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

I'm a particular fan of higher-order memoization:

memo :: HasTrie t => (t -> a) -> (t -> a)

(Given any function, return a memoized version of that function. Limited by the fact that the arguments of the function must be able to be encoded into a trie.)

This is from http://hackage.haskell.org/package/MemoTrie