Monad with no wrapped value?

Question

Most of the monad explanations use examples where the monad wraps a value. E.g. Maybe a, where the a type variable is what\'s wrapped. But I\'m won

Answer 1

Well there is

data Useless a = Useless
instance Monad Useless where
  return = const Useless
  Useless >>= f = Useless

but as I indicated, that isn't usefull.

What you want is the Writer monad, which wraps up a monoid as a monad so you can use do notation.