Proposal: add:
instance Monoid e => Alternative (Either e) where empty = Left mempty Left a <|> Left b = Left (a `mappend` b) Right a <|> _ = Right a _ <|> Right b = Right b instance Monoid e => MonadPlus (Either e) where ... to base. This is a reasonably obvious instance which I am pretty sure is law abiding. It'd be useful for defining a series of computations which may fail, where we only care about one success. _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries |
Alternatively :) or more like, something to think about, an Alt
instance for Either. https://hackage.haskell.org/package/semigroupoids/docs/Data-Functor-Alt.html There is something iffy about Monoid e => Alternative (Either
e) but I can't put my finger on it. On 06/14/2018 08:37 PM, Nathan van
Doorn wrote:
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I think the iffy feeling comes from the proposal breaking the distributive law. For example: (Right f <|> Right g) <*> Left x = Left x but (Right f <*> Left x) <|> (Right g <*> Left x) = Left (x <> x) On Thu, Jun 14, 2018, 22:42 Tony Morris <[hidden email]> wrote:
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