how about another method for result schemas instead of yldHd?
extract scan logic into its own method

this way we can do basic reading without op interpreter
extract printing schema and fields
experiment with loading schema from file

do we want to keep the filename params as Rep[String] or
should we change it to String?

once we parse sql, our input will be something like
select * from baz.csv, bar.csv where ..., i.e. imost likely
include the table/file names.