wrap.txt

> import Control.Monad.Morph
> import Control.Monad.Except
> let wrap f = hoist (withExceptT f)
> :t wrap
wrap
  :: (MFunctor t, Monad m) =>
     (e -> e') -> t (ExceptT e m) b -> t (ExceptT e' m) b
> let wrap = hoist . withExceptT

<interactive>:5:12: error:
    • Couldn't match type ‘ExceptT e m0 a0 -> ExceptT e' m0 a0’
                     with ‘forall a. m a -> n a’
      Expected type: (ExceptT e m0 a0 -> ExceptT e' m0 a0)
                     -> t m b -> t n b
        Actual type: (forall a. m a -> n a) -> t m b -> t n b
    • In the first argument of ‘(.)’, namely ‘hoist’
      In the expression: hoist . withExceptT
      In an equation for ‘wrap’: wrap = hoist . withExceptT
    • Relevant bindings include
        wrap :: (e -> e') -> t m b -> t n b (bound at <interactive>:5:5)
>