The linked site has implementations of the Y combinator in many, many different programming languages. The Y combinator is a famous idea in programming that lets a function call itself without knowing it’s own name. Understanding how it works is a brain-melting exercise.
Among pages and pages of barely-readable code, I came across this delightful little comment:
“Note that Perl 6 doesn’t actually need a Y combinator because you can name anonymous functions from the inside”
Brilliant. That demonstrates the idea that many programming patterns are just dumb hacks around limitations of the programming language.