A Row is something that can be expressed as a line. The output of repr' should be formatted such that it can be read and processed from the command line.
IO.putStrLn $ show [1,2,3,4][1,2,3,4]
Data.ByteString.Lazy.Char8.putStrLn $ repr' [1,2,3,4]1 2 3 4
A type that instantiate Rows is a type that can be represented as a list of rows, where typically a row is a line.
mapM_ Data.ByteString.Lazy.Char8.putStrLn $ repr [1,2,3,4]1 2 3 4