Expanding a Multiple Parameter List

In the following lesson, we will expand a multiple parameter list to see how a function with a multiple parameter list is executed.

We'll cover the following

General Form

The general form of a function with multiple parameter lists is as follows:

In the illustration above, n>1.

The above function is equivalent to the following:

The function f is taking the first n-1 lists of parameters and creating a new function h which takes the nth list of parameters. h then maps the nth list of parameters to the function body Exp with h being the function that gets returned.

The above, can also be written using anonymous functions as follows.

The above function can be further expanded:

If we do this n times, we would get the following:

An Example

We will expand the curriedSum function created in a previous lesson to better understand the general sequence of expansion explained above.

Just as a reminder. here is the curriedSum function:

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def curriedSum(x: Int)(y: Int) = x + y

Let’s start expanding!

In the first expansion CurriedSum is now a function which takes a single parameter of type Int and returns a function.

In conclusion, curriedSum is a combination of two nested function calls. As mentioned in a previous lesson, 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 and returns the sum of x and y.

Let’s try to implement both functions. The first function will be known as first and the second function will be known as second.

For our example, x = 3 and y = 2.

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def first(x: Int) = (y: Int) => x+y
def second = first(3)
val result = second(2)
print(result)

second is defined by calling first and passing the value of x to the first function. We can then call second by passing the value of y to the second function which will in turn return in the final sum, i.e. 5.

In the next lesson, you will be asked to make your own function using the currying syntax.