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Yes I know, 0 and "B" are not technically type constructors, but it's as close as you can get for the kinds Nat and Symbol.

Test cases:

{-# LANGUAGE DataKinds, KindSignatures #-}

import GHC.TypeLits (Nat, Symbol)

class A (n::Nat)
instance A 0

class B (s::Symbol)
instance B "B"

Result:

A.hs:6:10: error:
    • Illegal instance declaration for ‘A 0’
        (All instance types must be of the form (T a1 ... an)
         where a1 ... an are *distinct type variables*,
         and each type variable appears at most once in the instance head.
         Use FlexibleInstances if you want to disable this.)
    • In the instance declaration for ‘A 0’

A.hs:9:10: error:
    • Illegal instance declaration for ‘B "B"’
        (All instance types must be of the form (T a1 ... an)
         where a1 ... an are *distinct type variables*,
         and each type variable appears at most once in the instance head.
         Use FlexibleInstances if you want to disable this.)
    • In the instance declaration for ‘B "B"’

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler
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