add_and_mult_reduce.rs

fn reduce_addition(stack: &mut Vec<Token>) -> Result<Token, RuntimeError> {
    let operands = unwrap_operand_tokens(stack);
    match operands {
        Ok(operand_vec) => Ok(Token::Operand(
                operand_vec
                    .iter()
                    .fold(0, |sum, value| sum + value))),
        Err(_) => Err(RuntimeError{})
    }
}

fn reduce_multiplication(stack: &mut Vec<Token>) -> Result<Token, RuntimeError> {
    let operands = unwrap_operand_tokens(stack);
    match operands {
        Ok(operand_vec) => Ok(Token::Operand(
                operand_vec
                    .iter()
                    .fold(1, |prod, value| prod * value))),
        Err(_) => Err(RuntimeError{})
    }
}