Find all things of type a inside type b - dynamically at runtime.

find_any_type.hs

import           Data.Data
import           Data.Functor.Const
import           Data.Generics.Product.Types


-- This works on Data/Typeable, which is basically duck-typing from python
-- instead of GHC.Generics which work only at compile-time & have no runtime-cost.
extractAny :: (Data a, Typeable b) => a -> [b]
extractAny = getConst . gfoldl (\xs d -> case cast d of
                                Just a  -> Const (a:getConst xs)
                                Nothing -> Const (extractAny d <> getConst xs)
                    ) (\_ -> Const [])

-- use like this (implying JobPosting & PostalAddress exist & parsed :: [JobPosting])
main = print (extractAny @[JobPosting] @PostalAddress parsed)