GHC.Generics and instances of Functor, Applicative, etc?

Conal Elliott conal at
Wed Jan 13 01:28:01 UTC 2016

I'm using GHC.Generics and have noticed that the data types defined there
don't have instances of the standard classes (at least not defined in that
module), such as Functor, Applicative, Foldable and Traversable. It'd be
very useful to be able to rely on such instances, so that one can define
instances of custom types via instances of the generic types. (Hopefully,
the compiler can remove most or all conversion overhead) Is there any
reason not to add these generic instances?

-- Conal
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