grammar Math {
    rule TOP { ^ <expr> $ }
    rule expr { <term> [ <op> <expr> ]? }
    rule term { (\d+) }
    rule op { ('+'|'-') }
}
class Math::Actions {
    method TOP($/) { make $<expr>.ast }
    method expr($/) {
        if $<op> {
            my $lhs = +$<term>;
            my $rhs = +($<expr>[0].ast);
            given $<op>[0].ast {
                when '+' { make $lhs + $rhs }
                when '-' { make $lhs - $rhs }
            }
        } else {
            make $<term>;
        }
    }
    method op($/) { make $0 }
}
my $total = Math.parse("1 + 2 + 3", :actions(Math::Actions));
say "$total = {$total.ast}";

# Gives this error on call to Math.parse-
# too many named arguments: 1 passed, 0 used
#   in !cursor_init at src/stage2/QRegex.nqp:491
#   in method parse at src/gen/CORE.setting:5915
#   in <anon> at foo.pl:23
#   in <anon> at foo.pl:1