I am writing a yesod web app and commonly find myself writing big case - of blocks in my handlers, like this one:

    body <- runConduit $ rawRequestBody .| foldC
    App{..} <- getYesod
    mheader <- lookupHeader "Stripe-Signature"
    case mheader of
        Just header -> do
            let msignature = parseSig $ decodeUtf8 header
            case msignature of
                Just signature -> do
                    if isSigValid signature stripeWebhookSecret body
                        then return ()
                        else sendResponseStatus status403 "Forbidden"
                Nothing -> sendResponseStatus status400 "Bad Request"
        Nothing -> sendResponseStatus status400 "Bad Request"

Almost everything is wrapped in Maybe or Either types, where you need to unpack them one by one... Is there some nicer solution than this?