Structural undefined

[kokoro-aya]

Usually in programming languages we use undefined or null to specify a hole with absent of value, nor fields, and they are usually a single global value that retains a same meaning across the context and function scopes.

But I am wondering if there would be a interesting feature, if we enable these holes to "contain fields or values", and their "absent" are just a kind of hiding.

For example, these codes won’t be possible in an imperfect language like JavaScript or C#:

var hole = undefined!
hole.foo = 123!
print(hole) // undefined
print(hole.foo) // 123

Thanks to the different levels of equality check in DreamBerd, we can also do comparisons like this:

var hole1 = undefined!
var hole2 = undefined!

hole1 === hole2! // true

hole1.baaz = "bomb"!

hole1 === hole2! // false, or maybe?
hole1 == hole2! // true

Similarly, we can suggest functions and other complex structures inside a undefined value, and this would make things more exciting.

I hope that with this enhancement we can fill a hole in the semantics of undefined values that are often missed in those imperfect languages, to enforce a better programming language.