DIP 50 - AST macros

[Chris Cain]

On Thursday, 14 November 2013 at 09:12:38 UTC, Walter Bright 
wrote:
> I agree that async/await has to eventually be added to D. I'm 
> not convinced it can or should be done with AST macros.

Out of curiousity, how would that be implemented without macros? 
I could see it being done with macros with a rewrite and using 
some of the standard library (like std.parallelism), maybe. But 
with a language feature, you couldn't use the standard library. 
It seems like some parallelism code would have to leak into the 
runtime to get it to work as people might expect.

I guess I would have thought the exact opposite from you... that 
this is precisely something that *should* be done with a 
library-defined macro.