#: re/AST.pm#: Abastract Syntax Tree (also parse tree) for re-DFA#: Copyright (c) 2006 Agent Zhang#: 2006-05-13 2006-05-15package re::AST;use strict;use warnings;use re::AST::Element;use re::AST::Alternation;use re::AST::Concat;my @rules = qw(    expression alternation eof    concat modified_atom atom atom_star    char nil);for my $rule (@rules) {    no strict 'refs';    push @{"${rule}::ISA"}, "re::AST::Element";}package modified_atom;use strict;use warnings;sub modifier {    my $self = shift;    my $modifier = $self->{'modifier(?)'};    if (@$modifier) { $modifier->[0]; }    else { nil->new; }}1;__END__