put method
Implementation
IHashMap<K, V> put(K k, V v) => new IHashMap.internal(_map.modify(k.hashCode,
(existing) => new Cons(tuple2(k, v), existing.filter((kv) => kv.value1 != k)),
new Cons(tuple2(k, v), nil())));
IHashMap<K, V> put(K k, V v) => new IHashMap.internal(_map.modify(k.hashCode,
(existing) => new Cons(tuple2(k, v), existing.filter((kv) => kv.value1 != k)),
new Cons(tuple2(k, v), nil())));