pod::parser.3

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.\" ========================================================================
.\"
.IX Title "Pod::Parser 3"
.TH Pod::Parser 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Pod::Parser \- base class for creating POD filters and translators
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    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 \*(Aqhead1\*(Aq) { ... }
\&        elsif ($command eq \*(Aqhead2\*(Aq) { ... }
\&        ## ... 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 ($seq_command eq \*(AqB\*(Aq);
\&        return "\`$seq_argument\*(Aq"     if ($seq_command eq \*(AqC\*(Aq);
\&        return "_${seq_argument}_\*(Aq"  if ($seq_command eq \*(AqI\*(Aq);
\&        ## ... 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(\e*STDIN)  if (@ARGV == 0);
\&    for (@ARGV) { $parser\->parse_from_file($_); }
.Ve
.SH "REQUIRES"
.IX Header "REQUIRES"
perl5.005, Pod::InputObjects, Exporter, Symbol, Carp
.SH "EXPORTS"
.IX Header "EXPORTS"
Nothing.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBPod::Parser\fR is a base class for creating \s-1POD\s0 filters and translators.
It handles most of the effort involved with parsing the \s-1POD\s0 sections
from an input stream, leaving subclasses free to be concerned only with
performing the actual translation of text.
.PP
\&\fBPod::Parser\fR parses PODs, and makes method calls to handle the various
components of the \s-1POD\s0. Subclasses of \fBPod::Parser\fR override these methods
to translate the \s-1POD\s0 into whatever output format they desire.
.SH "QUICK OVERVIEW"
.IX Header "QUICK OVERVIEW"
To create a \s-1POD\s0 filter for translating \s-1POD\s0 documentation into some other
format, you create a subclass of \fBPod::Parser\fR which typically overrides
just the base class implementation for the following methods:
.IP "\(bu" 2
\&\fB\f(BIcommand()\fB\fR
.IP "\(bu" 2
\&\fB\f(BIverbatim()\fB\fR
.IP "\(bu" 2
\&\fB\f(BItextblock()\fB\fR
.IP "\(bu" 2
\&\fB\f(BIinterior_sequence()\fB\fR
.PP
You may also want to override the \fB\f(BIbegin_input()\fB\fR and \fB\f(BIend_input()\fB\fR
methods for your subclass (to perform any needed per-file and/or
per-document initialization or cleanup).
.PP
If you need to perform any preprocesssing of input before it is parsed
you may want to override one or more of \fB\f(BIpreprocess_line()\fB\fR and/or
\&\fB\f(BIpreprocess_paragraph()\fB\fR.
.PP
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 \fBPod::Parser\fR and override your methods to store the
intermediate results in memory somewhere for the \fB\f(BIend_pod()\fB\fR method to
process. You could use \fBPod::Parser\fR 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 \fB\f(BIgetline()\fB\fR method (which is all that
\&\fB\f(BIparse_from_filehandle()\fB\fR uses to read input).
.PP
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"\s-1PRIVATE\s0 \s-1METHODS\s0 \s-1AND\s0 \s-1DATA\s0\*(R"
to avoid name collisions.
.PP
For the most part, the \fBPod::Parser\fR base class should be able to
do most of the input parsing for you and leave you free to worry about
how to interpret the commands and translate the result.
.PP
Note that all we have described here in this quick overview is the
simplest most straightforward use of \fBPod::Parser\fR to do stream-based
parsing. It is also possible to use the \fBPod::Parser::parse_text\fR function
to do more sophisticated tree-based parsing. See \*(L"TREE-BASED \s-1PARSING\s0\*(R".
.SH "PARSING OPTIONS"
.IX Header "PARSING OPTIONS"
A \fIparse-option\fR is simply a named option of \fBPod::Parser\fR with a
value that corresponds to a certain specified behavior. These various
behaviors of \fBPod::Parser\fR may be enabled/disabled by setting
or unsetting one or more \fIparse-options\fR using the \fB\f(BIparseopts()\fB\fR method.
The set of currently accepted parse-options is as follows:
.IP "\fB\-want_nonPODs\fR (default: unset)" 3
.IX Item "-want_nonPODs (default: unset)"
Normally (by default) \fBPod::Parser\fR will only provide access to
the \s-1POD\s0 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 \fB\f(BIpreprocess_paragraph()\fB\fR). Setting this option to a
non-empty, non-zero value will allow \fB\f(BIpreprocess_paragraph()\fB\fR to see
non-POD sections of the input as well as \s-1POD\s0 sections. The \fB\f(BIcutting()\fB\fR
method can be used to determine if the corresponding paragraph is a \s-1POD\s0
paragraph, or some other input paragraph.
.IP "\fB\-process_cut_cmd\fR (default: unset)" 3
.IX Item "-process_cut_cmd (default: unset)"
Normally (by default) \fBPod::Parser\fR handles the \f(CW\*(C`=cut\*(C'\fR \s-1POD\s0 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 \fBPod::Parser\fR to
pass the \f(CW\*(C`=cut\*(C'\fR directive to the caller just like any other \s-1POD\s0 command
(and hence it may be processed by the \fB\f(BIcommand()\fB\fR method).
.Sp
\&\fBPod::Parser\fR will still interpret the \f(CW\*(C`=cut\*(C'\fR directive to mean that
\&\*(L"cutting mode\*(R" has been (re)entered, but the caller will get a chance
to capture the actual \f(CW\*(C`=cut\*(C'\fR paragraph itself for whatever purpose
it desires.
.IP "\fB\-warnings\fR (default: unset)" 3
.IX Item "-warnings (default: unset)"
Normally (by default) \fBPod::Parser\fR recognizes a bare minimum of
pod syntax errors and warnings and issues diagnostic messages
for errors, but not for warnings. (Use \fBPod::Checker\fR to do more
thorough checking of \s-1POD\s0 syntax.) Setting this option to a non-empty,
non-zero value will cause \fBPod::Parser\fR to issue diagnostics for
the few warnings it recognizes as well as the errors.
.PP
Please see \*(L"\fIparseopts()\fR\*(R" for a complete description of the interface
for the setting and unsetting of parse-options.
.SH "RECOMMENDED SUBROUTINE/METHOD OVERRIDES"
.IX Header "RECOMMENDED SUBROUTINE/METHOD OVERRIDES"
\&\fBPod::Parser\fR provides several methods which most subclasses will probably
want to override. These methods are as follows:
.SH "\fB\fP\f(BIcommand()\fP\fB\fP"
.IX Header "command()"
.Vb 1
\&            $parser\->command($cmd,$text,$line_num,$pod_para);
.Ve
.PP
This method should be overridden by subclasses to take the appropriate
action when a \s-1POD\s0 command paragraph (denoted by a line beginning with
\&\*(L"=\*(R") is encountered. When such a \s-1POD\s0 directive is seen in the input,
this method is called and is passed:
.ie n .IP "$cmd" 3
.el .IP "\f(CW$cmd\fR" 3
.IX Item "$cmd"
the name of the command for this \s-1POD\s0 paragraph
.ie n .IP "$text" 3
.el .IP "\f(CW$text\fR" 3
.IX Item "$text"
the paragraph text for the given \s-1POD\s0 paragraph command.
.ie n .IP "$line_num" 3
.el .IP "\f(CW$line_num\fR" 3
.IX Item "$line_num"
the line-number of the beginning of the paragraph
.ie n .IP "$pod_para" 3
.el .IP "\f(CW$pod_para\fR" 3
.IX Item "$pod_para"
a reference to a \f(CW\*(C`Pod::Paragraph\*(C'\fR object which contains further
information about the paragraph command (see Pod::InputObjects
for details).
.PP
\&\fBNote\fR that this method \fIis\fR called for \f(CW\*(C`=pod\*(C'\fR paragraphs.
.PP
The base class implementation of this method simply treats the raw \s-1POD\s0
command as normal block of paragraph text (invoking the \fB\f(BItextblock()\fB\fR
method with the command paragraph).
.SH "\fB\fP\f(BIverbatim()\fP\fB\fP"
.IX Header "verbatim()"
.Vb 1
\&            $parser\->verbatim($text,$line_num,$pod_para);
.Ve
.PP
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:
.ie n .IP "$text" 3
.el .IP "\f(CW$text\fR" 3
.IX Item "$text"
the block of text for the verbatim paragraph
.ie n .IP "$line_num" 3
.el .IP "\f(CW$line_num\fR" 3
.IX Item "$line_num"
the line-number of the beginning of the paragraph
.ie n .IP "$pod_para" 3
.el .IP "\f(CW$pod_para\fR" 3
.IX Item "$pod_para"
a reference to a \f(CW\*(C`Pod::Paragraph\*(C'\fR object which contains further
information about the paragraph (see Pod::InputObjects
for details).
.PP