Handler behaviour.

Arfficionado.read/4 will:

1. call init(arg) to obtain the initial handler state (arg defaults to nil)

2. parse the ARFF header and

   • call relation with the relation name and optional comment
   • call attributes with the list of attributes found in the header
   • call line_comment for lines that consists of commentary only
   • call begin_data with optional comment to indicate that the header is finished and instance data will follow

3. parse the ARFF data section

   • call instance for each line of data, reporting instance values, weight and optional comment
   • call line_comment for lines that consists of commentary only
4. call close

Arfficionado.read/4 will pass in the current handler state on each callback invocation. Callback functions return an updated handler state and generally indicate whether to continue reading the ARFF file or to stop early.

Once the ARFF file is exhausted, an error is encountered in the ARFF file, or the handler has indicated that it wishes to stop the processing, the close callback will be invoked, allowing the handler to create the final result state (and clean up resources).

Implement this behaviour as per your application's requirements (for example, including side effects such as creating and writing to an ETS table). The sources for Arfficionado.ListHandler and Arfficionado.MapHandler may provide some general guidance.