use List::MoreUtils qw( pairwise );
my @a=(1 .. 5 );
my @b=( 'a' .. 'c'  );

### Good point from JavaFan; bad idea to ignore 0
### my @combined = pairwise { ( $a || '' ) .':'. ( $b || '' ) } @a, @b;

### fixed:
my @combined = pairwise { ( defined $a ? $a : '' ) .':'. ( defined $b ? $b : '' ) } @a, @b;

{
  local $,="\n",
  print @combined;
}