What are some interesting uses of higher-order functions?

Question

I\'m currently doing a Functional Programming course and I\'m quite amused by the concept of higher-order functions and functions as first class citizens. However, I can\'t yet

Answer 1

Higher-order functions are also required for currying, which Haskell uses everywhere. Essentially, a function taking two arguments is equivalent to a function taking one argument and returning another function taking one argument. When you see a type signature like this in Haskell:

f :: A -> B -> C

...the (->) can be read as right-associative, showing that this is in fact a higher-order function returning a function of type B -> C:

f :: A -> (B -> C)

A non-curried function of two arguments would instead have a type like this:

f' :: (A, B) -> C

So any time you use partial application in Haskell, you're working with higher-order functions.