06-higher-order-functions

Higher Order Functions

• can take functions as parameters

• can return functions as return values

• define what stuff is

Curried

• Partially applied functions

High order functions

Maps and filters

Folds

foldl, foldr

• we usually use right folds when we're building up new lists from a list.

  • because ++ function is much more expensive than :

• right folds work on infinite lists, whereas left ones don't!

• if you take an infinite list at some point and you fold it up from the right, you'll eventually reach the beginning of the list

foldl1, foldr1

• If the function doesn't make sense when given an empty list

scanl, scanr

• they report all the intermediate accumulator states
• filter doesn't work on infinite lists

Function application with $

• $ function has the lowest precedence
• function application with $ is right-associative.

Function composition

• is right-associative