-- | Maps a function over the keys.
-- 
-- The supplied function must be bijective.
mapKeys :: (k2 -> k1) -> FunMap k1 v -> FunMap k2 v
mapKeys g (FunMap f) = FunMap (f . g)
mapKeys :: (k2 -> k1) -> FunMap k1 v -> FunMap k2 v
mapKeys g (FunMap f) = FunMap (f . g)
mapKeys g (FunMap f) = FunMap (f . g)