Higher-order Function - Example

Example

The following examples are not intended to compare and contrast programming languages, since each program performs a different task. Also, the idea of a "scripting language" is beyond the scope of this article.

This Python program contains the higher-order function g which takes a function as its first argument and returns a number. This example prints 100 ( g(f,7)= (7+3)×(7+3) ).

def f(x): return x + 3 def g(function, x): return function(x) * function(x) print g(f, 7)

This Haskell code is the equivalent of the Python program above.

f = (+3) g function x = function x * function x main = print $ g f 7

In this Scheme example the higher-order function g takes a number and returns a function. The function a takes a number and returns that number plus 7. (e.g. a(3)=10).

(define (g x) (lambda (y) (+ x y))) (define a (g 7)) (display (a 3))

In this Erlang example the higher-order function or_else/2 takes a list of functions (Fs) and argument (X). It evaluates the function F with the argument X as argument. If the function F returns false then the next function in Fs will be evaluated. If the function F returns {false,Y} then the next function in Fs with argument Y will be evaluated. If the function F returns R the higher-order function or_else/2 will return R. Note that X, Y and R can be functions. Example returns false.

or_else(, _) -> false; or_else(, X) -> or_else(Fs, X, F(X)). or_else(Fs, X, false) -> or_else(Fs, X); or_else(Fs, _, {false, Y}) -> or_else(Fs, Y); or_else(_, _, R) -> R. or_else(,3.23).

In this JavaScript example the higher-order function ArrayForEach takes an array and a method in as arguments and calls the method on every element in the array.

function ArrayForEach(array, func) { for(i = 0; i < array.length; i++) { if(i in array) { func(array); } } } function log(msg) { console.log(msg); } ArrayForEach(,log);