This is the purpose of the th-lift package, which provides exactly this functionality: http://hackage.haskell.org/package/th-lift
Defining TH Lift instances for algebraic data types
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29-03-2022 - |
Question
Suppose I have an algebraic data type with multiple constructors, like
data Animal a = Mouse a | Beaver a | Rabbit a
How would I create a Lift
instance effectively? The easiest way of doing so would be
instance (Lift a) => Lift (Animal a) where
lift (Mouse x) = [| Mouse x |]
lift (Beaver x) = [| Beaver x |]
lift (Rabbit x) = [| Rabbit x |]
This is very redundant though. Of course I can't directly abstract the different animals away like lift x = [| x |]
, although conceptually that's similar to what I want to achieve. Is there a way of doing this in TH so that I don't have to write the same line again for each data constructor?
Solution
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