[Haskell-cafe] Why isn't ArrowChoice a parent of of ArrowApply?

Ross Paterson R.Paterson at city.ac.uk
Thu Jun 20 12:16:20 CEST 2013

On Thu, Jun 20, 2013 at 09:02:48AM +0200, Petr Pudlák wrote:
> In Control.Arrow we have:
>     leftApp :: ArrowApply a => a b c -> a (Either b d) (Either c d)
>     Any instance of ArrowApply can be made into an instance of ArrowChoice by
>     defining left = leftApp.
> So why isn't ArrowChoice a parent of ArrowApply?

Probably because it wasn't in John Hughes's original paper.
I agree that it would make sense.

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