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<div class="section" id="getting-started">
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<h1>Getting started<a class="headerlink" href="#getting-started" title="Permalink to this headline">¶</a></h1>
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<p>Welcome to D:YAML! D:YAML is a <a class="reference external" href="http://en.wikipedia.org/wiki/YAML">YAML</a> parser
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library for the <a class="reference external" href="http://dlang.org">D programming language</a>. This tutorial will
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explain how to set D:YAML up and use it in your projects.</p>
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<p>This is meant to be the <strong>simplest possible</strong> introduction to D:YAML. Some of this
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information might already be known to you. Only basic usage is covered.</p>
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<div class="section" id="setting-up">
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<h2>Setting up<a class="headerlink" href="#setting-up" title="Permalink to this headline">¶</a></h2>
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<div class="section" id="install-the-dmd-compiler">
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<h3>Install the DMD compiler<a class="headerlink" href="#install-the-dmd-compiler" title="Permalink to this headline">¶</a></h3>
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<p>Digital Mars D compiler, or DMD, is the most commonly used D compiler. You can find its
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newest version <a class="reference external" href="http://dlang.org/download.html">here</a>. Download the version of DMD
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for your operating system and install it.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">Other D compilers exist, such as
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<a class="reference external" href="http://gdcproject.org/">GDC</a> and
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<a class="reference external" href="http://bitbucket.org/goshawk/gdc/wiki/Home">LDC</a>.</p>
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</div>
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</div>
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<div class="section" id="install-dub">
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<h3>Install dub<a class="headerlink" href="#install-dub" title="Permalink to this headline">¶</a></h3>
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<p><a class="reference external" href="http://code.dlang.org/about">dub</a> is a build system and package manager for D.
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It is the standard way to manage D projects and their dependencies, compilation and so
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on.</p>
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<p>DMD may include DUB in future releases, but at this point we need to install it
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separately. See
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<a class="reference external" href="https://github.com/D-Programming-Language/dub#installation">installation instructions</a>.</p>
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</div>
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</div>
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<div class="section" id="your-first-d-yaml-project">
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<h2>Your first D:YAML project<a class="headerlink" href="#your-first-d-yaml-project" title="Permalink to this headline">¶</a></h2>
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<p>Create a directory for your project and in that directory, create a new file named
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<tt class="docutils literal"><span class="pre">input.yaml</span></tt> and paste this code into the file:</p>
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<div class="highlight-yaml"><div class="highlight"><pre><span class="l-Scalar-Plain">Hello World</span> <span class="p-Indicator">:</span> <span class="p-Indicator">[</span><span class="nv">Hello</span><span class="p-Indicator">,</span> <span class="nv">World</span><span class="p-Indicator">]</span>
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<span class="l-Scalar-Plain">Answer</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">42</span>
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</pre></div>
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</div>
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<p>This will serve as input for our example.</p>
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<p>Now we need to parse it. Create a new file with name <tt class="docutils literal"><span class="pre">main.d</span></tt>. Paste following code
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into the file:</p>
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<div class="highlight-d"><div class="highlight"><pre><span class="k">import</span> <span class="n">std</span><span class="p">.</span><span class="n">stdio</span><span class="p">;</span>
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<span class="k">import</span> <span class="n">yaml</span><span class="p">;</span>
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<span class="kt">void</span> <span class="n">main</span><span class="p">()</span>
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<span class="p">{</span>
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<span class="c1">//Read the input.</span>
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<span class="n">Node</span> <span class="n">root</span> <span class="p">=</span> <span class="n">Loader</span><span class="p">(</span><span class="s">"input.yaml"</span><span class="p">).</span><span class="n">load</span><span class="p">();</span>
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<span class="c1">//Display the data read.</span>
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<span class="k">foreach</span><span class="p">(</span><span class="nb">string</span> <span class="n">word</span><span class="p">;</span> <span class="n">root</span><span class="p">[</span><span class="s">"Hello World"</span><span class="p">])</span>
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<span class="p">{</span>
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<span class="n">writeln</span><span class="p">(</span><span class="n">word</span><span class="p">);</span>
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<span class="p">}</span>
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<span class="n">writeln</span><span class="p">(</span><span class="s">"The answer is "</span><span class="p">,</span> <span class="n">root</span><span class="p">[</span><span class="s">"Answer"</span><span class="p">].</span><span class="n">as</span><span class="p">!</span><span class="kt">int</span><span class="p">);</span>
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<span class="c1">//Dump the loaded document to output.yaml.</span>
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<span class="n">Dumper</span><span class="p">(</span><span class="s">"output.yaml"</span><span class="p">).</span><span class="n">dump</span><span class="p">(</span><span class="n">root</span><span class="p">);</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<div class="section" id="explanation-of-the-code">
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<h3>Explanation of the code<a class="headerlink" href="#explanation-of-the-code" title="Permalink to this headline">¶</a></h3>
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<p>First, we import the <em>dyaml.all</em> module. This is the only D:YAML module you need to
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import - it automatically imports all needed modules.</p>
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<p>Next we load the file using the <em>Loader.load()</em> method. <em>Loader</em> is a struct used for
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parsing YAML documents. The <em>load()</em> method loads the file as <strong>one</strong> YAML document, or
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throws <em>YAMLException</em>, D:YAML exception type, if the file could not be parsed or
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contains more than one document. Note that we don’t do any error checking here in order
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to keep the example as simple as possible.</p>
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<p><em>Node</em> represents a node in a YAML document. It can be a sequence (array), mapping
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(associative array) or a scalar (value). Here the root node is a mapping, and we use the
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index operator to get subnodes with keys “Hello World” and “Answer”. We iterate over the
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former, as it is a sequence, and use the <em>Node.as()</em> method on the latter to read its
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value as an integer.</p>
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<p>You can iterate over a mapping or sequence as if it was an associative or normal array,
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respectively. If you try to iterate over a scalar, it will throw a <em>YAMLException</em>.</p>
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<p>You can iterate using <em>Node</em> as the iterated type, or specify the type iterated nodes
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are expected to have. D:YAML will automatically convert to that type if possible. Here
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we specify the <em>string</em> type, so we iterate over the “Hello World” sequence as an array
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of strings. If it is not possible to convert to iterated type, a <em>YAMLException</em> is
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thrown. For instance, if we specified <em>int</em> here, we would get an error, as “Hello”
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cannot be converted to an integer.</p>
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<p>The <em>Node.as()</em> method is used to read value of a scalar node as specified type. If the
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scalar does not have the specified type, D:YAML will try to convert it, throwing
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<em>YAMLException</em> if not possible.</p>
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<p>Finally we dump the document we just read to <tt class="docutils literal"><span class="pre">output.yaml</span></tt> with the <em>Dumper.dump()</em>
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method. <em>Dumper</em> is a struct used to dump YAML documents. The <em>dump()</em> method writes
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one or more documents to a file, throwing <em>YAMLException</em> if the file could not be
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written to.</p>
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<p>D:YAML tries to preserve style information in documents so e.g. <tt class="docutils literal"><span class="pre">[Hello,</span> <span class="pre">World]</span></tt> is
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not turned into:</p>
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<div class="line-block">
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<div class="line"><tt class="docutils literal"><span class="pre">-</span> <span class="pre">Hello</span></tt></div>
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<div class="line"><tt class="docutils literal"><span class="pre">-</span> <span class="pre">World</span></tt></div>
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</div>
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<p>However, comments are not preserved and neither are any extra formatting whitespace that
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doesn’t affect the meaning of YAML contents.</p>
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</div>
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<div class="section" id="compiling">
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<h3>Compiling<a class="headerlink" href="#compiling" title="Permalink to this headline">¶</a></h3>
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<p>We’re going to use dub, which we installed at the beginning, to compile our project.</p>
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<p>Create a file called <tt class="docutils literal"><span class="pre">dub.json</span></tt> with the following contents:</p>
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<div class="highlight-json"><div class="highlight"><pre><span class="p">{</span>
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<span class="nt">"name"</span><span class="p">:</span> <span class="s2">"getting-started"</span><span class="p">,</span>
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<span class="nt">"targetType"</span><span class="p">:</span> <span class="s2">"executable"</span><span class="p">,</span>
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<span class="nt">"sourceFiles"</span><span class="p">:</span> <span class="p">[</span><span class="s2">"main.d"</span><span class="p">],</span>
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<span class="nt">"mainSourceFile"</span><span class="p">:</span> <span class="s2">"main.d"</span><span class="p">,</span>
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<span class="nt">"dependencies"</span><span class="p">:</span>
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<span class="p">{</span>
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<span class="nt">"dyaml"</span><span class="p">:</span> <span class="p">{</span> <span class="nt">"version"</span> <span class="p">:</span> <span class="s2">"~>0.5.0"</span><span class="p">,</span> <span class="nt">"path"</span> <span class="p">:</span> <span class="s2">"../../"</span><span class="p">},</span>
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<span class="p">},</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<p>This file tells dub that we’re building an executable called <tt class="docutils literal"><span class="pre">getting-started</span></tt> from
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a D source file <tt class="docutils literal"><span class="pre">main.d</span></tt>, and that our project depends on D:YAML 0.5.0 or any newer,
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bugfix release of D:YAML 0.5 . DUB will automatically find and download the correct
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version of D:YAML when the project is built.</p>
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<p>Now run the following command in your project’s directory:</p>
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<div class="highlight-python"><div class="highlight"><pre>dub build
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</pre></div>
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</div>
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<p>dub will automatically download D:YAML and compile it, and then then it will compile our
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program. This will generate an executable called <tt class="docutils literal"><span class="pre">getting-started</span></tt> or
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<tt class="docutils literal"><span class="pre">getting-started.exe</span></tt> in your directory. When you run it, it should produce the
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following output:</p>
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<div class="highlight-python"><div class="highlight"><pre>Hello
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World
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The answer is 42
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</pre></div>
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</div>
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</div>
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<div class="section" id="conclusion">
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<h3>Conclusion<a class="headerlink" href="#conclusion" title="Permalink to this headline">¶</a></h3>
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<p>You should now have a basic idea about how to use D:YAML. To learn more, look at the
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<a class="reference external" href="../api/index.html">API documentation</a> and other tutorials. You can find code for this
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example in the <tt class="docutils literal"><span class="pre">example/getting_started</span></tt> directory in the package.</p>
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</div>
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</div>
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<img class="logo" src="../_static/logo210.png" alt="Logo"/>
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</a></p>
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<h3><a href="../index.html">Table Of Contents</a></h3>
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<ul>
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<li><a class="reference internal" href="#">Getting started</a><ul>
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<li><a class="reference internal" href="#setting-up">Setting up</a><ul>
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<li><a class="reference internal" href="#install-the-dmd-compiler">Install the DMD compiler</a></li>
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<li><a class="reference internal" href="#install-dub">Install dub</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#your-first-d-yaml-project">Your first D:YAML project</a><ul>
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<li><a class="reference internal" href="#explanation-of-the-code">Explanation of the code</a></li>
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<li><a class="reference internal" href="#compiling">Compiling</a></li>
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<li><a class="reference internal" href="#conclusion">Conclusion</a></li>
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</ul>
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</li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="clearer"></div>
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<h3>Navigation</h3>
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>next</a></li>
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>previous</a> |</li>
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<div class="footer">
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© Copyright 2011-2014, Ferdinand Majerech. Based on PyYAML http://www.pyyaml.org by Kirill Simonov.
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Last updated on Aug 06, 2014.
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