我正在编写一个函数mapper2,它将函数应用于两个列表:
mapper2 :: (a-> b -> c) -> [a] -> [b] -> [c]
mapper2 f (x:xs) (y:ys) = (f x y) : (mapper2 f xs ys)
mapper2 _ _ _ = []
我能够编译该函数但在应用它时会出错:
*Main> mapper2 (\x -> x*2) [2,4] [4,6]
<interactive>:4:1: error:
• Non type-variable argument in the constraint: Num (b -> c)
(Use FlexibleContexts to permit this)
• When checking the inferred type
it :: forall b c. (Num (b -> c), Num b) => [c]
有人可以向我解释如何解决这个问题以及错误意味着什么？
haskell ×1