[pod-constants.git] / lib / Pod / Constants.pm

# Copyright (C) 2001, 2002, 2007 Sam Vilain.  All Rights Reserved.
# This module is free software. It may be used, redistributed and/or
# modified under the terms of the Perl Artistic License, version 2 or
# later, OR the terms of the GNU General Public License, v3 or later.

package Pod::Constants;

use 5.006002;
use strict;
use warnings;

use base qw(Pod::Parser Exporter);
use Carp;

our $VERSION = 0.17;

# An ugly hack to go from caller() to the relevant parser state
# variable
my %parsers;

sub end_input {
	#my ($parser, $command, $paragraph, $line_num) = (@_);
	my $parser = shift;

	return unless $parser->{active};

	print "Found end of $parser->{active}\n" if $parser->{DEBUG};
	my $whereto = $parser->{wanted_pod_tags}->{$parser->{active}};
	print "\$_ will be set to:\n---\n$parser->{paragraphs}\n---\n" if $parser->{DEBUG};

	$parser->{paragraphs} =~ s/^\s*|\s*$//gs if $parser->{trimmed_tags}->{$parser->{active}};

	if (ref $whereto eq "CODE") {
		print "calling sub\n" if $parser->{DEBUG};
		local ($_) = $parser->{paragraphs};
		$whereto->();
		print "done\n" if $parser->{DEBUG};
	} elsif (ref $whereto eq "SCALAR") {
		print "inserting into scalar\n" if $parser->{DEBUG};
		$$whereto = $parser->{paragraphs};
	} elsif (ref $whereto eq "ARRAY") {
		print "inserting into array\n" if $parser->{DEBUG};
		@$whereto = split /\n/, $parser->{paragraphs};
	} elsif (ref $whereto eq "HASH") {
		print "inserting into hash\n" if $parser->{DEBUG};
		# Oh, sorry, should I be in LISP101?
		%$whereto = (
			map { map { s/^\s*|\s*$//g; $_ } split /=>/, $_ } grep m/^
					 ( (?:[^=]|=[^>])+ )   # scan up to "=>"
					 =>
					 ( (?:[^=]|=[^>])+ =? )# don't allow more "=>"'s
					 $/x, split /\n/, $parser->{paragraphs});
	} else { die $whereto }
	$parser->{active} = undef;
}

# Pod::Parser overloaded command
sub command {
	my ($parser, $command, $paragraph, $line_num) = @_;

	$paragraph =~ s/(?:\r\n|\n\r)/\n/g;

	print "Got command =$command, value=$paragraph\n" if $parser->{DEBUG};

	$parser->end_input() if $parser->{active};

	my ($lookup);
	# first check for a catch-all for this command type
	if ( exists $parser->{wanted_pod_tags}->{"*$command"} ) {
		$parser->{paragraphs} = $paragraph;
		$parser->{active} = "*$command";
	} elsif ($command =~ m/^(head\d+|item|(for|begin))$/) {
		if ( $2 ) {
			# if it's a "for" or "begin" section, the title is the
			# first word only
			($lookup, $parser->{paragraphs}) = $paragraph =~ m/^\s*(\S*)\s*(.*)/s;
		} else {
			# otherwise, it's up to the end of the line
			($lookup, $parser->{paragraphs}) = $paragraph =~ m/^\s*(\S[^\n]*?)\s*\n(.*)$/s;
		}

		# Look for a match by name
		if (defined $lookup && exists $parser->{wanted_pod_tags}->{$lookup}) {
			print "Found $lookup\n" if ($parser->{DEBUG});
			$parser->{active} = $lookup;
		} elsif ($parser->{DEBUG}) {
			local $^W = 0;
			print "Ignoring =$command $paragraph (lookup = $lookup)\n"
		}

	} else {
		# nothing
		print "Ignoring =$command (not known)\n" if $parser->{DEBUG};
	}
}

# Pod::Parser overloaded verbatim
sub verbatim {
	my ($parser, $paragraph, $line_num) = @_;
	$paragraph =~ s/(?:\r\n|\n\r)/\n/g;

	my $status = $parser->{active} ? "using" : "ignoring";
	print "Got paragraph: $paragraph ($status)\n" if $parser->{DEBUG};

	$parser->{paragraphs} .= $paragraph if defined $parser->{active}
}

# Pod::Parser overloaded textblock
sub textblock { goto \&verbatim }

sub import {
	my $class = shift;

	# if no args, just return
	return unless (@_);

	# try to guess the source file of the caller
	my $source_file;
	if (caller ne "main") {
		(my $module = caller().".pm") =~ s|::|/|g;
		$source_file = $INC{$module};
	}
	$source_file ||= $0;

	croak "Cannot find source file (guessed $source_file) for package ".caller unless -f $source_file;

	# nasty tricks with the stack so we don't have to be silly with
	# caller()
	unshift @_, $source_file;
	goto \&import_from_file;
}

sub import_from_file {
	my $filename = shift;

	my $parser = __PACKAGE__->new();

	$parser->{wanted_pod_tags} = {};
	$parser->{trimmed_tags} = {};
	$parser->{trim_next} = 0;
	$parser->{DEBUG} = 0;
	$parser->{active} = undef;
	$parsers{caller()} = $parser;

	$parser->add_hook(@_);

	print "Pod::Parser: DEBUG: Opening $filename for reading\n" if $parser->{DEBUG};
	open my $fh, "<$filename" or die "cannot open $filename for reading; $!";

	$parser->parse_from_filehandle($fh, \*STDOUT);

	close $fh;
}

sub add_hook {
	my $parser;
	if (UNIVERSAL::isa($_[0], __PACKAGE__)) {
		$parser = shift;
	} else {
		$parser = $parsers{caller()} or die "add_hook called, but don't know what for - caller = ".caller;
	}
	while (my ($pod_tag, $var) = splice @_, 0, 2) {
		#print "$pod_tag: $var\n";
		if (lc($pod_tag) eq "-trim") {
			$parser->{trim_next} = $var;
		} elsif ( lc($pod_tag) eq "-debug" ) {
			$parser->{DEBUG} = $var;
		} elsif (lc($pod_tag) eq "-usage") {
			# an idea for later - automatic "usage"
			#%wanted_pod_tags{@tags}
		} else {
			if ((ref $var) =~ /^(?:SCALAR|CODE|ARRAY|HASH)$/) {
				print "Will look for $pod_tag.\n" if $parser->{DEBUG};
				$parser->{wanted_pod_tags}->{$pod_tag} = $var;
				$parser->{trimmed_tags}->{$pod_tag} = 1 if $parser->{trim_next};
			} else {
				die "Sorry - need a reference to import POD sections into, not the scalar value $var"
			}
		}
	}
}

sub delete_hook {
	my $parser;
	if ( UNIVERSAL::isa($_[0], __PACKAGE__) ) {
		$parser = shift;
	} else {
		$parser = $parsers{caller()} or die "delete_hook called, but don't know what for - caller = ".caller;
	}
	while ( my $label = shift ) {
		delete $parser->{wanted_pod_tags}->{$label};
		delete $parser->{trimmed_tags}->{$label};
	}
}

1.4142;
__END__

=encoding utf-8

=head1 NAME

Pod::Constants - Include constants from POD

=head1 SYNOPSIS

 our ($myvar, $VERSION, @myarray, $html, %myhash);

 use Pod::Constants -trim => 1,
     'Pod Section Name' => \$myvar,
     'Version' => sub { eval },
     'Some list' => \@myarray,
     html => \$html,
     'Some hash' => \%myhash;

 =head2 Pod Section Name

 This string will be loaded into $myvar

 =head2 Version

 # This is an example of using a closure.  $_ is set to the
 # contents of the paragraph.  In this example, "eval" is
 # used to execute this code at run time.
 $VERSION = 0.17;

 =head2 Some list

 Each line from this section of the file
 will be placed into a separate array element.
 For example, this is $myarray[2].

 =head2 Some hash

 This text will not go into the hash, because
 it doesn't look like a definition list.
     key1 => Some value (this will go into the hash)
     var2 => Some Other value (so will this)
     wtf = This won't make it in.

 =head2 %myhash's value after the above:

    ( key1 => "Some value (this will go into the hash)",
      var2 => "Some Other value (so will this)"          )

 =begin html <p>This text will be in $html</p>

 =cut

=head1 DESCRIPTION

This module allows you to specify those constants that should be
documented in your POD, and pull them out a run time in a fairly
arbitrary fashion.

Pod::Constants uses Pod::Parser to do the parsing of the source file.
It has to open the source file it is called from, and does so directly
either by lookup in %INC or by assuming it is $0 if the caller is
"main" (or it can't find %INC{caller()})

=head2 ARBITARY DECISIONS

I have made this code only allow the "Pod Section Name" to match
`headN', `item', `for' and `begin' POD sections.  If you have a good
reason why you think it should match other POD sections, drop me a
line and if I'm convinced I'll put it in the standard version.

For `for' and `begin' sections, only the first word is counted as
being a part of the specifier, as opposed to `headN' and `item', where
the entire rest of the line counts.

=head1 FUNCTIONS

=head2 import(@args)

This function is called when we are "use"'d.  It determines the source
file by inspecting the value of caller() or $0.

The form of @args is HOOK => $where.

$where may be a scalar reference, in which case the contents of the
POD section called "HOOK" will be loaded into $where.

$where may be an array reference, in which case the contents of the
array will be the contents of the POD section called "HOOK", split
into lines.

$where may be a hash reference, in which case any lines with a "=>"
symbol present will have everything on the left have side of the =>
operator as keys and everything on the right as values.  You do not
need to quote either, nor have trailing commas at the end of the
lines.

$where may be a code reference (sub { }), in which case the sub is
called when the hook is encountered.  $_ is set to the value of the
POD paragraph.

You may also specify the behaviour of whitespace trimming; by default,
no trimming is done except on the HOOK names.  Setting "-trim => 1"
turns on a package "global" (until the next time import is called)
that will trim the $_ sent for processing by the hook processing
function (be it a given function, or the built-in array/hash
splitters) for leading and trailing whitespace.

The name of HOOK is matched against any "=head1", "=head2", "=item",
"=for", "=begin" value.  If you specify the special hooknames "*item",
"*head1", etc, then you will get a function that is run for every 

Note that the supplied functions for array and hash splitting are
exactly equivalent to fairly simple Perl blocks:

Array:

  HOOK => sub { @array = split /\n/, $_ }

Hash:

  HOOK => sub {
  %hash =
      (map { map { s/^\s+|\s+$//g; $_ } split /=>/, $_ }
        (grep m/^
            ( (?:[^=]|=[^>])+ )   # scan up to "=>"
            =>
            ( (?:[^=]|=[^>])+ =? )# don't allow more "=>"'s
            $/x, split /\n/, $_));
  }

Well, they're simple if you can grok map, a regular expression like
that and a functional programming style.  If you can't I'm sure it is
probably voodoo to you.

Here's the procedural equivalent:

  HOOK => sub {
     for my $line (split /\n/, $_) {
         my ($key, $value, $junk) = split /=>/, $line;
         next if $junk;
         $key =~ s/^\s+|\s+$//g
         $value =~ s/^\s+|\s+$//g
         $hash{$key} = $value;
     }
  },

=head2 import_from_file($filename, @args)

Very similar to straight "import", but you specify the source filename
explicitly.

=head2 add_hook(NAME => value)

This function adds another hook, it is useful for dynamic updating of
parsing through the document.

For an example, please see t/01-constants.t in the source
distribution.  More detailed examples will be added in a later
release.

=head2 delete_hook(@list)

Deletes the named hooks.  Companion function to add_hook

=head2 CLOSURES AS DESTINATIONS

If the given value is a ref CODE, then that function is called, with
$_ set to the value of the paragraph.  This can be very useful for
applying your own custom mutations to the POD to change it from human
readable text into something your program can use.

After I added this function, I just kept on thinking of cool uses for
it.  The nice, succinct code you can make with it is one of
Pod::Constant's strongest features.

Below are some examples.

=head1 EXAMPLES

=head2 Module Makefile.PL maintenance

Tired of keeping those module Makefile.PL's up to date?  Note: This
method seems to break dh-make-perl.

=head2 Example Makefile.PL

 eval "use Pod::Constants";
 ($Pod::Constants::VERSION >= 0.11)
     or die <<EOF
 ####
 ####  ERROR: This module requires Pod::Constants 0.11 or
 ####  higher to be installed.
 ####
 EOF

 my ($VERSION, $NAME, $PREREQ_PM, $ABSTRACT, $AUTHOR);
 Pod::Constants::import_from_file 
     (
      'MyTestModule.pm',
      'MODULE RELEASE' => sub { ($VERSION) = m/(\d+\.\d+)/ },
      'DEPENDENCIES' => ($PREREQ_PM = { }),
       -trim => 1,
      'NAME' => sub { $ABSTRACT=$_; ($NAME) = m/(\S+)/ },
      'AUTHOR' => \$AUTHOR,
     );

 WriteMakefile
     (
      'NAME'        => $NAME,
      'PREREQ_PM'        => $PREREQ_PM,
      'VERSION'          => $VERSION,
      ($] >= 5.005 ?    ## Add these new keywords supported since 5.005
       (ABSTRACT         => $ABSTRACT,
        AUTHOR           => $AUTHOR) : ()),
     );

=head2 Corresponding Module

 =head1 NAME

 MyTestModule - Demonstrate Pod::Constant's Makefile.PL usefulness

 =head2 MODULE RELEASE

 This is release 1.05 of this module.

 =head2 DEPENDENCIES

 The following modules are required to make this module:

    Some::Module => 0.02

 =head2 AUTHOR

 Ima Twat <ima@twat.name>

 =cut

 our $VERSION;
 use Pod::Constants -trim => 1,
     'MODULE RELEASE' => sub { ($VERSION) = m/(\d+\.\d+) or die };

=head1 AUTHOR

Sam Vilain, <samv@cpan.org>

=head1 BUGS/TODO

I keep thinking it would be nice to be able to import an =item list
into an array or something, eg for a program argument list.  But I'm
not too sure how it would be all that useful in practice; you'd end up
putting the function names for callbacks in the pod or something
(perhaps not all that bad).

Would this be useful?

 Pod::Constants::import(Foo::SECTION => \$myvar);

Debug output is not very readable

=head1 PATCHES WELCOME

If you have any suggestions for enhancements, they are much more likely
to happen if you submit them as a patch to the distribution.

Source is kept at

  git://utsl.gen.nz/Pod-Constants 


=cut
Commit	Line	Data
	1	# Copyright (C) 2001, 2002, 2007 Sam Vilain. All Rights Reserved.
	2	# This module is free software. It may be used, redistributed and/or
	3	# modified under the terms of the Perl Artistic License, version 2 or
	4	# later, OR the terms of the GNU General Public License, v3 or later.
	5
	6	package Pod::Constants;
	7
	8	use 5.006002;
	9	use strict;
	10	use warnings;
	11
	12	use base qw(Pod::Parser Exporter);
	13	use Carp;
	14
	15	our $VERSION = 0.17;
	16
	17	# An ugly hack to go from caller() to the relevant parser state
	18	# variable
	19	my %parsers;
	20
	21	sub end_input {
	22	#my ($parser, $command, $paragraph, $line_num) = (@_);
	23	my $parser = shift;
	24
	25	return unless $parser->{active};
	26
	27	print "Found end of $parser->{active}\n" if $parser->{DEBUG};
	28	my $whereto = $parser->{wanted_pod_tags}->{$parser->{active}};
	29	print "\$_ will be set to:\n---\n$parser->{paragraphs}\n---\n" if $parser->{DEBUG};
	30
	31	$parser->{paragraphs} =~ s/^\s\|\s$//gs if $parser->{trimmed_tags}->{$parser->{active}};
	32
	33	if (ref $whereto eq "CODE") {
	34	print "calling sub\n" if $parser->{DEBUG};
	35	local ($_) = $parser->{paragraphs};
	36	$whereto->();
	37	print "done\n" if $parser->{DEBUG};
	38	} elsif (ref $whereto eq "SCALAR") {
	39	print "inserting into scalar\n" if $parser->{DEBUG};
	40	$$whereto = $parser->{paragraphs};
	41	} elsif (ref $whereto eq "ARRAY") {
	42	print "inserting into array\n" if $parser->{DEBUG};
	43	@$whereto = split /\n/, $parser->{paragraphs};
	44	} elsif (ref $whereto eq "HASH") {
	45	print "inserting into hash\n" if $parser->{DEBUG};
	46	# Oh, sorry, should I be in LISP101?
	47	%$whereto = (
	48	map { map { s/^\s\|\s$//g; $_ } split /=>/, $_ } grep m/^
	49	( (?:[^=]\|=[^>])+ ) # scan up to "=>"
	50	=>
	51	( (?:[^=]\|=[^>])+ =? )# don't allow more "=>"'s
	52	$/x, split /\n/, $parser->{paragraphs});
	53	} else { die $whereto }
	54	$parser->{active} = undef;
	55	}
	56
	57	# Pod::Parser overloaded command
	58	sub command {
	59	my ($parser, $command, $paragraph, $line_num) = @_;
	60
	61	$paragraph =~ s/(?:\r\n\|\n\r)/\n/g;
	62
	63	print "Got command =$command, value=$paragraph\n" if $parser->{DEBUG};
	64
	65	$parser->end_input() if $parser->{active};
	66
	67	my ($lookup);
	68	# first check for a catch-all for this command type
	69	if ( exists $parser->{wanted_pod_tags}->{"*$command"} ) {
	70	$parser->{paragraphs} = $paragraph;
	71	$parser->{active} = "*$command";
	72	} elsif ($command =~ m/^(head\d+\|item\|(for\|begin))$/) {
	73	if ( $2 ) {
	74	# if it's a "for" or "begin" section, the title is the
	75	# first word only
	76	($lookup, $parser->{paragraphs}) = $paragraph =~ m/^\s(\S)\s(.)/s;
	77	} else {
	78	# otherwise, it's up to the end of the line
	79	($lookup, $parser->{paragraphs}) = $paragraph =~ m/^\s(\S[^\n]?)\s\n(.)$/s;
	80	}
	81
	82	# Look for a match by name
	83	if (defined $lookup && exists $parser->{wanted_pod_tags}->{$lookup}) {
	84	print "Found $lookup\n" if ($parser->{DEBUG});
	85	$parser->{active} = $lookup;
	86	} elsif ($parser->{DEBUG}) {
	87	local $^W = 0;
	88	print "Ignoring =$command $paragraph (lookup = $lookup)\n"
	89	}
	90
	91	} else {
	92	# nothing
	93	print "Ignoring =$command (not known)\n" if $parser->{DEBUG};
	94	}
	95	}
	96
	97	# Pod::Parser overloaded verbatim
	98	sub verbatim {
	99	my ($parser, $paragraph, $line_num) = @_;
	100	$paragraph =~ s/(?:\r\n\|\n\r)/\n/g;
	101
	102	my $status = $parser->{active} ? "using" : "ignoring";
	103	print "Got paragraph: $paragraph ($status)\n" if $parser->{DEBUG};
	104
	105	$parser->{paragraphs} .= $paragraph if defined $parser->{active}
	106	}
	107
	108	# Pod::Parser overloaded textblock
	109	sub textblock { goto \&verbatim }
	110
	111	sub import {
	112	my $class = shift;
	113
	114	# if no args, just return
	115	return unless (@_);
	116
	117	# try to guess the source file of the caller
	118	my $source_file;
	119	if (caller ne "main") {
	120	(my $module = caller().".pm") =~ s\|::\|/\|g;
	121	$source_file = $INC{$module};
	122	}
	123	$source_file \|\|= $0;
	124
	125	croak "Cannot find source file (guessed $source_file) for package ".caller unless -f $source_file;
	126
	127	# nasty tricks with the stack so we don't have to be silly with
	128	# caller()
	129	unshift @_, $source_file;
	130	goto \&import_from_file;
	131	}
	132
	133	sub import_from_file {
	134	my $filename = shift;
	135
	136	my $parser = __PACKAGE__->new();
	137
	138	$parser->{wanted_pod_tags} = {};
	139	$parser->{trimmed_tags} = {};
	140	$parser->{trim_next} = 0;
	141	$parser->{DEBUG} = 0;
	142	$parser->{active} = undef;
	143	$parsers{caller()} = $parser;
	144
	145	$parser->add_hook(@_);
	146
	147	print "Pod::Parser: DEBUG: Opening $filename for reading\n" if $parser->{DEBUG};
	148	open my $fh, "<$filename" or die "cannot open $filename for reading; $!";
	149
	150	$parser->parse_from_filehandle($fh, \*STDOUT);
	151
	152	close $fh;
	153	}
	154
	155	sub add_hook {
	156	my $parser;
	157	if (UNIVERSAL::isa($_[0], __PACKAGE__)) {
	158	$parser = shift;
	159	} else {
	160	$parser = $parsers{caller()} or die "add_hook called, but don't know what for - caller = ".caller;
	161	}
	162	while (my ($pod_tag, $var) = splice @_, 0, 2) {
	163	#print "$pod_tag: $var\n";
	164	if (lc($pod_tag) eq "-trim") {
	165	$parser->{trim_next} = $var;
	166	} elsif ( lc($pod_tag) eq "-debug" ) {
	167	$parser->{DEBUG} = $var;
	168	} elsif (lc($pod_tag) eq "-usage") {
	169	# an idea for later - automatic "usage"
	170	#%wanted_pod_tags{@tags}
	171	} else {
	172	if ((ref $var) =~ /^(?:SCALAR\|CODE\|ARRAY\|HASH)$/) {
	173	print "Will look for $pod_tag.\n" if $parser->{DEBUG};
	174	$parser->{wanted_pod_tags}->{$pod_tag} = $var;
	175	$parser->{trimmed_tags}->{$pod_tag} = 1 if $parser->{trim_next};
	176	} else {
	177	die "Sorry - need a reference to import POD sections into, not the scalar value $var"
	178	}
	179	}
	180	}
	181	}
	182
	183	sub delete_hook {
	184	my $parser;
	185	if ( UNIVERSAL::isa($_[0], __PACKAGE__) ) {
	186	$parser = shift;
	187	} else {
	188	$parser = $parsers{caller()} or die "delete_hook called, but don't know what for - caller = ".caller;
	189	}
	190	while ( my $label = shift ) {
	191	delete $parser->{wanted_pod_tags}->{$label};
	192	delete $parser->{trimmed_tags}->{$label};
	193	}
	194	}
	195
	196	1.4142;
	197	__END__
	198
	199	=encoding utf-8
	200
	201	=head1 NAME
	202
	203	Pod::Constants - Include constants from POD
	204
	205	=head1 SYNOPSIS
	206
	207	our ($myvar, $VERSION, @myarray, $html, %myhash);
	208
	209	use Pod::Constants -trim => 1,
	210	'Pod Section Name' => \$myvar,
	211	'Version' => sub { eval },
	212	'Some list' => \@myarray,
	213	html => \$html,
	214	'Some hash' => \%myhash;
	215
	216	=head2 Pod Section Name
	217
	218	This string will be loaded into $myvar
	219
	220	=head2 Version
	221
	222	# This is an example of using a closure. $_ is set to the
	223	# contents of the paragraph. In this example, "eval" is
	224	# used to execute this code at run time.
	225	$VERSION = 0.17;
	226
	227	=head2 Some list
	228
	229	Each line from this section of the file
	230	will be placed into a separate array element.
	231	For example, this is $myarray[2].
	232
	233	=head2 Some hash
	234
	235	This text will not go into the hash, because
	236	it doesn't look like a definition list.
	237	key1 => Some value (this will go into the hash)
	238	var2 => Some Other value (so will this)
	239	wtf = This won't make it in.
	240
	241	=head2 %myhash's value after the above:
	242
	243	( key1 => "Some value (this will go into the hash)",
	244	var2 => "Some Other value (so will this)" )
	245
	246	=begin html <p>This text will be in $html</p>
	247
	248	=cut
	249
	250	=head1 DESCRIPTION
	251
	252	This module allows you to specify those constants that should be
	253	documented in your POD, and pull them out a run time in a fairly
	254	arbitrary fashion.
	255
	256	Pod::Constants uses Pod::Parser to do the parsing of the source file.
	257	It has to open the source file it is called from, and does so directly
	258	either by lookup in %INC or by assuming it is $0 if the caller is
	259	"main" (or it can't find %INC{caller()})
	260
	261	=head2 ARBITARY DECISIONS
	262
	263	I have made this code only allow the "Pod Section Name" to match
	264	`headN', `item', `for' and `begin' POD sections. If you have a good
	265	reason why you think it should match other POD sections, drop me a
	266	line and if I'm convinced I'll put it in the standard version.
	267
	268	For `for' and `begin' sections, only the first word is counted as
	269	being a part of the specifier, as opposed to `headN' and `item', where
	270	the entire rest of the line counts.
	271
	272	=head1 FUNCTIONS
	273
	274	=head2 import(@args)
	275
	276	This function is called when we are "use"'d. It determines the source
	277	file by inspecting the value of caller() or $0.
	278
	279	The form of @args is HOOK => $where.
	280
	281	$where may be a scalar reference, in which case the contents of the
	282	POD section called "HOOK" will be loaded into $where.
	283
	284	$where may be an array reference, in which case the contents of the
	285	array will be the contents of the POD section called "HOOK", split
	286	into lines.
	287
	288	$where may be a hash reference, in which case any lines with a "=>"
	289	symbol present will have everything on the left have side of the =>
	290	operator as keys and everything on the right as values. You do not
	291	need to quote either, nor have trailing commas at the end of the
	292	lines.
	293
	294	$where may be a code reference (sub { }), in which case the sub is
	295	called when the hook is encountered. $_ is set to the value of the
	296	POD paragraph.
	297
	298	You may also specify the behaviour of whitespace trimming; by default,
	299	no trimming is done except on the HOOK names. Setting "-trim => 1"
	300	turns on a package "global" (until the next time import is called)
	301	that will trim the $_ sent for processing by the hook processing
	302	function (be it a given function, or the built-in array/hash
	303	splitters) for leading and trailing whitespace.
	304
	305	The name of HOOK is matched against any "=head1", "=head2", "=item",
	306	"=for", "=begin" value. If you specify the special hooknames "*item",
	307	"*head1", etc, then you will get a function that is run for every
	308
	309	Note that the supplied functions for array and hash splitting are
	310	exactly equivalent to fairly simple Perl blocks:
	311
	312	Array:
	313
	314	HOOK => sub { @array = split /\n/, $_ }
	315
	316	Hash:
	317
	318	HOOK => sub {
	319	%hash =
	320	(map { map { s/^\s+\|\s+$//g; $_ } split /=>/, $_ }
	321	(grep m/^
	322	( (?:[^=]\|=[^>])+ ) # scan up to "=>"
	323	=>
	324	( (?:[^=]\|=[^>])+ =? )# don't allow more "=>"'s
	325	$/x, split /\n/, $_));
	326	}
	327
	328	Well, they're simple if you can grok map, a regular expression like
	329	that and a functional programming style. If you can't I'm sure it is
	330	probably voodoo to you.
	331
	332	Here's the procedural equivalent:
	333
	334	HOOK => sub {
	335	for my $line (split /\n/, $_) {
	336	my ($key, $value, $junk) = split /=>/, $line;
	337	next if $junk;
	338	$key =~ s/^\s+\|\s+$//g
	339	$value =~ s/^\s+\|\s+$//g
	340	$hash{$key} = $value;
	341	}
	342	},
	343
	344	=head2 import_from_file($filename, @args)
	345
	346	Very similar to straight "import", but you specify the source filename
	347	explicitly.
	348
	349	=head2 add_hook(NAME => value)
	350
	351	This function adds another hook, it is useful for dynamic updating of
	352	parsing through the document.
	353
	354	For an example, please see t/01-constants.t in the source
	355	distribution. More detailed examples will be added in a later
	356	release.
	357
	358	=head2 delete_hook(@list)
	359
	360	Deletes the named hooks. Companion function to add_hook
	361
	362	=head2 CLOSURES AS DESTINATIONS
	363
	364	If the given value is a ref CODE, then that function is called, with
	365	$_ set to the value of the paragraph. This can be very useful for
	366	applying your own custom mutations to the POD to change it from human
	367	readable text into something your program can use.
	368
	369	After I added this function, I just kept on thinking of cool uses for
	370	it. The nice, succinct code you can make with it is one of
	371	Pod::Constant's strongest features.
	372
	373	Below are some examples.
	374
	375	=head1 EXAMPLES
	376
	377	=head2 Module Makefile.PL maintenance
	378
	379	Tired of keeping those module Makefile.PL's up to date? Note: This
	380	method seems to break dh-make-perl.
	381
	382	=head2 Example Makefile.PL
	383
	384	eval "use Pod::Constants";
	385	($Pod::Constants::VERSION >= 0.11)
	386	or die <<EOF
	387	####
	388	#### ERROR: This module requires Pod::Constants 0.11 or
	389	#### higher to be installed.
	390	####
	391	EOF
	392
	393	my ($VERSION, $NAME, $PREREQ_PM, $ABSTRACT, $AUTHOR);
	394	Pod::Constants::import_from_file
	395	(
	396	'MyTestModule.pm',
	397	'MODULE RELEASE' => sub { ($VERSION) = m/(\d+\.\d+)/ },
	398	'DEPENDENCIES' => ($PREREQ_PM = { }),
	399	-trim => 1,
	400	'NAME' => sub { $ABSTRACT=$_; ($NAME) = m/(\S+)/ },
	401	'AUTHOR' => \$AUTHOR,
	402	);
	403
	404	WriteMakefile
	405	(
	406	'NAME' => $NAME,
	407	'PREREQ_PM' => $PREREQ_PM,
	408	'VERSION' => $VERSION,
	409	($] >= 5.005 ? ## Add these new keywords supported since 5.005
	410	(ABSTRACT => $ABSTRACT,
	411	AUTHOR => $AUTHOR) : ()),
	412	);
	413
	414	=head2 Corresponding Module
	415
	416	=head1 NAME
	417
	418	MyTestModule - Demonstrate Pod::Constant's Makefile.PL usefulness
	419
	420	=head2 MODULE RELEASE
	421
	422	This is release 1.05 of this module.
	423
	424	=head2 DEPENDENCIES
	425
	426	The following modules are required to make this module:
	427
	428	Some::Module => 0.02
	429
	430	=head2 AUTHOR
	431
	432	Ima Twat <ima@twat.name>
	433
	434	=cut
	435
	436	our $VERSION;
	437	use Pod::Constants -trim => 1,
	438	'MODULE RELEASE' => sub { ($VERSION) = m/(\d+\.\d+) or die };
	439
	440	=head1 AUTHOR
	441
	442	Sam Vilain, <samv@cpan.org>
	443
	444	=head1 BUGS/TODO
	445
	446	I keep thinking it would be nice to be able to import an =item list
	447	into an array or something, eg for a program argument list. But I'm
	448	not too sure how it would be all that useful in practice; you'd end up
	449	putting the function names for callbacks in the pod or something
	450	(perhaps not all that bad).
	451
	452	Would this be useful?
	453
	454	Pod::Constants::import(Foo::SECTION => \$myvar);
	455
	456	Debug output is not very readable
	457
	458	=head1 PATCHES WELCOME
	459
	460	If you have any suggestions for enhancements, they are much more likely
	461	to happen if you submit them as a patch to the distribution.
	462
	463	Source is kept at
	464
	465	git://utsl.gen.nz/Pod-Constants
	466
	467
	468	=cut