/ 
XML-XPathScript-1.01
River stage one • 1 direct dependent • 1 total dependent
/ XML::XPathScript

NAME

XML::XPathScript - a Perl framework for XML stylesheets

SYNOPSIS

use XML::XPathScript;
my $xps = XML::XPathScript->new(xml => $xml, stylesheet => $stylesheet);

# The short way:

$xps->process();

# The long way (caching the compiled stylesheet for reuse and
# outputting to multiple files):

my $compiled = XML::XPathScript->new(stylesheetfile => $filename)
       ->compile('$r');

foreach my $xml (@xmlfiles) {
   use IO::File;

   my $currentIO=new IO::File(shift @outputfiles);

   XML::XPathScript->new(xml => $xml, compiledstylesheet=>$compiled)
       ->process(sub {$currentIO->print(shift)});
};

# Making extra variables available to the stylesheet dialect:

my $handler=$xps->compile('$r');

&$handler($xmltree,&Apache::print,Apache->request());

DESCRIPTION

XPathScript is a stylesheet language similar in many ways to XSLT (in concept, not in appearance), for transforming XML from one format to another (possibly HTML, but XPathScript also shines for non-XML-like output).

Like XSLT, XPathScript offers a dialect to mix verbatim portions of documents and code. Also like XSLT, it leverages the powerful ``templates/apply-templates'' and ``cascading stylesheets'' design patterns, that greatly simplify the design of stylesheets for programmers. The availability of the XPath query language inside stylesheets promotes the use of a purely document-dependent, side-effect-free coding style. But unlike XSLT which uses its own dedicated control language with an XML-compliant syntax, XPathScript uses Perl which is terse and highly extendable.

The result of the merge is an extremely powerful tool for rendering complex XML documents into other formats. Stylesheets written in XPathScript are very easy to create, extend and reuse, even if they manage hundreds of different XML tags.

STYLESHEET WRITER DOCUMENTATION

If you are interested to write stylesheets, refers to the XML::XPathScript::Stylesheet manpage. You might also want to take a peek at the manpage of xpathscript, a program bundled with this module to perform XPathScript transformations via the command line.

STYLESHEET UTILITY METHODS

Those methods are meants to be used from within a stylesheet.

current()

This class method (e.g. XML::XPathScript->current()) returns the stylesheet object currently being applied. This can be called from anywhere within the stylesheet, except a BEGIN or END block or similar. Beware though that using the return value for altering (as opposed to reading) stuff from anywhere except the stylesheet's top level is unwise.

interpolation
$XML::XPathScript::current->interpolation()
$XML::XPathScript::current->interpolation( $boolean )

Gets (first call form) or sets (second form) the XPath interpolation boolean flag. If true, values set in pre and post may contain expressions within curly braces, that will be interpreted as XPath expressions and substituted in place.

For example, when interpolation is on, the following code

$template->set( link => { pre  => '<a href="{@url}">',
                          post => '</a>'               } );

is enough for rendering a <link> element as an HTML hyperlink. The interpolation-less version is slightly more complex as it requires a testcode:

   sub link_testcode  {
      my ($currentnode, $t) = @_;
      my $url = findvalue('@url', $currentnode);
      $t->set({ pre  => "<a href='$url'>",
                post => "</a>"             });
	  return DO_SELF_AND_KIDS();
   };

Interpolation is on by default.

interpolation_regex
$regex = $XML::XPathScript::curent->interpolation_regex()
$XML::XPathScript::curent->interpolation_regex( $regex )

Gets or sets the regex to use for interpolation. The value to be interpolated must be capture by $1.

By default, the interpolation regex is qr/{(.*?)}/.

Example:

$XML::XPathScript::current->interpolation_regex( qr#\|(.*?)\|# );

$template->set( bird => { pre => '|@name| |@gender| |@type|' } );
binmode()

Declares that the stylesheet output is not in UTF-8, but instead in an (unspecified) character encoding embedded in the stylesheet source that neither Perl nor XPathScript should have any business dealing with. Calling XML::XPathScript->current()->binmode() is an irreversible operation with the consequences outlined in "The Unicode mess".

TECHNICAL DOCUMENTATION

The rest of this POD documentation is not useful to programmers who just want to write stylesheets; it is of use only to people wanting to call existing stylesheets or more generally embed the XPathScript engine into some wider framework.

XML::XPathScript is an object-oriented class with the following features:

  • an embedded Perl dialect that allows the merging of the stylesheet code with snippets of the output document. Don't be afraid, this is exactly the same kind of stuff as in Text::Template, HTML::Mason or other similar packages: instead of having text inside Perl (that one print()s), we have Perl inside text, with a special escaping form that a preprocessor interprets and extracts. For XPathScript, this preprocessor is embodied by the xpathscript shell tool (see "xpathscript Invocation") and also available through this package's API;

  • a templating engine, that does the apply-templates loop, starting from the top XML node and applying templates to it and its subnodes as directed by the stylesheet.

When run, the stylesheet is expected to fill in the template object $template, which is a lexically-scoped variable made available to it at preprocess time.

METHODS

new(key1=>value1,key2=>value2,...)

Creates a new XPathScript translator. The recognized named arguments are

xml => $xml

$xml is a scalar containing XML text, or a reference to a filehandle from which XML input is available, or an XML::XPath or XML::libXML object.

An XML::XPathscript object without an xml argument to the constructor is only able to compile stylesheets (see "SYNOPSIS").

stylesheet => $stylesheet

$stylesheet is a scalar containing the stylesheet text, or a reference to a filehandle from which the stylesheet text is available. The stylesheet text may contain unresolved <!--#include --> constructs, which will be resolved relative to ".".

stylesheetfile => $filename

Same as stylesheet but let XML::XPathScript do the loading itself. Using this form, relative <!--#include -->s in the stylesheet file will be honored with respect to the dirname of $filename instead of "."; this provides SGML-style behaviour for inclusion (it does not depend on the current directory), which is usually what you want.

compiledstylesheet => $function

Re-uses a previous return value of compile() (see "SYNOPSIS" and "compile"), typically to apply the same stylesheet to several XML documents in a row.

interpolation_regex => $regex

Sets the interpolation regex to be $regex. Whatever is captured in $1 will be used as the xpath expression. Defaults to qr/{(.*?)}/.

process()
process($printer)
process($printer,@varvalues)

Processes the document and stylesheet set at construction time, and prints the result to STDOUT by default. If $printer is set, it must be either a reference to a filehandle open for output, or a reference to a string, or a reference to a subroutine which does the output, as in

my $buffer="";
$xps->process(sub {$buffer.=shift;});

or

$xps->process(sub {print ANOTHERFD (shift);});

(not that the latter would be any good, since $xps-process(\*ANOTHERFD) > would do exactly the same, only faster)

If the stylesheet was compile()d with extra varnames, then the calling code should call process() with a corresponding number of @varvalues. The corresponding lexical variables will be set accordingly, so that the stylesheet code can get at them (looking at "SYNOPSIS") is the easiest way of getting the meaning of this sentence).

extract($stylesheet)
extract($stylesheet,$filename)
extract($stylesheet,@includestack) # from include_file() only

The embedded dialect parser. Given $stylesheet, which is either a filehandle reference or a string, returns a string that holds all the code in real Perl. Unquoted text and <%= stuff %> constructs in the stylesheet dialect are converted into invocations of XML::XPathScript->current()->print(), while <% stuff %> constructs are transcripted verbatim.

<!-- #include --> constructs are expanded by passing their filename argument to "include_file" along with @includestack (if any) like this:

$self->include_file($includefilename,@includestack);

@includestack is not interpreted by extract() (except for the first entry, to create line tags for the debugger). It is only a bandaid for include_file() to pass the inclusion stack to itself across the mutual recursion existing between the two methods (see "include_file"). If extract() is invoked from outside include_file(), the last invocation form should not be used.

This method does a purely syntactic job. No special framework declaration is prepended for isolating the code in its own package, defining $t or the like ("compile" does that). It may be overriden in subclasses to provide different escape forms in the stylesheet dialect.

$string = read_stylesheet( $stylesheet )

Read the $stylesheet (which can be a filehandler or a string). Used by extract and exists such that it can be overloaded in Apache::AxKit::Language::YPathScript.

include_file($filename)
include_file($filename,@includestack)

Resolves a <!--#include file="foo" --> directive on behalf of extract(), that is, returns the script contents of $filename. The return value must be de-embedded too, which means that extract() has to be called recursively to expand the contents of $filename (which may contain more <!--#include -->s etc.)

$filename has to be slash-separated, whatever OS it is you are using (this is the XML way of things). If $filename is relative (i.e. does not begin with "/" or "./"), it is resolved according to the basename of the stylesheet that includes it (that is, $includestack[0], see below) or "." if we are in the topmost stylesheet. Filenames beginning with "./" are considered absolute; this gives stylesheet writers a way to specify that they really really want a stylesheet that lies in the system's current working directory.

@includestack is the include stack currently in use, made up of all values of $filename through the stack, lastly added (innermost) entries first. The toplevel stylesheet is not in @includestack (that is, the outermost call does not specify an @includestack).

This method may be overridden in subclasses to provide support for alternate namespaces (e.g. ``axkit://'' URIs).

compile()
compile(varname1, varname2,...)

Compiles the stylesheet set at new() time and returns an anonymous CODE reference.

varname1, varname2, etc. are extraneous arguments that will be made available to the stylesheet dialect as lexically scoped variables. "SYNOPSIS" shows a way to use this feature to pass the Apache handler to AxKit XPathScript stylesheets, which explains this feature better than a lengthy paragraph would do.

The return value is an opaque token that encapsulates a compiled stylesheet. It should not be used, except as the compiledstylesheet argument to new() to initiate new objects and amortize the compilation time. Subclasses may alter the type of the return value, but will need to overload process() accordingly of course.

The compile() method is idempotent. Subsequent calls to it will return the very same token, and calls to it when a compiledstylesheet argument was set at new() time will return said argument.

print($text)

Outputs a chunk of text on behalf of the stylesheet. The default implementation is to use the second argument to "process". Overloading this method in a subclass provides yet another method to redirect output.

FUNCTIONS

gen_package_name()

Generates a fresh package name in which we would compile a new stylesheet. Never returns twice the same name.

$nodeset = $xps->document( $uri )

Reads XML given in $uri, parses it and returns it in a nodeset.

AUTHORS

Current maintainers: Yanick Champoux <yanick@cpan.org> and Dominique Quatravaux <dom@idealx.com>

Created by Matt Sergeant <matt@sergeant.org>

LICENSE

This is free software. You may distribute it under the same terms as Perl itself.

SEE ALSO

XML::XPathScript::Stylesheet, XML::XPathScript::Processor, XML::XPathScript::Template, XML::XPathScript::Template::Tag

Guide of the original Axkit XPathScript: http://axkit.org/wiki/view/AxKit/XPathScriptGuide

XPath documentation from W3C: http://www.w3.org/TR/xpath

Unicode character table: http://www.unicode.org/charts/charindex.html