Arrows that are also Functors

Maciej Marcin Piechotka uzytkownik2 at
Tue Apr 19 18:22:39 CEST 2011

On Tue, 2011-04-19 at 17:29 +0200, Henning Thielemann wrote:
> Is it common to make a type an instance of both Arrow and Functor type 
> class? If a type is both instance of Arrow and Functor, would you expect 
> that fmap = (^<<) ? If yes, how about adding this as expected law to the 
> Control.Arrow documentation? Same question for Applicative functors and 
> liftA2 (,) = (&&&). (Btw. Control.Arrow haddock documentation does not 
> mention any Arrow law so far.)

I believe reading in some paper/monad reader article that Arrow is
equivalent to Category that is Functor. 

In any case iff there have been instances I would expect such things (I
believe both are true for (->)).

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