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<title>What This Module Does</title>
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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="../index.html">home</a></li>
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</ul><h2>Compiler</h2><ul>
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<li><a href="../structure.html">structure</a></li>
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<li><a href="../inbuildn.html">inbuild</a></li>
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<li><a href="../inform7n.html">inform7</a></li>
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<li><a href="../intern.html">inter</a></li>
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<li><a href="../inform6.html">inform6</a></li>
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</ul><h2>Resources</h2><ul>
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<li><a href="../extensions.html">extensions</a></li>
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<li><a href="../kits.html">kits</a></li>
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</ul><h2>Repository</h2><ul>
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<li><a href="https://github.com/ganelson/inform"><img src="../docs-assets/github.png" height=18> github</a></li>
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<li><a href="../../../inweb/index.html">inweb</a></li>
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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="../inform7n.html">Inform7</a></li><li><a href="index.html">runtime</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 runtime 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. About this layer of Inform</a></li><li><a href="P-wtmd.html#SP3">§3. The Inter hierarchy</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. Prerequisites. </b>The runtime 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/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/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/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 just <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 compiler (see <a href="../structure.html" class="internal">structure</a>), and also
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uses a module of utility functions called <a href="../../../inweb/foundation-module/index.html" class="internal">foundation</a>.
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For more, see <a href="../../../inweb/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" class="paragraph-anchor"></a><b>§2. About this layer of Inform. </b>The <a href="index.html" class="internal">runtime</a> and <a href="../imperative-module/index.html" class="internal">imperative</a> modules (see <a href="../imperative-module/P-wtmd.html" class="internal">What This Module Does (in imperative)</a>)
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jointly make up a layer of Inform whose task is to take the conceptual structures
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now build up — rules, phrases, tables, the world model — and turn them into
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Inter code. For the bigger picture, see <a href="../structure.html" class="internal">structure</a>.
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</p>
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<p class="commentary">Neither module is in charge of the other. <a href="index.html" class="internal">runtime</a> makes extensive use of
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<a href="../imperative-module/3-fnc.html" class="internal">Functions (in imperative)</a>, while <a href="../imperative-module/index.html" class="internal">imperative</a> uses <a href="2-emt.html" class="internal">Emit (in runtime)</a> and
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<a href="2-hrr.html" class="internal">Hierarchy (in runtime)</a>. The demarcation line is that:
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</p>
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<ul class="items"><li>● <a href="../imperative-module/index.html" class="internal">imperative</a> provides general mechanisms for compiling Inter functions,
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and uses them to construct the functions needed for rules and phrases.
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</li><li>● <a href="index.html" class="internal">runtime</a> organises the hierarchical structure of the Inter code being
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made, and compiles the Inter representations of data structures like rulebooks
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or tables, and any Inter functions needed to manage them at runtime.
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</li></ul>
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<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. The Inter hierarchy. </b>Inter code is an intermediate-level representation of the program we are to
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compile. Inter can exist in binary or textual forms: see <a href="../inter/M-ui.html" class="internal">Manual (in inter)</a> for
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a general introduction to programming it in textual form. We will compile
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binary Inter for speed, but they are really very similar.
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</p>
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<p class="commentary">You can get a rough idea of what the Inter hierarchy looks like by compiling
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an Inform project with:
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="identifier-syntax">Include</span><span class="plain-syntax"> </span><span class="identifier-syntax">Inter</span><span class="plain-syntax"> </span><span class="identifier-syntax">hierarchy</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">debugging</span><span class="plain-syntax"> </span><span class="identifier-syntax">log</span><span class="plain-syntax">.</span>
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</pre>
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<p class="commentary">...and then looking at the log file. This will give an inventory, a summarised
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listing, at two stages: first when the main Inform compiler has completed, and
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second when linking with kits is all done, and we've reached the final state.
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</p>
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<p class="commentary">Inter code is not a linear stream, like the assembly language produced by a
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conventional compiler: rather, it is a hierarchy of nested "packages". Each
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package can contain some symbols, some other packages, and some actual code
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or data. This makes it possible for Inter code to be heavily structured, with
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similar resources grouped appropriately together. A package also has a "type",
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and this can be used to find resources of different sorts, or to regulate where
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they are placed. Types are written with an initial underscore: for example,
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one package type we will create is <span class="extract"><span class="extract-syntax">_module</span></span>.
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</p>
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<p class="commentary">The top of the final hierarchy might look like this:
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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">version number --> version 1</span>
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<span class="plain-syntax">package type declarations --> packagetype _plain</span>
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<span class="plain-syntax"> packagetype _code</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax">pragmas --> pragma Inform6 "$ALLOC_CHUNK_SIZE=32000"</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax">primitive declarations --> primitive !font val -> void</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax">main --> package main _plain</span>
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<span class="plain-syntax"> general material --> package veneer _module</span>
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<span class="plain-syntax"> package generic _module</span>
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<span class="plain-syntax"> package synoptic _module</span>
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<span class="plain-syntax"> from compilation units --> package basic_inform_by_graham_nelson _module</span>
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<span class="plain-syntax"> package english_language_by_graham_nelson _module</span>
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<span class="plain-syntax"> package standard_rules_by_graham_nelson _module</span>
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<span class="plain-syntax"> package source_text _module</span>
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<span class="plain-syntax"> from kits --> package BasicInformKit _module</span>
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<span class="plain-syntax"> package EnglishLanguageKit _module</span>
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<span class="plain-syntax"> package WorldModelKit _module</span>
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<span class="plain-syntax"> package CommandParserKit _module</span>
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<span class="plain-syntax"> to do with linking --> package connectors _linkage</span>
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<span class="plain-syntax"> package template _plain</span>
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</pre>
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<p class="commentary">The modest amount of global material is the same on every compilation, and just
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sets up our conventions. Inter also requires the top-level package to be <span class="extract"><span class="extract-syntax">main</span></span>.
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But it's our decision to then subdivide <span class="extract"><span class="extract-syntax">main</span></span> up into packages called "modules",
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which have the package type <span class="extract"><span class="extract-syntax">_module</span></span>. These come from several sources:
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</p>
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<ul class="items"><li>● The <span class="extract"><span class="extract-syntax">veneer</span></span> module is named after the veneer system in Inform 6, and provides
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access to its (very modest) facilities.
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</li><li>● The <span class="extract"><span class="extract-syntax">generic</span></span> module contains definitions which are built-in to the language:
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for example, kinds like <span class="extract"><span class="extract-syntax">K_number</span></span>.
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</li><li>● Each compilation unit of Inform 7 source text produces one module. See
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<a href="2-cu.html" class="internal">Compilation Units</a>; in particular, each included extension is a compilation unit,
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and the main source text puts material into <span class="extract"><span class="extract-syntax">source_text</span></span>.
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</li><li>● Each included kit of Inter code is a module.
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</li><li>● The <span class="extract"><span class="extract-syntax">synoptic</span></span> module contains material which gathers up references from all
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of the other modules.
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</li></ul>
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<p class="commentary">The role of <a href="index.html" class="internal">runtime</a> and <a href="../imperative-module/index.html" class="internal">imperative</a> is to build the generic, synoptic
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and compilation-unit modules; the modules from kits will come later in the
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linking stage (see <a href="../pipeline-module/index.html" class="internal">pipeline</a>).
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</p>
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<p class="commentary">Modules then have sub-departments called submodules, which are packages of type
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<span class="extract"><span class="extract-syntax">_submodule</span></span>. For example, the rules created in any given compilation unit live
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in the <span class="extract"><span class="extract-syntax">rules</span></span> submodule of its module; the properties in <span class="extract"><span class="extract-syntax">properties</span></span>; and
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so on. This is all very orderly, but there are a great many different structures
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to compile for a large number of different reasons. The <a href="2-hrr.html" class="internal">Hierarchy</a> section
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of code provides a detailed specification of exactly where everything goes.
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</p>
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<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. </b><a href="index.html" class="internal">runtime</a> and <a href="../imperative-module/index.html" class="internal">imperative</a> should not make raw Inter code directly, but
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through a three-level process:
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</p>
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<ul class="items"><li>● <a href="index.html" class="internal">runtime</a> and <a href="../imperative-module/index.html" class="internal">imperative</a> call the functions in <a href="2-hrr.html" class="internal">Chapter 2: Emission</a>
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to "emit" code and find out where to put it.
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</li><li>● Those functions in turn call the <a href="../building-module/index.html" class="internal">building</a> module, which gives
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general code (not tied to the Inform compiler) for constructing Inter.
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</li><li>● The <a href="../building-module/index.html" class="internal">building</a> module then calls down to <a href="../bytecode-module/index.html" class="internal">bytecode</a> to put the actual
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bytes in memory.
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</li></ul>
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<p class="commentary">In effect, then, <a href="2-hrr.html" class="internal">Chapter 2: Emission</a> is the bridge (or the shaft?) between the upper
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levels of Inform and the lower, and it provides an API for the rest of <a href="index.html" class="internal">runtime</a>
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and <a href="../imperative-module/index.html" class="internal">imperative</a> to use.
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</p>
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