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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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<!--Weave of 'Length Extremes' generated by Inweb-->
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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../services.html">Services</a></li><li><a href="index.html">words</a></li><li><a href="index.html#4">Chapter 4: Parsing</a></li><li><b>Length Extremes</b></li></ul></div>
<p class="purpose">To precalculate data which enables rapid parsing of source text against a Preform grammar.</p>
<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. </b>The "length extremes" system provides one of two optimisations enabling
the Preform parser quickly to reject non-matches, the other being
<a href="4-ni.html" class="internal">Nonterminal Incidences</a>, which is harder to understand.
</p>
<p class="commentary">It may elucidate both to see the actual optimisation data for nonterminals
as used in a typical run of Inform 7 &mdash; see <a href="../inform7/M-pm.html" class="internal">Performance Metrics (in inform7)</a>.
</p>
<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. </b>The "extremes" of something to be matched against are the minimum and maximum
number of words in a successful match; with <span class="extract"><span class="extract-syntax">INFINITE_WORD_COUNT</span></span> as maximum
where the number is unlimited.
</p>
<pre class="definitions code-font"><span class="definition-keyword">define</span> <span class="constant-syntax">INFINITE_WORD_COUNT</span><span class="plain-syntax"> </span><span class="constant-syntax">1000000000</span>
</pre>
<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">length_extremes</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">min_words</span><span class="plain-syntax">, </span><span class="identifier-syntax">max_words</span><span class="plain-syntax">;</span>
<span class="plain-syntax">} </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax">;</span>
</pre>
<ul class="endnotetexts"><li>The structure length_extremes is accessed in 4/to, 4/ni, 4/prf, 4/ins and here.</li></ul>
<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. </b></p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::new</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">LengthExtremes::new</span></span>:<br/>Nonterminals - <a href="4-nnt.html#SP4">&#167;4</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">min</span><span class="plain-syntax">, </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">max</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="identifier-syntax">min</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> = </span><span class="identifier-syntax">max</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">E</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>Four useful special cases:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::no_words_at_all</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">LengthExtremes::no_words_at_all</span></span>:<br/><a href="4-le.html#SP8">&#167;8</a></span></button><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">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</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">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::any_number_of_words</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">LengthExtremes::any_number_of_words</span></span>:<br/><a href="4-le.html#SP9">&#167;9</a></span></button><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">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">INFINITE_WORD_COUNT</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">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::at_least_one_word</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">LengthExtremes::at_least_one_word</span></span>:<br/><a href="4-le.html#SP9">&#167;9</a><br/>The Optimiser - <a href="4-to.html#SP2">&#167;2</a>, <a href="4-to.html#SP4">&#167;4</a>, <a href="4-to.html#SP7">&#167;7</a></span></button><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">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">1</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">INFINITE_WORD_COUNT</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">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::exactly_one_word</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">LengthExtremes::exactly_one_word</span></span>:<br/><a href="4-le.html#SP9">&#167;9</a></span></button><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">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">1</span><span class="plain-syntax">; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</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">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>&#167;5. </b>Testing:
</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">LengthExtremes::in_bounds</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">LengthExtremes::in_bounds</span></span>:<br/>Preform - <a href="4-prf.html#SP1">&#167;1</a>, <a href="4-prf.html#SP1_3_2_1">&#167;1.3.2.1</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">match_length</span><span class="plain-syntax">, </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</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">match_length</span><span class="plain-syntax"> &gt;= </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax">) &amp;&amp; (</span><span class="identifier-syntax">match_length</span><span class="plain-syntax"> &lt;= </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</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="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>
</pre>
<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>&#167;6. </b>Concatenation produces the length extremes for the text X followed by the
text Y:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::concatenate</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">LengthExtremes::concatenate</span></span>:<br/><a href="4-le.html#SP8">&#167;8</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E_X</span><span class="plain-syntax">, </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><span class="identifier-syntax">E_X</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> += </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</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">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">min_words</span><span class="plain-syntax"> &gt; </span><span class="constant-syntax">INFINITE_WORD_COUNT</span><span class="plain-syntax">) </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">INFINITE_WORD_COUNT</span><span class="plain-syntax">;</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> += </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</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">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> &gt; </span><span class="constant-syntax">INFINITE_WORD_COUNT</span><span class="plain-syntax">) </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> = </span><span class="constant-syntax">INFINITE_WORD_COUNT</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">E</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 union provides the wider bounds, whichever they are:
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::union</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">LengthExtremes::union</span></span>:<br/><a href="4-le.html#SP8">&#167;8</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E_X</span><span class="plain-syntax">, </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><span class="identifier-syntax">E_X</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">E_Y</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> &lt; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax">) </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</span><span class="plain-syntax"> = </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">.</span><span class="element-syntax">min_words</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">E_Y</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> &gt; </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax">) </span><span class="identifier-syntax">E</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</span><span class="plain-syntax"> = </span><span class="identifier-syntax">E_Y</span><span class="plain-syntax">.</span><span class="identifier-syntax">max_words</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">E</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>The minimum matched text length for a nonterminal is the smallest of the
minima for its possible productions; for a production, it's the sum of the
minimum match lengths of its tokens.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::calculate_for_nt</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">LengthExtremes::calculate_for_nt</span></span>:<br/>The Optimiser - <a href="4-to.html#SP8">&#167;8</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">nonterminal</span><span class="plain-syntax"> *</span><span class="identifier-syntax">nt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::no_words_at_all</span></a><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">first</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">for</span><span class="plain-syntax"> (</span><span class="reserved-syntax">production_list</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pl</span><span class="plain-syntax"> = </span><span class="identifier-syntax">nt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">first_pl</span><span class="plain-syntax">; </span><span class="identifier-syntax">pl</span><span class="plain-syntax">; </span><span class="identifier-syntax">pl</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pl</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next_pl</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">for</span><span class="plain-syntax"> (</span><span class="reserved-syntax">production</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pr</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pl</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">first_pr</span><span class="plain-syntax">; </span><span class="identifier-syntax">pr</span><span class="plain-syntax">; </span><span class="identifier-syntax">pr</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pr</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next_pr</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">pr</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">opt</span><span class="plain-syntax">.</span><span class="element-syntax">pr_extremes</span><span class="plain-syntax"> = </span><a href="4-le.html#SP8" class="function-link"><span class="function-syntax">LengthExtremes::calculate_for_pr</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">pr</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">first</span><span class="plain-syntax">) { </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pr</span><span class="plain-syntax">-&gt;</span><span class="identifier-syntax">opt</span><span class="plain-syntax">.</span><span class="element-syntax">pr_extremes</span><span class="plain-syntax">; </span><span class="identifier-syntax">first</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">else</span><span class="plain-syntax"> { </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP7" class="function-link"><span class="function-syntax">LengthExtremes::union</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">E</span><span class="plain-syntax">, </span><span class="identifier-syntax">pr</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">opt</span><span class="plain-syntax">.</span><span class="element-syntax">pr_extremes</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">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::calculate_for_pr</span><span class="plain-syntax">(</span><span class="reserved-syntax">production</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pr</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::no_words_at_all</span></a><span class="plain-syntax">();</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">for</span><span class="plain-syntax"> (</span><span class="reserved-syntax">ptoken</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pt</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pr</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">first_pt</span><span class="plain-syntax">; </span><span class="identifier-syntax">pt</span><span class="plain-syntax">; </span><span class="identifier-syntax">pt</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">next_pt</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP6" class="function-link"><span class="function-syntax">LengthExtremes::concatenate</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">E</span><span class="plain-syntax">, </span><a href="4-le.html#SP9" class="function-link"><span class="function-syntax">LengthExtremes::calculate_for_pt</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">));</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</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>An interesting point here is that the negation of a ptoken can in principle
have any length, except that we specified <span class="extract"><span class="extract-syntax">^ example</span></span> to match only a single
word &mdash; any word other than "example". So the extremes for <span class="extract"><span class="extract-syntax">^ example</span></span> are
1 and 1, whereas for <span class="extract"><span class="extract-syntax">^ &lt;sample-nonterminal&gt;</span></span> they would have to be 0 and
infinity.
</p>
<pre class="displayed-code all-displayed-code code-font">
<span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="function-syntax">LengthExtremes::calculate_for_pt</span><button class="popup" onclick="togglePopup('usagePopup10')"><span class="comment-syntax">?</span><span class="popuptext" id="usagePopup10">Usage of <span class="code-font"><span class="function-syntax">LengthExtremes::calculate_for_pt</span></span>:<br/><a href="4-le.html#SP8">&#167;8</a><br/>The Optimiser - <a href="4-to.html#SP9">&#167;9</a></span></button><span class="plain-syntax">(</span><span class="reserved-syntax">ptoken</span><span class="plain-syntax"> *</span><span class="identifier-syntax">pt</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">length_extremes</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::exactly_one_word</span></a><span class="plain-syntax">();</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">negated_ptoken</span><span class="plain-syntax">) {</span>
<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">ptoken_category</span><span class="plain-syntax"> != </span><span class="constant-syntax">FIXED_WORD_PTC</span><span class="plain-syntax">)</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::any_number_of_words</span></a><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="reserved-syntax">switch</span><span class="plain-syntax"> (</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">ptoken_category</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">NONTERMINAL_PTC:</span>
<span class="plain-syntax"> </span><a href="4-to.html#SP8" class="function-link"><span class="function-syntax">Optimiser::optimise_nonterminal</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nt_pt</span><span class="plain-syntax">); </span><span class="comment-syntax"> recurse as needed</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><span class="identifier-syntax">pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">nt_pt</span><span class="plain-syntax">-&gt;</span><span class="element-syntax">opt</span><span class="plain-syntax">.</span><span class="element-syntax">nt_extremes</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="identifier-syntax">MULTIPLE_WILDCARD_PTC:</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::at_least_one_word</span></a><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="identifier-syntax">POSSIBLY_EMPTY_WILDCARD_PTC:</span>
<span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax"> = </span><a href="4-le.html#SP4" class="function-link"><span class="function-syntax">LengthExtremes::any_number_of_words</span></a><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="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">E</span><span class="plain-syntax">;</span>
<span class="plain-syntax">}</span>
</pre>
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