use v6;

sub my_while(Code $expr, Code $whileblock) {
  while ($expr()) { $whileblock() };
}

my $i = 0;
my_while {$i < 10}, {
  say "i: $i";
  my $j = 0;
  my_while {$j < 10}, {
    say "j: $j";
    $j++;
  };
  $i++;
};