337 lines
11 KiB
XML
337 lines
11 KiB
XML
<documentation title="CXML Klacks parser">
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<h1>Klacks parser</h1>
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<p>
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The Klacks parser provides an alternative parsing interface,
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similar in concept to Java's <a
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href="http://jcp.org/en/jsr/detail?id=173">Streaming API for
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XML</a> (StAX).
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</p>
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<p>
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It implements a streaming, "pull-based" API. This is different
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from SAX, which is a "push-based" model.
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</p>
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<p>
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Klacks is implemented using the same code base as the SAX parser
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and has the same parsing characteristics (validation, namespace
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support, entity resolution) while offering a more flexible interface
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than SAX.
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</p>
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<p>
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See below for <a href="#examples">examples</a>.
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</p>
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<a name="sources"/>
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<h3>Parsing incrementally using sources</h3>
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<p>
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To parse using Klacks, create an XML <tt>source</tt> first.
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</p>
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<p>
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<div class="def">Function CXML:MAKE-SOURCE (input &key validate
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dtd root entity-resolver disallow-external-subset pathname)</div>
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Create and return a source for <tt>input</tt>.
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</p>
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<p>
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Exact behaviour depends on <tt>input</tt>, which can
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be one of the following types:
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</p>
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<ul>
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<li>
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<tt>pathname</tt> -- a Common Lisp pathname.
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Open the file specified by the pathname and create a source for
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the resulting stream. See below for information on how to
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close the stream.
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</li>
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<li><tt>stream</tt> -- a Common Lisp stream with element-type
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<tt>(unsigned-byte 8)</tt>. See below for information on how to
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close the stream.
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</li>
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<li>
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<tt>octets</tt> -- an <tt>(unsigned-byte 8)</tt> array.
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The array is parsed directly, and interpreted according to the
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encoding it specifies.
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</li>
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<li>
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<tt>string</tt>/<tt>rod</tt> -- a rod (or <tt>string</tt> on
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unicode-capable implementations).
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Parses an XML document from the input string that has already
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undergone external-format decoding.
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</li>
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</ul>
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<p>
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<b>Closing streams:</b> Sources can refer to Lisp streams that
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need to be closed after parsing. This includes a stream passed
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explicitly as <tt>input</tt>, a stream created implicitly for the
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<tt>pathname</tt> case, as well as any streams created
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automatically for external parsed entities referred to by the
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document.
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</p>
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<p>
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All these stream get closed automatically if end of file is
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reached normally. Use <tt>klacks:close-source</tt> or
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<tt>klacks:with-open-source</tt> to ensure that the streams get
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closed otherwise.
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</p>
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<p>
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<b>Buffering:</b> By default, the Klacks parser performs buffering
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of octets being read from the stream as an optimization. This can
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result in unwanted blocking if the stream is a socket and the
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parser tries to read more data than required to parse the current
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event. Use <tt>:buffering nil</tt> to disable this optimization.
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</p>
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<ul>
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<li>
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<tt>buffering</tt> -- Boolean, defaults to <tt>t</tt>. If
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enabled, read data several kilobytes at time. If disabled,
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read only single bytes at a time.
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</li>
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</ul>
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<p>
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The following <b>keyword arguments</b> have the same meaning as
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with the SAX parser, please refer to the documentation of <a
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href="sax.html#parser">parse-file</a> for more information:
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</p>
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<ul>
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<li>
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<tt>validate</tt>
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</li>
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<li>
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<tt>dtd</tt>
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</li>
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<li><tt>root</tt>
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</li>
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<li>
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<tt>entity-resolver</tt>
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</li>
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<li>
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<tt>disallow-internal-subset</tt>
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</li>
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</ul>
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<p>
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In addition, the following argument is for types of <tt>input</tt>
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other than <tt>pathname</tt>:
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</p>
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<ul>
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<li>
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<tt>pathname</tt> -- If specified, defines the base URI of the
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document based on this pathname instance.
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</li>
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</ul>
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<p>
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Events are read from the stream using the following functions:
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</p>
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<div class="def">Function KLACKS:PEEK (source)</div>
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<p> => :start-document<br/>
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or => :start-document, version, encoding, standalonep<br/>
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or => :dtd, name, public-id, system-id<br/>
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or => :start-element, uri, lname, qname<br/>
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or => :end-element, uri, lname, qname<br/>
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or => :characters, data<br/>
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or => :processing-instruction, target, data<br/>
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or => :comment, data<br/>
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or => :end-document, data<br/>
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or => nil
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</p>
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<p>
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<tt>peek</tt> returns the current event's key and main values.
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</p>
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<p>
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<div class="def">Function KLACKS:PEEK-NEXT (source) => key, value*</div>
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</p>
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<p>
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Advance the source forward to the next event and returns it
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like <tt>peek</tt> would.
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</p>
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<p>
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<div class="def">Function KLACKS:PEEK-VALUE (source) => value*</div>
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</p>
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<p>
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Like <tt>peek</tt>, but return only the values, not the key.
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</p>
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<p>
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<div class="def">Function KLACKS:CONSUME (source) => key, value*</div>
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</p>
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<p>
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Return the same values <tt>peek</tt> would, and in addition
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advance the source forward to the next event.
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</p>
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<p>
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<div class="def">Function KLACKS:CURRENT-URI (source) => uri</div>
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<div class="def">Function KLACKS:CURRENT-LNAME (source) => string</div>
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<div class="def">Function KLACKS:CURRENT-QNAME (source) => string</div>
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</p>
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<p>
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If the current event is :start-element or :end-element, return the
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corresponding value. Else, signal an error.
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</p>
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<p>
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<div class="def">Function KLACKS:CURRENT-CHARACTERS (source) => string</div>
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</p>
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<p>
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If the current event is :characters, return the character data
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value. Else, signal an error.
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</p>
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<p>
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<div class="def">Function KLACKS:CURRENT-CDATA-SECTION-P (source) => boolean</div>
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</p>
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<p>
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If the current event is :characters, determine whether the data was
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specified using a CDATA section in the source document. Else,
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signal an error.
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</p>
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<p>
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<div class="def">Function KLACKS:MAP-ATTRIBUTES (fn source)</div>
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</p>
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<p>
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Call <tt>fn</tt> for each attribute of the current start tag in
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turn, and pass the following values as arguments to the function:
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<ul>
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<li>namespace uri</li>
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<li>local name</li>
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<li>qualified name</li>
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<li>attribute value</li>
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<li>a boolean indicating whether the attribute was specified
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explicitly in the source document, rather than defaulted from
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a DTD</li>
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</ul>
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Only valid for :start-element.
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</p>
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<p>
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Return a list of SAX attribute structures for the current start tag.
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Only valid for :start-element.
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</p>
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<p>
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<div class="def">Function KLACKS:CLOSE-SOURCE (source)</div>
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Close all streams referred to by <tt>source</tt>.
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</p>
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<p>
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<div class="def">Macro KLACKS:WITH-OPEN-SOURCE ((var source) &body body)</div>
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Evaluate <tt>source</tt> to create a source object, bind it to
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symbol <tt>var</tt> and evaluate <tt>body</tt> as an implicit progn.
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Call <tt>klacks:close-source</tt> to close the source after
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exiting <tt>body</tt>, whether normally or abnormally.
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</p>
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<a name="convenience"/>
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<h3>Convenience functions</h3>
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<p>
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<div class="def">Function KLACKS:FIND-EVENT (source key)</div>
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Read events from <tt>source</tt> and discard them until an event
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of type <i>key</i> is found. Return values like <tt>peek</tt>, or
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NIL if no such event was found.
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</p>
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<p>
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<div class="def">Function KLACKS:FIND-ELEMENT (source &optional
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lname uri)</div>
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Read events from <tt>source</tt> and discard them until an event
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of type :start-element is found with matching local name and
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namespace uri is found. If <tt>lname</tt> is <tt>nil</tt>, any
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tag name matches. If <tt>uri</tt> is <tt>nil</tt>, any
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namespace matches. Return values like <tt>peek</tt> or NIL if no
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such event was found.
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</p>
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<a name="klacksax"/>
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<h3>Bridging Klacks and SAX</h3>
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<p>
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<div class="def">Function KLACKS:SERIALIZE-EVENT (source handler)</div>
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Send the current klacks events from <tt>source</tt> as a SAX
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events to the SAX <tt>handler</tt> and consume it.
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</p>
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<p>
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<div class="def">Function KLACKS:SERIALIZE-ELEMENT (source handler
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&key document-events)</div>
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Read all klacks events from the following <tt>:start-element</tt> to
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its <tt>:end-element</tt> and send them as SAX events
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to <tt>handler</tt>. When this function is called, the current
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event must be <tt>:start-element</tt>, else an error is
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signalled. With <tt>document-events</tt> (the default),
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<tt>sax:start-document</tt> and <tt>sax:end-document</tt> events
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are sent around the element.
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</p>
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<p>
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<div class="def">Function KLACKS:SERIALIZE-SOURCE (source handler)</div>
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Read all klacks events from <tt>source</tt> and send them as SAX
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events to the SAX <tt>handler</tt>.
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</p>
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<a name="examples"/>
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<h3>Examples</h3>
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<p>
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The following example illustrates creation of a klacks <tt>source</tt>,
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use of the <tt>peek-next</tt> function to read individual events,
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and shows some of the most common event types.
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</p>
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<pre>* <b>(defparameter *source* (cxml:make-source "<example>text</example>"))</b>
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*SOURCE*
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* <b>(klacks:peek-next *source*)</b>
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:START-DOCUMENT
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* <b>(klacks:peek-next *source*)</b>
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:START-ELEMENT
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NIL ;namespace URI
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"example" ;local name
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"example" ;qualified name
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* <b>(klacks:peek-next *source*)</b>
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:CHARACTERS
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"text"
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* <b>(klacks:peek-next *source*)</b>
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:END-ELEMENT
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NIL
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"example"
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"example"
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* <b>(klacks:peek-next *source*)</b>
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:END-DOCUMENT
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* <b>(klacks:peek-next *source*)</b>
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NIL</pre>
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<p>
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In this example, <tt>find-element</tt> is used to skip over the
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uninteresting events until the opening <tt>child1</tt> tag is
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found. Then <tt>serialize-element</tt> is used to generate SAX
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events for the following element, including its children, and an
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xmls-compatible list structure is build from those
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events. <tt>find-element</tt> skips over whitespace,
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and <tt>find-event</tt> is used to parse up
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to <tt>:end-document</tt>, ensuring that the source has been
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closed.
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</p>
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<pre>* <b>(defparameter *source*
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(cxml:make-source "<example>
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<child1><p>foo</p></child1>
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<child2 bar='baz'/>
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</example>"))</b>
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*SOURCE*
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* <b>(klacks:find-element *source* "child1")</b>
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:START-ELEMENT
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NIL
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"child1"
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"child1"
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* <b>(klacks:serialize-element *source* (cxml-xmls:make-xmls-builder))</b>
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("child1" NIL ("p" NIL "foo"))
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* <b>(klacks:find-element *source*)</b>
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:START-ELEMENT
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NIL
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"child2"
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"child2"
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* <b>(klacks:serialize-element *source* (cxml-xmls:make-xmls-builder))</b>
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("child2" (("bar" "baz")))
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* <b>(klacks:find-event *source* :end-document)</b>
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:END-DOCUMENT
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NIL
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NIL
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NIL
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</pre>
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</documentation>
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