DB<34> sub cross (&$$) { my ($code,$list1,$list2) = @_; local ($a,$b
+); my @res; for $a (@$list1) { for $b (@$list2) { push @res, &$code }
+}; return @res; }

  DB<35> x cross { $a + $b } [0..2], [10,20,30]
0  10
1  20
2  30
3  11
4  21
5  31
6  12
7  22
8  32
  DB<36>
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you can just let $list2 default to $list1 if undef to have a self-operation with only one list.

$list2 //= $list1