\version "2.22.0"

% some sequential music objects (to be concatenated with variation by gen-music function)
xa = { g'4. a'8 g'4 f' e' f' g'2 d'4 e' f'2 e'4 f' g'2 g' a'4 g'8 f' e'4 f' g'2 }
xb = { d'4 e' f'4 e' f' g'8 f' e'4 f'8 g' a'4 c'' e''4 d''8 c'' b'4 cis'' d''2 }
xc = { a'4 b' c''4 b' c'' d''8 c'' b'4 c''8 d'' e''2~ e''4 d''8 c'' b'4 cis'' d''2 }
xd = { a'4 b' c''4 b' c'' d''8 c'' b'4 g'8 f' e'4 d' cis'4 a'8 g' a'4 cis'' d''2 }
xe = { d''4 c'' b'4 g'8 f' g'4 b' c''4 d'' e''2 d''4 c''8 b' a'4 b' c''2 }
xf = { g'4 a' bes'4 a' bes' c''8 bes' a'2 b' c''4 b' c'' d''8 c'' b'4 a' bes'2 a'4 g'8 f' e'4 fis' g'2 }
xg = { d'4 e' f'4 e' f' g'8 f' e'4 c''8 b' a'4 g' fis'4 d''8 c'' d''4 fis' g'2 }
xh = { g'4 f' e'4 c''8 bes' c''4 e' f'4 a'8 g' f'4 e' d'2 g' e'4 c' }

% list of sequential music objects
smolist = #(list xa xb xc xd xe xf xg xh)

% to get a scheme list of music elements from a music object
#(define (get-elements mus) (ly:music-property mus 'elements))

% list of element-lists
elists = #(map get-elements smolist)
enum = #(length elists)

% recursively concatenate a range of elists (0 <= m <= n, possibly > enum)
#(define (cat-elists m n)
   (let ((elist-m (list-ref elists (modulo m enum))))
     (if (< m n) (append elist-m (cat-elists (1+ m) n)) elist-m )))

% generate music by concatenating contiguous members from list.
% i mod enum is the starting position in the list for the next gen-music.
% mincat is the minimum number of concatenations (mincat >= 0)
% maxcat is the max number of concatenations (maxcat >= mincat)
% actual number of cats is random between mincat and maxcat.
i = 0
mincat = 0
maxcat = 9
gen-music = #(define-music-function () ()
  (let* ((m i) (n (+ m (+ mincat (random (1+ (- maxcat mincat)))))))
    (set! i (1+ n))
    (make-sequential-music (cat-elists m n))))