Whatever the question was, here's an answer:

use constant ST => ('-1', ' =', ' 0', ' =', ' 1');
printf ' ' x 8 . "%s\n", join ' ', map sprintf('%2d', $_), -9 .. 10;
while (<DATA>) {
    my ($l, $r) = split;
    printf "[%2d %2d] %s\n", $l, $r, join ' ',
      map { (ST)[ ($_ <=> $l) + ($_ <=> $r) + 2 ] } -9 .. 10;
}
__DATA__
1 4
2 5
3 7
0 3
-1 5
-8 -2
[download]

Output:

        -9 -8 -7 -6 -5 -4 -3 -2 -1  0  1  2  3  4  5  6  7  8  9 10
[ 1  4] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  =  0  0  =  1  1  1  1  1  1
[ 2  5] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  =  0  0  =  1  1  1  1  1
[ 3  7] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  =  0  0  0  =  1  1  1
[ 0  3] -1 -1 -1 -1 -1 -1 -1 -1 -1  =  0  0  =  1  1  1  1  1  1  1
[-1  5] -1 -1 -1 -1 -1 -1 -1 -1  =  0  0  0  0  0  =  1  1  1  1  1
[-8 -2] -1  =  0  0  0  0  0  =  1  1  1  1  1  1  1  1  1  1  1  1
[download]

I don't see why 0 should not be legal. <=> is not a ternary operator.