Joined-Up Classes

Currently the Monad class is not a subclass of Functor. It should be.

Proposal:

1. Add this:

  class (Functor f) => Idiom f where -- or Applicative
    return :: a -> f a
    ap :: f (a -> b) -> f a -> f b
    (>>) :: f a -> f b -> f b
    fa >> fb = ap (fmap (const id) fa) fb

(See also Control.Applicative in GHC HEAD.)

1. Replace existing Monad class with this:

  class (Idiom m) => Monad m where
    (>>=) :: m a -> (a -> m b) -> m b
    fail :: String -> m a
    fail = error

1. Remove existing "ap", generalise and remove redundant Prelude functions as appropriate.

Trac metadata

Trac field	Value
Version
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Proposal
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture