Remember that macros work by substitution. So each line of label_for
becomes a separate line in the macro-expanded program. A label alone
on a line gets plotted at the current point, which in this case is
last box.e. (The macro definition begins with an empty line. If it
didn't, then the case-0 line would have been pasted on the end of
the dashed-box line and manifested as a syntax error.)
BTW, what are the empty strings ("") for? Formally, they make a
three-line label, too high for the dashed box.
(The code layout below differs slightly from the original. I inserted
the backslash-newline to keep gmail from breaking the line at an
awkward place.)
Doug
> .PS
>
> define label_for {
> if $1 == 0 then { "Ent?te Ethernet" } else {
> if $1 == 1 then { "Ent?te IP" } else {
> if $1 == 2 then { "Ent?te TCP" } else {
> if $1 == 3 then { "Donnees applicatives" } else {
> } } } }
> }
>
> w = 3 ; h = 2; margin = .2 ; tr = 2 * margin
> for layer = 0 to 3 do {
> s = layer * margin
> box width w height h with .sw at (s,s)
> box width w height margin with .nw at last box .nw dashed \
> "" label_for(layer) ""
> w = w - tr
> h = h - tr
> }
> .PE
