Soar with Haskell

4

Higher-Order Functions

One of the most important concepts in programming is the notion of abstraction. Abstraction is the ability to reuse a common code pattern without having to repeat its details and by referring to it by name. Functions themselves are a fundamental form of abstraction. For instance, in the expressions 1+2 and 1+40, the common part is (1+). We can abstract over this common pattern by defining a function:

inc :: Integer -> Integer
inc n = 1 + n

In this chapter, we go one step further by abstracting over these abstractions. Indeed, we allow functions to have other functions as parameters. Such functions are called HOF (HOFs). A HOF represents a whole family of different functions that have the same overall structure but differ ...