Function composition is one the key features (among others) of functional programming. Programming languages that offer higher order functions as a feature can potentially use function composition. But, still, programmers need to be aware of some key concepts to successfully apply this pattern in our code. Function composition, as defined on Wikipedia, is an act or mechanism to combine simple functions to build more complicated ones. In other words, we can define new functions, equivalent to the result of chaining a set of given functions, so the input of function i is the output (or result) of function i-1.