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Heredocs in Raku

Hey there, Raku enthusiasts! Today, we’re diving into the wonderful world of heredocs. Now, I know what you’re thinking: “Heredocs? Sounds like something from a medieval fantasy novel!” Well, you’re not entirely wrong – heredocs are indeed magical, but in the realm of programming! 😄

What’s a Heredoc, Anyway?

Imagine you’re writing a long, multi-line string in your code. You could use a bunch of quotation marks and line breaks, but that gets messy fast. Enter the heredoc – your multi-line string superhero! 🦸‍♀️

A heredoc in Raku is a way to write multi-line strings without all the fuss. It’s like giving your string its own cozy little house in your code. Let’s see how it works!

The Basics: Your First Heredoc

Here’s a simple heredoc in action:

say q:to/END/;
Roses are red,
Violets are blue,
Heredocs are awesome,
And so are you!
END

When you run this, you’ll see:

Roses are red,
Violets are blue,
Heredocs are awesome,
And so are you!

How cool is that? We just wrote a multi-line string without any quotation marks or concatenation. The q:to/END/ tells Raku, “Hey, start a heredoc here and keep going until you see a line that just says ‘END’.”

Getting Fancy: Interpolation with qq

Now, let’s say you want to use variables in your heredoc. That’s where qq comes in handy. It’s like the cool cousin of q that allows interpolation. Check this out:

my $name = "Alice";
my $age = 28;

say qq:to/BIO/;
Name: $name
Age: $age
Hobbies: Coding in Raku,
         Drinking coffee,
         Explaining heredocs to friends
BIO

This will output:

Name: Alice
Age: 28
Hobbies: Coding in Raku,
         Drinking coffee,
         Explaining heredocs to friends

Pro tip: Be careful with $ signs in your qq heredocs. If you have a $ that’s not meant to be a variable, you’ll need to escape it with a backslash (\$).

The Indentation Magic Trick 🎩✨

Here’s a neat feature: Raku is smart about indentation in heredocs. If your ending delimiter is indented, Raku will remove that same amount of indentation from every line. It’s like your code is doing a little dance to align everything nicely!

say q:to/SPELL/;
    Double, double toil and trouble;
    Fire burn and caldron bubble.
    Fillet of a fenny snake,
    In the caldron boil and bake;
    SPELL

Even though we indented the heredoc content, the output will be flush left:

Double, double toil and trouble;
Fire burn and caldron bubble.
Fillet of a fenny snake,
In the caldron boil and bake;

Heredocs in the Wild: Real-world Examples

Let’s look at some fun, practical examples of where heredocs shine:

1. Writing HTML Templates

my $page_title = "My Awesome Raku Blog";
my $content = "Heredocs rock!";

say qq:to/HTML/;
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>$page_title</title>
</head>
<body>
    <h1>$page_title</h1>
    <p>$content</p>
</body>
</html>
HTML

2. Crafting a Silly Mad Libs Game

my $noun = prompt "Give me a noun: ";
my $verb = prompt "Now a verb: ";
my $adjective = prompt "Finally, an adjective: ";

say qq:to/MADLIB/;
Once upon a time, there was a $adjective $noun.
This $noun loved to $verb all day long.
The end. (Hey, I never said it was a good story!)
MADLIB

3. Creating a Multi-line Regex Pattern

my $regex = rx:to/PATTERN/;
    ^ # Start of string
    \d+ # One or more digits
    \s* # Optional whitespace
    [:alpha:]+ # One or more letters
    $ # End of string
    PATTERN

say "42 answer" ~~ $regex; # True
say "Not a match" ~~ $regex; # False

Wrapping Up

Heredocs are like the Swiss Army knife of string literals in Raku. They’re flexible, readable, and can make your code look cleaner than a whistle. 🎶

Remember:

Use q:to/END/ for literal strings
Use qq:to/END/ when you need interpolation
Use qx:to/END/ for regular expression patterns.
The ending delimiter can be anything you want (not just END)
Indentation is magically handled for you

Next time you find yourself wrestling with a multi-line string, remember your new superhero friend: the heredoc!

Happy coding, Raku rockstars! 🎸✨

P.S. I once spent an hour debugging a heredoc only to realize I had misspelled the ending delimiter. Don’t be like me – double-check those delimiters! 😅

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