1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
<?xml version="1.0" standalone="no"?>
<!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
<!--
* Copyright 2001-2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
-->
<!-- $Id: xsl_choose_design.xml 337884 2004-02-17 19:29:35Z minchau $ -->
<s1 title="<xsl:choose> / <xsl:when> / <xsl:otherwise>">
<s2 title="Contents">
<ul>
<li><link anchor="functionality">Functionality</link></li>
<li><link anchor="implementation">Implementation</link></li>
</ul>
</s2>
<anchor name="functionality"/>
<s2 title="Functionality">
<p>The <code><xsl:choose></code> element is used to determine one
course of action based on a series of tests. Each test is done inside an
<code><xsl:when></code> element. If a test succeeds, the body of the
<code><xsl:when></code> element is executed. If no tests fail then
a <code><xsl:otherwise></code> element can be used to specify a
default action:</p>
<source>
<xsl:choose>
<xsl:when test="element-available('some-extension')">
...
</xsl:when>
<xsl:when test="function-availabe('saxon:nodeset')">
...
</xsl:when>
<xsl:otherwise>
...
</xsl:otherwise>
</xsl:choose></source>
</s2>
<anchor name="implementation"/>
<s2 title="Implementation">
<p>The <code>Choose</code> class places all <code>When</code> child-nodes
in a vector. The <code>Choose</code> class translates the "test"-attribute
of all <code>When</code> nodes (in strict order) and chains them together
in an if-else style. The expression that holds each test contains a true-
and a false-list. These lists are vectors of branch targets that should be
used if the test succeeds or fails, respectively. The first test's
false-list is pointed to the start of the next test (ie. if the first test
fails, then we run the next test). The last test's false-list points directly
to the code for the body of the <code><xsl:otherwise></code> element.
</p>
<p>Just as with the <code><xsl:if></code>-element, special care is
taken for the <code>element-available()</code> and
<code>function-available()</code> functions. These functions are evaluated at
compile-time (this can be done since all parameters for these functions are
literals) and the body of a <code><xsl:when></code> element is not
compiled if we know that it will never be needed at runtime.</p>
</s2>
</s1>
|
