MirOS Manual: Pod::Parser(3p)


Pod::Parser(3p) Perl Programmers Reference Guide  Pod::Parser(3p)

NAME

     Pod::Parser - base class for creating POD filters and trans-
     lators

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) { $parser->parse_from_file($_); }

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REQUIRES

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

EXPORTS

     Nothing.

DESCRIPTION

     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 subc-
     lasses free to be concerned only with performing the actual
     translation of text.

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

QUICK OVERVIEW

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

     + command()

     + verbatim()

     + textblock()

     + interior_sequence()

     You may also want to override the begin_input() and
     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
     preprocess_line() and/or 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 Pod::Parser and
     override your methods to store the intermediate results in
     memory somewhere for the end_pod() method to process. You
     could use 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 getline() method
     (which is all that parse_from_filehandle() uses to read
     input).

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     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 "PRIVATE METHODS AND DATA" to avoid name collisions.

     For the most part, the 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 Pod::Parser to
     do stream-based parsing. It is also possible to use the
     Pod::Parser::parse_text function to do more sophisticated
     tree-based parsing. See "TREE-BASED PARSING".

PARSING OPTIONS

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

     -want_nonPODs (default: unset)
        Normally (by default) 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
        preprocess_paragraph()). Setting this option to a
        non-empty, non-zero value will allow
        preprocess_paragraph() to see non-POD sections of the
        input as well as POD sections. The cutting() method can
        be used to determine if the corresponding paragraph is a
        POD paragraph, or some other input paragraph.

     -process_cut_cmd (default: unset)
        Normally (by default) Pod::Parser handles the "=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 Pod::Parser to pass the "=cut"
        directive to the caller just like any other POD command
        (and hence it may be processed by the command() method).

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

     -warnings (default: unset)
        Normally (by default) Pod::Parser recognizes a bare
        minimum of pod syntax errors and warnings and issues

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        diagnostic messages for errors, but not for warnings.
        (Use Pod::Checker to do more thorough checking of POD
        syntax.) Setting this option to a non-empty, non-zero
        value will cause Pod::Parser to issue diagnostics for the
        few warnings it recognizes as well as the errors.

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

RECOMMENDED SUBROUTINE/METHOD OVERRIDES
     Pod::Parser provides several methods which most subclasses
     will probably want to override. These methods are as fol-
     lows:

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:

     $cmd
        the name of the command for this POD paragraph

     $text
        the paragraph text for the given POD paragraph command.

     $line_num
        the line-number of the beginning of the paragraph

     $pod_para
        a reference to a "Pod::Paragraph" object which contains
        further information about the paragraph command (see
        Pod::InputObjects for details).

     Note that this method is called for "=pod" paragraphs.

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

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 encoun-
     tered. It is passed the following parameters:

     $text

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        the block of text for the verbatim paragraph

     $line_num
        the line-number of the beginning of the paragraph

     $pod_para
        a reference to a "Pod::Paragraph" object which contains
        further information about the paragraph (see
        Pod::InputObjects for details).

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

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:

     $text
        the block of text for the a POD paragraph

     $line_num
        the line-number of the beginning of the paragraph

     $pod_para
        a reference to a "Pod::Paragraph" object which contains
        further information about the paragraph (see
        Pod::InputObjects for details).

     In order to process interior sequences, subclasses implemen-
     tations of this method will probably want to invoke either
     interpolate() or parse_text(), passing it the text block
     $text, and the corresponding line number in $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).

interior_sequence()
                 $parser->interior_sequence($seq_cmd,$seq_arg,$pod_seq);

     This method should be overridden by subclasses to take the
     appropriate action when an interior sequence is encountered.
     An interior sequence is an embedded command within a block
     of text which appears as a command name (usually a single
     uppercase character) followed immediately by a string of
     text which is enclosed in angle brackets. This method is
     passed the sequence command $seq_cmd and the corresponding

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     text $seq_arg. It is invoked by the interpolate() method for
     each interior sequence that occurs in the string that it is
     passed. It should return the desired text string to be used
     in place of the interior sequence. The $pod_seq argument is
     a reference to a "Pod::InteriorSequence" object which con-
     tains further information about the interior sequence.
     Please see Pod::InputObjects for details if you need to
     access this additional information.

     Subclass implementations of this method may wish to invoke
     the nested() method of $pod_seq to see if it is nested
     inside some other interior-sequence (and if so, which kind).

     The base class implementation of the interior_sequence()
     method simply returns the raw text of the interior sequence
     (as it occurred in the input) to the caller.

OPTIONAL SUBROUTINE/METHOD OVERRIDES
     Pod::Parser provides several methods which subclasses may
     want to override to perform any special pre/post-processing.
     These methods do not have to be overridden, but it may be
     useful for subclasses to take advantage of them.

new()
                 my $parser = Pod::Parser->new();

     This is the constructor for Pod::Parser and its subclasses.
     You do not need to override this method! It is capable of
     constructing subclass objects as well as base class objects,
     provided you use any of the following constructor invocation
     styles:

         my $parser1 = MyParser->new();
         my $parser2 = new MyParser();
         my $parser3 = $parser2->new();

     where "MyParser" is some subclass of Pod::Parser.

     Using the syntax "MyParser::new()" to invoke the constructor
     is not recommended, but if you insist on being able to do
     this, then the subclass will need to override the new() con-
     structor method. If you do override the constructor, you
     must be sure to invoke the initialize() method of the newly
     blessed object.

     Using any of the above invocations, the first argument to
     the constructor is always the corresponding package name (or
     object reference). No other arguments are required, but if
     desired, an associative array (or hash-table) my be passed
     to the new() constructor, as in:

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         my $parser1 = MyParser->new( MYDATA => $value1, MOREDATA => $value2 );
         my $parser2 = new MyParser( -myflag => 1 );

     All arguments passed to the new() constructor will be
     treated as key/value pairs in a hash-table. The newly con-
     structed object will be initialized by copying the contents
     of the given hash-table (which may have been empty). The
     new() constructor for this class and all of its subclasses
     returns a blessed reference to the initialized object
     (hash-table).

initialize()
                 $parser->initialize();

     This method performs any necessary object initialization. It
     takes no arguments (other than the object instance of
     course, which is typically copied to a local variable named
     $self). If subclasses override this method then they must be
     sure to invoke "$self->SUPER::initialize()".

begin_pod()
                 $parser->begin_pod();

     This method is invoked at the beginning of processing for
     each POD document that is encountered in the input. Subc-
     lasses should override this method to perform any per-
     document initialization.

begin_input()
                 $parser->begin_input();

     This method is invoked by parse_from_filehandle() immedi-
     ately before processing input from a filehandle. The base
     class implementation does nothing, however, subclasses may
     override it to perform any per-file initializations.

     Note that if multiple files are parsed for a single POD
     document (perhaps the result of some future "=include"
     directive) this method is invoked for every file that is
     parsed. If you wish to perform certain initializations once
     per document, then you should use begin_pod().

end_input()
                 $parser->end_input();

     This method is invoked by parse_from_filehandle() immedi-
     ately after processing input from a filehandle. The base
     class implementation does nothing, however, subclasses may
     override it to perform any per-file cleanup actions.

     Please note that if multiple files are parsed for a single
     POD document (perhaps the result of some kind of "=include"

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     directive) this method is invoked for every file that is
     parsed. If you wish to perform certain cleanup actions once
     per document, then you should use end_pod().

end_pod()
                 $parser->end_pod();

     This method is invoked at the end of processing for each POD
     document that is encountered in the input. Subclasses should
     override this method to perform any per-document finaliza-
     tion.

preprocess_line()
               $textline = $parser->preprocess_line($text, $line_num);

     This method should be overridden by subclasses that wish to
     perform any kind of preprocessing for each line of input
     (before it has been determined whether or not it is part of
     a POD paragraph). The parameter $text is the input line; and
     the parameter $line_num is the line number of the
     corresponding text line.

     The value returned should correspond to the new text to use
     in its place.  If the empty string or an undefined value is
     returned then no further processing will be performed for
     this line.

     Please note that the preprocess_line() method is invoked
     before the preprocess_paragraph() method. After all (possi-
     bly preprocessed) lines in a paragraph have been assembled
     together and it has been determined that the paragraph is
     part of the POD documentation from one of the selected sec-
     tions, then preprocess_paragraph() is invoked.

     The base class implementation of this method returns the
     given text.

preprocess_paragraph()
                 $textblock = $parser->preprocess_paragraph($text, $line_num);

     This method should be overridden by subclasses that wish to
     perform any kind of preprocessing for each block (paragraph)
     of POD documentation that appears in the input stream. The
     parameter $text is the POD paragraph from the input file;
     and the parameter $line_num is the line number for the
     beginning of the corresponding paragraph.

     The value returned should correspond to the new text to use
     in its place If the empty string is returned or an undefined
     value is returned, then the given $text is ignored (not pro-
     cessed).

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     This method is invoked after gathering up all the lines in a
     paragraph and after determining the cutting state of the
     paragraph, but before trying to further parse or interpret
     them. After preprocess_paragraph() returns, the current cut-
     ting state (which is returned by "$self->cutting()") is
     examined. If it evaluates to true then input text (including
     the given $text) is cut (not processed) until the next POD
     directive is encountered.

     Please note that the preprocess_line() method is invoked
     before the preprocess_paragraph() method. After all (possi-
     bly preprocessed) lines in a paragraph have been assembled
     together and either it has been determined that the para-
     graph is part of the POD documentation from one of the
     selected sections or the "-want_nonPODs" option is true,
     then preprocess_paragraph() is invoked.

     The base class implementation of this method returns the
     given text.

METHODS FOR PARSING AND PROCESSING

     Pod::Parser provides several methods to process input text.
     These methods typically won't need to be overridden (and in
     some cases they can't be overridden), but subclasses may
     want to invoke them to exploit their functionality.

parse_text()
                 $ptree1 = $parser->parse_text($text, $line_num);
                 $ptree2 = $parser->parse_text({%opts}, $text, $line_num);
                 $ptree3 = $parser->parse_text(\%opts, $text, $line_num);

     This method is useful if you need to perform your own inter-
     polation of interior sequences and can't rely upon interpo-
     late to expand them in simple bottom-up order.

     The parameter $text is a string or block of text to be
     parsed for interior sequences; and the parameter $line_num
     is the line number curresponding to the beginning of $text.

     parse_text() will parse the given text into a parse-tree of
     "nodes." and interior-sequences.  Each "node" in the parse
     tree is either a text-string, or a Pod::InteriorSequence.
     The result returned is a parse-tree of type Pod::ParseTree.
     Please see Pod::InputObjects for more information about
     Pod::InteriorSequence and Pod::ParseTree.

     If desired, an optional hash-ref may be specified as the
     first argument to customize certain aspects of the parse-
     tree that is created and returned. The set of recognized
     option keywords are:

     -expand_seq => code-ref|method-name

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        Normally, the parse-tree returned by parse_text() will
        contain an unexpanded "Pod::InteriorSequence" object for
        each interior-sequence encountered. Specifying
        -expand_seq tells parse_text() to "expand" every
        interior-sequence it sees by invoking the referenced
        function (or named method of the parser object) and using
        the return value as the expanded result.

        If a subroutine reference was given, it is invoked as:

          &$code_ref( $parser, $sequence )

        and if a method-name was given, it is invoked as:

          $parser->method_name( $sequence )

        where $parser is a reference to the parser object, and
        $sequence is a reference to the interior-sequence object.
        [NOTE: If the interior_sequence() method is specified,
        then it is invoked according to the interface specified
        in "interior_sequence()"].

     -expand_text => code-ref|method-name
        Normally, the parse-tree returned by parse_text() will
        contain a text-string for each contiguous sequence of
        characters outside of an interior-sequence. Specifying
        -expand_text tells parse_text() to "preprocess" every
        such text-string it sees by invoking the referenced func-
        tion (or named method of the parser object) and using the
        return value as the preprocessed (or "expanded") result.
        [Note that if the result is an interior-sequence, then it
        will not be expanded as specified by the -expand_seq
        option; Any such recursive expansion needs to be handled
        by the specified callback routine.]

        If a subroutine reference was given, it is invoked as:

          &$code_ref( $parser, $text, $ptree_node )

        and if a method-name was given, it is invoked as:

          $parser->method_name( $text, $ptree_node )

        where $parser is a reference to the parser object, $text
        is the text-string encountered, and $ptree_node is a
        reference to the current node in the parse-tree (usually
        an interior-sequence object or else the top-level node of
        the parse-tree).

     -expand_ptree => code-ref|method-name
        Rather than returning a "Pod::ParseTree", pass the
        parse-tree as an argument to the referenced subroutine

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        (or named method of the parser object) and return the
        result instead of the parse-tree object.

        If a subroutine reference was given, it is invoked as:

          &$code_ref( $parser, $ptree )

        and if a method-name was given, it is invoked as:

          $parser->method_name( $ptree )

        where $parser is a reference to the parser object, and
        $ptree is a reference to the parse-tree object.

interpolate()
                 $textblock = $parser->interpolate($text, $line_num);

     This method translates all text (including any embedded
     interior sequences) in the given text string $text and
     returns the interpolated result. The parameter $line_num is
     the line number corresponding to the beginning of $text.

     interpolate() merely invokes a private method to recursively
     expand nested interior sequences in bottom-up order (inner-
     most sequences are expanded first). If there is a need to
     expand nested sequences in some alternate order, use
     parse_text instead.

parse_from_filehandle()
                 $parser->parse_from_filehandle($in_fh,$out_fh);

     This method takes an input filehandle (which is assumed to
     already be opened for reading) and reads the entire input
     stream looking for blocks (paragraphs) of POD documentation
     to be processed. If no first argument is given the default
     input filehandle "STDIN" is used.

     The $in_fh parameter may be any object that provides a get-
     line() method to retrieve a single line of input text
     (hence, an appropriate wrapper object could be used to parse
     PODs from a single string or an array of strings).

     Using "$in_fh->getline()", input is read line-by-line and
     assembled into paragraphs or "blocks" (which are separated
     by lines containing nothing but whitespace). For each block
     of POD documentation encountered it will invoke a method to
     parse the given paragraph.

     If a second argument is given then it should correspond to a
     filehandle where output should be sent (otherwise the
     default output filehandle is "STDOUT" if no output filehan-
     dle is currently in use).

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     NOTE: For performance reasons, this method caches the input
     stream at the top of the stack in a local variable. Any
     attempts by clients to change the stack contents during pro-
     cessing when in the midst executing of this method will not
     affect the input stream used by the current invocation of
     this method.

     This method does not usually need to be overridden by subc-
     lasses.

parse_from_file()
                 $parser->parse_from_file($filename,$outfile);

     This method takes a filename and does the following:

     + opens the input and output files for reading (creating the
       appropriate filehandles)

     + invokes the parse_from_filehandle() method passing it the
       corresponding input and output filehandles.

     + closes the input and output files.

     If the special input filename "-" or "<&STDIN" is given then
     the STDIN filehandle is used for input (and no open or close
     is performed). If no input filename is specified then "-" is
     implied.

     If a second argument is given then it should be the name of
     the desired output file. If the special output filename "-"
     or ">&STDOUT" is given then the STDOUT filehandle is used
     for output (and no open or close is performed). If the spe-
     cial output filename ">&STDERR" is given then the STDERR
     filehandle is used for output (and no open or close is per-
     formed). If no output filehandle is currently in use and no
     output filename is specified, then "-" is implied. Alterna-
     tively, an IO::String object is also accepted as an output
     file handle.

     This method does not usually need to be overridden by subc-
     lasses.

ACCESSOR METHODS

     Clients of Pod::Parser should use the following methods to
     access instance data fields:

errorsub()
                 $parser->errorsub("method_name");
                 $parser->errorsub(\&warn_user);
                 $parser->errorsub(sub { print STDERR, @_ });

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     Specifies the method or subroutine to use when printing
     error messages about POD syntax. The supplied
     method/subroutine must return TRUE upon successful printing
     of the message. If "undef" is given, then the warn builtin
     is used to issue error messages (this is the default
     behavior).

                 my $errorsub = $parser->errorsub()
                 my $errmsg = "This is an error message!\n"
                 (ref $errorsub) and &{$errorsub}($errmsg)
                     or (defined $errorsub) and $parser->$errorsub($errmsg)
                         or  warn($errmsg);

     Returns a method name, or else a reference to the user-
     supplied subroutine used to print error messages. Returns
     "undef" if the warn builtin is used to issue error messages
     (this is the default behavior).

cutting()
                 $boolean = $parser->cutting();

     Returns the current "cutting" state: a boolean-valued scalar
     which evaluates to true if text from the input file is
     currently being "cut" (meaning it is not considered part of
     the POD document).

                 $parser->cutting($boolean);

     Sets the current "cutting" state to the given value and
     returns the result.

parseopts()
     When invoked with no additional arguments, parseopts returns
     a hashtable of all the current parsing options.

                 ## See if we are parsing non-POD sections as well as POD ones
                 my %opts = $parser->parseopts();
                 $opts{'-want_nonPODs}' and print "-want_nonPODs\n";

     When invoked using a single string, parseopts treats the
     string as the name of a parse-option and returns its
     corresponding value if it exists (returns "undef" if it
     doesn't).

                 ## Did we ask to see '=cut' paragraphs?
                 my $want_cut = $parser->parseopts('-process_cut_cmd');
                 $want_cut and print "-process_cut_cmd\n";

     When invoked with multiple arguments, parseopts treats them
     as key/value pairs and the specified parse-option names are
     set to the given values. Any unspecified parse-options are
     unaffected.

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                 ## Set them back to the default
                 $parser->parseopts(-warnings => 0);

     When passed a single hash-ref, parseopts uses that hash to
     completely reset the existing parse-options, all previous
     parse-option values are lost.

                 ## Reset all options to default
                 $parser->parseopts( { } );

     See "PARSING OPTIONS" for more information on the name and
     meaning of each parse-option currently recognized.

output_file()
                 $fname = $parser->output_file();

     Returns the name of the output file being written.

output_handle()
                 $fhandle = $parser->output_handle();

     Returns the output filehandle object.

input_file()
                 $fname = $parser->input_file();

     Returns the name of the input file being read.

input_handle()
                 $fhandle = $parser->input_handle();

     Returns the current input filehandle object.

PRIVATE METHODS AND DATA

     Pod::Parser makes use of several internal methods and data
     fields which clients should not need to see or use. For the
     sake of avoiding name collisions for client data and
     methods, these methods and fields are briefly discussed
     here. Determined hackers may obtain further information
     about them by reading the Pod::Parser source code.

     Private data fields are stored in the hash-object whose
     reference is returned by the new() constructor for this
     class. The names of all private methods and data-fields used
     by Pod::Parser begin with a prefix of "_" and match the reg-
     ular expression "/^_\w+$/".

TREE-BASED PARSING
     If straightforward stream-based parsing wont meet your needs
     (as is likely the case for tasks such as translating PODs
     into structured markup languages like HTML and XML) then you
     may need to take the tree-based approach. Rather than doing

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     everything in one pass and calling the interpolate() method
     to expand sequences into text, it may be desirable to
     instead create a parse-tree using the parse_text() method to
     return a tree-like structure which may contain an ordered
     list of children (each of which may be a text-string, or a
     similar tree-like structure).

     Pay special attention to "METHODS FOR PARSING AND PROCESS-
     ING" and to the objects described in Pod::InputObjects. The
     former describes the gory details and parameters for how to
     customize and extend the parsing behavior of Pod::Parser.
     Pod::InputObjects provides several objects that may all be
     used interchangeably as parse-trees. The most obvious one is
     the Pod::ParseTree object. It defines the basic interface
     and functionality that all things trying to be a POD parse-
     tree should do. A Pod::ParseTree is defined such that each
     "node" may be a text-string, or a reference to another
     parse-tree.  Each Pod::Paragraph object and each
     Pod::InteriorSequence object also supports the basic parse-
     tree interface.

     The parse_text() method takes a given paragraph of text, and
     returns a parse-tree that contains one or more children,
     each of which may be a text-string, or an InteriorSequence
     object. There are also callback-options that may be passed
     to parse_text() to customize the way it expands or
     transforms interior-sequences, as well as the returned
     result. These callbacks can be used to create a parse-tree
     with custom-made objects (which may or may not support the
     parse-tree interface, depending on how you choose to do it).

     If you wish to turn an entire POD document into a
     parse-tree, that process is fairly straightforward. The
     parse_text() method is the key to doing this successfully.
     Every paragraph-callback (i.e. the polymorphic methods for
     command(), verbatim(), and textblock() paragraphs) takes a
     Pod::Paragraph object as an argument. Each paragraph object
     has a parse_tree() method that can be used to get or set a
     corresponding parse-tree. So for each of those paragraph-
     callback methods, simply call parse_text() with the options
     you desire, and then use the returned parse-tree to assign
     to the given paragraph object.

     That gives you a parse-tree for each paragraph - so now all
     you need is an ordered list of paragraphs. You can maintain
     that yourself as a data element in the object/hash. The most
     straightforward way would be simply to use an array-ref,
     with the desired set of custom "options" for each invocation
     of parse_text. Let's assume the desired option-set is given
     by the hash %options. Then we might do something like the
     following:

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         package MyPodParserTree;

         @ISA = qw( Pod::Parser );

         ...

         sub begin_pod {
             my $self = shift;
             $self->{'-paragraphs'} = [];  ## initialize paragraph list
         }

         sub command {
             my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
             my $ptree = $parser->parse_text({%options}, $paragraph, ...);
             $pod_para->parse_tree( $ptree );
             push @{ $self->{'-paragraphs'} }, $pod_para;
         }

         sub verbatim {
             my ($parser, $paragraph, $line_num, $pod_para) = @_;
             push @{ $self->{'-paragraphs'} }, $pod_para;
         }

         sub textblock {
             my ($parser, $paragraph, $line_num, $pod_para) = @_;
             my $ptree = $parser->parse_text({%options}, $paragraph, ...);
             $pod_para->parse_tree( $ptree );
             push @{ $self->{'-paragraphs'} }, $pod_para;
         }

         ...

         package main;
         ...
         my $parser = new MyPodParserTree(...);
         $parser->parse_from_file(...);
         my $paragraphs_ref = $parser->{'-paragraphs'};

     Of course, in this module-author's humble opinion, I'd be
     more inclined to use the existing Pod::ParseTree object than
     a simple array. That way everything in it, paragraphs and
     sequences, all respond to the same core interface for all
     parse-tree nodes. The result would look something like:

         package MyPodParserTree2;

         ...

         sub begin_pod {
             my $self = shift;
             $self->{'-ptree'} = new Pod::ParseTree;  ## initialize parse-tree
         }

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         sub parse_tree {
             ## convenience method to get/set the parse-tree for the entire POD
             (@_ > 1)  and  $_[0]->{'-ptree'} = $_[1];
             return $_[0]->{'-ptree'};
         }

         sub command {
             my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
             my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
             $pod_para->parse_tree( $ptree );
             $parser->parse_tree()->append( $pod_para );
         }

         sub verbatim {
             my ($parser, $paragraph, $line_num, $pod_para) = @_;
             $parser->parse_tree()->append( $pod_para );
         }

         sub textblock {
             my ($parser, $paragraph, $line_num, $pod_para) = @_;
             my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
             $pod_para->parse_tree( $ptree );
             $parser->parse_tree()->append( $pod_para );
         }

         ...

         package main;
         ...
         my $parser = new MyPodParserTree2(...);
         $parser->parse_from_file(...);
         my $ptree = $parser->parse_tree;
         ...

     Now you have the entire POD document as one great big
     parse-tree. You can even use the -expand_seq option to
     parse_text to insert whole different kinds of objects. Just
     don't expect Pod::Parser to know what to do with them after
     that. That will need to be in your code. Or, alternatively,
     you can insert any object you like so long as it conforms to
     the Pod::ParseTree interface.

     One could use this to create subclasses of Pod::Paragraphs
     and Pod::InteriorSequences for specific commands (or to
     create your own custom node-types in the parse-tree) and add
     some kind of emit() method to each custom node/subclass
     object in the tree. Then all you'd need to do is recursively
     walk the tree in the desired order, processing the children
     (most likely from left to right) by formatting them if they
     are text-strings, or by calling their emit() method if they
     are objects/references.

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SEE ALSO

     Pod::InputObjects, Pod::Select

     Pod::InputObjects defines POD input objects corresponding to
     command paragraphs, parse-trees, and interior-sequences.

     Pod::Select is a subclass of Pod::Parser which provides the
     ability to selectively include and/or exclude sections of a
     POD document from being translated based upon the current
     heading, subheading, subsubheading, etc.

AUTHOR

     Please report bugs using <http://rt.cpan.org>.

     Brad Appleton <bradapp@enteract.com>

     Based on code for Pod::Text written by Tom Christiansen
     <tchrist@mox.perl.com>

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