Gonna go out on a limb and guess... Perl 6?

`my` gives away perl

infinite symbol gives away 6

So, yeah. Correct me if I'm wrong.

Yup both right. All the clues were there >:3 I could have used Inf instead of the unicode but thats not really whimsical enough for Hacker News.

A slightly less listy pattern style is to declare types. Like I'd prefer this sort of declarative style:

     subset Prime of Int where *.is-prime;
     subset TwinPrime of Prime where (* + (2|-2)).is-prime;
     my @twin_primes = grep TwinPrime, ^Inf;

Just feels a lot more clear what my intent is and I get some cheap types for later, to use in function parameters that require twin primes.

Huh, this is actually making me want to give Perl 6 another try.

How is performance on a task like this compared to, say, Python?