lookup package:mono-traversable

Look up a value in a map with a specified key.

Insert a key-value pair into a map, return the previous key's value if it existed. Inserts the value directly if the key does not exist in the map. Otherwise, apply a supplied function that accepts the key, the new value, and the previous value and insert that result into the map.

Apply a function to the value of a given key. If the map does not contain the key this returns Nothing and the input map. If the map does contain the key but the function returns Nothing, this returns the previous value and the map with the key-value pair removed. If the map contains the key and the function returns a value, this returns the new value and the map with the key-value pair with the new value.