So I don't really consider myself a Haskell programmer, but the standard advice is to think about operation you are going to perform on those strings and numbers later, then think if there is a datatype you could create instead.

As an example, suppose I am trying to load a csv file with two fields being strings and one being Double. A list of lists representation isn't going to cut it. Instead I should make a Row datatype

  data Row = Row {field1 :: String, field2 :: String, field3 :: Double}

Then you can parse the csv file into a [Row] representation.

As an aside, if the task did involve parsing csv I suggest the cassava library which I found out about through the amazing What I Wish I Knew When Learning Haskell (http://dev.stephendiehl.com/hask/)