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<title>Textual Inter</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="../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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</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="index.html"><span class="selectedlink">inter</span></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="../words-module/index.html">words</a></li>
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<main role="main">
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<!--Weave of 'Textual Inter' 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">Compiler Tools</a></li><li><a href="index.html">inter</a></li><li><a href="index.html#M">Manual</a></li><li><b>Textual Inter</b></li></ul></div>
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<p class="purpose">A specification of the inter language, as written out in text file form.</p>
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<ul class="toc"><li><a href="M-ti.html#SP1">§1. Textual, Binary, Memory</a></li><li><a href="M-ti.html#SP2">§2. Global statements</a></li><li><a href="M-ti.html#SP7">§7. Package declarations</a></li><li><a href="M-ti.html#SP11">§11. Symbol annotations</a></li><li><a href="M-ti.html#SP12">§12. Splats</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>§1. Textual, Binary, Memory. </b>Inter code has three representations: as a binary file, as a textual file,
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and in memory — a sort of cross-referenced form of binary. For speed, the
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Inform compiler generates memory inter directly, and code-generates from
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that, so that the inter is normally never written out to disc. When Inter
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performs a conversion, it loads (say) textual inter into memory inter, then
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writes that out as binary inter.
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</p>
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<p class="commentary">The following specification covers the inter language in its textual form:
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a UTF-8 encoded text file which conventionally takes the file extension
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".intert".
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</p>
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<p class="commentary">It should be stressed that inter is designed for inspection — that is, for
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people to be able to read. It's not intended as a programming language for
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humans to write: the code is verbose and low-level. The idea is that inter
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code will be written by programs (such as Inform), but that this code will
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be possible for humans to check.
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</p>
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<p class="commentary">Like assembly language, inter code is line-based: each line is a "statement".
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Lines can be of arbitrary length. A line beginning with a <span class="extract"><span class="extract-syntax">#</span></span> (in column 1) is
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a comment, and blank lines are ignored.
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</p>
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<p class="commentary">The term "name" below means a string of one or more English upper or lower
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case letters, underscores, or digits, except that it must not begin with
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a digit.
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</p>
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<p class="commentary">As in Python, indentation from the left margin is highly significant, and
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should be in the form of tab characters.
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</p>
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<p class="commentary">Inform follows certain conventions in the inter that it writes, but these
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conventions are not part of the specification, and may change. Any paragraph
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below which begins with "Convention" records the current practice.
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</p>
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<p class="commentary">There are three forms of statement: global statements, data statements, and
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code statements. We will take these in turn.
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</p>
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<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>§2. Global statements. </b>These statements must appear first in the file, and must be unindented.
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There are only four of these:
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</p>
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<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>§3. </b><span class="extract"><span class="extract-syntax">version NUMBER</span></span> indicates that the file was written in that version of
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the inter language. At present there has only ever been one version, but
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that may not always be true. A <span class="extract"><span class="extract-syntax">version</span></span> statement number must come before
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anything else, even other global statements; in particular, there cannot be
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two such statements in the same file.
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</p>
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<p class="commentary">Convention. Inform always opens with the statement: <span class="extract"><span class="extract-syntax">version 1</span></span>
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</p>
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<p class="commentary firstcommentary"><a id="SP4" class="paragraph-anchor"></a><b>§4. </b><span class="extract"><span class="extract-syntax">packagetype NAME</span></span> declares that <span class="extract"><span class="extract-syntax">NAME</span></span> is the name of a type of package.
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Packages are the main hierarchical organisation for inter files, as we
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will see below. Each package has a type as well as a name, and the type
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must be one of those declared like this.
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</p>
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<p class="commentary">For example, <span class="extract"><span class="extract-syntax">packagetype _adjective</span></span> creates <span class="extract"><span class="extract-syntax">_adjective</span></span> as a possible type
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for packages in this file.
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</p>
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<p class="commentary">The first two package types must be <span class="extract"><span class="extract-syntax">_plain</span></span> and <span class="extract"><span class="extract-syntax">_code</span></span>, in that order.
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</p>
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<p class="commentary">Convention. All of Inform's package type names begin similarly with an
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underscore, to prevent name clashes. Inform uses package types semantically,
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to show what kind of thing is being defined in the content of a particular
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package. This makes it easier to search a large inter repository for all of
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the adjective defimitions, for example: we just need to look for packages of
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type <span class="extract"><span class="extract-syntax">_adjective</span></span>.
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</p>
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<p class="commentary firstcommentary"><a id="SP5" class="paragraph-anchor"></a><b>§5. </b><span class="extract"><span class="extract-syntax">pragma TARGET "WHATEVER"</span></span> does not change the meaning of the inter file;
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it simply provides pragmatic advice to the eventual compiler of code
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generated from this file. <span class="extract"><span class="extract-syntax">TARGET</span></span> indicates the context for which this
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is intended; at present, the only possible choice is <span class="extract"><span class="extract-syntax">target_I6</span></span>, meaning,
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"if you are compiling me to Inform 6".
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</p>
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<p class="commentary">Convention. Inform uses this to pass on ICL (Inform Command Language)
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commands to Inform 6, such as memory settings or command-line switches.
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For example,
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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="reserved-syntax">pragma</span><span class="plain-syntax"> target_I6 </span><span class="string-syntax">"$MAX_LABELS=200000"</span>
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</pre>
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<p class="commentary">(This would be meaningless if we were compiling to some other format.)
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</p>
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<p class="commentary firstcommentary"><a id="SP6" class="paragraph-anchor"></a><b>§6. </b><span class="extract"><span class="extract-syntax">primitive PRIMITIVE IN -> OUT</span></span> defines a new code statement — if inter
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were an assembly language, these would be the opcodes. For example,
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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="reserved-syntax">primitive</span><span class="plain-syntax"> </span><span class="function-syntax">!move</span><span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> </span><span class="reserved-syntax">val</span><span class="plain-syntax"> -> </span><span class="reserved-syntax">void</span>
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</pre>
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<p class="commentary">defines the primitive <span class="extract"><span class="extract-syntax">!move</span></span> as something which consumes two values and
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produces none. (Further details on this will appear in the section on code
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packages.)
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</p>
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<p class="commentary firstcommentary"><a id="SP7" class="paragraph-anchor"></a><b>§7. Package declarations. </b>After the global area, an inter file should declare a package called <span class="extract"><span class="extract-syntax">main</span></span>,
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which must have the package type <span class="extract"><span class="extract-syntax">_plain</span></span>.
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</p>
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<p class="commentary">The statement <span class="extract"><span class="extract-syntax">package NAME TYPE</span></span> declares a new package, and the <span class="extract"><span class="extract-syntax">TYPE</span></span>
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must be one of those declared by <span class="extract"><span class="extract-syntax">packagetype</span></span> statements in the global area.
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</p>
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<p class="commentary">The declaration line for a package begins at the level of indentation of
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the package's owner. For <span class="extract"><span class="extract-syntax">main</span></span>, it should be unindented, and this is the
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only package allowed to appear at the top level: all other packages should
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be inside <span class="extract"><span class="extract-syntax">main</span></span> in some way.
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</p>
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<p class="commentary">The contents of the package are then one tab stop in from the declaration. Thus:
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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="reserved-syntax">package</span><span class="plain-syntax"> main _plain</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> m1_RBLK1 _code</span>
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<span class="plain-syntax"> ...</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> m1_RBLK2 _code</span>
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<span class="plain-syntax"> ...</span>
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</pre>
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<p class="commentary">Here, <span class="extract"><span class="extract-syntax">main</span></span> contains two sub-packages, <span class="extract"><span class="extract-syntax">m1_RBLK1</span></span> and <span class="extract"><span class="extract-syntax">m1_RBLK2</span></span>, and
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indentation is used to show which package a statement belongs to.
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</p>
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<p class="commentary firstcommentary"><a id="SP8" class="paragraph-anchor"></a><b>§8. </b>After the declaration line, a package definition continues with a set
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of symbols definitions. In effect, this is the symbols table for the
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package written out explicitly. Each definition is a <span class="extract"><span class="extract-syntax">symbol</span></span> line, in
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one of these three forms:
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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="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">private</span><span class="plain-syntax"> TYPE NAME</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">public</span><span class="plain-syntax"> TYPE NAME</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">external</span><span class="plain-syntax"> TYPE NAME </span><span class="reserved-syntax">--></span><span class="plain-syntax"> SYMBOL</span>
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</pre>
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<p class="commentary">For example,
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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="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">public</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> MEMORY_HEAP_SIZE</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">external</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> AllowInShowme </span><span class="reserved-syntax">--></span><span class="plain-syntax"> /main/resources/template/AllowInShowme</span>
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</pre>
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<p class="commentary"><span class="extract"><span class="extract-syntax">private</span></span> means that the meaning and existence of <span class="extract"><span class="extract-syntax">NAME</span></span> are invisible
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from outside the current package; <span class="extract"><span class="extract-syntax">public</span></span> means that other packages are
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allowed to refer to <span class="extract"><span class="extract-syntax">NAME</span></span>; and <span class="extract"><span class="extract-syntax">external</span></span> means that this package is
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making just such a reference, and that <span class="extract"><span class="extract-syntax">NAME</span></span> in this package is equivalent
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to <span class="extract"><span class="extract-syntax">SYMBOL</span></span>, defined elsewhere. It is possible that <span class="extract"><span class="extract-syntax">SYMBOL</span></span> points only to
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another symbol which is also <span class="extract"><span class="extract-syntax">external</span></span>, so that we then have to follow
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another link to find the original non-external definition. However, it is
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a requirement that this process must eventually end. It would be illegal
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to write
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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="reserved-syntax">package</span><span class="plain-syntax"> main _plain</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> A _plain</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">external</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> S </span><span class="reserved-syntax">--></span><span class="plain-syntax"> /main/B/T</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> B _plain</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">external</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> T </span><span class="reserved-syntax">--></span><span class="plain-syntax"> /main/B/S</span>
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</pre>
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<p class="commentary">The symbol <span class="extract"><span class="extract-syntax">TYPE</span></span> must be one of four possibilities:
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</p>
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<ul class="items"><li>(a) <span class="extract"><span class="extract-syntax">label</span></span>, used to mark execution positions in code packages;
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</li><li>(b) <span class="extract"><span class="extract-syntax">package</span></span>, meaning that this is the name of a package;
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</li><li>(c) <span class="extract"><span class="extract-syntax">packagetype</span></span>, meaning that this is a package type;
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</li><li>(d) <span class="extract"><span class="extract-syntax">misc</span></span>, meaning "anything else" — most symbols have this type.
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</li></ul>
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<p class="commentary">The run of <span class="extract"><span class="extract-syntax">symbol</span></span> declarations at the top of a module can become quite
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long, since it has to give a complete description of all symbols used inside
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the module, whether they're defined internally or externally. As a
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convenience for people writing test cases by hand, it's in fact optional
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to predeclare a symbol in textual inter provided that this symbol is
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declared earlier in the file than its first use. However, when Inter
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writes out a textual inter file, it always writes the symbols table out
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in full, and never exercises this option.
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</p>
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<p class="commentary">Convention. A conspicuous feature of inter code generated by Inform is that
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many symbols have the form <span class="extract"><span class="extract-syntax">P_Name</span></span>, where <span class="extract"><span class="extract-syntax">P</span></span> is some prefix letter showing
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what sort of thing is referred to: for example, symbols for kinds all begin
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with the prefix <span class="extract"><span class="extract-syntax">K</span></span> (<span class="extract"><span class="extract-syntax">K_number</span></span>, <span class="extract"><span class="extract-syntax">K_text</span></span>, and so on), while variables
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begin with <span class="extract"><span class="extract-syntax">V</span></span>, instances with <span class="extract"><span class="extract-syntax">I</span></span>, properties with <span class="extract"><span class="extract-syntax">P</span></span>, and so on. This
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is all simply a convention used by Inform for clarity and to reduce the
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risk of accidental name clashes; it is not required by inter.
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</p>
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<p class="commentary firstcommentary"><a id="SP9" class="paragraph-anchor"></a><b>§9. </b>Where a local symbol is being equated with an external one, the <span class="extract"><span class="extract-syntax">SYMBOL</span></span>
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given is a sort of URL showing the package to look inside. Thus
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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"> /main/resources/template/AllowInShowme</span>
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</pre>
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<p class="commentary">means "the symbol <span class="extract"><span class="extract-syntax">AllowInShowme</span></span> in package <span class="extract"><span class="extract-syntax">template</span></span> inside package
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<span class="extract"><span class="extract-syntax">resources</span></span> inside package <span class="extract"><span class="extract-syntax">main</span></span>".
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</p>
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<p class="commentary firstcommentary"><a id="SP10" class="paragraph-anchor"></a><b>§10. </b>Optionally, a <span class="extract"><span class="extract-syntax">private</span></span> or <span class="extract"><span class="extract-syntax">public</span></span> symbol can also specify a name it
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wishes to be given when the Inter is translated into some other language
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(i.e., Inform 6 or similar). This is written 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"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">private</span><span class="plain-syntax"> TYPE NAME </span><span class="element-syntax">`TRANSLATION</span><span class="plain-syntax">`</span>
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</pre>
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<p class="commentary">So, for example,
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</p>
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<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">public</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> launcher </span><span class="element-syntax">`launcher_U32</span><span class="plain-syntax">`</span>
|
|
</pre>
|
|
<p class="commentary">Symbols tabulated as <span class="extract"><span class="extract-syntax">external</span></span> cannot be marked in this way, but of course
|
|
the original definition (to which the external link eventually leads) can be.
|
|
For example,
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> main _plain</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> A _plain</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">external</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> S </span><span class="reserved-syntax">--></span><span class="plain-syntax"> /main/B/T</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">package</span><span class="plain-syntax"> B _plain</span>
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">symbol</span><span class="plain-syntax"> </span><span class="reserved-syntax">public</span><span class="plain-syntax"> </span><span class="reserved-syntax">misc</span><span class="plain-syntax"> T </span><span class="element-syntax">`FancyName</span><span class="plain-syntax">`</span>
|
|
</pre>
|
|
<p class="commentary">would result in the names <span class="extract"><span class="extract-syntax">S</span></span> and <span class="extract"><span class="extract-syntax">T</span></span> both being compiled to the name
|
|
<span class="extract"><span class="extract-syntax">FancyName</span></span> in the final code.
|
|
</p>
|
|
|
|
<p class="commentary">Convention. Inform mostly makes use of this feature of inter late in code
|
|
generation, essentially to avoid namespace clashes in the final output code,
|
|
but it also needs to use it to implement low-level features of the Inform
|
|
language such as:
|
|
</p>
|
|
|
|
<blockquote>
|
|
<p>The marked for listing property translates into I6 as "workflag".</p>
|
|
</blockquote>
|
|
|
|
<p class="commentary firstcommentary"><a id="SP11" class="paragraph-anchor"></a><b>§11. Symbol annotations. </b>A useful feature of inter is that short-term or inessential metadata can
|
|
be attached to symbols; inter is flexible abput what this data might mean.
|
|
These annotations can also be represented in text form, which is useful
|
|
for looking at the output from different code-generation stages.
|
|
</p>
|
|
|
|
<p class="commentary">Annotations are written on the line where the symbol is created, not where
|
|
it is declared in the symbols table. For example, here is a creation of
|
|
a symbol for a constant:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">constant</span><span class="plain-syntax"> WORD_NEXTTOHIGHBIT </span><span class="identifier-syntax">K_typeless_int</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">x4000</span>
|
|
</pre>
|
|
<p class="commentary">And here it is with an annotation:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">constant</span><span class="plain-syntax"> WORD_NEXTTOHIGHBIT </span><span class="identifier-syntax">K_typeless_int</span><span class="plain-syntax"> = </span><span class="constant-syntax">0</span><span class="plain-syntax">x4000 </span><span class="identifier-syntax">__hex</span>
|
|
</pre>
|
|
<p class="commentary">The annotation, <span class="extract"><span class="extract-syntax">__hex</span></span>, simply means that the natural way to print the
|
|
value of this constant would be hexadecimal; it doesn't change the meaning
|
|
of the program, and this is typical of annotations.
|
|
</p>
|
|
|
|
<p class="commentary">All annotations begin with a double underscore, and some can take a number
|
|
or text literal:
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">__binary</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">__table_array</span><span class="plain-syntax">=1</span>
|
|
<span class="plain-syntax"> </span><span class="identifier-syntax">__name</span><span class="plain-syntax">=</span><span class="string-syntax">"matching key"</span>
|
|
</pre>
|
|
<p class="commentary">There is no built-in set of annotations, and their use does not need to be
|
|
predeclared anywhere: simply writing
|
|
</p>
|
|
|
|
<pre class="displayed-code all-displayed-code code-font">
|
|
<span class="plain-syntax"> </span><span class="reserved-syntax">constant</span><span class="plain-syntax"> MY_CONSTANT </span><span class="identifier-syntax">K_typeless_int</span><span class="plain-syntax"> = </span><span class="constant-syntax">27</span><span class="plain-syntax"> </span><span class="identifier-syntax">__plugh</span>
|
|
</pre>
|
|
<p class="commentary">would create the annotation <span class="extract"><span class="extract-syntax">__plugh</span></span> as a possibility, if it didn't already
|
|
exist. However, Inform has a conventional set of annotations which it uses
|
|
for symbols with various meanings, and that set will be covered later.
|
|
</p>
|
|
|
|
<p class="commentary firstcommentary"><a id="SP12" class="paragraph-anchor"></a><b>§12. Splats. </b>The special statement <span class="extract"><span class="extract-syntax">splat "TEXT"</span></span> or <span class="extract"><span class="extract-syntax">splat ANNOTATION "TEXT"</span></span> allows
|
|
raw Inform 6 code (or potentially raw code for any language) to be included
|
|
verbatim in inter. Splat is not a respectful term, and nor does it deserve
|
|
one. The annotation can be any of: <span class="extract"><span class="extract-syntax">IFDEF_PLM</span></span>, <span class="extract"><span class="extract-syntax">IFNDEF_PLM</span></span>, <span class="extract"><span class="extract-syntax">IFNOT_PLM</span></span>,
|
|
<span class="extract"><span class="extract-syntax">ENDIF_PLM</span></span>, <span class="extract"><span class="extract-syntax">IFTRUE_PLM</span></span>, <span class="extract"><span class="extract-syntax">CONSTANT_PLM</span></span>, <span class="extract"><span class="extract-syntax">ARRAY_PLM</span></span>, <span class="extract"><span class="extract-syntax">GLOBAL_PLM</span></span>,
|
|
<span class="extract"><span class="extract-syntax">STUB_PLM</span></span>, <span class="extract"><span class="extract-syntax">ROUTINE_PLM</span></span>, <span class="extract"><span class="extract-syntax">ATTRIBUTE_PLM</span></span>, <span class="extract"><span class="extract-syntax">PROPERTY_PLM</span></span>, <span class="extract"><span class="extract-syntax">VERB_PLM</span></span>,
|
|
<span class="extract"><span class="extract-syntax">FAKEACTION_PLM</span></span>, <span class="extract"><span class="extract-syntax">OBJECT_PLM</span></span>, <span class="extract"><span class="extract-syntax">DEFAULT_PLM</span></span>, <span class="extract"><span class="extract-syntax">MYSTERY_PLM</span></span>.
|
|
</p>
|
|
|
|
<p class="commentary">Convention. Inform creates no splats, except as needed to convert
|
|
Inform 6 template code into inter, in the code-generator.
|
|
</p>
|
|
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