raku hyperoperators

I first came across hyperoperators in Arne Sommer’s blog post detailing a Raku challenge, where the challenge was to see if a given array was “acronymous”. “Acronymous” is True when our inputs are ["coke", "sprite"] and "cs" (we take the first letters of the array, join them and compare them with the given string).

Here was my original solution:

my $str = @str.map({$_.comb.head}).join("").lc;

Here is Arne Sommer’s solution:

@str>>.substr(0,1).join.lc;

What in the >> was this? So I did some reading. From the docs (abridged):

Hyper operators… Apply a given operator… to one or two lists

What exactly does this mean? Well, lets look at some examples.

my @foods = <sushi pizza>;
my @nice-foods = @foods >>~>> " is delicious";
say @nice-foods; # [sushi is delicious pizza is delicious] 

So, we use the hyperoperator with the operator ~ (used for concatenation), and concatenate ” is delicious” to every item in the list. We could do it with a map, like so:

my @nice-foods = @foods.map: {$_ ~ " is delicious"}
my @nice-foods = @foods.map({$_ ~ " is delicious"});

But hyperoperators are more exotic. And exotic == fun.

What else can we do with hyperoperators? We can call methods on every item in a positional type:

@nice-foods>>.say; # sushi is delicious\npizza is delicious
sub add100 {$^n + 100}
my @nums = 1, 2, 3, 4, 5;
say @nums>>.&add100;

And we can get really crazy and chain hyperoperators with hyper method operators:

my @foods = <sushi pizza>;
(@foods >>~>> " is delicious")>>.say; # sushi is delicious\npizza is delicious

Overall… pretty cool.