Haskell，如何使用多个等式（等式a、等式b）=>

我想使用多次Eq， 因此，第一个元组的第二个元素来自其他类型

错了，但这正是我想要的

例如[a，a]->[a，a]->Bool-->[a，b]->[a，a]-> 布尔

代码

输入数据和期望值

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只需给它们不同类型的变量，并要求两者都使用Eq。我认为您正在寻找以下代码：

canColor :: (Eq a, Eq b) => [(a, b)] -> [(a, a)] -> Bool canColor _ [] = True canColor xs ((x,y):rest) = if findNeighbour xs x == findNeighbour xs y then False else canColor xs rest findNeighbour :: Eq a => [(a, b)] -> a -> Maybe b findNeighbour [] _ = Nothing findNeighbour ((x,y):rest) z = if x == z then Just y else findNeighbour rest z 或者这段更简洁、更惯用的代码：

canColor :: (Eq a, Eq b) => [(a, b)] -> [(a, a)] -> Bool canColor xs = all (\(x,y) -> lookup x xs /= lookup y xs)

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findNeighbour似乎正在进行参数交换的查找。请注意，查找允许a，b而不是a，a。这有帮助吗？Haskell的类型推断意味着许多问题都可以通过删除类型签名并在GHCi中使用：t检查函数来回答。即，如果没有显式类型签名，GHC将推断canColor:：Eq a，Eq b=>[a，b]->[a，a]->Bool。 canColor :: (Eq a, Eq b) => [(a, b)] -> [(a, a)] -> Bool canColor _ [] = True canColor xs ((x,y):rest) = if findNeighbour xs x == findNeighbour xs y then False else canColor xs rest findNeighbour :: Eq a => [(a, b)] -> a -> Maybe b findNeighbour [] _ = Nothing findNeighbour ((x,y):rest) z = if x == z then Just y else findNeighbour rest z canColor :: (Eq a, Eq b) => [(a, b)] -> [(a, a)] -> Bool canColor xs = all (\(x,y) -> lookup x xs /= lookup y xs)