sch.hs

import Data.Functor.Identity

data A = A
  deriving (Eq, Show)

data B = B
  deriving (Eq, Show)

data C = C
  deriving (Eq, Show)

data D = D
  deriving (Eq, Show)

-- solved by: classy lens
getC_ABC :: (A, B, C) -> C
getC_ABC (_, _, c) = c

getC_ABCD :: (A, B, C, D) -> C
getC_ABCD (_, _, c, _) = c

insertRecord_ABC' :: f (A, B, C) -> [f (A, B, C)] -> [f (A, B, C)]
insertRecord_ABC' = (:)

insertRecord_ABC :: (A, B, C) -> [(A, B, C)] -> [(A, B, C)]
insertRecord_ABC r rs = runIdentity <$> (insertRecord_ABC' (Identity r) (Identity <$> rs))

insertRecord_ABCD :: (A, B, C, D) -> [(A, B, C, D)] -> [(A, B, C, D)]
insertRecord_ABCD r rs =  let liftRec (a, b, c, d) = (d, (a, b, c))
                              unliftRec (d, (a, b, c)) = (a, b, c, d)
                          in  unliftRec <$> (insertRecord_ABC' (liftRec r) (liftRec <$> rs))