(* A queue for multiple readers/writers. *)

module Queue;

let q: All(X) {write: (X)=>(), read: ()=>X} =
  (let nonEmpty = condition();
   var q = [];
   
   {protected, serialized,
      write =>
        meth(s, e)
          q := q @ [e];
          signal(nonEmpty);
        end,
     
     read =>
       meth(s)
         watch nonEmpty until #(q)>0 end;
         let q0 = q[0];
         q := q[1 for #(q)-1];
         q0;
       end
   });

end module;

let t = 
  fork(proc() Queue_q.read() end, 0);

Queue_q.write(3);

join(t);