sub commit {
    require Carp;
    Carp::croak("Can't commit outside a transaction");
}

sub rollback {
    require Carp;
    Carp::croak("Can't rollback outside a transaction");
}


sub transaction (&) {
    my ($block) = @_;

    my $caller = caller();

    local *{"${caller}::commit"} = sub { die "!COMMIT\n" };
    local *{"${caller}::rollback"} = sub { die "!ROLLBACK\n" };

    local $@;
    eval {
        $T->begin_work;
        $block->();
    };

    if(!$@ or $@ eq "!COMMIT\n") {
        ${"${caller}::T"}->commit;
    }
    elsif($@ eq "!ROLLBACK\n") {
        ${"${caller}::T"}->rollback;
    }
    else {
        ${"${caller}::T"}->rollback;

        require Carp;
        Carp::croak($@ . "commit not safe after errors, transaction rolled back");
    }
}