Add an empty for OptionT

[DomBlack]

Currently OptionT has a pure method, but it can be useful to have a empty method on the object. At the moment we're simply using the apply to work around it;

def something(empty: Boolean): OptionT[Future, String] = {
  if (empty) OptionT(Future.success(None)) else OptionT.pure("Hi")
}

However empty would look cleaner and be easier to understand

def something(empty: Boolean): OptionT[Future, String] = {
  if (empty) OptionT.empty else OptionT.pure("Hi")
}

[ceedubs]

👍 sounds good to me.

It'd look something like this, right?

def empty[F[_]:Applicative, A]: OptionT[F, A]

[ceedubs]

I'm wondering if something like OptionT.none might be a better name. It might be a little counterintuitive to call empty[List, String] and get back a List that isn't actually empty (but instead contains a single None element). I'm also thinking of empty[NonemptyList, String].

[adelbertc]

+1 for OptionT.none

[mikejcurry]

I think this should be closed now because of: #946