[Groff] pic problem

[Larry Kollar]

The following pic code works right up through the box "32" but doesn't 
create any boxes within the for loop.

.P
This is a test.
This is only a test.
.S -3
.PS 4.5i
box wid 8 ht 1 "Chassis ID"
box wid 8 ht 1 "Slot ID"
box wid 16 ht 1 "Interface/Port Use"
box wid 1 ht 1 with .nw at 1st box .sw "32";
for n = 31 to 1 by -1 do {
        box wid 1 ht 1;
        print n;
}
.PE
.S
.P
If this had been an actual document
there would have been some content.

.\" the end

Any ideas?