docs: @Override
    public Choice<Unifier> visitCompoundAssignment(CompoundAssignmentTree assignOp, Unifier unifier) {
      return Choice.condition(getKind() == assignOp.getKind(), unifier)
          .thenChoose(unifications(getVariable(), assignOp.getVariable()))
          .thenChoose(unifications(getExpression(), assignOp.getExpression()));
    }