[Haskell-cafe] Re: Converting IO [XmlTree] to [XmlTree]

[Steffen Schuldenzucker]

On 22:19 Mon 27 Apr     , Martijn van Steenbergen wrote:
> Tillmann Rendel wrote:
>> Achim Schneider wrote:
>>> In other words:
>>>
>>> 1) Explain Pointed
>>> 2) Explain Functor
>>> 3) Explain Applicative
>>> 4) Explain Monad
>> Why Pointed first? Functor seems more useful and more basic.
>
> They are in order of power: every monad is an applicative; every 
> applicative is a functor; every functor is pointed.

Uhm, isn't it:

class (Functor f) => Pointed f where
    pure :: a -> f a -- singleton, return, unit etc.

Got it from: The Typeclassopedia by Brent Yorgey (forgot the URL, sorry)

Steffen