Fair, but seems inconsistent to have `fn` instead of `function` like we use for anonymous functions - unless `fn` acts like an alias to `function` now (which doesn't sound like is the case) which wouldn't be as ambiguous for the compiler to figure out

I don't think there's an ambiguity, since the key-value application of that operator only happens inside the array definition or when you do foreach ($x as $k => $v) {}.