Depending on the order of the instances you get a different error:
{- No type class instance was found for Show A -}
newtype A = A String
derive newtype instance showX :: Show A
newtype B = B A
derive newtype instance showX :: Show B{- The value showX has been defined multiple times -}
newtype B = B A
derive newtype instance showX :: Show B
newtype A = A String
derive newtype instance showX :: Show AI would expect to always see the showX has been defined multiple times first.
Depending on the order of the instances you get a different error:
I would expect to always see the
showX has been defined multiple timesfirst.