Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
Why is there no monad instance for Control.Applicative.Const? Is following definition correct, or violates it the monad laws?
instance Monoid a => Monad (Const a) where
return _ = Const mempty
(Const x) >>= _ = Const x
And can you think of any useful application?
It violates the left identity law:
return x >>= fmust be the same asf x, but considerf x = Const (x + 1).