anchor.diff:  /// Throws an [Exception] if an invalid direction is given.
   int partOne(String directions) {
     var houses = 1;
  -  var visited = new Set();
  +  var visited = new Set<String>();
     var x = 0;
     var y = 0;
     visited.add('${x}, ${y}');
  
positive.code: 
    return houses;
  }
  
negative.code:   try {
      var input = readInput('day3');
      print('Part one: ${partOne(input)}');
      print('Part two: ${partTwo(input)}');
    } on FileSystemException catch (e) {
      print('Error reading input from file: $e');
    } catch (e) {
  