unaryExpression method

Implementation

Parser<Expression> unaryExpression() {
  final ops = ['-', '+', '!', '~'];
  return ops.map(string).reduce((a, b) => a.or(b).cast<String>())
      .trim()
      .seq(token)
      .mapWithPosition((list, start, end) => UnaryExpression(list[0], list[1])..start = start..end = end);
}