> I copy & paste Hervert's reddit answer here , for ones who don't
> follow it:
> As the suffix "alpha" implies, this is a very bleeding edge release with
> very little guarantees regarding API stability (c.f. new GHC schedule
> Put differently, a package that works now with GHC 8.4.1-alpha1 may not
> necessarily work with the final GHC 8.4.1 release.
A package that works now with -alpha1 doesn't have to be the same as
the one that work with the final release.
(And that's only in the unlikely case that an alpha->final break API
which in most cases it really shouldn't)
Resorting to another system than the common system for testing, means
people are actually going to have the opportunity to integrate it in
their test suite,
which ultimately reduces GHC QA at large.