/usr/lib/swi-prolog/doc/Manual/iostream.html

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<h2 id="sec:iostream"><a id="sec:A.13"><span class="sec-nr">A.13</span> <span class="sec-title">library(iostream): 
Utilities to deal with streams</span></a></h2>

<p><a id="sec:iostream"></a>

<dl class="tags">
<dt class="tag">See also</dt>
<dd>
<code>library(archive)</code>, <code>library(process)</code>, <code>library(zlib)</code>,
<code>library(http/http_stream)</code>
</dd>
</dl>

<p>This library contains utilities that deal with streams, notably 
originating from non-built-in sources such as URLs, archives, windows, 
processes, etc.

<p>The predicate <a class="pred" href="iostream.html#open_any/5">open_any/5</a> 
acts as a <i>broker</i> between applications that can process data from 
a stream and libraries that can create streams from diverse sources. 
Without this predicate, processing data inevitally follows the pattern 
below. As <i>call_some_open_variation</i> can be anything, this blocks 
us from writing predicates such as <code>load_xml(From, DOM)</code> that 
can operate on arbitrary input sources.

<pre class="code">
setup_call_cleanup(
    call_some_open_variation(Spec, In),
    process(In),
    close(In)).
</pre>

<p>Libraries that can open streams can install the hook
<span class="pred-ext">iostream:open_hook/6</span> to make their 
functionality available through
<a class="pred" href="iostream.html#open_any/5">open_any/5</a>.

<dl class="latex">
<dt class="pubdef"><a id="open_any/5"><strong>open_any</strong>(<var>+Specification, 
+Mode, -Stream, -Close, +Options</var>)</a></dt>
<dd class="defbody">
Establish a stream from <var>Specification</var> that should be closed 
using <var>Close</var>, which can either be called or passed to
<span class="pred-ext">close_any/5</span>. <var>Options</var> processed:

<dl class="latex">
<dt><strong>encoding</strong>(<var>Enc</var>)</dt>
<dd class="defbody">
Set stream to encoding <var>Enc</var>.
</dd>
</dl>

<p>Without loaded plugins, the <a class="pred" href="iostream.html#open_any/5">open_any/5</a> 
processes the following values for <var>Specification</var>. If no rule 
matches, <a class="pred" href="iostream.html#open_any/5">open_any/5</a> 
processes <var>Specification</var> as <code>file(Specification)</code>.

<dl class="latex">
<dt><strong><var>Stream</var></strong></dt>
<dd class="defbody">
A plain stream handle. Possisible post-processing options such as 
encoding are applied. <var>Close</var> does <i>not</i> close the stream, 
but resets other side-effects such as the encoding.
</dd>
<dt><strong>stream</strong>(<var>Stream</var>)</dt>
<dd class="defbody">
Same as a plain <var>Stream</var>.
</dd>
<dt><strong><var>FileURL</var></strong></dt>
<dd class="defbody">
If <var>Specification</var> is of the form =file://...=, the pointed to 
file is opened using <a class="pred" href="IO.html#open/4">open/4</a>. 
Requires <code>library(uri)</code> to be installed.
</dd>
<dt><strong>file</strong>(<var>Path</var>)</dt>
<dd class="defbody">
Explicitly open the file <var>Path</var>. <var>Path</var> can be an <var>Path</var>(File) 
term as accepted by <a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
</dd>
<dt><strong>string</strong>(<var>String</var>)</dt>
<dd class="defbody">
Open a Prolog string, atom, list of characters or codes as an <i>input</i> 
stream.
</dd>
</dl>

<p>The typical usage scenario is given in the code below, where
<var>&lt;</var>process<var>&gt;</var> processes the input.

<pre class="code">
setup_call_cleanup(
    open_any(Spec, read, In, Close, Options),
    &lt;process&gt;(In),
    Close).
</pre>

<p>Currently, the following libraries extend this predicate:

<dl class="latex">
<dt><strong>library</strong>(<var>http/http_open</var>)</dt>
<dd class="defbody">
Adds support for URLs using the <code>http</code> and <code>https</code> 
schemes.
</dd>
</dl>

</dd>
<dt class="pubdef"><a id="close_any/1"><strong>close_any</strong>(<var>+Goal</var>)</a></dt>
<dd class="defbody">
Execute the <var>Close</var> closure returned by <a class="pred" href="iostream.html#open_any/5">open_any/5</a>. 
The closure can also be called directly. Using <a class="pred" href="iostream.html#close_any/1">close_any/1</a> 
can be considered better style and enhances tractability of the source 
code.</dd>
<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="open_hook/6"><strong>open_hook</strong>(<var>+Spec, 
+Mode, -Stream, -Close, +Options0, -Options</var>)</a></dt>
<dd class="defbody">
Open <var>Spec</var> in <var>Mode</var>, producing <var>Stream</var>.
<table class="arglist">
<tr><td><var>Close</var> </td><td>is unified to a goal that must be 
called to undo the side-effects of the action, e.g., typically the term <code>close(Stream)</code> </td></tr>
<tr><td><var>Options0</var> </td><td>are the options passed to <a class="pred" href="iostream.html#open_any/5">open_any/5</a> </td></tr>
<tr><td><var>Options</var> </td><td>are passed to the post processing 
filters that may be installed by <a class="pred" href="iostream.html#open_any/5">open_any/5</a>. </td></tr>
</table>
</dd>
</dl>

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swi-prolog-nox 7.2.3-2 / usr / lib / swi-prolog / doc / Manual / iostream.html
