Macro GO 

macro_rules! GO {
    ($f:path) => { ... };
    ($n:expr) => { ... };
    () => { ... };
}

Immediately return a transition-type Response.

This returns !, exiting the current function.

• $f:path: Switch to the given page.
• $n:expr: Go back $n steps.
• No arguments: go back 1 step.