[(x[i],x[j]) for i in range(len(x)) for j in range(i+1, len(x))] His problem is not with functional programming (i.e. avoiding state mutations). It is that he

[(x[i],x[j]) for i in range(len(x)) for j in range(i+1, len(x))] His problem is not with functional programming (i.e. avoiding state mutations). It is that he tries to do inductive definitions and functors in a language whose syntax is extremely unsupportive. In OCaml that would be (untested code): let rec pairs = function | a :: b -> List.map (fun x -> (a, x)) b @ (pairs b) | [] -> []