> 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.

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