Jon Pretty

But even if you do just want these operations, you’re far better off with a typeclass rather than sub typing.

Citation needed.

flatMap on List suspiciously allows the function parameter to return something that is not a List.

I saw this for the first time in our code base the other day. List flatmapping with Option return type. Did a double take until I realised it was the inheritance that allows it... so is this breaking the monadic laws? I suppose not if you start with the base type but yes for List

actually thinking about it, it feels more like an extension to the monad than a contravention of its laws

It's analogous to saying that the `|+|` operation on a monoid should allow the composition of different types. In other words, it is LITERALLY the same as claiming that we should be able to write `1 + "2"` and expect meaningful coercion.

I see what you're saying is that inheritance and variance full stop is a bad idea I think it makes life easier and some respects but can give you code soup in others... hmm

Inheritance and variance are both powerful concepts and can be very helpful in some cases, but they more often get radically over-applied. There are much more precise and controlled forms of abstraction and code-sharing that are often better choices.