Implicit parameters and classes

{-# language ImplicitParams #-}
module Gato where

import Data.Text

-- Implicit parameter
type WithConnectionString = ?connectionString :: Text

class DumbShowConnectionString a where
  dumb :: a -> Text

instance DumbShowConnectionString Text where
  dumb = id @Text

instance (?connectionString :: Text) => DumbShowConnectionString () where
  dumb () = ?connectionString

-- Fails
instance WithConnectionString => DumbShowConnectionString () where
  dumb () = ?connectionString

{-
[1 of 1] Compiling Gato             ( gato.hs, interpreted )

gato.hs:16:10: error: [GHC-75863]
    • Illegal implicit parameter ‘?connectionString::Text’
    • In the instance declaration for ‘DumbShowConnectionString ()’
   |
16 | instance WithConnectionString => DumbShowConnectionString () where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Failed, no modules loaded.
ghci> :r
[1 of 1] Compiling Gato             ( gato.hs, interpreted )

gato.hs:16:10: error: [GHC-75863]
    • Illegal implicit parameter ‘?connectionString::Text’
    • In the instance declaration for ‘DumbShowConnectionString ()’
   |
16 | instance (?connectionString :: Text) => DumbShowConnectionString () where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

gato.hs:20:10: error: [GHC-75863]
    • Illegal implicit parameter ‘?connectionString::Text’
    • In the instance declaration for ‘DumbShowConnectionString ()’
   |
20 | instance WithConnectionString => DumbShowConnectionString () where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Failed, no modules loaded.
ghci>
-}