anchor.diff:  
       if (type == EvaluationType.VECTOR) {
         //TODO apply function to all vector elements
  -      throw new UnimplementedError('Can not evaluate functions on vectors yet.');
       }
   
       if (type == EvaluationType.INTERVAL) {
  
positive.code: 
      if (type == EvaluationType.VECTOR) {
        //TODO apply function to all vector elements
        throw new UnimplementedError('Can not evaluate functions on vectors yet.');
      }
  
      throw new UnimplementedError('Can not evaluate tan on ${type} yet.');
  
negative.code: 
      if (type == EvaluationType.VECTOR) {
        //TODO apply function to all vector elements
      }
  
      if (type == EvaluationType.INTERVAL) {
  