How do you automatically derive a Gen for a product / coproduct based on its elements? Without using macros / template haskell that is?
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I guess I could whip up a Generic TC using Shapeless / Magnolia - and it'd be a proper TC. I like the idea of using just the core of the default Arbitrary to derive `defaultGen[A: Generic]`
Gotta try
How do I override just one (middle) level of the derivation tho?
You generally can override a middle level in the ADT just by having an implicit instance for it in scope. Magnolia will defer to any other implicit instance it finds.
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Sure thing! I do that all the time :) But in my hypothetical case I (no longer) have an `Arbitrary` TC derived - I derive a `Generic` TC and spawn `defaultGen` based on them. Overriding the Generic makes no sense, and would result in improper instances.
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Whis is my point, really: Arbitrary kind of defends itself as a TC because of the ease of overriding. It's an improper TC, with quite arbitrary (
) instances - but it's not the best example of why improper TCs are wrong, because it's sooo useful... - Show replies
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