I am against adding the instances for Monad Either to the base package
for the same reasons as the ones in the thread "proposal #4095: add
Applicative instance for Either".
http://www.haskell.org/pipermail/libraries/2010-June/013715.html
-Iavor
On Wed, Jul 7, 2010 at 6:06 PM, Edward Z. Yang
Excerpts from Isaac Dupree's message of Fri Jul 02 12:25:33 -0400 2010:
It's not quite as simple as that -- as soon as we start making Either an instance of kind (* -> *) classes, such as Functor and Monad, there inevitably becomes some kind of semantic difference between Left and Right.
Right, so what we end up with is short-circuiting computation with different results.
Cheers, Edward _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries