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#============================================================= -*-Perl-*- # # Pod::POM::Node # # DESCRIPTION # Base class for a node in a Pod::POM tree. # # AUTHOR # Andy Wardley <abw@wardley.org> # # COPYRIGHT # Copyright (C) 2000-2003 Andy Wardley. All Rights Reserved. # # This module is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. # # REVISION # $Id: Node.pm 88 2010-04-02 13:37:41Z ford $ # #======================================================================== package Pod::POM::Node; require 5.004; use strict; use Pod::POM::Nodes; use Pod::POM::Constants qw( :all ); use vars qw( $VERSION $DEBUG $ERROR $NODES $NAMES $AUTOLOAD ); use constant DUMP_LINE_LENGTH => 80; $VERSION = sprintf("%d.%02d", q$Revision: 1.5 $ =~ /(\d+)\.(\d+)/); $DEBUG = 0 unless defined $DEBUG; $NODES = { pod => 'Pod::POM::Node::Pod', head1 => 'Pod::POM::Node::Head1', head2 => 'Pod::POM::Node::Head2', head3 => 'Pod::POM::Node::Head3', head4 => 'Pod::POM::Node::Head4', over => 'Pod::POM::Node::Over', item => 'Pod::POM::Node::Item', begin => 'Pod::POM::Node::Begin', for => 'Pod::POM::Node::For', text => 'Pod::POM::Node::Text', code => 'Pod::POM::Node::Code', verbatim => 'Pod::POM::Node::Verbatim', }; $NAMES = { map { ( $NODES->{ $_ } => $_ ) } keys %$NODES, }; # overload stringification to present node via a view use overload '""' => 'present', fallback => 1, 'bool' => sub { 1 }; # alias meta() to metadata() *meta = \*metadata; #------------------------------------------------------------------------ # new($pom, @attr) # # Constructor method. Returns a new Pod::POM::Node::* object or undef # on error. First argument is the Pod::POM parser object, remaining # arguments are node attributes as specified in %ATTRIBS in derived class # package. #------------------------------------------------------------------------ sub new { my $class = shift; my $pom = shift; my ($type, $attribs, $accept, $key, $value, $default); $type = $NAMES->{ $class }; { no strict qw( refs ); $attribs = \%{"$class\::ATTRIBS"} || [ ]; $accept = \@{"$class\::ACCEPT"} || [ ]; unless (%{"$class\::ACCEPT"}) { %{"$class\::ACCEPT"} = ( map { ( $_ => $NODES->{ $_ } ) } @$accept, ); } } # create object with slots for each acceptable child and overall content my $self = bless { type => $type, content => bless([ ], 'Pod::POM::Node::Content'), map { ($_ => bless([ ], 'Pod::POM::Node::Content')) } (@$accept, 'code'), }, $class; # set attributes from arguments keys %$attribs; # reset hash iterator while(my ($key, $default) = each %$attribs) { $value = shift || $default; return $class->error("$type expected a $key") unless $value; $self->{ $key } = $value; } return $self; } #------------------------------------------------------------------------ # add($pom, $type, @attr) # # Adds a new node as a child element (content) of the current node. # First argument is the Pod::POM parser object. Second argument is the # child node type specified by name (e.g. 'head1') which is mapped via # the $NODES hash to a class name against which new() can be called. # Remaining arguments are attributes passed to the child node constructor. # Returns a reference to the new node (child was accepted) or one of the # constants REDUCE (child terminated node, e.g. '=back' terminates an # '=over' node), REJECT (child rejected, e.g. '=back' expected to terminate # '=over' but something else found instead) or IGNORE (node didn't expect # child and is implicitly terminated). #------------------------------------------------------------------------ sub add { my $self = shift; my $pom = shift; my $type = shift; my $class = ref $self; my ($name, $attribs, $accept, $expect, $nodeclass, $node); $name = $NAMES->{ $class } || return $self->error("no name for $class"); { no strict qw( refs ); $accept = \%{"$class\::ACCEPT"}; $expect = ${"$class\::EXPECT"}; } # SHIFT: accept indicates child nodes that can be accepted; a # new node is created, added it to content list and node specific # list, then returned by reference. if ($nodeclass = $accept->{ $type }) { defined($node = $nodeclass->new($pom, @_)) || return $self->error($nodeclass->error()) unless defined $node; push(@{ $self->{ $type } }, $node); push(@{ $self->{ content } }, $node); $pom->{in_begin} = 1 if $nodeclass eq 'Pod::POM::Node::Begin'; return $node; } # REDUCE: expect indicates the token that should terminate this node if (defined $expect && ($type eq $expect)) { DEBUG("$name terminated by expected $type\n"); $pom->{in_begin} = 0 if $name eq 'begin'; return REDUCE; } # REJECT: expected terminating node was not found if (defined $expect) { DEBUG("$name rejecting $type, expecting a terminating $expect\n"); $self->error("$name expected a terminating $expect"); return REJECT; } # IGNORE: don't know anything about this node DEBUG("$name ignoring $type\n"); return IGNORE; } #------------------------------------------------------------------------ # present($view) # # Present the node by making a callback on the appropriate method against # the view object passed as an argument. $Pod::POM::DEFAULT_VIEW is used # if $view is unspecified. #------------------------------------------------------------------------ sub present { my ($self, $view, @args) = @_; $view ||= $Pod::POM::DEFAULT_VIEW; my $type = $self->{ type }; my $method = "view_$type"; DEBUG("presenting method $method to $view\n"); my $txt = $view->$method($self, @args); if ($view->can("encode")){ return $view->encode($txt); } else { return $txt; } } #------------------------------------------------------------------------ # metadata() # metadata($key) # metadata($key, $value) # # Returns the metadata hash when called without any arguments. Returns # the value of a metadata item when called with a single argument. # Sets a metadata item to a value when called with two arguments. #------------------------------------------------------------------------ sub metadata { my ($self, $key, $value) = @_; my $metadata = $self->{ METADATA } ||= { }; return $metadata unless defined $key; if (defined $value) { $metadata->{ $key } = $value; } else { $value = $self->{ METADATA }->{ $key }; return defined $value ? $value : $self->error("no such metadata item: $key"); } } #------------------------------------------------------------------------ # error() # error($msg, ...) # # May be called as a class or object method to set or retrieve the # package variable $ERROR (class method) or internal member # $self->{ _ERROR } (object method). The presence of parameters indicates # that the error value should be set. Undef is then returned. In the # abscence of parameters, the current error value is returned. #------------------------------------------------------------------------ sub error { my $self = shift; my $errvar; # use Carp; { no strict qw( refs ); if (ref $self) { # my ($pkg, $file, $line) = caller(); # print STDERR "called from $file line $line\n"; # croak "cannot get/set error in non-hash: $self\n" # unless UNIVERSAL::isa($self, 'HASH'); $errvar = \$self->{ ERROR }; } else { $errvar = \${"$self\::ERROR"}; } } if (@_) { $$errvar = ref($_[0]) ? shift : join('', @_); return undef; } else { return $$errvar; } } #------------------------------------------------------------------------ # dump() # # Returns a representation of the element and all its children in a # format useful only for debugging. The structure of the document is # shown by indentation (inspired by HTML::Element). #------------------------------------------------------------------------ sub dump { my($self, $depth) = @_; my $output; $depth = 0 unless defined $depth; my $nodepkg = ref $self; if ($self->isa('REF')) { $self = $$self; my $cmd = $self->[CMD]; my @content = @{ $self->[CONTENT] }; if ($cmd) { $output .= (" " x $depth) . $cmd . $self->[LPAREN] . "\n"; } foreach my $item (@content) { if (ref $item) { $output .= $item->dump($depth+1); # recurse } else { # text node $output .= _dump_text($item, $depth+1); } } if ($cmd) { $output .= (" " x $depth) . $self->[RPAREN] . "\n", ; } } else { no strict 'refs'; my @attrs = sort keys %{"*${nodepkg}::ATTRIBS"}; $output .= (" " x $depth) . $self->type . "\n"; foreach my $attr (@attrs) { if (my $value = $self->{$attr}) { $output .= (" " x ($depth+1)) . "\@$attr\n"; if (ref $value) { $output .= $value->dump($depth+1); } else { $output .= _dump_text($value, $depth+2); } } } foreach my $item (@{$self->{content}}) { if (ref $item) { # element $output .= $item->dump($depth+1); # recurse } else { # text node $output .= _dump_text($item, $depth+1); } } } return $output; } sub _dump_text { my ($text, $depth) = @_; my $output = ""; my $padding = " " x $depth; my $max_text_len = DUMP_LINE_LENGTH - length($depth) - 2; foreach my $line (split(/\n/, $text)) { $output .= $padding; if (length($line) > $max_text_len or $line =~ m<[\x00-\x1F]>) { # it needs prettyin' up somehow or other my $x = (length($line) <= $max_text_len) ? $_ : (substr($line, 0, $max_text_len) . '...'); $x =~ s<([\x00-\x1F])> <'\\x'.(unpack("H2",$1))>eg; $output .= qq{"$x"\n}; } else { $output .= qq{"$line"\n}; } } return $output; } #------------------------------------------------------------------------ # AUTOLOAD #------------------------------------------------------------------------ sub AUTOLOAD { my $self = shift; my $name = $AUTOLOAD; my $item; $name =~ s/.*:://; return if $name eq 'DESTROY'; # my ($pkg, $file, $line) = caller(); # print STDERR "called from $file line $line to return ", ref($item), "\n"; return $self->error("can't manipulate \$self") unless UNIVERSAL::isa($self, 'HASH'); return $self->error("no such member: $name") unless defined ($item = $self->{ $name }); return wantarray ? ( UNIVERSAL::isa($item, 'ARRAY') ? @$item : $item ) : $item; } #------------------------------------------------------------------------ # DEBUG(@msg) #------------------------------------------------------------------------ sub DEBUG { print STDERR "DEBUG: ", @_ if $DEBUG; } 1; =head1 NAME Pod::POM::Node - base class for a POM node =head1 SYNOPSIS package Pod::POM::Node::Over; use base qw( Pod::POM::Node ); use vars qw( %ATTRIBS @ACCEPT $EXPECT $ERROR ); %ATTRIBS = ( indent => 4 ); @ACCEPT = qw( over item begin for text verbatim ); $EXPECT = q( back ); package main; my $list = Pod::POM::Node::Over->new(8); $list->add('item', 'First Item'); $list->add('item', 'Second Item'); ... =head1 DESCRIPTION This documentation describes the inner workings of the Pod::POM::Node module and gives a brief overview of the relationship between it and its derived classes. It is intended more as a guide to the internals for interested hackers than as general user documentation. See L<Pod::POM> for information on using the modules. This module implements a base class node which is subclassed to represent different elements within a Pod Object Model. package Pod::POM::Node::Over; use base qw( Pod::POM::Node ); The base class implements the new() constructor method to instantiate new node objects. my $list = Pod::POM::Node::Over->new(); The characteristics of a node can be specified by defining certain variables in the derived class package. The C<%ATTRIBS> hash can be used to denote attributes that the node should accept. In the case of an C<=over> node, for example, an C<indent> attribute can be specified which otherwise defaults to 4. package Pod::POM::Node::Over; use base qw( Pod::POM::Node ); use vars qw( %ATTRIBS $ERROR ); %ATTRIBS = ( indent => 4 ); The new() method will now expect an argument to set the indent value, or will use 4 as the default if no argument is provided. my $list = Pod::POM::Node::Over->new(8); # indent: 8 my $list = Pod::POM::Node::Over->new( ); # indent: 4 If the default value is undefined then the argument is mandatory. package Pod::POM::Node::Head1; use base qw( Pod::POM::Node ); use vars qw( %ATTRIBS $ERROR ); %ATTRIBS = ( title => undef ); package main; my $head = Pod::POM::Node::Head1->new('My Title'); If a mandatory argument isn't provided then the constructor will return undef to indicate failure. The $ERROR variable in the derived class package is set to contain a string of the form "$type expected a $attribute". # dies with error: "head1 expected a title" my $head = Pod::POM::Node::Head1->new() || die $Pod::POM::Node::Head1::ERROR; For convenience, the error() subroutine can be called as a class method to retrieve this value. my $type = 'Pod::POM::Node::Head1'; my $head = $type->new() || die $type->error(); The C<@ACCEPT> package variable can be used to indicate the node types that are permitted as children of a node. package Pod::POM::Node::Head1; use base qw( Pod::POM::Node ); use vars qw( %ATTRIBS @ACCEPT $ERROR ); %ATTRIBS = ( title => undef ); @ACCEPT = qw( head2 over begin for text verbatim ); The add() method can then be called against a node to add a new child node as part of its content. $head->add('over', 8); The first argument indicates the node type. The C<@ACCEPT> list is examined to ensure that the child node type is acceptable for the parent node. If valid, the constructor for the relevant child node class is called passing any remaining arguments as attributes. The new node is then returned. my $list = $head->add('over', 8); The error() method can be called against the I<parent> node to retrieve any constructor error generated by the I<child> node. my $list = $head->add('over', 8); die $head->error() unless defined $list; If the child node is not acceptable to the parent then the add() method returns one of the constants IGNORE, REDUCE or REJECT, as defined in Pod::POM::Constants. These return values are used by the Pod::POM parser module to implement a simple shift/reduce parser. In the most common case, IGNORE is returned to indicate that the parent node doesn't know anything about the new child node. The parser uses this as an indication that it should back up through the parse stack until it finds a node which I<will> accept this child node. Through this mechanism, the parser is able to implicitly terminate certain POD blocks. For example, a list item initiated by a C<=item> tag will I<not> accept another C<=item> tag, but will instead return IGNORE. The parser will back out until it finds the enclosing C<=over> node which I<will> accept it. Thus, a new C<=item> implicitly terminates any previous C<=item>. The C<$EXPECT> package variable can be used to indicate a node type which a parent expects to terminate itself. An C<=over> node, for example, should always be terminated by a matching C<=back>. When such a match is made, the add() method returns REDUCE to indicate successful termination. package Pod::POM::Node::Over; use base qw( Pod::POM::Node ); use vars qw( %ATTRIBS @ACCEPT $EXPECT $ERROR ); %ATTRIBS = ( indent => 4 ); @ACCEPT = qw( over item begin for text verbatim ); $EXPECT = q( back ); package main; my $list = Pod::POM::Node::Over->new(); my $item = $list->add('item'); $list->add('back'); # returns REDUCE If a child node isn't specified in the C<@ACCEPT> list or doesn't match any C<$EXPECT> specified then REJECT is returned. The parent node sets an internal error of the form "$type expected a terminating $expect". The parser uses this to detect missing POD tags. In nearly all cases the parser is smart enough to fix the incorrect structure and downgrades any errors to warnings. # dies with error 'over expected terminating back' ref $list->add('head1', 'My Title') # returns REJECT || die $list->error(); Each node contains a 'type' field which contains a simple string indicating the node type, e.g. 'head1', 'over', etc. The $NODES and $NAMES package variables (in the base class) reference hash arrays which map these names to and from package names (e.g. head1 E<lt>=E<gt> Pod::POM::Node::Head1). print $list->{ type }; # 'over' An AUTOLOAD method is provided to access to such internal items for those who don't like violating an object's encapsulation. print $list->type(); Nodes also contain a 'content' list, blessed into the Pod::POM::Node::Content class, which contains the content (child elements) for the node. The AUTOLOAD method returns this as a list reference or as a list of items depending on the context in which it is called. my $items = $list->content(); my @items = $list->content(); Each node also contains a content list for each individual child node type that it may accept. my @items = $list->item(); my @text = $list->text(); my @vtext = $list->verbatim(); The present() method is used to present a node through a particular view. This simply maps the node type to a method which is then called against the view object. This is known as 'double dispatch'. my $view = 'Pod::POM::View::HTML'; print $list->present($view); The method name is constructed from the node type prefixed by 'view_'. Thus the following are roughly equivalent. $list->present($view); $view->view_list($list); The benefit of the former over the latter is, of course, that the caller doesn't need to know or determine the type of the node. The node itself is in the best position to determine what type it is. =head1 AUTHOR Andy Wardley E<lt>abw@kfs.orgE<gt> =head1 COPYRIGHT Copyright (C) 2000, 2001 Andy Wardley. All Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. =head1 SEE ALSO Consult L<Pod::POM> for a general overview and examples of use.