fantasy-land: Traversable definition uses undefined terms

I’m bothered by the definition of Traversable. The remaining specifications use plain English, depend on one another, and build on “value” and “equivalent” from the Terminology section.

But Traversable uses three terms not covered in any of these places:

• natural transformation
• Id
• Compose

My least favorite course in grad school was Category Theory, and I remember little of it, but it means that when I run across this stuff 25 years later, it’s at least familiar, and I have some intuitive feel for what makes something a natural transformation. But intuitive feel is not a good basis for a specification.

And it’s pretty easy to guess at what Id and Compose should be and how they should work. But there should be no guessing in a spec.

Unfortunately, I don’t feel a strong enough grasp of Traversable to offer a reasonable alternative, and I apologize. But I still think it’s worth pointing out the issue.