I'm not certain of the syntax, but for a max function, something like this would probably work (in 7.40)
If I have i,j and k, all integers, and I want the max, I can create a method max, that takes an internal table of integers as importing parameter (and returns the max). I can then call max like this:
data(maximum) = my_class->max( VALUE #((i)( j)(k)).