mapM和forM

Question

您能告诉我mapM和forM之间是否存在一些差异？ 看签名：

mapM :: Monad m => (a -> m b) -> [a] -> m [b]
forM :: Monad m => [a] -> (a -> m b) -> m [b]

唯一的问题是参数的顺序。这是不可取的，但它真的只是区别吗？

Answer 1

forM在base中定义为flip mapM：

-- | 'forM' is 'mapM' with its arguments flipped. For a version that
-- ignores the results see 'Data.Foldable.forM_'.
forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b)
{-# INLINE forM #-}
forM = flip mapM