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<!--Weave of 'The Nop Construct' 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="../intern.html">Inter Modules</a></li><li><a href="index.html">bytecode</a></li><li><a href="index.html#4">Chapter 4: Void Constructs</a></li><li><b>The Nop Construct</b></li></ul></div>
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<p class="purpose">Defining the nop construct.</p>
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<ul class="toc"><li><a href="4-tnc.html#SP1">§1. Definition</a></li><li><a href="4-tnc.html#SP2">§2. Instructions</a></li><li><a href="4-tnc.html#SP3">§3. Writing to textual Inter syntax</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. Definition. </b>This instruction does nothing at all, has no textual representation and is
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nevertheless useful when constructing Inter in memory.
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</p>
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<p class="commentary">It exists as a convenience used by Inform when it needs to write simultaneously to
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multiple positions within the same node's child list — the idea being that
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a nop statement acts as a divider. For example, by placing the A write
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position just before a nop N, and the B write position just after, Inform
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will generate A1, A2, A3, ..., N, B1, B2, ..., rather than (say) A1, B1, A2,
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A3, B2, ... The extra N is simply ignored in code generation, so it causes
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no problems to have it.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">NopInstruction::define_construct</span><button class="popup" onclick="togglePopup('usagePopup1')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup1">Usage of <span class="code-font"><span class="function-syntax">NopInstruction::define_construct</span></span>:<br/>Inter Constructs - <a href="3-ic.html#SP15">§15</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">void</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">inter_construct</span><span class="plain-syntax"> *</span><span class="identifier-syntax">IC</span><span class="plain-syntax"> = </span><a href="3-ic.html#SP1" class="function-link"><span class="function-syntax">InterInstruction::create_construct</span></a><span class="plain-syntax">(</span><span class="constant-syntax">NOP_IST</span><span class="plain-syntax">, </span><span class="identifier-syntax">I</span><span class="string-syntax">"nop"</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><a href="3-ic.html#SP4" class="function-link"><span class="function-syntax">InterInstruction::data_extent_always</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IC</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><a href="3-ic.html#SP3" class="function-link"><span class="function-syntax">InterInstruction::allow_in_depth_range</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="constant-syntax">0</span><span class="plain-syntax">, </span><span class="constant-syntax">INFINITELY_DEEP</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><a href="3-ic.html#SP3" class="function-link"><span class="function-syntax">InterInstruction::permit</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="constant-syntax">OUTSIDE_OF_PACKAGES_ICUP</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><a href="3-ic.html#SP3" class="function-link"><span class="function-syntax">InterInstruction::permit</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="constant-syntax">INSIDE_PLAIN_PACKAGE_ICUP</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><a href="3-ic.html#SP3" class="function-link"><span class="function-syntax">InterInstruction::permit</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="constant-syntax">INSIDE_CODE_PACKAGE_ICUP</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">METHOD_ADD</span><span class="plain-syntax">(</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="constant-syntax">CONSTRUCT_WRITE_MTID</span><span class="plain-syntax">, </span><a href="4-tnc.html#SP3" class="function-link"><span class="function-syntax">NopInstruction::write</span></a><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. Instructions. </b>In bytecode, the frame of a <span class="extract"><span class="extract-syntax">nop</span></span> instruction consists only of the two
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compulsory words — see <a href="2-in.html" class="internal">Inter Nodes</a>.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="reserved-syntax">inter_error_message</span><span class="plain-syntax"> *</span><span class="function-syntax">NopInstruction::new</span><span class="plain-syntax">(</span><span class="reserved-syntax">inter_bookmark</span><span class="plain-syntax"> *</span><span class="identifier-syntax">IBM</span><span class="plain-syntax">, </span><span class="constant-syntax">inter_ti</span><span class="plain-syntax"> </span><span class="identifier-syntax">level</span><span class="plain-syntax">,</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">inter_error_location</span><span class="plain-syntax"> *</span><span class="identifier-syntax">eloc</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax"> = </span><a href="2-in.html#SP5" class="function-link"><span class="function-syntax">Inode::new_with_0_data_fields</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IBM</span><span class="plain-syntax">, </span><span class="constant-syntax">NOP_IST</span><span class="plain-syntax">,</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">eloc</span><span class="plain-syntax">, </span><span class="identifier-syntax">level</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">inter_error_message</span><span class="plain-syntax"> *</span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="3-vi.html#SP1" class="function-link"><span class="function-syntax">VerifyingInter::instruction</span></a><span class="plain-syntax">(</span><a href="2-bkm.html#SP6" class="function-link"><span class="function-syntax">InterBookmark::package</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">IBM</span><span class="plain-syntax">), </span><span class="identifier-syntax">P</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">E</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><a href="2-np.html#SP3" class="function-link"><span class="function-syntax">NodePlacement::move_to_moving_bookmark</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">P</span><span class="plain-syntax">, </span><span class="identifier-syntax">IBM</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">NULL</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. Writing to textual Inter syntax. </b>The <span class="extract"><span class="extract-syntax">nop</span></span> construct is not expressible in textual Inter, but can be printed out
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all the same, purely so that a stack backtrace will show it.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">NopInstruction::write</span><button class="popup" onclick="togglePopup('usagePopup2')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup2">Usage of <span class="code-font"><span class="function-syntax">NopInstruction::write</span></span>:<br/><a href="4-tnc.html#SP1">§1</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">inter_construct</span><span class="plain-syntax"> *</span><span class="identifier-syntax">IC</span><span class="plain-syntax">, </span><span class="identifier-syntax">OUTPUT_STREAM</span><span class="plain-syntax">, </span><span class="reserved-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"nop"</span><span class="plain-syntax">);</span>
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<span class="plain-syntax">}</span>
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