> I've never seen a type with multiple monad instances but I don't know if there could be one. There can, it's just like there can two monoid structures on th

> I've never seen a type with multiple monad instances but I don't know if there could be one. There can, it's just like there can two monoid structures on the same set. In fact if you have an example of a set S which has two monoid structures, you have an example of a functor with two monad structures: _ × S. join multiplies the two elements of S, so you get a different monad structure for every monoid structure on S.