Hands-On Functional Programming with TypeScript

Function arity

The arity of a function is the number of arguments that the function takes. A unary function is a function that only takes a single argument:

function isNull<T>(a: T|null) {    return (a === null);}

Unary functions are very important in functional programming because they facilitate utilization of the function composition pattern.

We will learn more about function composition patterns later in Chapter 6, Functional Programming Techniques.

A binary function is a function that takes two arguments:

function add(a: number, b: number) {    return a + b;}

Functions with two or more arguments are also important because some of the most common FP patterns and techniques (for example, partial application and currying) have been designed ...