[Haskell-cafe] monoids induced by Applicative/Alternative/Monad/MonadPlus?

[Petr Pudlák]

Or, if there are no such definitions, where would be a good place to add 
them?

Petr

Dne 08/20/2013 06:55 PM, Petr Pudlák napsal(a):
>
> Dear Haskellers,
>
> are these monoids defined somewhere?
>
> |import  Control.Applicative
> import  Data.Monoid
>
> newtype  AppMonoid  m a =AppMonoid  (m  a)
> instance  (Monoid  a,Applicative  m) =>Monoid  (AppMonoid  m a)where
>      mempty =AppMonoid  $ pure mempty
>      mappend (AppMonoid  x) (AppMonoid  y) =AppMonoid  $ mappend <$> x <*> y
> -- With the () monoid for `a` this becames the monoid of effects.
>
> newtype  AltMonoid  m a =AltMonoid  (m  a)
> instance  Alternative  m =>Monoid  (AltMonoid  m a)where
>      mempty =AltMonoid  empty
>      mappend (AltMonoid  x) (AltMonoid  y) =AltMonoid  $ x <|> y|
>
> (and similarly for Monad/MonadPlus, until they become subclasses of 
> Applicative?)
>
> Best regards,
> Petr
>

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