Re: D in the TIOBE top

[Timon Gehr]

On 09/12/2011 01:36 PM, bearophile wrote:
A more complex version that does't yield distinct sub-arrays to allocate less 
memory:

import std.stdio, std.array, std.range;

struct PowerSet(T) {
     T[] items;

     int opApply(int delegate(ref T[]) dg) {
         int result;
         T[] res;
         T[30] buf;

         if (!items.length) {
             result = dg(res);
         } else {
             outer:
             foreach (opt; [items[0..1], []]) {
                 buf[0 .. opt.length] = opt[];
                 foreach (r; PowerSet(items[1..$])) {
                     buf[opt.length .. opt.length + r.length] = r[];
                     res = buf[0 .. (opt.length + r.length)];
                     result = dg(res);
                     if (result) break outer;
                 }
             }
         }

         return result;
     }
}

void main() {
     size_t count;
     foreach (x; PowerSet!int(array(iota(22))))
         count++;
     writeln(count);
}


This runs in about 4.5 seconds, and uses less than 10 MB RAM.


You lose vs haskell because haskell does not recompute the same PowerSet 
multiple times.