How do you define and use curry and uncurry (Prelude functions) in Haskell?

You get errors because your type signatures are wrong, you should use tuples instead of functions for arguments, a

and b

:

curry' :: ((a, b) -> c) -> a -> b -> c
uncurry' :: (a -> b -> c) -> ((a, b) -> c)

      

        
        
        
      

    

Also note the parentheses I added to the type uncurry'

, which are important in this case. What you have is equivalent to

uncurry' :: a -> (b -> (c -> ((a -> b) -> c)))

      

        
        
        
      

    

It is not the same, it is a function that takes 3 arguments and creates a function instead of a function that takes a function of 2 arguments and returns a function of one tuple argument.

You can use these functions like

> uncurry (+) (1, 2)
3
> curry fst 1 2
1
> curry snd 1 2
2

      

        
        
        
      

    

(I have not seen any other functions Prelude

that take tuples as arguments)

EDIT: On requesting chi, here's a clearer explanation of that last sentence:

a -> (b -> (c -> ((a, b) -> c)))

      

        
        
        
      

    

- a type of function that takes 3 arguments a

, b

and c

, and returns a function of type (a, b) -> c

.

(a -> b -> c) -> ((a, b) -> c)

      

        
        
        
      

    

- the type of a function that takes one argument a -> b -> c

and returns a function (a, b) -> c

.