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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>Terms</title>
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<main role="main">
<!--Weave of 'Terms' generated by Inweb-->
<div class="breadcrumbs">
<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../services.html">Services</a></li><li><a href="index.html">calculus</a></li><li><a href="index.html#4">Chapter 4: Propositions</a></li><li><b>Terms</b></li></ul></div>
<p class="purpose">Terms are the representations of values in predicate calculus: variables, constants or functions of other terms.</p>
<ul class="toc"><li><a href="4-trm.html#SP1">&#167;1. About terms</a></li><li><a href="4-trm.html#SP4">&#167;4. Creating new terms</a></li><li><a href="4-trm.html#SP5">&#167;5. Copying</a></li><li><a href="4-trm.html#SP6">&#167;6. Variable letters</a></li><li><a href="4-trm.html#SP8">&#167;8. Underlying terms</a></li><li><a href="4-trm.html#SP9">&#167;9. Adjective-noun conversions</a></li><li><a href="4-trm.html#SP11">&#167;11. Writing to text</a></li></ul><hr class="tocbar">
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. About terms. </b>A "term" can be a constant, a variable, or a function of another term: see
<a href="P-wtmd.html" class="internal">What This Module Does</a>. Our data structure therefore falls into three
cases. At all times exactly one of the three relevant fields, <span class="extract"><span class="extract-syntax">variable</span></span>,
<span class="extract"><span class="extract-syntax">constant</span></span> and <span class="extract"><span class="extract-syntax">function</span></span> is used.
</p>
<ul class="items"><li>(a) Variables are represented by the numbers 0 to 25, and <span class="extract"><span class="extract-syntax">-1</span></span> means
"not a variable".
</li><li>(b) Constants are pointers to <span class="extract"><span class="extract-syntax">specification</span></span> structures of main
type <span class="extract"><span class="extract-syntax">VALUE</span></span>, and <span class="extract"><span class="extract-syntax">NULL</span></span> means "not a constant".
</li><li>(c) Functions are pointers to <span class="extract"><span class="extract-syntax">pcalc_func</span></span> structures (see below), and
<span class="extract"><span class="extract-syntax">NULL</span></span> means "not a function".
</li></ul>
<p class="commentary">Cinders are discussed in <a href="../imperative-module/4-cad.html" class="internal">Cinders and Deferrals (in imperative)</a>, and can be ignored for now.
</p>
<p class="commentary">In order to verify that a proposition makes sense and does not mix up
incompatible kinds of value, we will need to type-check it, and one part
of that involves assigning a kind of value \(K\) to every term \(t\) occurring
in the proposition. This calculation does involve some work, so we cache
the result in the <span class="extract"><span class="extract-syntax">term_checked_as_kind</span></span> field.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">typedef</span><span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">variable</span><span class="plain-syntax">; </span><span class="comment-syntax"> 0 to 25, or </span><span class="extract"><span class="extract-syntax">-1</span></span><span class="comment-syntax"> for "not a variable"</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">constant</span><span class="plain-syntax">; </span><span class="comment-syntax"> or </span><span class="extract"><span class="extract-syntax">NULL</span></span><span class="comment-syntax"> for "not a constant"</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_func</span><span class="plain-syntax"> *</span><span class="identifier-syntax">function</span><span class="plain-syntax">; </span><span class="comment-syntax"> or </span><span class="extract"><span class="extract-syntax">NULL</span></span><span class="comment-syntax"> for "not a function of another term"</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">cinder</span><span class="plain-syntax">; </span><span class="comment-syntax"> complicated, this: used to worry about scope of I6 local variables</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">kind</span><span class="plain-syntax"> *</span><span class="identifier-syntax">term_checked_as_kind</span><span class="plain-syntax">; </span><span class="comment-syntax"> or </span><span class="extract"><span class="extract-syntax">NULL</span></span><span class="comment-syntax"> if unchecked</span>
<span class="plain-syntax">} </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax">;</span>
</pre>
<ul class="endnotetexts"><li>The structure pcalc_term is accessed in 4/ap, 4/prp, 4/bas, 4/tcp, 5/sc, 5/smp and here.</li></ul>
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. </b>The <span class="extract"><span class="extract-syntax">pcalc_func</span></span> structure represents a usage of a function inside a term.
Terms such as \(f_A(f_B(f_C(x)))\) often occur, an example which would be stored
as:
</p>
<ul class="items"><li>(1) A <span class="extract"><span class="extract-syntax">pcalc_term</span></span> structure which has a <span class="extract"><span class="extract-syntax">function</span></span> field pointing to
</li><li>(2) A <span class="extract"><span class="extract-syntax">pcalc_func</span></span> structure whose <span class="extract"><span class="extract-syntax">bp</span></span> field points to A, and whose <span class="extract"><span class="extract-syntax">fn_of</span></span>
field is
</li><li>(3) A <span class="extract"><span class="extract-syntax">pcalc_term</span></span> structure which has a <span class="extract"><span class="extract-syntax">function</span></span> field pointing to
</li><li>(4) A <span class="extract"><span class="extract-syntax">pcalc_func</span></span> structure whose <span class="extract"><span class="extract-syntax">bp</span></span> field points to B, and whose <span class="extract"><span class="extract-syntax">fn_of</span></span>
field is
</li><li>(5) A <span class="extract"><span class="extract-syntax">pcalc_term</span></span> structure which has a <span class="extract"><span class="extract-syntax">function</span></span> field pointing to
</li><li>(6) A <span class="extract"><span class="extract-syntax">pcalc_func</span></span> structure whose <span class="extract"><span class="extract-syntax">bp</span></span> field points to C, and whose <span class="extract"><span class="extract-syntax">fn_of</span></span>
field is
</li><li>(7) A <span class="extract"><span class="extract-syntax">pcalc_term</span></span> structure which has a <span class="extract"><span class="extract-syntax">variable</span></span> field set to 0 (which is \(x\)).
</li></ul>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">typedef</span><span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_func</span><span class="plain-syntax"> {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">binary_predicate</span><span class="plain-syntax"> *</span><span class="identifier-syntax">bp</span><span class="plain-syntax">; </span><span class="comment-syntax"> the predicate B</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">from_term</span><span class="plain-syntax">; </span><span class="comment-syntax"> which term of the predicate this derives from</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">fn_of</span><span class="plain-syntax">; </span><span class="comment-syntax"> the term to which we apply the function</span>
<span class="plain-syntax">} </span><span class="reserved-syntax">pcalc_func</span><span class="plain-syntax">;</span>
</pre>
<ul class="endnotetexts"><li>The structure pcalc_func is accessed in 4/bas, 4/tcp, 5/smp and here.</li></ul>
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. </b>Terms are really quite simple, as the following <a href="../calculus-test/index.html" class="internal">calculus-test</a> exercise shows:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax">'</span><span class="element-syntax">new binary sees (none, sees-f1)</span><span class="plain-syntax">':</span><span class="string-syntax"> ok</span>
<span class="plain-syntax">'</span><span class="element-syntax">new binary knows (knows-f0, none)</span><span class="plain-syntax">':</span><span class="string-syntax"> ok</span>
<span class="plain-syntax">'</span><span class="element-syntax">term 7</span><span class="plain-syntax">':</span><span class="string-syntax"> '7'</span>
<span class="plain-syntax">'</span><span class="element-syntax">term z</span><span class="plain-syntax">':</span><span class="string-syntax"> z</span>
<span class="plain-syntax">'</span><span class="element-syntax">term sees-f1 (7)</span><span class="plain-syntax">':</span><span class="string-syntax"> &lt;sees-f1(*1) : '7'&gt;</span>
<span class="plain-syntax">'</span><span class="element-syntax">term knows-f0 (sees-f1 (x))</span><span class="plain-syntax">':</span><span class="string-syntax"> &lt;knows-f0(*1) : &lt;sees-f1(*1) : x&gt;&gt;</span>
<span class="plain-syntax">'</span><span class="element-syntax">constant underlying 7</span><span class="plain-syntax">':</span><span class="string-syntax"> '7'</span>
<span class="plain-syntax">'</span><span class="element-syntax">constant underlying y</span><span class="plain-syntax">':</span><span class="string-syntax"> --</span>
<span class="plain-syntax">'</span><span class="element-syntax">constant underlying sees-f1 (7)</span><span class="plain-syntax">':</span><span class="string-syntax"> '7'</span>
<span class="plain-syntax">'</span><span class="element-syntax">variable underlying 7</span><span class="plain-syntax">':</span><span class="string-syntax"> --</span>
<span class="plain-syntax">'</span><span class="element-syntax">variable underlying y</span><span class="plain-syntax">':</span><span class="string-syntax"> y</span>
<span class="plain-syntax">'</span><span class="element-syntax">variable underlying knows-f0 (sees-f1 (x))</span><span class="plain-syntax">':</span><span class="string-syntax"> x</span>
</pre>
<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>&#167;4. Creating new terms. </b></p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::new_variable</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">Terms::new_variable</span></span>:<br/><a href="4-trm.html#SP9">&#167;9</a><br/>Compilation Schemas - <a href="3-cs.html#SP4">&#167;4</a><br/>Atomic Propositions - <a href="4-ap.html#SP6">&#167;6</a>, <a href="4-ap.html#SP11">&#167;11</a><br/>Propositions - <a href="4-prp.html#SP28">&#167;28</a>, <a href="4-prp.html#SP29">&#167;29</a><br/>Sentence Conversions - <a href="5-sc.html#SP3_3">&#167;3.3</a>, <a href="5-sc.html#SP3_7">&#167;3.7</a><br/>Simplifications - <a href="5-smp.html#SP2_2">&#167;2.2</a>, <a href="5-smp.html#SP3">&#167;3</a>, <a href="5-smp.html#SP7">&#167;7</a>, <a href="5-smp.html#SP9_3_2">&#167;9.3.2</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">v</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">; </span><span class="named-paragraph-container code-font"><a href="4-trm.html#SP4_1" class="named-paragraph-link"><span class="named-paragraph">Make new blank term structure pt</span><span class="named-paragraph-number">4.1</span></a></span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><span class="identifier-syntax">v</span><span class="plain-syntax"> &lt; </span><span class="constant-syntax">0</span><span class="plain-syntax">) || (</span><span class="identifier-syntax">v</span><span class="plain-syntax"> &gt;= </span><span class="constant-syntax">26</span><span class="plain-syntax">)) </span><span class="identifier-syntax">internal_error</span><span class="plain-syntax">(</span><span class="string-syntax">"bad variable term created"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">variable</span><span class="plain-syntax"> = </span><span class="identifier-syntax">v</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::new_constant</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">Terms::new_constant</span></span>:<br/><a href="4-trm.html#SP9">&#167;9</a><br/>Atomic Propositions - <a href="4-ap.html#SP11">&#167;11</a><br/>Propositions - <a href="4-prp.html#SP29">&#167;29</a><br/>Binding and Substitution - <a href="4-bas.html#SP15">&#167;15</a><br/>Sentence Conversions - <a href="5-sc.html#SP2">&#167;2</a>, <a href="5-sc.html#SP3_3">&#167;3.3</a>, <a href="5-sc.html#SP3_5">&#167;3.5</a><br/>Simplifications - <a href="5-smp.html#SP3">&#167;3</a>, <a href="5-smp.html#SP14">&#167;14</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">c</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">; </span><span class="named-paragraph-container code-font"><a href="4-trm.html#SP4_1" class="named-paragraph-link"><span class="named-paragraph">Make new blank term structure pt</span><span class="named-paragraph-number">4.1</span></a></span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">constant</span><span class="plain-syntax"> = </span><span class="identifier-syntax">c</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::new_function</span><button class="popup" onclick="togglePopup('usagePopup3')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup3">Usage of <span class="code-font"><span class="function-syntax">Terms::new_function</span></span>:<br/><a href="4-trm.html#SP5">&#167;5</a><br/>Simplifications - <a href="5-smp.html#SP12">&#167;12</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">binary_predicate</span><span class="plain-syntax"> *</span><span class="identifier-syntax">bp</span><span class="plain-syntax">, </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">ptof</span><span class="plain-syntax">, </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">t</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><span class="identifier-syntax">t</span><span class="plain-syntax"> &lt; </span><span class="constant-syntax">0</span><span class="plain-syntax">) || (</span><span class="identifier-syntax">t</span><span class="plain-syntax"> &gt;= </span><span class="constant-syntax">MAX_ATOM_ARITY</span><span class="plain-syntax">)) </span><span class="identifier-syntax">internal_error</span><span class="plain-syntax">(</span><span class="string-syntax">"term out of range"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">; </span><span class="named-paragraph-container code-font"><a href="4-trm.html#SP4_1" class="named-paragraph-link"><span class="named-paragraph">Make new blank term structure pt</span><span class="named-paragraph-number">4.1</span></a></span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">pcalc_func</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pf</span><span class="plain-syntax"> = </span><span class="identifier-syntax">CREATE</span><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_func</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pf</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">bp</span><span class="plain-syntax"> = </span><span class="identifier-syntax">bp</span><span class="plain-syntax">; </span><span class="identifier-syntax">pf</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">fn_of</span><span class="plain-syntax"> = </span><span class="identifier-syntax">ptof</span><span class="plain-syntax">; </span><span class="identifier-syntax">pf</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">from_term</span><span class="plain-syntax"> = </span><span class="identifier-syntax">t</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">function</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pf</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP4_1" class="paragraph-anchor"></a><b>&#167;4.1. </b>Where, in all three cases:
</p>
<p class="commentary"><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Make new blank term structure pt</span><span class="named-paragraph-number">4.1</span></span><span class="comment-syntax"> =</span>
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">variable</span><span class="plain-syntax"> = -1;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">constant</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">function</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">cinder</span><span class="plain-syntax"> = -1; </span><span class="comment-syntax"> that is, no cinder</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">term_checked_as_kind</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
</pre>
<ul class="endnotetexts"><li>This code is used in <a href="4-trm.html#SP4">&#167;4</a> (three times).</li></ul>
<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>&#167;5. Copying. </b></p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::copy</span><button class="popup" onclick="togglePopup('usagePopup4')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup4">Usage of <span class="code-font"><span class="function-syntax">Terms::copy</span></span>:<br/>Propositions - <a href="4-prp.html#SP13">&#167;13</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="identifier-syntax">constant</span><span class="plain-syntax">) </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">constant</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::duplicate</span><span class="plain-syntax">(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">constant</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="identifier-syntax">function</span><span class="plain-syntax">) </span><span class="identifier-syntax">pt</span><span class="plain-syntax"> = </span><a href="4-trm.html#SP4" class="function-link"><span class="function-syntax">Terms::new_function</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">bp</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><a href="4-trm.html#SP5" class="function-link"><span class="function-syntax">Terms::copy</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">fn_of</span><span class="plain-syntax">), </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">from_term</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>&#167;6. Variable letters. </b>The number 26 turns up quite often in this chapter, and while it's normally
good style to define named constants, here we're not going to. 26 is a number
which anyone<sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup> will immediately associate with the size of the alphabet.
Moreover, we can't really raise the total, because we will want to compile
these with single-character identifier names, <span class="extract"><span class="extract-syntax">a</span></span> to <span class="extract"><span class="extract-syntax">z</span></span>.<sup id="fnref:2"><a href="#fn:2" rel="footnote">2</a></sup> To have a
variable limit lower than 26 would be artificial, since there are no memory
constraints arguing for it; but a proposition with 27 or more variables would
be too huge to evaluate at run-time in any remotely plausible length of time.
So although the 26-variables-only limit is embedded in Inform, it really is
not any restriction, and it greatly simplifies the code.
</p>
<ul class="footnotetexts"><li class="footnote" id="fn:1"><p class="inwebfootnote"><sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup> Well, perhaps not a string theorist. "There aren't enough small numbers to
meet the many demands made of them" (Richard Guy).
<a href="#fnref:1" title="return to text"> &#x21A9;</a></p></li><li class="footnote" id="fn:2"><p class="inwebfootnote"><sup id="fnref:2"><a href="#fn:2" rel="footnote">2</a></sup> Strictly speaking there is also <span class="extract"><span class="extract-syntax">_</span></span>, but we won't go there.
<a href="#fnref:2" title="return to text"> &#x21A9;</a></p></li></ul>
<p class="commentary firstcommentary"><a id="SP7" class="paragraph-anchor"></a><b>&#167;7. </b>The variables 0 to 25 are referred to by the letters \(x, y, z, a, b, c, ..., w\),
as provided for by this lookup array:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">char</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pcalc_vars</span><span class="plain-syntax"> = </span><span class="string-syntax">"xyzabcdefghijklmnopqrstuvw"</span><span class="plain-syntax">;</span>
</pre>
<p class="commentary firstcommentary"><a id="SP8" class="paragraph-anchor"></a><b>&#167;8. Underlying terms. </b>Routines to see if a term is a constant \(C\), or if it is a chain of functions
at the bottom of which is a constant \(C\); and similarly for variables.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="function-syntax">Terms::constant_underlying</span><button class="popup" onclick="togglePopup('usagePopup5')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup5">Usage of <span class="code-font"><span class="function-syntax">Terms::constant_underlying</span></span>:<br/>Type Check Propositions - <a href="4-tcp.html#SP4_1">&#167;4.1</a><br/>Simplifications - <a href="5-smp.html#SP2">&#167;2</a>, <a href="5-smp.html#SP3">&#167;3</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> *</span><span class="identifier-syntax">t</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</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">"null term"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">constant</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">function</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="4-trm.html#SP8" class="function-link"><span class="function-syntax">Terms::constant_underlying</span></a><span class="plain-syntax">(&amp;(</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">fn_of</span><span class="plain-syntax">));</span>
<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>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::variable_underlying</span><button class="popup" onclick="togglePopup('usagePopup6')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup6">Usage of <span class="code-font"><span class="function-syntax">Terms::variable_underlying</span></span>:<br/>Propositions - <a href="4-prp.html#SP25">&#167;25</a>, <a href="4-prp.html#SP27">&#167;27</a><br/>Binding and Substitution - <a href="4-bas.html#SP1">&#167;1</a>, <a href="4-bas.html#SP7">&#167;7</a>, <a href="4-bas.html#SP13_1">&#167;13.1</a><br/>Sentence Conversions - <a href="5-sc.html#SP3_2">&#167;3.2</a><br/>Simplifications - <a href="5-smp.html#SP13">&#167;13</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> *</span><span class="identifier-syntax">t</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</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">"null term"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">variable</span><span class="plain-syntax"> &gt;= </span><span class="constant-syntax">0</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">variable</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">function</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="4-trm.html#SP8" class="function-link"><span class="function-syntax">Terms::variable_underlying</span></a><span class="plain-syntax">(&amp;(</span><span class="identifier-syntax">t</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">fn_of</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> -1;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP9" class="paragraph-anchor"></a><b>&#167;9. Adjective-noun conversions. </b>As we shall see, a general unary predicate stores a type-reference
pointer to an adjectival phrase &mdash; the adjective it tests. But
sometimes the same word acts both as adjective and noun in English. In
"the green door", clearly "green" is an adjective; in "the door
is green", it is possibly a noun; in "the colour of the door is
green", it must surely be a noun. Yet these are all really the same
meaning. To cope with this ambiguity, we need a way to convert the
adjectival form of such an adjective into its noun form, and back
again.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax">#</span><span class="identifier-syntax">ifdef</span><span class="plain-syntax"> </span><span class="identifier-syntax">CORE_MODULE</span>
<span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::adj_to_noun_conversion</span><button class="popup" onclick="togglePopup('usagePopup7')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup7">Usage of <span class="code-font"><span class="function-syntax">Terms::adj_to_noun_conversion</span></span>:<br/>Propositions - <a href="4-prp.html#SP29">&#167;29</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">unary_predicate</span><span class="plain-syntax"> *</span><span class="identifier-syntax">tr</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">adjective</span><span class="plain-syntax"> *</span><span class="identifier-syntax">aph</span><span class="plain-syntax"> = </span><span class="identifier-syntax">AdjectivalPredicates::to_adjective</span><span class="plain-syntax">(</span><span class="identifier-syntax">tr</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">instance</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax"> = </span><span class="identifier-syntax">AdjectiveAmbiguity::has_enumerative_meaning</span><span class="plain-syntax">(</span><span class="identifier-syntax">aph</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">I</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="4-trm.html#SP4" class="function-link"><span class="function-syntax">Terms::new_constant</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">Rvalues::from_instance</span><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">property</span><span class="plain-syntax"> *</span><span class="identifier-syntax">prn</span><span class="plain-syntax"> = </span><span class="identifier-syntax">AdjectiveAmbiguity::has_either_or_property_meaning</span><span class="plain-syntax">(</span><span class="identifier-syntax">aph</span><span class="plain-syntax">, </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">prn</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="4-trm.html#SP4" class="function-link"><span class="function-syntax">Terms::new_constant</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">Rvalues::from_property</span><span class="plain-syntax">(</span><span class="identifier-syntax">prn</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="4-trm.html#SP4" class="function-link"><span class="function-syntax">Terms::new_variable</span></a><span class="plain-syntax">(0);</span>
<span class="plain-syntax">}</span>
<span class="plain-syntax">#</span><span class="identifier-syntax">endif</span>
</pre>
<p class="commentary firstcommentary"><a id="SP10" class="paragraph-anchor"></a><b>&#167;10. </b>And conversely:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">unary_predicate</span><span class="plain-syntax"> *</span><span class="function-syntax">Terms::noun_to_adj_conversion</span><button class="popup" onclick="togglePopup('usagePopup8')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup8">Usage of <span class="code-font"><span class="function-syntax">Terms::noun_to_adj_conversion</span></span>:<br/>Type Check Propositions - <a href="4-tcp.html#SP4_6">&#167;4.6</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> </span><span class="identifier-syntax">pt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> #</span><span class="identifier-syntax">ifdef</span><span class="plain-syntax"> </span><span class="identifier-syntax">CORE_MODULE</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">C</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">.</span><span class="element-syntax">constant</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">, </span><span class="identifier-syntax">CONSTANT_NT</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FALSE</span><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>
<span class="plain-syntax"> </span><span class="identifier-syntax">kind</span><span class="plain-syntax"> *</span><span class="identifier-syntax">K</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::get_kind_of_value</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Properties::property_with_same_name_as</span><span class="plain-syntax">(</span><span class="identifier-syntax">K</span><span class="plain-syntax">) == </span><span class="identifier-syntax">NULL</span><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>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Kinds::Behaviour::is_an_enumeration</span><span class="plain-syntax">(</span><span class="identifier-syntax">K</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">instance</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::get_constant_instance</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">AdjectivalPredicates::new_up</span><span class="plain-syntax">(</span><span class="identifier-syntax">Instances::as_adjective</span><span class="plain-syntax">(</span><span class="identifier-syntax">I</span><span class="plain-syntax">), </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> #</span><span class="identifier-syntax">endif</span>
<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>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP11" class="paragraph-anchor"></a><b>&#167;11. Writing to text. </b>The art of this is to be unobtrusive; when a proposition is being logged,
we don't much care about the constant terms, and want to display them
concisely and without fuss.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::log</span><button class="popup" onclick="togglePopup('usagePopup9')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup9">Usage of <span class="code-font"><span class="function-syntax">Terms::log</span></span>:<br/>Calculus Module - <a href="1-cm.html#SP3">&#167;3</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><a href="4-trm.html#SP11" class="function-link"><span class="function-syntax">Terms::write</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">DL</span><span class="plain-syntax">, </span><span class="identifier-syntax">pt</span><span class="plain-syntax">);</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">void</span><span class="plain-syntax"> </span><span class="function-syntax">Terms::write</span><button class="popup" onclick="togglePopup('usagePopup10')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup10">Usage of <span class="code-font"><span class="function-syntax">Terms::write</span></span>:<br/>Calculus Module - <a href="1-cm.html#SP5">&#167;5</a><br/>Compilation Schemas - <a href="3-cs.html#SP7">&#167;7</a><br/>Atomic Propositions - <a href="4-ap.html#SP14_1">&#167;14.1</a>, <a href="4-ap.html#SP14_4">&#167;14.4</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">text_stream</span><span class="plain-syntax"> *</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="reserved-syntax">pcalc_term</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"&lt;null-term&gt;"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> } </span><span class="reserved-syntax">else</span><span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">C</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">cinder</span><span class="plain-syntax"> &gt;= </span><span class="constant-syntax">0</span><span class="plain-syntax">) { </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"const_%d"</span><span class="plain-syntax">, </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">cinder</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax">; }</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Wordings::nonempty</span><span class="plain-syntax">(</span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">))) { </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"'%W'"</span><span class="plain-syntax">, </span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">)); </span><span class="reserved-syntax">return</span><span class="plain-syntax">; }</span>
<span class="plain-syntax"> #</span><span class="identifier-syntax">ifdef</span><span class="plain-syntax"> </span><span class="identifier-syntax">CORE_MODULE</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">, </span><span class="identifier-syntax">CONSTANT_NT</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">instance</span><span class="plain-syntax"> *</span><span class="identifier-syntax">I</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Rvalues::to_object_instance</span><span class="plain-syntax">(</span><span class="identifier-syntax">C</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">I</span><span class="plain-syntax">) { </span><span class="identifier-syntax">Instances::write</span><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">I</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax">; }</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> #</span><span class="identifier-syntax">endif</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Node::log_node</span><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">C</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> } </span><span class="reserved-syntax">else</span><span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">binary_predicate</span><span class="plain-syntax"> *</span><span class="identifier-syntax">bp</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">bp</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">i6_schema</span><span class="plain-syntax"> *</span><span class="identifier-syntax">fn</span><span class="plain-syntax"> = </span><a href="3-bp.html#SP7" class="function-link"><span class="function-syntax">BinaryPredicates::get_term_as_fn_of_other</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">bp</span><span class="plain-syntax">, </span><span class="constant-syntax">1</span><span class="plain-syntax">-</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">from_term</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">fn</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">"function of non-functional predicate"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><a href="3-cs.html#SP7" class="function-link"><span class="function-syntax">Calculus::Schemas::write_applied</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">fn</span><span class="plain-syntax">, &amp;(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">function</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">fn_of</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> } </span><span class="reserved-syntax">else</span><span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">variable</span><span class="plain-syntax"> &gt;= </span><span class="constant-syntax">0</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">j</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">variable</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">j</span><span class="plain-syntax">&lt;26) </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"%c"</span><span class="plain-syntax">, </span><span class="identifier-syntax">pcalc_vars</span><span class="plain-syntax">[</span><span class="identifier-syntax">j</span><span class="plain-syntax">]); </span><span class="reserved-syntax">else</span><span class="plain-syntax"> </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"&lt;bad-var=%d&gt;"</span><span class="plain-syntax">, </span><span class="identifier-syntax">j</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> } </span><span class="reserved-syntax">else</span><span class="plain-syntax"> {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"&lt;bad-term&gt;"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax">}</span>
</pre>
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