我正在编写的以下函数是否有标准/优化的实现(可能是不必要的):
filterFirstM :: (Monad m, Foldable t) => (a -> Bool) -> t m a -> m a
filterFirstM predicate actions = foldlM fn Nothing actions
where
fn memo action = case memo of
Just _ -> pure memo
Nothing -> do
x <- action
pure $ if predicate x then (Just x) else Nothing
示例用法:
filterFirstM (== 1) [pure 0 :: IO Int, pure 1, error "not evaluated"] == (pure 1)