In order to eliminate duplicate code, all the ByteString and Text specific functions are merged into functions that have a type parameter b with the constraints forall b. (Pack b) =>. The forall, along with {-# LANGUAGE ScopedTypeVariables #-}, lets you use b in signatures throughout the function to refer to the exact type used in the main signature. Remove the B and T suffixes from all functions and types. You may also need {-# LANGUAGE TypeFamilies #-}.

I have looked over this package briefly, and I am wondering how you could take the result of, say, textToBWTToRLET :: Text -> RLET and convert it to a string in such a way that it can be uniquely converted back to an RLET, so it could then be decompressed? I read over some general RLE papers and they seem to always use examples that have no digits.