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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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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../inform7n.html">Inform7</a></li><li><a href="index.html">knowledge</a></li><li><a href="index.html#2">Chapter 2: Instances and Variables</a></li><li><b>Nonlocal Variables</b></li></ul></div>
<p class="purpose">To manage variables whose scope is wider than the current rule.</p>
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. </b>The term "nonlocal variable" is less than elegant,<sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup> but it expresses a basic
truth &mdash; that Inform, in contrast to C-like languages, has two different sorts
of variables:
</p>
<ul class="items"><li>&#9679; Local variables exist only in the current stack frame and therefore die
with it; assertions cannot declare their values; they are created with the
"let" phrase or similar, not by assertion sentences.
</li><li>&#9679; Nonlocal variables, all of the others, exist across multiple stack frames,
and are longer-lived. We don't call these "global" because intermediate scopes
are also possible: rulebook, activity and action variables, for example, have
a limited scope and lifetime, but are nevertheless not local to any one rule.
These variables are created by assertion sentences.
</li></ul>
<p class="commentary">These semantics are so different that it makes no compelling sense to try to
give them a common implementation inside the compiler; so, nonlocal variables
are handled below, but local variables have a different implementation at
<a href="../imperative-module/3-lv.html" class="internal">Local Variables (in imperative)</a>.
</p>
<p class="commentary">A pragmatic, but questionable,<sup id="fnref:2"><a href="#fn:2" rel="footnote">2</a></sup> implementation decision by Inform is that
names created as aliases for constant values are implemented as being variables
that happen not to vary.
</p>
<p class="commentary">Nonlocal variables are stored in all kinds of ways at run-time. See
<a href="../runtime-module/5-vrb.html" class="internal">Variables (in runtime)</a> for more.
</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> At one time the term used here was "quantity", which sounded philosophical
and was too vague.
<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> Does it really make sense to regard named constants as being conceptually
closer to global variables than to literals such as <span class="extract"><span class="extract-syntax">true</span></span> or <span class="extract"><span class="extract-syntax">false</span></span>?
<a href="#fnref:2" title="return to text"> &#x21A9;</a></p></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">nonlocal_variable</span><span class="plain-syntax"> {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">name</span><span class="plain-syntax">; </span><span class="comment-syntax"> text of the name</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">nlv_kind</span><span class="plain-syntax">; </span><span class="comment-syntax"> what kind of value it holds</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">shared_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">scope</span><span class="plain-syntax">; </span><span class="comment-syntax"> where it exists, or </span><span class="extract"><span class="extract-syntax">NULL</span></span><span class="comment-syntax"> for everywhere</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="identifier-syntax">as_subject</span><span class="plain-syntax">; </span><span class="comment-syntax"> so that assertions can discuss it...</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="identifier-syntax">alias_subject</span><span class="plain-syntax">; </span><span class="comment-syntax"> ...or perhaps the thing it aliases</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">constant_at_run_time</span><span class="plain-syntax">; </span><span class="comment-syntax"> for instance, for "story title"</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">substitution_marker</span><span class="plain-syntax">; </span><span class="comment-syntax"> to prevent infinite regress when substituting</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">var_is_bibliographic</span><span class="plain-syntax">; </span><span class="comment-syntax"> one of the bibliographic constants set at the end</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">var_is_allowed_to_be_zero</span><span class="plain-syntax">; </span><span class="comment-syntax"> for an empty enumerated kind, despite non-safety</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">variable_compilation_data</span><span class="plain-syntax"> </span><span class="identifier-syntax">compilation_data</span><span class="plain-syntax">;</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">nlv_created_at</span><span class="plain-syntax">; </span><span class="comment-syntax"> sentence creating the variable</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">struct</span><span class="plain-syntax"> </span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">var_documentation_symbol</span><span class="plain-syntax">; </span><span class="comment-syntax"> reference to manual, if any</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">CLASS_DEFINITION</span>
<span class="plain-syntax">} </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax">;</span>
</pre>
<ul class="endnotetexts"><li>The structure nonlocal_variable is accessed in 2/ins, 3/prp, 3/vp, 3/spr, 3/msr, 4/vs, 4/pp, 5/pi, 5/tmw, 5/tnt and here.</li></ul>
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. </b>We can create a new variable provided we give its name, kind and scope.
When the scope isn't global, the variable is said to be "stacked", which is a
reference to how it's stored at run-time.
</p>
<p class="commentary">Note that we only register the name of the variable as a proper noun if it's
global and will live forever, because nouns are both of those things. Anyone
creating a shared variable will have to make their own arrangements to parse
the names of them.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::new_global</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">NonlocalVariables::new_global</span></span>:<br/>Assert Propositions - <a href="1-ap.html#SP6_5_2">&#167;6.5.2</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">W</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="plain-syntax"> </span><span class="constant-syntax">PROTECTED_MODEL_PROCEDURE</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax"> = </span><a href="2-nv.html#SP4" class="function-link"><span class="function-syntax">NonlocalVariables::new</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</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="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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">name</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Nouns::new_proper_noun</span><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">name</span><span class="plain-syntax">, </span><span class="identifier-syntax">NEUTER_GENDER</span><span class="plain-syntax">, </span><span class="identifier-syntax">ADD_TO_LEXICON_NTOPT</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">VARIABLE_MC</span><span class="plain-syntax">, </span><span class="identifier-syntax">Lvalues::new_actual_NONLOCAL_VARIABLE</span><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">),</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="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. </b>The following then parses for those nouns, and note that it therefore can
only match globals, since variables of lesser scope are not in the lexicon.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::parse_global</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">NonlocalVariables::parse_global</span></span>:<br/><a href="2-nv.html#SP7">&#167;7</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">W</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">W</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Articles::remove_the</span><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="function-syntax">&lt;s-global-variable&gt;</span><span class="plain-syntax">(</span><span class="identifier-syntax">W</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">val</span><span class="plain-syntax"> = </span><span class="function-syntax">&lt;&lt;rp&gt;&gt;</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">Node::get_constant_nonlocal_variable</span><span class="plain-syntax">(</span><span class="identifier-syntax">val</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">NULL</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>&#167;4. </b>We record the one most recently made:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">latest_nonlocal_variable</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::get_latest</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</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">latest_nonlocal_variable</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::new</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">NonlocalVariables::new</span></span>:<br/><a href="2-nv.html#SP2">&#167;2</a></span></button><span class="plain-syntax">(</span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">W</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">shared_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">shv</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="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">"created variable without kind"</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::definite</span><span class="plain-syntax">(</span><span class="identifier-syntax">K</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FALSE</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::get_construct</span><span class="plain-syntax">(</span><span class="identifier-syntax">K</span><span class="plain-syntax">) == </span><span class="identifier-syntax">CON_phrase</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="2-nv.html#SP4_2" class="named-paragraph-link"><span class="named-paragraph">Issue problem message for a phrase used before its kind is known</span><span class="named-paragraph-number">4.2</span></a></span>
<span class="plain-syntax"> </span><span class="reserved-syntax">else</span>
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="2-nv.html#SP4_1" class="named-paragraph-link"><span class="named-paragraph">Issue problem message for an indefinite variable</span><span class="named-paragraph-number">4.1</span></a></span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax"> = </span><span class="identifier-syntax">CREATE</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">latest_nonlocal_variable</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">var_documentation_symbol</span><span class="plain-syntax"> = </span><span class="identifier-syntax">DocReferences::position_of_symbol</span><span class="plain-syntax">(&amp;</span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">name</span><span class="plain-syntax"> = </span><span class="identifier-syntax">W</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_created_at</span><span class="plain-syntax"> = </span><span class="identifier-syntax">current_sentence</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_kind</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">alias_subject</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">var_is_allowed_to_be_zero</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">scope</span><span class="plain-syntax"> = </span><span class="identifier-syntax">shv</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">substitution_marker</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">as_subject</span><span class="plain-syntax"> = </span><a href="4-vs.html#SP1" class="function-link"><span class="function-syntax">VariableSubjects::new</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">compilation_data</span><span class="plain-syntax"> = </span><span class="identifier-syntax">RTVariables::new_compilation_data</span><span class="plain-syntax">();</span>
<span class="plain-syntax"> </span><span class="named-paragraph-container code-font"><a href="2-nv.html#SP4_5" class="named-paragraph-link"><span class="named-paragraph">Notice a few special variables</span><span class="named-paragraph-number">4.5</span></a></span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">PluginCalls::new_variable_notify</span><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">LOGIF</span><span class="plain-syntax">(</span><span class="identifier-syntax">VARIABLE_CREATIONS</span><span class="plain-syntax">, </span><span class="string-syntax">"Created nonlocal variable: $Z\n"</span><span class="plain-syntax">, </span><span class="identifier-syntax">nlv</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">nlv</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><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Issue problem message for an indefinite variable</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">Problems::quote_wording</span><span class="plain-syntax">(1, </span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::quote_kind</span><span class="plain-syntax">(2, </span><span class="identifier-syntax">K</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::handmade_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_IndefiniteVariable</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_segment</span><span class="plain-syntax">(</span>
<span class="plain-syntax"> </span><span class="string-syntax">"I am unable to create the variable '%1', because its kind (%2) is too "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"vague. I need to know exactly what kind of value goes into each "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"variable: for instance, it's not enough to say 'L is a list of values "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"that varies', because I don't know what the entries have to be - 'L "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"is a list of numbers that varies' would be better."</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_end</span><span class="plain-syntax">();</span>
</pre>
<ul class="endnotetexts"><li>This code is used in <a href="2-nv.html#SP4">&#167;4</a>.</li></ul>
<p class="commentary firstcommentary"><a id="SP4_2" class="paragraph-anchor"></a><b>&#167;4.2. </b>This typically arises for timing reasons. At the time the variable has to be
created, and given a kind, the kind of the initial value has not been fully
determined. So <span class="extract"><span class="extract-syntax">K</span></span> here will be something like <span class="extract"><span class="extract-syntax">phrase value -&gt; value</span></span>. If this
case arose often enough it might be worth refactoring everything, but it's
rarely occurring and has an easy workaround. So we will just give a fairly
helpful problem message:
</p>
<p class="commentary"><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Issue problem message for a phrase used before its kind is known</span><span class="named-paragraph-number">4.2</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">LOG</span><span class="plain-syntax">(</span><span class="string-syntax">"W = %W, Domain = %u\n"</span><span class="plain-syntax">, </span><span class="identifier-syntax">W</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">Problems::quote_wording</span><span class="plain-syntax">(1, </span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::handmade_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_IndefiniteVariable2</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_segment</span><span class="plain-syntax">(</span>
<span class="plain-syntax"> </span><span class="string-syntax">"I am unable to create '%1', because the text was too vague about what "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"its kind should be - I can see it's a phrase, but not what kind of phrase. "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"(You may be able to fix this by declaring the kind directly first. For "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"example, rather than 'The magic word is initially my deluxe phrase.', "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"something like 'The magic word is a phrase nothing -&gt; nothing variable. "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"The magic word is initially my deluxe phrase.')"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_end</span><span class="plain-syntax">();</span>
</pre>
<ul class="endnotetexts"><li>This code is used in <a href="2-nv.html#SP4">&#167;4</a>.</li></ul>
<p class="commentary firstcommentary"><a id="SP4_3" class="paragraph-anchor"></a><b>&#167;4.3. </b>Four oddball cases have special behaviour:
</p>
<ul class="items"><li>&#9679; <span class="extract"><span class="extract-syntax">Inter_nothing_VAR</span></span> is translated not to an Inter variable, but to the
Inter constant <span class="extract"><span class="extract-syntax">nothing</span></span>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">temporary_global_VAR</span></span> is translated to an Inter global used as temporary
storage space, and which has no fixed kind. An author cannot access this
directly in source text.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">parameter_object_VAR</span></span> is translated to an Inter global used during the
run of certain rulebooks, and which has no fixed kind. (This could have been
handled as a rulebook variable, but having it as a global is more efficient.)
</li><li>&#9679; <span class="extract"><span class="extract-syntax">command_prompt_VAR</span></span> is a quite ordinary Inform 7 variable, except that
it is compiled in an unusual way, to achieve backwards compatibility with
the code in <a href="../CommandParserKit/index.html" class="internal">CommandParserKit</a>, which dates back to the era of Inform 1 to 6.
</li></ul>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">temporary_global_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">Inter_nothing_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">; </span><span class="comment-syntax"> the </span><span class="extract"><span class="extract-syntax">nothing</span></span><span class="comment-syntax"> constant</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">command_prompt_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">; </span><span class="comment-syntax"> the command prompt text</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">parameter_object_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">;</span>
</pre>
<p class="commentary firstcommentary"><a id="SP4_4" class="paragraph-anchor"></a><b>&#167;4.4. </b></p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::nothing_pseudo_variable</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</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">Inter_nothing_VAR</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::command_prompt_variable</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</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">command_prompt_VAR</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::parameter_object_variable</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</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">parameter_object_VAR</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::temporary_global_variable</span><span class="plain-syntax">(</span><span class="reserved-syntax">void</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">temporary_global_VAR</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP4_5" class="paragraph-anchor"></a><b>&#167;4.5. </b><span class="named-paragraph-container code-font"><span class="named-paragraph-defn">Notice a few special variables</span><span class="named-paragraph-number">4.5</span></span><span class="comment-syntax"> =</span>
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="function-syntax">&lt;notable-variables&gt;</span><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">switch</span><span class="plain-syntax"> (</span><span class="function-syntax">&lt;&lt;r&gt;&gt;</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="constant-syntax">0</span><span class="plain-syntax">: </span><span class="identifier-syntax">temporary_global_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">; </span><span class="reserved-syntax">break</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax">: </span><span class="identifier-syntax">Inter_nothing_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">; </span><span class="reserved-syntax">break</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="constant-syntax">2</span><span class="plain-syntax">: </span><span class="identifier-syntax">command_prompt_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">; </span><span class="reserved-syntax">break</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">case</span><span class="plain-syntax"> </span><span class="constant-syntax">3</span><span class="plain-syntax">: </span><span class="identifier-syntax">parameter_object_VAR</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">; </span><span class="reserved-syntax">break</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> }</span>
</pre>
<ul class="endnotetexts"><li>This code is used in <a href="2-nv.html#SP4">&#167;4</a>.</li></ul>
<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>&#167;5. </b>Inform recognises these special variables by their English names:
</p>
<pre class="Preform-displayed-code all-displayed-code code-font">
<span class="Preform-function-syntax">&lt;notable-variables&gt;</span><span class="Preform-plain-syntax"> </span><span class="Preform-reserved-syntax">::=</span>
<span class="Preform-plain-syntax"> </span><span class="Preform-constant-syntax">i6-varying-global</span><span class="Preform-plain-syntax"> </span><span class="Preform-reserved-syntax">|</span>
<span class="Preform-plain-syntax"> </span><span class="Preform-constant-syntax">i6-nothing-constant</span><span class="Preform-plain-syntax"> </span><span class="Preform-reserved-syntax">|</span>
<span class="Preform-plain-syntax"> </span><span class="Preform-constant-syntax">command</span><span class="Preform-plain-syntax"> </span><span class="Preform-constant-syntax">prompt</span><span class="Preform-plain-syntax"> </span><span class="Preform-reserved-syntax">|</span>
<span class="Preform-plain-syntax"> </span><span class="Preform-constant-syntax">parameter-object</span>
</pre>
<ul class="endnotetexts"><li>This is <a href="../words-module/4-ap.html" class="internal">Preform grammar</a>, not regular C code.</li></ul>
<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>&#167;6. </b>So much for creation; and here's how we log and write them:
</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">NonlocalVariables::log</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><a href="2-nv.html#SP6" class="function-link"><span class="function-syntax">NonlocalVariables::write</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">DL</span><span class="plain-syntax">, </span><span class="identifier-syntax">nlv</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">NonlocalVariables::write</span><span class="plain-syntax">(</span><span class="identifier-syntax">OUTPUT_STREAM</span><span class="plain-syntax">, </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">) { </span><span class="identifier-syntax">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"&lt;null variable&gt;"</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">WRITE</span><span class="plain-syntax">(</span><span class="string-syntax">"'%W'(%s)"</span><span class="plain-syntax">, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">name</span><span class="plain-syntax">, (</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</span><span class="plain-syntax">)?</span><span class="string-syntax">"const"</span><span class="plain-syntax">:</span><span class="string-syntax">"var"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Kinds::Textual::write</span><span class="plain-syntax">(</span><span class="identifier-syntax">OUT</span><span class="plain-syntax">, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_kind</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>The author can demand with a "translates as" sentence that a given
variable is equivalent to an Inter variable supplied in some kit:
</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">NonlocalVariables::translates</span><span class="plain-syntax">(</span><span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="identifier-syntax">W</span><span class="plain-syntax">, </span><span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="identifier-syntax">p2</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax"> = </span><a href="2-nv.html#SP3" class="function-link"><span class="function-syntax">NonlocalVariables::parse_global</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</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">nlv</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NULL</span><span class="plain-syntax">) || (</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">scope</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">LOG</span><span class="plain-syntax">(</span><span class="string-syntax">"Tried %W\n"</span><span class="plain-syntax">, </span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::sentence_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_NonQuantityTranslated</span><span class="plain-syntax">),</span>
<span class="plain-syntax"> </span><span class="string-syntax">"this is not the name of a variable"</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="string-syntax">"or at any rate not one global in scope."</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="identifier-syntax">TEMPORARY_TEXT</span><span class="plain-syntax">(</span><span class="identifier-syntax">name</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">WRITE_TO</span><span class="plain-syntax">(</span><span class="identifier-syntax">name</span><span class="plain-syntax">, </span><span class="string-syntax">"%N"</span><span class="plain-syntax">, </span><span class="identifier-syntax">Wordings::first_wn</span><span class="plain-syntax">(</span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">p2</span><span class="plain-syntax">)));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">RTVariables::identifier_translates</span><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">, </span><span class="identifier-syntax">name</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">DISCARD_TEXT</span><span class="plain-syntax">(</span><span class="identifier-syntax">name</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">LOGIF</span><span class="plain-syntax">(</span><span class="identifier-syntax">VARIABLE_CREATIONS</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="string-syntax">"Translated variable: $Z as %N\n"</span><span class="plain-syntax">, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Wordings::first_wn</span><span class="plain-syntax">(</span><span class="identifier-syntax">Node::get_text</span><span class="plain-syntax">(</span><span class="identifier-syntax">p2</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>Nonlocal variables are inference subjects in order that they can be given
initial values by inference: see <a href="4-vs.html" class="internal">Variable Subjects</a> for more.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::to_subject</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">NonlocalVariables::to_subject</span></span>:<br/><a href="2-nv.html#SP11">&#167;11</a><br/>Variable Subjects - <a href="4-vs.html#SP2">&#167;2</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">as_subject</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>Now for some basic properties:
</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">NonlocalVariables::is_global</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">scope</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</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">TRUE</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="identifier-syntax">kind</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::kind</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">NonlocalVariables::kind</span></span>:<br/>Variable Subjects - <a href="4-vs.html#SP3">&#167;3</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</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">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_kind</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">NonlocalVariables::allow_to_be_zero</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">var_is_allowed_to_be_zero</span><span class="plain-syntax"> = </span><span class="identifier-syntax">TRUE</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>The kind can in fact be changed after creation, though this never happens
to variables declared in source text: it allows us to have a few globals which
are reused for different purposes and are typeless.
</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">NonlocalVariables::set_kind</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">nlv</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">"set kind for null variable"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_kind</span><span class="plain-syntax"> = </span><span class="identifier-syntax">K</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. </b>This is a curiosity, used to force the textual contents of a bibliographic
data variable (such as "story title") to be treated as text.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="identifier-syntax">wording</span><span class="plain-syntax"> </span><span class="function-syntax">NonlocalVariables::initial_value_as_plain_text</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">inference</span><span class="plain-syntax"> *</span><span class="identifier-syntax">inf</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="identifier-syntax">infs</span><span class="plain-syntax"> = </span><a href="2-nv.html#SP8" class="function-link"><span class="function-syntax">NonlocalVariables::to_subject</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">POSITIVE_KNOWLEDGE_LOOP</span><span class="plain-syntax">(</span><span class="identifier-syntax">inf</span><span class="plain-syntax">, </span><span class="identifier-syntax">infs</span><span class="plain-syntax">, </span><span class="identifier-syntax">property_inf</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><a href="5-pi.html#SP7" class="function-link"><span class="function-syntax">PropertyInferences::get_property</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">inf</span><span class="plain-syntax">) == </span><span class="identifier-syntax">P_variable_initial_value</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">Node::get_text</span><span class="plain-syntax">(</span>
<span class="plain-syntax"> </span><a href="5-pi.html#SP8" class="function-link"><span class="function-syntax">PropertyInferences::set_value_kind</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">inf</span><span class="plain-syntax">, </span><span class="identifier-syntax">K_text</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">EMPTY_WORDING</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. </b>"Constant" means that no change is permitted at run-time; "initialisable"
means that a value can be set by an assertion in the source text.
</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">NonlocalVariables::make_constant</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">NonlocalVariables::make_constant</span></span>:<br/>Assert Propositions - <a href="1-ap.html#SP6_5_2">&#167;6.5.2</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">, </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">bib</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">nlv</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">"no such var"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</span><span class="plain-syntax"> = </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">var_is_bibliographic</span><span class="plain-syntax"> = </span><span class="identifier-syntax">bib</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">RTVariables::make_initialisable</span><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</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">NonlocalVariables::is_constant</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</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">"no such var"</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</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">NonlocalVariables::must_be_constant</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::sentence_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_CantChangeConstants</span><span class="plain-syntax">),</span>
<span class="plain-syntax"> </span><span class="string-syntax">"this is a name for a value which never changes during the story"</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="string-syntax">"so it can't be altered with 'now'."</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">TRUE</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">FALSE</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">NonlocalVariables::warn_about_change</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">score_VAR</span><span class="plain-syntax">) &amp;&amp; (</span><span class="identifier-syntax">nlv</span><span class="plain-syntax"> == </span><span class="identifier-syntax">score_VAR</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">global_compilation_settings</span><span class="plain-syntax">.</span><span class="identifier-syntax">scoring_option_set</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">global_compilation_settings</span><span class="plain-syntax">.</span><span class="identifier-syntax">scoring_option_set</span><span class="plain-syntax"> == </span><span class="identifier-syntax">NOT_APPLICABLE</span><span class="plain-syntax">)) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::sentence_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_CantChangeScore</span><span class="plain-syntax">),</span>
<span class="plain-syntax"> </span><span class="string-syntax">"this is a story with no scoring"</span><span class="plain-syntax">,</span>
<span class="plain-syntax"> </span><span class="string-syntax">"so it makes no sense to change the 'score' value. You can add "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"scoring to the story by including the sentence 'Use scoring.', "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"in which case this problem message will go away; or you can "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"remove it with 'Use no scoring.' (Until 2011, the default was "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"to have scoring, but now it's not to have scoring.)"</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> }</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>Substitution is the down-side if handling constants as if they were variables.
At some point, the constant has to be replaced by its value, and this is where.
Note that it's easy to imagine a chain of constants defined each as being
equal to the next, but that a cycle of those is illegal.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">substitution_session_id</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">;</span>
<span class="identifier-syntax">parse_node</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::substitute_constants</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="identifier-syntax">substitution_session_id</span><span class="plain-syntax">++;</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">while</span><span class="plain-syntax"> (</span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax"> = </span><span class="identifier-syntax">Lvalues::get_nonlocal_variable_if_any</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">nlv</span><span class="plain-syntax">) &amp;&amp; (</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">constant_at_run_time</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">substitution_marker</span><span class="plain-syntax"> == </span><span class="identifier-syntax">substitution_session_id</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::quote_source</span><span class="plain-syntax">(1, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_created_at</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::quote_wording</span><span class="plain-syntax">(2, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">name</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::quote_kind</span><span class="plain-syntax">(3, </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nlv_kind</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">StandardProblems::handmade_problem</span><span class="plain-syntax">(</span><span class="identifier-syntax">Task::syntax_tree</span><span class="plain-syntax">(),</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">_p_</span><span class="plain-syntax">(</span><span class="identifier-syntax">PM_MeaningRecursive</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_segment</span><span class="plain-syntax">(</span>
<span class="plain-syntax"> </span><span class="string-syntax">"The sentence %1 tells me that '%2', which should be %3 "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"that varies, is to have an initial value which can't "</span>
<span class="plain-syntax"> </span><span class="string-syntax">"be worked out without going round in circles."</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">Problems::issue_problem_end</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">Specifications::new_UNKNOWN</span><span class="plain-syntax">(</span><span class="identifier-syntax">Node::get_text</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">break</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">substitution_marker</span><span class="plain-syntax"> = </span><span class="identifier-syntax">substitution_session_id</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">sspec</span><span class="plain-syntax"> = </span><a href="4-vs.html#SP2" class="function-link"><span class="function-syntax">VariableSubjects::get_initial_value</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</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">sspec</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="identifier-syntax">spec</span><span class="plain-syntax"> = </span><span class="identifier-syntax">sspec</span><span class="plain-syntax">; </span><span class="reserved-syntax">continue</span><span class="plain-syntax">; }</span>
<span class="plain-syntax"> }</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">break</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">spec</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP14" class="paragraph-anchor"></a><b>&#167;14. </b>"Aliasing" is the ability to divert inferences about a variable to
inferences about something else. Inform uses this for interactive fiction
projects with "the player"; authors tend to think "the player" is an instance
and they write assertions accordingly, but in fact it's a variable. Because
of this aliasing, however, an inference about "the player" is diverted to
become an inference about "yourself", the actual default player instance.
</p>
<p class="commentary">At present this is the only use made of aliasing.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="function-syntax">NonlocalVariables::get_alias</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">NonlocalVariables::get_alias</span></span>:<br/>Assert Propositions - <a href="1-ap.html#SP9">&#167;9</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</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">nlv</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">val</span><span class="plain-syntax"> = </span><a href="4-vs.html#SP2" class="function-link"><span class="function-syntax">VariableSubjects::get_initial_value</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">);</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="identifier-syntax">vals</span><span class="plain-syntax"> = </span><a href="4-is.html#SP14" class="function-link"><span class="function-syntax">InferenceSubjects::from_specification</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">val</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">vals</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">vals</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">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">alias_subject</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">NULL</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">NonlocalVariables::set_alias</span><span class="plain-syntax">(</span><span class="reserved-syntax">nonlocal_variable</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nlv</span><span class="plain-syntax">, </span><span class="reserved-syntax">inference_subject</span><span class="plain-syntax"> *</span><span class="identifier-syntax">infs</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">nlv</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">alias_subject</span><span class="plain-syntax"> = </span><span class="identifier-syntax">infs</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
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