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<!--Weave of 'Detect Indirect Calls Stage' 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">pipeline</a></li><li><a href="index.html#4">Chapter 4: Linking</a></li><li><b>Detect Indirect Calls Stage</b></li></ul></div>
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<p class="purpose">To handle function calls made to functions identified by symbols which turn out, during linking, to be variables rather than constants.</p>
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. </b>Suppose kit A makes the function call <span class="extract"><span class="extract-syntax">Mystery(1, 2, 3)</span></span>, where <span class="extract"><span class="extract-syntax">Mystery</span></span> is a
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function defined in kit B; and suppose further that <span class="extract"><span class="extract-syntax">Mystery</span></span> is not the name of
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a function, but the name of a variable in kit B, whose value at runtime will be
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the address of the function which must be called. The original call in Kit A
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will be a function invocation like so:
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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="reserved-syntax">inv</span><span class="plain-syntax"> Mystery</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">2</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">3</span>
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</pre>
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<p class="commentary">But this is incorrect, because only explicitly identified functions can be
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invoked like this, and <span class="extract"><span class="extract-syntax">Mystery</span></span> turns out to be a variable. (The compiler
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of kit A has no way to know this.) We must correct to:
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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="reserved-syntax">inv</span><span class="plain-syntax"> </span><span class="function-syntax">!indirect3v</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_unchecked</span><span class="plain-syntax"> Mystery</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">2</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="identifier-syntax">K_number</span><span class="plain-syntax"> </span><span class="constant-syntax">3</span>
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</pre>
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<p class="commentary">This looks like an edge case, and it would certainly be possible to rewrite the
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kits so that it doesn't arise. But rejecting such usages with an error message
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would be as slow as correcting them, so we might as well get them right.
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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">DetectIndirectCallsStage::create_pipeline_stage</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">DetectIndirectCallsStage::create_pipeline_stage</span></span>:<br/>Parsing Pipelines - <a href="2-pp.html#SP10">§10</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><a href="2-pp.html#SP3" class="function-link"><span class="function-syntax">ParsingPipelines::new_stage</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="string-syntax">"detect-indirect-calls"</span><span class="plain-syntax">,</span>
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<span class="plain-syntax"> </span><a href="4-dics.html#SP1" class="function-link"><span class="function-syntax">DetectIndirectCallsStage::run</span></a><span class="plain-syntax">, </span><span class="constant-syntax">NO_STAGE_ARG</span><span class="plain-syntax">, </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">);</span>
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<span class="plain-syntax">}</span>
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<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">DetectIndirectCallsStage::run</span><span class="plain-syntax">(</span><span class="reserved-syntax">pipeline_step</span><span class="plain-syntax"> *</span><span class="identifier-syntax">step</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">InterTree::traverse</span><span class="plain-syntax">(</span><span class="identifier-syntax">step</span><span class="plain-syntax">-></span><span class="element-syntax">ephemera</span><span class="plain-syntax">.</span><span class="element-syntax">tree</span><span class="plain-syntax">,</span>
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<span class="plain-syntax"> </span><a href="4-dics.html#SP1" class="function-link"><span class="function-syntax">DetectIndirectCallsStage::visitor</span></a><span class="plain-syntax">, </span><span class="identifier-syntax">step</span><span class="plain-syntax">, </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">, </span><span class="identifier-syntax">PACKAGE_IST</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">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">DetectIndirectCallsStage::visitor</span><span class="plain-syntax">(</span><span class="identifier-syntax">inter_tree</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax">, </span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax">, </span><span class="reserved-syntax">void</span><span class="plain-syntax"> *</span><span class="identifier-syntax">state</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">pipeline_step</span><span class="plain-syntax"> *</span><span class="identifier-syntax">step</span><span class="plain-syntax"> = (</span><span class="reserved-syntax">pipeline_step</span><span class="plain-syntax"> *) </span><span class="identifier-syntax">state</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_package</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pack</span><span class="plain-syntax"> = </span><span class="identifier-syntax">PackageInstruction::at_this_head</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">InterPackage::is_a_function_body</span><span class="plain-syntax">(</span><span class="identifier-syntax">pack</span><span class="plain-syntax">)) {</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">D</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InterPackage::head</span><span class="plain-syntax">(</span><span class="identifier-syntax">pack</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><a href="4-dics.html#SP2" class="function-link"><span class="function-syntax">DetectIndirectCallsStage::traverse_code_tree</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">D</span><span class="plain-syntax">, </span><span class="identifier-syntax">step</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. </b>Within each code package (i.e., function body), we make a depth-first traverse,
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though as it happens this transformation would work just as well either way:
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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">DetectIndirectCallsStage::traverse_code_tree</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">DetectIndirectCallsStage::traverse_code_tree</span></span>:<br/><a href="4-dics.html#SP1">§1</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">P</span><span class="plain-syntax">, </span><span class="reserved-syntax">pipeline_step</span><span class="plain-syntax"> *</span><span class="identifier-syntax">step</span><span class="plain-syntax">) {</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">PROTECTED_LOOP_THROUGH_INTER_CHILDREN</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</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><a href="4-dics.html#SP2" class="function-link"><span class="function-syntax">DetectIndirectCallsStage::traverse_code_tree</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">, </span><span class="identifier-syntax">step</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">PROTECTED_LOOP_THROUGH_INTER_CHILDREN</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</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">Inode::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">, </span><span class="identifier-syntax">INV_IST</span><span class="plain-syntax">)) &&</span>
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<span class="plain-syntax"> (</span><span class="identifier-syntax">InvInstruction::method</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FUNCTION_INVMETH</span><span class="plain-syntax">)) {</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_symbol</span><span class="plain-syntax"> *</span><span class="identifier-syntax">var</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InvInstruction::function</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</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">var</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">) </span><span class="identifier-syntax">internal_error</span><span class="plain-syntax">(</span><span class="string-syntax">"bad invocation"</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_tree_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">D</span><span class="plain-syntax"> = </span><span class="identifier-syntax">var</span><span class="plain-syntax">-></span><span class="identifier-syntax">definition</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">Inode::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">D</span><span class="plain-syntax">, </span><span class="identifier-syntax">VARIABLE_IST</span><span class="plain-syntax">))</span>
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<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="4-dics.html#SP2_1" class="named-paragraph-link"><span class="named-paragraph">This is an invocation of a variable not a function</span><span class="named-paragraph-number">2.1</span></a></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_1" class="paragraph-anchor"></a><b>§2.1. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">This is an invocation of a variable not a function</span><span class="named-paragraph-number">2.1</span></span><span class="comment-syntax"> =</span>
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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">inter_tree</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax"> = </span><span class="identifier-syntax">F</span><span class="plain-syntax">-></span><span class="element-syntax">tree</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="4-dics.html#SP2_1_1" class="named-paragraph-link"><span class="named-paragraph">Change to be an invocation of a primitive</span><span class="named-paragraph-number">2.1.1</span></a></span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="4-dics.html#SP2_1_2" class="named-paragraph-link"><span class="named-paragraph">Insert the variable as the new first argument</span><span class="named-paragraph-number">2.1.2</span></a></span><span class="plain-syntax">;</span>
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</pre>
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<ul class="endnotetexts"><li>This code is used in <a href="4-dics.html#SP2">§2</a>.</li></ul>
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<p class="commentary firstcommentary"><a id="SP2_1_1" class="paragraph-anchor"></a><b>§2.1.1. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Change to be an invocation of a primitive</span><span class="named-paragraph-number">2.1.1</span></span><span class="comment-syntax"> =</span>
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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="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">arity</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="identifier-syntax">LOOP_THROUGH_INTER_CHILDREN</span><span class="plain-syntax">(</span><span class="identifier-syntax">X</span><span class="plain-syntax">, </span><span class="identifier-syntax">F</span><span class="plain-syntax">) </span><span class="identifier-syntax">arity</span><span class="plain-syntax">++;</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_ti</span><span class="plain-syntax"> </span><span class="identifier-syntax">prim</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Primitives::BIP_for_indirect_call_returning_value</span><span class="plain-syntax">(</span><span class="identifier-syntax">arity</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_symbol</span><span class="plain-syntax"> *</span><span class="identifier-syntax">prim_s</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Primitives::from_BIP</span><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="plain-syntax">, </span><span class="identifier-syntax">prim</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">InvInstruction::write_primitive</span><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="plain-syntax">, </span><span class="identifier-syntax">F</span><span class="plain-syntax">, </span><span class="identifier-syntax">prim_s</span><span class="plain-syntax">);</span>
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</pre>
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<ul class="endnotetexts"><li>This code is used in <a href="4-dics.html#SP2_1">§2.1</a>.</li></ul>
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<p class="commentary firstcommentary"><a id="SP2_1_2" class="paragraph-anchor"></a><b>§2.1.2. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Insert the variable as the new first argument</span><span class="named-paragraph-number">2.1.2</span></span><span class="comment-syntax"> =</span>
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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">inter_bookmark</span><span class="plain-syntax"> </span><span class="identifier-syntax">IBM</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InterBookmark::first_child_of</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">inter_pair</span><span class="plain-syntax"> </span><span class="identifier-syntax">val</span><span class="plain-syntax"> = </span><span class="identifier-syntax">InterValuePairs::symbolic</span><span class="plain-syntax">(&</span><span class="identifier-syntax">IBM</span><span class="plain-syntax">, </span><span class="identifier-syntax">var</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">ValInstruction::new</span><span class="plain-syntax">(&</span><span class="identifier-syntax">IBM</span><span class="plain-syntax">, </span><span class="identifier-syntax">InterTypes::unchecked</span><span class="plain-syntax">(), </span><span class="identifier-syntax">Inode::get_level</span><span class="plain-syntax">(</span><span class="identifier-syntax">F</span><span class="plain-syntax">) + </span><span class="constant-syntax">1</span><span class="plain-syntax">, </span><span class="identifier-syntax">val</span><span class="plain-syntax">, </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">);</span>
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</pre>
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<ul class="endnotetexts"><li>This code is used in <a href="4-dics.html#SP2_1">§2.1</a>.</li></ul>
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<nav role="progress"><div class="progresscontainer">
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