CODEWITHSUNDEEP
haskell
Y N
Y N

Reputation: 841

What is haskell's arrow associativity?

I am currently learning haskell and struggling with the following test : Suppose we have such a type : 

type Endo a = a -> a

I have to choose all types that are equivalent to Endo (Endo Int)

(Int -> Int) -> (Int -> Int)
(Int -> Int) -> Int -> Int
Int
Int -> Int
Int -> Int -> Int -> Int
(Int -> Int) -> Int
Int -> Int -> (Int -> Int)
Int -> (Int -> Int)
Int -> Int -> Int

Since the type of Endo Int is Int -> Int I understand that type I need has 4 Ints such as (Int -> Int) -> (Int -> Int). But I do not really understand which parenthesis are unnecessary

Upvotes: 1

Views: 1636

Answers (2)

zch
zch

Reputation: 15278

It is right associative in Haskell, so following are equivalent:

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

Function that takes arguments a and b is equivalent to function that given argument a returns function that takes argument b.

It is not left associative.

So the answer is first two.

Upvotes: 5

chi
chi

Reputation: 116139

Your intuition is correct: (Int -> Int) -> (Int -> Int) is indeed Endo (Endo Int).

Just recall that -> associates on the right, i.e.

a -> b -> c     means    a -> (b -> c)

Given that, you should now be able to solve the exercise.

Upvotes: 0

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