('x':'x':name2) -> return obj { clientReqHdr = ((name2, vv) : prev) }

                           where prev = clientReqHdr obj

                                 vv = case value of

                                        "client_ip_addr" -> clientIp request

                                        "now" -> do utcTime <- currentUTCTime

                                                    return $ formatRFC1123 utcTime

                                        _ -> value

                        _ -> return obj

However, above code does not compile also :-( 

*Main> :l test

[1 of 1] Compiling Main             ( test.hs, interpreted )

test.hs:101:64:

    Couldn't match expected type `[t0]' with actual type `IO UTCTime'

    In a stmt of a 'do' block: utcTime <- currentUTCTime

    In the expression:

      do { utcTime <- currentUTCTime;

           return $ formatRFC1123 utcTime }

    In a case alternative:

        "now"

          -> do { utcTime <- currentUTCTime;

                  return $ formatRFC1123 utcTime }

Failed, modules loaded: none.

Obviously outer do-block is inside IO monad, as the type of scanQuery is 

Request -> IO Object. But GHC puts inner do-block (in "now" case)  inside list monad,

doesn't it? Why does ghc look for List monad?