Few programming languages actually support returning multiple values, and those that do are I think all quite old: the usual course these days is just to support record or tuple/list types and some kind of destructuring syntax, with the completely incidental effect of simulating returning multiple values, typically without any syntax sugar (unless you count destructuring, which is normally strictly sugar, but it’s often more a fundamental language feature and not really related to multiple return values).

KatLang’s algorithms look to me to just be functions that return tuples. Am I wrong?

Requiring that the reader read the entire expression before they can know the arguments they need to provide and the order they need to provide them in is not a good thing. Add the Grace~ operator and they have to parse even more, maintain a list of arguments in their head and even reorder them mentally! That’s massive cognitive overhead. If people start using this for anything of even moderate size, you will observe people writing the signature in comments—or perhaps, if I’ve read your docs properly, writing `A = #x, #y, x * y + y`. There’s a reason why serious programming languages all specify the signature separately from the body.