How to make a macro_rule! like macro

help
#1 
macro_rules! fun {
    ($name:ident,$block:block) => {
        fn $name() -> Result<(),String>
            $block
    };
}
fun! {abc, {
     // ...
     Ok(())
    }
}

I want to simplify function writing by macro fun!, but found no way to implement a macro_rule! like macro, to be used as

fun! abc {
     // ...
     Ok(())
}

Is there any approach?

The second question is how to hide the Ok(()) ending into macro definition.

#2

This is impossible. You have to use some delimiter (parentheses, brackets, braces).

#3

It used to be possible to define foo! bar {} macros in some way (I think using the unstable compiler plugin api which has been almost entirely removed since, but supported for example a predecessor to proc macros), but since rustc 1.38.0 macro_rules! is a special case in the parser and anything else will give a syntax error.