"instance HasModLogger a => HasLogFunc a" overlaps on bare LogFunc

[akhra]

    • Overlapping instances for HasLogFunc ModLogger
        arising from a use of ‘logFuncL’
      Matching instances:
        instance Has ModLogger α => HasLogFunc α
          -- Defined at /home/tejon/magicbane/library/Magicbane/Logging.hs:17:10
        instance HasLogFunc LogFunc
          -- Defined in ‘rio-0.1.3.0:RIO.Prelude.Logger’

I tried fixing this via Data.Type.Equality:

instance ((α == ModLogger) ~ 'False, Has ModLogger α) ⇒ HasLogFunc α where
  logFuncL = hasLens

But this doesn't work for reasons I haven't yet grasped. There's a procedural workaround described on Stack Overflow by @treeowl; I didn't immediately grok how to adapt it, and in any case it involves an additional class and newtype so I'd want your feedback on module style (per #12) before doing something like that.

[valpackett]

How is this happening? Where is the bare LogFunc coming from? Are you trying to use a bare LogFunc as the context?

[akhra]

Yes, while trying to test some logging stuff in isolation. And I intended to mention (whoops) that it was trivially worked around by using (LogFunc, ()) as the environment instead, so it's in no way a critical issue. But still a surprising error, and one I probably couldn't have sidestepped so quickly a year ago.

[valpackett]

Heh, what was surprising to me was using a bare LogFunc, since only tuples were intended / are mentioned in the readme :)

[akhra]

Unfortunately there is no standard unary tuple. ;)

[akhra]

Looks like the reason I couldn't find a nice constraint-based solution was because instead we got a nice compiler-based one!