Find all single letter publicly-exported modules and make sure they are private

[MatthewDaggitt]

Currently we have many single letter modules that are unintentionally being exported publicly by other modules. In v3.0 we should do a sweep and make them all private (or rename them to something more meaningful if we really do want to export them!).

[MatthewDaggitt]

See #2407 (comment) for an example

[jamesmckinna]

Ha!/Oops! 🤦‍♂️

The final merged version of #2407 in fact does make R a private module definition now... so we have just merged a breaking change... sorry about that! ...
... but hopefully a harmless one (given that the Algebra.Solver.* machinery appears to have been superseded by Tactic.*Solver, but without being deprecated... so perhaps there are clients uses out there, hopefully they don't explicitly refer to R!?)

If anyone reports breaking behaviour, I'll post a follow-up PR, but perhaps better to let sleeping dogs lie? Let me know!

[jamesmckinna]

A quick pass via grep suggests that the Solver export might have been the only such instance? Additional eyes welcome on this...

[MatthewDaggitt]

A quick pass via grep suggests that the Solver export might have been the only such instance? Additional eyes welcome on this...

That is a little surprising. I definitely remember having seen the pattern used in Data.List.Relation hierarchy, but given that this is a v3.0 change, I'm not going to spend too long digging now. We should just bear it in mind when writing new code for the moment.

[jamesmckinna]

No need to dig now, but we could make a task list here?