Oh. See also Algorithm::Loops, Algorithm::Permute (and others, I'm sure). Also, an iterator approach:

c:\@Work\Perl>perl -wMstrict -le
"sub Iterator (&) { return $_[0]; }
 ;;
 sub pairs {
   my @set = @_;
   my ($i, $j) = (0, 0);
   ;;
   return Iterator {
     $j = ++$i + 1 if ++$j > $#set;
     ($i, $j) = (0, 0) and return unless $i < $#set;
     return [ @set[ $i, $j ] ];
     };
   }
 ;;
 my $abcd = pairs(qw(a bee c d));
 while (my $p = $abcd->()) { printf qq{(@$p) }; }
 print '';
 ;;
 while (my $p = $abcd->()) { printf qq{(@$p) }; }
"
(a bee) (a c) (a d) (bee c) (bee d) (c d)
(a bee) (a c) (a d) (bee c) (bee d) (c d)
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