Re: [Haskell-cafe] Pointed, but not Applicative

On Sun, 2011-08-28 at 11:48 -0300, Felipe Almeida Lessa wrote:

On Sun, Aug 28, 2011 at 7:41 AM, Tony Morris wrote:

...

Pointed f => Pointed (StateT s f)

but not

Applicative f => Applicative (StateT s f)

But we do have

(Functor m, Monad m) => Applicative (StateT s m)

so I'm not sure if this is a valid example.

Cheers,

newtype StateT s m a = StateT (s -> m (a, s)) instance Functor m => Functor (StateT s m) where f `fmap` StateT g = StateT $ fmap (first f) . g instance Pointed m => Pointed (StateT s m) where point x = StateT $ point . (,) x Regards