applyMod (ReduceCost mana) = castCost %~ modifyCost
  where modifyCost cost = case cost of
          ManaCost m -> ManaCost (f m)
          _ -> cost
        f = \cost -> foldr delete cost mana
applyMod (ReduceCost mana) = castCost %~ modifyCost
  where modifyCost cost = case cost of
          ManaCost m -> ManaCost (f m)
          _ -> cost
        f = \cost -> foldr delete cost mana
applyMod (ReduceCost mana) = castCost %~ modifyCost
  where modifyCost cost = case cost of
          ManaCost m -> ManaCost (f m)
          _ -> cost
        f = \cost -> foldr delete cost mana