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<head><title>needsPackage -- load a package if not already loaded</title>
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<div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_packages.html" title="">packages</a> > <a href="_needs__Package.html" title="load a package if not already loaded">needsPackage</a></div>
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<div><h1>needsPackage -- load a package if not already loaded</h1>
<div class="single"><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>needsPackage "PACKAGENAME"</tt></div>
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<li><div class="single">Inputs:<ul><li><span><tt>PACKAGENAME</tt>, the name of the package</span></li>
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<li><div class="single">Consequences:<ul><li>Loads the package <tt>PACKAGENAME</tt> in the file <tt>PACKAGENAME.m2</tt></li>
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<li><div class="single">Outputs:<ul><li><span>either the <a href="___Package.html" title="the class of all packages">Package</a> just loaded, or <a href="_null.html" title="the unique member of the empty class">null</a> if the package has already been loaded.</span></li>
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</li>
<li><div class="single"><a href="_using_spfunctions_spwith_spoptional_spinputs.html">Optional inputs</a>:<ul><li><span><tt>FileName => </tt><span><span>a <a href="___String.html">string</a></span>, <span>default value null</span>, the name of the file containing the source code of the package, from which it should be loaded</span></span></li>
<li><span><tt>LoadDocumentation => </tt><span><span>a <a href="___Boolean.html">Boolean value</a></span>, <span>default value false</span>, whether to load the documentation of the package, too; see <a href="_begin__Documentation.html" title="package item: start documentation section">beginDocumentation</a></span></span></li>
<li><span><tt>DebuggingMode => </tt><span><span>a <a href="___Boolean.html">Boolean value</a></span>, <span>default value null</span>, the value of <a href="_debugging__Mode.html" title="whether to enter the debugger when an error occurs">debuggingMode</a> during loading the package; specifying it here overrides the value specified as an option to <a href="_new__Package_lp__String_rp.html" title="package item: start a new package">newPackage</a> by the package itself</span></span></li>
<li><span><tt>Configuration => </tt><span><span>a <a href="___List.html">list</a></span>, <span>default value {}</span>, a list of options <tt>KEY => VALUE</tt>, overriding the defaults specified in the source code of the package and the (possibly updated) values in the file in the user's application directory.</span></span></li>
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<div class="single"><h2>Description</h2>
<div><p>The file <tt>PACKAGENAME.m2</tt> should be on the load <a href="_path.html" title="list of directories to look in">path</a> and should contain a package named <tt>PACKAGENAME</tt>.</p>
<p>For example, to load the sample package <tt>FirstPackage</tt>:</p>
<p>If the variable <a href="_notify.html" title="whether to notify the user when a file is loaded">notify</a> is set to true, then an informational message is displayed after the file is loaded.</p>
<table class="examples"><tr><td><pre>i1 : notify = true
o1 = true</pre>
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<tr><td><pre>i2 : needsPackage "FirstPackage"
--database not present: /builddir/build/BUILD/Macaulay2-1.3.1-r10737/StagingArea/common/lib/Macaulay2/i686-Linux-Fedora-15/FirstPackage/cache/rawdocumentation-dcba-4.db
--beginDocumentation: reading the rest of /builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/FirstPackage.m2
--package "FirstPackage" loaded
--loaded /builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/FirstPackage.m2
o2 = FirstPackage
o2 : Package</pre>
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<tr><td><pre>i3 : needsPackage "FirstPackage"
o3 = FirstPackage
o3 : Package</pre>
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The second time the package was not reloaded.</div>
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<div class="single"><h2>See also</h2>
<ul><li><span><a href="_packages.html" title="">packages</a></span></li>
<li><span><a href="_an_spexample_spof_spa_sppackage.html" title="">an example of a package</a></span></li>
<li><span><a href="_load__Package.html" title="load a package">loadPackage</a> -- load a package</span></li>
</ul>
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<div class="waystouse"><h2>Ways to use <tt>needsPackage</tt> :</h2>
<ul><li>needsPackage(String)</li>
</ul>
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