void performer(Offset) (CodaTerminal *left, CodaTerminal *right);
void perform(Offset, CodaInteger) (CodaInteger *left, CodaInteger *right) {
left->value += right->value;
}
void perform(Offset, Point) (Point *left, Point *right) {
left->x += right->x;
left->y += right->y;
}