When implementing reverse polish notation, what about the unary minus sign?

Question

Algorithms

I'm trying to solve one katu where you need to spread out a line with a mathematical expression.
And I found that this is solved with the help of the OPN, and took it as a basis, but with a unary minus, it is proposed either to replace the character or to convert the expression, for example, for -3 to OPN -> 0 3 - . I settled on replacing the symbol, I will replace it with ±.
The problem with expressions like: -(-1 + 2) , in my Polish implementation it will be like ± ± 1 2 +. how to insert the unary correctly?
And I'll attach my code . I just really want to solve this problem with the parser already. I torture her for a couple of days. There are only 2 tests left in the kata, I need to somehow take into account the unary one in front of the brackets, I don’t know how. As I understand it, I do not insert ± there.

Answer 1

If the notation is reversed, then the ± sign, like binary operations, must come after the operands. Then -(-1 + 2) becomes 1 ± 2 + ±. By ±, you need to change the sign of the number at the top of the stack.
Accordingly, in the parser, if you see a unary minus before the brackets, then translate the brackets into the notation, and then add ±.