Named parameters

In contrast to positional parameters, named parameters are referred

by their names.  The following function takes two parameters called 

$from and $to:

sub distance(:$from, :$to) { $from - $to }

Now, to call the function, you need to name the arguments:

say distance(from => 30, to => 10); # 20

It is an error to pass the arguments as if they were positional.
For example, a call distance(30, 10) generates an error: ...