Feedback received was, 1. It is not functional enough (functional refers to functional programming) 2. There should have been more unit tests

Can FP experts of interwebz review my code and tell me, why my solution is not functional enough? My opinion is, it is either functional or not. Don't tell me, because it is not lazy. I do have free monad based implementation of this toy. I use it to teach FP concepts to other developers. I would say it is over engineering in this context and hence did not submit it.

As far as unit test goes, coverage is 100%. I feel the reviewer is probably from a dynamic language background and does not appreciate the real use of compiler.

I really want to know, am I missing something or the reviewer is an idiot?

Thanks in advance