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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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<html>
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<head>
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<title>What This Module Does</title>
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</head>
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<body class="commentary-font">
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<nav role="navigation">
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<h1><a href="../index.html">
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<img src="../docs-assets/Inform.png" height=72">
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</a></h1>
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<ul><li><a href="../compiler.html">compiler tools</a></li>
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<li><a href="../other.html">other tools</a></li>
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<li><a href="../extensions.html">extensions and kits</a></li>
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<li><a href="../units.html">unit test tools</a></li>
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</ul><h2>Compiler Webs</h2><ul>
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<li><a href="../inbuild/index.html">inbuild</a></li>
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<li><a href="../inform7/index.html">inform7</a></li>
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<li><a href="../inter/index.html">inter</a></li>
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</ul><h2>Inbuild Modules</h2><ul>
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<li><a href="../supervisor-module/index.html">supervisor</a></li>
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</ul><h2>Inform7 Modules</h2><ul>
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<li><a href="../core-module/index.html">core</a></li>
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<li><a href="../inflections-module/index.html">inflections</a></li>
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<li><a href="../linguistics-module/index.html">linguistics</a></li>
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<li><a href="../kinds-module/index.html">kinds</a></li>
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<li><a href="../if-module/index.html">if</a></li>
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<li><a href="../multimedia-module/index.html">multimedia</a></li>
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<li><a href="../problems-module/index.html">problems</a></li>
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<li><a href="../index-module/index.html">index</a></li>
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</ul><h2>Inter Modules</h2><ul>
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<li><a href="../bytecode-module/index.html">bytecode</a></li>
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<li><a href="../building-module/index.html">building</a></li>
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<li><a href="../codegen-module/index.html">codegen</a></li>
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</ul><h2>Shared Modules</h2><ul>
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<li><a href="../arch-module/index.html">arch</a></li>
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<li><a href="index.html"><span class="selectedlink">syntax</span></a></li>
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<li><a href="../words-module/index.html">words</a></li>
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<li><a href="../html-module/index.html">html</a></li>
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<li><a href="../../../inweb/docs/foundation-module/index.html">foundation</a></li>
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</ul>
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</nav>
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<main role="main">
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<!--Weave of 'What This Module Does' generated by Inweb-->
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<div class="breadcrumbs">
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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../compiler.html">Shared Modules</a></li><li><a href="index.html">syntax</a></li><li><a href="index.html#P">Preliminaries</a></li><li><b>What This Module Does</b></li></ul></div>
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<p class="purpose">An overview of the syntax module's role and abilities.</p>
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<ul class="toc"><li><a href="P-wtmd.html#SP1">§1. Prerequisites</a></li><li><a href="P-wtmd.html#SP2">§2. Syntax trees</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1"></a><b>§1. Prerequisites. </b>The syntax module is a part of the Inform compiler toolset. It is
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presented as a literate program or "web". Before diving in:
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</p>
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<ul class="items"><li>(a) It helps to have some experience of reading webs: see <a href="../../../inweb/docs/index.html" class="internal">inweb</a> for more.
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</li><li>(b) The module is written in C, in fact ANSI C99, but this is disguised by the
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fact that it uses some extension syntaxes provided by the <a href="../../../inweb/docs/index.html" class="internal">inweb</a> literate
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programming tool, making it a dialect of C called InC. See <a href="../../../inweb/docs/index.html" class="internal">inweb</a> for
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full details, but essentially: it's C without predeclarations or header files,
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and where functions have names like <span class="extract"><span class="extract-syntax">Tags::add_by_name</span></span> rather than <span class="extract"><span class="extract-syntax">add_by_name</span></span>.
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</li><li>(c) This module uses other modules drawn from the <a href="../compiler.html" class="internal">compiler</a>, and also
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uses a module of utility functions called <a href="../../../inweb/docs/foundation-module/index.html" class="internal">foundation</a>.
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For more, see <a href="../../../inweb/docs/foundation-module/P-abgtf.html" class="internal">A Brief Guide to Foundation (in foundation)</a>.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP2"></a><b>§2. Syntax trees. </b>Most algorithms for parsing natural language involve the construction of
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trees, in which the original words appear as leaves at the top of the tree,
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while the grammatical functions they serve appear as the branches and trunk:
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thus the word "orange", as an adjective, might be growing from a branch
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which represents a noun clause ("the orange envelope"), growing in turn from
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a trunk which in turn might represent a assertion sentence:
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</p>
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<blockquote>
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<p>The card is in the orange envelope.</p>
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</blockquote>
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<p class="commentary">The Inform tools represent syntax trees by <a href="2-st.html#SP2" class="internal">parse_node_tree</a> structures
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(see <a href="2-st.html#SP2" class="internal">SyntaxTree::new</a>), but there are very few of these: the entire
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source text compiled by <a href="../inform7/index.html" class="internal">inform7</a> is just one syntax tree. When <a href="../supervisor-module/index.html" class="internal">supervisor</a>
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manages extensions, it may generate one <a href="2-st.html#SP2" class="internal">parse_node_tree</a> object for each
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extension whose text it reads. Still — there are few trees.
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</p>
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<p class="commentary">But there are many nodes. Syntax trees are made up of <a href="2-pn.html#SP1" class="internal">parse_node</a> structures.
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While these are in principle individual nodes, they effectively represent
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subtrees, because they carry with them links to the nodes below. A <a href="2-pn.html#SP1" class="internal">parse_node</a>
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object can therefore equally represent "orange", "the orange envelope", or
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"now the card is in the orange envelope".
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</p>
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<p class="commentary">Meaning is an ambiguous thing, and so the tree needs to be capable of
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representing multiple interpretations of the same wording. So nodes have not
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only <span class="extract"><span class="extract-syntax">next</span></span> and <span class="extract"><span class="extract-syntax">down</span></span> links to other nodes, but also <span class="extract"><span class="extract-syntax">next_alternative</span></span> links,
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which — if used — fork the syntax tree into different possible readings.
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</p>
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<p class="commentary firstcommentary"><a id="SP3"></a><b>§3. </b>The main trunk of the tree can be grown in any sequence: call <a href="2-st.html#SP3" class="internal">SyntaxTree::push_bud</a>
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to begin "budding" from a particular branch, and <a href="2-st.html#SP3" class="internal">SyntaxTree::pop_bud</a> to go back
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to where you were. These are also used automatically to ensure that sentences
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arriving at <a href="2-st.html#SP4" class="internal">SyntaxTree::graft_sentence</a> are grafted under the headings to
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which they belong. Thus, the sentences
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"> </span><span class="identifier-syntax">Chapter</span><span class="plain-syntax"> </span><span class="constant-syntax">20</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">Section</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">The</span><span class="plain-syntax"> </span><span class="identifier-syntax">cat</span><span class="plain-syntax"> </span><span class="identifier-syntax">is</span><span class="plain-syntax"> </span><span class="identifier-syntax">in</span><span class="plain-syntax"> </span><span class="identifier-syntax">the</span><span class="plain-syntax"> </span><span class="identifier-syntax">cardboard</span><span class="plain-syntax"> </span><span class="identifier-syntax">box</span><span class="plain-syntax">.</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">Section</span><span class="plain-syntax"> </span><span class="constant-syntax">2</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">The</span><span class="plain-syntax"> </span><span class="identifier-syntax">ball</span><span class="plain-syntax"> </span><span class="identifier-syntax">of</span><span class="plain-syntax"> </span><span class="identifier-syntax">yarn</span><span class="plain-syntax"> </span><span class="identifier-syntax">is</span><span class="plain-syntax"> </span><span class="identifier-syntax">here</span><span class="plain-syntax">.</span>
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</pre>
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<p class="commentary">would actually be grafted like so:
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"> RESULT BUD STACK BEFORE THIS</span>
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<span class="plain-syntax"> Chapter 20 (empty)</span>
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<span class="plain-syntax"> Section 1 Chapter 20</span>
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<span class="plain-syntax"> The cat is in the cardboard box. Chapter 20 > Section 1</span>
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<span class="plain-syntax"> Section 2 Chapter 20 > Section 1</span>
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<span class="plain-syntax"> The ball of yarn is here. Chapter 20 > Section 2</span>
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</pre>
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<p class="commentary">But it is also possible to graft smaller (not-whole-sentence) cuttings onto
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each other using <a href="2-st.html#SP7" class="internal">SyntaxTree::graft</a>, which doesn't involve the bud stack
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at all.
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</p>
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<p class="commentary firstcommentary"><a id="SP4"></a><b>§4. </b>An extensive suite of functions is provided to make it easy to traverse
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a syntax tree, calling a visitor function on each node: see <a href="2-st.html#SP11" class="internal">SyntaxTree::traverse</a>.
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</p>
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<nav role="progress"><div class="progresscontainer">
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<ul class="progressbar"><li class="progressprevoff">❮</li><li class="progresscurrentchapter">P</li><li class="progresscurrent">wtmd</li><li class="progresschapter"><a href="1-sm.html">1</a></li><li class="progresschapter"><a href="2-st.html">2</a></li><li class="progresschapter"><a href="3-snt.html">3</a></li><li class="progressnext"><a href="1-sm.html">❯</a></li></ul></div>
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</nav><!--End of weave-->
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</main>
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</body>
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</html>
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