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With AutoDeriveTypeable, data families get a Typeable instance, but associated data types in a class don't (and even standalone deriving doesn't work for them).

λ> data family Foo a
λ> typeRep (Proxy :: Proxy Foo)
Foo
λ> class K a where { data Bar a }
λ> typeRep (Proxy :: Proxy Bar)

<interactive>:6:1:
    No instance for (Typeable Bar) arising from a use of ‘typeRep’
    In the expression: typeRep (Proxy :: Proxy Bar)
    In an equation for ‘it’: it = typeRep (Proxy :: Proxy Bar)
λ> deriving instance Typeable Bar

<interactive>:7:1:
    Can't make a derived instance of ‘Typeable Bar’:
      Deriving Typeable is not allowed for family instances;
      derive Typeable for ‘Bar’ alone
    In the stand-alone deriving instance for ‘Typeable Bar’

Trac metadata

Trac field	Value
Version	7.8.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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