I'm not really sure what niche this fills.

To me, the main draw looks to be the invariants that you can supply within functions, but this isn't a new concept outside of it being a dedicated keyword. Otherwise this looks like rust without all of the functionality

> Note that \\ is the syntax for multiline strings. Not to be confused with the comments, which are prefixed with //.

The fact that you need to note this highlights the problem with this design decision.