217 lines
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HTML
217 lines
13 KiB
HTML
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Documentation License." -->
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<title>Records (Guile Reference Manual)</title>
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<meta name="description" content="Records (Guile Reference Manual)">
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<meta name="keywords" content="Records (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Data-Types.html" rel="up" title="Data Types">
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<link href="Structures.html" rel="next" title="Structures">
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<link href="SRFI_002d9-Records.html" rel="prev" title="SRFI-9 Records">
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<body lang="en">
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<div class="subsection-level-extent" id="Records">
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<div class="nav-panel">
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<p>
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Next: <a href="Structures.html" accesskey="n" rel="next">Structures</a>, Previous: <a href="SRFI_002d9-Records.html" accesskey="p" rel="prev">SRFI-9 Records</a>, Up: <a href="Data-Types.html" accesskey="u" rel="up">Data Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="Records-1"><span>6.6.17 Records<a class="copiable-link" href="#Records-1"> ¶</a></span></h4>
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<p>A <em class="dfn">record type</em> is a first class object representing a user-defined
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data type. A <em class="dfn">record</em> is an instance of a record type.
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</p>
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<p>Note that in many ways, this interface is too low-level for every-day
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use. Most uses of records are better served by SRFI-9 records.
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See <a class="xref" href="SRFI_002d9-Records.html">SRFI-9 Records</a>.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-record_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a record of any type and <code class="code">#f</code>
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otherwise.
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</p>
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<p>Note that <code class="code">record?</code> may be true of any Scheme value; there is no
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promise that records are disjoint with other Scheme types.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002drecord_002dtype"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-record-type</strong> <var class="def-var-arguments">type-name field-names [print] [#:parent=<code class="code">#f</code>] [#:uid=<code class="code">#f</code>] [#:extensible?=<code class="code">#f</code>] [#:opaque?=<code class="code">#f</code>] [#:allow-duplicate-field-names?=<code class="code">#t</code>]</var><a class="copiable-link" href="#index-make_002drecord_002dtype"> ¶</a></span></dt>
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<dd><p>Create and return a new <em class="dfn">record-type descriptor</em>.
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</p>
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<p><var class="var">type-name</var> is a string naming the type. Currently it’s only used
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in the printed representation of records, and in diagnostics.
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<var class="var">field-names</var> is a list of elements of the form <code class="code">(immutable
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<var class="var">name</var>)</code>, <code class="code">(mutable <var class="var">name</var>)</code>, or <var class="var">name</var>, where
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<var class="var">name</var> are symbols naming the fields of a record of the type.
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Duplicates are not allowed among these symbols, unless
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<var class="var">allow-duplicate-field-names?</var> is true.
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</p>
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<div class="example">
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<pre class="example-preformatted">(make-record-type "employee" '(name age salary))
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</pre></div>
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<p>The optional <var class="var">print</var> argument is a function used by
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<code class="code">display</code>, <code class="code">write</code>, etc, for printing a record of the new
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type. It’s called as <code class="code">(<var class="var">print</var> record port)</code> and should look
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at <var class="var">record</var> and write to <var class="var">port</var>.
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</p>
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<p>Pass the <code class="code">#:parent</code> keyword to derive a record type from a
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supertype. A derived record type has the fields from its parent type,
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followed by fields declared in the <code class="code">make-record-type</code> call. Record
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predicates and field accessors for instance of a parent type will also
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work on any instance of a subtype.
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</p>
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<a class="index-entry-id" id="index-extensible-record-types"></a>
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<a class="index-entry-id" id="index-record-types_002c-extensible"></a>
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<p>Allowing record subtyping has a small amount of overhead. To avoid this
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overhead, prevent extensibility by passing <code class="code">#:extensible? #f</code>.
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By default, record types in Guile are not extensible.
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</p>
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<a class="index-entry-id" id="index-prefab-record-types"></a>
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<a class="index-entry-id" id="index-record-types_002c-prefab"></a>
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<a class="index-entry-id" id="index-record-types_002c-nongenerative"></a>
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<p>Generally speaking, calling <code class="code">make-record-type</code> returns a fresh
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record type; it <em class="emph">generates</em> new record types. However sometimes
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you only want to define a record type if one hasn’t been defined
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already. For a <em class="emph">nongenerative</em> record type definition, pass a
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symbol as the <code class="code">#:uid</code> keyword parameter. If a record with the
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given <var class="var">uid</var> was already defined, it will be returned instead. The
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type name, fields, parent (if any), and so on for the previously-defined
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type must be compatible.
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</p>
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<a class="index-entry-id" id="index-record-types_002c-opaque"></a>
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<p>R6RS defines a notion of “opaque” record types. Given an instance of
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an opaque record type, one cannot obtain a run-time representation of
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the record type. See <a class="xref" href="rnrs-records-procedural.html">rnrs records procedural</a>, for full details. The
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<code class="code">#:opaque?</code> flag is used by Guile’s R6RS layer to record this
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information. The default is determined by whether the parent type, if
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any, was opaque.
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</p>
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<p>Fields are mutable by default, meaning that <code class="code">record-modifier</code> will
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return a procedure that can update a record in place. Specifying a
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field using the form <code class="code">(immutable <var class="var">name</var>)</code> instead marks a field
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as immutable.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dconstructor"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-constructor</strong> <var class="def-var-arguments">rtd</var><a class="copiable-link" href="#index-record_002dconstructor"> ¶</a></span></dt>
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<dd><p>Return a procedure for constructing new members of the type represented
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by <var class="var">rtd</var>. The result will be a procedure accepting exactly as many
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arguments as there are fields in the record type.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dpredicate"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-predicate</strong> <var class="def-var-arguments">rtd</var><a class="copiable-link" href="#index-record_002dpredicate"> ¶</a></span></dt>
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<dd><p>Return a procedure for testing membership in the type represented by
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<var class="var">rtd</var>. The returned procedure accepts exactly one argument and
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returns a true value if the argument is a member of the indicated record
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type; it returns a false value otherwise.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002daccessor"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-accessor</strong> <var class="def-var-arguments">rtd field-name</var><a class="copiable-link" href="#index-record_002daccessor"> ¶</a></span></dt>
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<dd><p>Return a procedure for reading the value of a particular field of a
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member of the type represented by <var class="var">rtd</var>. The returned procedure
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accepts exactly one argument which must be a record of the appropriate
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type; it returns the current value of the field named by the symbol
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<var class="var">field-name</var> in that record.
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</p>
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<p>If <var class="var">field-name</var> is a symbol, it must be a member of the list of
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field-names in the call to <code class="code">make-record-type</code> that created the type
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represented by <var class="var">rtd</var>. If multiple fields in <var class="var">rtd</var> have the same
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name, <code class="code">record-accessor</code> returns the first one.
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</p>
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<p>If <var class="var">field-name</var> is an integer, it should be an index into
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<code class="code">(record-type-fields <var class="var">rtd</var>)</code>. This allows accessing fields
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with duplicate names.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dmodifier"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-modifier</strong> <var class="def-var-arguments">rtd field-name</var><a class="copiable-link" href="#index-record_002dmodifier"> ¶</a></span></dt>
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<dd><p>Return a procedure for writing the value of a particular field of a
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member of the type represented by <var class="var">rtd</var>. The returned procedure
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accepts exactly two arguments: first, a record of the appropriate type,
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and second, an arbitrary Scheme value; it modifies the field named by
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the symbol <var class="var">field-name</var> in that record to contain the given value.
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The returned value of the modifier procedure is unspecified. The symbol
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<var class="var">field-name</var> is a field name or a field index, as in
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<code class="code">record-modifier</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dtype_002ddescriptor"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-type-descriptor</strong> <var class="def-var-arguments">record</var><a class="copiable-link" href="#index-record_002dtype_002ddescriptor"> ¶</a></span></dt>
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<dd><p>Return a record-type descriptor representing the type of the given
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record. That is, for example, if the returned descriptor were passed to
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<code class="code">record-predicate</code>, the resulting predicate would return a true
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value when passed the given record. Note that it is not necessarily the
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case that the returned descriptor is the one that was passed to
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<code class="code">record-constructor</code> in the call that created the constructor
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procedure that created the given record.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dtype_002dname"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-type-name</strong> <var class="def-var-arguments">rtd</var><a class="copiable-link" href="#index-record_002dtype_002dname"> ¶</a></span></dt>
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<dd><p>Return the type-name associated with the type represented by rtd. The
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returned value is <code class="code">eqv?</code> to the <var class="var">type-name</var> argument given in
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the call to <code class="code">make-record-type</code> that created the type represented by
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<var class="var">rtd</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-record_002dtype_002dfields"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">record-type-fields</strong> <var class="def-var-arguments">rtd</var><a class="copiable-link" href="#index-record_002dtype_002dfields"> ¶</a></span></dt>
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<dd><p>Return a list of the symbols naming the fields in members of the type
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represented by <var class="var">rtd</var>. The returned value is <code class="code">equal?</code> to the
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field-names argument given in the call to <code class="code">make-record-type</code> that
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created the type represented by <var class="var">rtd</var>.
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</p></dd></dl>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Structures.html">Structures</a>, Previous: <a href="SRFI_002d9-Records.html">SRFI-9 Records</a>, Up: <a href="Data-Types.html">Data Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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