Slighlty confusing error message with data families

Example code:

data family T a

foo :: T a -> a
foo (Just x) = x

Error message:

    Couldn't match expected type `T a' against inferred type `Maybe a1'
      NB: `T' is a type function
    In the pattern: Just x
    In the definition of `foo': foo (Just x) = x

Calling T a type function is confusing, I had to double check that I hadn't accidentally declared it as a type family. I would

• call these things type families and data families in messages and
• omit the message for data families altogether because it doesn't matter that T is one in this case.

Trac metadata

Trac field	Value
Version	6.13
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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