Haskell Language Common functors as the base of cofree comonads Cofree (Either e) ~~ NonEmptyT (Writer e)
Example
Given
data Either e a = Left e
| Right a
we have
data Cofree (Either e) a
= a :< Left e
| a :< Right (Cofree (Either e) a)
which is isomorphic to
data Hospitable e a
= Sorry_AllIHaveIsThis_Here'sWhy a e
| EatThis a (Hospitable e a)
or, if you promise to only evaluate the log after the complete result, NonEmptyT (Writer e) a with
data NonEmptyT (Writer e) a = NonEmptyT (e,a,[a])
