[Haskell-cafe] Re: Converting IO [XmlTree] to [XmlTree]
Steve.Schuldenzucker at web.de
Tue Apr 28 03:36:18 EDT 2009
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)
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