182 lines
7.4 KiB
HTML
182 lines
7.4 KiB
HTML
|
<!DOCTYPE html>
|
||
|
|
<html>
|
||
|
|
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<!-- This manual documents Guile version 3.0.10.
|
||
|
|
|
||
|
|
Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
|
||
|
|
Inc.
|
||
|
|
|
||
|
|
Copyright (C) 2021 Maxime Devos
|
||
|
|
|
||
|
|
Copyright (C) 2024 Tomas Volf
|
||
|
|
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation; with no
|
||
|
|
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
|
||
|
|
copy of the license is included in the section entitled "GNU Free
|
||
|
|
Documentation License." -->
|
||
|
|
<title>SRFI-0 (Guile Reference Manual)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="SRFI-0 (Guile Reference Manual)">
|
||
|
|
<meta name="keywords" content="SRFI-0 (Guile Reference Manual)">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content=".texi2any-real">
|
||
|
|
<meta name="viewport" content="width=device-width,initial-scale=1">
|
||
|
|
|
||
|
|
<link href="index.html" rel="start" title="Top">
|
||
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="SRFI-Support.html" rel="up" title="SRFI Support">
|
||
|
|
<link href="SRFI_002d1.html" rel="next" title="SRFI-1">
|
||
|
|
<link href="About-SRFI-Usage.html" rel="prev" title="About SRFI Usage">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
span:hover a.copiable-link {visibility: visible}
|
||
|
|
strong.def-name {font-family: monospace; font-weight: bold; font-size: larger}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<div class="subsection-level-extent" id="SRFI_002d0">
|
||
|
|
<div class="nav-panel">
|
||
|
|
<p>
|
||
|
|
Next: <a href="SRFI_002d1.html" accesskey="n" rel="next">SRFI-1 - List library</a>, Previous: <a href="About-SRFI-Usage.html" accesskey="p" rel="prev">About SRFI Usage</a>, Up: <a href="SRFI-Support.html" accesskey="u" rel="up">SRFI Support Modules</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>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<h4 class="subsection" id="SRFI_002d0-_002d-cond_002dexpand"><span>7.5.2 SRFI-0 - cond-expand<a class="copiable-link" href="#SRFI_002d0-_002d-cond_002dexpand"> ¶</a></span></h4>
|
||
|
|
<a class="index-entry-id" id="index-SRFI_002d0"></a>
|
||
|
|
|
||
|
|
<p>This SRFI lets a portable Scheme program test for the presence of
|
||
|
|
certain features, and adapt itself by using different blocks of code,
|
||
|
|
or fail if the necessary features are not available. There’s no
|
||
|
|
module to load, this is in the Guile core.
|
||
|
|
</p>
|
||
|
|
<p>A program designed only for Guile will generally not need this
|
||
|
|
mechanism, such a program can of course directly use the various
|
||
|
|
documented parts of Guile.
|
||
|
|
</p>
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-cond_002dexpand"><span class="category-def">syntax: </span><span><strong class="def-name">cond-expand</strong> <var class="def-var-arguments">(feature body…) …</var><a class="copiable-link" href="#index-cond_002dexpand"> ¶</a></span></dt>
|
||
|
|
<dd><p>Expand to the <var class="var">body</var> of the first clause whose <var class="var">feature</var>
|
||
|
|
specification is satisfied. It is an error if no <var class="var">feature</var> is
|
||
|
|
satisfied.
|
||
|
|
</p>
|
||
|
|
<p>Features are symbols such as <code class="code">srfi-1</code>, and a feature
|
||
|
|
specification can use <code class="code">and</code>, <code class="code">or</code> and <code class="code">not</code> forms to
|
||
|
|
test combinations. The last clause can be an <code class="code">else</code>, to be used
|
||
|
|
if no other passes.
|
||
|
|
</p>
|
||
|
|
<p>For example, define a private version of <code class="code">alist-cons</code> if SRFI-1
|
||
|
|
is not available.
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">(cond-expand (srfi-1
|
||
|
|
)
|
||
|
|
(else
|
||
|
|
(define (alist-cons key val alist)
|
||
|
|
(cons (cons key val) alist))))
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>Or demand a certain set of SRFIs (list operations, string ports,
|
||
|
|
<code class="code">receive</code> and string operations), failing if they’re not
|
||
|
|
available.
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">(cond-expand ((and srfi-1 srfi-6 srfi-8 srfi-13)
|
||
|
|
))
|
||
|
|
</pre></div>
|
||
|
|
</dd></dl>
|
||
|
|
|
||
|
|
<p>The Guile core has the following features,
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">guile
|
||
|
|
guile-2 ;; starting from Guile 2.x
|
||
|
|
guile-2.2 ;; starting from Guile 2.2
|
||
|
|
guile-3 ;; starting from Guile 3.x
|
||
|
|
guile-3.0 ;; starting from Guile 3.0
|
||
|
|
r5rs
|
||
|
|
r6rs
|
||
|
|
r7rs
|
||
|
|
exact-closed ieee-float full-unicode ratios ;; R7RS features
|
||
|
|
srfi-0
|
||
|
|
srfi-4
|
||
|
|
srfi-6
|
||
|
|
srfi-13
|
||
|
|
srfi-14
|
||
|
|
srfi-16
|
||
|
|
srfi-23
|
||
|
|
srfi-30
|
||
|
|
srfi-39
|
||
|
|
srfi-46
|
||
|
|
srfi-55
|
||
|
|
srfi-61
|
||
|
|
srfi-62
|
||
|
|
srfi-87
|
||
|
|
srfi-105
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>Other SRFI feature symbols are defined once their code has been loaded
|
||
|
|
with <code class="code">use-modules</code>, since only then are their bindings available.
|
||
|
|
</p>
|
||
|
|
<p>The ‘<samp class="samp">--use-srfi</samp>’ command line option (see <a class="pxref" href="Invoking-Guile.html">Invoking Guile</a>) is
|
||
|
|
a good way to load SRFIs to satisfy <code class="code">cond-expand</code> when running a
|
||
|
|
portable program.
|
||
|
|
</p>
|
||
|
|
<p>Testing the <code class="code">guile</code> feature allows a program to adapt itself to
|
||
|
|
the Guile module system, but still run on other Scheme systems. For
|
||
|
|
example the following demands SRFI-8 (<code class="code">receive</code>), but also knows
|
||
|
|
how to load it with the Guile mechanism.
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">(cond-expand (srfi-8
|
||
|
|
)
|
||
|
|
(guile
|
||
|
|
(use-modules (srfi srfi-8))))
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<a class="index-entry-id" id="index-guile_002d2-SRFI_002d0-feature"></a>
|
||
|
|
<a class="index-entry-id" id="index-portability-between-2_002e0-and-older-versions"></a>
|
||
|
|
<p>Likewise, testing the <code class="code">guile-2</code> feature allows code to be portable
|
||
|
|
between Guile 2.<var class="var">x</var> and previous versions of Guile. For instance, it
|
||
|
|
makes it possible to write code that accounts for Guile 2.<var class="var">x</var>’s compiler,
|
||
|
|
yet be correctly interpreted on 1.8 and earlier versions:
|
||
|
|
</p>
|
||
|
|
<div class="example">
|
||
|
|
<pre class="example-preformatted">(cond-expand (guile-2 (eval-when (compile)
|
||
|
|
;; This must be evaluated at compile time.
|
||
|
|
(fluid-set! current-reader my-reader)))
|
||
|
|
(guile
|
||
|
|
;; Earlier versions of Guile do not have a
|
||
|
|
;; separate compilation phase.
|
||
|
|
(fluid-set! current-reader my-reader)))
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>It should be noted that <code class="code">cond-expand</code> is separate from the
|
||
|
|
<code class="code">*features*</code> mechanism (see <a class="pxref" href="Feature-Tracking.html">Feature Tracking</a>), feature
|
||
|
|
symbols in one are unrelated to those in the other.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<div class="nav-panel">
|
||
|
|
<p>
|
||
|
|
Next: <a href="SRFI_002d1.html">SRFI-1 - List library</a>, Previous: <a href="About-SRFI-Usage.html">About SRFI Usage</a>, Up: <a href="SRFI-Support.html">SRFI Support Modules</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>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|