Problem Statement

Given non-negative integers   m   and   n,   generate all size   m   combinations   of the integers from   0   (zero)   to   n-1   in sorted order   (each combination is sorted and the entire table is sorted).

3   comb   5     is: If it is more "natural" in your language to start counting from   1   (unity) instead of   0   (zero), the combinations can be of the integers from   1   to   n.

Let's start with the solution:

fun comb (0, _    ) = [[]]
  | comb (_, []   ) = []
  | comb (m, x::xs) = map (fn y => x :: y) (comb (m-1, xs)) @
                  comb (m, xs)
;
comb (3, [0,1,2,3,4]);