DIP 50 - AST macros

[deadalnix]

On Wednesday, 13 November 2013 at 19:25:18 UTC, Walter Bright 
wrote:
> On 11/13/2013 11:24 AM, Walter Bright wrote:
>> Actually, there is a way to do this. I wrote an article years 
>> back on how to
>> write "statement" workalikes using lazy function parameters. I 
>> suppose I should
>> dig that up if I can find it.
>
> Ah, found the code:
>
> void ifthen(bool cond, lazy void dg)
> {
>     if (cond)
>         dg();
> }
>
> void ifthen(bool cond, lazy void dgthen, lazy void dgelse)
> {
>     if (cond)
>         dgthen();
>     else
>         dgelse();
> }
>
> void dotimes(int i, lazy int dg)
> {
>     for (int j = 0; j < i; j++)
>         dg();
> }
>
> void switcher(bool delegate()[] cases...)
> {
>     foreach (c; cases)
>     {
>         if (c())
>             break;
>     }
> }
>
> bool scase(bool b, lazy void dg)
> {
>     if (b)
>     {
>         dg();
>         return true;
>     }
>     return false;
> }
>
> bool sdefault(lazy void dg)
> {
>     dg();
>     return true;
> }
>
> void whiler(lazy bool cond, lazy void bdy)
> {
>     while (cond())
>         bdy();
> }
>
> void test1()
> {
>     int x = 3;
>     dotimes(5, printf("%d\n", ++x));
>
>     ifthen(true, printf("yes\n"));
>     ifthen(false, printf("no\n"));
>
>     ifthen(true, printf("yes\n"), printf("no\n"));
>     ifthen(false, printf("yes\n"), printf("no\n"));
>
>     int v = 2;
>     switcher(
>         scase(v == 1, printf("it is 1\n")),
>         scase(v == 2, printf("it is 2\n")),
>         scase(v == 3, printf("it is 3\n")),
>         sdefault( printf("it is default\n"))
>     );
>
>     whiler( x < 100,
>         (printf("%d\n", x), x *= 2)
>     );
> }

Was is missing is the capability to look into the lazy 
parameter's ast and act accordingly.

Here you can wrap something around code, not generation code 
depending on passed code.