lst := [0, 1, 2, 4, 6, 7, 8, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
25, 27, 28, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39]:
r1,r2:= lst[1],lst[1]:
for i from 2 to numelems(lst) do
	if lst[i] - lst[i-1] = 1 then  #consecutive
		r2 := lst[i]:
	else #break
		printf(piecewise(r2-r1=1, "%d,%d,", r2-r1>1,"%d-%d,", "%d,"), r1, r2):
		r1,r2:= lst[i],lst[i]:
	fi:
od:
printf(piecewise(r2-r1=1, "%d,%d", r2-r1>1,"%d-%d", "%d"), r1, r2):