for! {"a": 1, "b": 2}.keys(), s =>
    print! "key: " + s
for! {"a": 1, "b": 2}.values(), i =>
    print! i + 0

dic = { "a": 1, "b": 2 }
assert dic.concat({ "c": 3 }) == { "a": 1, "b": 2, "c": 3 }
assert dic.diff({ "a": 1 }) == { "b": 2 }
assert dic.get("a"+"b", 3) == 3
rec = dic.as_record()
assert rec.a == 1 and rec.b == 2

gdic as {Obj: Obj} = dic
assert "a" in gdic
assert not 1 in gdic

l as List! {Str: Int} = ![{"a": 1}]
l.push!({"b": 2}) # OK