immut_dict = {"Alice": 1, "Bob": 2, "Charlie": 3}
assert immut_dict["Alice"] == 1
_ = immut_dict["Bob"]
_ = immut_dict.get("Charlie")
_ = immut_dict.get("Charlie", 4)

for! immut_dict.keys(), k =>
    print! k
for! immut_dict.values(), v =>
    print! v
for! immut_dict.items(), ((k, v),) =>
    print! k, v

_ = immut_dict.copy()

mut_dict = !{ "a": 1 }
mut_dict.update! [("a", 2)], (a, b) -> a + b
assert mut_dict == {"a": 3}
mut_dict.insert! "b", 4
i = mut_dict.remove! "a"
assert i == 3