yield, C# etc

[downs]

bearophile wrote:
> Denis Koroskin:
>> I don't see much difference between "yield return i;" and "int result =  
>> dg(i);".
>> First one is slightly cleaner while second one allows overloading.
> 
> You are right, probably I prefer Python semantics & syntax here, not C# (or D) ones. I most of the cases you don't need overloading, but you always want a nicer syntax. (For people coming from C++ syntax is less important, I know).
> 
> 
>> Everything else is an implementation details.
> 
> Syntax matters, when you have recursive generators every bit of help you receive from the language is precious to avoid distracting you from messing the algorithm.
> The current syntax of D for the lazy iteration is very bad.
> 
> The following series generates the inverse Gray code:
> http://www.research.att.com/projects/OEIS?Anum=A006068
> 
> 
> In Python:
> 
> def A006068():
>     yield 0
>     for x in A006068():
>         if x & 1:
>             yield 2*x+1
>             yield 2*x
>         else:
>             if x:
>                 yield 2*x
>             yield 2*x+1
> 
> 
> In D using my libs, that use code modified from Witold Baryluk:
> 
> struct A006068 {
>     void generator() {
>         yield(0);
>         foreach(x; A006068()) {
>             if (x & 1) {
>                 yield(2 * x + 1);
>                 yield(2 * x);
>             } else {
>                 if (x)
>                     yield(2 * x);
>                 yield(2 * x + 1);
>             }
>         }
>     }
>     mixin Generator!(int);
> }
> 

FWIW, in tools:

module test92;
import tools.stackthreads, tools.log;

Source!(int) A006068() {
  return new Source!(int)((void delegate(int) yield) {
    yield(0);
    foreach (x; A006068()) {
      if (x & 1) {
        yield(2 * x + 1);
        yield(2 * x);
      } else {
        if (x) yield(2 * x);
        yield(2 * x + 1);
      }
    }
  });
}

void main() { foreach (v; A006068()) logln(v); }

Also .. is it expected that this does an infinite loop?