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Comment by gnufx | Hacker News Reader

This was posted several times recently without anyone noting that it was the origin of "A monad is a monoid in the category of endofunctors, what's the problem?", which often seems to be quoted as if it wasn't attributed to Wadler satirically.

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The funny part is that it's completely true, albeit not very useful if one doesn't know how monoid constructions work categorically (good explanation at [0]).

Algebra: Chapter 0 has a similar overly technical definition for groups (which they elaborate of course). Also see[1]

  Joke 1.1. Definition: A group is a groupoid with a single object.

[0] https://old.reddit.com/r/math/comments/ap25mr/a_monad_is_a_m...

[1] https://i.pinimg.com/originals/e3/b6/23/e3b62382a9eb1021ff30...

I don't think anyone doubts the technical fact, or it wouldn't be a decent joke. The problem is if people think Wadler (might have) said it as such, and that it reflects a community attitude. It's trotted out often enough in a disparaging way. As far as I remember, Milewski left it to the end as something he just felt obliged to show.

It means monad is a thing that sequentially combines computations on the same type. Of course there is more to it but i believe this definition is useful as a starting point

And burritos are just tacoids in the category of enchiladafunctors.

https://twitter.com/rickasaurus/status/705134684427128833

Without the 'what's the problem', It's in 'categories for the working mathematician' by Saunders Mac Lane. Of course, it's entirely seriously in that book.

And a perfectly fine turn of phrase in that context, too.

For anyone looking for an explanation, this StackOverflow question [1] is worth a read.

[1] https://stackoverflow.com/questions/3870088/a-monad-is-just-...

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