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<a name="Troubleshooting-(taking-it-all-apart)"></a>
<a name="Troubleshooting-_0028taking-it-all-apart_0029"></a>
Next: <a rel="next" accesskey="n" href="Minimal-examples.html#Minimal-examples">Minimal examples</a>,
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<h4 class="subsection">5.2.2 Troubleshooting (taking it all apart)</h4>
<p>Sooner or later, you will write a file that LilyPond cannot
compile. The messages that LilyPond gives may help
you find the error, but in many cases you need to do some
investigation to determine the source of the problem.
<p>The most powerful tools for this purpose are the
single line comment (indicated by <code>%</code>) and the block
comment (indicated by <code>%{ ... %}</code>). If you don't
know where a problem is, start commenting out huge portions
of your input file. After you comment out a section, try
compiling the file again. If it works, then the problem
must exist in the portion you just commented. If it doesn't
work, then keep on commenting out material until you have
something that works.
<p>In an extreme case, you might end up with only
<pre class="example">\score {
<<
% \melody
% \harmony
% \bass
>>
\layout{}
}
</pre>
<p class="noindent">(in other words, a file without any music)
<p>If that happens, don't give up. Uncomment a bit – say,
the bass part – and see if it works. If it doesn't work,
then comment out all of the bass music (but leave
<code>\bass</code> in the <code>\score</code> uncommented.
<pre class="example">bass = \relative c' {
%{
c4 c c c
d d d d
%}
}
</pre>
<p>Now start slowly uncommenting more and more of the
<code>bass</code> part until you find the problem line.
<p>Another very useful debugging technique is constructing
<a href="Minimal-examples.html#Minimal-examples">Minimal examples</a>.
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