[solosoyokaze]

> There is nothing preventing people from writing their own reduce() in their own utilities package, and I expect a thriving ecosystem of "even-more-functional-constructs" packages to spring up as soon as generics hit stable.

I really hope this doesn't happen because then you have random utility libraries that "infect" projects for what is essentially basic flow control. I would say stuff like this is best supported in the standard lib and not home rolled.