Everyday Perl 6
by Jonathan Scott Duff
 
Perl 6 will soon be here. How will programming in Perl 6 be different from programming in Perl 5 for your average Perl programmer? The answer is: very different yet very much the same. A Perl 6 program viewed at arm's length will look much like a Perl 5 program viewed at arm's length. Programming in Perl 6 will still feel like programming in Perl. What will change however, is that Perl 6 will enable programmers to be more expressive by giving them more tools to work with (making easy things easy) and allowing them to be more precise in their expressions.

While many of the changes in Perl 6 make it easier for people new to programming or coming from other programming languages to understand the language, none of the changes were made solely on those grounds. If your favorite part of Perl 5 syntax is that it uses an arrow for method dispatch on objects, don't be dismayed that Perl 6 uses a dot instead. The designers carefully considered each syntactic change to ensure that Perl 6 still has the Perlish nature and that the change was an overall improvement. Some Perl programmers delight in the syntactic differences of the language, but some of those differences aren't that important when compared to the big picture of Perl's culture (which includes the language, CPAN, and the community of programmers).

Sigil Invariance

One of the fundamental changes is that whenever you refer to individual elements of an aggregate (an array or hash), rather than changing the sigil to denote the type of thing you get back, the sigil remains the same.

For example, in both Perl 5 and Perl 6 you can create and initialize aggregates:

    my @array = (1,3,5,12,37,42);
    my %hash  = ( alpha => 4, beta => 6 );

How you access the individual elements of those aggregates looks just a little different:

    # Perl 6                            # Perl 5
    my $third = @array[2];              my $third = $array[2];
    my $beta  = %hash{'beta'};          my $beta = $hash{'beta'};

Long-time Perl 5 programmers might wonder how slices work in Perl 6. The answer is: the same way as in Perl 5.

    my @odds = @array[1,3,5];           # array slice
    my @bets = %hash{'alpha','beta'};   # hash slice

The only difference is that in Perl 5 the hash slice would have started with a @ sigil.

New Brackets

In these hash examples, it's awkward quoting the indexes into the hash. Perl 5 allows a syntactic shortcut where $hash{word} works as if you had written $hash{'word'}. A problem with that is that it can cause confusion when your word happens to be the name of a subroutine and you really want Perl to execute that subroutine.

In Perl 6, a syntactic shortcut for accessing hash elements takes advantage of a name change of the "quote word" operator:

    # Perl 6                        # Perl 5
    my @array = <foo bar baz>;      my @array = qw(foo bar baz);
    my %hash  = <a b c d e f g h>;  my %hash = qw(a b c d e f g h);
    my $queue = %hash<q>;           my $queue = $hash{'q'};
    my @vows  = %hash<c a g e>;     my @vows = @hash{qw(c a g e)};

Also, just as double-quoted strings interpolate while single-quoted strings do not, double-bracketed "quote word" constructs also interpolate:

    my $foo  = "This is";
    my $bar  = "the end";
    my @blah = << $foo $bar >>;     # ('This','is','the','end');

Note that the interpolation happens before the "quote word" aspect of this operator.

Speaking of interpolation, interpolating into double-quoted strings has changed slightly. Now to interpolate an array into a string, you must provide a set of empty brackets at the end of the array name. This has the side benefit of eliminating the ambiguity of whether you meant interpolation if you happen to include (for instance) an email address in your double-quoted string.

    my @items = <names addresses email>;
    say "Send @items[] to test@foo.com";
    # Send names addresses email to test@foo.com

You can also interpolate more things into your double-quoted strings:

    say "Send me $person.name()";         # results of a method call
    say "2 + 2 = { 2+2 }";                # any bit of perl code

That second one means that you'll have to be careful about inserting curly braces in your double-quoted strings, but that's a small price to pay for the ability to interpolate the results of arbitrary Perl code.

By the way, get used to the say subroutine. It's the same as print, but it appends a newline to the end. Quite useful, that.

Fewer Parentheses

The usual places in Perl 5 that require parentheses no longer do in Perl 6:

    # Perl 6                        # Perl 5
        if $cond  { ... }                if ($cond)  { ... }
    unless $cond  { ... }            unless ($cond)  { ... }
     while $cond  { ... }             while ($cond)  { ... }
       for @array { ... }               for (@array) { ... }

In Perl 6, parentheses are now only necessary for grouping.