{-# LANGUAGE DeriveDataTypeable #-}
import Data.Generics
 
data D1 = D1 Int String deriving (Data, Typeable)
data D2 = D2 D1 Int (Int -> Int) deriving (Data, Typeable)
 
count :: (Data a, Typeable b) => b -> a -> Int
count t = everything (+) (0 `mkQ` c t)
  where
    c :: a -> a -> Int
    c _ _ = 1
 
main = do
  let c = undefined :: Char
      i = undefined :: Int
      ii = undefined :: Int -> Int
      s = [c,c,c]
      d = D2 (D1 i s) i ii
  print . count c $ d
  print . count i $ d
  print . count ii $ d
  print . count s $ d
 

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