`左边是一个半群

Question

这样的事情是否已经存在，或者我应该将其打包为Hackage（我发现它对收集错误很有用）：

module EitherSemigroup where

import Prelude hiding (Right, Left)
import Data.Semigroup (Semigroup)

data EitherSemigroup l r = Left l | Right r

instance Functor (EitherSemigroup l) where
  fmap f (Right x) = Right (f x)
  fmap _ (Left x) = Left x

instance Semigroup l => Applicative (EitherSemigroup l) where
  pure = Right
  (<*>) (Right f) (Right x) = Right (f x)
  (<*>) (Right _) (Left x) = Left x
  (<*>) (Left x) (Right _) = Left x
  (<*>) (Left x1) (Left x2) = Left (x1 <> x2)

instance Semigroup l => Monad (EitherSemigroup l) where
  (>>=) (Right x) f = f x
  (>>=) (Left x) _ = Left x

值得注意的是Applicative的{​​{1}}和Monad实例与此非常相似，但对于产品类型，它可以收集“警告”。

如果我把它打包成Hackage，我可能会添加更多实例，但如果有人已经这样做了，我不想重新发明轮子。