public JCTree visitCompoundAssignment(CompoundAssignmentTree node, P p) {
        JCAssignOp t = (JCAssignOp) node;
        JCTree lhs = copy(t.lhs, p);
        JCTree rhs = copy(t.rhs, p);
        return M.at(t.pos).Assignop(t.getTag(), lhs, rhs);
    }