Chapter 7. Transforming Functions - Currying and Partial Application

In Chapter 6, Producing Functions - Higher-Order Functions, we saw several ways of manipulating functions, to get new versions with some change in their functionality. In this chapter, we will go into a particular kind of transformation, a sort of factory method, that lets you produce new versions of any given function, with some fixed arguments.

We will be considering the following:

• Currying, a classic FP theoretical function that transforms a function with many parameters into a sequence of unary functions
• Partial application, another time-honored FP transformation, which produces new versions of functions by fixing some of their arguments
• Something I'll call partial currying, that can be seen as a mixture of the two previous transformations

To be fair, we'll also see that some of these techniques can be emulated, with possibly greater clarity, by simple arrow functions. However, since you are quite liable to find currying...