'impossible' happened when deriving Functor on a type with a type family application
The following should fail with an appropriate error message.
I discovered this by accident when I changed the definition of type 'U' and forgot to remove 'deriving Functor'.
> {-# LANGUAGE TypeFamilies, DeriveFunctor #-}
> data U a = U (G a) deriving Functor
>
> class A a where
> type G a
Trac metadata
Trac field | Value |
---|---|
Version | 7.2.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
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Blocking | |
CC | |
Operating system | |
Architecture |