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<section id="creating-our-own-functions">
<h1>Creating our own functions<a class="headerlink" href="#creating-our-own-functions" title="Permalink to this heading">¶</a></h1>
<p><strong>05-define-function.py</strong></p>
<p>The define keyword starts the definition of a custom function. The syntax is:</p>
<div class="highlight-scheme notranslate"><div class="highlight"><pre><span></span><span class="p">(</span><span class="k">define</span><span class="w"> </span><span class="nv">funcname</span><span class="w"> </span><span class="p">(</span><span class="nf">body</span><span class="p">))</span><span class="w"></span>
</pre></div>
</div>
<p><cite>funcname</cite> is the name used to call the function in the expression and body
is the sequence of expressions to execute. Arguments of the function are
extracted directly from the body. They must be named $1, $2, $3, …, $9.</p>
<p>The following example defines two functions, a simple oscillator and a
frequency modulation function using the former one.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <a class="sphinx-codeautolink-a" href="../../api/alphabetical.html#module-pyo" title="pyo"><span class="nn">pyo</span></a> <span class="kn">import</span> <span class="o">*</span>
<span class="n">s</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/server.html#pyo.Server" title="pyo.lib.server.Server"><span class="n">Server</span></a><span class="p">()</span><span class="o">.</span><span class="n">boot</span><span class="p">()</span>
<span class="n">expression</span> <span class="o">=</span> <span class="s2">"""</span>
<span class="s2">// usage: (osc freq)</span>
<span class="s2">(define osc (</span>
<span class="s2"> sin (* twopi (~ $1))</span>
<span class="s2"> )</span>
<span class="s2">)</span>
<span class="s2">// usage: (fm carrier ratio lfo_freq)</span>
<span class="s2">(define fm (</span>
<span class="s2"> (let #car $1) // carrier</span>
<span class="s2"> (let #rat $2) // ratio</span>
<span class="s2"> (let #ind (+ (* (osc $3) 5) 5)) // lfo on the index</span>
<span class="s2"> (osc (+ #car (* (osc (* #car #rat)) (* #car (* #rat #ind)))))</span>
<span class="s2"> )</span>
<span class="s2">)</span>
<span class="s2">// Two FM generators.</span>
<span class="s2">* (+ (fm 172 0.251 .1)</span>
<span class="s2"> (fm 86 0.499 .15))</span>
<span class="s2"> 0.5</span>
<span class="s2">"""</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/expression.html#pyo.Expr" title="pyo.lib.expression.Expr"><span class="n">expr</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/expression.html#pyo.Expr" title="pyo.lib.expression.Expr"><span class="n">Expr</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">Sig</span></a><span class="p">(</span><span class="mi">0</span><span class="p">),</span> <span class="n">expression</span><span class="p">,</span> <span class="n">mul</span><span class="o">=</span><span class="mf">0.5</span><span class="p">)</span>
<span class="n">expr</span><span class="o">.</span><span class="n">editor</span><span class="p">()</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Scope" title="pyo.lib.analysis.Scope"><span class="n">sc</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Scope" title="pyo.lib.analysis.Scope"><span class="n">Scope</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/expression.html#pyo.Expr" title="pyo.lib.expression.Expr"><span class="n">expr</span></a><span class="p">)</span>
<span class="n">pan</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/pan.html#pyo.Pan" title="pyo.lib.pan.Pan"><span class="n">Pan</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/expression.html#pyo.Expr" title="pyo.lib.expression.Expr"><span class="n">expr</span></a><span class="p">)</span><span class="o">.</span><span class="n">out</span><span class="p">()</span>
<span class="n">s</span><span class="o">.</span><span class="n">gui</span><span class="p">(</span><span class="nb">locals</span><span class="p">())</span>
</pre></div>
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