The arity of a function is the number of arguments that the function takes. A unary function is a function that only takes one argument:
function isNull<T>(a: T|null) {
return (a === null);
}
Unary functions are very important in FP because they facilitate the usage of the function composition pattern.
We will learn more about the function composition pattern later in this chapter.
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 to transform functions that allow multiple arguments ...
