Dear Cafe,

MonadFail.fail takes String.

I wasn't able to find MonadFail for custom error type.

Is there any proposals to base?

Let's say Data.Text, which gains popularity with OverloadedStrings extensions.

class MonadFail m where

fail :: String -> m a

Why not ?

class MonadFail m where

fail :: (forall s. IsString s => s) -> m a

class MonadFailWith m s where

fail :: s -> m a

Best regards,
Daniil Iaitskov