isNegativeUnaryOperator function

bool isNegativeUnaryOperator(String expression, int index)

Implementation

bool isNegativeUnaryOperator(String expression, int index) {
  // If the index is invalid, the character cannot be a negative unary operator.
  if (index >= expression.length) {
    return false;
  }

  // Extract the character at the given index.
  final String operator = expression.substring(index, index + 1);

  // If the character is not a minus sign,
  // it cannot be a negative unary operator.
  if (operator != '-') {
    return false;
  }

  // If the character is a minus sign, check if it's a negative unary operator
  // by examining the previous character in the expression.
  if (index == 0) {
    // If the minus sign is the first character in the expression, it is a
    // unary operator.
    return true;
  }

  // Extract the previous character in the expression.
  final String prevChar = expression.substring(index - 1, index);

  // Check if the previous character is an operator, left parenthesis.
  // If it is any of these, then the minus sign is a unary operator.
  if (isOperator(prevChar) || prevChar == '(') {
    return true;
  }

  // If the previous character is not an operator, left parenthesis, or
  // space, the minus sign is not a unary operator.
  return false;
}