如何解决此类型错误？
我无法将以下程序加载到 GHCi：
minList :: Ord a => [a] -> a
minList (x:[]) = x
minList (x:y:xs) = minList( min x y : xs)
bubList :: Ord a => [a] -> [a]
bubList [] = []
bubList ( x:y:[] ) = min x y : max x y
bubList ( x:y:xs ) = minList(x:y:xs) : bubList(xs)
当我编译它时，我收到以下错误消息：
Couldn't match type `a' with `[a]'
`a' is a rigid type variable bound by
the type signature for bubList :: Ord a => [a] -> [a]
at ex1.hs:11:1
In the second argument of `max', namely `y'
In the second argument of `(:)', namely `max x y'
In the expression: min x y : max x y
I fail to load the following program to GHCi:
minList :: Ord a => [a] -> a
minList (x:[]) = x
minList (x:y:xs) = minList( min x y : xs)
bubList :: Ord a => [a] -> [a]
bubList [] = []
bubList ( x:y:[] ) = min x y : max x y
bubList ( x:y:xs ) = minList(x:y:xs) : bubList(xs)
When I compile it I get the following error message:
Couldn't match type `a' with `[a]'
`a' is a rigid type variable bound by
the type signature for bubList :: Ord a => [a] -> [a]
at ex1.hs:11:1
In the second argument of `max', namely `y'
In the second argument of `(:)', namely `max x y'
In the expression: min x y : max x y
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max x y将返回一个值 (a)，而不是列表 ([a])。您只能将 cons (:) 放入列表中。你需要写：max x ywill return a value (a), not a list ([a]). You can only cons (:) into a list. You are going to need to write, instead: