úÎ`ýBnon-portable (multi-parameter type classes, undecidable instances) experimentalEA monad transformer which adds Maybe semantics to an existing monad. Lift a  value to a .  Remove the  using a default value.  Remove the  using a monadic default value.  MaybeT-transformers-0.2Control.Monad.MaybeMaybeT runMaybeTmaybeT fromMaybeT fromMaybeTMbase Data.MaybeMaybe