Learning Perl 6

Chapter 6. Positionals

Your programming career is likely to be, at its heart, about moving and transforming ordered lists of some kind. Those might be to-do lists, shopping lists, lists of web pages, or just about anything else.

The broad term for such as list is Positional. Not everything in this chapter is strictly one of those; it’s okay to pretend that they are, though. The language easily interchanges among many of the types you’ll see in this chapter, and it’s sometimes important to keep them straight. Mind their differences and their different uses to get exactly the behavior you want.

This is the first chapter where you’ll experience the laziness of the language. Instead of computing things immediately as you specify them in your code, your program will remember it needs to do something. It then only does it if you later use it. This feature allows you to have infinite lists and sequences without actually creating them.

Constructing a List

A List is an immutable series of zero or more items. The simplest List is the empty list. You can construct one with no arguments. The List as a whole is one thingy and you can store it in a scalar:

my $empty-list = List.new;
put 'Elements: ', $empty-list.elems;  # Elements: 0

The .elems method returns the number of elements, which is 0 for the empty List. This might seem like a trivial result, but imagine those cases where you want to return no results: an empty List can be just as meaningful as a nonempty one.

Instead of the call to .new, you ...