For sure, as long as that's not how they/I write code normally! :D It demonstrates very in-depth understanding of the structure of the language, just as any good writing demonstrates expert-level understanding of natural language.

Two caveats:

- A lot of this knowledge might be kind of useless (for example, how to create unreachable code which nevertheless compiles), but I expect it would be difficult to demonstrate equally thorough understanding of the syntax of a language using exercises or looking at previous work (which ideally uses the minimum of sophistication to achieve the necessary functionality).

- It proves mastery of the syntax, but not of idioms, security, maintainability, speed, or any other metric relevant for production code. These might be correlated, but I'd rather see/present some examples of these as well to be sure.