[Groff] looping in Pic

[emmanuel chemla]

A newbie question in Pic:
Having to draw a ruled paper, I finally succeeded in writing this short
program :
----
.PS
lineWidth=3i
interlineHeight=0.2

line lineWidth;
line lineWidth at last line.start +(0i, -interlineHeight)
line lineWidth at last line.start +(0i, -interlineHeight)
line lineWidth at last line.start +(0i, -interlineHeight)
.PE

----
the program is correct but I would like it to work in a loop, with the
number of lines set in a register or as a variable or send as an argument
to a recursive macro.
(and I don't want to output as much as *".PS blabla .PE"* blocks as lines
needed, I'd like to solve this matter just staying in Pic environment).

Any ideas ?