Return Bool from insert indicating whether the value was inserted or not

[bennofs]

Currently, the insert function has () as return type. However, it's often useful to know whether the value was actually inserted (didn't exist yet) or not. I think this should be easy to determine while inserting.

[gregorycollins]

Right now insert always inserts, i.e. it is really replace. That won't change without a major API overhaul.

[bennofs]

yeah, but it could still return a Maybe a perhaps with the old value?