Oleksandr Zahorulia

It's not crucial, but it's gonna make code more readable and clear in a way. But It would be even greater if we had literals for passing functions instead of strings, (e.g. |> htmlentities(...) instead of |> 'htmlentities').

A big NO for this one. Interfaces are interfaces, they declare the signature and introducing a contract for the implementing classes. If you need "default" implementation, you must do that in an abstract class. Let's not confuse different things into one.

So many times I had to drop array_map/reduce or similar functions just because I didn't want to use "classic" closure syntax. Honestly, I don't even see a big need in having the "classic" syntax nowadays, but having a multiline new-style closure looks very logical to me.