NAME

Pod::Simple::Subclassing -- write a formatter as a Pod::Simple subclass

SYNOPSIS

package Pod::SomeFormatter;
use Pod::Simple;
@ISA = qw(Pod::Simple);
$VERSION = '1.01';
use strict;

sub _handle_element_start {
  my($parser, $element_name, $attr_hash_r) = @_;
  ...
}

sub _handle_element_end {
  my($parser, $element_name) = @_;
  ...
}

sub _handle_text {
  my($parser, $text) = @_;
  ...
}
1;

DESCRIPTION

This document is about using Pod::Simple to write a Pod processor, generally a Pod formatter. If you just want to know about using an existing Pod formatter, instead see its documentation and see also the docs in Pod::Simple.

The zeroeth step in writing a Pod formatter is to make sure that there isn't already a decent one in CPAN. See http://search.cpan.org/, and run a search on the name of the format you want to render to. Also consider joining the Pod People list http://lists.perl.org/showlist.cgi?name=pod-people and asking whether anyone has a formatter for that format -- maybe someone cobbled one together but just hasn't released it.

The first step in writing a Pod processor is to read perlpodspec, which contains notes information on writing a Pod parser (which has been largely taken care of by Pod::Simple), but also a lot of requirements and recommendations for writing a formatter.

The second step is to actually learn the format you're planning to format to -- or at least as much as you need to know to represent Pod, which probably isn't much.

The third step is to pick which of Pod::Simple's interfaces you want to use -- the basic interface via Pod::Simple or Pod::Simple::Methody is event-based, sort of like HTML::Parser's interface, or sort of like XML::Parser's "Handlers" interface), but Pod::Simple::PullParser provides a token-stream interface, sort of like HTML::TokeParser's interface; Pod::Simple::SimpleTree provides a simple tree interface, rather like XML::Parser's "Tree" interface. Users familiar with XML-handling will find one of these styles relatively familiar; but if you would be even more at home with XML, there are classes that produce an XML representation of the Pod stream, notably Pod::Simple::XMLOutStream; you can feed the output of such a class to whatever XML parsing system you are most at home with.

The last step is to write your code based on how the events (or tokens, or tree-nodes, or the XML, or however you're parsing) will map to constructs in the output format. Also sure to consider how to escape text nodes containing arbitrary text, and also what to do with text nodes that represent preformatted text (from verbatim sections).

Events

TODO intro... mention that events are supplied for implicits, like for missing closures.

$parser->_handle_element_start( element_name, attr_hashref )
$parser->_handle_element_end( element_name )
$parser->_handle_text( text_string )

TODO describe

events with an element_name of Document: TODO...
events with an element_name of Para: TODO...
events with an element_name of B, C, F, or I.: TODO...
events with an element_name of S: TODO...
events with an element_name of X: TODO...
events with an element_name of L: TODO...
events with an element_name of E or Z: TODO...
events with an element_name of Verbatim: TODO...
events with an element_name of head1 .. head4: TODO...
events with an element_name of over-bullet: TODO...
events with an element_name of over-number: TODO...
events with an element_name of over-text: TODO...
events with an element_name of over-block: TODO...
events with an element_name of item-bullet: TODO...
events with an element_name of item-number: TODO...
events with an element_name of item-text: TODO...
events with an element_name of for: TODO...
events with an element_name of Data: TODO...

More Pod::Simple Methods

Pod::Simple provides a lot of methods that aren't generally interesting to the end user of an existing Pod formatter, but some of which you might find useful in writing a Pod formatter. They are listed below. The first several methods (the accept_* methods) are for declaring the capabilites of your parser, notably what =for targetname sections it's interested in, what extra N<...> codes it accepts beyond the ones described in the perlpod.

$parser->accept_targets( SOMEVALUE )

As the parser sees sections like:

=for html  <img src="fig1.jpg">

=begin html

  <img src="fig1.jpg">

=end html

...the parser will ignore these sections unless your subclass has specified that it wants to see sections targetted to "html" (or whatever the formatter name is).

If you want to process all sections, even if they're not targetted for you, call this before you start parsing:

$parser->accept_targets('*');

$parser->accept_targets_as_text( SOMEVALUE )

This is like accept_targets, except that it specifies also that the content of sections for this target should be treated as Pod text even if the target name in "=for targetname" doesn't start with a ":".

At time of writing, I don't think you'll need to use this.

$parser->accept_codes( Codename, Codename... )

This tells the parser that you accept additional formatting codes, beyond just the standard ones (I B C L F S X, plus the two weird ones you don't actually see in the parse tree, Z and E). For example, to also accept codes "N", "R", and "W":

$parser->accept_codes( qw( N R W ) );

TODO: document how this interacts with =extend, and long element names

$parser->accept_directive_as_data( directive_name )

$parser->accept_directive_as_verbatim( directive_name )

$parser->accept_directive_as_processed( directive_name )

In the unlikely situation that you need to tell the parser that you will accept additional directives ("=foo" things), you need to first set the parset to treat its content as data (i.e., not really processed at all), or as verbatim (mostly just expanding tabs), or as processed text (parsing formatting codes like B<...>).

For example, to accept a new directive "=method", you'd presumably use:

$parser->accept_directive_as_processed("method");

so that you could have Pod lines like:

=method I<$whatever> thing B<um>

Making up your own directives breaks compatibility with other Pod formatters, in a way that using "=for target ..." lines doesn't; however, you may find this useful if you're making a Pod superset format where you don't need to worry about compatibility.

$parser->nbsp_for_S(VALUE);

Setting this attribute to a true value (and by default it is false) will take "S<...>" sequences to sequences of words separated by \xA0 (non-breaking space) characters. For example, it will take this:

I like S<Dutch apple pie>, don't you?

and treat it as if it were:

I like DutchE<nbsp>appleE<nbsp>pie, don't you?

This is handy for output formats that don't have anything quite like an "S<...>" code, but which do have a code for non-breaking space.

There is currently no method for going the other way; but I can probably provide one upon request.

$parser->version_report()

This returns a string reporting the $VERSION value from your module (and its classname) as well as the $VERSION value of Pod::Simple. Note that perlpodspec requires output formats to (wherever possible) note this detail in a comment in the output format. For example, for some kind of SGML output format:

print OUT "<!-- \n", $parser->version_report, "\n -->";

$parser->pod_para_count()

This returns the count of Pod paragraphs seen so far.

$parser->line_count()

This is the current line number being parsed. But you might find the "line_number" event attribute more accurate, when it is present.

$parser->nix_X_codes( SOMEVALUE )

This attribute, when set to a true value (and it is false by default) ignores any "X<...>" sequences in the document being parsed. Many formats don't actually use the content of these codes, so have no reason to process them.

$parser->merge_text( SOMEVALUE )

This attribute, when set to a true value (and it is false by default) makes sure that only one event (or token, or node) will be created for any single contiguous sequence of text. For example, consider this somewhat contrived example:

I just LOVE Z<>hotE<32>apple pie!

When that is parsed and events are about to be called on it, it may actually seem to be four different text events, one right after another: one event for "I just LOVE ", one for "hot", one for " ", and one for "apple pie!". But if you have merge_text on, then you're guaranteed that it will be fired as one text event: "I just LOVE hot apple pie!".

$parser->code_handler( CODE_REF )

This specifies code that should be called when a code line is seen (i.e., a line outside of the Pod). Normally this is undef, meaning that no code should be called. If you provide a routine, it should start out like this:

sub get_code_line {  # or whatever you'll call it
  my($line, $line_number, $parser) = @_;
  ...
}

Note, however, that sometimes the Pod events aren't processed in exactly the same order as the code lines are -- i.e., if you have a file with Pod, then code, then more Pod, sometimes the code will be processed (via whatever you have code_handler call) before the all of the preceding Pod has been processed.

$parser->cut_handler( CODE_REF )

This is just like the code_handler attribute, except that it's for "=cut" lines, not code lines. The same caveats apply. "=cut" lines are unlikely to be interesting, but this is included for completeness.

$parser->whine( linenumber, complaint string )

This notes a problem in the Pod, which will be reported to in the "Pod Errors" section of the document and/or send to STDERR, depending on the values of the attributes no_whining, no_errata_section, and complain_stderr.

$parser->scream( linenumber, complaint string )

This notes an error like whine does, except that it is not suppressable with no_whining. This should be used only for very serious errors.

$parser->source_dead(1)

This aborts parsing of the current document, by switching on the flag that indicates that EOF has been seen. In particularly drastic cases, you might want to do this. It's rather nicer than just calling die!

$parser->hide_line_numbers( SOMEVALUE )

Some subclasses that indescriminately dump event attributes (well, except for ones beginning with "~") can use this object attribute for refraining to dump the "start_line" attribute.

COPYRIGHT AND DISCLAIMERS

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

This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.

AUTHOR

Sean M. Burke sburke@cpan.org

To install Pod::Simple, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Pod::Simple

CPAN shell

perl -MCPAN -e shell
install Pod::Simple

For more information on module installation, please visit the detailed CPAN module installation guide.

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