# This one constructs a simple glob and returns the sub that will
# iterate through it.
sub iter_powerset {
  my @elems = @_;
  my $glob_str = join 'X', map {"{$_,}"} 0..$#elems;
  sub { @elems[grep length, split 'X', scalar glob $glob_str] };
}

# This is an auxiliary to iter_powerset2 (below). The glob expression 
+is
# more complex, in order to get the desired order of output. As the nu
+mber
# of elements grows, the glob string balloons, quickly becoming too la
+rge
# to work.
sub powerset_glob {
  my ($car, @cdr) = @_;
  if (@cdr) {
    my $cdr_globstr = powerset_glob(@cdr);
    return (join ',', "{$car", "$car+$cdr_globstr", "$cdr_globstr}");
  }
  else { return $car }
}

# Call the glob string builder and return the iterator subroutine
sub iter_powerset2 {
  my @elems = @_;
  my $glob_str = powerset_glob(0..$#elems);
  sub { @elems[grep length, split /\+/, scalar glob $glob_str] };
}

# Demonstration code. Call either iter_powerset function
my $iter = iter_powerset2(2,3,5,7);
while (my @set = $iter->()) {
   print "<@set>\n";
}
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