hmmm...have you tried adding a second rule for print_instruction that has the optional parens? not the most elegant solution, but it seems like it should work.

print_instruction  : /print/i expression
                     {
                        use Data::Dumper;
                        print Dumper \%item;
                        print $item{expression}."\n"
                     }
                            | /print/i '(' expression ')'
                     {
                        use Data::Dumper;
                        print Dumper \%item;
                        print $item{expression}."\n"
                     }
[download]

HTH

/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"