sub iter { my $vals = \@_; my $i = 0; sub { $i >= @$vals ? do { $i = 0; undef } : $vals->[$i++]; }; } sub enumerate_iter { local $Data::Dumper::Indent = 0; local $Data::Dumper::Terse = 1; my ($iter) = @_; my $i = 0; while (defined($_ = $iter->())) { printf "%2d: (%s)\n", $i++, Dumper($_); } print "\n"; } enumerate_iter( iter( qw[a b c] ) ); # 0: ('a') # 1: ('b') # 2: ('c') #### sub iter_to_seq { my ($iter) = @_; sub { my $val = $iter->(); defined $val ? ($val) : (); }; } sub seq_to_iter { my ($seq) = @_; sub { my @val = $seq->(); @val ? [@val] : undef; }; } enumerate_iter( seq_to_iter( iter_to_seq( iter( qw[a b c] ) ) ) ); # 0: (['a']) # 1: (['b']) # 2: (['c']) #### use List::Util qw( reduce ); sub seq_prod { no warnings 'once'; reduce { seq_prod2($a,$b) } @_ ; } sub seq_prod2 { my ($s, $t) = @_; my @sval; sub { my @tval; while ( !@sval || !(@tval = $t->()) ) { return () unless @sval = $s->(); } ( @sval, @tval ); }; } sub iter_prod { seq_to_iter( seq_prod( map iter_to_seq($_), @_ ) ); } #### my $abcees = iter(qw(a b c)); my $xyzees = iter(qw(x y z)); enumerate_iter( iter_prod( $abcees, $xyzees ) ); # 0: (['a','x']) # 1: (['a','y']) # 2: (['a','z']) # 3: (['b','x']) # 4: (['b','y']) # 5: (['b','z']) # 6: (['c','x']) # 7: (['c','y']) # 8: (['c','z']) #### my $product = iter_prod( $abcees, $xyzees ); while (defined (my $vals = $product->())) { my @vars = @$vals; print "Got vars: @vars\n"; # do real work here } # Got vars: a x # Got vars: a y # Got vars: a z # Got vars: b x # Got vars: b y # Got vars: b z # Got vars: c x # Got vars: c y # Got vars: c z