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

2013-06-20 Thread Petr Pudlák 

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|?

Best regards,
Petr

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

2013-06-20 Thread Ross Paterson 
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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