EXSLT Script Extension

This module implements the <script> extension element decribed in exslt.org with a few minor differences.

<script>

xmlns:func="http://exslt.org/functions"

<func:script implements-prefix=ncname
             language=qname
             src=uri-reference
             archive=uri-reference/>

The top-level <func:script> element provides an implementation of extension functions in the specified namespace.

The function implementations may be provided as a separate resource or as element content.

implements-prefix

The implements-prefix attribute is an ncname expanded to a URI using the namespace declarations in scope for the script element. This URI is the namespace URI identifying the local name of the XPath extension functions being implemented.

language

A qname identifying programming language used for the extension. If the language value is not supported, the script element is ignored.

src

Optional URI for the resource containing the extension functions. A relative URI is resolved relative to the base URI of the script element.

If omitted the script is read from the element content instead. Element content should be protected by enclosing it in a CDATA section or by using XML entities where these conflict with symbols used in the programming language. An example is given below.

archive

Not implemented, ignored.

Lua

Currently the only supported script language is Lua 5.3. The language property should be specified as Lua.

Lua functions are exported when the script is compiled, by returning a table of functions where the key is a string naming the XPath function.

For example the following will create the XPath functions my:func1(), my:func2() and my:func3(). Func3() illustrates that it is possible to create XPath functions with a closure.

<xsl:stylesheet ...
                xmlns:func="http://exslt.org/functions"
                xmlns:my="http://example.org/lua"
                extension-element-prefixes="func">

<func:script implements-prefix="my" language="Lua" src="functions.lua"/>

...

</xsl:stylesheet>

-- content of functions.lua

exports = {}

function exports.func1(...)
    return ""
end

function exports.func2(...)
    return ""
end

function func3_factory()
    local closure_var = ""

    return function(...)
        -- do some work involving the closure variables
        return closure_var
    end
end

exports.func3 = func3_factory()

return exports

If the above example were implemented as script element content it would read as follows. In this case to avoid issues with CDATA quoting, multi-line comments and strings should be written as --[=[ ... ]=] and [=[ ... ]=] respectively.

<xsl:stylesheet ...
                xmlns:func="http://exslt.org/functions"
                xmlns:my="http://example.org/lua"
                extension-element-prefixes="func">

<func:script implements-prefix="my" language="Lua">
<![CDATA[
exports = {}

function exports.func1(...)
    return ""
end

function exports.func2(...)
    return ""
end

function func3_factory()
    local closure_var = ""

    return function(...)
        -- do some work involving the closure variables
        return closure_var
    end
end

exports.func3 = func3_factory()

return exports
]]>
</func:script>

...

</xsl:stylesheet>