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Manual Reference Pages  -  POD::POM::VIEW::HTML::FILTER (3)

.ds Aq ’

NAME

Pod::POM::View::HTML::Filter - Use filters on sections of your pod documents

CONTENTS

SYNOPSIS

In your POD:



    Some coloured Perl code:

    =begin filter perl

        # now in full colour!
        $A++;

    =end filter

    =for filter=perl $A++; # this works too

    This should read C<bar bar bar>:

    =begin filter foo

    bar foo bar

    =end filter



In your code:



    my $view = Pod::POM::View::HTML::Filter->new;
    $view->add(
        foo => {
            code => sub { my $s = shift; $s =~ s/foo/bar/gm; $s },
            # other options are available
        }
    );

    my $pom = Pod::POM->parse_file( /my/pod/file );
    $pom->present($view);



DESCRIPTION

This module is a subclass of Pod::POM::View::HTML that support the filter extension. This can be used in =begin / =end and =for pod blocks.

Please note that since the view maintains an internal state, only an instance of the view can be used to present the POM object. Either use:



    my $view = Pod::POM::View::HTML::Filter->new;
    $pom->present( $view );



or



    $Pod::POM::DEFAULT_VIEW = Pod::POM::View::HTML::Filter->new;
    $pom->present;



Even though the module was specifically designed for use with Perl::Tidy, you can write your own filters quite easily (see Writing your own filters).

FILTERING POD?

The whole idea of this module is to take advantage of all the syntax colouring modules that exist (actually, Perl::Tidy was my first target) to produce colourful code examples in a POD document (after conversion to HTML).

Filters can be used in two different POD constructs:
=begin filter filter The data in the =begin filter ... =end filter region is passed to the filter and the result is output in place in the document.

The general form of a =begin filter block is as follow:



    =begin filter lang optionstring

    # some text to process with filter "lang"

    =end filter



The optionstring is trimed for whitespace and passed as a single string to the filter routine which must perform its own parsing.

=for filter=filter =for filters work just like =begin/C=<end> filters, except that a single paragraph is the target.

The general form of a =for filter block is as follow:



    =for filter=lang:option1:option2
    # some code in language lang



The option string sent to the filter lang would be option1 option2 (colons are replaced with spaces).

    Options

Some filters may accept options that alter their behaviour. Options are separated by whitespace, and appear after the name of the filter. For example, the following code will be rendered in colour and with line numbers:



    =begin filter perl -nnn

        $a = 123;
        $b = 3;
        print $a * $b;     # prints 369
        print $a x $b;     # prints 123123123

    =end filter



=for filters can also accept options, but the syntax is less clear. (This is because =for expects the formatname to match \S+.)

The syntax is the following:



    =for filter=html:nnn=1
         <center><img src="camel.png" />
         A camel</center>



In summary, options are separated by space for =begin blocks and by colons for =for paragraphs.

The options and their paramater depend on the filter, but they cannot contain the pipe (|) or colon (:) character, for obvious reasons.

    Pipes

Having filter to modify a block of text is usefule, but what’s more useful (and fun) than a filter? Answer: a stack of filters piped together!

Take the imaginary filters foo (which does a simple s/foo/bar/g) and bang (which does an even simpler tr/r/!/). The following block



    =begin filter foo|bar

    foo bar baz

    =end



will become ba! ba! baz.

And naturally,



    =for filter=bar|foo
    foo bar baz



will return bar ba! baz.

    A note on verbatim and text blocks

<B>Note:B> The fact that I mention verbatim and paragraph in this section is due to an old bug in Pod::POM, which parses the content of begin/end sections as the usual POD paragraph and verbatim blocks. This is a bug in Pod::POM, around which Pod::POM::View::HTML::Filter tries to work around.

As from version 0.06, Pod::POM::View::HTML::Filter gets to the original text contained in the =begin / =end block (it was easier than I thought, actually) and put that string throught all the filters.

If any filter in the stack is defined as verbatim, or if Pod::POM detect any block in the =begin / =end block as verbatim, then the output will be produced between <pre> and </pre> tags. Otherwise, no special tags will be added (his is left to the formatter).

    Examples

An example of the power of pipes can be seen in the following example. Take a bit of Perl code to colour:



    =begin filter perl

        "hot cross buns" =~ /cross/;
        print "Matched: <$`> $& <$>\n";    # Matched: <hot > cross < buns>
        print "Left:    <$`>\n";            # Left:    <hot >
        print "Match:   <$&>\n";            # Match:   <cross>
        print "Right:   <$>\n";            # Right:   < buns>

    =end



This will produce the following HTML code:



    <pre>    <span class="q">"hot cross buns"</span> =~ <span class="q">/cross/</span><span class="sc">;</span>
         <span class="k">print</span> <span class="q">"Matched: <$`> $& <$>\n"</span><span class="sc">;</span>    <span class="c"># Matched: <hot > cross < buns></span>
         <span class="k">print</span> <span class="q">"Left:    <$`>\n"</span><span class="sc">;</span>            <span class="c"># Left:    <hot ></span>
         <span class="k">print</span> <span class="q">"Match:   <$&>\n"</span><span class="sc">;</span>            <span class="c"># Match:   <cross></span>
         <span class="k">print</span> <span class="q">"Right:   <$>\n"</span><span class="sc">;</span>            <span class="c"># Right:   < buns></span></pre>



Now if you want to colour and number the HTML code produced, it’s as simple as tackling the html on top of the perl filter:



    =begin filter perl | html nnn=1

        "hot cross buns" =~ /cross/;
        print "Matched: <$`> $& <$>\n";    # Matched: <hot > cross < buns>
        print "Left:    <$`>\n";            # Left:    <hot >
        print "Match:   <$&>\n";            # Match:   <cross>
        print "Right:   <$>\n";            # Right:   < buns>

    =end



Which produces the rather unreadable piece of HTML:



    <pre><span class="h-lno">  1</span>     <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span><span class="h-ent">&quot;</span>hot cross buns<span class="h-ent">&quot;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span> =~ <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span>/cross/<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span><span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"sc</span>"<span class="h-ab">></span>;<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>
    <span class="h-lno">  2</span>     <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"k</span>"<span class="h-ab">></span>print<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span> <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span><span class="h-ent">&quot;</span>Matched: <span class="h-ent">&lt;</span>$`<span class="h-ent">&gt;</span> $<span class="h-ent">&amp;</span> <span class="h-ent">&lt;</span>$<span class="h-ent">&gt;</span>\n<span class="h-ent">&quot;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span><span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"sc</span>"<span class="h-ab">></span>;<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>    <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"c</span>"<span class="h-ab">></span># Matched: <span class="h-ent">&lt;</span>hot <span class="h-ent">&gt;</span> cross <span class="h-ent">&lt;</span> buns<span class="h-ent">&gt;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>
    <span class="h-lno">  3</span>     <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"k</span>"<span class="h-ab">></span>print<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span> <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span><span class="h-ent">&quot;</span>Left:    <span class="h-ent">&lt;</span>$`<span class="h-ent">&gt;</span>\n<span class="h-ent">&quot;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span><span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"sc</span>"<span class="h-ab">></span>;<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>            <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"c</span>"<span class="h-ab">></span># Left:    <span class="h-ent">&lt;</span>hot <span class="h-ent">&gt;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>
    <span class="h-lno">  4</span>     <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"k</span>"<span class="h-ab">></span>print<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span> <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span><span class="h-ent">&quot;</span>Match:   <span class="h-ent">&lt;</span>$<span class="h-ent">&amp;</span><span class="h-ent">&gt;</span>\n<span class="h-ent">&quot;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span><span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"sc</span>"<span class="h-ab">></span>;<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>            <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"c</span>"<span class="h-ab">></span># Match:   <span class="h-ent">&lt;</span>cross<span class="h-ent">&gt;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>
    <span class="h-lno">  5</span>     <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"k</span>"<span class="h-ab">></span>print<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span> <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"q</span>"<span class="h-ab">></span><span class="h-ent">&quot;</span>Right:   <span class="h-ent">&lt;</span>$<span class="h-ent">&gt;</span>\n<span class="h-ent">&quot;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span><span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"sc</span>"<span class="h-ab">></span>;<span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span>            <span class="h-ab"><</span><span class="h-tag">span</span> <span class="h-attr">class</span>=<span class="h-attv">"c</span>"<span class="h-ab">></span># Right:   <span class="h-ent">&lt;</span> buns<span class="h-ent">&gt;</span><span class="h-ab"></</span><span class="h-tag">span</span><span class="h-ab">></span></pre>



    Caveats

There were a few things to keep in mind when mixing verbatim and text paragraphs in a =begin block. These problems do not exist any more as from version 0.06.
Text paragraphs are not processed for POD escapes any more Because the =begin / =end block is now processed as a single string of text, the following block:



    =begin filter html

    B<foo>

    =end



will not be transformed into <bfoo</b> > before being passed to the filters, but will produce the expected:



    <pre>B<span class="h-ab"><</span><span class="h-tag">foo</span><span class="h-ab">></span></pre>



And the same text in a verbatim block



    =begin filter html
   
        B<foo>

    =end



will produce the same results.



    <pre>    B<span class="h-ab"><</span><span class="h-tag">foo</span><span class="h-ab">></span></pre>



Which looks quite the same, doesn’t it?

Separate paragraphs aren’t filtered separately any more As seen in A note on verbatim and text blocks, the filter now processes the begin block as a single string of text. So, if you have a filter that replace each * character with an auto-incremented number in square brackets, like this:



    $view->add(
        notes => {
            code => sub {
                my ( $text, $opt ) = @_;
                my $n = $opt =~ /(\d+)/ ? $1 : 1;
                $text =~ s/\*/[ . $n++ . ]/ge;
                $text;
              }
        }
    );



And you try to process the following block:



    =begin filter notes 2
   
    TIMTOWDI*, but your library should DWIM* when possible.
   
    You cant always claims that PICNIC*, can you?
   
    =end filter



You’ll get the expected result (contrary to previous versions):



    <p>TIMTOWDI[2], but your library should DWIM[3] when possible.
   
    You cant always claims that PICNIC[4], can you?</p>



The filter was really called only once, starting at 2, just like requested.

Future versions of Pod::POM::View::HTML::Filter may support init, begin and end callbacks to run filter initialisation and clean up code.

METHODS

    Public methods

The following methods are available:
add( lang => { options }, ... ) Add support for one or more languages. Options are passed in a hash reference.

The required code option is a reference to the filter routine. The filter must take a string as its only argument and return the formatted HTML string (coloured accordingly to the language grammar, hopefully).

Available options are:



    Name       Type       Content
    ----       ----       -------

    code       CODEREF    filter implementation

    verbatim   BOOLEAN    if true, force the full content of the
                          =begin/=end block to be passed verbatim
                          to the filter

    requires   ARRAYREF   list of required modules for this filter



Note that add() is both a class and an instance method.

When used as a class method, the new language is immediately available for all future and existing instances.

When used as an instance method, the new language is only available for the instance itself.

delete( $lang ) Remove the given language from the list of class or instance filters. The deleted filter is returned by this method.

delete() is both a class and an instance method, just like add().

filters() Return the list of languages supported.
know( $lang ) Return true if the view knows how to handle language $lang.

    Overloaded methods

The following Pod::POM::View::HTML methods are overridden in Pod::POM::View::HTML::Filter:
new() The overloaded constructor initialises some internal structures. This means that you’ll have to use a instance of the class as a view for your Pod::POM object. Therefore you must use new.



    $Pod::POM::DEFAULT_VIEW = Pod::POM::View::HTML::Filter; # WRONG
    $pom->present( Pod::POM::View::HTML::Filter );          # WRONG

    # this is CORRECT
    $Pod::POM::DEFAULT_VIEW = Pod::POM::View::HTML::Filter->new;

    # this is also CORRECT
    my $view = Pod::POM::View::HTML::Filter->new;
    $pom->present( $view );



The only option at this time is auto_unindent, which is enabled by default. This option remove leading indentation from all verbatim blocks within the begin blocks, and put it back after highlighting.

view_begin()
view_for() These are the methods that support the filter format.

FILTERS

    Built-in filters

Pod::POM::View::HTML::Filter is shipped with a few built-in filters.

The name for the filter is obtained by removing _filter from the names listed below (except for default):
default This filter is called when the required filter is not known by Pod::POM::View::HTML::Filter. It does nothing more than normal POD processing (POD escapes for text paragraphs and <pre> for verbatim paragraphs.

You can use the delete() method to remove a filter and therefore make it behave like default.

perl_tidy_filter This filter does Perl syntax highlighting with a lot of help from Perl::Tidy.

It accepts options to Perl::Tidy, such as -nnn to number lines of code. Check Perl::Tidy’s documentation for more information about those options.

perl_ppi_filter This filter does Perl syntax highlighting using PPI::HTML, which is itself based on the incredible PPI.

It accepts the same options as PPI::HTML, which at this time solely consist of line_numbers to, as one may guess, add line numbers to the output.

html_filter This filter does HTML syntax highlighting with the help of Syntax::Highlight::HTML.

The filter supports Syntax::Highlight::HTML options:



    =begin filter html nnn=1

    <p>The lines of the HTML code will be numbered.</p>
    <p>This is line 2.</p>

    =end filter



See Syntax::Highlight::HTML for the list of supported options.

shell_filter This filter does shell script syntax highlighting with the help of Syntax::Highlight::Shell.

The filter supports Syntax::Highlight::Shell options:



    =begin filter shell nnn=1

        #!/bin/sh
        echo "This is a foo test" | sed -e s/foo/shell/

    =end filter



See Syntax::Highlight::Shell for the list of supported options.

kate_filter This filter support syntax highlighting for numerous languages with the help of Syntax::Highlight::Engine::Kate.

The filter supports Syntax::Highlight::Engine::Kate languages as options:



     =begin filter kate Diff
    
         Index: lib/Pod/POM/View/HTML/Filter.pm
         ===================================================================
         --- lib/Pod/POM/View/HTML/Filter.pm     (revision 99)
         +++ lib/Pod/POM/View/HTML/Filter.pm     (working copy)
         @@ -27,6 +27,11 @@
                  requires => [qw( Syntax::Highlight::Shell )],
                  verbatim => 1,
              },
         +    kate => {
         +        code     => \&kate_filter,
         +        requires => [qw( Syntax::Highlight::Engine::Kate )],
         +        verbatim => 1,
         +    },
          );
         
          my $HTML_PROTECT = 0;
    
     =end filter



Check the Syntax::Highlight::Engine::Kate documentation for the full list of supported languages. Please note that some of them aren’t well supported yet (by Syntax::Highlight::Engine::Kate), so the output may not be what you expect.

Here is a list of languages we have successfully tested with Syntax::Highlight::Engine::Kate version 0.02: C, Diff, Fortran, JavaScript, LDIF, SQL.

wiki_filter This filter converts the wiki format parsed by Text::WikiFormat in HTML.

The supported options are: prefix, extended, implicit_links, absolute_links. The option and value are separated by a = character, as in the example below:



    =begin filter wiki extended=1

    [link|title]

    =end



wikimedia_filter This filter converts the wiki format parsed by Text::MediawikiFormat in HTML.

The supported options are: prefix, extended, implicit_links, absolute_links and process_html. The option and value are separated by a = character.

    Writing your own filters

Write a filter is quite easy: a filter is a subroutine that takes two arguments (text to parse and option string) and returns the filtered string.

The filter is added to Pod::POM::View::HTML::Filter’s internal filter list with the add() method:



    $view->add(
        foo => {
            code     => \&foo_filter,
            requires => [],
        }
    );



When presenting the following piece of pod,



    =begin filter foo bar baz

    Some text to filter.

    =end filter



the foo_filter() routine will be called with two arguments, like this:



    foo_filter( "Some text to filter.", "bar baz" );



If you have a complex set of options, your routine will have to parse the option string by itself.

Please note that in a =for construct, whitespace in the option string must be replaced with colons:



    =for filter=foo:bar:baz Some text to filter.



The foo_filter() routine will be called with the same two arguments as before.

BUILT-IN FILTERS CSS STYLES

Each filter uses its own CSS classes, so that one can define their favourite colours in a custom CSS file.

CWperl filter

Perl::Tidy’s HTML code looks like:



    <span class="i">$A</span>++<span class="sc">;</span>



Here are the classes used by Perl::Tidy:



    n        numeric
    p        paren
    q        quote
    s        structure
    c        comment
    v        v-string
    cm       comma
    w        bareword
    co       colon
    pu       punctuation
    i        identifier
    j        label
    h        here-doc-target
    hh       here-doc-text
    k        keyword
    sc       semicolon
    m        subroutine
    pd       pod-text



CWppi filter

PPI::HTML uses the following CSS classes:



    comment           
    double            
    heredoc_content   
    interpolate       
    keyword            for language keywords (my, use
    line_number       
    number            
    operator           for language operators
    pragma             for pragmatas (strict, warnings)
    single            
    structure          for syntaxic symbols
    substitute        
    symbol            
    word               for module, function and method names
    words             
    match



CWhtml filter

Syntax::Highlight::HTML makes use of the following classes:



    h-decl   declaration    # declaration <!DOCTYPE ...>
    h-pi     process        # process instruction <?xml ...?>
    h-com    comment        # comment <!-- ... -->
    h-ab     angle_bracket  # the characters < and > as tag delimiters
    h-tag    tag_name       # the tag name of an element
    h-attr   attr_name      # the attribute name
    h-attv   attr_value     # the attribute value
    h-ent    entity         # any entities: é «



CWshell filter

Syntax::Highlight::Shell makes use of the following classes:



    s-key                   # shell keywords (like if, for, while, do...)
    s-blt                   # the builtins commands
    s-cmd                   # the external commands
    s-arg                   # the command arguments
    s-mta                   # shell metacharacters (|, >, \, &)
    s-quo                   # the single () and double (") quotes
    s-var                   # expanded variables: $VARIABLE
    s-avr                   # assigned variables: VARIABLE=value
    s-val                   # shell values (inside quotes)
    s-cmt                   # shell comments



CWkate filter

Output formatted with Syntax::Highlight::Engine::Kate makes use of the following classes:



    k-alert                 # Alert
    k-basen                 # BaseN
    k-bstring               # BString
    k-char                  # Char
    k-comment               # Comment
    k-datatype              # DataType
    k-decval                # DecVal
    k-error                 # Error
    k-float                 # Float
    k-function              # Function
    k-istring               # IString
    k-keyword               # Keyword
    k-normal                # Normal
    k-operator              # Operator
    k-others                # Others
    k-regionmarker          # RegionMarker
    k-reserved              # Reserved
    k-string                # String
    k-variable              # Variable
    k-warning               # Warning



HISTORY

The goal behind this module was to produce nice looking HTML pages from the articles the French Perl Mongers are writing for the French magazine GNU/Linux Magazine France (<http://www.linuxmag-france.org/>).

The resulting web pages can be seen at <http://articles.mongueurs.net/magazines/>.

AUTHOR

Philippe BooK Bruhat, <book@cpan.org>

THANKS

Many thanks to Se\k:'Aperghis-Tramoni (Maddingue), who helped debugging the module and wrote Syntax::Highlight::HTML and Syntax::Highlight::Shell so that I could ship PPVHF with more than one filter. He also pointed me to Syntax::Highlight::Engine::Kate, which led me to clean up PPVHF before adding support for SHEK.

Perl code examples where borrowed in Amelia, aka Programming Perl, 3rd edition.

TODO

There are a few other syntax highlighting modules on CPAN, which I should try to add support for in Pod::POM::View::HTML::Filter:
o Syntax::Highlight::Universal
o Syntax::Highlight::Mason
o Syntax::Highlight::Perl (seems old)
o Syntax::Highlight::Perl::Improved

BUGS

Please report any bugs or feature requests to bug-pod-pom-view-html-filter@rt.cpan.org, or through the web interface at <http://rt.cpan.org>. I will be notified, and then you’ll automatically be notified of progress on your bug as I make changes.

COPYRIGHT & LICENSE

Copyright 2004 Philippe BooK Bruhat, All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

POD ERRORS

Hey! <B>The above document had some coding errors, which are explained below:B>
Around line 1164: Non-ASCII character seen before =encoding in ’Se\k:'Assuming ISO8859-1
Search for    or go to Top of page |  Section 3 |  Main Index


perl v5.20.3 POD::POM::VIEW::HTML::FILTER (3) 2007-01-28

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