calling D from perl 6 (windows)

main.p6

use NativeCall;

sub routine(int64) returns Str is native('mydll') { * }

my $start = now;
my $foo = routine(100_000);
say $foo;
say now - $start, " seconds";

mydll.d

module mydll;
import std.stdio;

extern(C)
export immutable(char)* routine(int n) {
  import std.bigint : BigInt;
  import std.format : format;
  import std.range : iota;
  import std.string : toStringz;
  BigInt prev = "1";
  BigInt curr = "1";
  foreach(int x; n.iota) {
    prev = curr;
    curr = prev + curr;
  }
  return "%d".format(curr).toStringz;
}


version(Windows)
extern(Windows) bool DllMain(void* hInstance, uint ulReason, void*) {
  import std.c.windows.windows;
  import core.sys.windows.dll;
  switch (ulReason)
  {
  default: assert(0);
  case DLL_PROCESS_ATTACH:
    dll_process_attach( hInstance, true );
    break;

  case DLL_PROCESS_DETACH:
    dll_process_detach( hInstance, true );
    break;

  case DLL_THREAD_ATTACH:
    dll_thread_attach( true, true );
    break;

  case DLL_THREAD_DETACH:
    dll_thread_detach( true, true );
    break;
  }
  return true;
}