We've resolved the issue in the purescript-either repo, but on second thoughts, I think this example is probably not best suited because of the use of instance chains, which I would consider to be something of a 'power user' feature. What about, say, MonadState instead?

I was thinking of something simpler along the lines of IsTypeEqual

Yeah, that's a good option, although another problem with both of these is that the functional dependencies could also risk obscuring what we're trying to get across. Are there even any good examples of MPTCs with no functional dependencies?

I think it would be good to use something like MonadAsk both with and without functional dependencies. While we don't have a version of MonadAsk without the constraints, it highlights the use case and tradeoffs.

MonadError is another good one. I think these are better than MonadState because the case of wanting to project different environments or throw different errors comes up more often for me than modifying multiple states.

Cleaning up my github notifications