"spirit" like template parser generator in 100 Lines of code (almost)

[BCS]

Don Clugston wrote:
> Another alternative workaround is this:
> -------
> template countTo(int a, A...)
> {
>     static if (a==0) alias A countTo;
>     else static if (a&1) alias countTo!(a-1, void, A) countTo;
>     else alias countTo!(a/2, A, A) countTo;
> }
> 
> foreach(j,_; countTo!(tempTuple.length)) {
>   const i = tempTuple[j];
> }
> In fact, if you can calculate the value of 'i' based only on 'j', this 
> can be a much more general solution, for example for your Bignum 
> template. It is very quick, can cope with numbers as high as 20000 or 
> so, and doesn't generate any runtime code (in fact, it can't, because 
> there's nothing you can do with a tuple of 20000 voids, except count it).
> It works well for cases like:
> 
> foreach(i,_; countTo!(s.length)) {
>   static if (s[i]=='+') { ... }
>   ...
> }
> allowing you to iterate over the contents of a string.
> There are some pretty cool things that work here -- you can add labels 
> in one iteration, and generate goto statements (or asm jmp instructions) 
> in a different iteration. I don't know how that works, but it's awesome 
> because it lets you turn a compile-time string into a run-time state 
> machine...

That would be interesting to try. In fact the use of a "make dummy tuple 
list" meta function was the next thing I planed to do for BigNum. (BTW, 
my first hack at it soaked up my whole system with a~=5k)

OTOH that still doesn't solve the "instance for each" case. For that you 
still need a local const. Anyway, neat stuff.