Sublist

sublist.sml

(* sublist *)
fun sublist _ _ nil = nil
  | sublist 0 0 (x::xs) = [x]
  | sublist 0 e (x::xs) = x::(sublist 0 (e-1) xs)
  | sublist b e (x::xs) = let
    val b_ = b + (if b < 0 then (length (x::xs)) else 0)
  in
    sublist (b_-1) (e-1) xs
  end;

sublist 2 5 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
(* val it = [2,3,4,5] : int list *)

sublist ~6 7 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
(* val it = [4,5,6,7] : int list *)

(* filter *)
fun filter _ [] = []
  | filter pred (x::xs) = 
let
  val ys = filter pred xs
in
  if pred x then x::ys else ys
end;