Proposal: Make Semigroup as a superclass of Monoid

[Henning Thielemann]

On Tue, 5 May 2015, Greg Weber wrote:

> The issue you have not raised that I am more concerned with is that NonEmpty only works for lists.
> Michael and I figured out how to extend the concept to any (Mono)Foldable structure and also to be able to
> demand lengths of > 1.

It's possible with the structure provided by "non-empty". It is also 
possible to construct types for lists of fixed length or lists with an 
arbitrary set of allowed lengths.