On: A lambda is not necessarily a closure

[Ono-Sendai]

It's probably because, in an implementation of a staticly typed language, you have to treat all functions being passed around as closures. E.g. the type of a lambda expression needs to be one thing, and that is a closure. Whether or not any variables are actually closed over is irrelevant.

[nailer → Ono-Sendai]

Couldn't the type of a passed around function simply be 'function'? Why does it have to be inaccurate?

[Ono-Sendai → nailer]

Well a function may in general have closed over arguments. Therefore it needs to be a closure. (If you have lexical scoping that is)