yield, C# etc

[Don]

Denis Koroskin wrote:
> On Wed, 13 Aug 2008 15:49:58 +0400, bearophile 
> <bearophileHUGS at lycos.com> wrote:
> 
>> In normal D:
>>
>> struct A006068b {
>>     int opApply(int delegate(ref int) dg) {
>>         int result, aux;
>>         aux = 0; result = dg(aux); if (result) return result;
>>         foreach(x; A006068b()) {
>>             if (x & 1) {
>>                 aux = 2 * x + 1; result = dg(aux); if (result) break;
>>                 aux = 2 * x; result = dg(aux); if (result) break;
>>             } else {
>>                 if (x)
>>                     { aux = 2 * x; result = dg(aux); if (result) break; }
>>                 aux = 2 * x + 1; result = dg(aux); if (result) break;
>>             }
>>         }
>>         return result;
>>     }
>> }
>>
>> The D version is bad to read and bad to write, there's too much noise.
>>
>> Bye,
>> bearophile
> 
> 
> template yield(char[] value)
> {
>     const char[] yield = "{ int aux = " ~ value ~ "; int res = dg(aux); 
> if (res) { return res; } }";
> }
> 
> struct A006068b {
>     int opApply(int delegate(ref int) dg) {
>         mixin(yield!("0"));
>         foreach(int x; A006068b()) {
>             if (x & 1) {
>                 mixin(yield!("2 * x + 1"));
>                 mixin(yield!("2 * x"));
>             } else {
>                 if (x) {
>                     mixin(yield!("2 * x"));
>                 }
>                 mixin(yield!("2 * x + 1"));
>             }
>         }
> 
>         return 0;
>     }
> }
> 
> I hope we will be able to write yield(2*x + 1); instead of mixin soon 
> (as an AST macros or a built-in feature).

Yup. And it'd be alright even without any AST stuff. Just something like:

mixin auto char[] yield(char [] value) {...}

to indicate that yield(x+2) automatically converts into mixin(yield("x+2"));

Then all the complicated AST stuff could be put in a library.