%{
use base q{DebugTail}; 
%}

%%
S:                 { print "S -> epsilon\n" }
    |   'a' S 'b'  { print "S -> a S b\n" }
;
%%

__PACKAGE__->main('Provide a statement like "a a b b" and press <CR><CTRL-D>: ') unless caller;