+
+ return $a <=> $b;
+}
+
+sub any (&@) {
+ my $f = shift;
+ return if ! @_;
+ for (@_) {
+ return 1 if $f->();
+ }
+ return 0;
+}
+
+sub cross(&\@\@) {
+ my $op = shift;
+ use vars qw/@A @B/;
+ local (*A, *B) = @_; # syms for caller's input arrays
+
+ # Localise $a, $b
+ my ($caller_a, $caller_b) = do {
+ my $pkg = caller();
+ no strict 'refs';
+ \*{$pkg.'::a'}, \*{$pkg.'::b'};
+ };
+
+ local(*$caller_a, *$caller_b);
+
+ # This map expression is also the return value.
+ map { my $a_index = $_;
+ map { my $b_index = $_;
+ # assign to $a, $b as refs to caller's array elements
+ (*$caller_a, *$caller_b) = \($A[$a_index], $B[$b_index]);
+ $op->(); # perform the transformation
+ } 0 .. $#B;
+ } 0 .. $#A;
+}
+
+sub _ary_calc_union_intersect {
+ my ($a, $b) = @_;
+
+ my %count = ();
+
+ foreach my $e (@$a, @$b) { $count{$e}++ }
+
+ my @union = ();
+ my @isect = ();
+ foreach my $e (keys %count) {
+ push @union, $e;
+ push @isect, $e if $count{$e} == 2;
+ }
+
+ return (\@union, \@isect);
+}
+
+sub ary_union {
+ return @{ (_ary_calc_union_intersect @_)[0] };
+}
+
+sub ary_intersect {
+ return @{ (_ary_calc_union_intersect @_)[1] };
+}
+
+sub ary_diff {
+ my ($a, $b) = @_;
+ my %in_b = map { $_ => 1 } @$b;
+ return grep { !$in_b{$_} } @$a;
+}
+
+sub listify {
+ my @ary = scalar @_ > 1 ? @_ : ref $_[0] eq 'ARRAY' ? @{ $_[0] } : (@_);
+ return wantarray ? @ary : scalar @ary;