Forgot to copy `libraries` on my answer to your question:

On Wed, Jun 12, 2013 at 3:28 AM, Herbert Valerio Riedel <hvr@gnu.org> wrote:

On 2013-06-12 at 00:04:04 +0200, Gabriel Gonzalez wrote:
> I think types that lack an empty element are a misfeature.

...so having a data-type for representing non-empty lists (on which
operation such as head/last/minimum/maximum et. al can be proper
statically guaranteed total functions as opposed to resorting to
'Maybe'-wrapped results which need to be checked dynamically at runtime)
is a misfeature?

I phrased that poorly. Non-empty data types are useful, but having a combining operation on those types of type:

A -> A -> A

... is not.

The very example you gave (non-empty lists) shows why. If you combine two non-empty lists you can actually prove a stronger result, that the combined list has at least two elements. However, you lose that information if you use the `mappend` operation. I'm not saying that non-empty lists shouldn't have a combining operation, but rather that `mappend` is not the appropriate operation for the task.

> They usually end up contaminating everything they touch, which is why
> semigroups forms an entire parallel ecosystem of its own.

Can you provide a concrete example showing the kind of problematic
"contamination" that is caused by semigroup-forming types?

The non-empty list example shows what I meant. The moment you start including extra information like non-emptiness you have to re-engineer all downstream operations to preserve that information as faithfully as possible. Again, there's nothing wrong with that, but it's not deserving of its own type class or a special place in the Prelude.

cheers,
hvr