1Pod::Parser(3)        User Contributed Perl Documentation       Pod::Parser(3)
2
3
4

NAME

6       Pod::Parser - base class for creating POD filters and translators
7

SYNOPSIS

9           use Pod::Parser;
10
11           package MyParser;
12           @ISA = qw(Pod::Parser);
13
14           sub command {
15               my ($parser, $command, $paragraph, $line_num) = @_;
16               ## Interpret the command and its text; sample actions might be:
17               if ($command eq 'head1') { ... }
18               elsif ($command eq 'head2') { ... }
19               ## ... other commands and their actions
20               my $out_fh = $parser->output_handle();
21               my $expansion = $parser->interpolate($paragraph, $line_num);
22               print $out_fh $expansion;
23           }
24
25           sub verbatim {
26               my ($parser, $paragraph, $line_num) = @_;
27               ## Format verbatim paragraph; sample actions might be:
28               my $out_fh = $parser->output_handle();
29               print $out_fh $paragraph;
30           }
31
32           sub textblock {
33               my ($parser, $paragraph, $line_num) = @_;
34               ## Translate/Format this block of text; sample actions might be:
35               my $out_fh = $parser->output_handle();
36               my $expansion = $parser->interpolate($paragraph, $line_num);
37               print $out_fh $expansion;
38           }
39
40           sub interior_sequence {
41               my ($parser, $seq_command, $seq_argument) = @_;
42               ## Expand an interior sequence; sample actions might be:
43               return "*$seq_argument*"     if ($seq_command eq 'B');
44               return "`$seq_argument'"     if ($seq_command eq 'C');
45               return "_${seq_argument}_'"  if ($seq_command eq 'I');
46               ## ... other sequence commands and their resulting text
47           }
48
49           package main;
50
51           ## Create a parser object and have it parse file whose name was
52           ## given on the command-line (use STDIN if no files were given).
53           $parser = new MyParser();
54           $parser->parse_from_filehandle(\*STDIN)  if (@ARGV == 0);
55           for (@ARGV) { $parser->parse_from_file($_); }
56

REQUIRES

58       perl5.005, Pod::InputObjects, Exporter, Symbol, Carp
59

EXPORTS

61       Nothing.
62

DESCRIPTION

64       NOTE: This module is considered legacy; modern Perl releases (5.18 and
65       higher) are going to remove Pod-Parser from core and use Pod-Simple for
66       all things POD.
67
68       Pod::Parser is a base class for creating POD filters and translators.
69       It handles most of the effort involved with parsing the POD sections
70       from an input stream, leaving subclasses free to be concerned only with
71       performing the actual translation of text.
72
73       Pod::Parser parses PODs, and makes method calls to handle the various
74       components of the POD. Subclasses of Pod::Parser override these methods
75       to translate the POD into whatever output format they desire.
76

QUICK OVERVIEW

78       To create a POD filter for translating POD documentation into some
79       other format, you create a subclass of Pod::Parser which typically
80       overrides just the base class implementation for the following methods:
81
82       · command()
83
84       · verbatim()
85
86       · textblock()
87
88       · interior_sequence()
89
90       You may also want to override the begin_input() and end_input() methods
91       for your subclass (to perform any needed per-file and/or per-document
92       initialization or cleanup).
93
94       If you need to perform any preprocessing of input before it is parsed
95       you may want to override one or more of preprocess_line() and/or
96       preprocess_paragraph().
97
98       Sometimes it may be necessary to make more than one pass over the input
99       files. If this is the case you have several options. You can make the
100       first pass using Pod::Parser and override your methods to store the
101       intermediate results in memory somewhere for the end_pod() method to
102       process. You could use Pod::Parser for several passes with an
103       appropriate state variable to control the operation for each pass. If
104       your input source can't be reset to start at the beginning, you can
105       store it in some other structure as a string or an array and have that
106       structure implement a getline() method (which is all that
107       parse_from_filehandle() uses to read input).
108
109       Feel free to add any member data fields you need to keep track of
110       things like current font, indentation, horizontal or vertical position,
111       or whatever else you like. Be sure to read "PRIVATE METHODS AND DATA"
112       to avoid name collisions.
113
114       For the most part, the Pod::Parser base class should be able to do most
115       of the input parsing for you and leave you free to worry about how to
116       interpret the commands and translate the result.
117
118       Note that all we have described here in this quick overview is the
119       simplest most straightforward use of Pod::Parser to do stream-based
120       parsing. It is also possible to use the Pod::Parser::parse_text
121       function to do more sophisticated tree-based parsing. See "TREE-BASED
122       PARSING".
123

PARSING OPTIONS

125       A parse-option is simply a named option of Pod::Parser with a value
126       that corresponds to a certain specified behavior. These various
127       behaviors of Pod::Parser may be enabled/disabled by setting or
128       unsetting one or more parse-options using the parseopts() method.  The
129       set of currently accepted parse-options is as follows:
130
131       -want_nonPODs (default: unset)
132          Normally (by default) Pod::Parser will only provide access to the
133          POD sections of the input. Input paragraphs that are not part of the
134          POD-format documentation are not made available to the caller (not
135          even using preprocess_paragraph()). Setting this option to a non-
136          empty, non-zero value will allow preprocess_paragraph() to see non-
137          POD sections of the input as well as POD sections. The cutting()
138          method can be used to determine if the corresponding paragraph is a
139          POD paragraph, or some other input paragraph.
140
141       -process_cut_cmd (default: unset)
142          Normally (by default) Pod::Parser handles the "=cut" POD directive
143          by itself and does not pass it on to the caller for processing.
144          Setting this option to a non-empty, non-zero value will cause
145          Pod::Parser to pass the "=cut" directive to the caller just like any
146          other POD command (and hence it may be processed by the command()
147          method).
148
149          Pod::Parser will still interpret the "=cut" directive to mean that
150          "cutting mode" has been (re)entered, but the caller will get a
151          chance to capture the actual "=cut" paragraph itself for whatever
152          purpose it desires.
153
154       -warnings (default: unset)
155          Normally (by default) Pod::Parser recognizes a bare minimum of pod
156          syntax errors and warnings and issues diagnostic messages for
157          errors, but not for warnings. (Use Pod::Checker to do more thorough
158          checking of POD syntax.) Setting this option to a non-empty, non-
159          zero value will cause Pod::Parser to issue diagnostics for the few
160          warnings it recognizes as well as the errors.
161
162       Please see "parseopts()" for a complete description of the interface
163       for the setting and unsetting of parse-options.
164
166       Pod::Parser provides several methods which most subclasses will
167       probably want to override. These methods are as follows:
168

command()

170                   $parser->command($cmd,$text,$line_num,$pod_para);
171
172       This method should be overridden by subclasses to take the appropriate
173       action when a POD command paragraph (denoted by a line beginning with
174       "=") is encountered. When such a POD directive is seen in the input,
175       this method is called and is passed:
176
177       $cmd
178          the name of the command for this POD paragraph
179
180       $text
181          the paragraph text for the given POD paragraph command.
182
183       $line_num
184          the line-number of the beginning of the paragraph
185
186       $pod_para
187          a reference to a "Pod::Paragraph" object which contains further
188          information about the paragraph command (see Pod::InputObjects for
189          details).
190
191       Note that this method is called for "=pod" paragraphs.
192
193       The base class implementation of this method simply treats the raw POD
194       command as normal block of paragraph text (invoking the textblock()
195       method with the command paragraph).
196

verbatim()

198                   $parser->verbatim($text,$line_num,$pod_para);
199
200       This method may be overridden by subclasses to take the appropriate
201       action when a block of verbatim text is encountered. It is passed the
202       following parameters:
203
204       $text
205          the block of text for the verbatim paragraph
206
207       $line_num
208          the line-number of the beginning of the paragraph
209
210       $pod_para
211          a reference to a "Pod::Paragraph" object which contains further
212          information about the paragraph (see Pod::InputObjects for details).
213
214       The base class implementation of this method simply prints the
215       textblock (unmodified) to the output filehandle.
216

textblock()

218                   $parser->textblock($text,$line_num,$pod_para);
219
220       This method may be overridden by subclasses to take the appropriate
221       action when a normal block of POD text is encountered (although the
222       base class method will usually do what you want). It is passed the
223       following parameters:
224
225       $text
226          the block of text for the a POD paragraph
227
228       $line_num
229          the line-number of the beginning of the paragraph
230
231       $pod_para
232          a reference to a "Pod::Paragraph" object which contains further
233          information about the paragraph (see Pod::InputObjects for details).
234
235       In order to process interior sequences, subclasses implementations of
236       this method will probably want to invoke either interpolate() or
237       parse_text(), passing it the text block $text, and the corresponding
238       line number in $line_num, and then perform any desired processing upon
239       the returned result.
240
241       The base class implementation of this method simply prints the text
242       block as it occurred in the input stream).
243

interior_sequence()

245                   $parser->interior_sequence($seq_cmd,$seq_arg,$pod_seq);
246
247       This method should be overridden by subclasses to take the appropriate
248       action when an interior sequence is encountered. An interior sequence
249       is an embedded command within a block of text which appears as a
250       command name (usually a single uppercase character) followed
251       immediately by a string of text which is enclosed in angle brackets.
252       This method is passed the sequence command $seq_cmd and the
253       corresponding text $seq_arg. It is invoked by the interpolate() method
254       for each interior sequence that occurs in the string that it is passed.
255       It should return the desired text string to be used in place of the
256       interior sequence.  The $pod_seq argument is a reference to a
257       "Pod::InteriorSequence" object which contains further information about
258       the interior sequence.  Please see Pod::InputObjects for details if you
259       need to access this additional information.
260
261       Subclass implementations of this method may wish to invoke the nested()
262       method of $pod_seq to see if it is nested inside some other interior-
263       sequence (and if so, which kind).
264
265       The base class implementation of the interior_sequence() method simply
266       returns the raw text of the interior sequence (as it occurred in the
267       input) to the caller.
268

OPTIONAL SUBROUTINE/METHOD OVERRIDES

270       Pod::Parser provides several methods which subclasses may want to
271       override to perform any special pre/post-processing. These methods do
272       not have to be overridden, but it may be useful for subclasses to take
273       advantage of them.
274

new()

276                   my $parser = Pod::Parser->new();
277
278       This is the constructor for Pod::Parser and its subclasses. You do not
279       need to override this method! It is capable of constructing subclass
280       objects as well as base class objects, provided you use any of the
281       following constructor invocation styles:
282
283           my $parser1 = MyParser->new();
284           my $parser2 = new MyParser();
285           my $parser3 = $parser2->new();
286
287       where "MyParser" is some subclass of Pod::Parser.
288
289       Using the syntax "MyParser::new()" to invoke the constructor is not
290       recommended, but if you insist on being able to do this, then the
291       subclass will need to override the new() constructor method. If you do
292       override the constructor, you must be sure to invoke the initialize()
293       method of the newly blessed object.
294
295       Using any of the above invocations, the first argument to the
296       constructor is always the corresponding package name (or object
297       reference). No other arguments are required, but if desired, an
298       associative array (or hash-table) my be passed to the new()
299       constructor, as in:
300
301           my $parser1 = MyParser->new( MYDATA => $value1, MOREDATA => $value2 );
302           my $parser2 = new MyParser( -myflag => 1 );
303
304       All arguments passed to the new() constructor will be treated as
305       key/value pairs in a hash-table. The newly constructed object will be
306       initialized by copying the contents of the given hash-table (which may
307       have been empty). The new() constructor for this class and all of its
308       subclasses returns a blessed reference to the initialized object (hash-
309       table).
310

initialize()

312                   $parser->initialize();
313
314       This method performs any necessary object initialization. It takes no
315       arguments (other than the object instance of course, which is typically
316       copied to a local variable named $self). If subclasses override this
317       method then they must be sure to invoke "$self->SUPER::initialize()".
318

begin_pod()

320                   $parser->begin_pod();
321
322       This method is invoked at the beginning of processing for each POD
323       document that is encountered in the input. Subclasses should override
324       this method to perform any per-document initialization.
325

begin_input()

327                   $parser->begin_input();
328
329       This method is invoked by parse_from_filehandle() immediately before
330       processing input from a filehandle. The base class implementation does
331       nothing, however, subclasses may override it to perform any per-file
332       initializations.
333
334       Note that if multiple files are parsed for a single POD document
335       (perhaps the result of some future "=include" directive) this method is
336       invoked for every file that is parsed. If you wish to perform certain
337       initializations once per document, then you should use begin_pod().
338

end_input()

340                   $parser->end_input();
341
342       This method is invoked by parse_from_filehandle() immediately after
343       processing input from a filehandle. The base class implementation does
344       nothing, however, subclasses may override it to perform any per-file
345       cleanup actions.
346
347       Please note that if multiple files are parsed for a single POD document
348       (perhaps the result of some kind of "=include" directive) this method
349       is invoked for every file that is parsed. If you wish to perform
350       certain cleanup actions once per document, then you should use
351       end_pod().
352

end_pod()

354                   $parser->end_pod();
355
356       This method is invoked at the end of processing for each POD document
357       that is encountered in the input. Subclasses should override this
358       method to perform any per-document finalization.
359

preprocess_line()

361                 $textline = $parser->preprocess_line($text, $line_num);
362
363       This method should be overridden by subclasses that wish to perform any
364       kind of preprocessing for each line of input (before it has been
365       determined whether or not it is part of a POD paragraph). The parameter
366       $text is the input line; and the parameter $line_num is the line number
367       of the corresponding text line.
368
369       The value returned should correspond to the new text to use in its
370       place.  If the empty string or an undefined value is returned then no
371       further processing will be performed for this line.
372
373       Please note that the preprocess_line() method is invoked before the
374       preprocess_paragraph() method. After all (possibly preprocessed) lines
375       in a paragraph have been assembled together and it has been determined
376       that the paragraph is part of the POD documentation from one of the
377       selected sections, then preprocess_paragraph() is invoked.
378
379       The base class implementation of this method returns the given text.
380

preprocess_paragraph()

382                   $textblock = $parser->preprocess_paragraph($text, $line_num);
383
384       This method should be overridden by subclasses that wish to perform any
385       kind of preprocessing for each block (paragraph) of POD documentation
386       that appears in the input stream. The parameter $text is the POD
387       paragraph from the input file; and the parameter $line_num is the line
388       number for the beginning of the corresponding paragraph.
389
390       The value returned should correspond to the new text to use in its
391       place If the empty string is returned or an undefined value is
392       returned, then the given $text is ignored (not processed).
393
394       This method is invoked after gathering up all the lines in a paragraph
395       and after determining the cutting state of the paragraph, but before
396       trying to further parse or interpret them. After preprocess_paragraph()
397       returns, the current cutting state (which is returned by
398       "$self->cutting()") is examined. If it evaluates to true then input
399       text (including the given $text) is cut (not processed) until the next
400       POD directive is encountered.
401
402       Please note that the preprocess_line() method is invoked before the
403       preprocess_paragraph() method. After all (possibly preprocessed) lines
404       in a paragraph have been assembled together and either it has been
405       determined that the paragraph is part of the POD documentation from one
406       of the selected sections or the "-want_nonPODs" option is true, then
407       preprocess_paragraph() is invoked.
408
409       The base class implementation of this method returns the given text.
410

METHODS FOR PARSING AND PROCESSING

412       Pod::Parser provides several methods to process input text. These
413       methods typically won't need to be overridden (and in some cases they
414       can't be overridden), but subclasses may want to invoke them to exploit
415       their functionality.
416

parse_text()

418                   $ptree1 = $parser->parse_text($text, $line_num);
419                   $ptree2 = $parser->parse_text({%opts}, $text, $line_num);
420                   $ptree3 = $parser->parse_text(\%opts, $text, $line_num);
421
422       This method is useful if you need to perform your own interpolation of
423       interior sequences and can't rely upon interpolate to expand them in
424       simple bottom-up order.
425
426       The parameter $text is a string or block of text to be parsed for
427       interior sequences; and the parameter $line_num is the line number
428       corresponding to the beginning of $text.
429
430       parse_text() will parse the given text into a parse-tree of "nodes."
431       and interior-sequences.  Each "node" in the parse tree is either a
432       text-string, or a Pod::InteriorSequence.  The result returned is a
433       parse-tree of type Pod::ParseTree. Please see Pod::InputObjects for
434       more information about Pod::InteriorSequence and Pod::ParseTree.
435
436       If desired, an optional hash-ref may be specified as the first argument
437       to customize certain aspects of the parse-tree that is created and
438       returned. The set of recognized option keywords are:
439
440       -expand_seq => code-ref|method-name
441          Normally, the parse-tree returned by parse_text() will contain an
442          unexpanded "Pod::InteriorSequence" object for each interior-sequence
443          encountered. Specifying -expand_seq tells parse_text() to "expand"
444          every interior-sequence it sees by invoking the referenced function
445          (or named method of the parser object) and using the return value as
446          the expanded result.
447
448          If a subroutine reference was given, it is invoked as:
449
450            &$code_ref( $parser, $sequence )
451
452          and if a method-name was given, it is invoked as:
453
454            $parser->method_name( $sequence )
455
456          where $parser is a reference to the parser object, and $sequence is
457          a reference to the interior-sequence object.  [NOTE: If the
458          interior_sequence() method is specified, then it is invoked
459          according to the interface specified in "interior_sequence()"].
460
461       -expand_text => code-ref|method-name
462          Normally, the parse-tree returned by parse_text() will contain a
463          text-string for each contiguous sequence of characters outside of an
464          interior-sequence. Specifying -expand_text tells parse_text() to
465          "preprocess" every such text-string it sees by invoking the
466          referenced function (or named method of the parser object) and using
467          the return value as the preprocessed (or "expanded") result. [Note
468          that if the result is an interior-sequence, then it will not be
469          expanded as specified by the -expand_seq option; Any such recursive
470          expansion needs to be handled by the specified callback routine.]
471
472          If a subroutine reference was given, it is invoked as:
473
474            &$code_ref( $parser, $text, $ptree_node )
475
476          and if a method-name was given, it is invoked as:
477
478            $parser->method_name( $text, $ptree_node )
479
480          where $parser is a reference to the parser object, $text is the
481          text-string encountered, and $ptree_node is a reference to the
482          current node in the parse-tree (usually an interior-sequence object
483          or else the top-level node of the parse-tree).
484
485       -expand_ptree => code-ref|method-name
486          Rather than returning a "Pod::ParseTree", pass the parse-tree as an
487          argument to the referenced subroutine (or named method of the parser
488          object) and return the result instead of the parse-tree object.
489
490          If a subroutine reference was given, it is invoked as:
491
492            &$code_ref( $parser, $ptree )
493
494          and if a method-name was given, it is invoked as:
495
496            $parser->method_name( $ptree )
497
498          where $parser is a reference to the parser object, and $ptree is a
499          reference to the parse-tree object.
500

interpolate()

502                   $textblock = $parser->interpolate($text, $line_num);
503
504       This method translates all text (including any embedded interior
505       sequences) in the given text string $text and returns the interpolated
506       result. The parameter $line_num is the line number corresponding to the
507       beginning of $text.
508
509       interpolate() merely invokes a private method to recursively expand
510       nested interior sequences in bottom-up order (innermost sequences are
511       expanded first). If there is a need to expand nested sequences in some
512       alternate order, use parse_text instead.
513

parse_from_filehandle()

515                   $parser->parse_from_filehandle($in_fh,$out_fh);
516
517       This method takes an input filehandle (which is assumed to already be
518       opened for reading) and reads the entire input stream looking for
519       blocks (paragraphs) of POD documentation to be processed. If no first
520       argument is given the default input filehandle "STDIN" is used.
521
522       The $in_fh parameter may be any object that provides a getline() method
523       to retrieve a single line of input text (hence, an appropriate wrapper
524       object could be used to parse PODs from a single string or an array of
525       strings).
526
527       Using "$in_fh->getline()", input is read line-by-line and assembled
528       into paragraphs or "blocks" (which are separated by lines containing
529       nothing but whitespace). For each block of POD documentation
530       encountered it will invoke a method to parse the given paragraph.
531
532       If a second argument is given then it should correspond to a filehandle
533       where output should be sent (otherwise the default output filehandle is
534       "STDOUT" if no output filehandle is currently in use).
535
536       NOTE: For performance reasons, this method caches the input stream at
537       the top of the stack in a local variable. Any attempts by clients to
538       change the stack contents during processing when in the midst executing
539       of this method will not affect the input stream used by the current
540       invocation of this method.
541
542       This method does not usually need to be overridden by subclasses.
543

parse_from_file()

545                   $parser->parse_from_file($filename,$outfile);
546
547       This method takes a filename and does the following:
548
549       · opens the input and output files for reading (creating the
550         appropriate filehandles)
551
552       · invokes the parse_from_filehandle() method passing it the
553         corresponding input and output filehandles.
554
555       · closes the input and output files.
556
557       If the special input filename "", "-" or "<&STDIN" is given then the
558       STDIN filehandle is used for input (and no open or close is performed).
559       If no input filename is specified then "-" is implied. Filehandle
560       references, or objects that support the regular IO operations (like
561       "<$fh>" or "$fh-<Egt"getline>) are also accepted; the handles must
562       already be opened.
563
564       If a second argument is given then it should be the name of the desired
565       output file. If the special output filename "-" or ">&STDOUT" is given
566       then the STDOUT filehandle is used for output (and no open or close is
567       performed). If the special output filename ">&STDERR" is given then the
568       STDERR filehandle is used for output (and no open or close is
569       performed). If no output filehandle is currently in use and no output
570       filename is specified, then "-" is implied.  Alternatively, filehandle
571       references or objects that support the regular IO operations (like
572       "print", e.g. IO::String) are also accepted; the object must already be
573       opened.
574
575       This method does not usually need to be overridden by subclasses.
576

ACCESSOR METHODS

578       Clients of Pod::Parser should use the following methods to access
579       instance data fields:
580

errorsub()

582                   $parser->errorsub("method_name");
583                   $parser->errorsub(\&warn_user);
584                   $parser->errorsub(sub { print STDERR, @_ });
585
586       Specifies the method or subroutine to use when printing error messages
587       about POD syntax. The supplied method/subroutine must return TRUE upon
588       successful printing of the message. If "undef" is given, then the carp
589       builtin is used to issue error messages (this is the default behavior).
590
591                   my $errorsub = $parser->errorsub()
592                   my $errmsg = "This is an error message!\n"
593                   (ref $errorsub) and &{$errorsub}($errmsg)
594                       or (defined $errorsub) and $parser->$errorsub($errmsg)
595                           or  carp($errmsg);
596
597       Returns a method name, or else a reference to the user-supplied
598       subroutine used to print error messages. Returns "undef" if the carp
599       builtin is used to issue error messages (this is the default behavior).
600

cutting()

602                   $boolean = $parser->cutting();
603
604       Returns the current "cutting" state: a boolean-valued scalar which
605       evaluates to true if text from the input file is currently being "cut"
606       (meaning it is not considered part of the POD document).
607
608                   $parser->cutting($boolean);
609
610       Sets the current "cutting" state to the given value and returns the
611       result.
612

parseopts()

614       When invoked with no additional arguments, parseopts returns a
615       hashtable of all the current parsing options.
616
617                   ## See if we are parsing non-POD sections as well as POD ones
618                   my %opts = $parser->parseopts();
619                   $opts{'-want_nonPODs}' and print "-want_nonPODs\n";
620
621       When invoked using a single string, parseopts treats the string as the
622       name of a parse-option and returns its corresponding value if it exists
623       (returns "undef" if it doesn't).
624
625                   ## Did we ask to see '=cut' paragraphs?
626                   my $want_cut = $parser->parseopts('-process_cut_cmd');
627                   $want_cut and print "-process_cut_cmd\n";
628
629       When invoked with multiple arguments, parseopts treats them as
630       key/value pairs and the specified parse-option names are set to the
631       given values. Any unspecified parse-options are unaffected.
632
633                   ## Set them back to the default
634                   $parser->parseopts(-warnings => 0);
635
636       When passed a single hash-ref, parseopts uses that hash to completely
637       reset the existing parse-options, all previous parse-option values are
638       lost.
639
640                   ## Reset all options to default
641                   $parser->parseopts( { } );
642
643       See "PARSING OPTIONS" for more information on the name and meaning of
644       each parse-option currently recognized.
645

output_file()

647                   $fname = $parser->output_file();
648
649       Returns the name of the output file being written.
650

output_handle()

652                   $fhandle = $parser->output_handle();
653
654       Returns the output filehandle object.
655

input_file()

657                   $fname = $parser->input_file();
658
659       Returns the name of the input file being read.
660

input_handle()

662                   $fhandle = $parser->input_handle();
663
664       Returns the current input filehandle object.
665

PRIVATE METHODS AND DATA

667       Pod::Parser makes use of several internal methods and data fields which
668       clients should not need to see or use. For the sake of avoiding name
669       collisions for client data and methods, these methods and fields are
670       briefly discussed here. Determined hackers may obtain further
671       information about them by reading the Pod::Parser source code.
672
673       Private data fields are stored in the hash-object whose reference is
674       returned by the new() constructor for this class. The names of all
675       private methods and data-fields used by Pod::Parser begin with a prefix
676       of "_" and match the regular expression "/^_\w+$/".
677

TREE-BASED PARSING

679       If straightforward stream-based parsing wont meet your needs (as is
680       likely the case for tasks such as translating PODs into structured
681       markup languages like HTML and XML) then you may need to take the tree-
682       based approach. Rather than doing everything in one pass and calling
683       the interpolate() method to expand sequences into text, it may be
684       desirable to instead create a parse-tree using the parse_text() method
685       to return a tree-like structure which may contain an ordered list of
686       children (each of which may be a text-string, or a similar tree-like
687       structure).
688
689       Pay special attention to "METHODS FOR PARSING AND PROCESSING" and to
690       the objects described in Pod::InputObjects. The former describes the
691       gory details and parameters for how to customize and extend the parsing
692       behavior of Pod::Parser. Pod::InputObjects provides several objects
693       that may all be used interchangeably as parse-trees. The most obvious
694       one is the Pod::ParseTree object. It defines the basic interface and
695       functionality that all things trying to be a POD parse-tree should do.
696       A Pod::ParseTree is defined such that each "node" may be a text-string,
697       or a reference to another parse-tree.  Each Pod::Paragraph object and
698       each Pod::InteriorSequence object also supports the basic parse-tree
699       interface.
700
701       The parse_text() method takes a given paragraph of text, and returns a
702       parse-tree that contains one or more children, each of which may be a
703       text-string, or an InteriorSequence object. There are also callback-
704       options that may be passed to parse_text() to customize the way it
705       expands or transforms interior-sequences, as well as the returned
706       result. These callbacks can be used to create a parse-tree with custom-
707       made objects (which may or may not support the parse-tree interface,
708       depending on how you choose to do it).
709
710       If you wish to turn an entire POD document into a parse-tree, that
711       process is fairly straightforward. The parse_text() method is the key
712       to doing this successfully. Every paragraph-callback (i.e. the
713       polymorphic methods for command(), verbatim(), and textblock()
714       paragraphs) takes a Pod::Paragraph object as an argument. Each
715       paragraph object has a parse_tree() method that can be used to get or
716       set a corresponding parse-tree. So for each of those paragraph-callback
717       methods, simply call parse_text() with the options you desire, and then
718       use the returned parse-tree to assign to the given paragraph object.
719
720       That gives you a parse-tree for each paragraph - so now all you need is
721       an ordered list of paragraphs. You can maintain that yourself as a data
722       element in the object/hash. The most straightforward way would be
723       simply to use an array-ref, with the desired set of custom "options"
724       for each invocation of parse_text. Let's assume the desired option-set
725       is given by the hash %options. Then we might do something like the
726       following:
727
728           package MyPodParserTree;
729
730           @ISA = qw( Pod::Parser );
731
732           ...
733
734           sub begin_pod {
735               my $self = shift;
736               $self->{'-paragraphs'} = [];  ## initialize paragraph list
737           }
738
739           sub command {
740               my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
741               my $ptree = $parser->parse_text({%options}, $paragraph, ...);
742               $pod_para->parse_tree( $ptree );
743               push @{ $self->{'-paragraphs'} }, $pod_para;
744           }
745
746           sub verbatim {
747               my ($parser, $paragraph, $line_num, $pod_para) = @_;
748               push @{ $self->{'-paragraphs'} }, $pod_para;
749           }
750
751           sub textblock {
752               my ($parser, $paragraph, $line_num, $pod_para) = @_;
753               my $ptree = $parser->parse_text({%options}, $paragraph, ...);
754               $pod_para->parse_tree( $ptree );
755               push @{ $self->{'-paragraphs'} }, $pod_para;
756           }
757
758           ...
759
760           package main;
761           ...
762           my $parser = new MyPodParserTree(...);
763           $parser->parse_from_file(...);
764           my $paragraphs_ref = $parser->{'-paragraphs'};
765
766       Of course, in this module-author's humble opinion, I'd be more inclined
767       to use the existing Pod::ParseTree object than a simple array. That way
768       everything in it, paragraphs and sequences, all respond to the same
769       core interface for all parse-tree nodes. The result would look
770       something like:
771
772           package MyPodParserTree2;
773
774           ...
775
776           sub begin_pod {
777               my $self = shift;
778               $self->{'-ptree'} = new Pod::ParseTree;  ## initialize parse-tree
779           }
780
781           sub parse_tree {
782               ## convenience method to get/set the parse-tree for the entire POD
783               (@_ > 1)  and  $_[0]->{'-ptree'} = $_[1];
784               return $_[0]->{'-ptree'};
785           }
786
787           sub command {
788               my ($parser, $command, $paragraph, $line_num, $pod_para) = @_;
789               my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
790               $pod_para->parse_tree( $ptree );
791               $parser->parse_tree()->append( $pod_para );
792           }
793
794           sub verbatim {
795               my ($parser, $paragraph, $line_num, $pod_para) = @_;
796               $parser->parse_tree()->append( $pod_para );
797           }
798
799           sub textblock {
800               my ($parser, $paragraph, $line_num, $pod_para) = @_;
801               my $ptree = $parser->parse_text({<<options>>}, $paragraph, ...);
802               $pod_para->parse_tree( $ptree );
803               $parser->parse_tree()->append( $pod_para );
804           }
805
806           ...
807
808           package main;
809           ...
810           my $parser = new MyPodParserTree2(...);
811           $parser->parse_from_file(...);
812           my $ptree = $parser->parse_tree;
813           ...
814
815       Now you have the entire POD document as one great big parse-tree. You
816       can even use the -expand_seq option to parse_text to insert whole
817       different kinds of objects. Just don't expect Pod::Parser to know what
818       to do with them after that. That will need to be in your code. Or,
819       alternatively, you can insert any object you like so long as it
820       conforms to the Pod::ParseTree interface.
821
822       One could use this to create subclasses of Pod::Paragraphs and
823       Pod::InteriorSequences for specific commands (or to create your own
824       custom node-types in the parse-tree) and add some kind of emit() method
825       to each custom node/subclass object in the tree. Then all you'd need to
826       do is recursively walk the tree in the desired order, processing the
827       children (most likely from left to right) by formatting them if they
828       are text-strings, or by calling their emit() method if they are
829       objects/references.
830

CAVEATS

832       Please note that POD has the notion of "paragraphs": this is something
833       starting after a blank (read: empty) line, with the single exception of
834       the file start, which is also starting a paragraph. That means that
835       especially a command (e.g. "=head1") must be preceded with a blank
836       line; "__END__" is not a blank line.
837

SEE ALSO

839       Pod::InputObjects, Pod::Select
840
841       Pod::InputObjects defines POD input objects corresponding to command
842       paragraphs, parse-trees, and interior-sequences.
843
844       Pod::Select is a subclass of Pod::Parser which provides the ability to
845       selectively include and/or exclude sections of a POD document from
846       being translated based upon the current heading, subheading,
847       subsubheading, etc.
848

AUTHOR

850       Please report bugs using <http://rt.cpan.org>.
851
852       Brad Appleton <bradapp@enteract.com>
853
854       Based on code for Pod::Text written by Tom Christiansen
855       <tchrist@mox.perl.com>
856

LICENSE

858       Pod-Parser is free software; you can redistribute it and/or modify it
859       under the terms of the Artistic License distributed with Perl version
860       5.000 or (at your option) any later version. Please refer to the
861       Artistic License that came with your Perl distribution for more
862       details. If your version of Perl was not distributed under the terms of
863       the Artistic License, than you may distribute PodParser under the same
864       terms as Perl itself.
865
866
867
868perl v5.30.0                      2019-07-26                    Pod::Parser(3)
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