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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../compiler.html">Inform7</a></li><li><a href="index.html">values</a></li><li><a href="index.html#2">Chapter 2: Specifications</a></li><li><b>Conditions</b></li></ul></div>
<p class="purpose">States of being which at any given point, at run-time, might be true or false.</p>
<ul class="toc"><li><a href="2-cnd.html#SP1">&#167;1. Creation</a></li><li><a href="2-cnd.html#SP11">&#167;11. Pretty-printing</a></li><li><a href="2-cnd.html#SP12">&#167;12. Specificity</a></li></ul><hr class="tocbar">
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. Creation. </b>In Inform, conditions are not values, nor can values be used directly as
conditions: we therefore need to provide the logical operations of AND, OR,
and NOT structurally in the parse tree rather than implementing them as phrases
like the arithmetic operators.
</p>
<p class="commentary">So <span class="extract"><span class="extract-syntax">LOGICAL_AND_NT</span></span> and <span class="extract"><span class="extract-syntax">LOGICAL_OR_NT</span></span> imitate the effect of logical
operators. They have two arguments which must themselves be CONDITIONs;
and similarly for the unary <span class="extract"><span class="extract-syntax">LOGICAL_NOT_NT</span></span>. A unique feature of Inform
among programming languages is that it has a fourth: <span class="extract"><span class="extract-syntax">LOGICAL_TENSE_NT</span></span>,
which expresses that a condition holds at a different time from the present.
</p>
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. </b><span class="extract"><span class="extract-syntax">TEST_PROPOSITION_NT</span></span> contains a predicate calculus sentence in the
<span class="extract"><span class="extract-syntax">proposition</span></span> field of its SP: there are no arguments.
</p>
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. </b><span class="extract"><span class="extract-syntax">TEST_PHRASE_OPTION_NT</span></span> tests the use of a phrase option, and is the
actual SP parsed for the second usage of the word "thoroughly" in
the following example:
</p>
<blockquote>
<p>To prognosticate, swiftly or thoroughly: ...; if thoroughly, ...</p>
</blockquote>
<p class="commentary">It uses the SP's data field to refer to the option in question: its value is the
bitmap value of the option, which will usually be \(2^n\) where the option
is the \(n\)-th in the list for this phrase, counting upwards from 0.
</p>
<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>&#167;4. </b><span class="extract"><span class="extract-syntax">TEST_VALUE_NT</span></span> tests the value beneath it in a condition context. For
truth state values, this does the obvious thing: <span class="extract"><span class="extract-syntax">true</span></span> passes and
<span class="extract"><span class="extract-syntax">false</span></span> fails. For stored actions or descriptions of actions, the current
action is tested to see if it matches.
</p>
<p class="commentary">For constant descriptions, whatever is currently being discussed (the I6 value
<span class="extract"><span class="extract-syntax">self</span></span>, generally speaking) is tested to see if it matches. But in order to
make definitions like this one work, we also need to treat descriptions as
values:
</p>
<blockquote>
<p>To decide which number is total (P - property) of (D - description):</p>
</blockquote>
<p class="commentary">The way this is done is that type-checking a description (say, "closed doors
in lighted rooms") against the expectation of finding the kind constructor
"description of K" forces Inform to convert it to a constant of that type,
compiling it as an iterator routine in I6 capable of (among other things)
supplying the members in turn, and then using the address of this routine as
the actual I6 value. (Constants with the kind "description of K" cannot arise
in any other way.)
</p>
<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>&#167;5. </b>Now some creator routines.
</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">Conditions::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">time_period</span><span class="plain-syntax"> *</span><span class="identifier-syntax">tp</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">TEST_PROPOSITION_NT</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><a href="2-cnd.html#SP10" class="function-link"><span class="function-syntax">Conditions::attach_historic_requirement</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">tp</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">spec</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. </b>So, some more specific creators. The operators are easy:
</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">Conditions::new_LOGICAL_AND</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">Conditions::new_LOGICAL_AND</span></span>:<br/>Conditions and Phrases - <a href="4-cap.html#SP2">&#167;2</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec1</span><span class="plain-syntax">, </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec2</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOGICAL_AND_NT</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax"> = </span><span class="identifier-syntax">spec1</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next</span><span class="plain-syntax"> = </span><span class="identifier-syntax">spec2</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">spec</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="function-syntax">Conditions::new_LOGICAL_OR</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">Conditions::new_LOGICAL_OR</span></span>:<br/>Conditions and Phrases - <a href="4-cap.html#SP2">&#167;2</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec1</span><span class="plain-syntax">, </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec2</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOGICAL_OR_NT</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax"> = </span><span class="identifier-syntax">spec1</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next</span><span class="plain-syntax"> = </span><span class="identifier-syntax">spec2</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">spec</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP7" class="paragraph-anchor"></a><b>&#167;7. </b></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">Conditions::negate</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">Conditions::negate</span></span>:<br/>Verbal and Relative Clauses - <a href="4-varc.html#SP11_3">&#167;11.3</a><br/>Conditions and Phrases - <a href="4-cap.html#SP4">&#167;4</a>, <a href="4-cap.html#SP5">&#167;5</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">cond</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">cond</span><span class="plain-syntax">, </span><span class="identifier-syntax">LOGICAL_NOT_NT</span><span class="plain-syntax">)) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">cond</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new_with_words</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOGICAL_NOT_NT</span><span class="plain-syntax">, </span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</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">spec</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP8" class="paragraph-anchor"></a><b>&#167;8. </b>Testing propositions is also straightforward. There's no creator for
<span class="extract"><span class="extract-syntax">NOW_PREPOSITION_VNT</span></span>, since this is formed only by coercion of one of these.
</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">Conditions::new_TEST_PROPOSITION</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">Conditions::new_TEST_PROPOSITION</span></span>:<br/>Verbal and Relative Clauses - <a href="4-varc.html#SP11_3">&#167;11.3</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">pcalc_prop</span><span class="plain-syntax"> *</span><span class="identifier-syntax">prop</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">TEST_PROPOSITION_NT</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Node::set_proposition</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">prop</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">spec</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP9" class="paragraph-anchor"></a><b>&#167;9. </b>The option number here is actually \(2^i\), where \(0\leq i&lt;15\). This is just
exactly feasible, since the specification data field is 16 bits wide.
</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">Conditions::new_TEST_PHRASE_OPTION</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">Conditions::new_TEST_PHRASE_OPTION</span></span>:<br/>Conditions and Phrases - <a href="4-cap.html#SP6">&#167;6</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">opt_num</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new</span><span class="plain-syntax">(</span><span class="identifier-syntax">TEST_PHRASE_OPTION_NT</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Annotations::write_int</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">phrase_option_ANNOT</span><span class="plain-syntax">, </span><span class="identifier-syntax">opt_num</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">spec</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP10" class="paragraph-anchor"></a><b>&#167;10. </b>Since, in principle, any condition might also have a time period attached
to it, we need a follow-up routine to attach this as necessary to a newly
created condition:
</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">Conditions::attach_tense</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">Conditions::attach_tense</span></span>:<br/>Verbal and Relative Clauses - <a href="4-varc.html#SP11_3">&#167;11.3</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">cond</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="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec</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">grammatical_usage</span><span class="plain-syntax"> *</span><span class="identifier-syntax">gu</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Stock::new_usage</span><span class="plain-syntax">(</span><span class="identifier-syntax">NULL</span><span class="plain-syntax">, </span><span class="identifier-syntax">Task::language_of_syntax</span><span class="plain-syntax">());</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Stock::add_form_to_usage</span><span class="plain-syntax">(</span><span class="identifier-syntax">gu</span><span class="plain-syntax">, </span><span class="identifier-syntax">Lcon::set_tense</span><span class="plain-syntax">(</span><span class="identifier-syntax">Lcon::base</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">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">, </span><span class="identifier-syntax">LOGICAL_TENSE_NT</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new_with_words</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOGICAL_TENSE_NT</span><span class="plain-syntax">, </span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Node::set_tense_marker</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">gu</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">spec</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="function-syntax">Conditions::attach_historic_requirement</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">Conditions::attach_historic_requirement</span></span>:<br/><a href="2-cnd.html#SP5">&#167;5</a><br/>Conditions and Phrases - <a href="4-cap.html#SP3">&#167;3</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">cond</span><span class="plain-syntax">, </span><span class="identifier-syntax">time_period</span><span class="plain-syntax"> *</span><span class="identifier-syntax">tp</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">cond</span><span class="plain-syntax">, </span><span class="identifier-syntax">AMBIGUITY_NT</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">amb</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">for</span><span class="plain-syntax"> (</span><span class="identifier-syntax">cond</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">; </span><span class="identifier-syntax">cond</span><span class="plain-syntax">; </span><span class="identifier-syntax">cond</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">next_alternative</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">reading</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::duplicate</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">reading</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">next_alternative</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">reading</span><span class="plain-syntax"> = </span><a href="2-cnd.html#SP10" class="function-link"><span class="function-syntax">Conditions::attach_historic_requirement</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">reading</span><span class="plain-syntax">, </span><span class="identifier-syntax">tp</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">reading</span><span class="plain-syntax">, </span><span class="identifier-syntax">UNKNOWN_NT</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">amb</span><span class="plain-syntax"> = </span><span class="identifier-syntax">SyntaxTree::add_reading</span><span class="plain-syntax">(</span><span class="identifier-syntax">amb</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">reading</span><span class="plain-syntax">, </span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">));</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">amb</span><span class="plain-syntax">;</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">spec</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">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">, </span><span class="identifier-syntax">LOGICAL_TENSE_NT</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</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">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Node::new_with_words</span><span class="plain-syntax">(</span><span class="identifier-syntax">LOGICAL_TENSE_NT</span><span class="plain-syntax">, </span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">cond</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax"> = </span><span class="identifier-syntax">cond</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Node::set_condition_tense</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">tp</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">spec</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. Pretty-printing. </b></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">Conditions::write_out_in_English</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">Conditions::write_out_in_English</span></span>:<br/>Specifications - <a href="2-spc.html#SP7">&#167;7</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">OUTPUT_STREAM</span><span class="plain-syntax">, </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><a href="2-spc.html#SP3" class="function-link"><span class="function-syntax">Specifications::is_description</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><a href="2-dsc.html#SP11" class="function-link"><span class="function-syntax">Descriptions::write_out_in_English</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">spec</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">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">, </span><span class="identifier-syntax">TEST_VALUE_NT</span><span class="plain-syntax">)) &amp;&amp; (</span><span class="identifier-syntax">Node::is</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</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">kind</span><span class="plain-syntax"> *</span><span class="identifier-syntax">K</span><span class="plain-syntax"> = </span><a href="2-spc.html#SP1" class="function-link"><span class="function-syntax">Specifications::to_kind</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</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">K</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Kinds::Textual::write_articled</span><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">K</span><span class="plain-syntax">);</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="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">"a condition"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP12" class="paragraph-anchor"></a><b>&#167;12. Specificity. </b>We will need a way of determining which of two conditions is more complex,
so that action-based rules with "when..." clauses tacked on can be sorted:
the following is used to compare such "when..." conditions.
</p>
<p class="commentary">This is essentially a counting argument. Long conditions, with many clauses,
beat shorter ones.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">Conditions::compare_specificity_of_CONDITIONs</span><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec1</span><span class="plain-syntax">, </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec2</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">spec1</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">) &amp;&amp; (</span><span class="identifier-syntax">spec2</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="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">count1</span><span class="plain-syntax"> = </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec1</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">count2</span><span class="plain-syntax"> = </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec2</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">count1</span><span class="plain-syntax"> &gt; </span><span class="identifier-syntax">count2</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="constant-syntax">1</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">count1</span><span class="plain-syntax"> &lt; </span><span class="identifier-syntax">count2</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> -1;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP13" class="paragraph-anchor"></a><b>&#167;13. </b>The only justification for the following complexity score is that it does
seem to accord well with what people expect. (There's clearly no theoretically
perfect way to define complexity of conditions in a language as complex as
Inform; this bit of scruffy, rather than neat, logic will have to do.)
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="function-syntax">Conditions::count</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">Conditions::count</span></span>:<br/><a href="2-cnd.html#SP12">&#167;12</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">spec</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">spec</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="constant-syntax">0</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><a href="2-spc.html#SP1" class="function-link"><span class="function-syntax">Specifications::is_condition</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</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="constant-syntax">1</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">switch</span><span class="plain-syntax"> (</span><span class="identifier-syntax">Node::get_type</span><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">LOGICAL_AND_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> + </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">LOGICAL_OR_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> -1;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">LOGICAL_NOT_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">LOGICAL_TENSE_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><a href="2-cnd.html#SP13" class="function-link"><span class="function-syntax">Conditions::count</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">down</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">TEST_PROPOSITION_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">Propositions::length</span><span class="plain-syntax">(</span><a href="2-spc.html#SP4" class="function-link"><span class="function-syntax">Specifications::to_proposition</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">spec</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">TEST_PHRASE_OPTION_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="identifier-syntax">TEST_VALUE_NT:</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
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