/ˌhaɪər ˈɔːrdər ˈfʌŋkʃən/
noun … “A function that operates on other functions.”
Higher-Order Function is a function that either takes one or more functions as arguments, returns a function as its result, or both. This concept is fundamental in Functional Programming, allowing programs to abstract behavior, compose operations, and manipulate computations as first-class values. By treating functions as data, developers can build flexible, reusable, and declarative pipelines.
Key characteristics of Higher-Order Functions include:
- Function as parameter: accepts functions to customize behavior dynamically.
- Function as return: produces new functions for deferred execution or composition.
- Abstraction: encapsulates common patterns of computation, reducing duplication.
- Composability: enables chaining and nesting of operations for expressive data pipelines.
Workflow example: In Scala, the map function is higher-order because it takes a transformation function and applies it to each element of a collection, returning a new collection without modifying the original.
val numbers = List(1, 2, 3, 4)
val doubled = numbers.map(n => n * 2)
println(doubled) -- Output: List(2, 4, 6, 8)Another example: a function that returns a logging wrapper can dynamically generate new functions that add behavior without changing the original logic.
def logger(f: Int => Int): Int => Int ={
x => { println("Input: " + x); f(x) }
}Conceptually, Higher-Order Functions are like adaptable machines on a production line: you can feed in different tools (functions) or create new machines dynamically to handle changing tasks. This design provides flexibility and modularity in computation.
See Functional Programming, Scala, Immutability, Actor Model.