Thanks Eric Elliott, you pushed me to fix what was a pretty huge mistake in my functor example. I was not even returning a functor from the map function (was a copy and paste error that propagated).

Believe I now have a working functor example with map working as expected.

Given the mental gymnastics that I did to get this to work, I am thinking I am up to the challenge of typing a transducer. But first, I need to read your article (again) on what a transducer is. 😃