parser.pm

mrtg 监控,请认真阅读您的文件包然后写出其具体功能

This method might be invoked when printing diagnostic messages, for example,
to obtain the name and line number of the all input files that are currently
being processed.

=end __PRIVATE__

=cut

sub input_streams {
   return $_[0]->{_INPUT_STREAMS};
}

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

=begin __PRIVATE__

=head1 B<top_stream()>

            $hashref = $parser->top_stream();

Returns a reference to the hash-table that represents the element
that is currently at the top (end) of the input stream stack
(see L<"input_streams()">). The return value will be the C<undef>
if the input stack is empty.

This method might be used when printing diagnostic messages, for example,
to obtain the name and line number of the current input file.

=end __PRIVATE__

=cut

sub top_stream {
   return $_[0]->{_TOP_STREAM} || undef;
}

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

=head1 PRIVATE METHODS AND DATA

B<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 B<Pod::Parser> source code.

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

=cut

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

=begin _PRIVATE_

=head1 B<_push_input_stream()>

            $hashref = $parser->_push_input_stream($in_fh,$out_fh);

This method will push the given input stream on the input stack and
perform any necessary beginning-of-document or beginning-of-file
processing. The argument C<$in_fh> is the input stream filehandle to
push, and C<$out_fh> is the corresponding output filehandle to use (if
it is not given or is undefined, then the current output stream is used,
which defaults to standard output if it doesnt exist yet).

The value returned will be reference to the hash-table that represents
the new top of the input stream stack. I<Please Note> that it is
possible for this method to use default values for the input and output
file handles. If this happens, you will need to look at the C<INPUT>
and C<OUTPUT> instance data members to determine their new values.

=end _PRIVATE_

=cut

sub _push_input_stream {
    my ($self, $in_fh, $out_fh) = @_;
    local *myData = $self;

    ## Initialize stuff for the entire document if this is *not*
    ## an included file.
    ##
    ## NOTE: we need to be *very* careful when "defaulting" the output
    ## filehandle. We only want to use a default value if this is the
    ## beginning of the entire document (but *not* if this is an included
    ## file).
    unless (defined  $myData{_TOP_STREAM}) {
        $out_fh  = \*STDOUT  unless (defined $out_fh);
        $myData{_CUTTING}       = 1;   ## current "cutting" state
        $myData{_INPUT_STREAMS} = [];  ## stack of all input streams
    }

    ## Initialize input indicators
    $myData{_OUTFILE} = '(unknown)'  unless (defined  $myData{_OUTFILE});
    $myData{_OUTPUT}  = $out_fh      if (defined  $out_fh);
    $in_fh            = \*STDIN      unless (defined  $in_fh);
    $myData{_INFILE}  = '(unknown)'  unless (defined  $myData{_INFILE});
    $myData{_INPUT}   = $in_fh;
    my $input_top     = $myData{_TOP_STREAM}
                      = new Pod::InputSource(
                            -name        => $myData{_INFILE},
                            -handle      => $in_fh,
                            -was_cutting => $myData{_CUTTING}
                        );
    local *input_stack = $myData{_INPUT_STREAMS};
    push(@input_stack, $input_top);

    ## Perform beginning-of-document and/or beginning-of-input processing
    $self->begin_pod()  if (@input_stack == 1);
    $self->begin_input();

    return  $input_top;
}

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

=begin _PRIVATE_

=head1 B<_pop_input_stream()>

            $hashref = $parser->_pop_input_stream();

This takes no arguments. It will perform any necessary end-of-file or
end-of-document processing and then pop the current input stream from
the top of the input stack.

The value returned will be reference to the hash-table that represents
the new top of the input stream stack.

=end _PRIVATE_

=cut

sub _pop_input_stream {
    my ($self) = @_;
    local *myData = $self;
    local *input_stack = $myData{_INPUT_STREAMS};

    ## Perform end-of-input and/or end-of-document processing
    $self->end_input()  if (@input_stack > 0);
    $self->end_pod()    if (@input_stack == 1);

    ## Restore cutting state to whatever it was before we started
    ## parsing this file.
    my $old_top = pop(@input_stack);
    $myData{_CUTTING} = $old_top->was_cutting();

    ## Dont forget to reset the input indicators
    my $input_top = undef;
    if (@input_stack > 0) {
       $input_top = $myData{_TOP_STREAM} = $input_stack[-1];
       $myData{_INFILE}  = $input_top->name();
       $myData{_INPUT}   = $input_top->handle();
    } else {
       delete $myData{_TOP_STREAM};
       delete $myData{_INPUT_STREAMS};
    }

    return  $input_top;
}

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

=head1 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 everything in one pass and
calling the B<interpolate()> method to expand sequences into text, it
may be desirable to instead create a parse-tree using the B<parse_text()>
method to return a tree-like structure which may contain an ordered list
list of children (each of which may be a text-string, or a similar
tree-like structure).

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

The B<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 B<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 B<parse_text()> method is the key to doing
this successfully. Every paragraph-callback (i.e. the polymorphic methods
for B<command()>, B<verbatim()>, and B<textblock()> paragraphs) takes
a B<Pod::Paragraph> object as an argument. Each paragraph object has a
B<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
B<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 B<parse_text>. Let's assume the desired option-set is
given by the hash C<%options>. Then we might do something like the
following:

    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 B<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
    }

    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 B<-expand_seq> option to B<parse_text> to insert
whole different kinds of objects. Just don't expect B<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 B<Pod::ParseTree> interface.

One could use this to create subclasses of B<Pod::Paragraphs> and
B<Pod::InteriorSequences> for specific commands (or to create your own
custom node-types in the parse-tree) and add some kind of B<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 B<emit()> method if they
are objects/references.

=head1 SEE ALSO

L<Pod::InputObjects>, L<Pod::Select>

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

B<Pod::Select> is a subclass of B<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.

=for __PRIVATE__
B<Pod::Callbacks> is a subclass of B<Pod::Parser> which gives its users
the ability the employ I<callback functions> instead of, or in addition
to, overriding methods of the base class.

=for __PRIVATE__
B<Pod::Select> and B<Pod::Callbacks> do not override any
methods nor do they define any new methods with the same name. Because
of this, they may I<both> be used (in combination) as a base class of
the same subclass in order to combine their functionality without
causing any namespace clashes due to multiple inheritance.

=head1 AUTHOR

Brad Appleton E<lt>[e-mail]<gt>

Based on code for B<Pod::Text> written by
Tom Christiansen E<lt>[e-mail]<gt>

=cut

1;