Figure out what should happen with haskeline's exceptions dependency
As of https://github.com/judah/haskeline/commit/f61f592988c2de16c1ab10c617b8c4f6db851f3f
haskeline now has a dependency on
exceptions. This will be something we will need to sort out for %8.10.1.
exceptions' current transitive closure would add
stm to our current core library set. I suspect
transformers-compat can be made optional.
stm shouldn't pose a problem as it is already a submodule.