从 Either 提升到 IO

Question

我想在没有 Either 的任何线索的情况下从 Either monad 转换为 IO。有更优雅的方法吗？

我写了这个函数，但我想使用库或 Prelude 中的东西：

liftEither :: forall t (m :: * -> *) a. Monad m => (t -> m a) -> Either String t -> m a
liftEither f (Right a)  = f a
liftEither _ (Left msg) = fail msg

Answer 1

使用 Data.Either 中的 either 函数类似这样：

liftEither :: Monad m => (t -> m a) -> Either String t -> m a
liftEither f xs = either fail f xs

或者更简单：

liftEither :: Monad m => (t -> m a) -> Either String t -> m a
liftEither = either fail

从 Either 提升到 IO

Lifting from Either to IO

monads

haskell