Merci Gilles,
Unfortunately I still cannot get anything.
So, if I follow your instructions here's what I get:
#(define-markup-command (staff-lines-it layout props n pad long) (number? number? number?)
(interpret-markup layout props
(if (= n 0)
(markup (#:path 0.15 `((moveto 0 ,(* pad 0))(lineto ,long ,(* pad 0)))))
(markup
(#:combine
(#:path 0.15
(fold
(lambda(i,prev)
(cons
(moveto 0 (* pad i))
(cons
(lineto long (* pad i))
prev)))
'()
(reverse (iota (1+ n))))
)))
)))
\markup\staff-lines-it #5 #1 #10And does not compile.