`+-` here is an entirely new operator though. The shuffling of arguments might look a bit weird though, it could also be written

    (+-) x y = (x + x) - (y + y)

Symbol operators are automatically infix though, and you can make them normal using (), same as backticks make normal functions infix, `a la 2 `plus` 3.

what exactly is crazy about this?

The simplicity with which a new operator is defined.

I think this is a downside. It just makes reading new code that uses esoteric symbols defined elsewhere.

This[0] operator glossary reviews the most used operators.

[0]: https://haskell-lang.org/tutorial/operators

This. Incredible elegant. I always enjoy these types of things when programming Lisp.