treat polymorphic function with no value parameters as by-name

[bishabosha]

Reducing Boilerplate

val none: [T] => Option[T] =
  [T] => None

expands to

val none: [T] => () => Option[T] =
  [T] => () => None

with this inference, call sites would still look like the following:

val m = none[Int]() // : Option[Int]
val n = none() // : Option[Nothing]
val o = none[Int] // error - method apply must be called with () argument

[smarter]

Having parens at the use-site but not the definition site looks confusing and doesn't match any other construct in the language, if we do accept [T] => Option[T] I suggest treating it as a "polymorphic by-name", so val n = none by itself would have type Option[Nothing], this is also similar to how context functions work.