Haskell:是否可以确定哪个函数作为参数传递给高阶函数？

Question

我想确定哪个函数作为参数传递给高阶函数。
我怎样才能做到这一点？使用模式匹配？
我想做类似以下代码的事情:

add x y = x+y
sub x y = x-y

myFunc :: (a->a->a) -> a -> a -> IO a
myFunc add x y = do print "add was performed"
                    add x y 
myFunc sub x y = do print "sub was performed"
                    sum x y
myFunc f x y = do print "another function was performed"
                  f x y

如果这是不可能的，有没有人有其他想法可以做到这一点？

Answer 1

不，这是不可能的。

您可以通过具有表示操作的数据类型来实现该效果，也许

data Operation
    = Add (a -> a -> a)
    | Sub (a -> a -> a)
    | Other (a -> a -> a)

myFunc :: Operation -> a -> a -> IO a
myFunc (Add f) x y = do print "add was performed"
                     return (f x y)
myFunc (Sub f) x y = do print "sub was performed"
                     return (f x y)
myFunc (Other f) x y = do print "another function was performed"
                     return (f x y)