-functions*</code> list, expecting a
pathname to be returned.  The resulting pathname is loaded if either
of the following conditions is true:

          <ul>
<li>there is no system of that name in memory
<li>the file's last-modified time exceeds the last-modified time of the
  system in memory
</ul>

        <p>When system definitions are loaded from <samp><span class="file">.asd</span></samp> files, a new
scratch package is created for them to load into, so that different
systems do not overwrite each others operations.  The user may also
wish to (and is recommended to) include <code>defpackage</code> and
<code>in-package</code> forms in his system definition files, however, so
that they can be loaded manually if need be.

        <p>The default value of <code>*system-definition-search-functions*</code> is a
function that looks in each of the directories given by evaluating
members of <code>*central-registry*</code> for a file whose name is the
name of the system and whose type is <samp><span class="file">asd</span></samp>.  The first such file
is returned, whether or not it turns out to actually define the
appropriate system.  Hence, it is strongly advised to define a system
<var>foo</var> in the corresponding file <var>foo.asd</var>. 
</p></blockquote></div>

<ul class="menu">
<li><a accesskey="1" href="Common-attributes-of-components.html#Common-attributes-of-components">Common attributes of components</a>
<li><a accesskey="2" href="Pre_002ddefined-subclasses-of-component.html#Pre_002ddefined-subclasses-of-component">Pre-defined subclasses of component</a>
<li><a accesskey="3" href="Creating-new-component-types.html#Creating-new-component-types">Creating new component types</a>
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