gistfile1.txt

v6;

grammar BUU {
    token TOP { <abc>+ };
    token abc { ('a') <bc>* };
    token bc { [ ('b') <c>* ]+ }
    token c { 'c' };
};

class BuuAbc {
    method TOP($/) { make "TOP" => $<abc>>>.ast; }
    method abc($/) { make ~$0 => $<bc>>>.ast; }
    method bc($/) { make ~$0 => $<c>>>.ast; }
    method c($/) { make 3;  }
};

my $r = BUU.parse( "abcabccabbccaababc", :actions( BuuAbc ) );

say $r.ast;