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Path to FP - Fancy functions

We already know FP is about programming just with functions, pure and descriptive functions.

There are some really fancy kind of functions out there:

HOF (High Order Function)

Yep, a HOF is one that can take in as parameter or spit out as its result a function, and guess what, if for some weird reason you’ve been doing some JavaScript there’s a super high probability that you already used HOF.

function add1(x) { return x + 1; }
var number = [1, 2, 3, 4, 5].map(add1);

Where map is a HOF. Now let’s see the same example in Scala:

val numbers = (0 to 10).toList

numbers.map(x => x * x)


Let’s get some diabetes by syntactic sugar 🤣

numbers.map(_ + 1)

When doing Scala code and working with HOF is super normal to pass around anonymous functions (as we did in number.map example) rather than declaring a val or a def.

Partial Functions

A partial function is a function that will only work for a given set of its domain. A function that will not produce a value for every possible input value it can be given. We can use this type of function whenever we have functions with a ton of guard code (a bunch if and else testing the inputs). A simple example is when dividing by zero.

def divide(x: Int, y: Int) = x / y

// dividing(1, 0) will throw
// we can use partial function for testing valid y values

val devidePF: PartialFunction[(Int, Int), Int] = {
  case (x, y) if y > 0 => x / y
println("8/2 equals " + devidePF(8, 2))
// println("8/2 equals " + devidePF(2, 0)) this will throw, the value of y is not valid