Functor, Pointed, Applicative, Monad
As pointed out on StackOverflow, Functor, Pointed, Applicative and Monad all belong in a hierarchy thus:
class Functor f where
map :: (a -> b) -> f a -> f b
class Functor f => Pointed f where
pure :: a -> f a
class Pointed f => Applicative f where
(<*>) :: f (a -> b) -> f a -> f b
(*>) :: f a -> f b -> f b
(<*) :: f a -> f b -> f a
class Applicative m => Monad m where
(>>=) :: (m a) -> (a -> m b) -> m b
(>>) :: m a -> m b -> m b
return :: a -> m a
As well as eliminating much duplication (where every Applicative must also be given a Monad instance), this will make it easier to eliminate such duplication as [fmap,liftM,map,liftA], [(<*>),ap], and [concat,join].
fail does not belong in Monad; it only makes sense monadically as mzero.
Trac metadata
Trac field | Value |
---|---|
Version | 6.12.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | libraries/base |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | gideon@accursoft.com |
Operating system | |
Architecture |