[Haskell-cafe] Functor and Haskell
Kim-Ee Yeoh
a.biurvOir4 at asuhan.com
Wed Apr 22 03:18:54 EDT 2009
Daryoush Mehrtash-2 wrote:
>
> I am not sure I follow how the endofunctor gave me the 2nd functor.
>
> As I read the transformation there are two catagories C and D and two
> functors F and G between the same two catagories. My problem is that I
> only
> have one functor between the Hask and List catagories. So where does the
> 2nd functor come into picture that also maps between the same C and D
> catagories?
>
Consider
singleton :: a -> [a]
singleton x = [x]
Here F is the identity functor, and G is the list functor. And yes, C=D=
category of (a subset of) Haskell types.
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