Currying
In this lesson you will be introduced to a method of writing functions with multiple parameter lists.
Currying is a style of defining functions where essentially every function is mapped to an expression that consists of nested anonymous functions, that in turn take one parameter each.
In other words, rather than a single parameter list, a currying function is passed or applied to multiple parameter lists.
The best way to understand currying is by looking at a simple example. Let’s define a simple summation function which adds two integers together.
def simpleSum(x: Int, y:Int) = x + yprintln(simpleSum(3,2))
The function above is applied to a single parameter list which contains two parameters.
Now, let’s define a curried function which has the same functionality as simpleSum.
def curriedSum(x: Int)(y: Int) = x + yprintln(curriedSum(3)(2))
This function is applied to two-parameter lists with a single parameter in each list.
What’s happening here is that when we call curriedSum, we actually get two back-to-back traditional function calls. The first function call takes a single parameter of type Int and returns a function value which will be used by the second function. The function returned by the first function is the second function. The second function, in turn, takes a parameter y of type Int.
Currying will become a lot more clear in the next few lessons.
In the next lesson, we will be applying the currying syntax to our summation program.