Chapter 5. SAX

# initialize the parser
#
use XML::Parser::PerlSAX;
my $parser = XML::Parser::PerlSAX->new( Handler => MyHandler->new( ) );

if( my $file = shift @ARGV ) {
    $parser->parse( Source => {SystemId => $file} );
} else {
    my $input = "";
    while( <STDIN> ) { $input .= $_; }
    $parser->parse( Source => {String => $input} );
}
exit;

#
# global variables
#
my @element_stack;                # remembers element names
my $in_intset;                    # flag: are we in the internal subset?

###
### Document Handler Package
###
package MyHandler;

#
# initialize the handler package
#
sub new {
    my $type = shift;
    return bless {}, $type;
}

#
# handle a start-of-element event: output start tag and attributes
#
sub start_element {
    my( $self, $properties ) = @_;
    # note: the hash %{$properties} will lose attribute order

    # close internal subset if still open
    output( "]>\n" ) if( $in_intset );
    $in_intset = 0;

    # remember the name by pushing onto the stack
    push( @element_stack, $properties->{'Name'} );

    # output the tag and attributes UNLESS it's a <literal>
    # inside a <programlisting>
    unless( stack_top( 'literal' ) and
            stack_contains( 'programlisting' )) {
        output( "<" . $properties->{'Name'} );
        my %attributes = %{$properties->{'Attributes'}};
        foreach( keys( %attributes )) {
            output( " $_=\"" . $attributes{$_} . "\"" );
        }
        output( ">" );
    }
} 

#
# handle an end-of-element event: output end tag UNLESS it's from a
# <literal> inside a <programlisting>
#
sub end_element {
    my( $self, $properties ) = @_;
    output( "</" . $properties->{'Name'} . ">" )
         unless( stack_top( 'literal' ) and
                stack_contains( 'programlisting' ));
    pop( @element_stack );
}

#
# handle a character data event
#
sub characters {
    my( $self, $properties ) = @_;
    # parser unfortunately resolves some character entities for us,
    # so we need to replace them with entity references again
    my $data = $properties->{'Data'};
    $data =~ s/\&/\&/;
    $data =~ s/</\&lt;/;
    $data =~ s/>/\&gt;/;
    output( $data );
}

#
# handle a comment event: turn into a <comment> element
#
sub comment {
    my( $self, $properties ) = @_;
    output( "<comment>" . $properties->{'Data'} . "</comment>" );
}

#
# handle a PI event: delete it
#
sub processing_instruction {
  # do nothing!
}

#
# handle internal entity reference (we don't want them resolved)
#
sub entity_reference {
    my( $self, $properties ) = @_;
    output( "&" . $properties->{'Name'} . ";" );
}

sub stack_top {
    my $guess = shift;
    return $element_stack[ $#element_stack ] eq $guess;
}

sub stack_contains {
    my $guess = shift;
    foreach( @element_stack ) {
        return 1 if( $_ eq $guess );
    }
    return 0;
}

sub output {
    my $string = shift;
    print $string;
}

<?xml version="1.0"?>
<!DOCTYPE book
  SYSTEM "/usr/local/prod/sgml/db.dtd"
[
  <!ENTITY thingy "hoo hah blah blah">
]>

<book id="mybook">
<?print newpage?>
  <title>GRXL in a Nutshell</title>
  <chapter id="intro">
    <title>What is GRXL?</title>
<!-- need a better title -->
    <para>
Yet another acronym.  That was our attitude at first, but then we saw 
the amazing uses of this new technology called
<literal>GRXL</literal>.  Consider the following program:
    </para>
<?print newpage?>
    <programlisting>AH aof -- %%%%
{{{{{{ let x = 0 }}}}}}
  print!  <lineannotation><literal>wow</literal></lineannotation>
or not!</programlisting>
<!-- what font should we use? -->
    <para>
What does it do?  Who cares?  It's just lovely to look at.  In fact,
I'd have to say, "&thingy;".
    </para>
<?print newpage?>
  </chapter>
</book>

<book id="mybook">
  <title>GRXL in a Nutshell</title>
  <chapter id="intro">
    <title>What is GRXL?</title>
<comment> need a better title </comment>
    <para>
Yet another acronym.  That was our attitude at first, but then we saw 
the amazing uses of this new technology called
<literal>GRXL</literal>.  Consider the following program:
    </para>

    <programlisting>AH aof -- %%%%
{{{{{{ let x = 0 }}}}}}
  print!  <lineannotation>wow</lineannotation>
or not!</programlisting>
<comment> what font should we use? </comment>
    <para>
What does it do?  Who cares?  It's just lovely to look at.  In fact,
I'd have to say, "&thingy;".
    </para>

  </chapter>
</book>