Redundant Type Equivalence Constraint

BebeSparkelSparkel · April 2, 2024, 4:03pm

I have a type equivalence in my constraints that is required but receive the warning -Wredundant-contraints. Is there a way to just disable the warning for the equivalence constraint but not other redundant constraints? Something like -Wno-equivalence-constrints ? If not, should I post this in proposals?

tomjaguarpaw · April 2, 2024, 4:04pm

If it is required by GHC says it’s redundant then that’s a bug in GHC. Can you post the code?

BebeSparkelSparkel · April 2, 2024, 4:11pm

It is required in the external not internal context, so I do not think it is a bug.

If in line 30 I use m' instead of (MonadProgenitor mProgenitor s') then I get the warning for line 18. I find it annoying not simply using simple m'.

github.com

BebeSparkelSparkel/biparsing/blob/adf0c67d76ecd92386366a2e5c93e38233b4220b/biparsing-core/src/Biparse/Biparser/PolyKinds.hs#L23

    
      
          -- | Similar to zoom but allows for lazy evaluation of the Iso.
          focus :: forall is c' c'' mProgenitor n' m' c s s' m n u v ss ss'.
            -- m
            ( MonadState s m
            -- m'
            , m' ~ MonadProgenitor mProgenitor s'
            , MonadState s' m'
            -- change monad
            , ChangeMonad    is m' m
            , ChangeFunction is m' m ~ (ss -> ss', ss' -> ss)
            , ChangeMonad    is n' n
            , ChangeFunction is n' n ~ (ss' -> ss)
            -- substate
            , ReplaceSubState s ss' s'
            , ReplaceSubState s ss s
            )
            => Iso c'' (State s) (Writer ss) s ss'
            -> Biparser c' s' (MonadProgenitor mProgenitor s') n' u v
            -> Biparser c  s  m  n  u v
          focus (Biparser fw bw) (Biparser fw' bw') = Biparser
            do

tomjaguarpaw · April 2, 2024, 4:19pm

Do you mean that it’s not a constraint that the body of focus needs, but it’s a constraint that you want to impose on callers anyway?

BebeSparkelSparkel · April 2, 2024, 7:02pm

Yes, m' is just the type result of the type family MonadProgenitor mProgenitor s' and would have to be explicitly given by the caller, but the mProgenitor is an easier type to pass.