小编Chr*_*Dee的帖子

我得到的问题说:

以类似于mapMaybe的方式,定义函数:composeMaybe ::(a-> Maybe b) - >(b - > Maybe c) - >(a-> Maybe c),它组成两个错误提升函数.

类型Maybe a和函数mapMaybe的编码如下:

data Maybe a = Nothing | Just a

mapMaybe g Nothing = Nothing
mapMaybe g (Just x) = Just (g x)

我尝试使用这样的组合:

composeMaybe f g = f.g

但它没有编译.

有人能指出我正确的方向吗？