data MyRecF f = MyRec { foo :: String 
                       -- many other fields here as well 
                      , bar :: f Int 
                      } 
                     
type MyRecWithAFoo = MyRecF Identity 

data VoidF a 

type MyRecWithoutFoo = MyRecF VoidF 
-- Q1) So how is MyRecWithoutFoo actually represented by GHC? 
-- I guess ideally I would not want to represent the bar field 
-- at all. 


-- Q2) So how would I even go about creating a RecWithoutFoo?
-- Q2b, ideally I would want to have some sort of function 'defaultRec'
--that is usable for both RecWithAFoo and RecWithoutAFoo 

-- | some way of creating a defualtRec, which ideally I 
-- could use for both MyRecWithAFoo and MyRecWitoutFoo
defaultRec :: ??? => MyRecF f 
defaultRec = myRec "foo" ????

-- Q3) Any alternative, ergonomic way of defining this? 
-- I guess I could use some data family; but that would 
-- involve duplicating the many fields I guess.