For example, the following code:
module Main where
class C a
data NotNewtype a = NotNewtype a
derive newtype instance c :: C (NotNewtype String)
produces
Cannot derive newtype instance for
Main.C (NotNewtype String)
Make sure this is a newtype.
Perhaps it would be better to say something like this?
Error 1 of 1
Cannot derive newtype instance for
Main.C (NotNewtype String)
since NotNewtype is not a newtype.
Note: NotNewtype is defined in Main as:
data NotNewtype a = NotNewtype a
For example, the following code:
produces
Perhaps it would be better to say something like this?