coerce1.hs

{-@ LIQUID "--exact-data-con" @-} 
{-# LANGUAGE GADTs #-}

module Foo where 

data Foo a where 
  FInt :: Foo Int 
  FBool :: Foo Bool

f :: Foo Int -> Int 
f z = 10 

bar :: Foo a -> Int 
bar z = case z of FInt -> f z
                  FBool -> 10