Functions

Functions in Lantern are a way to bundle reusable behavior. In fact, the entrypoint of every Lantern program is itself a function! It provides the behavior of the program when executed.

Functions are defined using the fun keyword and can have any number of parameters and a return type. For example, take a look at this function definition:

fun add(a: int, b: int) -> int {
  val sum = a + b;
  return sum;
}

This function is named add and it takes two different parameters, a and b. In this case, both of these parameters are integers. Additionally, it returns an int back to the caller. In the function body, we are doing a simple addition calculation and storing in the sum variable. Then, we return that sum and give it back to the caller. Calling this function should look familiar:

add(2, 5);

We can also store the result of the function (what it returns) in a variable:

val sum = add(2, 5);

Note that sum here is an int, since the add function returns an int.