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<head>
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<title>State Template</title>
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<h1><a href="../index.html">
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<img src="../docs-assets/Inform.png" height=72">
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</a></h1>
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<ul><li><a href="../index.html">home</a></li>
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</ul><h2>Compiler</h2><ul>
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</ul><h2>Other Tools</h2><ul>
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<li><a href="../inform6.html">inform6</a></li>
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</ul><h2>Resources</h2><ul>
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<li><a href="https://github.com/ganelson/inform"><img src="../docs-assets/github.png" height=18> github</a></li>
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</ul><h2>Related Projects</h2><ul>
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<li><a href="../../../intest/index.html">intest</a></li>
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</nav>
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<main role="main">
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<!--Weave of 'State Template' generated by Inweb-->
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<div class="breadcrumbs">
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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../extensions.html">Kits</a></li><li><a href="index.html">Architecture16Kit</a></li><li><b>State Template</b></li></ul></div>
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<p class="purpose">Saving, restoring, restarting and verifying the program from within itself.</p>
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<ul class="toc"><li><a href="S-stt.html#SP1">§1. Environment</a></li><li><a href="S-stt.html#SP2">§2. Verification</a></li><li><a href="S-stt.html#SP3">§3. Save, restore, restart</a></li><li><a href="S-stt.html#SP4">§4. Undo</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. Environment. </b>The language "interpreter" here supposes that the eventual program is
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running in a VM which is being interpreted, and that may not be the case,
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but it's traditional.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_ReportOnInterpreter</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">standard_interpreter</span><span class="plain-syntax"> > </span><span class="constant-syntax">0</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> </span><span class="string-syntax">"Standard interpreter "</span><span class="plain-syntax">,</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">standard_interpreter</span><span class="plain-syntax">/256, </span><span class="string-syntax">"."</span><span class="plain-syntax">, </span><span class="identifier-syntax">standard_interpreter</span><span class="plain-syntax">%256,</span>
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<span class="plain-syntax"> </span><span class="string-syntax">" ("</span><span class="plain-syntax">, </span><span class="identifier-syntax">HDR_TERPNUMBER</span><span class="plain-syntax">->0;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> (</span><span class="identifier-syntax">char</span><span class="plain-syntax">) </span><span class="identifier-syntax">HDR_TERPVERSION</span><span class="plain-syntax">->0;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> </span><span class="string-syntax">")^"</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> } </span><span class="reserved-syntax">else</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> </span><span class="string-syntax">"Interpreter "</span><span class="plain-syntax">, </span><span class="identifier-syntax">HDR_TERPNUMBER</span><span class="plain-syntax">->0, </span><span class="string-syntax">" Version "</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> (</span><span class="identifier-syntax">char</span><span class="plain-syntax">) </span><span class="identifier-syntax">HDR_TERPVERSION</span><span class="plain-syntax">->0;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">print</span><span class="plain-syntax"> </span><span class="string-syntax">"^"</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax">];</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>§2. Verification. </b>This verifies that the current story file is intact.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Verify</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> @</span><span class="identifier-syntax">verify</span><span class="plain-syntax"> ?</span><span class="identifier-syntax">Vmaybe</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">rfalse</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> .</span><span class="identifier-syntax">Vmaybe</span><span class="plain-syntax">; </span><span class="reserved-syntax">rtrue</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. Save, restore, restart. </b>Restart does what it says: restarts the program as if it had just loaded for
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the first time.
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</p>
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<p class="commentary"><span class="extract"><span class="extract-syntax">VM_Save()</span></span> attempts to save the current state of the program to a file, and
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returns 0 if this fails, 1 if this succeeds, or 2 if in fact a restore has
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just succeeded. (A successful restoration should resume execution where the
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save succeeded, but we want to distinguish those cases.)
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</p>
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<p class="commentary"><span class="extract"><span class="extract-syntax">VM_Restore()</span></span> pretends to return <span class="extract"><span class="extract-syntax">true</span></span> or <span class="extract"><span class="extract-syntax">false</span></span> according to whether or not
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it succeeds, but in fact it can only return <span class="extract"><span class="extract-syntax">false</span></span> to indicate failure, because
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a successful restoration means that execution has transferred to <span class="extract"><span class="extract-syntax">VM_Save</span></span>
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instead.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Restart</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> @</span><span class="identifier-syntax">restart</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Restore</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">restore</span><span class="plain-syntax"> </span><span class="identifier-syntax">RMaybe</span><span class="plain-syntax">; </span><span class="reserved-syntax">rfalse</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> .</span><span class="identifier-syntax">RMaybe</span><span class="plain-syntax">; </span><span class="reserved-syntax">rtrue</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Save</span><span class="plain-syntax"> </span><span class="identifier-syntax">flag</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> @</span><span class="reserved-syntax">save</span><span class="plain-syntax"> -> </span><span class="identifier-syntax">flag</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">flag</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. Undo. </b>These also simply wrap the relevant opcodes.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Undo</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> @</span><span class="identifier-syntax">restore_undo</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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<span class="plain-syntax">[ </span><span class="identifier-syntax">VM_Save_Undo</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> @</span><span class="identifier-syntax">save_undo</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">result_code</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">];</span>
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</pre>
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