parser.pm

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#############################################################################
# Pod/Parser.pm -- package which defines a base class for parsing POD docs.
#
# Copyright (C) 1996-2000 by Bradford Appleton. All rights reserved.
# This file is part of "PodParser". PodParser is free software;
# you can redistribute it and/or modify it under the same terms
# as Perl itself.
#############################################################################

package Pod::Parser;

use vars qw($VERSION);
$VERSION = 1.12;  ## Current version of this package
require  5.005;    ## requires this Perl version or later

#############################################################################

=head1 NAME

Pod::Parser - base class for creating POD filters and translators

=head1 SYNOPSIS

    use Pod::Parser;

    package MyParser;
    @ISA = qw(Pod::Parser);

    sub command { 
        my ($parser, $command, $paragraph, $line_num) = @_;
        ## Interpret the command and its text; sample actions might be:
        if ($command eq 'head1') { ... }
        elsif ($command eq 'head2') { ... }
        ## ... other commands and their actions
        my $out_fh = $parser->output_handle();
        my $expansion = $parser->interpolate($paragraph, $line_num);
        print $out_fh $expansion;
    }

    sub verbatim { 
        my ($parser, $paragraph, $line_num) = @_;
        ## Format verbatim paragraph; sample actions might be:
        my $out_fh = $parser->output_handle();
        print $out_fh $paragraph;
    }

    sub textblock { 
        my ($parser, $paragraph, $line_num) = @_;
        ## Translate/Format this block of text; sample actions might be:
        my $out_fh = $parser->output_handle();
        my $expansion = $parser->interpolate($paragraph, $line_num);
        print $out_fh $expansion;
    }

    sub interior_sequence { 
        my ($parser, $seq_command, $seq_argument) = @_;
        ## Expand an interior sequence; sample actions might be:
        return "*$seq_argument*"     if ($seq_command eq 'B');
        return "`$seq_argument'"     if ($seq_command eq 'C');
        return "_${seq_argument}_'"  if ($seq_command eq 'I');
        ## ... other sequence commands and their resulting text
    }

    package main;

    ## Create a parser object and have it parse file whose name was
    ## given on the command-line (use STDIN if no files were given).
    $parser = new MyParser();
    $parser->parse_from_filehandle(\*STDIN)  if (@ARGV == 0);
    for (@ARGV) { $parser->parse_from_file($_); }

=head1 REQUIRES

perl5.005, Pod::InputObjects, Exporter, Symbol, Carp

=head1 EXPORTS

Nothing.

=head1 DESCRIPTION

B<Pod::Parser> is a base class for creating POD filters and translators.
It handles most of the effort involved with parsing the POD sections
from an input stream, leaving subclasses free to be concerned only with
performing the actual translation of text.

B<Pod::Parser> parses PODs, and makes method calls to handle the various
components of the POD. Subclasses of B<Pod::Parser> override these methods
to translate the POD into whatever output format they desire.

=head1 QUICK OVERVIEW

To create a POD filter for translating POD documentation into some other
format, you create a subclass of B<Pod::Parser> which typically overrides
just the base class implementation for the following methods:

=over 2

=item *

B<command()>

=item *

B<verbatim()>

=item *

B<textblock()>

=item *

B<interior_sequence()>

=back

You may also want to override the B<begin_input()> and B<end_input()>
methods for your subclass (to perform any needed per-file and/or
per-document initialization or cleanup).

If you need to perform any preprocesssing of input before it is parsed
you may want to override one or more of B<preprocess_line()> and/or
B<preprocess_paragraph()>.

Sometimes it may be necessary to make more than one pass over the input
files. If this is the case you have several options. You can make the
first pass using B<Pod::Parser> and override your methods to store the
intermediate results in memory somewhere for the B<end_pod()> method to
process. You could use B<Pod::Parser> for several passes with an
appropriate state variable to control the operation for each pass. If
your input source can't be reset to start at the beginning, you can
store it in some other structure as a string or an array and have that
structure implement a B<getline()> method (which is all that
B<parse_from_filehandle()> uses to read input).

Feel free to add any member data fields you need to keep track of things
like current font, indentation, horizontal or vertical position, or
whatever else you like. Be sure to read L<"PRIVATE METHODS AND DATA">
to avoid name collisions.

For the most part, the B<Pod::Parser> base class should be able to
do most of the input parsing for you and leave you free to worry about
how to intepret the commands and translate the result.

Note that all we have described here in this quick overview is the
simplest most straightforward use of B<Pod::Parser> to do stream-based
parsing. It is also possible to use the B<Pod::Parser::parse_text> function
to do more sophisticated tree-based parsing. See L<"TREE-BASED PARSING">.

=head1 PARSING OPTIONS

A I<parse-option> is simply a named option of B<Pod::Parser> with a
value that corresponds to a certain specified behavior. These various
behaviors of B<Pod::Parser> may be enabled/disabled by setting or
or unsetting one or more I<parse-options> using the B<parseopts()> method.
The set of currently accepted parse-options is as follows:

=over 3

=item B<-want_nonPODs> (default: unset)

Normally (by default) B<Pod::Parser> will only provide access to
the POD sections of the input. Input paragraphs that are not part
of the POD-format documentation are not made available to the caller
(not even using B<preprocess_paragraph()>). Setting this option to a
non-empty, non-zero value will allow B<preprocess_paragraph()> to see
non-POD sections of the input as well as POD sections. The B<cutting()>
method can be used to determine if the corresponding paragraph is a POD
paragraph, or some other input paragraph.

=item B<-process_cut_cmd> (default: unset)

Normally (by default) B<Pod::Parser> handles the C<=cut> POD directive
by itself and does not pass it on to the caller for processing. Setting
this option to a non-empty, non-zero value will cause B<Pod::Parser> to
pass the C<=cut> directive to the caller just like any other POD command
(and hence it may be processed by the B<command()> method).

B<Pod::Parser> will still interpret the C<=cut> directive to mean that
"cutting mode" has been (re)entered, but the caller will get a chance
to capture the actual C<=cut> paragraph itself for whatever purpose
it desires.

=item B<-warnings> (default: unset)

Normally (by default) B<Pod::Parser> recognizes a bare minimum of
pod syntax errors and warnings and issues diagnostic messages
for errors, but not for warnings. (Use B<Pod::Checker> to do more
thorough checking of POD syntax.) Setting this option to a non-empty,
non-zero value will cause B<Pod::Parser> to issue diagnostics for
the few warnings it recognizes as well as the errors.

=back

Please see L<"parseopts()"> for a complete description of the interface
for the setting and unsetting of parse-options.

=cut

#############################################################################

use vars qw(@ISA);
use strict;
#use diagnostics;
use Pod::InputObjects;
use Carp;
use Exporter;
BEGIN {
   if ($] < 5.6) {
      require Symbol;
      import Symbol;
   }
}
@ISA = qw(Exporter);

## These "variables" are used as local "glob aliases" for performance
use vars qw(%myData %myOpts @input_stack);

#############################################################################

=head1 RECOMMENDED SUBROUTINE/METHOD OVERRIDES

B<Pod::Parser> provides several methods which most subclasses will probably
want to override. These methods are as follows:

=cut

##---------------------------------------------------------------------------

=head1 B<command()>

            $parser->command($cmd,$text,$line_num,$pod_para);

This method should be overridden by subclasses to take the appropriate
action when a POD command paragraph (denoted by a line beginning with
"=") is encountered. When such a POD directive is seen in the input,
this method is called and is passed:

=over 3

=item C<$cmd>

the name of the command for this POD paragraph

=item C<$text>

the paragraph text for the given POD paragraph command.

=item C<$line_num>

the line-number of the beginning of the paragraph

=item C<$pod_para>

a reference to a C<Pod::Paragraph> object which contains further
information about the paragraph command (see L<Pod::InputObjects>
for details).

=back

B<Note> that this method I<is> called for C<=pod> paragraphs.

The base class implementation of this method simply treats the raw POD
command as normal block of paragraph text (invoking the B<textblock()>
method with the command paragraph).

=cut

sub command {
    my ($self, $cmd, $text, $line_num, $pod_para)  = @_;
    ## Just treat this like a textblock
    $self->textblock($pod_para->raw_text(), $line_num, $pod_para);
}

##---------------------------------------------------------------------------

=head1 B<verbatim()>

            $parser->verbatim($text,$line_num,$pod_para);

This method may be overridden by subclasses to take the appropriate
action when a block of verbatim text is encountered. It is passed the
following parameters:

=over 3

=item C<$text>

the block of text for the verbatim paragraph

=item C<$line_num>

the line-number of the beginning of the paragraph

=item C<$pod_para>

a reference to a C<Pod::Paragraph> object which contains further
information about the paragraph (see L<Pod::InputObjects>
for details).

=back

The base class implementation of this method simply prints the textblock
(unmodified) to the output filehandle.

=cut

sub verbatim {
    my ($self, $text, $line_num, $pod_para) = @_;
    my $out_fh = $self->{_OUTPUT};
    print $out_fh $text;
}

##---------------------------------------------------------------------------

=head1 B<textblock()>

            $parser->textblock($text,$line_num,$pod_para);

This method may be overridden by subclasses to take the appropriate
action when a normal block of POD text is encountered (although the base
class method will usually do what you want). It is passed the following
parameters:

=over 3

=item C<$text>

the block of text for the a POD paragraph

=item C<$line_num>

the line-number of the beginning of the paragraph

=item C<$pod_para>

a reference to a C<Pod::Paragraph> object which contains further
information about the paragraph (see L<Pod::InputObjects>
for details).

=back

In order to process interior sequences, subclasses implementations of
this method will probably want to invoke either B<interpolate()> or
B<parse_text()>, passing it the text block C<$text>, and the corresponding
line number in C<$line_num>, and then perform any desired processing upon
the returned result.

The base class implementation of this method simply prints the text block
as it occurred in the input stream).

=cut

sub textblock {