Why can't list[?str] support Eq ?

[plajjan]

We had this code the other day where something produced a list[?str] and then we try to compare it like if my_list == ["a", "b"] and this doesn't compile... but I feel it should. I don't know exactly how, but it should. Clearly, if a list contains some None elements, it can't equal a list that only contains str. Similarly, for if foo == ["a", None], since the foo list starts with a None, then it's obvious that it won't equal the list we compare with since the first element "a" is a str, which clearly isn't None, so the overall result of this list comparison must be false. I don't understand enough of how Eq on a list works to know what needs to do what in order to support this, but it feels doable and all these checks around None are silly.

Everything could have a default Eq implementation that is the same as Identity, so if it's the actual same instance, then it's Eq==True, otherwise False. That would be enough to make the comparison in the example work and maybe it's useful for other things too.