Is it possible to write an improper list in Gleam?

[CrowdHailer]

An improper list is one where the tail of a list is not a list. This stack overflow answer explains it pretty well.

I can't see how one could be made in Gleam. Yet it looks like the gleam source code supports it.
In the printing code the case of a NotList is handled.
https://github.com/gleam-lang/gleam/blob/main/src/erl.rs#L889

Could anyone share an example of creating some Gleam source that produces a NotList?

[lpil]

NotList here means a variable or something. A more descriptive name might be NotALiteralList, but it will still be a list at runtime as the type checker as passed.

[1, 2, ..this_is_a_variable]

All lists have to be proper for the type checker to be happy.

Good use of the questions section! I like this a lot!