code: public static BinaryExpression newAssignmentExpression(Variable variable, Expression rhs) {
          VariableExpression lhs = new VariableExpression(variable);
          Token operator = Token.newPlaceholder(Types.ASSIGN);
  
          return new BinaryExpression(lhs, operator, rhs);
      }
docs: Creates an assignment expression in which the specified expression
  is written into the specified variable name.