Haskell 复杂 Function 类型

Question

A Haskell function I am struggling with has the following type

func1:: (Integer -> Integer -> Integer) -> Integer -> Integer -> Integer

I am unsure of how to handle the Parenthesis piece in the actual implementation. I know that a function should be passed into the input in this scenario. (Integer -> Integer -> Integer)

Answer 1

When a function is passed to you as a parameter, the only useful thing you can do with it in the end is to call it. That's what functions are for. That's what they do.

For example, in this case it may look something like this:

func1 :: (Integer -> Integer -> Integer) -> Integer -> Integer -> Integer
func1 f a b = f (a*2) (b+5)

Here, the first parameter is named f and it's a function that takes two parameters, both Integer , and returns another Integer - that much is conveyed by its type (Integer -> Integer -> Integer) .

The second and third parameters are named a and b respectively, and they're both Integer .

The body of function func1 consists of calling its function-parameter f , passing it (a*2) and (b+5) as parameters.