T14265.hs:7:12: error:
    • Found type wildcard ‘_’ standing for ‘_ :: k’
      Where: ‘k’, ‘_’ are rigid type variables bound by
               the inferred type of f :: proxy _ -> ()
               at T14265.hs:8:1-8
      To use the inferred type, enable PartialTypeSignatures
    • In the first argument of ‘proxy’, namely ‘_’
      In the type ‘proxy _ -> ()’
      In the type signature: f :: proxy _ -> ()

T14265.hs:10:15: error:
    • Found type wildcard ‘_’ standing for ‘_’
      Where: ‘_’ is a rigid type variable bound by
               the inferred type of foo :: StateT _ _1 ()
               at T14265.hs:11:1-15
      To use the inferred type, enable PartialTypeSignatures
    • In the first argument of ‘StateT’, namely ‘_’
      In the type ‘StateT _ _ ()’
      In the type signature: foo :: StateT _ _ ()

T14265.hs:10:17: error:
    • Found type wildcard ‘_’ standing for ‘_1 :: * -> *’
      Where: ‘_1’ is a rigid type variable bound by
               the inferred type of foo :: StateT _ _1 ()
               at T14265.hs:11:1-15
      To use the inferred type, enable PartialTypeSignatures
    • In the second argument of ‘StateT’, namely ‘_’
      In the type ‘StateT _ _ ()’
      In the type signature: foo :: StateT _ _ ()