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219 lines
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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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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>Expect (Guile Reference Manual)</title>
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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="Guile-Modules.html" rel="up" title="Guile Modules">
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<link href="sxml_002dmatch.html" rel="next" title="sxml-match">
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<link href="Buffered-Input.html" rel="prev" title="Buffered Input">
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</head>
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<body lang="en">
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<div class="section-level-extent" id="Expect">
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<div class="nav-panel">
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<p>
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Next: <a href="sxml_002dmatch.html" accesskey="n" rel="next"><code class="code">sxml-match</code>: Pattern Matching of SXML</a>, Previous: <a href="Buffered-Input.html" accesskey="p" rel="prev">Buffered Input</a>, Up: <a href="Guile-Modules.html" accesskey="u" rel="up">Guile 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>
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</div>
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<hr>
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<h3 class="section" id="Expect-1"><span>7.16 Expect<a class="copiable-link" href="#Expect-1"> ¶</a></span></h3>
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<p>The macros in this section are made available with:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(use-modules (ice-9 expect))
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</pre></div>
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<p><code class="code">expect</code> is a macro for selecting actions based on the output from
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a port. The name comes from a tool of similar functionality by Don Libes.
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Actions can be taken when a particular string is matched, when a timeout
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occurs, or when end-of-file is seen on the port. The <code class="code">expect</code> macro
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is described below; <code class="code">expect-strings</code> is a front-end to <code class="code">expect</code>
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based on regexec (see the regular expression documentation).
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</p>
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<dl class="first-deffn first-defmac-alias-first-deffn">
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<dt class="deffn defmac-alias-deffn" id="index-expect_002dstrings"><span class="category-def">Macro: </span><span><strong class="def-name">expect-strings</strong> <var class="def-var-arguments">clause …</var><a class="copiable-link" href="#index-expect_002dstrings"> ¶</a></span></dt>
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<dd><p>By default, <code class="code">expect-strings</code> will read from the current input port.
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The first term in each clause consists of an expression evaluating to
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a string pattern (regular expression). As characters
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are read one-by-one from the port, they are accumulated in a buffer string
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which is matched against each of the patterns. When a
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pattern matches, the remaining expression(s) in
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the clause are evaluated and the value of the last is returned. For example:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(with-input-from-file "/etc/passwd"
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(lambda ()
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(expect-strings
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("^nobody" (display "Got a nobody user.\n")
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(display "That's no problem.\n"))
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("^daemon" (display "Got a daemon user.\n")))))
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</pre></div>
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<p>The regular expression is compiled with the <code class="code">REG_NEWLINE</code> flag, so
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that the ^ and $ anchors will match at any newline, not just at the start
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and end of the string.
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</p>
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<p>There are two other ways to write a clause:
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</p>
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<p>The expression(s) to evaluate
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can be omitted, in which case the result of the regular expression match
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(converted to strings, as obtained from regexec with match-pick set to "")
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will be returned if the pattern matches.
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</p>
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<p>The symbol <code class="code">=></code> can be used to indicate that the expression is a
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procedure which will accept the result of a successful regular expression
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match. E.g.,
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">("^daemon" => write)
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("^d(aemon)" => (lambda args (for-each write args)))
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("^da(em)on" => (lambda (all sub)
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(write all) (newline)
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(write sub) (newline)))
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</pre></div>
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<p>The order of the substrings corresponds to the order in which the
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opening brackets occur.
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</p>
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<p>A number of variables can be used to control the behavior
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of <code class="code">expect</code> (and <code class="code">expect-strings</code>).
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Most have default top-level bindings to the value <code class="code">#f</code>,
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which produces the default behavior.
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They can be redefined at the
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top level or locally bound in a form enclosing the expect expression.
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</p>
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<dl class="table">
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<dt><code class="code">expect-port</code></dt>
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<dd><p>A port to read characters from, instead of the current input port.
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</p></dd>
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<dt><code class="code">expect-timeout</code></dt>
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<dd><p><code class="code">expect</code> will terminate after this number of
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seconds, returning <code class="code">#f</code> or the value returned by expect-timeout-proc.
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</p></dd>
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<dt><code class="code">expect-timeout-proc</code></dt>
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<dd><p>A procedure called if timeout occurs. The procedure takes a single argument:
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the accumulated string.
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</p></dd>
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<dt><code class="code">expect-eof-proc</code></dt>
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<dd><p>A procedure called if end-of-file is detected on the input port. The
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procedure takes a single argument: the accumulated string.
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</p></dd>
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<dt><code class="code">expect-char-proc</code></dt>
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<dd><p>A procedure to be called every time a character is read from the
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port. The procedure takes a single argument: the character which was read.
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</p></dd>
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<dt><code class="code">expect-strings-compile-flags</code></dt>
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<dd><p>Flags to be used when compiling a regular expression, which are passed
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to <code class="code">make-regexp</code> See <a class="xref" href="Regexp-Functions.html">Regexp Functions</a>. The default value
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is <code class="code">regexp/newline</code>.
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</p></dd>
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<dt><code class="code">expect-strings-exec-flags</code></dt>
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<dd><p>Flags to be used when executing a regular expression, which are
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passed to regexp-exec See <a class="xref" href="Regexp-Functions.html">Regexp Functions</a>.
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The default value is <code class="code">regexp/noteol</code>, which prevents <code class="code">$</code>
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from matching the end of the string while it is still accumulating,
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but still allows it to match after a line break or at the end of file.
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</p></dd>
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</dl>
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<p>Here’s an example using all of the variables:
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</p>
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<div class="example smalllisp lisp">
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<pre class="lisp-preformatted">(let ((expect-port (open-input-file "/etc/passwd"))
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(expect-timeout 1)
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(expect-timeout-proc
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(lambda (s) (display "Times up!\n")))
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(expect-eof-proc
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(lambda (s) (display "Reached the end of the file!\n")))
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(expect-char-proc display)
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(expect-strings-compile-flags (logior regexp/newline regexp/icase))
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(expect-strings-exec-flags 0))
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(expect-strings
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("^nobody" (display "Got a nobody user\n"))))
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</pre></div>
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</dd></dl>
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<dl class="first-deffn first-defmac-alias-first-deffn">
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<dt class="deffn defmac-alias-deffn" id="index-expect"><span class="category-def">Macro: </span><span><strong class="def-name">expect</strong> <var class="def-var-arguments">clause …</var><a class="copiable-link" href="#index-expect"> ¶</a></span></dt>
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<dd><p><code class="code">expect</code> is used in the same way as <code class="code">expect-strings</code>,
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but tests are specified not as patterns, but as procedures. The
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procedures are called in turn after each character is read from the
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port, with two arguments: the value of the accumulated string and
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a flag to indicate whether end-of-file has been reached. The flag
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will usually be <code class="code">#f</code>, but if end-of-file is reached, the procedures
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are called an additional time with the final accumulated string and
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<code class="code">#t</code>.
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</p>
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<p>The test is successful if the procedure returns a non-false value.
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</p>
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<p>If the <code class="code">=></code> syntax is used, then if the test succeeds it must return
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a list containing the arguments to be provided to the corresponding
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expression.
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</p>
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<p>In the following example, a string will only be matched at the beginning
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of the file:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(let ((expect-port (open-input-file "/etc/passwd")))
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(expect
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((lambda (s eof?) (string=? s "fnord!"))
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(display "Got a nobody user!\n"))))
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</pre></div>
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<p>The control variables described for <code class="code">expect-strings</code> also
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influence the behavior of <code class="code">expect</code>, with the exception of
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variables whose names begin with <code class="code">expect-strings-</code>.
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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="sxml_002dmatch.html"><code class="code">sxml-match</code>: Pattern Matching of SXML</a>, Previous: <a href="Buffered-Input.html">Buffered Input</a>, Up: <a href="Guile-Modules.html">Guile 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>
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</div>
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</body>
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