The Devils code

powerset.pl

#!/usr/bin/perl

sub sos_as_string ($;$) {
    my ( $set, $string ) = @_;
    $$string .= '{';             
    my $i;                 

    foreach my $key ( keys %{ $set } ) {
        $$string .= ' ' if $i++;
        if ( ref $set->{ $key } ) {
            sos_as_string( $set->{ $key }, $string ); 
        } else {
            $$string .= $key;                       
        }
    }
    return $$string .= '}';   
}

sub powerset_recurse ($;@) {
  my ($set, $powerset, $keys, $values, $n, $i) = @_;

	if( @_ == 1 ) {
		my $null = {};
		$powerset = { $null, $null };
		$keys = [ keys %{ $set }];
		$values = [ values %{ $set }];
		$nmembers = keys %{ $set};
		$i= 0;
	}
	return $powerset if $i == $nmembers;

	my @powerkeys = keys %{ $powerset };
	my @powervalues = values %{ $powerset };
	my $powern = @powerkeys;
	my $j;

	for( $j = 0; $j < $powern; $j++ ) {
		my %subset = ( );
		@subset{keys %{ $powerset->{ $powerkeys [$j]}}} =
			values %{ $powerset->{ $powervalues [$j]}};
		$subset{$keys->[ $i]}= $values->[$i];
		$powerset->{\%subset } = \%subset;
	}
	powerset_recurse($set, $powerset, $keys, $values, $nmembers, $i+1);
}

my $a= { a => 12, b => 34, c => 56};
my $pr= powerset_recurse($a);
print "pr = " . sos_as_string($pr) . "\n";

questions

What is the purpose of $n? It is never referenced anywhere else than line 20
What is the value of $nmembers if @_ != 1?
Why does this return different results every time  I run this? E.g:

~/D/g/h/c5 (master=) ./powerset.pl
pr = {{a b} {c a} {c} {} {a} {c b} {b} {c a b}}
~/D/g/h/c5 (master=) ./powerset.pl
pr = {{a b} {c b} {b} {a} {} {c a} {c} {c a b}}
~/D/g/h/c5 (master=) ./powerset.pl
pr = {{} {a b} {a} {c a} {c b} {b} {c} {c a b}}
~/D/g/h/c5 (master=) ./powerset.pl
pr = {{c} {c a b} {a} {c a} {} {b} {c b} {a b}}
~/D/g/h/c5 (master=) ./powerset.pl
pr = {{c} {c a b} {} {a b} {c b} {b} {c a} {a}}

What is going on here? From where is the randomness coming from?

Figured it must be that n should be nmembers but finding it in the original (through Amazon) had me thoroughly confused. The randomness I could not make any sense of no matter how often I read the code. Happy to know it's some obscure Perlish thing rather than my eyes and general comprehension!