Learning Perl 6

Coolnamehere> Geekery> Perl> Perl 6> Learning Perl 6

Okay, let's see what we can do to get the basics of Perl 6 down.

The Shell

pugs> say "Hello"
Hello
bool::true

Notice that you don't need to use semi-colons in the shell. Pugs is pretty generous in that regard. Perl 6 uses say to print out a line of text. This is a bit easier than earlier versions, which forced you to append a newline at the end of all your print statements. That bool::true bit is the return value of the expression, which we usually don't worry about with functions like say.

So now we know how to print a line of text. Okay, now let's get some user input.

pugs> my $name = =$IN
Brian
"Brian\n"

This is a pretty simple example of declaration and assignment. Perl users should already be familiar with my, which declares a new lexical variable. The $name tells Perl it's a scalar variable named, well, name. So far so good.

But what's that on the other side of the equal sign? It's certainly not how we're used to getting our user input. This is the new Perl 6 way. Hey, I'll be honest. I don't really understand what's going on with the extra dollar sign, but I do get that $IN is the (probably) global variable representing STDIN. Until we get a clue, we'll just follow this practice blindly, and use =$IN whenever we need to get something from the standard input stream.

I enter my name, and the Pugs shell shows us the return value that gets assigned to $name: "Brian\n". There's that newline at the end of all input. Well, this is Perl after all, so we still need to chomp our input so we can make good use of it in our own code.

pugs> $name = chomp($name)
"Brian"

chomp makes a little more sense to me now than it did in earlier versions of Perl. Instead of directly altering the string and returning the number of characters "chomped" from the end, it returns an altered copy of the string. It's a small thing, but it shows a big shift in how Perl 6 works. Less hackery magic, more straightforward coding.

After all these little changes, I need to see something that works the same.

pugs> say "Hello $name"
"Hello Brian"
bool::true

String interpolation seems to work the same as it always has, at least for simple scalars like $name. This is a pleasant relief, even if I do lean towards concatenating rather than interpolating. But concatenation has changed as well:

pugs> say "Hello " ~ $name
"Hello Brian"
bool::true

So interpolate or concatenate, whichever.

Now that we've played a little bit in the Pugs shell, handling input and output from the Perl 6 perspective, let's put it all into a script.

Writing a Quick Script

Let's write a script version of what we did, with a little addition.

print "What's your name? ";
my $name = =$IN;
$name = chomp($name);
say "Hello, $name!";

Since I'm still doing a lot of Perl 5 work, I chose to save this file as hello.p6. I lose my precious syntax highlighting, but I can live without that for now.

First thing you'll notice is that we're back to using semi-colons; We may not need them inside the shell, but the interpreter still needs them to separate statements while handling a file.

I also used the good old print function to display some text without a newline at the end. We have say to save us from using print a lot of times, but occasionally print still makes more sense.

Running this script is very easy, assuming that pugs is on your path.

C:\projects>pugs hello.p6
What is your name? Brian
Hello, Brian!

And that's our quick glance at some of the small differences between Perl 5 and Perl 6. I'll look at more when I get the opportunity.