[Haskell-cafe] automatic instance derivation

[Greg Fitzgerald]

How do you automatically derive an instance for a data type defined in an
imported module?

-- automatic instance derivation directly after type declaration
data Val1 = V1 Int deriving Show

-- manual instance derivation can be in separate file
data Val2 = V2 Int
instance Show Val2 where
   show (V2 i) = show i


-- Is something like this possible?
data Val1 = V1 Int
...
derive Show Val2


Thanks,
Greg
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