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    "### Contravariant Functors"
   ]
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    "{-# LANGUAGE KindSignatures #-}\n",
    "\n",
    "-- (.)        :: (b -> c) -> (a -> b) -> a -> c\n",
    "-- contraComp :: (a -> b) -> (b -> c) -> a -> c\n",
    "\n",
    "-- (.)        f g x = f (g x)\n",
    "-- contraComp f g x = g (f x)\n",
    "\n",
    "-- instance Functor (a ->) where\n",
    "--    fmap = (.)\n",
    "\n",
    "-- instance Contravariant (-> z) where\n",
    "--    contramap = flip (.)\n",
    "\n",
    "newtype Predicate a = Predicate { getPredicate :: a -> Bool }\n",
    "\n",
    "newtype Op b a = Op { getOp :: a -> b }\n",
    "  \n",
    "class Contravariant (f :: * -> *) where\n",
    "  contramap :: (a -> b) -> f b -> f a\n",
    "  \n",
    "instance Contravariant (Op a) where\n",
    "    contramap f g = Op $ let bToa = getOp g in bToa . f"
   ]
  }
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