haskell types

addedroute.hs

        get "/io" - do
            file <- readFile "sandbox.hs"
            text "hello"

error.txt

/Users/seanhess/sandbox/Haskell/web/minmiku.hs:46:21:
    Couldn't match expected type `Control.Monad.Trans.Reader.ReaderT
                                    Network.Miku.Type.AppReader
                                    (Control.Monad.Trans.State.Lazy.StateT
                                       Network.Miku.Type.AppState IO)
                                    t0'
                with actual type `IO String'
    In the return type of a call of `readFile'
    In a stmt of a 'do' expression: file <- readFile "sandbox.hs"
    In the second argument of `(-)', namely
      `do { file <- readFile "sandbox.hs";
            text "WOOT" }'