Higher-order functions and lambdas

The [+] reduction operator that we have just seen in the previous section is performing the action of the + operator as many times as needed to add up all the elements of the provided data.

In Perl 6, there is an alternative way of doing reduction operations. There exists a built-in function reduce that expects a code block that will execute the action. First, we will use the function add($a, $b) that we created in Chapter 2, Writing Code:

sub add($a, $b) {
    return $a + $b;
}

say reduce &add, 10..15;

The reduce function takes the reference to a function as the first argument and a flattened list of values. In &add, the ampersand before the name of the function tells Perl 6 that this is not a function call but a code reference to a function.

The reduce function is an example of the higher-order function. One of its arguments is another function. In Perl 6, functions are the first-class objects, which means that they can be passed as arguments to...