For folding containers of size >=1 with a semigroup I usually turn to classes from the semigroupoids package:

http://hackage.haskell.org/package/semigroupoids-4.3/docs/Data-Semigroup-Foldable.html

http://hackage.haskell.org/package/semigroupoids-4.3/docs/Data-Semigroup-Traversable.html

They are placed there, rather than in something like semigroups, because the 'return-less' variants of Monad and Applicative they need to provide most operations are placed in that package.

-Edward

On Tue, May 12, 2015 at 3:05 PM, Henning Thielemann <lemming@henning-thielemann.de> wrote:

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.

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