20 Nov
2010
20 Nov
'10
8:19 p.m.
On Sat, Nov 20, 2010 at 05:25:23PM -0500, roconnor@theorem.ca wrote:
Data.Functor.Backwards is a wrapper for functors that allow Foldable, Traversable, and Applicative functors to be operated backwards. It is similar to Dual for Monoids. The Applicative instance runs effects in reversed order. The Foldable instance folds from right to left, The Traversable instance traverses from right to left.
It probably should also have an Alternative instance. I expect that wouldn't reverse the order of alternatives: instance (Alternative f) => Alternative (Backwards f) where empty = Backwards empty Backwards x <|> Backwards y = Backwards (x <|> y)