如果将控制结构作为表达式(以一种很好的方式),如何制作一个if then else

Question

我想知道做这种事的正确和优雅的方式

function candy = case (color candy) of
    Blue -> if (isTasty candy) then eat candy
            else if (isSmelly candy) then dump candy
            else leave candy

我试过了

function candy = case (color candy) of
    Blue -> dealWith candy
        where dealWith c
                | isTasty c = eat candy
                | isSmelly c = dump candy
                | otherwise = leave candy

谁知道如何改进这个？

更多

我知道我可以用它

function candy = case (color candy) of
    Blue -> case () of
                _ | isTasty candy -> eat candy
                  | isSmelly candy -> dump candy
                  | otherwise -> leave candy

但是使用一段case时间不匹配任何东西似乎都不是正确的方法.

Answer 1

您可以直接在外部case表达式中使用警卫.

fun candy = case color candy of
    Blue | isTasty candy  -> eat candy
         | isSmelly candy -> dump candy
         | otherwise      -> leave candy

Answer 2

您可以在GHC 7.6中使用多向if表达式:

fun candy = case color candy of
    Blue -> if | isTasty candy -> eat candy
               | isSmelly candy -> dump candy
               | otherwise -> leave candy