141 lines
6.8 KiB
HTML
141 lines
6.8 KiB
HTML
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>R6RS Records (Guile Reference Manual)</title>
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<meta name="description" content="R6RS Records (Guile Reference Manual)">
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<meta name="keywords" content="R6RS Records (Guile Reference Manual)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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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="R6RS-Standard-Libraries.html" rel="up" title="R6RS Standard Libraries">
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<link href="rnrs-records-syntactic.html" rel="next" title="rnrs records syntactic">
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<link href="rnrs-control.html" rel="prev" title="rnrs control">
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<style type="text/css">
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<!--
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a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
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span:hover a.copiable-link {visibility: visible}
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</style>
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="R6RS-Records">
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<div class="nav-panel">
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<p>
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Next: <a href="rnrs-records-syntactic.html" accesskey="n" rel="next">rnrs records syntactic</a>, Previous: <a href="rnrs-control.html" accesskey="p" rel="prev">rnrs control</a>, Up: <a href="R6RS-Standard-Libraries.html" accesskey="u" rel="up">R6RS Standard Libraries</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="subsubsection" id="R6RS-Records-1"><span>7.6.2.8 R6RS Records<a class="copiable-link" href="#R6RS-Records-1"> ¶</a></span></h4>
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<p>The manual sections below describe Guile’s implementation of R6RS
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records, which provide support for user-defined data types. The R6RS
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records API provides a superset of the features provided by Guile’s
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“native” records, as well as those of the SRFI-9 records API;
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See <a class="xref" href="Records.html">Records</a>, and <a class="ref" href="SRFI_002d9-Records.html">SRFI-9 Records</a>, for a description of those
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interfaces.
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</p>
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<p>As with SRFI-9 and Guile’s native records, R6RS records are constructed
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using a record-type descriptor that specifies attributes like the
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record’s name, its fields, and the mutability of those fields.
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</p>
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<p>R6RS records extend this framework to support single inheritance via the
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specification of a “parent” type for a record type at definition time.
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Accessors and mutator procedures for the fields of a parent type may be
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applied to records of a subtype of this parent. A record type may be
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<em class="dfn">sealed</em>, in which case it cannot be used as the parent of another
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record type.
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</p>
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<p>The inheritance mechanism for record types also informs the process of
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initializing the fields of a record and its parents. Constructor
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procedures that generate new instances of a record type are obtained
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from a record constructor descriptor, which encapsulates the record-type
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descriptor of the record to be constructed along with a <em class="dfn">protocol</em>
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procedure that defines how constructors for record subtypes delegate to
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the constructors of their parent types.
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</p>
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<p>A protocol is a procedure used by the record system at construction time
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to bind arguments to the fields of the record being constructed. The
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protocol procedure is passed a procedure <var class="var">n</var> that accepts the
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arguments required to construct the record’s parent type; this
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procedure, when invoked, will return a procedure <var class="var">p</var> that accepts
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the arguments required to construct a new instance of the record type
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itself and returns a new instance of the record type.
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</p>
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<p>The protocol should in turn return a procedure that uses <var class="var">n</var> and
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<var class="var">p</var> to initialize the fields of the record type and its parent
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type(s). This procedure will be the constructor returned by
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</p>
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<p>As a trivial example, consider the hypothetical record type
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<code class="code">pixel</code>, which encapsulates an x-y location on a screen, and
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<code class="code">voxel</code>, which has <code class="code">pixel</code> as its parent type and stores an
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additional coordinate. The following protocol produces a constructor
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procedure that accepts all three coordinates, uses the first two to
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initialize the fields of <code class="code">pixel</code>, and binds the third to the single
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field of <code class="code">voxel</code>.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> (lambda (n)
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(lambda (x y z)
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(let ((p (n x y)))
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(p z))))
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</pre></div>
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<p>It may be helpful to think of protocols as “constructor factories”
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that produce chains of delegating constructors glued together by the
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helper procedure <var class="var">n</var>.
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</p>
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<p>An R6RS record type may be declared to be <em class="dfn">nongenerative</em> via the
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use of a unique generated or user-supplied symbol—or
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<em class="dfn">uid</em>—such that subsequent record type declarations with the same
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uid and attributes will return the previously-declared record-type
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descriptor.
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</p>
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<p>R6RS record types may also be declared to be <em class="dfn">opaque</em>, in which case
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the various predicates and introspection procedures defined in
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<code class="code">(rnrs records introspection)</code> will behave as if records of this
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type are not records at all.
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</p>
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<p>Note that while the R6RS records API shares much of its namespace with
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both the SRFI-9 and native Guile records APIs, it is not currently
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compatible with either.
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</p>
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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="rnrs-records-syntactic.html">rnrs records syntactic</a>, Previous: <a href="rnrs-control.html">rnrs control</a>, Up: <a href="R6RS-Standard-Libraries.html">R6RS Standard Libraries</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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</html>
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