Instance resolution error message unclear, because of missing kind information

consider the following modules:

module A where

(.) :: forall (a :: TYPE 'UnliftedRep) (b :: TYPE 'UnliftedRep) (c :: TYPE 'UnliftedRep).
     (b -> c)
  -> (a -> b)
  -> (a -> c)
(.) f g = \x -> f (g x)

data UList (a :: TYPE 'UnliftedRep) where
  UNil :: UList a
  UCons :: a -> UList a -> UList a

mapFB :: forall (a :: TYPE 'UnliftedRep)
                (elt :: TYPE 'UnliftedRep)
                (lst :: Type).
  (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
mapFB c f = \x ys -> c (f x) ys

{-# RULES
"mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f . g)
   #-}

module B where

import Control.Category ((.))

data UList (a :: TYPE 'UnliftedRep) where
  UNil :: UList a
  UCons :: a -> UList a -> UList a

mapFB :: forall (a :: TYPE 'UnliftedRep)
                (elt :: TYPE 'UnliftedRep)
                (lst :: Type).
  (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
mapFB c f = \x ys -> c (f x) ys

{-# RULES
"mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f . g)
   #-}

Module 'A' works fine. Module 'B', fails with the following error:

    • No instance for (Category (->)) arising from a use of ‘.’
    • In the second argument of ‘mapFB’, namely ‘(f . g)’
      In the expression: mapFB c (f . g)
      When checking the transformation rule "mapFB"
    |
line| "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f . g)
    |                                                      ^^^

I expected this failure because of the kind mismatch; the category instance for (->) obviously requires that it be kinded Type -> Type -> Type. However, it confused someone I am teaching, who said to me that they didn't understand the error, since they expected it to work as (->) does indeed have a Category instance. (They are very unfamiliar with Levity-Polymorphism).

My question is this: Would it be preferable to include such kind information in the error message?

Trac metadata

Trac field	Value
Version	8.6.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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