DIP 50 - AST macros

[deadalnix]

On Tuesday, 12 November 2013 at 17:20:20 UTC, Andrei Alexandrescu 
wrote:
>> As I have already mentioned, it is the
>> very same thing we do now with __traits and UDA's but not 
>> limited to
>> only declarations.
>
> Interesting.
>

The thing I'd like to be able to do it to create a 
async/await/yield like mechanism, purely as library.

@generator
uint foo() {
     writeln("generating !");
     return 0;
     return 1;

     writeln("and the last one");
     return 2;
}

=>

auto foo() {
     enum States {
         S0,
         S1,
         S2,
     }

     struct Generator {
         State s;
         uint current;

         @property front() {
             return current;
         }

         void popFront() {
             final switch(s) with(State) {
                 case S0:
                     current = 1;
                     s = S1;
                     return;
                 case S1:
                     writeln("and the last one");
                     current = 2;
                     s = S2;
                     return;
                 case S2:
                     assert(0, "Nothing more in here");
             }
         }

         @property empty() {
             return s == State.S2;
         }
     }

     auto g = Generator();

     writeln("generating !");
     g.current = 0;
     g.state = State.S0;

     return g;
}