A browser interface to the Rust compiler to experiment with the language

I hit a case where I need to apply HRTB to multiple generics. I can write the code I want without generics, but I can't figure out how to make it generic.  (Thanks in advance if you decide to read through this whole thing! 🙂)  Let me take you on a journey. First, let's look at some working code that does everything I need (but without generics):  fn print_func_result<F>(func: F) where     for<'a> F: FnOnce(&'a str) -> &'a str, {     let local_string = String::from("test");     let r...