[Haskell-cafe] why does Data.Text.Lazy.IO.readFile return the internal type Data.Text.Lazy.Internal.Text, when Data.Text.IO.readFile returns plain IO Data.Text.Text?

[Thomas Hartman]

*Main> :t Data.Text.IO.readFile
Data.Text.IO.readFile :: FilePath -> IO T.Text

but

*Main> :t Data.Text.Lazy.IO.readFile
Data.Text.Lazy.IO.readFile
  :: FilePath -> IO text-0.7.1.0:Data.Text.Lazy.Internal.Text

why does the lazy version use the internal type, whereas the strict
version of Text IO just using plain Data.Text type?
and how can I get from internal type to regular type when using Data.Text?

also the internal type doesn't appear to be reflected in the haddock:
 http://hackage.haskell.org/packages/archive/text/0.7.1.0/doc/html/Data-Text-Lazy-IO.html

ghc-pkg list | grep -i text
    text-0.7.1.0

thanks for any help!