anchor.diff:  %% expose functions for test
   %% none?
   
  -make_data2( #{ height := Height
  +make_data( #{ height := Height
                , yImaginaryLow := YImaginaryLow
                , yImaginaryHigh := YImaginaryHigh
                , width := Width
  
positive.code: %% use epocxy to spawn actual computations
  
  %% public API
  -export([ make_data/1 % create a block of fractal data
          , make_data2/1
          , compute_row/8 % so spawned process can run
          , data2file/2  % write fractal data to file
          , data2svr/2  % write fractal data to svr
  
negative.code:              , DeltaX
               , NewRowData
               ).
  
  data2file( _Data, _ConfigMap) ->
    lager:debug("need to implement data2file using binary"),
  