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<ul><li><a href="../index.html">home</a></li>
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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">assertions</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 assertions 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. Assertions</a></li><li><a href="P-wtmd.html#SP4">§4. Special meanings</a></li><li><a href="P-wtmd.html#SP5">§5. Regular meanings</a></li><li><a href="P-wtmd.html#SP6">§6. Imperative definitions</a></li><li><a href="P-wtmd.html#SP7">§7. Other gadgets</a></li><li><a href="P-wtmd.html#SP8">§8. Making use of the calculus module</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 assertions 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. Assertions. </b>This module's task is to read the declarative sentences in the source text,
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such as "Mrs Jones is wearing a trilby hat" or "Brightness is a kind of value",
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which assert that something is true. These are converted into propositions
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in predicate calculus, which are sent in a stream to the <a href="../knowledge-module/index.html" class="internal">knowledge</a> module.
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Those propositions may be mutually inconsistent, or not even be self-consistent
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or meaningful: but that is for <a href="../knowledge-module/index.html" class="internal">knowledge</a> to worry about. Our task is just
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to provide a list of supposedly true statements.
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</p>
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<p class="commentary">Between the <a href="../linguistics-module/index.html" class="internal">linguistics</a> and <a href="../calculus-module/index.html" class="internal">calculus</a> modules we have extensive
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equipment for parsing regular sentences already, so it would seem simple
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to act on a sentence like "Mr Herries knows Howarth." And so it would be if
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people called "Mr Herries" and "Howarth" were already known to exist.
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Unfortunately, this may be the first mention of them, and that makes things
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much more complicated.
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</p>
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<p class="commentary">Even if they do exist, they may be referred to ambiguously. If there are
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two different people both called Kassava, who is meant by "Carter knows
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Kassava"? This depends on context: see <a href="4-nr.html" class="internal">Name Resolution</a>.
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</p>
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<p class="commentary">Though it is rather under-developed at present, Inform also has minimal
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support for "anaphora", that is, for cross-references between sentences using
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pronouns such as "it". See <a href="2-ar.html" class="internal">Anaphoric References</a>, but don't expect much.
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</p>
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<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. </b>So, then, top-level declarations are dealt with like so:
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</p>
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<ul class="items"><li>● The tree is subdivided into <a href="../runtime-module/2-cu.html" class="internal">Compilation Units (in runtime)</a>. The project's own
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source text is one unit, as is each extension used.
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</li><li>● A minimal set of kinds, such as "number", verbs, such as "to mean", relations,
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such as "meaning", and so on, is created. See in particular <a href="2-bv.html" class="internal">Booting Verbs (in assertions)</a>.
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</li><li>● Three passes are made through the "major nodes" of the parse tree, meaning,
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assertion sentences and top-level declarations of structures such as tables,
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equations and rules. See <a href="2-ptmn.html" class="internal">Passes through Major Nodes</a>.
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<ul class="items"><li>(0) During the "pre-pass" names of tables and other top-level structures are
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recorded, and sentences are classified by <a href="2-cs.html#SP3" class="internal">Classifying::sentence</a>. This is
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done by asking the <a href="../linguistics-module/index.html" class="internal">linguistics</a> module to diagram them and determine whether
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the meaning is "regular" — a typical sentence asserting some relationship,
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such as "the ball is on the table" — or "special" — a sentence with some
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other purpose, such as "Test ... with ...", often but not always written in
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the imperative.
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</li><li>(1) During "pass 1", noun phrases in these assertion sentences are understood,
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which may involve creating new instances or other values. For example, the
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sentence "The fedora hat is on the can of Ubuntu cola" may cause new instances
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"fedora hat" and "can of Ubuntu cola" to be created. This process is called
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"refinement": see <a href="4-rpt.html" class="internal">Refine Parse Tree</a>, which calls <a href="4-tc.html" class="internal">The Creator</a> to bring
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things into being.<sup id="fnref:1"><a href="#fn:1" rel="footnote">1</a></sup> The function <a href="4-ass.html#SP6" class="internal">Assertions::make_coupling</a> is then
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called to draw out information from this pairing of values.
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</li><li>(2) During "pass 2", <a href="4-ass.html#SP6" class="internal">Assertions::make_coupling</a> is again called, and this
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time is able to draw out relationships between values: for example, that the
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hat is indeed spatially on top of the can.
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</li></ul>
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</li></ul>
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<pre class="undisplayed-code all-displayed-code code-font">
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<span class="plain-syntax">1. Jane is a woman</span>
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<span class="plain-syntax">Classification:</span>
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<span class="plain-syntax">SENTENCE_NT'jane is a woman' {classified}</span>
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<span class="plain-syntax"> VERB_NT'is' {verb 'be' 3p s act IS_TENSE +ve}</span>
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<span class="plain-syntax"> UNPARSED_NOUN_NT'jane'</span>
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<span class="plain-syntax"> UNPARSED_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s}</span>
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<span class="plain-syntax">Refined:</span>
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<span class="plain-syntax"> CREATED_NT'jane' {refined}</span>
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<span class="plain-syntax"> COMMON_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s} {refined} {refers: infs'woman'} {creation: << woman(x) >>} {eval: TEST_VALUE_NT}</span>
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<span class="plain-syntax">After creation:</span>
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<span class="plain-syntax">SENTENCE_NT'jane is a woman' {classified}</span>
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<span class="plain-syntax"> VERB_NT'is' {verb 'be' 3p s act IS_TENSE +ve}</span>
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<span class="plain-syntax"> PROPER_NOUN_NT'jane' {refined} {refers: infs'jane'} {eval: CONSTANT_NT'jane' {kind: object} {instance: 'jane'} {enumeration: 0}} {created here}</span>
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<span class="plain-syntax"> COMMON_NOUN_NT'woman' {indefinite 'a' n/m/f nom/acc s} {refined} {refers: infs'woman'} {creation: << woman(x) >>} {eval: TEST_VALUE_NT}</span>
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</pre>
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<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> There really is an Ubuntu cola; it's a fair-trade product which it amuses my
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more Linux-aware students to drink.
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<a href="#fnref:1" title="return to text"> ↩</a></p></li></ul>
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<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. Special meanings. </b>In the same way that programming languages have a few "reserved words" which
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cue up built-in language features, even though they may look like user-defined
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functions or variables, Inform has a few verbs with "special meanings", which
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make requests directly to the compiler. These occupy <a href="3-dlr.html" class="internal">Chapter 3: Requests</a>, which is
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really just a catalogue of ways to ask for things.
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</p>
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<p class="commentary">All that we do is parse such sentences and then make a call to some
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appropriate function, usually in one of the other modules. For example, the
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section <a href="3-nar.html" class="internal">New Activity Requests</a> dismantles sentences like "Counting is an
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activity on numbers", but calls the <a href="../knowledge-module/index.html" class="internal">knowledge</a> module to do the actual
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making of the new activity.
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</p>
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<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>§5. Regular meanings. </b>As noted above, <a href="4-ass.html#SP6" class="internal">Assertions::make_coupling</a> is called on each regular
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assertion: coupling being a linguistic term for placing subject and object into
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a relationship with each other. What it does is to split into cases according to
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the subject and object phrases of a sentence. These can take 12 different forms,
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so there are \(12\times 12 = 144\) possible combinations of subject with object,
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and a \(12\times 12\) matrix is used to determine which of 42 cases the sentence
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falls into.
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</p>
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<p class="commentary">Each case then leads either to a proposition being formed, or to
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a problem message being issued. Most of the easier cases are dealt with in
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the (admittedly quite long) <a href="index.html" class="internal">assertions</a> section, but harder ones are
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delegated to the remaining sections in <a href="4-nr.html" class="internal">Chapter 4: Assertions</a>.
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</p>
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<p class="commentary">The brief story above implied that each sentence is turned into a single
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proposition, as if this part of Inform can act as a sort of pipeline: text
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in, proposition out. But it is not quite so simple, and for the hardest
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sentences we must store notes on what to add later. For example, in
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<a href="4-ass2.html" class="internal">Assemblies</a>, a sentence like "In every container is a coin" cannot
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take immediate effect. It clearly creates a whole lot of coin instances,
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but we don't yet know what is a container and what is not. That will
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depend on conclusions to be drawn by the <a href="../knowledge-module/index.html" class="internal">knowledge</a> module later on.
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Similarly, though a little easier, <a href="4-imp.html" class="internal">Implications</a> like "Something worn is
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usually wearable" do not immediately lead to propositions being drawn up.
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</p>
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<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>§6. Imperative definitions. </b>At the top level, Inform source text consists of more than just assertion
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sentences: other constructions are made with different syntaxes. The most
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obvious of these are "imperative definitions", which are lists of instructions
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for what to do in different circumstances. They take the form
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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">a</span><span class="plain-syntax"> </span><span class="identifier-syntax">preamble</span><span class="plain-syntax"> </span><span class="identifier-syntax">text</span><span class="plain-syntax">:</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">first</span><span class="plain-syntax"> </span><span class="identifier-syntax">instruction</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">second</span><span class="plain-syntax"> </span><span class="identifier-syntax">instruction</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax"> </span><span class="identifier-syntax">last</span><span class="plain-syntax"> </span><span class="identifier-syntax">instruction</span><span class="plain-syntax">.</span>
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</pre>
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<p class="commentary">The preamble is parsed into an <a href="5-id.html#SP1" class="internal">imperative_defn</a>, which falls into one of
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a small range of <a href="5-idf.html" class="internal">Imperative Definition Families</a>: the most important being
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the <a href="5-rf.html" class="internal">Rule Family</a>, for interactive-fiction-style rules, and <a href="5-tpf.html" class="internal">To Phrase Family</a>,
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for declaring new "To..." phrases. Each definition is eventually joined to an
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<a href="5-id.html#SP6" class="internal">id_body</a> representing the list of what to do, and this may be compiled to
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one or more functions in the final output.
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</p>
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<p class="commentary"><a href="6-rls.html" class="internal">Rules</a> need more infrastructure, since they must live inside <a href="6-rlb.html" class="internal">Rulebooks</a>
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to take effect. Rulebooks contain <a href="6-bl.html" class="internal">Booking Lists</a> of <a href="6-rb.html" class="internal">Rule Bookings</a> to
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hold these; it all takes some juggling because of the features Inform has to
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allow authors to move rules around or customise their applicability. Finally,
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we introduce <a href="6-act.html" class="internal">Activities</a>, which are really just triplets of related rulebooks.
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</p>
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<p class="commentary firstcommentary"><a id="SP7" class="paragraph-anchor"></a><b>§7. Other gadgets. </b>And there are a few other constructions, too. Actions are left to <a href="../if-module/4-ap.html" class="internal">Actions Plugin (in if)</a>,
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but even Basic Inform has <a href="7-tbl.html" class="internal">Tables</a> (and their <a href="7-tc.html" class="internal">Table Columns</a>), along with
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the quirkier inclusion of <a href="7-eqt.html" class="internal">Equations</a>.
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</p>
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<p class="commentary firstcommentary"><a id="SP8" class="paragraph-anchor"></a><b>§8. Making use of the calculus module. </b><a href="8-kpr.html" class="internal">Chapter 8: Predicates</a> simply stocks up our predicate calculus system with some
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basic unary and binary predicates, and provides a few shorthand functions
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to make commonly-needed propositions (see <a href="8-cu.html" class="internal">Calculus Utilities</a>).
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</p>
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<p class="commentary">More specialised predicates will also be added by other modules, so the
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roster here is not complete, but these are the essentials.
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</p>
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