Question

I wanna create a function that have the type int -> 'a list -> 'a list list

Function call:

grupper 2 [3, 1, 4, 1, 5, 9] shall return [[3, 1], [4, 1], [5, 9]]

grupper 4 [3, 1, 4, 1, 5, 9] shall return [[3, 1, 4, 1], [5, 9]]

grupper 42 [3, 1, 4, 1, 5, 9] shall return [[3, 1, 4, 1, 5, 9]].

I got this so far

fun grupper _ [] = []
| grupper n (x::xs) = if n > length(x::xs) then [x::xs]
                      else [List.take(x::xs, n)] @ grupper (n) xs

some help please.

Answer 1

You should use both List.take and List.drop:

fun grupper _ [] = []
  | grupper n xs = if n >= length xs then [xs]
                   else List.take(xs, n)::(grupper n (List.drop(xs, n)))