insertWith package:hashmap

insertWith :: (Hashable k, Ord k) => (a -> a -> a) -> k -> a -> Map k a -> Map k a
hashmap Data.HashMap
Insert with a combining function. insertWith f key value mp will insert the pair (key, value) into mp if key does not exist in the map. If the key does exist, the function will insert f new_value old_value.
insertWithKey :: (Hashable k, Ord k) => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
hashmap Data.HashMap
Insert with a combining function. insertWithKey f key value mp will insert the pair (key, value) into mp if key does not exist in the map. If the key does exist, the function will insert f key new_value old_value.